GB2541368A - Fluid delivery apparatus - Google Patents

Fluid delivery apparatus Download PDF

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Publication number
GB2541368A
GB2541368A GB1512454.8A GB201512454A GB2541368A GB 2541368 A GB2541368 A GB 2541368A GB 201512454 A GB201512454 A GB 201512454A GB 2541368 A GB2541368 A GB 2541368A
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Prior art keywords
pressure
sensor
fluid
proximal
conduit
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GB1512454.8A
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GB201512454D0 (en
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Weinberger Paul
Scott Gutsell Graham
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DIASOLVE Ltd
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DIASOLVE Ltd
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Priority to GB1512454.8A priority Critical patent/GB2541368A/en
Publication of GB201512454D0 publication Critical patent/GB201512454D0/en
Priority to PCT/GB2016/052162 priority patent/WO2017009668A1/en
Publication of GB2541368A publication Critical patent/GB2541368A/en
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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • A61B5/0215Measuring pressure in heart or blood vessels by means inserted into the body
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6846Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive
    • A61B5/6847Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive mounted on an invasive device
    • A61B5/6851Guide wires
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • A61B5/02141Details of apparatus construction, e.g. pump units or housings therefor, cuff pressurising systems, arrangements of fluid conduits or circuits
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/021Measuring pressure in heart or blood vessels
    • A61B5/0215Measuring pressure in heart or blood vessels by means inserted into the body
    • A61B5/02156Calibration means
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/026Measuring blood flow
    • A61B5/0265Measuring blood flow using electromagnetic means, e.g. electromagnetic flowmeter
    • A61B5/027Measuring blood flow using electromagnetic means, e.g. electromagnetic flowmeter using catheters
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/48Other medical applications
    • A61B5/4836Diagnosis combined with treatment in closed-loop systems or methods
    • A61B5/4839Diagnosis combined with treatment in closed-loop systems or methods combined with drug delivery
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Measuring for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6846Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive
    • A61B5/6847Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive mounted on an invasive device
    • A61B5/6852Catheters

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Cardiology (AREA)
  • Engineering & Computer Science (AREA)
  • Public Health (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Medical Informatics (AREA)
  • Molecular Biology (AREA)
  • Surgery (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Pathology (AREA)
  • Veterinary Medicine (AREA)
  • Biophysics (AREA)
  • Physiology (AREA)
  • Vascular Medicine (AREA)
  • Electromagnetism (AREA)
  • Hematology (AREA)
  • Media Introduction/Drainage Providing Device (AREA)
  • Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)
  • Infusion, Injection, And Reservoir Apparatuses (AREA)

Abstract

Cardiac/coronary catheter, comprises a fluid delivery conduit for connection, at a distal end of the conduit, to a patients circulatory system, pressuring monitoring means 238 for monitoring the blood pressure, said pressure monitoring means being in fluid communication with the system via the conduit, the apparatus includes compensation means 260 for use in compensating for, or reducing the effect of, the flow of fluid through the conduit on the output of the pressuring monitoring means. The apparatus may be used in fractional flow reserve (FFR) procedure. The compensation means may combine the outputs of the pressure monitoring means and another pressure sensor to give an output of the blood pressure. The compensation means may comprise a Wheatstone bridge. The pressure monitoring means may be a differential pressure sensor and may comprise a Venturi tube.

Description

Title: Fluid Delivery Apparatus Field of Invention
This invention relates to fluid delivery apparatus for use with a system for containing or conveying fluid.
Background to the Invention
The invention is applicable to apparatuses having various, different purposes, including the supply of a fluid to, and/or extraction of samples of fluid from, a system. Typically, the fluid(s) to be delivered and the fluid(s) contained or conveyed by this system are in their liquid form. The invention is particularly applicable to coronary catheterization apparatus which may be used, for example, in Fractional Flow Reserve (FFR) analysis of a coronary artery stenosis. If the apparatus is to be used as coronary catheterization, then the system is the patient, and the fluid in the patient is blood.
The coronary catheterization procedure involves inserting a guide catheter into one of the patient’s peripheral arteries (for example in the wrist or groin) and then guiding the catheter through the patient’s arterial network to a coronary artery.
The catheter may contain a pressure wire the tip of which has a miniature pressure sensor. This can be advanced through the structures of the heart to measure the actual local blood pressure at different locations, for example downstream of an arterial stenosis. This can be compared to an aortic blood pressure measurement obtained using a proximal pressure sensor connected to the proximal end of the catheter and supported, for example on a drip stand, at the same height as the patient’s heart, to avoid systematic errors arising from a hydrostatic head of pressure.
The proximal pressure sensor provides an effective means of measuring aortic pressure when there is no flow of liquid along the guide catheter, so that the prevailing conditions at the tip of the guide catheter (i.e. the distal end) are replicated at the proximal sensor. However, the guide catheter is also used to deliver drugs (in liquid form), such as adenosine to stimulate maximal blood flow in the coronary artery under investigation, or a contrast agent for facilitating the imaging of the coronary artery using, for example, an x-ray imager.
When a contrast agent or drug is being injected along the catheter, the proximal pressure sensor measurement would no longer bear a simple relationship to the aortic pressure and the proximal sensor is therefore typically isolated, normally by means of a valve, from the catheter during this part of the procedure.
This interruption in monitoring of aortic blood pressure can be disadvantageous. For example, if a vasodilator drug such as adenosine is being introduced, while the proximal sensor is in effect disabled, the exact time of maximal blood flow (hyperemia) through the stenosis may occur when the pressure measurements for FFR are not being taken. As a result, the resultant data may have been obtained in less than ideal circumstances.
The generally accepted view is that if a drug were to be delivered down the guide catheter while measurements were being taken by the proximal pressure sensor, there would need to be an additional lumen, such as a micro catheter introduced either parallel to or over the pressure wire, so as to provide a passage for the drug to be injected, whilst leaving an outer passage (the annulus between the micro catheter and the interior or the guide catheter) along which the pressure is transmitted to the proximal sensor. However, such an approach significantly increases the complexity of the apparatus.
Summary of the Invention
According to the invention, there is provided fluid delivery apparatus for use with a system for containing or conveying fluid, the apparatus comprising a fluid delivery conduit for connection, at a distal end of the conduit, to the system, pressure monitoring means for monitoring the pressure of fluid in the system, said pressure monitoring means being in fluid communication with the system via the conduit, the apparatus including compensation means for use in compensating for, or reducing the effect of, the flow of fluid through the conduit on the output of the pressure monitoring means.
The compensation means allows the apparatus to monitor the fluid pressure within the system even while the fluid, through which the pressure monitoring means is coupled to the distal end of the conduit, is travelling along the conduit. The pressure change caused by said travelling does not therefore prevent the measurement of pressure in the system.
The apparatus could be used to extract fluid, for example a sample, from the system, along the delivery conduit. Alternatively, fluid may be supplied to the system along the delivery conduit, in either case the apparatus preferably includes injector means for supplying or extracting fluid to the system, through the delivery conduit.
Delivery is the more common use of the apparatus, but wherever this document makes references to fluid delivery and the associated physical effects, it will be understood by the reader that this could equally be extraction and the corresponding physical effects.
Preferably the compensation means is operable to quantify an effect of the flow of fluid through the delivery conduit and to use said quantity to compensate for, or reduce said effect of, the flow of fluid in the conduit on the output of the pressure monitoring means.
The compensation means may quantify the effect by means of direct measurement of the effect. Alternatively, the compensation means may determine the quantity indirectly, for example from data on the relationship between the effect and the operation of the injector means.
Preferably the compensation means generates an output whose magnitude is nominally equal to the change in the output of the pressure monitoring means caused by the travelling of said liquid along the conduit. In such a way the former output can be summed with the latter output to compensate for, or reduce the effect of, said travelling.
The reader will appreciate that “summing” in a mathematical function and so does not necessarily imply that the two output quantities have the same sign. For example, where the flow of liquid in the conduit is towards the system (i.e. liquid delivery), this will cause an increase in the output of the pressure monitoring means and so, to achieve the correct compensation, the output generated by the compensation means will be ascribed a negative value. Thus when the two outputs are summed, the output of the pressure monitoring means returns to being representative of the pressure in the system.
Preferably, the two outputs are electrical signals.
For delivering or extracting fluids along the delivery conduit, the injector means may be either a passive or active device, such as a pressurised bag or a manually operated syringe, respectively. Preferably, however, the injector means comprises a pump for pumping fluid along the delivery conduit.
In this case, the compensation means may be operable or arranged to derive said quantity by a process of derivation from control signals or power supplied to the pump. In such a case, the compensation means does not measure the effect of the flow of fluid through the conduit.
Preferably, however, the compensation means includes flow sensor means for measuring said effect of the flow of fluid through the conduit or a related effect for example in fluid upstream (in the case of fluid delivery to the system), or downstream (in the case of fluid extraction from the system), of the conduit.
Thus variations in the performance of the pump will not produce errors in the quantification of said effect. The sensor means may be integral to the pump, but is preferably separate from the pump and connected distal (upstream or downstream) of the latter.
In this case, the output of the sensor means may be particularly suitable for analysis by the rest of the compensation means as the supply of fluid to the conduit by routes other than via the pump will be taken into account in the output of the sensor means. An example of an apparatus in which fluid from more than one source may be supplied to the conduit is coronary catheterization apparatus for use in fractional flow reserve analysis. Such apparatus may include a pressurised saline bag connected to the fluid delivery conduit (in this case a coronary catheter) in parallel with an infusion pump for supplying a drug, such as adenosine, along the conduit. In addition, this type of apparatus may include an arrangement of a reservoir, valve(s) and a syringe for injecting a contrast agent along the conduit.
Preferably, the pressure monitoring means comprises a proximal pressure sensor situated at a position spaced from the distal end of the fluid delivery conduit.
The proximal pressure sensor may be so arranged relative to the conduit, that, in use, fluid to be injected into the system, or sampled from the system along the conduit also travels through the proximal sensor.
Consequently, the height of the proximal pressure sensor relative to that of the system is not dictated by the position of the fluid delivery conduit.
The height of the proximal pressure sensor can thus be selected to be such that there is substantially no head of hydrostatic pressure as between the system and proximal pressure sensor. In the case of coronary catheterization apparatus, this equates to the proximal pressure sensor being situated at substantially the same height as the patient’s heart. The sensor means for measuring said effect of the flow of fluid preferably comprises sensor means which is sensitive to said flow.
The sensor means may comprise a flow rate sensor, for example an impellor or Doppler ultrasound-based device, for measuring the rate of flow of fluid.
Preferably, however, the sensor means comprises pressure change sensor means for measuring the pressure change in a fluid flowing through a passage.
This enables the apparatus to automatically take into account the effect of variations which could affect the relationship between flow rate and its effect on the output of the pressure monitoring means. Examples of such variations are variations in temperature and/or fluid viscosity.
Preferably, the pressure change sensor means comprises a first sensor coupled, in use, to fluid at a first position relative to the passage, and a second sensor coupled to fluid, in use, at a second position, spaced from said first position, wherein fluid travelling from one to the other of the positions travels along at least part of the passage.
Thus the difference in simultaneous measurements from the two sensors will be indicative of the pressure change along the passage or a portion of the passage, and this can be used to calculate the pressure change along the delivery conduit.
The first sensor may be said proximal sensor.
Preferably, however, the pressure change sensor means comprises a differential pressure sensor. The differential pressure sensor is preferably such that, in use, the difference in pressure at two locations is measured without reference to any other common reference pressure such as atmosphere pressure.
Such a sensor preferably has a common pressure sensitive element having a first face coupled, in use, to fluid at said first position, and a second face coupled, in use, to fluid at said second position.
Preferably, said pressure sensitive element comprises a flexible diaphragm one face of which is, in use, exposed to fluid at said first position, the other face, in use, to fluid at said second position.
Since the differential pressure sensor measures pressure difference, its output would be substantially unaffected by the actual pressure of fluid on either side (i.e. upstream or downstream) of the passage. The differential sensor can thus be designed to have a high sensitivity, because it does not need to have a dynamic range large enough to match the range of actual pressures that might occur. In addition, errors arising from variations over time in sensitivities of separate sensors are avoided if a single differential pressure sensor is used.
The passage may be of constant cross section. In the case of coronary catheterization apparatus, the passage may, for example, be constituted by a length or portion of additional catheter which mimics the pressure drop of fluid travelling along the coronary catheter.
Preferably, however, the passage comprises restriction in a conduit.
This increases the pressure drop for a given flow rate and enables the pressure change sensor means to use a shorter passage than a constant cross section conduit and thus to be of a relatively compact construction.
Preferably, the restriction profile is such that the passage progressively tapers and then widens.
Preferably, this is achieved by means of a restriction in the form of a Venturi.
This facilitates laminar, non-turbulent flow so that the pressure change across the passage may be linearly related to the pressure change along the fluid delivery conduit, since ordinarily the flow therethrough will also be the laminar, non-turbulent flow.
Preferably, said first position is upstream, of the restriction and said second position is downstream of the restriction, if the apparatus is being used to inject fluid into the system.
Preferably, the compensation means further comprises analogue circuitry for combining the outputs of the proximal sensor and a pressure sensor, other than the proximal sensor, of the compensation means to give an output representative of fluid pressure in the system.
Preferably, the circuitry comprises a bridge circuit.
Preferably, the bridge circuit comprises a Wheatstone bridge, or modified Wheatstone bridge circuit. A bridge circuit is particularly suitable for coronary catheterization apparatus, since the individual detecting elements of a proximal pressure sensor of a conventional arrangement of such apparatus are typically connected in the form of a Wheatstone bridge. Thus the use of a bridge circuit provides an output which provides the desired compensated pressure measurement, but which closely resembles existing apparatus and is thereby directly compatible with the instrumentation means to which these are typically connected.
Preferably, the proximal pressure sensor includes piezo-resistive elements, each connected between a respective pair of junctions of the bridge.
Additionally, a sensor of the pressure change monitoring means, other than said proximal sensor, preferably also has piezo-resistive elements, each connected between a respective pair of junctions of the bridge.
The sensor which is not the proximal sensor may be the second pressure sensor of the pressure change monitoring means, if the pressure change monitoring means is such that it includes the proximal and second pressure sensors. If the pressure change monitoring means has a differential pressure sensor, this may constitute the sensor which also has piezo-resistive elements connected to the bridge as described above.
Where the pressure change sensor means comprises said proximal pressure sensor and second pressure sensor, those two sensors preferably have differing sensitivities such that, provided there is no change in system pressure, the voltage outputs of the two sensors are identical at any given rate of flow of fluid through the passage.
It will be appreciated that although the voltages are identical, they represent different pressures, by virtue of the difference in sensitivity.
If the sensors have a linear response, a simple summation or subtraction of the sensor outputs can produce a resultant output the only variable affecting which is the pressure in the system (i.e. the pressure to be monitored).
Where the pressure change sensor means comprises a differential pressure sensor, the sensitivities of that sensor and the proximal pressure sensor and the relationship between the flow rate of fluid through the passage with the measured pressure difference may be such that the pressure in the system may be the only variable affecting the combined output of the sensors.
Preferably, the apparatus is for use with a system for containing or conveying fluid when in its liquid state, the fluid delivery conduit functioning as a liquid delivery conduit, the fluid pressure to be monitored to being the pressure of liquid in the system.
Preferably, the apparatus comprises coronary or cardiac catheterization apparatus, for the delivery or extraction of blood, drugs or other liquids to or from the vascular systems of or around the human heart.
Preferably the apparatus is for use in an FFR procedure.
Preferably, at least one pressure sensor of the pressure change monitoring system is situated in a bifurcated fitting for attachment to the proximal end of a fluid delivery conduit constituted by a guide catheter of the apparatus.
Brief Description of the Drawings
The invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a diagrammatic view of known coronary catheterization apparatus;
Figure 2 shows the apparatus in situ in a cardiology lab, and connected to a pressure analyser and display;
Figure 3 shows the circuitry of a pressure sensor of the known apparatus;
Figure 4 is a diagrammatic view of a first embodiment of fluid delivery apparatus in accordance with the invention; the apparatus taking the form of coronary catheterization apparatus;
Figure 5 is a corresponding view of a second embodiment of coronary catheterization apparatus in accordance with the invention;
Figures 6 and 7 are respective sectional side and exploded isometric views of a modified arrangement of pressure sensors for the apparatus shown in Figure 5, the Figure 7 view omitting a printed circuit board;
Figure 7A is a partially exploded view of the arrangement of Figures 6 and 7, including the circuit board;
Figure 8 schematically illustrates the pressure sensors of Figures 6 and 7 and Figures 11-13; Figure 9 shows the circuitry for the pressure sensors of Figures 6-8 and 11-13;
Figure 10 illustrates the sensitivities of the pressure sensors of Figures 6-9 and Figures 11-13;
Figures 11-13 are respective isometric, sectional and exploded isometric views of an alternative arrangement of pressure sensors to that shown in Figures 6 and 7, the sensors of Figures 11-13 being incorporated into a bifurcated housing that constitutes a fitting to be connected directly to a guide catheter, and the circuit board of the arrangement being omitted from Figures 11 and 13;
Figure 13 A is a partially exploded view of the arrangement of Figures 11-13, including the circuit board;
Figure 14 is a schematic view of the arrangement shown in Figures 11-13 when connected to a guide catheter;
Figures 15-17 are respective isometric, exploded isometric and side sectional views of a differential pressure sensor for use in a further embodiment of coronary catheterization apparatus in accordance with the invention;
Figure 18 is a schematic view of the sensor of Figures 15-17 in combination with a separate proximal sensor;
Figure 19 shows the sensor circuitry for the differential pressure sensor in combination with a separate proximal sensor;
Figures 20-22 are respective isometric, exploded isometric and sectional side views of an alternative type of differential pressure sensor, forming part of a further embodiment of apparatus in accordance with the invention, the differential pressure sensor in this case being incorporated into a bifurcated housing constituting a fitting for direct connection a guide catheter;
Figure 23 is a schematic diagram of an alternative type of fitting which contains both the differential pressure and proximal pressure sensors;
Figure 24 shows a further embodiment of coronary catheterization apparatus, when in use, the apparatus having pressure change sensor means comprising the arrangements show in Figures 6-8 or 15-17, with a separate proximal pressure sensor;
Figure 25 is similar to Figure 24, but shows an arrangement in which the pressure change sensor means is housed within a bifurcated fitting, such as either of the fittings shown in Figures 11-13 or 20-22, along with a separate proximal pressure sensor;
Figure 26 shows alternative circuitry for a pressure change sensor means which includes the proximal pressure sensor, the circuitry showing two pressure sensors each connected as a respective Wheatstone bridge; and
Figure 27 shows analogue processing circuitry for combining the outputs of the circuitry shown in Figure 26.
Detailed Description
The apparatus shown in Figure 1 comprises a guide catheter 1 in the form of a tube, typically of a diameter of about 2mm, having a distal, open end 2. The opposite end of the catheter 1, i.e. the proximal end, is connected to a bifurcated fitting 4.
The end of the fitting 4, referenced 6, has a device entry gland (not shown) through which a pressure wire 8 or other devices can be passed into the catheter 1. The wire 8 extends through the lumen of the catheter 1, has a tip 10 which can be extended, by a controlled distance, beyond the distal end 2 of the catheter 1. The tip of the wire 8 contains a miniature pressure sensor which can be advanced through the structures of the heart to measure the actual local blood pressure at different locations, for example downstream of an arterial stenosis.
The bifurcated fitting 4 includes a liquid inlet branch 12 which is itself connected to a Tee piece housing 14 that has main and auxiliary inlet ports 16 and 18 and which contains a three-way valve controlled by a rotary manual control 20 to enable liquid to be injected into the catheter 1 through a selected one of either of the two ports 18 and 16, whilst the port which has not been selected is, in effect, isolated. A length of tubing 22 connects the inlet port 16 to a two-valve manifold 24 which contains two three-way valves, each controlled by a respective one of two rotary controls 26 and 28 selectively to connect the inlet 16 to the contents of a pressurised saline bag 30 or a contrast agent syringe 34. In addition, the valve operated by the control 28 can connect the contrast agent syringe 34 to a contrast agent reservoir 32, so that contrast agent may be drawn from the reservoir 32 into the syringe 34 (while the valve controlled by the control 26 isolates the reservoir 32 and syringe 34 from the inlet 16). When the controls 26 and 28 are set so that the bag 30 is isolated from the inlet 16, whilst the syringe 34 is in liquid communication with that inlet, contrast agent can then be injected using the syringe 34 along the tube 22 and into the lumen of the catheter 1 via the valve 14 and fitting 4.
The bag 30 is connected to the manifold 24 via a tube 36 which carries an inline proximal pressure sensor 38. The proximal pressure sensor 38 is of the type having a silicon diaphragm having four piezo-resistive strain gauges applied to it. Each strain gauge constitutes a respective one of four piezo-resistive elements 40-43 connected together as a Wheatstone bridge circuit as shown in Figure 3, in which reference numeral 45 denotes a power supply line, and (a) (b) outputs for a voltage signal which is amplified by differential amplifier 46. The piezo resistors can be formed by micro-machining or etching of the silicon diaphragm.
One face of the diaphragm is exposed to atmospheric pressure, whilst the other is in contact with the liquid in the tube 36 so that the differential voltage (i.e. the voltage difference between outputs (a) and (b)) may be used as a direct measure of the applied pressure so that this voltage, AV, increases with increasing liquid pressure. It will be understood that
(0)
Figure 2 shows the apparatus when in use in a cath lab on a patient denoted by reference numeral 48 supported on a table 50.
The catheter 1 has been inserted into the patient so that the distal end 2 is, in effect, connected to the blood in a coronary artery under investigation. The pressure sensor 38 and saline bag 30 are supported on a drip stand 52, with the pressure sensor 38 situated at precisely the same elevation as the patient’s heart. This positioning of the sensor 38 prevents measurable errors in the measured blood pressure of the patient as a consequence of the difference in hydrostatic pressure between the proximal sensor 38 and the sensor on the tip of the pressure wire 8. It will be appreciated that the valves in the housing 24 and 14 can be set so that the sensor 38 is coupled to the environment in the region of the distal end 2 of the catheter 1 via the liquid in the catheter 1 and in the tubing 22 and 36. Since liquids are substantially incompressible, the proximal pressure sensor 38 provides an effective means of measuring aortic pressure while there is no flow of liquid in the catheter 1, since the prevailing conditions at the distal end of the catheter 1 will then be replicated at the sensor 38. However, the sensor 38 will be isolated from the distal end 2 if the valves in the housing 24 are set so that the contrast agent may be injected along the catheter 1 using the syringe 34. The valve in the housing 14 will also isolate the sensor 38 when a vaso-dilator drug, such as adenosine is injected into the catheter 1 through the inlet 18.
The output of the pressure sensor 38 is connected to a pressure analyser and display 54 which is also connected to the further pressure sensor at the tip of the wire 8 so that the analyser and display 54 can simultaneously show the aortic pressure measured by the sensor 38 and also the pressure (on the other side of a stenosis) measured by the sensor at the tip of the wire 8. These are real time signals that display pulsatile blood pressure and include details of important clinical significance, such as the artefact known as the “dichrotic notch” associated with the closure of the aortic heart valve.
Isolating the sensor 38 during the introduction of the liquid along the catheter 1 is consistent with conventional thinking which is that in those circumstances the sensor 38 is no longer able accurately to measure aortic pressure, by virtue of the effect of the flow of liquid in the apparatus.
However, it would be highly beneficial to be able to continue to use the proximal pressure sensor accurately to monitor aortic pressure when various procedures, involving the flow of liquid along the catheter, are being performed. Potentially, the most important time to be monitoring a patient could be precisely when such a procedure is under way, for example when a drug or other liquid is being infused or injected.
In that connection, it has been realised that, even though there might be flow of liquid along the catheter 1, the oscillating pressure pulses in the blood vessel where the catheter tip is located (such as the aorta) will still be transmitted through the catheter. Those pressure signals will be superimposed onto the pressures associated with any flowing liquid, and hence can still be “communicated” to a proximal sensor.
The clarity of the superimposed pressure signal may deteriorate if pressures within the liquid in the catheter are chaotic, such as during turbulent flow. However, the delivery of most liquids through typical catheters is generally such that prevailing flow conditions are laminar. In this case, the pressure pulse signal can be preserved.
The apparatus shown in Figure 4 has many features in common with the apparatus of Figures 1-3, and corresponding components are indicated by the reference numerals of Figures 1-3 raised by 100.
In the apparatus shown in Figure 4, the three-way valve attached to the bifurcated fitting 104 has been replaced by an open Tee 156 which is located proximal and upstsream of the manifold valve, and which, in effect, provides two inlets for one of the ports of the housing 124. More specifically, the Tee connects the saline bag 130 and pressure sensor 138 to the housing 124 in parallel with an infusion pump 158 which is operable to inject a drug into a patient via the lumen of the catheter 101 (and the housing 124 and connecting tubing).
The infusion pump 158 has no need for flow rate sensors for measuring the rate at which liquid is being pumped by the pump 158 since its operating mechanism delivers liquid at a pre-determined rate (for example, as programmed by an operator through a user-interface resulting in the mechanism driving the plunger of a syringe at a fixed linear speed). This flow rate information is fed to a signal compensating processor 160, which also receives a signal from the proximal pressure sensor 138. The processor 160 analyses the two input signals so as to compensate for the effect of the flow of liquid along the catheter 101 on the relationship between the pressure measured by the sensor 138 and the actual aortic pressure at the distal end 102. As with the known arrangement, the proximal pressure sensor 138 is positioned at the same elevation as the patient’s heart.
An example of the type of analysis that may be conducted by the compensating processor 160 is as follows:
At the typical flow rates involved, the flow conditions in the guide catheter 101 are predominantly laminar, in which case the pressure drop along the catheter will be directly proportional to the flow rate, Q. i.e.
(1)
The convention adopted in this document is that Q is positive for liquid being delivered to the patient (c.f. liquid sampling from the patient) and hence positive APcatheter denotes an elevated pressure at the proximal end.
The pressure detected at the proximal pressure sensor 138 (Pmeasured) will be equal to the sum of the actual aortic blood pressure (BP) plus the catheter pressure drop. i.e.
(2)
Hence, in order to communicate the actual aortic pressure (BP) to the analyser/display, the processor 160 needs to generate an output signal, as follows:
(3)
In order to derive APcatheter, the unit 160 needs to first read flow rate information from the pump 156, and then to convert this into a pressure-related signal, based on equation 1 (which will have been empirically determined previously for the type of catheter in use). Most modem infusion pumps are equipped with a serial data interface, such as RS232 or USB, and the unit 160 has a corresponding interface to input the necessary information. To perform the calculation of equation 1, the unit 160 also has a processor to implement this as an algorithm.
Many types of small processor could be used here, although the inventors have found a PIC microcontroller to be ideal for the purpose.
The compensating unit 160 therefore needs to produce a voltage output, corresponding to the flowrate and with equivalent calibration as the sensor, and to superimpose this onto the pressure signal, ready to send to the analyser/display 154. Since said pressure signal is the output from a Wheatstone bridge pressure sensor, it is of very small magnitude, and so the compensating signal is of similarly very small magnitude. The inventors have found that a suitable way to achieve this is to output a signal in the form of a pulse width modulated signal from the processor and to heavily attenuate this by means of an operational amplifier (so that the voltage level is compatible with the bridge output) and finally to add this to the bridge output by means of a summing amplifier.
The apparatus shown in Figure 5 is similar in many respects to that shown in Figure 4 and corresponding components are therefore denoted by the reference numerals used in Figure 4, raised by 100. The apparatus shown in Figure 5 obtains flow information by means of measurement.
In this case, the proximal pressure sensor 238 is interposed between the open Tee 256 and the housing 224 to which the proximal sensor 238 is connected in series with a further pressure sensor 262 the output of which is also connected to the signal compensating processor 260. In this case, the infusion pump 258 is connected to the Tee 256 via a three-way valve in a Tee shaped housing 264.
The sensors 238 and 262 are substantially identical to each other, and are connected by a short length of connecting tubing 266 which defines a passage through which liquid being injected into the system (from the infusion pump or other source) via the auxiliary input on the Tee-shaped housing 264 or the pressurised saline bag 230 flows from the sensor 238 to the sensor 262. It will be appreciated that the sensors 238 and 262 and connecting tubing 266 comprise pressure change monitoring means that can be used to monitor the drop of pressure caused by liquid flowing along the tubing 266, from which the corresponding drop of pressure caused by the liquid flowing along the catheter 201 can be inferred. The sensor 238 is coupled to fluid at a first position, whilst the sensor 262 is coupled to fluid at a second position, wherein fluid travelling from sensor 238 to sensor 262 travels along the passage 262.
Liquid flowing through the pressure sensors 238 and 262 from either the saline bag, infusion pump or auxiliary input in the Tee-shaped housing 264 will cause a pressure drop down the catheter 201. However, if the pressure drop or flowrate in the catheter can be measured or inferred, it can also be corrected for by the compensating circuit 260.
Similarly, if blood is sampled from the patient, there is a pressure drop in the opposite direction, and correction can also be made for this.
Note, as described above, to avoid hydrostatic pressure errors, the proximal pressure sensor 238 is located at the same elevation as the patient’s heart. This can be achieved by locating it away from the surgical table as shown in Figure 2.
The pressure drop along the catheter inferred from the pressure change monitoring means output can be subtracted from the measured pressure signal.
Hence:
(4)
In a modification of the Figure 5 apparatus the proximal pressure sensor can be a separate third pressure sensor. As in the known arrangement, it can be positioned at the same elevation as the patient’s heart, thereby avoiding any potential hydrostatic pressure errors that could otherwise be introduced, ft will also be appreciated that it can be located proximal, and upstream of Tee 256 in the limb connecting to saline bag 230.
An advantage of measuring the pressure drop across the passage 266 is that this measurement would be affected by changes in temperature or viscosity in the same way as the pressure drop along the catheter. Thus effectively, the pressure change sensor means mimics the catheter and so responds in a similar way to extraneous changes.
Despite the assumption made above, the relationship between APcatheter and the pressure drop along the passage 266 is not necessarily linear, but will depend on the prevailing flow
conditions in the two at any point in time. The catheter is a long regular conduit and under many circumstances the Reynolds number is relatively low, so it provides opportunity for steady laminar flow to develop. Under laminar flow conditions, the pressure drop as a function of flow rate is governed by the Hagen-Poiselle equation
(5) where μ, L, Q and r are the liquid viscosity, length (of catheter), volumetric flowrate and radius respectively. Note that this is a linear relationship between pressure drop and flowrate.
If the passage 266 is of constant internal cross section, then it might take the form of a long tube (mimicking the catheter itself) in order to achieve lamina flow conditions.
However, the passage 266 can include a flow restriction (not shown) across which most of the pressure drop will occur so that the pressure drop along the passage will, in effect, be substantially the same as that across the restriction (APrestriction·)· This enables a shorter passage to be used.
If the passage were to have a flow restriction comprising a simple orifice, the flow regime through would be unlikely to be laminar (unless the viscosity is very high or the flowrate very low), and under these (i.e. turbulent or transition) flow conditions, the relationship between pressure drop and flowrate might no longer be a simple linear one (under many turbulent conditions it will follow a square law).
Thus, the restriction is such that the flow conditions through it are laminar, then both APcatheter and Prestriction will be linear relationships with flowrate and hence with each other. To that end the restriction in example could be a Venturi.
In which case: (6)
And hence with the proximal pressure sensor is proximal and upstream of the passage (as shown):
(7)
Or if the proximal sensor were situated distal and downstream of the passage:
(8)
Figures 6-8 show an arrangement of sensors which can be used as a dedicated pressure change sensor means or as a combined proximal pressure sensor and pressure change sensor means to be used in the arrangement of Figure 5 in place of the sensors 238 and 262 and connecting tubing 266. The arrangement comprises a tubular housing 268 formed as a single injection moulding of a suitable plastics material such as polypropylene or polycarbonate.
The housing 268 is formed with standard luer end connectors 270 and 272 for connection to tubing so that the housing can be situated in series with the flow path of fluid being supplied to the catheter. The moulding is formed with two square pockets 274 and 276 which are axially spaced along, and at the same angular position on, the housing 278. At the base of each of the pockets there is provided a central, square aperture leading to the hollow interior of the housing 268, and surrounded by a respective square shoulder that provides a support for the components of a respective pressure sensor.
The pressure sensor which is situated in the pocket 276 comprises a lower elastomeric sealing gasket 278, produced in a material such as EPDM, which sits on the square shoulder of the base of the shoulder 276 and supports an etched silicon membrane which carries piezo-resistive elements, and which is sandwiched between the gasket 278 (which acts as a sealing gasket) and an electrically conductive upper gasket 282. Gasket 282 could also be manufactured in a material such as EPDM, but with localised areas impregnated with electrically conducting particles so that it forms selective electrical connections between the connection points on the silicon membrane and the external connection (see below).
The second pressure sensor, situated in the pocket 274 is constituted by a similar arrangement of an etched silicone membrane 284 sandwiched between a lower sealing gasket 286 (which itself sits on the square shoulder at the base of the pocket 274) and an upper electrically conductive gasket 288.
The two pressure sensors are held in place in the pockets 274 and 276 by means of an overlying PCB 287 attached to the housing by means of thermally deformed (heat staked) pegs 289 so as to retain the sensors in place and maintain a sealing contact between the elastomeric gaskets 278 and 286 and the housing 268 and membranes 283 an 284. The PCB can support a series of printed resistive elements which can be laser machined during production, if necessary, to match the sensors to each other and to achieve a combined output having suitable performance characteristics (discussed below). The lower face of each diaphragm is exposed, in use, to liquid flowing through the housing, each upper face being exposed to atmospheric pressure.
The two sensors may be from the 2xPC family manufactured by Honeywell, in which case only two of the four piezo resistive elements in those devices would be electrically connected. By comparing Figures 3 and 9 it will be apparent to the reader which of the two elements are connected in the two sensors. A custom manufactured silicon device with just two piezo-resistive elements would provide a number of benefits, such as reduced cost and the freedom to configure the precise sensitivity of the two sensors and the dimensions of the flow restriction as a specifically designed subsystem.
The housing 268 includes a restriction constituted by a throat in a form of a Venturi 290 situated downstream (in the flow path of liquid through the housing in use) one of the pockets 276 and 274 and upstream of the other of the pockets 276 and 274. The restriction is thus interposed between the positions at which the pressure sensors are coupled to fluid in the fluid passage by the housing 268. If liquid is being injected into the system, the Venturi 290 will be downstream the pocket 276 and upstream the pocket 274. Extraction of liquid would involve flow of liquid through the fitting in the reverse direction so that the Venturi would then be downstream of the pocket 274 and upstream of the pocket 276.
In Figure 8, the pressure sensor contained in the pocket 276 is denoted by reference numeral 292 whilst 294 is the sensor in the pocket 274.
If the assembly shown in Figures 6-8 is used in the apparatus of Figure 5 as described above, then the housing 268 is connected in series between the open Tee 256 and valve housing 224. Once they are connected, the sensor 294 is the lower of the two sensors, but may be used as the proximal pressure sensor. In such a case, the apparatus is to be set up so that the sensor 294 is at the same level as the patient’s heart. With this arrangement, in use, the sensor 294 obtains a measurement of aortic blood pressure, whilst the combined output of the sensors 294 and 292 compensates for the effect of the flow of liquid along the catheter into the patient.
When the sensor 294 is employed as the proximal pressure sensor, the sensors 292 and 294 are connected in a split bridge configuration as shown in Figure 9 in which the piezo-resistive elements of the sensor 294 in the bridge are shown at 296 and 298 whilst 300 and 302 denote the piezo-resistive elements of the sensor 292 in the other half of the bridge.
Hence the two sides of a conventional Wheatstone bridge circuit have been split between the two sensors.
In the following, the output from sensor 294 is referred to as Pi and the output of the sensor 292 is P2.
Now, initially suppose that there is zero blood pressure (relative to atmospheric pressure) and that the sensitivity of the two sensors 292 294 and the magnitude of the restrictor are designed such that, at any flowrate, the voltage output of the two sensors are identical. This is illustrated in Figure 10, in which the line 304 shows the response of sensor 294, whilst line 306 shows the response of the sensor 292.
Note that, in this specific situation, Pi = APcatheter and P2 - Pi = APrestriction
The voltage output from the two sensors for flow, but zero BP (blood pressure) is: and
Where L is the gradient of line 304, and M is that of line 306, L and M can be designed such that: hence
If now blood pressure (BP) is re-introduced at the tip of the catheter, then the voltage output (corresponding to Figure 3 and Equation 0) is:
Or, expressed using the terminology of Equation (0), the voltage output from the sensor system is:
(12)
Notice that this is a function of variable BP alone and that L and M can be selected so that the signal magnitude is equal to that of existing proximal sensors. Hence this arrangement successfully removes the effect of any flowrate in the catheter and can be used as a “drop-in” replacement to display true BP on the patient monitor.
Figures 11-13 show a similar arrangement of pressure sensors and a restriction within a housing, but in this case, the housing is a bifurcated fitting for direct connection to the guide catheter.
The housing 308 has a standard, distal luer fitting 310 which, in use, is inserted into the catheter. The opposite end of the housing 308 is provided with a known type of device entry gland 312 providing a central port 314 into which a pressure wire or other devices may be inserted. The housing may, for example, be formed by injection moulding of a suitable plastics material, and is provided with a liquid supply branch 316 via which liquid may be introduced into the fitting for injection into the patient along the catheter.
The underside of the housing 308 is provided with square pockets 318 and 320 which are similar in form and function to the square pockets to the fitting shown in Figures 6 and 7, and which thus accommodate two pressure sensors 322 and 324 which are of the same type as the pressure sensors 292 and 294 (and thus comprise etched silicone membranes each of which is sandwiched between an elastomeric sealing gasket and a conductive gasket). For the sensor 324, reference numerals 326, 328 and 330 respectively denote the sealing gasket, the membrane and the conductive gasket. The arrangement of gaskets and membrane for the sensor 322 is identical. It will be appreciated that, since the pockets are on the underside of the housing 308, the uppermost gasket of each sensor is the elastomeric sealing gasket whilst the conductive gasket that connects the sensor to a PCB 309 is the lowermost gasket. The PCB 309 is directly comparable to the PCB 287 of the Figure 6-8 arrangement, and is attached to the housing by means of thermally deformed (heat staked pegs) 311.
As can be seen from Figure 12, the sensors 324 and 322 are positioned one on either side of a throat in the form of a Venturi 332, so that the Venturi 332 is interposed between the sensors.
It will be appreciated that, if in this case the sensor 322 is to be used to house the proximal pressure sensor, then the fitting should be maintained at the same elevation as the patient’s heart. Alternatively, the pressure sensors 322 and 324 and Venturi 332 could just be used as means for measuring the pressure change across the restriction (which, for laminar flow through the restriction will bear a simple relationship to the pressure change resulting from fluid flowing along the catheter) and using this in conjunction with a pressure reading taken from a separate proximal pressure sensor. Such an arrangement is shown in Figure 25, in which components corresponding to those shown in Figure 5 are indicted by the reference numerals of Figure 5 raised by 200. The bifurcated fitting is referenced 500 and is shown connected to the catheter 401, whilst the proximal pressure sensor 438 is supported on a trip stand 502 at the same height of the heart of the patient 504. The schematic view shown in Figure 14 illustrates a guide catheter with a bifurcated fitting that includes pressure change sensor means in the form two pressure sensors (Pi and P2 positioned one either side of a restriction. The fitting only differs from the fitting shown in Figures 12 and 13 in that the pressure sensors are on top of the housing rather than the underside).
Figures 15-17 show dedicated pressure sensing means which include a differential pressure sensor. This type of pressure sensing means would be used in conjunction with a separate proximal pressure sensor as illustrated in, for example, Figure 24 which corresponds in many respects to Figure 25 and in which corresponding components are therefore indicated by the same reference numerals as are used in Figure 25. In this case, however, the bifurcated fitting 500 is a standard fitting which therefore lacks any pressure sensors. Instead, the arrangement shown in Figures 15-17 is installed at 506.
The inline pressure sensor means shown in Figure 15-17 is a differential pressure sensor having a three-part housing 508 having a female luer connector 510 into which liquid flows into housing 508, through a passage (described below) and then out through an outlet, male luer connector 512 on the other side of the housing 508.
The connectors 522 and 510 are provided on respective end plates 514 and 516 between which are sandwiched a mid-plate 518. The three plates being bonded together by means of a suitable adhesive such as UV curing epoxy the end plate 514 includes on its inner face a channel along which liquid can flow, and which is aligned with a corresponding channel 522 (Figure 17) in the plate 516. These two channels are, at their upper end, aligned with a bore 524 in the mid-plate 518. The channels 520 and 522 and the bore 524 thus, between them, define a serpentine path for liquid flowing through the housing 508. Housing 508 could be injection moulding material such as polypropylene or polycarbonate.
It will be appreciated that the bore 524 is of a smaller cross-sectional area than the channels 520 and 522 and therefore constitutes a restriction and in addition, the bore is flared at both ends so that laminar flow of liquid through the bore is promoted.
The mid-plate 518 includes a square aperture 526 which accommodates a pressure sensor generally referenced 528 similar in construction to the pressure sensors shown in Figures 6 and 7 and 11-13 (for example the pressure sensor 324). The pressure sensor 528 thus has an elastomeric gasket 530 and an electrically conductive gasket 532 between which is sandwiched an etched silicone diaphragm 534. The conductive gasket 532 abuts a square, inturned flange at the edge of the aperture 526 closest the plate 516. The gasket 532 is in contact with electrically conductive pins 538 which connect the diaphragm 534 to analysing circuitry. In use, both bases of the diaphragm 534 are exposed to liquid flowing through the housing 508. However, in the case of liquid delivery, the liquid in contact with the face open to the channel 522 is upstream of the bore 524, whilst the liquid in contact with the opposite face, i.e. the face open to the channel 520, is downstream of the bore 524. The diaphragm 534 will thus flex in response to changes in the pressure drop across the bore 524, but will not be substantially affected by the absolute pressure of liquid in the housing 508. Thus, if no liquid is flowing, then the pressure sensor should give a zero reading whatever the absolute pressure of liquid.
Since only pressure change is being monitored in this arrangement, this type of pressure change sensor means is, in use, used with a separate proximal pressure sensor, as is shown at 540 in Figure 18. The sensors 528 and 540 can be connected together in a split bridge configuration as shown in Figure 19 in which 542 and 544 denote the piezo-resistive elements of the sensor 528, and 546 and 548 show the piezo resistance of the corresponding elements for the sensor 540.
The dedicated differential flow sensor has several benefits: even if the absolute pressure in the flowline is high, the differential pressure will remain moderately low, so it can be designed as a much more sensitive device since flow is measured by a single device, any variances (e.g. from manufacturing) between individual devices are eliminated - the voltage output from the bridge circuit associated with the sensor is a direct indication of flowrate.
Thus, if the flow conditions through the orifice are laminar, the relationship is simplified to the following:
(11)
If the differential and proximal transducers have sensitivity and output R, e and S, f respectively then: and
Hence:
Now if R, S and k are selected so that S (1 + k) = R, then the voltage output (corresponding to Equation 9) is:
Or, expressed using the terminology of Equation 9, the voltage output from the sensor system is:
(13)
This is a function of BP, i.e. blood pressure, alone (and not of flow) so if the value of S is chosen appropriately this can provide a “drop-in” replacement for existing BP proximal sensors.
Figures 20-22 show a bifurcated catheter fitting similar to that shown in Figures 11-13, but in this case incorporating a differential pressure sensor.
Thus the pressure change sensor means comprises a housing 550 provided at one end with a male luer connector 552 and at the other end with a gland 554 of a known type for receiving a pressure wire. The connector 552 is for connection to a guide catheter.
The fitting also includes a liquid supply branch 556 through which liquid can be introduced into the guide catheter via the fitting. As can be seen from Figure 21, the housing 550 is of a two part construction having a main body part 556 the upper face of which includes an elongate slot 558 surrounded by an upstanding peripheral wall 560. The body portion 556 and wall 560 also provide a square socket 562 for accommodating a pressure sensor 564 of
the same type as the pressure sensor 528, thus including a silicon diaphragm 566 which is etched with piezo resistant elements and is interposed inbetween an upper, elastomeric ceiling gasket 568 and a lower electrically conductive gasket 570 which is, in use, in contact with conductive pins 572 for connecting the sensor 564 to the circuitry for operating the sensor and analysing its output.
The other part of the housing 550 comprises the branch element 556, the underside of which is channelled so as to define, with the slot 558, part of the serpentine passage for liquid through the fitting. The channel in the portion 556 is shown at 574 in Figure 22. As can be seen from Figure 22 liquid supplied along the branch 556 will flow along the passage defined by the spot 558 and channel 574, where it will be in contact with one face of the diaphragm 566. The liquid will then pass into the main passage of the housing 550 (referenced 576), past a throat in the form of a Venturi 578 and past the opposite face of the diaphragm 566, before leaving the fitting. The sensor 564 thus acts as a differential pressure sensor in a similar fashion to the sensor 528 of the arrangement shown in Figures 15-17.
Figure 23 shows a slightly modified version of the fitting, in which there is also provided a proximal pressure sensor 580.
In either case, the output from the differential pressure sensor and the proximal pressure sensor (which may be in the fitting or separate) can be combined by means of a split bridge circuit in the way described above. A further advantage of the embodiments shown in Figures 20-23 is derived from the fact that any additional devices, such as pressure wires, balloons, stents or micro-catheters, introduced to the patient’s heart through the guide catheter, also pass through the flow restriction. Any said additional devices will cause a partial occlusion of the guide catheter resulting in increased pressure drop of any flowing liquid. However, since the additional devices also pass through the restriction, it also will be affected in a similar way with a corresponding increase in pressure difference across it. Thus the embodiments of Figures 20-23 provide the capability to compensate for additional devices introduced to the patient’s heart.
It will be appreciated that, to realise this benefit, the flow restriction has to be located in the main passage 576 which is axially co-located with the guide catheter, whereas it could otherwise be located at any point in the flow path between the opposite faces of the sensor diaphragm, such as at location 558.
The split bridge sensor systems above offer simple and reliable design solutions, but under some circumstances it may be beneficial to modify the signal provided to the patient monitor, such as if either: - the flow through the restrictor cannot easily be controlled to laminar conditions, or it would be desirable to make the sensor configurable by the user, such as to be able to switch between catheters of different diameter.
In such circumstances, the output signals from the full Wheatstone bridges connected to the sensors would need to be manipulated by one or more amplifiers. An example of such an arrangement is shown in Figure 26, in which Pi represents the proximal sensor and P2 the pressure sensor on the other side of the restriction from Pi.
In electronic terms, the output needs to be compatible with the two wire system, with voltage signals to resemble the situation in Figure 3 (i.e. AVbP = a - b).
If the sensors are configured with a restrictor as shown in Figure 8, the pressures are as follows: and but if then
If the voltages generated at the nodes of the two Wheatstone bridge circuits in Pi and P2 are a, b and c, d respectively, then the final voltage representing actual BP is given by:
However, to mimic the output of existing proximal sensors supplied to the pressure analyser, this needs to be in the form AV = a - b. It can thus be rearranged to the following form:
(14)
This is in a form that could be manipulated by a network of operational amplifiers or even a single summing differential amplifier as shown in Figure 27.
In the summing differential amplifier the resistors can be selected so that the output voltage is of the correct form.
Note also that a suitable amplifier circuit(s) could be arranged to provide the correct output if the sensors are configured with a restrictor as in Figure 9.
It will also be clear that any of these circuits could be configured to achieve different objectives. For example: if it is preferable to use a simple orifice (for the restrictor) where the flow will almost inevitably be turbulent, the circuit output can be arranged to provide a matching nonlinear output. This can be done in analogue electronics (with the use of MOSFET devices in the feedback loop) or by converting the signal to digital format (using an A to D converter) and using a microprocessor to perform the necessary signal processing. if the system needs to be user-configurable for different size catheters, for example the gain of the amplifier(s) could be switchable to provide matching output. Alternatively, this might be easier to implement using digital electronics.
In much of this document, the catheterisation configurations have been described within the context of FFR. However, many of the ideas and principles described could apply to other procedures (probably, but not limited to, medical procedures) where liquids (not limited to drugs) are delivered, or samples (not limited to blood samples) are taken whilst simultaneously measuring pressures at the tip of a catheter (or other conduit).
For example, it could be desirable in cardiac catheterisation procedures (in addition to FFR) for a various agents to be delivered to, or samples taken from, the chambers of the heart or the arterial structure surrounding it, whilst simultaneously monitoring the patient’s blood pressure.
Thus specific references made in this document could be applied more broadly (e g. “guide catheter” can also apply to other cardiac catheters and catheters in general).

Claims (34)

Claims
1. Fluid delivery apparatus for use with a system for containing or conveying fluid, the apparatus comprising a fluid delivery conduit for connection, at a distal end of the conduit, to the system, pressure monitoring means for monitoring the pressure of fluid in the system, said pressure monitoring means being in fluid communication with the system via the conduit, the apparatus including compensation means for use in compensating for, or reducing the effect of, the flow of fluid through the conduit on the output of the pressure monitoring means.
2. Apparatus according to claim 1, in which the compensation means is operable to quantify an effect of the flow of fluid and to use said quantity to compensate for, or reduce the effect of, the fluid flow through the conduit on the output of the pressure monitoring means.
3. Apparatus according to claim 2, in which the compensation means includes sensor means for quantifying an effect of the flow of fluid by means of measurement.
4. Apparatus according to claim 2 or claim 3 in which the apparatus includes injector means for supplying or extracting fluid to the system, through the delivery conduit.
5. Apparatus according to claim 4, in which, the injector means comprises a pump.
6. Apparatus according to claim 4 or claim 5, in which the sensor means is separate from the injector means and connected between the latter and the delivery conduit.
7. Apparatus according to any of claims 4 to 6, in which the pressure monitoring means comprises a proximal pressure sensor situated at a position spaced from the distal end of the fluid delivery conduit.
8. Apparatus according to claim 7 in which the proximal pressure sensor is so situated relative to the conduit, that, in use, the fluid to be injected into the system or sampled from the system also travels along the conduit through the proximal sensor.
9. Apparatus according to any of claims 3 to 8, in which the sensor means comprises pressure change sensor means for measuring the pressure change in a fluid flowing through a passage, or part of a passage.
10. Apparatus according to claim 9, in which the pressure change sensor means comprises a first sensor coupled, in use, to fluid at a first position and a second sensor coupled, in use, to fluid at a second position spaced from the first position, wherein fluid travelling from one to the other of the positions travels along at least part of the passage.
11. Apparatus according to claim 10, when dependent on claim 7 or claim 8, in which, one of the first and second sensors is said proximal sensor.
12. Apparatus according to claim 9, in which the pressure change sensor means comprises a differential pressure sensor.
13. Apparatus according to claim 12, in which the differential pressure sensor has a common pressure sensitive element having a first face coupled, in use, to fluid at the first position and a second face coupled, in use, to fluid at the second position.
14. Apparatus according to claim 13, in which said pressure sensitive element comprises a flexible diaphragm.
15. Apparatus according to any one of claims 9 to 14, in which the passage comprises a restriction in a conduit, the restriction being interposed between the first and second positions.
16. Apparatus according to claim 15, in which the restriction profile is such that the passage progressively tapers and widens.
17. Apparatus according to claim 16, in which the restriction comprises a Venturi.
18. Apparatus according to any of claims 9 to 17, in which the sensor means is located between the delivery conduit and a device entry gland such that any devices introduced to the system via the device entry gland and delivery conduit also pass through the passage.
19. Apparatus according to claim 7 or claim 8, in which the compensating means generates an electrical signal of magnitude equal to the effect on the output of the proximal pressure sensor of the flow of fluid through the delivery conduit.
20. Apparatus according to claim 19 in which said electrical signal is summed with the output of the proximal pressure sensor to give a pressure representative of the fluid pressure in the system.
21. Apparatus according to claim 7 or claim 8, in which the compensation means further comprises analogue circuitry for combining the outputs of the proximal pressure sensor and a pressure sensor, other than the proximal pressure sensor, of the compensation means to give an output representative of fluid pressure in the system.
22. Apparatus according to claim 21, in which the circuitry comprises a bridge circuit, which incorporates the pressure sensors.
23. Apparatus according to claim 22, in which the bridge circuit comprises a Wheatstone bridge.
24. Apparatus according to claim 22 or claim 23, in which the proximal pressure sensor includes piezo-resistive elements, each connected between a respective pair of junctions of the bridge.
25. Apparatus according to claim 24, in which said sensor other than said proximal sensor, also has piezo-resistive elements, each connected between a respective pair of junctions of the bridge.
26. Apparatus according to claim 11, in which the proximal sensor and the second sensor have differing sensitivities such that the pressure in the system is the only variable affecting the combined output of the sensors.
27. Apparatus according to claim 12, when claim 9 is dependent on claim 7, in which the sensitivities of the differential sensor and the proximal pressure sensor and the relationship between the flow rate of fluid through the passage with the measured pressure difference are be such that the pressure in the system is the only variable affecting the combined output of the sensors.
28. Apparatus according to any of the preceding claims, in which the apparatus is for use with a system for containing or conveying fluid when in its liquid state, the fluid delivery conduit functioning as a liquid delivery conduit, the fluid pressure to be monitored to being the pressure of liquid in the system.
29. Apparatus according to claim 28, in which the apparatus comprises coronary or cardiac catheterization apparatus.
30. Apparatus according to claim 29, in which the apparatus is for use in an FFR procedure.
31. Apparatus according to any of claims 9 to 17, in which at least one pressure sensor of the pressure change monitoring system is situated in a bifurcated fitting for attachment to the proximal end of a fluid delivery conduit constituted by a guide catheter of the apparatus.
32. Compensation means for use with fluid delivery apparatus in accordance with any of the preceding claims, the compensation means being programmed or arranged to compensate for, or reduce the effect of, the flow of fluid through the fluid delivery conduit of the apparatus on the output of the pressure monitoring means of the apparatus.
33. Compensation means according to claim 32, in which the compensation means is connected in series, to the fluid delivery conduit of the apparatus, and includes sensor means for measuring said effect.
34. Apparatus according to any of the claims 3 to 27, in which the sensor means is located between the delivery conduit and a device entry gland such that any devices introduced to the system via the device entry gland and delivery conduit also pass through the passage in said flow sensor.
GB1512454.8A 2015-07-16 2015-07-16 Fluid delivery apparatus Withdrawn GB2541368A (en)

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US11724030B2 (en) 2018-09-21 2023-08-15 Corflow Therapeutics Ag Method and apparatus for diagnosis and treatment of microvascular dysfunction
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Cited By (6)

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US12100516B2 (en) 2018-05-31 2024-09-24 Corflow Therapeutics Ag Microfluidic coronary circulatory model
US11724030B2 (en) 2018-09-21 2023-08-15 Corflow Therapeutics Ag Method and apparatus for diagnosis and treatment of microvascular dysfunction
US20220276110A1 (en) * 2019-07-18 2022-09-01 Semitec Corporation Pressure sensor
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US11786140B2 (en) * 2019-08-21 2023-10-17 Corflow Therapeutics Ag Controlled-flow infusion catheter and method
WO2023116789A1 (en) * 2021-12-23 2023-06-29 华为技术有限公司 Blood pressure measuring device and electronic device

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