GB2276456A - A pnematic pressure pulse generator for testing blood pressure monitors - Google Patents

Abstract

A pneumatic pressure pulse generator comprises a main chamber having two compartments separated by a diaphragm 14 which is displacable by a audio drive unit 2 and 11, and a smaller chamber connected to one compartment 18 of the main chamber. An electrical pulse signal applied to the drive unit produces a positive pressure pulse in compartment 18 which passes through a port 25 to an outlet 16 to simulate an adult's pulse. A flow restrictor 3 prevents corresponding negative pulse in the other compartment passing through a port 21 to the outlet 16, while equalising the static pressure in the compartments. A smaller pressure pulse to simulate a neonate's pulse is produced at an outlet 17 via a diaphragm 13 in the smaller chamber. The pulse may be applied directly to the blood pressure monitor or to a cylinder about which the cuff of the monitor is wrapped. <IMAGE>

Description

PNEUMATIC PRESSURE PULSE INDUCER INCORPORATING FLEXIBLE PRESSURE TRANSFER CHAMBER.

This invention relates to a pneumatic pressure pulse inducer incorporating a flexible pressure transfer chamber.

Bloodpressure is one of the most important physiological measurements that can be obtained from a human being and a whole range of monitors are available to perform this function. By far the most popular type is the non-invasive oscillametric bloodpressure monitor and these monitors are used extensively in hospitals throughout the world. The correct operation of these monitors is paramount and hence a reliable and accurate way of testing them was needed. The main problem of testing these monitors was the requirement to superimpose small pressure pulses on to a varying system pressure. This can be done either directly by connecting in to the monitors pressure system or indirectly by inducing pulses through the monitors cuff wall. The latter method being what the human arm does.

Hence this invention was conceived to satisfy the above requirements.

According to the present invention there is provided a pneumatic pressure pulse inducer incorporating a flexible pressure transfer chamber.

Comprising a main equalisation of pressure chamber with front and rear pneumatic entry ports. Inside this chamber, dividing it in to two seperate compartments is the pressure drive unit (standard audio drive unit e.g. Bose 4 inch 802-2). A Tee-piece and tubing connect the front, rear and external port together. The tube connected to the rear port contains a dynamic flow restrictor in the form of a microbore tube.

An additional microchamber of reduced volume is coupled via a rubber membrane to the main chamber, its output can be accessed via a seperate port.

A full component and technical description follows with reference to figures 1 and 2.

The pneumatic pressure pulse inducer consists of the following component parts (see figure 2). A main equalisation of pressure chamber consisting of a cylindrical container 1 with entry port 21 and pressure sealed electrical connections 10, the drive unit consisting of 2,11,14, seats on to the shoulder 23 of the cylindrical container 1 and air tight sealing is povided by 0 ring 4. The drive unit 2,11,14, is secured within the cylindrical container 1 by chamber lid 9. The profile of same is such as to minimise the chamber volume, a hole 24 drilled through the chamber lid 9 provides the pneumatic coupling to the microchamber diaphragm 13, a futher hole 19 provides direct connection to the front chamber port 25.

An air tight seal is provided between chamber lid 9 and cylindrical container 1 by sealing washer 21. Five countersunk screws (not shown) secure chamber lid 9 to cylindrical container 1. The microchamber lid 7 seats within the chamber lid 9 recess and an air tight seal is provided between the two via 0 ring 8. The microchamber lid 7 and diaphram 13 are secured to chamber lid 9 with four countersunk screws outwardly concentric to the 0 ring 8.

A hole 20 provides access to externs port 26. A foam compression return ring 12 of circular cross section is inserted between chamber lid 9 and drive unit diaphragm 14. A dynamic flow restrictor 3 consisting of a short length of capillary tubing is secured within tube 22. T-piece 5 connects together tubes 22,27 and 16, tube 27 connects from T-piece 5 to chamber lid entry port 25. Tube 16 allows external connection to the rest of the system. Tube 17 allows external connection to the microchamber lid 7.

Refering to figure 1. The flexible pressure transfer chamber 28 consists of a cylinder manufactured from a non - elastic, flexible, airtight material capable of with standing an air pressure of 300mmhg (40x103NImZ).

Pneumatic entry to the chamber is provided by tube 29.

Refering to figure 2 the following describes the operation of the pneumatic pressure inducer.

Two methods of inducing pressure pulses into an external system will now be explained. Direct inducement i.e. not incorporating the flexible pressure transfer chamber 28,29 and indirect inducement incorporating the flexible pressure transfer chamber 28,29. Considering the direct method first, an external pressure system can be connected to the cylindrical container 1 via tube 16 with tube 17 occluded, or can be connected to the microchamber via tube 17 with tube 16 occluded. With the external pressure system connected to tube 16, the pressure input from this system enters the cylindrical container 1 via ports 25 and 21. The holes 30 in the drive unit frame 11 allow this pressure to equalise on either side of the diaphragm 14.

If a positive pulse electrical drive signal is applied via the electrical connections 10 to the drive unit 2,11,14. Then displacement of the diaphragm 14 occurs (normal loudspeaker action) in the direction of the chamber lid 9 this produces a dynamic pressure pulse with amplitude and shape proportional to that of the electrical drive pulse applied. The dynamic pressure pulse appears at port 25. Due to the action of dynamic restrictor 3, preventing any rapid changes in pressure passing into the volume contained behind the diaphragm 14 the majority of the induced pressure pulse appears at tube 16. This enables pressure pulses to be superimposed on to the external system pressure. With tube 16 occluded a pressure system of low volume can be connected via tube 17 to the microchamber input port 26. Pressure from this system is mechanically coupled via diaphragm 13 to orifice 24. The dynamic pulse producing action as described previously causes a pressure pulse to pass through orifice 24 deflecting diaphragm 13. This action superimposes the pulse on to the external pressure system connected to tube 17.

Refering to figures 1 and 2 the indirect method of pulse inducement using the flexible pressure transfer chamber will now be described.

Using this method the flexible pressure transfer chamber is connected to tube 16 of the pneumatic pressure pulse inducer. Flexible chamber 31 is now pressurized to a known pressure e.g. 40 mmHg (5-33xl9N/t). This residual pressure provides efficient mechanical coupling between the external pressure system and chamber 31. Dynamic pressure pulses produced at tube 16 as described previously are introduced in to the chamber 31 via tube 29. These pressure pulses cause mechanical deflection of the non-elastic flexible wall of chamber 31. If a flexible volume (e.g. non-invasive bloodpressure cuff) being the whole or part of the external pressure system volume is now wrapped around chamber 31 then the pressure pulses induced in chamber 31 will be mechanically coupled via the deflection of the non-elastic flexible wall 28 of chamber 31, to the external pressure system. The resulting induced pulses will be superimposed on to the pressure of the external system. This indirect method can also be used by connecting a similar flexible pressure transfer chamber to the microchamber port 26 via tube 17.

Specific embodiments of the invention will now be described by way of examples with reference to the accompanying drawings in which: Figure 3 shows a non-invasive oscillametric bloodpressure monitor being tested by the direct method i.e. without the use of the flexible pressure transfer chamber.

Figure 4 shows a non-invasive oscillametric bloodpressure monitor being tested by the indirect method i.e. incorporating the flexible pressure transfer chamber.

Refering to figure 3 the bloodpressure monitor 36 is connected as shown to adult pressure port 43 with its cuff 37 wrapped around rigid mandrel 44. Port 40 of valve 38 is connected to port 42, neonate port 39 is occluded. Pressure measuring transducer 32 constantly monitors the system pressure. Microprocessor controller 34 in conjunction with pressure input signal from pressure measuring transducer 32, and electrical pulse production/drive module 33 causes diaphragm 14 to deflect (normal loudspeaker action) producing pressure pulses at the adult port 43. These pulses which are superimposed onto the external system pressure of monitor 36 and cuff 37 follow a pre-programmed bloodpressure envelope whose parameters can be adjusted by the parameter input module 35.

This simulates the pressure pulse response of a human arm during a noninvasive bloodpressure monitor determination. This simulated adult bloodpressure can be repeated indefinitely or changed via the parameter input module 35.

Again refering to figure 3 if it is required to test the neonate capabilities of a monitor the procedure is as follows: Adult cuff 37 and mandrel 44 are replaced by the neonate equivalents, port 43 is occluded, valve 38 is energised via microprocessor controller 34 connecting port 40 of valve 38 to occluded port 41. This reduces the volume of the pneumatic pressure pulse inducer to that of the microchamber.

The monitor and cuff are now connected directly to neonate port 39 where neonate pressure pulses are superimposed onto the monitors system pressure in accordance with pressure envelope valves set by the parameter input module 35. Again this neonatal bloodpressure can be repeated indefinitely or changed via the parameter input module.

Refering to figure 4 the production of a simulated bloodpressure for both adult and neonate is virtually the same as in the direct method. The only difference being in the actual connection of the monitors to the simulator. Using the indirect method the monitor 36 under tests cuff 37 is wrapped around the flexible pressure transfer chamber 31. Which itself is connected via tube 29 to either the adult port 43 or the neonate port 39. The flexible pressure transfer chamber 31 is pressurized to a residual known pressure (e.g. 40 mmHg5-33xlR by the pump/valve unit 45 controled by microprocessor controller 34 in conjunction with pressure measuring transducer 32. The monitor 36 under tests cuff 37 is then wrapped around the chamber 31. The changes in the non-elastic flexible chamber 31 pressure are proportional to the changes in monitor cuff 37 pressure. Although pressure changes in chamber 31 are proportional to those in monitor cuff 37 the constant of proporionality is less than unity. Hence a residual pressure is required within chamber 31 to allow cuff 37 to produce sufficient pressure change in chamber 31 to enable a human bloodpressure of acceptable parameters (e.g. systolic 120 mmHgf diastolic 80 mmHg(wSfl01Nbto be simulated. The pressure pulses induced into the flexible pressure transfer chamber 31 are then coupled to the monitor 36 under tests pressure system by the deflection of the non-elastic flexible chamber wall 28, deflecting the monitors 36 cuff 37 wall.

Claims (11)

1. A A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber. Comprising a main equalisation of pressure chamber divided into two compartments by the diaphragm and frame of a standard audio drive unit, two pressure entry ports at the front and rear of the chamber. the rear port incorporating a dynamic flow restrictor, a small volume microchamber coupled to the main chamber lid with a pneumatic entry port giving access to chamber.
2. 2. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claim 1 where in a means is provided to equalise the pressure in front of and behind the drive unit diaphragm by way of a tube connecting the enclosed volume in front of the diaphragm to the enclosed volume behind the diaphragm.
3. 3. Apneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claimes 1 and 2. Where in the means out lined in claim 2 allows for an external pressure to be applied via a tube and T-connector to the front and rear compartments as outlined in claim 1.
4. 4. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claim 2 or claim 3. In that there being no difference in pressure between the front and rear of the drive unit diaphragm, it is therefore claimed that any dynamic change in pressure produced by the drive unit Is not attenuated in any way as would be the case if a differential pressure did exist.
5. 5. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claimes 2, 3 and 4. Wherein a microbore dynamic flow restrictor secured with in the tube connecting to the rear pneumatic port restricts the rapidly changing pressure pulses produced by the drive unit but allows slow changes in system pressure to equalise on the front and rear of the drive unit diapragm.
6. 6. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claim 5. The action of the dynamic flow restrictor is such as to cause any rapidly changing pressure pulse produced by the drive unit to be available at the output tube and not be dissipated within the rear compartment.
7. 7. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claim l. Where in the drive unit is provided with a compressable ring of circular cross section being placed between the front of the drive unit diaphragm and the chamber lid to cause a returning force to act upon the diaphragm when the electrical drive signal is reduced.
8. 8. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as in claim 1. Where in the pressure pulses produced by the diaphragm of the main drive unit are transferred via the

   deflection of a smaller seperate diaphragm to the microchamber.
9. 9. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claim 1. Where in the pneumatic pressure pulse inducer is provided with the addition of the flexible pressure transfer chamber which enables an external system pressure to be mechanically coupled with, but pneumatically isolated from the pneumatic pressure pulse inducer. Where in dynamic pressure pulses produced by the pneumatic pressure pulse inducer can thus be superimposed on to any external pressure system.
10. 10. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber as claimed in claim 1 and claim 9. Where in the flexible pressure transfer chamber when pressurized to a known residual pressure and mechanically coupled but pneumatically isolated can enable the changes in pressure of an external pressure system to be measured indirectly by a system incorporating the flexible pressure transfer chamber.
11. 11. A pneumatic pressure pulse inducer incorporating flexible pressure transfer chamber substantially as described here in with reference to figures 1 to 4 of the accompanying drawings.