WO2017023500A1

WO2017023500A1 - Apparatus and method for the noninvasive monitoring of nitric oxide and other blood gases

Info

Publication number: WO2017023500A1
Application number: PCT/US2016/041966
Authority: WO
Inventors: Carter R. Anderson; Russell L. Morris; Thomas W. Burke; Clayton J. Anderson
Original assignee: Vail Scientific, Llc
Priority date: 2015-08-05
Filing date: 2016-07-13
Publication date: 2017-02-09

Abstract

The present disclose describes both apparatus and methods for the continuous measurement of NO and other gases that are contained in blood through transcutaneous sampling means.

Description

APPARATUS AND METHOD FOR THE NONINVASIVE MONITORING OF NITRIC OXIDE AND OTHER BLOOD GASES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This application claims priority to U.S. Provisional Patent Application No.

62/282,553, filed August 5, 2015, the entire contents of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] Arterial blood gas measurement is used to determine the levels of oxygen (02), carbon dioxide (C02), and pH (acidity) of a patient's blood. When conducted, this information can be critical in determining a patient's respiratory health. It is usually an invasive test, requiring a sample of blood drawn from a patient's artery. Typically, the measurements are made in a laboratory blood gas analyzer, which utilizes electrochemical sensors such as Clark 02 sensors, Severinghaus C02 sensors, and an ion selective electrode to measure pH. Further, measurements are made on an intermittent basis, with timing often dictated by the severity of the patient's condition.

[0003] Collection of blood gas measurements on a continuous, non-invasive basis would be of particular advantage. This would allow timely monitoring for change without the need for collection of blood and its subsequent remote analysis in a laboratory. Transcutaneous blood gas measurements for 02 (tcp02) and C02 (tcpC02) have been successfully completed. In these measurements, sensors are fixed against the patient's skin, and the underlying skin is heated to as high as 45 °C to facilitate the diffusion of 02 and C02 through the outer stratum corneum of the skin to the sensor. This method has several disadvantages, including 1) heating of the skin over a prolonged period in some patients can cause burning, which, to avoid burning, requires frequent change of skin location, and 2) sensors do not remain in calibration, and must be recalibrated frequently while in use.

[0004] More recently, interest in nitric oxide (NO) measurement has increased. NO is produced naturally in the vasculature and causes relaxation of the muscles underlying blood vessels. This relaxation results in vasodilation and an increase in blood flow and 02 delivery. The discovery of NO as a critical signaling molecule was deemed so significant it was the subject of the 1998 Nobel Prize in Physiology/Medicine. Despite this deemed significance, the accurate and convenient measurement of blood NO remains elusive in marketed clinical analyzers. One significant obstacle for measurement is due to the short half-life of NO in liquid biological samples, as it is a free radical and is known to rapidly react with proteins and/or degrade by oxidation. Some estimates are that NO continuously degrades to half its content each few seconds when present in blood. Recently, saliva measurements for NO have been introduced that are based on the indirect measurement of the oxidation products of NO such as nitrates or nitrites. However, this process is neither a continuous measurement, nor is it a direct measurement of NO. In a published study investigating NO measurement, (Hunter et al, Anal. Chem., 2013), blood samples were collected and analyzed over time so as to investigate changes in blood NO concentrations during the course of induced sepsis in an animal model. These study results indicated a significantly increased concentration of NO over time, indicating the potential for its clinical use to monitor the course of sepsis. This study proposed an in-vivo/in-dwelling NO sensor system to monitor sepsis, but this method is invasive and would consequently suffer from complications such as sensor stability, calibration drift, or possible cause for infection.

5] Others have proposed NO analysis systems with detectors/sensors placed in direct contact with the skin surface so as to monitor the NO on the skin surface as an indication of infection (Kane 8,628,728) (Allen 20140039280). This approach suffers from several complexities. First, placement of the detector/sensor on the skin surface with associated tapes will occlude the skin location and facilitate sweating, thus the measurement will be of NO in a thin liquid sweat layer where NO is inherently unstable. Second, sensors in direct contact with the skin will be susceptible to contamination from salts, proteins, oils, etc. present on the skin surface. Lastly, the devices proposed do not have temperature control or temperature correction functionality for the skin measurement.

[0006] It also would be clinically advantageous to couple the NO measurement with other confirmatory measurements so that clinicians can have a more reliable combination of information for diagnosis of a serious condition such as sepsis. For example, it is known that blood pC02 can drop to below 32 mmHg in severe sepsis, so that a rise in NO and a decrease in pC02 can help clinicians more reliably detect onset of sepsis.

[0007] There exists a need for an accurate, convenient, and reliable measurement for NO that can be coupled with other measurements such as pC02, p02 and/or 02 saturation for informed knowledge of a patient's health status during conditions such as infection or hemorrhagic shock.

SUMMARY OF THE INVENTION

[0008] This invention relates to an apparatus and methods for the continuous measurement of NO and other gases that are contained in blood through transcutaneous sampling means.

[0009] In a first embodiment, an impermeable collection chamber of defined volume is fixed to a location on the skin of a patient. The collection chamber may optionally include a gas input and output for the introduction and removal of ozone (03). The collection chamber is restrictive to ambient light and is also fitted with a photodetector positioned toward the patient's skin (but importantly it is not in direct contact with the skin). The collection chamber may also be temperature controlled so as to: 1) adjust the skin temperature higher in a manner to facilitate the transfer of gases through the stratum corneum of patient's skin and into the chamber and 2) protect the measurement from interference from readings associated with localized temperature change effects. In this embodiment, NO passes through the skin into a gaseous collection reservoir (e.g. the sample chamber) and then reacts with 03, producing light (hv) that is proportional to NO concentrations and measured by the photodetector positioned toward the skin. The photodetector is connected to remote electrical measurement circuitry. The chemical reaction below summarizes the reaction that produces light (hv) measured by the photodetector:

NO + 03—► N02 + 02 + hv

[0010] The amount of light generated is directly proportional to the concentration of NO. A significant advantage of measuring NO through the chemiluminescence reaction above resides in its very low detection limit, reported to be as low as 0.4 ppb.

[0011] In a second embodiment, the photodetector is replaced with an amperometric electrochemical NO sensor known to those skilled in the art. This approach does not require the complexity of the 03 introduction and chemiluminescence reaction, but it may suffer from a lower limit of detection that is inferior to the 03/photodetector approach. Importantly (as with all embodiments in this invention), the NO that has passed from the skin into the collection chamber is in a gaseous state, where it is much more stable than when it is present in a liquid state. Further, the amperometric NO sensor is not in contact with the skin, so that it is much less prone to contamination. It is within the scope of this invention to include other measurement sensors capable of measuring gaseous analytes that have passed through the skin and into the collection chamber. For example, a Clark 02 sensor and a Severinghaus C02 sensor can be placed in the reservoir in a manner analogous to the NO sensor, allowing for simultaneous readings of transcutaneous NO, C02 and 02.

[0012] In a third embodiment, a collection chamber of a defined volume has a gas output port and an optional gas inlet port, but lacks any photodetector (or other sensor) and does not have a port to introduce 03. In this configuration, the optional input port is for an inert gas such as air, nitrogen, helium or argon, and the output port is connected to a remote sensor/detector measurement apparatus capable of measuring NO and/or other blood gases such as 02 and C02. The collection chamber is isolated from the sensor/detector that is located in the measurement apparatus, and the gaseous sample of transcutaneously-collected gases are transported from the collection chamber to the sensor/detector by means of a pump (operating continuously periodically or intermittently) contained in the apparatus where the sensor/detector measurements take place. As with other embodiments, it is preferred that the collection chamber of this configuration be temperature controlled (or temperature compensated) for consistency in measurements. In the configuration for this third embodiment, the sensors/detectors are significantly isolated from the collection chamber, such that little or no meaningful data could be acquired without a means to transport the sample to the measurement apparatus. This isolated configuration maximizes the stability of the sensors by reducing the contamination that may occur if the sensors are positioned and held for prolonged periods in the collection chamber. Further, in this configuration larger, more stable sensors can be utilized without encumbering the size or weight of the collection chamber that is attached to the patient. The measurement of NO in the remote measurement apparatus does not necessarily require the 03 based chemiluminescence reaction; but, as an example, can alternatively utilize an amperometric sensor for NO or other suitable sensors known to those skilled in the art. Measurement of 02 and C02 in the remote measurement apparatus can be through conventional means, such as by utilizing Clark 02 sensors and Severinghaus C02 sensors. Those skilled in the art will recognize that remotely contained sensors for p02 and pC02 will be more convenient for calibration, as they may not require physical disconnection of the sensors from a patient for the calibration process to occur. Ideally, calibration can occur automatically in a way that requires little or no effort from clinicians.

13] In a fourth embodiment, the collection chamber is comprised of an open cell porous foam matrix encased in a thin polymer shell and adhered to the skin. We have discovered that the porous foam matrix serves to mix the gaseous sample as it is drawn from the collection chamber for transport to the remote measurement apparatus. This embodiment may result in a more consistent and accurate measurement of NO. In this fourth embodiment, the foam can be designed of a size and shape optimal for the placement on the patient, and in a total volume with a sample size suitable for the measurement. In this configuration (and in other configurations where a pump is used to draw the gaseous sample from the collection chamber to the detector), we have discovered that drawing the sample from the collection chamber in such a way that the sample then flows past the sensors in the remote measurement apparatus results in a NO signal that looks much like a chromatogram. Quantification of the NO signal can be accomplished by measuring peak height, integrating peak volume, or combinations thereof. The design of the fourth embodiment can have a gas inlet port for air, etc, or it can be absent an inlet port. In the case where the inlet port is absent, the pump of the remote measurement apparatus draws the gaseous sample causing the foam material to compress as the gas exits.

[0014] In a fifth embodiment, the collection chamber is designed in such a way as to allow quantitative removal of a quantity of the gas sample. For example, the sample may be extracted with a syringe or similar apparatus. Alternatively, the collection chamber can be designed to allow convenient removal of the chamber with its contained gaseous sample or removal of the open cell foam matrix. The gas sample is then transported to the remote measurement apparatus for analysis as described in previous embodiments.

[0015] In all embodiments of this invention, temperature of the collection chamber has a direct influence on the gaseous concentrations measured. Local heating can facilitate the transport of NO through skin, but it can also facilitate localized production of NO (e.g. even in the absence of an infection). Thus any device lacking temperature control will be subject to significant interference with potential for variable and/or false positive readings. Consequently, it is recommended that the collection chamber be temperature controlled to a level from 35-47 °C to optimize the skin permeability. Temperature control can be accomplished by embedding a temperature probe and heating element into the collection chamber and using a feedback electrical mechanism to heat the collection chamber to a known temperature. As an alternative to temperature control, temperature correction can be accomplished by incorporating a temperature measurement probe into the collection chamber to identify its temperature, and using a mathematical relationship to correct the signal output for a temperature compensated result. For the NO analysis, we have discovered that temperature control has more complex consequences. First, heating the skin locally activates the eNOS system in the skin and produces NO, while additionally increasing the skin permeability for NO. Following the initial activation of the eNOS, the amount of NO released by this mechanism declines to a steady state. The appropriate method to determine a patient's NO result to ascertain conditions such as infections is by using the steady state period which follows the initial "temperature warm up" effect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a representation of the collection chamber for the first embodiment described above, where a photodetector is positioned within the collection chamber but isolated from contact with the skin, to ascertain an amount of NO present in a gaseous state within the chamber by use of a chemiluminescence reaction.

[0017] Figure 2 is a representation of the collection chamber for the second embodiment described above, where an amperometric NO sensor is positioned within the collection chamber but isolated from contact with the skin, to ascertain an amount of NO present in a gaseous state within the chamber by use of an electrochemical reaction,

[0018] Figure 3 is a representation of the third embodiment described above, where the sensors/detectors for measuring gaseous NO are contained in a remote measurement apparatus

[0019] Figure 4 is an example of results collected using the third embodiment configuration, illustrating a signal generated and the impact of controlling heat for the measured result. DETAILED DESCRIPTION OF THE INVENTION

[0020] Figure 1 is a representation of the first embodiment of this invention, an apparatus for the measurement of transcutaneously-collected NO in a gaseous state that is measured through use of a chemical reaction between NO and 03. The patient's skin 1 has a collection chamber 2 fixed to the skin surface. The collection chamber can be made of a molded plastic or similar material. Collection chamber 2 has an inlet line 3 for a gas containing 03, and an exit line 4 for venting of waste gas. Inlet lines 2 and exit line 4 can be Teflon tubing or similar. Preferably, collection chamber 2 is thermally regulated to a temperature of about 35-47 °C by a temperature control circuit (not depicted) known to those skilled in the art. One way to create a controlled temperature environment is to encase the collection chamber in a thermal blanket maintained to a desired temperature (not pictured). The 03 introduced through inlet line 3 is of a quantity in excess of that necessary for complete reaction with NO to be measured through means of a chemiluminescence reaction. Positioned inside collection chamber 2 is a photodetector sensor 5 isolated from contact with the skin. The photodetector sensor 5 is connected by an electrical connection 6 to analysis circuitry and display (not depicted), which is used to convert the signal output of the photodetector sensor 5 into a NO concentration that is recorded and displayed.

[0021] Suitable displays or display units for the disclosed apparatus include visual or audible displays or indicators known to those skilled in art as well as known data recording and data transfer processes suitable for use with known communication or data storage devices.

[0022] In figure 2, the collection chamber 2 is similarly constructed to that of figure 1 but has an electrochemical NO sensor 8 instead of a photodetector. The electrochemical NO sensor 8 is isolated from contact with the skin and positioned to measure gaseous NO collected within the chamber. In this configuration, the introduction of 03 is not required. The electrochemical sensor 8 is connected by an electrical connection 6 to analysis circuitry and display (not depicted), which is used to convert the signal output of the electrochemical sensor 8 into a NO concentration that is recorded and displayed. Sample collection chamber 2 has an optional exit line 4 for venting of waste gas. Preferably, collection chamber 2 is thermally regulated to a temperature of about 35-47 °C, alternatively about 36-39 °C by a temperature control circuit (not depicted) known to those skilled in the art (such as by the thermal blanket previously described).

23] Figure 3 represents an embodiment where the sensors/detectors for NO are present in an instrument that is remote from the collection chamber 2. Preferably, collection chamber 2 is thermally regulated to a temperature of about 35-47 °C by a temperature control circuit (not depicted) known to those skilled in the art. An optional inlet port 9 is for introduction of an inert gas such as air, nitrogen, argon, or helium. The inert gas mixes with NO and other gases released from the skin transcutaneously within chamber 2, and the gaseous mixture is transported from the collection chamber 2 through an exit tube 10 to an analyzer 16. In certain configurations, such as when using a collapsible foam collection chamber or a chamber containing a collapsible bladder, an inlet port may not be required for efficient sample removal from the chamber. Also, connecting collection chamber 2 is an optional electrical connection 11, which serves to provide temperature control feedback connection to the analyzer 16. Analyzer 16 contains the sensors and circuitry to measure the concentrations of the transcutaneously-released gases, and may use sensors known to those skilled in the art, such as Clark sensor for 02, a Severinghaus sensor for C02, and an amperometric sensor for NO. Alternatively, Analyzer 16 may utilize chemiluminescence or UV/Vis measurements as a means to measure gaseous NO concentrations. As with all configurations, the detection sensors are not in contact with the skin so as to minimize contamination from skin oils, etc. Within the analyzer 16 are a sample line 14 connecting the exit tube 10 to detection means 12 (to measure the concentration of gaseous NO), and a pump means 13 that serves to facilitate transport of the transcutaneously-collected gaseous NO from the collection chamber 2 to the detection means 12. Pump means 13 may operate on a continuous or timed interval basis so as to provide means to measure changes in NO concentration that are occurring over time within the patient. For example, NO concentrations will rise within the patient in the event of an infection that is spreading (e.g. sepsis). In figure 3, an optional open cell foam 17 is depicted which occupies and defines the volume for the collection chamber 2. This open cell foam 17 serves to improve the efficiency of removal of the gaseous NO from the collection chamber 2 by a 'mixing action' forced by the movement of NO gas through multiple pathways within the open cells.

24] A device as depicted in figure 3 will have significant clinical benefit. For example, a patient in an emergency room suspected of having infection could have a collection chamber 2 placed on a body location (such as an upper arm location). Following this placement a physical connection would then be made by the clinician between the collection chamber 2 located on the patient and an analyzer 16 located (for example) on a nearby tabletop (using exit tube 10 and optional electrical connection 11). Following this connection and clinician instruction, the analyzer will self-initiate by heating the chamber (and underlying skin) to a pre-set temperature, and the collection chamber 2 will receive NO emitted transcutaneously from the patient. After a set time period of approximately 5-30 minutes, the analyzer 16 will automatically draw gas from the collection chamber 2 to the analyzer 16 where a NO concentration analysis will take place. The patient's NO concentration will then be compared to a normal 'healthy' individual reading. If the patient's NO level or reading is higher than normal, clinicians may use this information as justification for the patient to be admitted to the intensive care unit (ICU) for prompt treatment of infection (such as with antibiotics). The patient's NO level or reading may be displayed numerically on a screen or as any other visual indicator or as an audible indication or as data that is transferred to any other communication or data storage device. Further, if the patient's NO levels continue to rise with additional measurements taken over time; clinicians may utilize this information to justify more aggressive patient resuscitation measures.

[0025] The following examples are meant to serve only as examples, as those skilled in the art will recognize various alternative ways in which this invention can be utilized.

EXAMPLE

[0026] Two impermeable collection chambers were attached to intact skin of a healthy volunteer, one on each arm. The collection chamber on the left arm location was not temperature regulated, while the collection chamber on the right arm location was encased in a thermal blanket designed to maintain skin temperature at approximately 38 °C (MaxHeat thermal pad, Kaz USA Inc.). Following a short gas collection period, samples were drawn to a ThermoEnvironmental Inc. Chemiluminescence Model 42 Nitric Oxide analyzer by means of a pump contained within the analyzer and analyzed for NO content. As illustrated in figure 4, repeat sample draws from the heated sample chamber on the right arm location resulted in NO readings peaking at approximately 10-12 ppb. Repeated sample draws from the unhealed left arm location resulted in significantly lower readings of approximately 5 ppb. Reversing the heating blanket to the opposing side resulted in NO readings that were reversed in magnitude. This experiment 1) confirms the ability to collect transcutaneous NO in a gaseous state in a collection device of this invention; 2) confirms that the magnitude of NO drawn from a healthy volunteer is measurable and reproducible and 3) demonstrates the sensitivity to temperature of the collection chamber and thus the advantages and need for thermal control.

Claims

1. A noninvasive diagnostic device comprising a an impermeable chamber, shaped to cover a skin surface having a sealable opening at the skin surface, to receive and contain transcutaneous NO, a port to inject a NO reactant into the chamber, an interior detector in the chamber not in contact with the skin surface, and a detection display unit.

2. The diagnostic device of claim 1, wherein the NO reactant is ozone.

3. The device of claim 1, wherein the chamber is restrictive to ambient light.

4. The diagnostic device of claim 3, wherein the interior detector is a photodetector.

5. The diagnostic device of claim 1, further comprising an 02 sensor, a C02 sensor, or both an 02 and C02 sensor.

6. The diagnostic device of claim 1 further comprising a heater component to increase the temperature of the skin surface.

7. The diagnostic device of claim 6, wherein the heating component controls the temperature of the skin at temperatures of about 35-47 °C.

8. The diagnostic device of claim 7, wherein the heating component controls the temperature of the skin at temperatures of about 36-39 °C.

9. The diagnostic device any one of claims 1-8, wherein detected amounts of NO are about 0.4-1000 ppb.

10. A noninvasive diagnostic device comprising a an impermeable chamber, shaped to cover a skin surface having a sealable opening at the skin surface, to receive and contain transcutaneous NO, an interior amperometric electrochemical sensor in the chamber not in contact with the skin surface to detect transcutaneous NO, and a detection display unit.

11. The diagnostic device of claim 10, further comprising an 02 sensor, a C02 sensor, or both an 02 and C02 sensor.

12. The diagnostic device of claim 10 further comprising a heating component to increase the temperature of the skin surface.

13 The diagnostic device of claim 12, wherein the heater component controls the temperature of the skin at temperatures of about 35-47 °C.

14. The diagnostic device of claim 13, wherein the heating component controls the temperature of the skin at temperatures of about 36-39 °C.

15. The diagnostic device any one of claims 10-15, wherein detected amounts of NO are about 0.4-1000 ppb.

16. An noninvasive diagnostic device comprising an impermeable chamber, shaped to cover a skin surface having a sealable opening at the skin surface, to receive and contain transcutaneous NO, a gas outlet port, wherein the gas outlet port removes transcutaneous NO from the chamber, an external reactor operably connected to the chamber to contact NO with a NO reactant, and an external display unit.

17. The diagnostic device of claim 16 further comprising an inert gas inlet port to inject an inert gas into the impermeable chamber.

18. The diagnostic device of claim 17 wherein the inert gas is air, nitrogen, helium or argon.

19. The diagnostic device of claim 16, wherein the NO reactant is ozone.

20. The diagnostic device of claim 16 wherein the external display unit is a photodetector

21. The diagnostic device of claim 16 further comprising an 02 sensor, a C02 sensor, or both an 02 and C02 sensor.

22. The diagnostic device of claim 16 further comprising a heating component to increase the temperature of the skin surface.

23. The diagnostic device of claim 22, wherein the heating component controls the temperature of the skin at temperatures of about 35-47 °C.

24. The diagnostic device of claim 23, wherein the heating component controls the temperature of the skin at temperatures of about 36-39 °C.

25. A noninvasive diagnostic device comprising an impermeable chamber, shaped to cover a skin surface having a sealable opening at the skin surface, to receive and contain transcutaneous NO, a gas outlet port, wherein the gas outlet port removes transcutaneous NO from the chamber, and an external detector.

26. The diagnostic device of claim 25 further comprising an inert gas inlet to inject an inert gas into the impermeable chamber.

27. The diagnostic device of claim 26, wherein the inert gas is air, nitrogen, helium or argon.

28. The diagnostic device of claim 25 wherein the external detector is an amperometric electrochemical sensor detector.

29. The diagnostic device of claim 25 further comprising an 02 sensor, a C02 sensor, or both an 02 and C02 sensor.

30. The diagnostic device of claim 25 further comprising a heating component to increase the temperature of the skin surface.

31 The diagnostic device of claim 30, wherein the heating component controls the temperature of the skin at temperatures of about 35-47 °C.

32. The diagnostic device of claim 31, wherein the heating component controls the temperature of the skin at temperatures of about 36-39 °C.

33. A method of using a diagnostic device of any one of claims 1-32 to detect infection or inflammation is a patient.

34. The method of claim 33 wherein the infection is sepsis.

35. A method of a measuring transcutaneous NO in a patient comprising the steps of contacting a portion of the patient's skin with a gaseous sample collection chamber consisting essentially of an open cell porous foam matrix encased in a polymer shell, adhering the foam matrix to the patient's skin for a period of time sufficient to entrap cutaneous NO in the foam matrix, and measuring the amount of NO entrapped in the foam matrix.

36. The use diagnostic device of any one of claims 1-32 to detect infection or inflammation in a patient.

37. The use of the diagnostic device of any one of claims 1-32 to detect sepsis.