Methods for monitoring carboxyhemoglobin, inspired and expired CO2 and calibration of non-invasive arterial O2 saturation

Abstract

The present invention is directed to system and method for effectively monitoring critical respiratory parameters including SpO.sub.2, PR, COHb, inspired CO.sub.2, expired CO.sub.2, respiration rate, respiration pattern, hyperventilation (hypocapnia), hypoventilation (hypercapnia), CO.sub.2 contamination, and CO.sub.2 rebreathing. The system according to the present invention comprises a pulse oximetry sensor and a CO.sub.2 sensor connected to a central portable unit. The central unit comprising a barometer, an accelerometer, a capnography circuit, and a control unit. The control unit including the method for effectively monitoring critical respiratory parameters.

Claims

1. A system comprising: a housing; a control unit enclosed in the housing; a pulse oximetry (PO) sensor operably coupled to the control unit, the pulse oximetry sensor removably configured in a head gear and configured to be positioned over an arterial microcirculation of blood in a forehead of an aircraft pilot; a barometer operably coupled to the control unit; and an accelerometer operably coupled to the control unit, wherein the control unit is configured to: detect the arterial microcirculation by using an infrared (IR) photometric technique, receive arterial oxygen saturation (SpO.sub.2)values, pulse rate (PR) values, a signal strength value and a signal quality value from the pulse oximetry sensor, create indices corresponding to an altitude index (AI), a vibration index (VI) and a gravitation index (GI) under a controlled condition of hypobaria as well as a varying condition of hypobaria, create a scale based on index values of the AI, VI and GI; combine the index values of the AI, VI and GI with the signal strength value and the signal quality value of the PO sensor to calculate a weighted confidence index for SpO.sub.2 (CI.sub.sat) and a weighted confidence index for PR (CI.sub.pr); and combine CI.sub.sat and CI.sub.pr to calculate an overall weighted confidence index (CI); wherein the value of CI determines an accuracy of measurements of the SpO.sub.2 values and the PR values.

2. The system of claim 1, wherein the system further comprises: a CO.sub.2 sensor configured to be removably coupled with an aviator's mask of the pilot; and capnography circuitry operably coupled with the CO.sub.2 sensor and the control unit, the capnography circuitry configured to estimate, based on CO.sub.2 waveforms, respiratory rate, respiratory pattern, end tidal CO.sub.2, hyperventilation, hypoventilation, hypocapnia, hypercapnia, CO.sub.2 contamination and CO.sub.2 rebreathing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying figures, which are incorporated herein, form part of the specification and illustrate embodiments of the present invention. Together with the description, the figures further explain the principles of the present invention and to enable a person skilled in the relevant arts to make and use the invention.

(2) FIG. 1 is a block diagram showing the system, according to an embodiment of the present invention.

(3) FIG. 2 shows a PO sensor applied to a pilot and a central unit stored in the pocket of the pilot, according to an embodiment of the present invention.

(4) FIG. 3 shows the PO sensor and an airbladder, according to an embodiment of the present invention.

(5) FIG. 4 is a flow chart showing a method, according to an embodiment of the present invention.

DETAILED DESCRIPTION

(6) Subject matter will now be described more fully hereinafter. Subject matter may, however, be embodied in a variety of different forms and, therefore, covered or claimed subject matter is intended to be construed as not being limited to any exemplary embodiments set forth herein; exemplary embodiments are provided merely to be illustrative. Likewise, a reasonably broad scope for claimed or covered subject matter is intended. Among other things, for example, the subject matter may be embodied as devices and methods of use thereof. The following detailed description is, therefore, not intended to be taken in a limiting sense.

(7) The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the term “embodiments of the present invention” does not require that all embodiments of the invention include the discussed feature, advantage, or mode of operation.

(8) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of embodiments of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

(9) The following detailed description includes the best currently contemplated mode or modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention will be best defined by the allowed claims of any resulting patent.

(10) The following detailed description is described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, specific details may be set forth in order to provide a thorough understanding of the subject innovation. It may be evident, however, that the claimed subject matter may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the subject innovation. Moreover, the drawings may not be to scale.

(11) The present invention is directed to a system and method for effectively monitoring critical respiratory parameters including SpO.sub.2, PR, COHb, inspired CO.sub.2, expired CO.sub.2, respiration rate, respiration pattern, hyperventilation (hypocapnia), hypoventilation (hypercapnia), CO.sub.2 contamination, and CO.sub.2 rebreathing. Now referring to FIG. 1 which shows an exemplary embodiment of the Enhanced Pulse Oximetry system (EPO) 100. The system 100 comprises a central unit 105, a PO sensor 110, a CO.sub.2 sensor 120, and an airbladder 130. The central unit 105 further includes a barometer 110, a three-dimension accelerometer 150, a capnography circuitry 160, and a control unit 170. Further is shown in FIG. 1 is a battery powering the system 100.

(12) The PO sensor 110 is configured to non-invasively determine SpO.sub.2 and PR of a person. The PO sensor 110 can be configured in a headband of the pilot's helmet and held in place by a combination of padding, spring tension device and/or airbladder 130 connected to a pressure source that will be in concert with the anti-gravity systems, e.g., the anti-gravity suit ensemble (BRAG). Helmets that are equipped with a separate bladder, the sensor bladder can be connected to the system of separate bladder.

(13) FIG. 2 shows the PO sensor 110 applied to a forehead portion of a pilot 210. The forehead has a unique microcirculation that is supplied from the internal carotid artery that has no vasoconstrictive properties. The rest of the head skin is supplied by the external carotid artery that does have vasoconstrictor properties. In fact, the forehead circulation is the only microcirculation in the entire skin that has no vasoconstrictor properties. Another advantage of monitoring on the forehead is that it provides a direct measure of brain or central arterial oxygenation as opposed to other sites that are far removed from vital organs and are the first sites to vasoconstrict when the body is faced with hypoxic stress. Illustrating with example of extreme cold and frostbite. The forehead is unaffected while fingers, toes, extremities, ears, and nose are the first to be compromised. A third advantage of monitoring on the forehead is the rapid response to changes in arterial oxygenation. Because the supraorbital microcirculation is supplied from the internal carotid artery, it directly reflects changes in brain or central arterial oxygenation. Lastly, it is advisable to avoid large arteries for sensor placement.

(14) In one embodiment, the Infrared photometric technique can be used to a locate large arteries in the head's circulation. The IR photometric technique is well known method in the prior arts for determination of arterial flow and is easily understood by the ordinary person skilled in the art. The PO sensor 110 can be optimally positioned over the microcirculation for accurate performance. Moreover, the exact position of the PO sensor 110 can be determined by arterial blood accuracy studies that meet FDA Guideline PO standards under the novel conditions of hypobaria (equivalent altitudes of 0 to 25,000 ft), high vibration simulating tactical, transport and rotary aircraft and increased gravitational forces via centrifuge from 1 to 9 G's. Arterial blood SaO.sub.2 and heart rate data can be compared to SpO.sub.2 and PR values to determine accuracy under control conditions and varying conditions of hypobaria, vibration and increased gravitational forces. The numerical relationships between accuracy (bias, precision, root mean square of the differences and linear regression coefficients) under the above conditions can be used to calculate indices of AI, VI and GI.

(15) The EPO system 100 contains a central unit 105 which can be portable and housed in a metallic or plastic casing. The central unit 105 can fit in a front pocket of the aviator's (aircraft pilot) vest or to be placed in cockpit or cabin as a stand-alone. The central unit 105 comprises a control unit 170 that contain all the algorithms for SpO.sub.2, PR and COHb measurements as well as motion, vibration, pressure and acceleration tolerance, low perfusion performance, alarms and indices of signal strength and signal quality for all parameters. A barometer 140 or pressure manometer can also be provided for continuous monitoring of cabin pressure. A three-dimensional accelerometer 150 can also be housed in the central unit 105 that can be used for continuously monitoring direction and magnitude of G forces (G.sub.x, G.sub.y and G.sub.z). A capnography board 160 for integration of inspired and expired CO.sub.2 for measurement and detection of respiratory rate and pattern, end tidal CO.sub.2, hyperventilation, hypoventilation hypocapnia, hypercapnia, CO.sub.2 contamination and CO.sub.2 rebreathing. The system 100 can be powered by a rechargeable battery 180 that can be enclosed in the central unit 105. The control unit 170 is further configured for storing data acquired during functioning of the system 100. The control unit can be connected to an external computing system for transferring data to allow real-time data acquisition. The PO sensor 110 and the CO.sub.2 sensor 120 can be connected to the control unit 170 through one or more electrical conduits.

(16) The CO.sub.2 sensor can be positioned directly into an aviator's mask of the pilot to detect inspired and expired CO.sub.2, to generate continuous CO.sub.2 breath-by-breath waveforms. This system and method according to the present invention can monitor Carboxyhemoglobin (COHb), inspired and expired CO.sub.2 and calibration of non-invasive arterial oxygen saturation (SpO.sub.2) for pilots and aircrew of tactical fighter, transport, and rotary aircraft. Monitoring can occur during all stages and conditions of flight including pre-flight checks, takeoff, mission flight and landing. Monitoring may be conducted during the extreme conditions of increased gravitational forces, reduced cabin pressures, wearing required anti-gravity aircrew flight equipment and during high vibration. The overall method for monitoring is to place a pulse oximetry (PO) sensor 110 above the eyebrow with the photo emitter and detector placed over the microcirculation fed by the supraorbital arterial supply. Exact placement will be individualized for each pilot using infra-red photographic technology to locate arteries in the forehead so they may be avoided to optimize sensor performance by placing the sensor over the desired microcirculation. Inspired and expired CO.sub.2 can be monitored utilizing principles of Capnography for analysis of the data from the CO.sub.2 sensor configured in the aviator's mask. Calibration of SpO.sub.2 can be achieved by developing calibration curves for one or more combinations of red-light emitting diode wavelength (LED) and secondary emission. The calibration curve or curves can be embedded into the pulse oximetry algorithms and based on arterial blood studies conducted during hypoxia, CO exposure, hypobaria, high frequency vibration and increased gravitational forces.

(17) The method further includes creation of indices corresponding to AI, VI, and GI under controlled conditions and varying conditions of hypobaria. The barometer, the accelerometer and the spring tension device can be used to measure the AI, VI, and GI. AI, VI and GI are indexes of values of altitude, vibration, and gravitation respectively which is easily comprehensible by an ordinary person skilled in the art. Also, a controlled condition of hypobaria relates to known medical practices of assessing the parameters (AI, VI and GI) during a flight simulation while the variable condition corresponds to measuring of parameters during an in-flight situation. Upon creation of the indices, a scale can be designed based on the values of the AI, VI and GI. The scale corresponds to the index values of AI, VI and GI and is shown as an understandable format over the pilot's HUD. The scale provides a relative reading to real-time readings of AI, GI and VI, so that a ground station and a pilot can understand the readings.

(18) The values of AI, VI and GI are combined with a signal strength value and a signal quality value of the PO sensor 110 to calculate a weighted confidence index for SpO.sub.2 (CI.sub.sat) and a weighted confidence index for PR (CI.sub.PR). The measured values of CI.sub.sat and CI.sub.pr can then be combined to calculate an overall weighted confidence index (CI). The value of the CI determines an accuracy of measurements of SpO.sub.2 and PR. In one case, the scale is having a highest value of one that indicate an accurate functioning of the PO sensor. The lowest value can be zero that may indicate failure of the PO sensor. In one case, the indices can be scaled according to accuracy under the various conditions. For example, an index of 1.0 could be optimal conditions where there is no error and accuracy meet specifications (sea level, no vibration, 1 G). The index number will decrease below one as error increases until it reaches 0 which indicates PO failure or dropout of SpO.sub.2 or PR values. These three novel indices can be combining with the existing measures of signal strength value (SS) and signal quality value (SQ) to develop an algorithm to calculate a final index of confidence (CI) of the SpO.sub.2 and PR measurements based on numerical relations from arterial blood accuracy studies. The algorithm will weigh the values of AI, VI,

(19) GI, SS and SQ according to their effects on the accuracy measurements. A scale for CI can be computed that best fits the combined effects of AI, VI, GI, SS and SQ on accuracy.

(20) According to one embodiment herein, the method further comprises a computer readable program to assess rapid changes in gravitational forces in multiple directions simultaneously. The changes affect an accuracy to calculate the vibration index (VI).

(21) According to one embodiment herein, the method further comprises a computer readable program and a barometer to measure a cabin pressure. A change in a cabin pressure affects an accuracy to calculate the altitude index (AI).

(22) According to one embodiment herein, the method further comprises a three-dimensional accelerometer and a computer readable program to measure gravitational forces in at-least three directions (G.sub.x, G.sub.y and G.sub.z. A magnitude of gravitational forces affects an accuracy to calculate the gravitational index (GI). The algorithms further enable calculation of motion and vibration tolerance, low perfusion performance, alarms and indices of signal strength and signal quality.

(23) While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above-described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention as claimed.