TRANSCUTANEOUS INERT GAS MONITOR

ARTERIAL OXYGEN MEASUREMENTS (OBTAINED INVASIVELY) ARE FREQUENTLY USED FOR MEASURING THE PHYSIOLOGICAL OR "EFFECTIVE" SHUNT FRACTION RESULTING FROM GAS EXCHANGE UNITSHAVING LOWER THAN AVERAGE VENTILATION/PERFUSION RATIOS. A METHOD EMPLOYING INERT GAS INSERTION AND BLOOD CONCENTRATIONMEASUREMENT (BOTH INVASIVE) OF THE INERT GASES HAS DEMONSTRATED THE CAPABILITY OF MEASURING THE DISTRIBUTION OFLOW UNITS AND ACCURATELY PREDICTING THE RESULTING REDUCED ARTERIAL OXYGEN CONCENTRATION. THE PURPOSE OF THIS PROPOSAL IS TO DEMONSTRATE THE FEASIBILITY OF DEVELOPING A NONINVASIVE MEANS OF BOTH INERT GAS INSERTION AND ARTERIAL BLOOD CONCENTRATION MEASUREMENT FOR THE PURPOSE OF MONITORING THE SHUNT FRACTION NONINVASIVELY. A TRANSCUTANEOUS METHOD, ANALOGOUS TO THE TRANSCUTANEOUS METHOD FOR OBTAINING ARTERIAL OXYGEN ESTIMATES IS TO BE EMPLOYED. AN IMPORTANT DIFFERENCE IS THAT INERT GASES ARE UNDISTURBED BY TISSUE METABOLISM, WHILE SKIN METABOLISM, COUPLED WITH AN UNCERTAIN SKIN PERFUSION, CAN DEFEAT THE INTENT OF THE OXYGEN MEASUREMENTS. THIS GIVES THE INERT GASTRANSCUTANEOUS APPROACH A MAJOR ADVANTAGE IN THAT IT SHOULD NOT BE DEFEATED BY PHYSIOLOGICAL UNCERTAINTIES; HOWEVER, THEMAJOR PROBLEM WITH THE APPROACH IS THAT SENSITIVITY REQUIREMENTS FOR THE SENSING UNIT EXCEED THE MINIMUM DETECTION LIMITS FOR THE MOST SENSITIVE GAS SENSORS AVAILABLE. THE MAJOR OBJECTIVES OF THE PROPOSAL ARE 1) TO EXPERIMENTALLY VERIFY THE SENSITIVITY REQUIREMENTS FOR THE METHOD, AND 2) CONSTRUCT A WORKING MODEL OF A SENSING DEVICEWHICH MEETS THESE SENSITIVITY REQUIREMENTS. A TECHNICALLY FAVORABLE FEATURE OF THE METHOD IS THAT ITS ACCURACY DEPENDSPRIMARILY ON GAS MEASUREMENT RATIOS AND THE RATIOS OF MEMBRANE SOLUBILITIES OF THE VARIOUS GASES.