The unprecedented popularity of the pulse oximeter is due primarily to the size and cost reduction afforded by present light emitting diode (LED) and microprocessor technologies as well as the clever idea to use the pulsatile optical signal to discriminate between light absorption due to hemolytic and nonhemolytic absorptive elements. However because capillary blood contributes significantly to the pulse signal, the reliability of the measurement as a reflection of arterial oxygen saturation still depends on the adequacy of peripheral blood flow, a condition which is not always present in many of the most important clinical applications. A key to addressing this problem is found in the oscillometric principle for noninvasive arterial pressure monitoring, which utilizes enhancement of the pulse signal (as a function of externally applied cuff pressure) to measure mean arterial blood pressure. Since the pulse signal enhancement is assumed to result from the increased arterial compliance resulting from the decreased transluminal pressure difference, it follows that the arterial vs capillary contributions to the pulse signal should increase no less than proportionally to the magnitude of signal enhancement. Since the finger has become a popular site for noninvasive and continuous monitoring of blood pressure as well as oxygen saturation (both methodologies using the same LED technologies for measuring the pulse signal), it would be logical to combine two instruments into one in order to achieve this benefit to oximetry while reducing the combined cost and increasing the convenience to that of a single instrument with a single sensor and placement site. However, the principle presently applied to continuous pressure monitoring is too interfering with circulation for combining with oximetry. We therefore propose to test the feasibility of using a noncontactive principle for continuous pressure monitoring, developed recently in Shanghai, which would utilize the oscillometric principle for periodic calibrations of both pressure and oximetry.
