Nonpulsatile and Noninvasive Transmittance and Reflectance Tissue-bed Oximetry

Abstract

A new optical device was developed that measures blood pressure noninvasively, in small human subjects (neonates and premature infants) and small animals (Roeder RAR. Transducer for indirect measurement of blood pressure in small human subjects and animals, Purdue University, BME; 2003.: xi, 50 p.). The ability of this device to measure oxygen saturation enhances its value. The objective of this research was to add the ability to obtain SaO₂ from the same device and to obtain the calibration curve. Another objective was to determine which measurement method (transmittance or reflectance) is preferable. This new oximeter is unlike the conventional pulse oximeter in that it does not require a pulse, making it ideal for measuring oxygen saturation noninvasively in small human subjects with small amplitude pulses or without a pulse. A study was performed in 11 pigs, ranging in weight 20–27 kg. The pig tail was used as the measuring site for %SaO₂ measurements. Arterial blood samples were obtained from the femoral artery and oxygen saturation was measured with a blood-gas analyzer. A small blood-pressure cuff was used to render the optical path bloodless. A comparison of the transmittance and reflectance methods for measuring oxygen saturation was made. %SaO₂ measurements ranged from 4% to 100%. It was found that both the transmittance and reflectance methods can be used to measure %SaO₂ reliably in situations with or without a pulse.