Near-infrared spiroximetry: noninvasive measurements of venous saturation in piglets and human subjects

Abstract

We present a noninvasive method to measure the venous oxygen saturation (SvO2) in tissues using near-infrared spectroscopy (NIRS). This method is based on the respiration-induced oscillations of the near-infrared absorption in tissues, and we call it spiroximetry (the prefix spiro means respiration). We have tested this method in three piglets (hind leg) and in eight human subjects (vastus medialis and vastus lateralis muscles). In the piglet study, we compared our NIRS measurements of the SvO2(SvO2-NIRSresp) with the SvO2of blood samples. SvO2-NIRSrespand SvO2of blood samples agreed well over the whole range of SvO2considered (20–95%). The two measurements showed an average difference of 1.0% and a standard deviation of the difference of 5.8%. In the human study, we found a good agreement between SvO2-NIRSrespand the SvO2values measured with the NIRS venous occlusion method. Finally, in a preliminary test involving muscle exercise, SvO2-NIRSrespshowed an expected postexercise decrease from the initial baseline value and a subsequent recovery to baseline.