NONINVASIVE MEASUREMENT OF HUMAN FOREARM OXYGEN-CONSUMPTION BY NEAR-INFRARED SPECTROSCOPY

This study reported on the application of near infrared spectroscopy (NIRS) to noninvasive measurements of forearm brachio-radial muscle oxygen consumption (VO2) and recovery time (t(r)) in untrained volunteers. Seven healthy subjects were submitted to four consecutive protocols involving measurements made at rest, the induction of an ischaemia, and during a maximal increase of metabolic demand achieved with and without vascular occlusion. Two isometric maximal voluntary contractions (MVC) of 30-s duration were executed with and without vascular occlusion and a 50% MVC lasting 125 s was also performed. The protocols were repeated on 2 different days. The results showed that, during vascular occlusion at rest, the time to 95% of the final haemoglobin (Hb) + myoglobin (Mb) desaturation value was independent of VO2. The MVC, performed during vascular occlusion, caused complete Hb+Mb desaturation in 15-20 s, which was not followed by any further desaturation when the second contraction was performed. No difference was found between VO2 during MVC with and without vascular occlusion. A consistent difference was seen between VO2, measured during occlusion at rest and VO2 measured during MVC with and without occlusion. During prolonged exercise (125 s) Hb + Mb desaturation was maintained for the whole contraction period. The results of this study show that VO2 can be measured noninvasively by NIRS. The VO2 during MVC was very similar both in the presence and absence of blood flow limitation in most of the subjects tested. This would suggest that muscle VO2 Might be accurately evaluated dynamically without cuff occlusion.