Noninvasive measurement of human forearm oxygen consumption by near infrared spectroscopy

Summary

This study reported on the application of near infrared spectroscopy (NIRS) to noninvasive measurements of forearm brachio-radial muscle oxygen consumption ($\dot V$O₂) 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 $\dot V$O₂. 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 $\dot V$O₂during MVC with and without vascular occlusion. A consistent difference was seen between $\dot V$O₂measured during occlusion at rest and $\dot V$O₂measured 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 $\dot V$O₂can be measured noninvasively by NIRS. The $\dot V$O₂during 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 $\dot V$O₂might be accurately evaluated dynamically without cuff occlusion.