Noninvasive measurement of human forearm oxygen consumption by near infrared spectroscopy

SummaryThis 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 (tr) 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.