814179.fig.006
Figure 6: A NIRS study of the effects of forearm muscle contraction and induced ischemia on chromophore change. Reproduced with permission from; [6]. Raw NIRS signals during 1 min of rhythmic isometric handgrip exercise at 20% of the maximum voluntary contraction force (MVC) followed by 45 seconds of arterial occlusion (sphygmomanometer generated). The sum of [O2Hb] and [HHb] reflects the total amount of haemoglobin [tHb] (interpreted as change in blood volume in tissue). When exercise begins an increase in [O2Hb] is evident that overlies the coincident change in [tHb] (720–740 sec). This reflects a normal hemodynamic response. With continued isometric contraction (740–780 sec) a progressive increase in [HHb] and rise in [tHb] with coincident decline in [O2Hb] occurs. This reflects increasing oxygen extraction and higher blood volume. Following arterial occlusion (and tissue hypoxia), an abrupt increase in [HHb] is matched by an equal and opposite decrease in [O2Hb] and [tHb] plateaus. This reflects the cumulative effects of tissue hypoxia, oxygen debt, and stable blood volume. On release of occlusion (830 sec), [O2Hb] rebounds above baseline with an associated increase in [tHb] and fall in [HHb]. This reflects reperfusion with increased oxygenated blood volume and recovery of tissue oxygenation. A return of [O2Hb], [HHb], and [tHb] to baseline (890 sec) indicates recovery of normal haemodynamics and oxygenation.