Vascular responsiveness measured by tissue oxygen saturation reperfusion slope is sensitive to different occlusion durations and training status

The reperfusion rate of near-infrared spectroscopy-derived measures of tissue oxygen saturation (S-tO2) represents vascular responsiveness. This study examined whether the reperfusion slope of S-tO2 is sensitive to different ischaemic conditions (i.e. a dose-response relationship) and whether differences exist between two groups of different fitness levels. Nine healthy trained (T; age 25 +/- 3 years; maximal oxygen uptake 63.4 +/- 6.7ml kg(-1) min(-1)) and nine healthy untrained men (UT; age 21 +/- 1 years; maximal oxygen uptake 46.6 +/- 2.5 ml kg(-1) min(-1)) performed a series of vascular occlusion tests of different durations (30 s, 1, 2, 3 and 5 min), each separated by 30 min. The S-tO2 was measured over the tibialis anterior using near-infrared spectroscopy, with the S-tO2 reperfusion slope calculated as the upslope during 10 s following cuff release. The reperfusion slope was steeper in T compared with UT at all occlusion durations (P < 0.05). For the T group, the reperfusion slopes for 30 s and 1 min occlusions were less than for all longer durations (P < 0.05). The reperfusion slope following 2 min occlusion was similar to that for 3 min (P > 0.05), but both were less steep than for 5 min of occlusion. In UT, the reperfusion slope at 30 s was smaller than for all longer occlusion durations (P < 0.05), and 1 in occlusion resulted in a reperfusion slope that was less steep than following 2 and 3 min (P < 0.05), albeit not different from 5 min (P > 0.05). The present study demonstrated that the reperfusion rate of S-tO2 is sensitive to different occlusion durations, and that changes in the reperfusion rate in response to a variety of ischaemic challenges can be used to detect differences in vascular responsiveness between trained and untrained groups.