LAUSR

Reactive hyperemia tests create mismatches in oxygen (O2) delivery and demand by occluding blood flow and O2 delivery in the face of stable quiescent skeletal muscle O2 demand. We tested the hypothesis that skeletal muscle reactive hyperemia is dependent on the specific deoxygenation stimulus. We hypothesized that the magnitude of deoxygenation (Δ=nadir-baseline) would correlate with the magnitude of the reactive hyperemic response (Δ=peak-baseline), whereas the total deoxygenation (O2 debt, calculated as the total area under the curve of deoxygenation, below baseline) would correlate with the total reactive hyperemic response (area under the reactive hyperemia curve, above baseline). In six (3M:3F) young healthy adults, we continuously measured forearm blood flow using doppler ultrasound on the brachial artery and muscle O2 saturation via near-infrared spectroscopy (MOXY) during three lengthening occlusion timed-reactive hyperemia tests (1, 5, or 10 minutes in duration). The magnitude of deoxygenation was significantly (P<0.05 via paired t-test) less during 1 min occlusion (-13±1.6%) compared to either 5 min occlusion (-67±14%; P=0.0015) or 10 min occlusion (-74±10%; P=0.0004), but 5 min vs 10 min occlusion were not different (P=0.40). Similarly, the magnitude of the RH was greater in both the 10 min occlusion (329±102 ml/min; P=0.0004) and 5 min occlusion (295±123 ml/min; P=0.005) vs 1 min occlusion (131±69 ml/min; P<0.0001), but were not different from one another (P=0.11). However, the total deoxygenation increased progressively from 1 min (-335±51 units), to 5 min (-10732±2209 units), to 10 min (-32357±5053 units; all P<0.01) as did the total reactive hyperemic response (1 min:1326±927 ml; 5 min:7865±4055 ml; 10 min:17447±9698 ml; P<0.01). These results suggest that two distinct deoxygenation factors, the absolute magnitude of and the total mismatch between O2 supply and demand, may guide human skeletal muscle's reactive hyperemic response profile. The increased duration in a deoxygenated state observed in the 10 min occlusion leads to a greater overall reactive hyperemia response, potentially mediated by increased muscle metabolite production and greater bioavailability of vasoactive products mediated by the fully deoxygenated erythrocytes. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.