Cinética de la reoxigenación muscular post-oclusiva y biodisponibilidad del óxido nítrico tras 10 días de reposo en...

Bed rest (BR) studies have demonstrated the detrimental effects of microgravity and physical inactivity on cardiovascular function, including the negative consequences on microvascular function and O₂ extraction. However, whether a short period of BR affects microvascular responsiveness and its molecular mediator, nitric oxide (NO), remain unclear.Nine male volunteers (23±5 yr) completed 10-day horizontal BR. Microvascular post-occlusive reactive hyperemia in the vastus lateralis (VL) and rectus femoris (RF) muscles were assessed by Near-Infrared Spectroscopy during a vascular occlusion test. We calculated the rate of muscle deoxygenation during the first minute of occlusion (Slope 1) and the half-time of the reperfusion kinetics (t_1/2) during the 30 s post-ischemia. The inverse of t_1/2, K (velocity constant) was "normalized" for the intensity of the ischemic/hypoxic stimulus, as estimated by Δ[deoxy(Hb+Mb)]_peak, the highest Δ[deoxy(Hb+Mb)] value at the end of ischemia. Plasma nitrite (NO₂^-) and nitrate (NO₃^-) concentrations (NO bioavailability indexes) were determined by chemiluminescence.Slope 1 and were slower after BR in both VL (0.08±0.03 vs. 0.06±0.02 µM·s^-1 p=0.016, and 12±3 vs. 17±2 s, p=0.002) and RF (0.07±0.02 vs. 0.05±0.02 µM·s^-1 p=0.008, and 12±3 vs. 18±4 s, p<0.001). No differences were detected in K/Δ[deoxy(Hb+Mb)]_peakafter BR (VL: 0.15±0.04 vs. 0.17±0.03 µM·min^-1, p=0.166; RF: 0.20±0.06 vs. 0.21±0.05 µM·min^-1, p=0.220). Plasma NO₂^- concentration was reduced after BR (87±37 vs. 67±48 nM, p=0.011), but not plasma NO₃^- concentration (43±24 vs. 29±11 µM, p=0.130).In conclusion, 10-day horizontal BR does not impair microvascular post-occlusive reactive hyperemia parameters, despite decreasing plasma NO₂^- concentration.