Males Exhibit Greater Reperfusion During Ischemic Preconditioning At High, But Not Low Or Moderate Occlusion Pressures

PURPOSE: Ischemic preconditioning (IPC) can protect against reperfusion injuries. The rate of reperfusion following IPC provides insight to microvascular health and may differ between sexes. The purpose of this investigation was to examine reperfusion slopes following IPC performed at different pressures between men and women. METHODS: Twelve (22.1 ± 2.6 years; 168.1 ± 8.9 cm; 66.6 ± 10.3 kg) recreationally active males (n = 6) and females (n = 6) randomly completed (on separate visits) three cycles of IPC at low (SHAM [20 mmHg]), moderate (80% of total arterial occlusion pressure), and high (220 mmHg) pressures. Each cycle consisted of five minutes of pressure and five minutes of rest with a pneumatic cuff placed most proximal on the dominant leg. Near infrared spectroscopy (NIRS) was placed on the vastus lateralis muscle to measure muscle tissue oxygenation (StO2) and the reperfusion slopes of StO2 were derived from the first 10-seconds immediately following each five-minute occlusion. A 2 (Sex [male, female]) x 3 (Pressure [low, moderate, high]) x 3 (Time [cycle 1, 2, 3]) mixed factorial ANOVA was used to examine potential mean differences in sex and/or pressure across the cycles. RESULTS: There was a significant three-way (p = 0.035) and significant (p = 0.001) follow-up two-way (Sex x Pressure, collapsed across Time) interaction for StO2 reperfusion slopes. Males exhibited a greater StO2 reperfusion slope than females during the high-pressure condition (1.5 ± 0.7 s-1 versus 0.7 ± 0.4 s-1) (p < 0.001). Males also exhibited a pressure-specific response (SHAM: 0.01 ± 0.02 s-1 < moderate: 0.9 ± 0.4 s-1 < high: 1.5 ± 0.7 s-1) (p < 0.001-0.004), whereas females did not (SHAM: 0.02 ± 0.03 s-1 < moderate: 0.9 ± 0.3 s-1 = high: 0.7 ± 0.4 s-1) (p < 0.001-0.004). CONCLUSIONS: Relative to females, males exhibited a greater reperfusion rate during the high-pressure condition, and experienced pressure-specific reperfusion rates. These responses suggest there may exist a pressure-dependent vascular response in males, but not females. Additionally, these sex differences may be due to physiological differences in skeletal muscle mass and/or oxidative capacity.