Time-course and pressure-dependent changes in microvascular responses during ischemic preconditioning

This investigation examined a moderate individualized pressure (i.e., percentage of total arterial occlusion pressure [TAOP]) compared to low and high absolute pressures on muscle tissue oxygenation (StO₂) throughout ischemic preconditioning (IPC). Fifteen males randomly completed three cycles of IPC at a low (20 mmHg [IPC_SHAM]), moderate (80% of TAOP [IPC_80%]), and high (220 mmHg [IPC_220mmHg]) pressure. Each cycle lasted 5 min at the assigned pressure, followed by 5 min of zero pressure on the dominant leg. StO₂ was measured continuously and StO₂ indices (i.e., downslope [StO_2down], minimum [StO_2min], upslope [StO_2up], maximum [StO_2max]) were analyzed with Bayesian models. StO_2down and StO_2min were pressure-dependent (IPC_SHAM < IPC_80% < IPC_220mmHg) as indicated by zero absent from all 95% high-density intervals (95% HDI) and 100% probability of an effect (Prob = 100%). During IPC_220mmHg, StO_2up increased from cycle 1 to cycles 2 and 3 but plateaued from cycle 2 to 3 as indicated by zero absent from all 95% HDI's and Prob ≥87.6%. Additionally, StO_2up was greater for IPC_80% and IPC_220mmHg relative to IPC_SHAM for cycles 1 and 2 but was pressure-dependent during cycle 3 as indicated by zero absent from all 95% HDI's and Prob = 98.8%. Lastly, StO_2max was greater for IPC_220mmHg than IPC_SHAM and IPC_80% as indicated by zero absent from all 95% HDI's and Prob = 100%. Collectively, using moderate individualized pressure elicited similar StO_2up as high absolute pressure, but only for cycles 1 and 2. These findings may be attributed to differences in the hypoxic-insult and/or vascular-related mechano-transduction stimuli.