Combined Effects of Remote Ischemic Preconditioning and Aerobic Exercise on Sympathetic Responses: A Novel Adaptation of Blood Flow Restriction Exercise

Purpose: Remote ischemic preconditioning (RIPC) is an innovative therapy used to attenuate tissue damage sustained by ischemia-reperfusion injury. Blood flow restriction exercise (BFRE) is a training method that also limits blood flow to the active muscles during exercise. We implemented a novel approach to BFRE with cyclical bouts of blood flow restriction and reperfusion, reflecting the RIPC model, which could elicit similar protection against ischemia-reperfusion injury. A concern about the use of BFRE, however, is the potential amplification of the exercise pressor reflex, which could be unsafe in at-risk populations. We hypothesized that cyclical BFRE would elicit a greater increase in sympathetic outflow and arterial pressure than conventional exercise (CE) when performed at the same relative heart rate (HR) intensity. Methods: 11 subjects (6M/5F) performed two 40-min treadmill exercise bouts at 65-70% of maximal HR. In the BFRE condition, cuffs around the upper thighs were inflated to 220 mmHg for 4 cycles of 5-min cuff inflation (occlusion)/5-min cuff deflation (reperfusion). The CE condition was identical, but without application of the cuffs. Mean arterial pressure (MAP), and plasma norepinephrine concentrations [NE] were compared between trials. Results: As hypothesized, BFRE resulted in higher [NE] compared to CE (923±92 vs 782±68 pg/ml; P=0.05). Unexpectedly, however, there were no differences in MAP between conditions during the cuff inflation time periods (BFRE vs. CE; P≥0.12)), and MAP was lower with BFRE during all 4 reperfusion periods compared to the CE trial (Cycle 1: BFRE vs. CE, 103±3 vs 107±2 mmHg; Cycle 2: 98±2 vs 103±2 mmHg; Cycle 3: 96±2 vs 102±2 mmHg; Cycle 4: 95±2 vs 100±2 mmHg; P≤0.04). Conclusion: BFRE elicited an exaggerated sympatho-excitatory response compared to CE as evidenced by higher plasma [NE]. This response was not accompanied by higher arterial pressures, however, most likely due to the cyclical nature of the occlusion/reperfusion protocol. The reactive hyperemia resulting from each cuff deflation may have offset the expected sympathetically-mediated increase in arterial pressure, resulting in an attenuation of the exercise pressor reflex. In conclusion, this novel cyclical BFRE paradigm could be applied to the clinical setting, such as cardiac or stroke-rehabilitation, where patients are already engaged in an exercise program, but where they could also benefit from the protection associated with RIPC.