Combined Effects of Remote Ischemic Preconditioning and Aerobic Exercise on Sympathetic and Cerebrovascular Responses: A Novel Adaptation of Blood Flow Restriction Exercise
Authors: Sprick Justin , Colby Hannah , Rickards Caroline Alice 
Published: November 2023

Introduction

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 method of training in which a restrictive device is applied around the working muscles during the exercise bout. We implemented a novel approach to BFRE with cyclical bouts of blood flow restriction and reperfusion, reflecting the RIPC model. This novel form of exercise could elicit similar protection against ischemia‐reperfusion injury as RIPC. 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, arterial pressure, and cerebral blood flow than conventional exercise (CE) when performed at the same relative heart rate (HR) intensity.

Methods

11 subjects (6M/5F; age 28±2 y) performed two 40‐min continuous treadmill exercise bouts at 65–70% of maximal HR (randomized, cross‐over design). In the BFRE condition, inflatable cuffs were secured to the upper thighs and inflated to 220 mmHg for 4 cycles of 5‐min cuff inflation/5‐min cuff deflation (reperfusion). The CE condition was identical to the BFRE condition but without application of the cuffs. Mean arterial pressure (MAP), mean middle cerebral artery velocity (MCAv), cerebral oxygen saturation (ScO2) and plasma norepinephrine concentrations ([NE]) were compared between trials.

Results

As expected, 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 periods (BFRE) and the corresponding time point during CE (P≥0.12), and MAP was lower with BFRE during all 4 cuff deflation/reperfusion periods compared to the same time point during 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). While MCAv increased with exercise in both conditions (P<0.001), there were no differences between trials (P=0.40), and ScO2 did not change with time (P=0.30) or condition (P=0.71).

Discussion

BFRE elicited an exaggerated sympatho‐excitatory response compared to CE as evidenced by the greater elevation in plasma [NE]. This response was not accompanied by a greater increase in arterial pressure, 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. The similarity in MCAv and ScO2 responses between trials suggests equivalent cerebro‐metabolic demand between conditions. 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 cardio‐ and cerebro‐protection associated with RIPC.

Support or Funding Information

UNTHSC Institute for Aging and Alzheimer's Disease Research, NIH Training Grant (T32 AG 020494) (Sprick)

Texas Chapter of the American College of Sports Medicine (TACSM) Student Research Development Award (Sprick)

UNTHSC Faculty Research Pilot Grant (Rickards)