Serial Lower Limb Occlusion and Reperfusion Augments Muscle Oxygen Saturation despite Attenuated Cardiac Hemodynamics

Abstract

INTRODUCTION: Remote ischemic preconditioning (RIPC) involves brief, serial manually-imposed blood flow restriction of the limbs. The alternating periods of occlusion and reperfusion lead to endothelial adaptations, capable of enhancing blood flow and oxygen delivery. An understanding of the cardiovascular, ventilatory, and local metabolic adjustments to RIPC is essential to optimize the technique as a physiological stimulus. PURPOSE: To investigate reactive and sustained changes in cardiac hemodynamics, local muscle oxygen saturation, and ventilation in response to serial RIPC application. METHODS: Ten (M:4, F:6) recreationally aerobically trained college students (22 ± 2 y, 170.4 ± 9.8 cm, 73.6 ± 8.7 kg, 19.8 ± 6.4 % BF, VO2peak: 45.5 ± 5.0 mL·kg-1·min-1 at 208 ± 31 W) received 5-min of alternating-leg blood flow occlusion using a blood pressure cuff (220 mmHg) placed on the upper thighs for a total of 40 min in a supine position. Muscle oxygen saturation (SmO2) was measured continuously using a portable NIRS-based sensor placed over the vastus lateralis. Cardiac hemodynamics were measured continuously using impedance cardiography. Continuous ventilatory changes in response to RIPC were measured in a small subset (n=4) using a metabolic cart. RESULTS: Serial occlusion resulted in a more rapid decrease in SmO2 over time (15.13 ± 2.95 vs. 16.67 ± 2.12 %·min-1), and a lower heart rate (61 ± 9 vs. 58 ± 7 bpm) and cardiac output (5.1 ± 0.8 vs. 4.9 ± 0.7 L·min-1) from occlusion 1 to 4. Serial reperfusion resulted in a greater reactive peak SmO2 (86.7 ± 2.4 vs. 88.3 ± 2.8%), and a lower peak heart rate (74 ± 9 vs. 70 ± 10 bpm) and cardiac output (6.6 ± 0.8 vs. 6.2 ± 0.8 L·min-1) from reperfusion 1 to 4. Ventilatory data suggest a decrease in oxygen consumption from the first to last occlusion (-0.046 ± 0.013 L·min-1) and from the first to last reperfusion (-0.030 ± 0.009 L·min-1). CONCLUSIONS: Both the occlusion and reperfusion stimuli appear less physiologically stressful when applied serially, despite a heightened peak SmO2 following reperfusion. The serial reperfusion response indicates vascular modulation and/or lower local metabolic demand, rather than cardiac hemodynamics, may be responsible for enhancement of local muscle oxygen saturation.