The Effect of Supine Cycling and Progressive Lower Body Negative Pressure on Cerebral Blood Velocity Responses.

Abstract

Moderate-intensity aerobic exercise increases cerebral blood velocity (CBv) primarily due to hyperpnea-induced vasodilation; however, the integrative control of cerebral blood flow (CBF) allows other factors to contribute to vasodilation. Lower body negative pressure (LBNP) can reduce CBv, the exact LBNP-intensity required to blunt the aforementioned exercise-induced CBv response is unknown. This could hold utility for concussion recovery, allowing individuals to exercise at higher-intensities without symptom exacerbation. Thirty-two healthy adults (age: 20-33 years; 19 females) completed a stepwise maximal-exercise test to determine each participant's wattage associated with their exercise-induced maximal CBv increase. During the second visit, participants completed moderate-intensity exercise at their determined threshold, while progressive LBNP was applied at 0, -20, -40, -60, -70, -80, and ~88 Torr. Bilateral middle cerebral artery blood velocities (MCAv), mean arterial pressure (MAP), heart rate, respiratory rate, and end-tidal carbon dioxide levels were measured continuously. Two-way analysis of variance with effect sizes compared between sexes and stages. Compared to resting-supine baseline, averaged MCAv was elevated during 0 and -20 Torr LBNP (q-value>7.73; p<0.001); no differences were noted between baseline and -40 to -70 Torr (q-value<|4.24|; p>0.262). Differences were present between females and males for absolute MCAv measures (q-value>11.2; p<0.001), but not when normalized to baseline (q-value<0.03; p>0.951). Supine cycling-elicited increases in MCAv were blunted during the application of LBNP ranging from -40 to -70 Torr. The blunted CBv response demonstrates the potential benefit of allowing individuals to aerobically train (moderate-intensity supine cycling with LBNP) without exacerbating symptoms during concussion recovery.