Reducing Venous Return Using BFR: Alterations In Blood Volume Regulating Hormones And Short-term Training Responses

Abstract

Partitioning blood from central circulation to the legs via blood flow restricted (BFR) exercise will impact venous return acutely, though the relationship between occlusion pressure and reduced venous return is unknown. A reduction in central volume, which can be tracked by measuring ventricular filling, is likely to affect renin and anti-diuretic hormone (ADH) concentrations, that regulate blood volume via water retention. Blood volume has a strong influence on maximal aerobic capacity (VO2max); thus, BFR exercise training could augment aerobic capacity when performed repeatedly. PURPOSE: To determine the impact of BFR during and following exercise on ventricular filling, hormone release, and training response. METHODS: Venous return was estimated via ultrasound measures of inferior vena cava diameter (IVCD) and end-diastolic volume (EDV) while participants (n = 13) had tourniquets inflated around their upper thigh during and following semi-recumbent cycling. Graded occlusion pressures were tested in each exercise condition to determine the greatest reduction in venous return and these pressures were used in two separate 2-week BFR training models: 1) BFR during walking (20 min) and 2) BFR following sprint cycling (5x10s). For both styles of BFR exercise, the hormonal response to a single training bout was analyzed using pre/post blood draws with VO2max measured before and after training. RESULTS: Compared to the control, BFR effectively reduced venous return during exercise at 100% arterial occlusion pressure (IVCD 15%; EDV 11%, both p < 0.05) and at 75% occlusion pressure during recovery (IVCD 20%; EDV 18%, both p < 0.02). Increased plasma renin and ADH concentrations were observed following exercise (pooled, p < 0.05) for BFR during walking (renin: 19.6 ± 9.4 to 40.8 ± 16.7 ng/L; ADH: 6.3 ± 4.1 to 28.5 ± 30.8 pmol/L) and post sprint exercise (renin: 24.2 ± 14.9 to 121 ± 72.7 ng/L; ADH:7.1 ± 3.4 to 374.1 ± 311 pmol/L). Following two weeks of training with BFR during walking, absolute VO2max improved (6.8 ± 6.4%) but was unchanged in the post exercise BFR model, with large inter-individual variability. CONCLUSION: Reducing venous return via leg BFR leads to increases in circulating blood-volume regulating hormones. Preliminary work suggests BFR during exercise results in greater changes in VO2max.