Impact of Blood Flow Restriction Exercise on Central Hemodynamics and Fluid Regulating Hormones

Abstract

Purpose To characterize both the efficacy of altered restriction pressures and consequences of optimized blood flow restriction (BFR) for altering the cardiovascular and fluid regulating response in humans. Methods This work comprised a series of related trials. Phase 1: during semi-recumbent cycling (5 min, 60 W) with BFR at 0, 50, 75, 100 and 125% of participants’ lowest arterial occlusion pressure (LOP) echocardiographic images were collected alongside continuous heart rate (HR) and blood pressure (BP). In phase 2, 24 h fluid balance (intake-output) and fluid-regulating hormone responses were measured after a practical BFR exercise session (treadmill walking: 5·3 min, 1 min rest, 5 km/h, 5% incline, 100% LOP). Phase 3 examined the magnitude and effect of blood volume distribution following BFR treadmill walking using a modified CO-rebreathe technique. Results Cardiac ejection fraction remained stable irrespective of cuff pressure and despite a reduction in end-diastolic volume (Δ of 11 ± 9 mL, p = 0.02). HR and BP were highest at 100% LOP (ΔHR = 18 ± 19 bpm, ΔSBP = 51 ± 30 mmHg, ΔDBP = 33 ± 15 mmHg, ΔRate Pressure Product = 76 ± 32 bpm·mmHg·100-1). BFR treadmill walking stimulated a greater release of fluid-regulating hormones than normal walking (Δrenin = BFR: 25.3 ± 24.2 vs. CON: 9.1 ± 11.8 ng/L; Δcopeptin = BFR: 50.1 ± 97.9 vs. CON: 0.43 ± 0.8 pmol/L), but no difference in fluid retention was observed (p = 0.2). Approximately 27% of total blood volume was confined to the legs during BFR, but the relative volume trapped in the legs was not related to fluid-regulating hormone release (renin r = -0.04, p = 0.9; copeptin r = 0.27, p = 0.3). Conclusions BFR exercise elicits the largest cardiovascular effect using 100% LOP, with evidence of appreciable fluid regulating hormonal response during a typical BFR exercise session. The relative volume of blood sequestered in the limb does not appear to drive this response.

Low‐ and high‐volume blood‐flow restriction treadmill walking both improve maximal aerobic capacity independently of blood volume

“…Our hypothesis, that blood volume or blood oxygen carrying capacity would increase following BFR training, was based on the expected time course of blood volume adaptation, which fit with the timelines of previous BFR training studies reporting an increase in VO 2 max, and the observation that highly trained athletes still adapt. We have previously observed large increases in blood volume regulating hormones after BFR exercise, 27 and again observed increased renin and copeptin concentrations after BFR exercise in the current study. Given that these hormones are involved with blood pressure regulation via body fluid retention, 39,40 we reasoned that the repeated exposure to these hormones would induce an increase in blood volume; however, no changes in plasma volume, RBCV or Hb mass were observed following BFR training despite the hormonal response and, thus, we must reject this hypothesis.…”

“…Although VO 2 max did not disproportionately in favor of the DL testing condition, the fact that the VO 2 max ratio between testing conditions did not change suggests central adaptations must still be occurring, as we would have observed disproportionate increases in favor of SL oxygen consumption if adaptations were only occurring locally. 27 and again observed increased renin and copeptin concentrations after BFR exercise in the current study. Given that these hormones are involved with blood pressure regulation via body fluid retention, 39,40 we reasoned that the repeated exposure to these hormones would induce an increase in blood volume; however, no changes in plasma volume, RBCV or Hb mass were observed following BFR training despite the hormonal response and, thus, we must reject this hypothesis.…”

“…Plasma/serum from all centrifuged samples was aliquoted into separate, no additive vacutainer tubes before being analyzed for renin and copeptin concentrations at a certified blood testing facility (LifeLabs, Guelph, Ontario, Canada). Blood analysis pre/post training was only performed in the BFR HV group due to analysis costs and because hormonal response to acute treadmill walking without BFR has previously been characterized by our laboratory, with treadmill walking alone causing no changes in circulating hormone (renin and copeptin) concentrations 27 …”

“…Blood analysis pre/post training was only performed in the BFR HV group due to analysis costs and because hormonal response to acute treadmill walking without BFR has previously been characterized by our laboratory, with treadmill walking alone causing no changes in circulating hormone (renin and copeptin) concentrations. 27…”

“…Following an acute bout of BFR treadmill walking, our laboratory has demonstrated large increases in plasma renin and copeptin (a marker of anti-diuretic hormone that also causes water retention). 27 Given that these hormones are elevated following a single bout of BFR exercise, repeated exposure is expected to induce a degree of fluid retention, leading to hypervolemia. While anti-diuretic hormone can independently stimulate erythropoiesis, 28 erythropoietin release is stimulated during periods of relative hypoxemia.…”