Effect of Leg Blood Flow Restriction during Cycling on Cerebral Perfusion: Role of Carbon Dioxide

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Exercise with blood flow restriction (BFR) enhances skeletal muscle metabolite accumulation and has been used to stimulate training‐induced improvements in strength and endurance, but the consequences for the cerebral circulation are unknown. The activation of group III and IV skeletal muscle afferents by exercise‐induced metabolites (muscle metaboreflex) has been suggested to increase cerebral perfusion during exercise. However, this may be masked by a hyperventilation related decrease in the partial pressure of arterial carbon dioxide (indexed by partial pressure of end‐tidal carbon dioxide; PETCO2). We sought to determine how muscle metaboreflex activation with BFR affects cerebral blood flow and whether this is secondary to confounding changes in PETCO2. In 11 healthy male participants (age 25±4 years; height 180±1 cm; weight 71±7 kg; mean±SD) we measured middle cerebral artery mean blood velocity (MCAVm), internal carotid artery blood flow (ICAQ) and PETCO2, during leg cycling exercise under free‐flow conditions (target heart rate at 120 bpm) and with BFR. Trials were conducted where PETCO2 was permitted to fluctuate spontaneously (control) and where PETCO2 was clamped at 1 mmHg above resting levels. In the control trial, PETCO2 was slightly increased from rest during leg cycling (Δ2.2±0.3 mmHg; P<0.05) and significantly decreased during exercise with BFR (Δ‐4.8±0.9 mmHg; P<0.05). PETCO2 remained unchanged throughout the clamp trial. Leg cycling under free‐flow conditions evoked similar increases in MCAVm during the control (Δ6.5±1.8 cm.s−1) and PETCO2 clamp (Δ6.8±2.4 cm.s−1) trials (P<0.05 vs. rest). During exercise with BFR a further increase in MCAVm was noted in the PETCO2 clamp trial (Δ5.9±1.4 cm.s−1; P<0.05 vs. rest and free‐flow exercise), but not in the control trial. In both trials, ICAQ was not significantly changed from rest during leg cycling under free‐flow conditions (control Δ‐3.5±10.31 ml.min−1; PETCO2 clamp Δ7.2±7.41 ml.min−1; P>0.05 vs. rest). During exercise with BFR, ICAQ was significantly increased when PETCO2 was clamped (Δ27.2±6.6 ml.min−1; P<0.05 vs. rest), but was decreased in the control trial (Δ‐22.7±12.1 ml.min−1; P<0.05 vs. rest). In conclusion, enhanced muscle metaboreflex activation with leg BFR during cycling increases cerebral blood flow, but only when PETCO2 is maintained at resting levels.Support or Funding InformationThis study was supported by Coordination for the Improvement of Higher Education Personnel (CAPES‐Brazil) through the program Science without Borders.