title: Muscle metaboreflex and cerebral blood flow regulation in humans: implications for exercise with blood flow restriction.
abstract: We investigated the effect of activating metabolically sensitive skeletal muscle afferents (muscle metaboreflex) on cerebral blood flow and the potentially confounding influence of concomitant changes in the partial pressure of arterial carbon dioxide. Eleven healthy males (25 ± 4 yr) performed submaximal leg cycling exercise on a semirecumbent cycle ergometer (heart rate: ∼120 beats/min), and assessments were made of the partial pressure of end-tidal carbon dioxide (PetCO2 ), internal carotid artery blood flow (ICAQ) and conductance (ICACVC), and middle cerebral artery mean blood velocity (MCAvm) and conductance index (MCACVCi).The muscle metaboreflex was activated during cycling with leg blood flow restriction (BFR) or isolated with postexercise ischemia (PEI). In separate trials, PetCO2 was either permitted to fluctuate spontaneously (control trial) or was clamped at 1 mmHg above resting levels (PetCO2 clamp trial). In the control trial, leg cycling with BFR decreased PetCO2 (Δ-4.8 ± 0.9 mmHg vs. leg cycling exercise) secondary to hyperventilation, while ICAQ, ICACVC, and MCAvm were unchanged and MCACVCi decreased. However, in the PetCO2 clamp trial, leg cycling with BFR increased both MCAvm (Δ5.9 ± 1.4 cm/s) and ICAQ (Δ20.0 ± 7.8 ml/min) and attenuated the decrease in MCACVCi, while ICACVC was unchanged. In the control trial, PEI decreased PetCO2 (Δ-7.0 ± 1.3 mmHg vs. rest), MCAvm and MCACVCi, whereas ICAQ and ICACVC were unchanged. In contrast, in the PetCO2 clamp trial both ICAQ (Δ18.5 ± 11.9 ml/min) and MCAvm (Δ8.8 ± 2.0 cm/s) were elevated, while ICACVC and MCACVCi were unchanged. In conclusion, when hyperventilation-related decreases in PetCO2 are prevented the activation of metabolically sensitive skeletal muscle afferent fibers increases cerebral blood flow.
authors.affiliation: School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom; Department of Physiology and Pharmacology, Fluminense Federal University, Niterói, Brazil; and.
authors.forename: Eliza
authors.identifier: 0000-0003-2700-0409
authors.initials: E
authors.lastname: Prodel
authors.affiliation: School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom;
authors.forename: George M
authors.initials: GM
authors.lastname: Balanos
authors.affiliation: School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom;
authors.forename: Igor D
authors.initials: ID
authors.lastname: Braz
authors.affiliation: Department of Physiology and Pharmacology, Fluminense Federal University, Niterói, Brazil; and.
authors.forename: Antonio C L
authors.initials: AC
authors.lastname: Nobrega
authors.affiliation: Faculty of Physical Education, University of Brasília, Brasília, Distrito Federal, Brazil.
authors.forename: Lauro C
authors.initials: LC
authors.lastname: Vianna
authors.affiliation: School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom; j.p.fisher@bham.ac.uk.
authors.forename: James P
authors.identifier: 0000-0001-7851-9222
authors.initials: JP
authors.lastname: Fisher
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001642:Bicycling; D015415:Biomarkers / Q000097:blood; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000097:blood; D002343:Carotid Artery, Internal / Q000502:physiology*; D002560:Cerebrovascular Circulation; D002628:Chemoreceptor Cells / Q000378:metabolism*; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D006801:Humans; D006985:Hyperventilation / Q000378:metabolism / Q000503:physiopathology; D007511:Ischemia / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation / Q000378:metabolism; D010313:Partial Pressure; D012018:Reflex; D012039:Regional Blood Flow; D015398:Signal Transduction; D013997:Time Factors; D055815:Young Adult
chemical_list: D015415:Biomarkers; D002245:Carbon Dioxide
keywords: cerebrovascular circulation; exercise; metabolic activation