title: Cerebral blood flow and oxygenation at maximal exercise: the effect of clamping carbon dioxide.
abstract: During exercise, as end-tidal carbon dioxide (P(ET)(CO₂)) drops after the respiratory compensation point (RCP), so does cerebral blood flow velocity (CBFv) and cerebral oxygenation. This low-flow, low-oxygenation state may limit work capacity. We hypothesized that by preventing the fall in P(ET)(CO₂) at peak work capacity (W(max)) with a newly designed high-flow, low-resistance rebreathing circuit, we would improve CBFv, cerebral oxygenation, and W(max). Ten cyclists performed two incremental exercise tests, one as control and one with P(ET)(CO₂) constant (clamped) after the RCP. We analyzed , middle cerebral artery CBFv, cerebral oxygenation, and cardiopulmonary measures. At W(max), when we clamped P(ET)(CO₂) (39.7 ± 5.2 mmHg vs. 29.6 ± 4.7 mmHg, P < 0.001), CBFv increased (92.6 ± 15.9 cm/s vs. 73.6 ± 12.5 cm/s, P < 0.001). However, cerebral oxygenation was unchanged (ΔTSI -21.3 ± 13.1% vs. -24.3 ± 8.1%, P = 0.33), and W(max) decreased (380.9 ± 20.4W vs. 405.7 ± 26.8 W, P < 0.001). At W(max), clamping P(ET)(CO₂) increases CBFv, but this does not appear to improve W(max).
authors.affiliation: Altitude Research Center, Department of Emergency Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO 80045-0508, USA. olin.tod@tchden.edu
authors.forename: J Tod
authors.initials: JT
authors.lastname: Olin
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Dimmen
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Subudhi
authors.forename: Robert C
authors.initials: RC
authors.lastname: Roach
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001776:Blood Circulation Time; D001783:Blood Flow Velocity / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003250:Constriction; D018592:Cross-Over Studies; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D012119:Respiration; D016037:Single-Blind Method; D019265:Spectroscopy, Near-Infrared; D013997:Time Factors; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods; D014666:Vasomotor System / Q000502:physiology; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide