title: Cerebrovascular reactivity is increased with acclimatization to 3,454 m altitude.
abstract: Controversy exists regarding the effect of high-altitude exposure on cerebrovascular CO2 reactivity (CVR). Confounding factors in previous studies include the use of different experimental approaches, ascent profiles, duration and severity of exposure and plausibly environmental factors associated with altitude exposure. One aim of the present study was to determine CVR throughout acclimatization to high altitude when controlling for these. Middle cerebral artery mean velocity (MCAv mean) CVR was assessed during hyperventilation (hypocapnia) and CO2 administration (hypercapnia) with background normoxia (sea level (SL)) and hypoxia (3,454 m) in nine healthy volunteers (26 ± 4 years (mean ± s.d.)) at SL, and after 30 minutes (HA0), 3 (HA3) and 22 (HA22) days of high-altitude (3,454 m) exposure. At altitude, ventilation was increased whereas MCAv mean was not altered. Hypercapnic CVR was decreased at HA0 (1.16% ± 0.16%/mm Hg, mean ± s.e.m.), whereas both hyper- and hypocapnic CVR were increased at HA3 (3.13% ± 0.18% and 2.96% ± 0.10%/mm Hg) and HA22 (3.32% ± 0.12% and 3.24% ± 0.14%/mm Hg) compared with SL (1.98% ± 0.22% and 2.38% ± 0.10%/mm Hg; P < 0.01) regardless of background oxygenation. Cerebrovascular conductance (MCAv mean/mean arterial pressure) CVR was determined to account for blood pressure changes and revealed an attenuated response. Collectively our results show that hypocapnic and hypercapnic CVR are both elevated with acclimatization to high altitude.
authors: 1] Zurich Center for Integrative Human Physiology (ZIHP), Zurich, Switzerland [2] Institute of Physiology, ZIHP, University of Zurich, Zurich, Switzerland.
authors: Daniela
authors: D
authors: Flück
authors: Institute of Physiology, ZIHP, University of Zurich, Zurich, Switzerland.
authors: Christoph
authors: C
authors: Siebenmann
authors: 1] Zurich Center for Integrative Human Physiology (ZIHP), Zurich, Switzerland [2] Institute of Physiology, ZIHP, University of Zurich, Zurich, Switzerland.
authors: Stefanie
authors: S
authors: Keiser
authors: Institute of Human Movement Sciences, ETH Zurich, Zurich, Switzerland.
authors: Adrian
authors: A
authors: Cathomen
authors: 1] Zurich Center for Integrative Human Physiology (ZIHP), Zurich, Switzerland [2] Institute of Physiology, ZIHP, University of Zurich, Zurich, Switzerland [3] Department of Food and Nutrition and Sport Science, Gothenburg University, Gothenburg, Sweden.
authors: Carsten
authors: C
authors: Lundby
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000502:physiology*; D000328:Adult; D000531:Altitude; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D002245:Carbon Dioxide / Q000008:administration & dosage; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D016857:Hypocapnia / Q000503:physiopathology; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide