title: AltitudeOmics: enhanced cerebrovascular reactivity and ventilatory response to CO2 with high-altitude acclimatization and reexposure.
abstract: The present study is the first to examine the effect of high-altitude acclimatization and reexposure on the responses of cerebral blood flow and ventilation to CO2. We also compared the steady-state estimates of these parameters during acclimatization with the modified rebreathing method. We assessed changes in steady-state responses of middle cerebral artery velocity (MCAv), cerebrovascular conductance index (CVCi), and ventilation (V(E)) to varied levels of CO2 in 21 lowlanders (9 women; 21 ± 1 years of age) at sea level (SL), during initial exposure to 5,260 m (ALT1), after 16 days of acclimatization (ALT16), and upon reexposure to altitude following either 7 (POST7) or 21 days (POST21) at low altitude (1,525 m). In the nonacclimatized state (ALT1), MCAv and V(E) responses to CO2 were elevated compared with those at SL (by 79 ± 75% and 14.8 ± 12.3 l/min, respectively; P = 0.004 and P = 0.011). Acclimatization at ALT16 further elevated both MCAv and Ve responses to CO2 compared with ALT1 (by 89 ± 70% and 48.3 ± 32.0 l/min, respectively; P < 0.001). The acclimatization gained for V(E) responses to CO2 at ALT16 was retained by 38% upon reexposure to altitude at POST7 (P = 0.004 vs. ALT1), whereas no retention was observed for the MCAv responses (P > 0.05). We found good agreement between steady-state and modified rebreathing estimates of MCAv and V(E) responses to CO2 across all three time points (P < 0.001, pooled data). Regardless of the method of assessment, altitude acclimatization elevates both the cerebrovascular and ventilatory responsiveness to CO2. Our data further demonstrate that this enhanced ventilatory CO2 response is partly retained after 7 days at low altitude.
authors.affiliation: Institute of Sports Sciences, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland;
authors.forename: Jui-Lin
authors.initials: JL
authors.lastname: Fan
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Subudhi
authors.forename: Oghenero
authors.initials: O
authors.lastname: Evero
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bourdillon
authors.forename: Bengt
authors.initials: B
authors.lastname: Kayser
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Lovering
authors.forename: Robert C
authors.initials: RC
authors.lastname: Roach
mesh_terms: D000064:Acclimatization; D000136:Acid-Base Equilibrium; D000531:Altitude; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D002628:Chemoreceptor Cells / Q000378:metabolism; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology*; D008168:Lung / Q000503:physiopathology*; D008297:Male; D020768:Middle Cerebral Artery / Q000503:physiopathology*; D012123:Pulmonary Ventilation; D013997:Time Factors; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: altitude acclimatization; cerebral CO2 reactivity; cerebral blood flow; rebreathing