title: Differences in the control of breathing between Himalayan and sea-level residents.
abstract: We compared the control of breathing of 12 male Himalayan highlanders with that of 21 male sea-level Caucasian lowlanders using isoxic hyperoxic ( = 150 mmHg) and hypoxic ( = 50 mmHg) Duffin's rebreathing tests. Highlanders had lower mean +/- s.e.m. ventilatory sensitivities to CO(2) than lowlanders at both isoxic tensions (hyperoxic: 2.3 +/- 0.3 vs. 4.2 +/- 0.3 l min(1) mmHg(1), P = 0.021; hypoxic: 2.8 +/- 0.3 vs. 7.1 +/- 0.6 l min(1) mmHg(1), P < 0.001), and the usual increase in ventilatory sensitivity to CO(2) induced by hypoxia in lowlanders was absent in highlanders (P = 0.361). Furthermore, the ventilatory recruitment threshold (VRT) CO(2) tensions in highlanders were lower than in lowlanders (hyperoxic: 33.8 +/- 0.9 vs. 48.9 +/- 0.7 mmHg, P < 0.001; hypoxic: 31.2 +/- 1.1 vs. 44.7 +/- 0.7 mmHg, P < 0.001). Both groups had reduced ventilatory recruitment thresholds with hypoxia (P < 0.001) and there were no differences in the sub-threshold ventilations (non-chemoreflex drives to breathe) between lowlanders and highlanders at both isoxic tensions (P = 0.982), with a trend for higher basal ventilation during hypoxia (P = 0.052). We conclude that control of breathing in Himalayan highlanders is distinctly different from that of sea-level lowlanders. Specifically, Himalayan highlanders have decreased central and absent peripheral sensitivities to CO(2). Their response to hypoxia was heterogeneous, with the majority decreasing their VRT indicating either a CO(2)-independent increase in activity of peripheral chemoreceptor or hypoxia-induced increase in [H(+)] at the central chemoreceptor. In some highlanders, the decrease in VRT was accompanied by an increase in sensitivity to CO(2), while in others VRT remained unchanged and their sub-threshold ventilations increased, although these were not statistically significant.
authors.affiliation: Department of Anesthesia, University Health Network, University of Toronto, Toronto, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Slessarev
authors.forename: E
authors.initials: E
authors.lastname: Prisman
authors.forename: S
authors.initials: S
authors.lastname: Ito
authors.forename: R R
authors.initials: RR
authors.lastname: Watson
authors.forename: D
authors.initials: D
authors.lastname: Jensen
authors.forename: D
authors.initials: D
authors.lastname: Preiss
authors.forename: R
authors.initials: R
authors.lastname: Greene
authors.forename: T
authors.initials: T
authors.lastname: Norboo
authors.forename: T
authors.initials: T
authors.lastname: Stobdan
authors.forename: D
authors.initials: D
authors.lastname: Diskit
authors.forename: A
authors.initials: A
authors.lastname: Norboo
authors.forename: M
authors.initials: M
authors.lastname: Kunzang
authors.forename: O
authors.initials: O
authors.lastname: Appenzeller
authors.forename: J
authors.initials: J
authors.lastname: Duffin
authors.forename: J A
authors.initials: JA
authors.lastname: Fisher
mesh_terms: D000531:Altitude; D002245:Carbon Dioxide; D002560:Cerebrovascular Circulation; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D008297:Male; D010092:Oximetry; D010100:Oxygen / Q000097:blood; D011999:Recruitment, Neurophysiological; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen