title: The in-vivo oxyhaemoglobin dissociation curve at sea level and high altitude.
abstract: Animals native to hypoxic environments have adapted by increasing their haemoglobin oxygen affinity, but in-vitro studies of the oxyhaemoglobin dissociation curve (ODC) in humans show no changes in affinity under physiological conditions at altitudes up to 4000m. We conducted the first in-vivo measurement of the ODC; inducing progressive isocapnic hypoxia in lowlanders at sea level, acutely acclimatized lowlanders at 3600m, and native Andeans at that altitude. ODC curves were determined by administering isocapnic steps of increasing hypoxia, and measuring blood oxygen partial pressure and saturation. The ODC data were fitted using the Hill equation and extrapolated to predict the oxygen partial pressure at which haemoglobin was 50% saturated (P50). In contrast to findings from in-vitro studies, we found a pH-related reduction in P50 in subjects at altitude, compared to sea-level subjects. We conclude that a pH-mediated increase in haemoglobin oxygen affinity in-vivo may be part of the acclimatization process in humans at altitude.
authors: Institute of Medical Science, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors: Dahlia Y
authors: DY
authors: Balaban
authors: James
authors: J
authors: Duffin
authors: David
authors: D
authors: Preiss
authors: Alexandra
authors: A
authors: Mardimae
authors: Alex
authors: A
authors: Vesely
authors: Marat
authors: M
authors: Slessarev
authors: G R
authors: GR
authors: Zubieta-Calleja
authors: Ernest R
authors: ER
authors: Greene
authors: David B
authors: DB
authors: Macleod
authors: Joseph A
authors: JA
authors: Fisher
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000531:Altitude; D005260:Female; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D008297:Male; D009792:Oceans and Seas; D010100:Oxygen / Q000097:blood* / Q000737:chemistry; D010108:Oxyhemoglobins / Q000737:chemistry*; D055815:Young Adult
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; D010100:Oxygen