Reversal of hypoxia-induced decrease in human cardiac response to isoproterenol infusion.
A decrease in heart rate response to isoproterenol (IP) infusion has been previously described in humans exposed to acute (2-3 days) or chronic (21 days) exposure to altitude hypoxia (J. Appl. Physiol. 65: 1957-1961, 1988). To evaluate this cardiac response in subacute (8 days) hypoxia and to explore its reversal with restoration of normoxia, six subjects received an IP infusion under normoxia (condition N), after 8 days in altitude (4,350 m, condition H8), on the same day in altitude after inhalation of O2 restoring normoxic arterial O2 saturation (SaO2, condition HO), and 6-11 h (condition RN) and 4-5 mo (condition ND) after the return to sea level. Cardiac chronotropic response to IP, evaluated by the mean increase in heart rate from base value (delta HR, min-1), was lower in condition H8 [mean 30 +/- 13 (SD)] than in condition N (50 +/- 14, P less than 0.03); it was slightly higher in condition HO (38 +/- 14) or condition RN (42 +/- 15) than condition H8 but still significantly different from condition N (P less than 0.03), despite normal values of SaO2. delta HR in condition ND (55 +/- 10) returned to base N value. These findings confirm the hypothesis of a hypoxia-induced decrease in cardiac chronotropic function. Two possible mechanisms are suggested: an O2-dependent one, rapidly reversible with recent restoration of normoxia, and a more slowly reversible mechanism, probably a downregulation of the cardiac beta-receptors.
Richalet
J P
JP
Institut National de la Santé et de la Recherche Médicale U138 et U296, Faculté de Médecine, Créteil, France.
Le-Trong
J L
JL
Rathat
C
C
Merlet
P
P
Bouissou
P
P
Keromes
A
A
Veyrac
P
P
D000328:Adult; D001794:Blood Pressure; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption; D013997:Time Factors
D007545:Isoproterenol; D009638:Norepinephrine