Acute hypoxia decreases cardiac response to catecholamines in exercising humans.
Cardiac chronotropic response to adrenergic activity at rest and exercise has been studied in 8 sea-level natives on the first two days of exposure to high altitude hypoxia (3823 m, 473 mmHg). Maximal O2 uptake (VO2max) was determined at low altitude (day 0:D0) and high altitude (day 2:D2). Submaximal exercise tests were performed at low altitude (day 1:D1) and high altitude (days 3 and 4: D3, D4). Plasma venous norepinephrine (NE) and epinephrine (E) concentrations were determined at rest and at the end of submaximal exercise. From D0 to D2, maximal heart rate decreased by 7% (p less than 0.01), and VO2max decreased by 17% (p less than 0.01). During submaximal exercise, plasma NE did not vary significantly (D1: 1.36 +/- 0.57, D3: 1.48 +/- 0.51, D4: 1.31 +/- 0.54 ng.ml-1). In contrast, relative work load decreased at high altitude (% VO2max at D1, D3 and D4 were respectively: 90.2 +/- 6.1, 83.3 +/- 9.8, 76.9 +/- 8.2). Linear relationships were found, both at low and high altitudes, between NE and VO2, NE and % VO2max, and between the increases in NE and heart rate during exercise. Covariance analysis indicates that these relations shifted to the left at high altitude:for the same NE or increase in NE, VO2 or increase in heart rate was lower at high altitude. Variations in E were similar but not significant. We conclude that hypoxia induced a decrease in cardiac chronotropic response to adrenergic activation during submaximal exercise.
Richalet
J P
JP
Association pour la Recherche en Physiologie de l'Environnement, Faculté de Médecine, Université Paris XII, Créteil, France.
Mehdioui
H
H
Rathat
C
C
Vignon
P
P
Keromes
A
A
Herry
J P
JP
Sabatier
C
C
Tanche
M
M
Lhoste
F
F
D000328:Adult; D000531:Altitude; D002395:Catecholamines / Q000097:blood*; D004837:Epinephrine / Q000097:blood; D005260:Female; D006321:Heart / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption; D005082:Physical Exertion
D002395:Catecholamines; D009638:Norepinephrine; D004837:Epinephrine