Decreased cardiac response to isoproterenol infusion in acute and chronic hypoxia

Abstract

The hypothesis of a blunted chronotropic response of cardiac beta-adrenergic receptors in altitude hypoxia was tested in nine subjects at sea level (SL) by infusion of isoproterenol. Observations were made at SL, in acute hypoxia (2 days at 4,350 m, condition H1), in more prolonged hypoxia [13 days between 850 and 4,800 m, condition H2] and in chronic hypoxia [21 days at 4,800 m, condition H3]. Resting heart rate was higher in all hypoxic conditions. Resting norepinephrine concentrations were found to be significantly higher in conditions H2 (1.64 +/- 0.59) and H3 (1.74 +/- 0.76) than at SL (0.77 +/- 0.18 ng/ml). Isoproterenol, diluted in saline, was infused at increasing doses of 0.0, 0.02, 0.04, and 0.06 micrograms.kg-1.min-1. For the highest dose, there was a significantly smaller increase in heart rate in conditions H1 (35 +/- 9), H2 (33 +/- 11), and H3 (31 +/- 11) than at SL (45 +/- 8 min-1). The increase in pulse (systolic/diastolic) pressure, considered as the vascular response to isoproterenol infusion, was smaller in condition H3 (29 +/- 16) than at SL (51 +/- 24 mmHg). There was a significant increase in the dose of isoproterenol required to increase heart rate by 25 min-1 and decrease in slope of heart rate increase vs. log(dose) relationship in conditions H2 and H3. Thus an hypoxia-related attenuated response of beta-adrenergic receptors to exogenous stimulation was found in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Decrease in peak heart rate with acute hypoxia in relation to sea level V?O2max

“…Conflict surrounds the interpretation of the effect of the HR peak modification in hypoxia on _ V O 2max . According to the Fick equation _ V O 2 =HRAESV(Cao 2 -Cvo 2 ), it has been postulated that the alteration in DHR peak and SaO 2 would modify _ V O 2max (Richalet et al 1988). Gonzalez et al (1998) demonstrated that an increase in HR peak by atrial pacing induced an increase both in maximal cardiac output and _ V O 2max in hypoxia.…”

“…Decreased maximal heart rate (HR peak ) is well established in subjects acclimatized to high altitude (Pugh 1964;Reeves et al 1987;Richalet et al 1988). This lower HR peak is linked to the severity and the duration of the hypoxemia (Savard et al 1995) and contributes to the decrease in maximal oxygen uptake ( _ V O 2max ) observed when these subjects are exposed to chronic hypoxia (Richalet et al 1988).…”

“…This lower HR peak is linked to the severity and the duration of the hypoxemia (Savard et al 1995) and contributes to the decrease in maximal oxygen uptake ( _ V O 2max ) observed when these subjects are exposed to chronic hypoxia (Richalet et al 1988). The situation is less clear in acute hypoxia.…”

Variability in pulmonary function following rapid altitude ascent to the Amundsen–Scott South Pole station

“…Norepinephrine and epinephrine levels have been observed not to change (Bouissou et al 1989;Mazzeo et al 1995;Richalet et al 1988), decrease (Rostrup 1998) or increase (Bartsch et al 1991;Mazzeo et al 1995) during acute hypobaric hypoxic exposure. We observed a significant increase in both norepinephrine and epinephrine levels following rapid ascent to altitude.…”

The effect of sucrose ingestion on autonomic nervous system function in young subjects during acute moderate hypoxia

“…Another factor, which has been demonstrated to aVect the activity in autonomic nervous system, is exposure to hypoxia (Richalet et al 1988). During acute hypoxic exposure, a general decrease in cardiac autonomic nervous function has usually been reported as reXected in a decrease of HRV, and a dominance of sympathetic over the parasympathetic modulation has been observed (Hughson et al 1994;Farinelli et al 1994;Perini et al 1996;Kanai et al 2001).…”