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Effect of beta-adrenergic blockade during exercise on ventilation and gas exchange.

Authors
  • Brown, H V
  • Wasserman, K
  • Whipp, B J
Type
Published Article
Journal
Journal of applied physiology
Publication Date
Dec 01, 1976
Volume
41
Issue
6
Pages
886–892
Identifiers
PMID: 1002642
Source
Medline
License
Unknown

Abstract

The ventilatory effects of beta-adrenergic blockade during steady-state exercise were studied in eight normal subjects using intravenous propranolol hydrochloride (0.2 mg/kg). Heart rate decreased in all subjects by an average of 17%. Coincident with the phase of decreasing heart rate was a significant decrease in both minute ventilation (VE) and CO2 output (VCO2), averaging 9.6 and 9.2%, respectively. Both functions returned to prepropranolol levels after heart rate had reached its reduced steady-state value. The change in VE was significantly correlated with the change in VCO2 (r = 0.85, P less than 0.005), and was associated with negligible changes in endtidal CO2 tensions and ventilatory equivalents for CO2. We interpret these studies as showing that the transient isocapnic hypopnea concomitant with an acute reduction in cardiac output was secondary to a transient decrease in CO2 flux (cardiac output x mixed venous CO2 content). This decrease in VE appears to be induced by the acute decrease in cardiac output ("cardiodynamic hypopnea"), in fashion similar to the previously described cardiodynamic hyperpnea.

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