Ventilatory response to carbon dioxide and to isometric muscle contraction after administration of placebo, propranolol, mepindolol and salbutamol.

Healthy males (23-29 years) volunteered as subjects. We studied the ventilatory response to carbon dioxide and to isometric exercise (50% of maximum voluntary contraction) after administration of propranolol (20 mg), mepindolol (5 mg), salbutamol (20 mg) and placebo (single dose orally). The increase of pulmonary ventilation (VE) activated by central (CO2) and reflex stimulus (hand-grip) did not differ statistically between the four drugs. Analysis of VE in terms of inspiratory drive (Vt/Ti) and timing ratio (Ti/Ttot) showed that during CO2 stimulation mepindolol and salbutamol increased VE predominantly by the increase of Vt/Ti, presumably through the direct stimulation on the respiratory center. During rebreathing, Ti/Ttot increased significantly after administration of placebo and propranolol, so VE increased by a rise of Vt/Ti and by an increase of an effective 'timing component' (Ti/Ttot). Propranolol does not modify the ventilatory response to CO2 and hand-grip when VE is analyzed in terms of Vt/Ti and Ti/Ttot.