EFFECTS OF FENOTEROL ON VENTILATORY RESPONSES TO HYPOXIA AND HYPERCAPNIA IN NORMAL SUBJECTS

Background - The effects of beta(2) adrenergic agonists on chemorecept ors remain controversial. This study was designed to examine whether f enoterol, a beta(2) adrenergic agonist, increases the ventilatory resp onses to hypercapnia (HCVR) and hypoxia (HVR) in normal subjects. Meth ods - HCVR was tested with a rebreathing method and HVR was examined w ith a progressive isocapnic hypoxic method in 11 normal subjects. Both HCVR and HVR were assessed by the slope of occlusion pressure (P-0.1) or ventilation (VE) plotted against end tidal carbon dioxide pressure and arterial oxygen saturation, respectively. Respiratory muscle stre ngth, spirometric values and lung volume were measured. After a single oral administration of 5 mg fenoterol or placebo HCVR and HVR were ev aluated. Results - Fenoterol treatment did not change the specific air way conductance or forced expiratory volume in one second. Respiratory muscle strength did not change. Fenoterol increased the slope of the HCVR of both P-0.1 (from 0.251 (0.116) to 0.386 (0.206) kPa/kPa, avera ge increase 71%) and Ve (from 10.7 (3.4) to 15.1 (4.2) 1/min/kPa, aver age increase 52%), and shifted the response curves to higher values. F or the HVR fenoterol increased the slopes of both P-0.1 and VE (from - 4.06 (2.00) x 10(-3) to -7.99 (4.29) x 10(-3) kPa/ %, an average incre ase of 83%, and from -0.221 (0.070) to -0.313 (0.112) 1/min/%, a 44.5% increase, respectively), and shifted the response curves to higher va lues. Conclusion - Acute administration of fenoterol increases the ven tilatory responses to both hypercapnia and hypoxia in normal subjects.