EFFECTS OF FENOTEROL ON VENTILATORY RESPONSE TO HYPERCAPNIA AND HYPOXIA IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Background - It has previously been shown that fenoterol, a beta(2) ad renergic agonist, increases the ventilatory response to hypoxia (HVR) and hypercapnia (HCVR) in normal subjects. The effects of beta(2) adre nergic agonists on chemoreceptors in patients with chronic obstructive pulmonary disease (COPD) controversial. This study was designed to ex amine whether fenoterol increases the HVR and HCVR in patients with CO PD. Methods - The HCVR was tested in 20 patients using a rebreathing m ethod and the HVR was examined using a progressive isocapnic hypoxic m ethod. The HCVR and HVR were assessed by calculating the slopes of plo ts of occlusion pressure (P-0.1) and ventilation (V-E) against end tid al carbon dioxide pressure (PETCO(2)) and arterial oxygen saturation ( Sao(2)), respectively. Spirometric values, lung volumes, and respirato ry muscle strength were also measured. The HCVR and HVR were examined after the oral administration of fenoterol (15 mg/day) or placebo for seven days. Results - Fenoterol treatment increased the forced expirat ory volume in one second (FEV(1)) and inspiratory muscle strength. In the HCVR the slope of P-0.1 versus PETCO(2) was increased by fenoterol from 0.35 (0.23) to 0.43 (0.24) (p<0.01). Moreover, the P-0.1 at PETC O(2) Of 8 kPa was higher on fenoterol than on placebo (p<0.05) and the V-E was also greater (p<0.01). In the HVR fenoterol treatment increas ed the P-0.1 at 80% Sao(2) from 0.90 (0.72) to 0.97 (0.55) kPa (p<0.05 ) while the slopes of the response of P-0.1 and V-E were not changed. Conclusions - Fenoterol increases the ventilatory response to hypercap nia in patients with COPD, presumably by stimulation of the central ch emoreceptor. The hypoxic ventilatory response is only slightly affecte d by fenoterol.