CATECHOLAMINES CONTRIBUTE TO EXERTIONAL DYSPNEA AND TO THE VENTILATORY RESPONSE TO EXERCISE IN NORMAL HUMANS

Background Exogenous catecholamine administration in humans stimulates ventilation. The present study was designed to investigate whether in creased endogenous catecholamine release influences objective measures of ventilation and subjective measures of breathlessness in normal su bjects. Methods Yohimbine, a pre-synaptic a, adrenoceptor antagonist, or placebo was administered to 10 normal male subjects in a double-bli nd cross-over fashion. Ventilation and metabolic gas exchange were mea sured during steady state exercise at 60% of previously determined max imal oxygen consumption. Venous lactate and noradrenaline were measure d during exercise. Subjects' sensation of breathlessness and fatigue w ere recorded using visual analogue scales. Results Plasma noradrenalin e was higher following yohimbine administration (at 6 min exercise; 4. 58 +/- 0.56 nmol.l(-1) vs 8.74 +/- 1.53; P < 0.05). Oxygen consumption was unchanged, but ventilation was greater throughout exercise follow ing yohimbine. The sensation of exertion was greater following yohimbi ne, and at any given level of ventilation, the sensation of exertion w as greater. Conclusions Yohimbine administration causes increased nora drenaline release. This is associated with an increased ventilatory re sponse and an increase in the sensation of exertion during steady stat e exercise. An increase in circulating noradrenaline might be a mechan ism for both increased ventilation and pathological conditions of brea thlessness such as chronic heart failure.