EFFECT OF BETA(2)-ADRENOCEPTOR AGONISTS ON PLASMA POTASSIUM AND CARDIOPULMONARY RESPONSES ON EXERCISE IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Objective: The effect of beta(2)-adrenoceptor agonist-induced hypokala emia on cardiac arrhythmias might be exacerbated during exercise, espe cially in patients with more compromised airway function. Methods: To evaluate the effect of beta(2)-adrenoceptor agonists on plasma potassi um and cardiopulmonary function during exercise, two identical submaxi mal treadmill exercise tests were performed, at least 48 h apart, by 1 3 patients with moderate to severe COPD (11 men and 2 women, mean age 66 y, mean FEV(1)/FVC ratio 48.9(2.8)%) 30 min after they had received nebulised fenoterol or salbutamol (2 mg). The experiment was done as a randomised, double-blind, crossover trial after an initial baseline study with vehicle (0.45% saline). Plasma potassium concentration, spi rometry and the degree of breathlessness (Borg scale) were measured be fore treatment and immediately after exercise; oxygen saturation, QTc interval and cardiac rhythm were monitored continuously before, during and for 30 min after exercise. Results: After the saline control, exe rcise caused an increase in Borg rating (of 4.9), a premature ventricu lar contractions (VPC) (2.8 beats/min), and a fall in oxygen saturatio n (-6.7%), but no significant change in plasma potassium (+ 0.04 mEq . dl(-1)); FEV(1) or QTc interval. Inhalation of fenoterol and salbutam ol did not affect QTc interval, Borg scale or VPC frequency at rest, b ut significantly increased the duration of exercise undertaken to reac h the submaximal levels (786 s, versus 783 s) compared to the vehicle control. Following exercise, plasma potassium fell after fenoterol by 0.2 mEq . dl(-1) and it increased after salbutamol by 0.1 mEq . dl(-1) compared to baseline levels. Plasma potassium after exercise was sign ificantly lower after fenoterol (3.2 mEq . dl(-1)) compared to the sal ine control (3.7 mEq . dl(-1)) and (3.6 mEq . dl(-1)). Neither fenoter ol nor had any significant effect on the change in FEV(1), oxygen satu ration, Borg scale, frequency of VPCs or QTc interval during or after exercise compared to the saline control. Conclusion: When compared to salbutamol 2 mg, fenoterol 2 mg caused more marked hypokalaemia but no significant difference in cardiopulmonary response in patients with C OPD during exercise.