The relationship between diuretic dose, and the haemodynamic response to captopril in patients with cardiac failure.

The effect of diuretic dose on the haemodynamic response to captopril was assessed in nine patients with chronic cardiac failure. Each patient was given an intravenous dose of captopril while maintained on (a) a low dose diuretic regime, and (b) a high dose diuretic regime. Activity of the renin angiotensin aldosterone system, as assessed by plasma concentrations of these hormones, was greater when patients were receiving the higher dose diuretic regime. The magnitude of haemodynamic response produced by intravenous captopril was greater when the patients were maintained on the high dose diuretic regime, although no significant correlation was found between resting plasma renin activity and resting plasma angiotensin II concentration and the change produced by captopril in any haemodynamic response on either diuretic regime. An increased dosage of loop diuretic potentiates the haemodynamic effects of captopril in patients with cardiac failure. Reduction of diuretic dose prior to introduction of captopril may protect against severe first dose hypotension.