Haemodynamic responses to intravenous cimetidine in subjects with normal lung function and in subjects with chronic airway obstruction.

1 The haemodynamic responses to a bolus intravenous injection of 400 mg cimetidine were studied in eight subjects with normal lung function and sixteen with chronic obstructive airway disease (COAD), under continuous systemic and pulmonary arterial monitoring. In all subjects there were significant immediate but transient (less than 10 min) drops in the systemic and pulmonary arterial pressures (both systolic and diastolic), the systemic vascular resistance and total pulmonary resistance. The percentage drops were significant more marked in the COAD group in the following: systemic arterial pressures (systolic and diastolic), systemic vascular resistance and total pulmonary resistance. The cardiac output showed no significant change in the group with normal lung function but rose significantly in the COAD group. None of the subjects had any symptoms associated with the haemodynamic changes. 2 These results can be explained by a generalized vasodilatory effect of cimetidine, but the relationship to its H2-receptor blocking effect is undetermined. Hypoxia and/or hypercapnia may sensitize an individual to the vasodilatory effect of cimetidine.