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SUMMARYHaemodynamic and respiratory effects of i.v. morphine (10 mg/70 kg body weight) were studied in 10 adults with unimpaired circulatory function. There were significant changes in mean arterial pressure, mean heart rate, respiratory rate and tidal volume, at 10-, 30-and 60-min intervals. Transient changes in mean total systemic resistance and mean stroke volume were also seen at 10 min. The results strongly suggest a peripheral vasodilator response to morphine. Respiratory depression was not demonstrated.Although opium has been used from antiquity and despite the lack of knowledge of the precise haemodynamic effects of morphine, there are large amounts of data concerning the actions of narcotics on circulation and respiration (Kreuger, Eddy and Sumwalt, 1941;Eddy, Halbach and Braenden, 1957;Reynolds and Randall, 1957). Many published studies show lack of appreciation of the importance of standardization of patient population regarding such factors as their mental and emotional state, physical condition, intensity of pain and type of anaesthesia. In many instances, concomitant respiratory depression secondary to administration of morphine had not been taken into account while assessing the haemodynamic effects. Sufficient attention had not been given to standardization of the dose (in relation to body size), the rate or even the site of injection. Moreover, many studies were undertaken when methods of measuring circulatory and respiratory changes were less accurate than those available today. Results from animal experiments have even been taken to represent a human response, disregarding the species difference.Since a review of published data on the cardiorespiratory effects of morphine failed to reveal a consistent pattern of response, it was felt that a re-evaluation of its cardiovascular effects, under rigidly controlled clinical conditions, would be both relevant and justifiable. The present study, therefore, is to assess the haemodynamic effeas of a clinically used dose (10 mg/70 kg body weight) of morphine, in patients with unimpaired circulatory function. This investigation not only provides a "baseline" for studies on patients with impaired cardiovascular

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Cardiac output was measured in 10 patients using the dye dilution method, before and after the intravenous injection of 400 mg cimetidine. The subjects were in the intensive care unit and required intermittent positive pressure ventilation. There was no change in the average blood pressure, heart rate and cardiac output during the 60 minutes following the cimetidine, although one patient showed a marked fall in cardiac output. The results suggest that cimetidine is without a marked depressant effect on cardiovascular system.

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