Haemodynamic effects of coffee and purified caffeine in normal volunteers: a placebo-controlled clinical study.J Hum Hypertens 1992; 6(2):95-9JH
In order to evaluate the effects of 'espresso' Italian coffee on resting flow, blood pressure, and peripheral resistance, 15 non-coffee drinking healthy volunteers received 2 cups of regular coffee, 200 mg purified caffeine or placebo in a latin square double-blind crossover protocol. Before and 30, 60, 90 and 120 min after ingestion, segmental resting flow and BP were measured and peripheral resistance was calculated. An echocardiogram was also performed before and 60 and 120 min after caffeine intake. Both regular coffee and caffeine produced a significant decrease in resting flow and a significant increase in resistance; both systolic and diastolic BP also increased, although not significantly. No variation was observed in heart rate and in cardiac contractility. Placebo (highly decaffeinated coffee for regular coffee and china bitter extract for caffeine) did not produce any haemodynamic effect. In five other healthy volunteers used to drinking more than 5 cups of coffee a day, coffee administration had no effect. These data demonstrate that the caffeine contained in espresso Italian coffee is a vasoconstrictor agent whose effects however are completely blunted in usual coffee drinkers as a consequence of adaptation.