Systematic and regional haemodynamic effects of caffeine and alcohol in fasting subjects.

It is well established that caffeine and alcohol can have acute effects on heart rate and blood pressure, but it is not known whether cardiac output and peripheral blood flow are also affected. Such information is needed before any possible effects of caffeine or alcohol on the haemodynamic responses to food can be assessed. Thus, the present study determined the haemodynamic effects of caffeine or alcohol. Eight healthy young subjects were studied in the fasting state before and after ingestion of water (200 ml), coffee containing caffeine (3.5 mg/kg in 200 ml) or alcohol (0.5 g/kg made up to 200 ml) , in random order on three separate occasions. All of the subjects had abstained from both caffeine and alcohol for at least 12 h. Measurements of blood pressure (BP), heart rate (HR), cardiac output (CO), superior mesenteric artery blood flow (SMABF) and calf blood flow (CBF) were made at baseline and for 2 h after each drink. With the alcohol drink, blood alcohol levels estimated using breath measurement peaked at 18.8 mmol/l. HR fell slightly after water but increased after alcohol (+ 7 beats/min) and after caffeine (+ 16 beats/min, group × time interaction analysis of variance, p < 0.03), with peak responses at 40-60 min and a return to baseline by 120 min. Systolic BP increased significantly with time after all three drinks , with no significant differences between the drinks. CBF rose slightly after the drink of water, more so after alcohol but fell slightly after caffeine (group × time interaction analysis of variance, p < 0.01). Total peripheral resistance rose slightly after water and alcohol but much more markedly after caffeine (group effect analysis of variance, p < 0.001). There were no significant effects of alcohol or caffeine on the other variables. Thus, caffeine and alcohol themselves have haemodynamic effects which might interact with the effects of food.