Maximum cognitive performance and physiological time trend measurements after caffeine intake.

The effect of caffeine on the central nervous system and cardiorespiratory system was tested under resting conditions and while undertaking a multitask performance test. The subjects abstained from caffeine for a week before the study. Each subject performed the test after oral administration of 90 and 250 mg of caffeine on two separate days. Sum of Squares was recorded during the whole period of the study. Heart rate (HR) and respiration rates (RR) were continuously recorded and blood pressure (BP) was recorded before and after each stage of the experiment (Test(0), Test(1), Test(2), Test(3)). Sixteen healthy volunteers participated in the study divided into three groups: Group A, non-smokers and non-coffee drinkers; Group B, smokers and coffee drinkers; and Group C, non-smokers and coffee drinkers. Comparison of the performance of each stage with the resting conditions revealed statistically significant differences of group B compared to the other two groups and no significant differences between Groups A and C in both doses of caffeine. Non-coffee drinkers needed a low dose of caffeine for their optimal performance while a higher dose significantly increased their blood pressure. Coffee drinkers and smokers needed a higher dose of caffeine for optimal performance, which increased very quickly, but did not last and increased their BP. This increase in BP was not statistically significant, probably because of nicotine's effect. Heart rate was decreased and respiration rate increased significantly. The optimal performance was dose-dependent, increasing significantly with the higher dose of caffeine but with adverse effects on BP and RR.