No psychophysiological interactions between caffeine and stress?

In earlier studies, the predominantly beta-adrenergic effects of mental tasks and the alpha-adrenergic effects of caffeine on cardiovascular functions were observed to be simply additive without interaction. In the present study, annoying electrical shocks were superimposed on a mental task affording either active coping, which specifically raises beta-adrenergic activation, or passive coping, and the 40 female subjects were preselected so as to differ in subjective stress susceptibility. Caffeine as well as the type of coping and the considered personality dimension produced significant effects, but almost no interactions were obtained. The stress resistant subjects, who tended toward more extraversion, emotional stability and more masculinity, had lower anxiety scores, rated their performance higher and had a greater cardiac output than the stress non-resistant subjects, who represented a rather normal population according to the FPI personality dimensions. Caffeine increased EEG alpha and beta frequency and delta power and decreased beta power, raised blood pressure and enhanced stress reactions in respiration amplitude and pre-ejection period. Active stress coping induced greater stress reactions in heart rate (increase), left ventricular ejection time (decrease) and ear pulse arrival time (decrease) than passive coping.