The combined effects of orthostatic and mental stress on heart rate, T-wave amplitude, and pulse transit time.

The purpose of the present study was to determine whether cardiovascular reactivity to mental stress may be comparable in sitting and standing postures. Fifteen healthy males performed two 1-min mental arithmetic tasks, either while sitting or while standing, in counterbalanced order. Heart rate, pulse transit time, and T-wave amplitude were recorded in the last 10 s of the minute before, during, and after the mental arithmetic. Reactivity scores for each of the dependent measures were computed by calculating the percentage change from baseline values. Data were analyzed with multivariate and univariate repeated measures analysis of variance. Heart rate reactivity to the combination of orthostatic and mental stress was greater than to either stressor alone. Cardiac-sympathetic reactivity was greater in response to orthostatic than to mental stress as revealed by greater changes in T-wave amplitude and pulse transit time in response to the former. No additional decreases in T-wave amplitude, in response to mental stress, were observed during standing, but pulse transit time decreased in the same situation. However, no changes in pulse transit time in response to mental stress were observed in the sitting position. These results demonstrate that cardiovascular reactivity to mental stress depends on the body position in which the stressor is encountered.