Differences between ECG and pulse when measuring heart rate and reactivity under two physical and two psychological stressors

To test the level of agreement of heart rate and reactivity to stressor tasks as measured via noninvasive ECG and pulse, 38 healthy subjects underwent four stressor tasks: mental arithmetic, reaction time, cold pressor and bicycling. Data on resting and stressor heart rate were collected via ECG and photoplethysmography, and heart rate reactivity was calculated via five methods noted in the wider literature. Results indicated that, although resting heart rate values did not differ significantly across the two instruments, there were some significant differences in heart rate during certain periods of mental and physical stress reactivity. Calculation of heart rate reactivity revealed that there were few significant differences between data from the two measures but that the tasks themselves produced markedly different patterns of reactivity, questionning assumptions underlying comparison of reactivity data under different stress tasks. Implications for the assessment of reactivity are discussed.