INDIVIDUAL-DIFFERENCES IN THE AUTONOMIC ORIGINS OF HEART-RATE REACTIVITY - THE PSYCHOMETRICS OF RESPIRATORY SINUS ARRHYTHMIA AND PREEJECTION PERIOD

Heart rate reactivity has been conceptualized, at least implicitly, as a unidimensional construct ranging from low to high, reflecting indiv idual differences in adrenergic reactivity to daily stressors. However , an individual's classification as high in heart rate reactivity igno res possible individual differences in the autonomic origins of this r eactivity. Sixty-eight women were exposed to orthostatic and speech st ressors to determine the psychometric properties (postural stability, convergent and discriminant validity) of heart rate, preejection perio d, and respiratory sinus arrhythmia. Results revealed that (a) basal, stress, simple reactivity (stress - baseline), and residualized change indices of heart rate, preejection period, and respiratory sinus arrh ythmia were stable across postures and (b) heart rate reactivity was s ignificantly related to preejection period and respiratory sinus arrhy thmia reactivity, whereas the latter two measures were unrelated. Reac tivity classifications may therefore be significantly improved by atte ntion to concurrent estimates of the activity of both autonomic branch es.