In this study, we examined autonomic influences on pulse transit time measured from the R-wave of the electrocardiogram (R-PTT). Six subjects received three doses each of isoproterenol and atropine. Isoproterenol produced a significant linear decrease in R-PTT, a significant linear increase in heart rate (HR), and a significant linear decrease in diastolic blood pressure (DBP). Atropine produced a significant linear decrease in R-PTT and significant linear increases in HR and DBP. The R-PTT shortening effect of isoproterenol may reflect positive inotropic effects of beta-sympathetic myocardial stimulation. The R-PTT shortening effect of atropine may reflect reduction of parasympathetic inhibition of ventricular myocardial activity. However, possible vascular contributions to these effects remain to be determined. Nonetheless, the results encourage further examination of R-PTT in research concerning autonomic regulation of cardiovascular activity.

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The present study examined the acute effects of drugs that stimulate or block sympathetic nervous system activity on components of Type A behavior, affect, and cardiovascular responses to mental stressors. Either propranolol (a beta-adrenergic blocker), isoproterenol (a beta-agonist), or placebo was infused intravenously at different times in 12 healthy males. In two sessions, placebo (saline) was administered first, followed by a structured interview, challenging mental arithmetic test, and completion of affect scales. The procedure was then repeated with one of the active drugs, presented in counterbalanced order. Results indicated reliable drug effects on both heart rate (HR) and systolic blood pressure (SBP) reactivity to the tasks, with change scores to the tasks markedly increased by isoproterenol. Anxiety and hostility ratings paralleled results for HR and BP, with much of this effect being due to higher affect ratings for isoproterenol. The effect of the drugs on Type A behavior was unexpected, with global Type A and several components lowered by isoproterenol and unaffected by propranolol. These data are discussed in terms of the interfering effects of anxiety on Type A speech components. The influence of isoproterenol on affect and reactivity might reflect the physiologic action of a beta 2-adrenergic positive feedback loop which increases release of endogenous norepinephrine, and/or potentiating effects of emotion on reactivity to stress.