Effect of cholinergic blockade on heart rate, blood pressure and plasma catecholamine responses to mental stress in normal subjects.

The effects of cholinergic blockade on haemodynamic reactivity to standardized mental stress has been studied in nine normotensive males during infusion of atropine (bolus dose 10 micrograms x kg-1 followed by a constant-rate infusion of 0.02 microgram x kg-1 x min-1) or placebo given in a randomized order on two different days. Partial cholinergic blockade increased resting heart rate by 25-30 beats per minute. The magnitude of the heart rate response to stress (reactivity) however was unaffected by the atropine infusion. Also, in four subjects who received a higher dose of atropine (approximately 1.8-1.9 mg), heart rate responses to stress were the same as during placebo infusion. Cholinergic blockade was associated with a small but prolonged increase in diastolic blood pressure. These findings suggest that parasympathetic withdrawal does not contribute to the tachycardia caused by mental arithmetic, and that the pattern of neurogenic activation may differ from that elicited during a classic defence-alarm reaction and by somatomotor activation.