Differentiated Sympathetic Activation During Mental Stress Evoked by the Stroop Test

Sympatho-adrenal and hemodynamic responses to mental stress induced by Stroop's color word test (CWT) were examined in 12 healthy volunteers. CWT increased heart rate and blood pressures by 28 beats/min and 29/14 mmHg, on the average. The pressor response was caused by an increase in cardiac output (from 6.3 +/- 0.3 to 10.9 +/- 0.6 l/min, p less than 0.001), since systemic vascular resistance was reduced by approximately 30% during CWT. Calf vascular resistance (mainly muscle) was also reduced. At rest there was a net production of NA and a net removal of adrenaline (ADR) in the forearm tissues. About 45% of the NA in antecubital venous plasma appeared to be derived from the forearm tissues. During CWT arterial NA increased (from 1.53 +/- 0.20 to 2.13 +/- 0.15 nM, p less than 0.001), but antecubital venous NA levels remained unchanged. There was removal of ADR (about 19%) and a calculated production of NA by the lungs at rest, both of which disappeared during stress. CWT caused a "defence reaction"-like hemodynamic response with cardiac activation, but unchanged or reduced peripheral sympathetic nerve activity. This explains the lack of increase in antecubital venous NA, which is markedly influenced by sympathetic activity in the forearm tissues. Arterial plasma catecholamine measurements provide better information concerning sympatho-adrenal activity in the body as a whole than do peripheral venous measurements. Regional sympathetic activity is preferably studied by NA outflow determinations from the target organs.