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To examine sympathetic and vagal cardiovascular regulatory mechanisms in the pathogenesis of orthostatic hypotension in pheochromocytoma, we continuously monitored blood pressure (Finapres) and RR interval (electrocardiogram) in supine and standing positions in 12 patients with pheochromocytoma, 43 patients with essential hypertension, and 30 normotensive subjects. Mayer wave power spectrum of systolic blood pressure variability (approximately 0.1 Hz) and respiratory power spectrum of the RR interval variability (approximately 0.25 Hz) were taken as measures of sympathetic vascular and cardiac vagal modulations, respectively. Systolic blood pressure decreased more upon standing in pheochromocytoma patients (-21 +/- 7 mm Hg) than in normotensive subjects (-5 +/- 2 mm Hg) or essential hypertensive patients (-3 +/- 2 mm Hg) (P &lt; .005 for both), whereas heart rate tended to increase most in the pheochromocytoma group. Postural reduction in systolic blood pressure was highly correlated with postural increase in heart rate (reciprocal change in RR interval) in the pheochromocytoma group (r = 0.716, P &lt; .01) suggesting that baroreflex is well functioning in those patients. The Mayer wave power spectrum in recumbency was extremely depressed in pheochromocytoma patients (1.1 +/- 0.2 mm Hg2) compared with normotensives (4.5 +/- 0.8 mm Hg2) or essential hypertensives (5.6 +/- 0.6 mm Hg2) (P &lt; .001 for both). This parameter increased significantly with standing in all groups but remained lower in patients with pheochromocytoma (5.1 +/- 1.0 mm Hg2) than in normotensives (7.1 +/- 0.9 mm Hg2, P = NS), whereas essential hypertensive patients demonstrated far greater value (19.2 +/- 3.8, P &lt; .01 for both). The respiratory power spectrum of the RR interval in recumbency of pheochromocytoma patients (189 +/- 54 msec2) was less than in normotensive subjects (714 +/- 100 msec2, P &lt; .001) but did not differ from that in patients with essential hypertension (214 +/- 41 msec2). The respiratory power spectrum of the RR interval upon standing was markedly suppressed in pheochromocytoma patients (36.9 +/- 16.7 msec2) compared with normotensive subjects (129.5 +/- 23.6 msec2) or essential hypertensive patients (126.6 +/- 28.6 msec2) (P &lt; .001 for both). Postural decrement in the respiratory power spectrum of the RR interval correlated positively with postural increase in heart rate (r = 0.577, P &lt; .05) in patients with pheochromocytoma. After successful surgery (n = 9), the Mayer wave power spectrum of the systolic blood pressure and the blood pressure response to orthostasis were normalized. These data suggest that altered sympathetic vascular regulation is central to the pathogenesis of orthostatic hypotension in pheochromocytoma, whereas cardiac vagal regulation acts to compensate.

Altered sympathetic and vagal modulations of the cardiovascular system in patients with pheochromocytoma Their relations to orthostatic hypotension