Evaluation of orthostatic hypotension using power spectral analysis.

To evaluate the pathogenesis of orthostatic hypotension, we studied the autonomic regulation system by measuring heart rate variability during 60 degrees passive head-up tilt using power spectral analysis in 21 patients with orthostatic hypotension (mean age 62 +/- 2 years, five with histories of cerebrovascular accidents, five with Parkinsonism, five with diabetes mellitus, three with pheochromocytoma, and three with unknown causes) and 15 normal healthy subjects as a control (mean age 63 +/- 2 years). We also assessed plasma epinephrine and norepinephrine response to tilt. During tilt, control subjects showed an increase in heart rate with no change in blood pressure. Spectral analysis of heart rate variability demonstrated increases in the low frequency band (LFB, mainly sympathetic) and low frequency band/high frequency band ratio (LFB/HFB, sympatho-vagal balance). All patients with orthostatic hypotension showed a significant reduction in blood pressure with an increase in heart rate. In patients with histories of cerebrovascular accidents and with Parkinsonism, LFB and the LFB/HFB ratio did not increase. However, in other patients with orthostatic hypotension, LFB and the LFB/HFB ratio increased during tilt. Norepinephrine increased in control subjects and in patients with diabetes mellitus, pheochromocytoma, and unknown causes. In contrast, patients with histories of cerebrovascular accidents and patients with Parkinsonism showed no increase in norepinephrine. Epinephrine responses paralleled those of norepinephrine, but the changes were not significant. Thus, neurological response to tilt is not uniform in patients with orthostatic hypotension. Patients with histories of cerebrovascular accidents and patients with Parkinsonism may have impaired function of central neural mechanisms controlling blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)