Uremic autonomic neuropathy studied by spectral analysis of heart rate

Background. There is good evidence that power spectral analysis (PSA) of he art rate variability may provide an insight into the understanding of auton omic disorders. Methods. We investigated 30 chronic uremic patients who were on periodic bi carbonate hemodialysis by a battery of six cardiovascular autonomic tests ( beat-to-beat variations during quiet breathing and deep breathing, heart ra te responses to the Valsalva maneuver and standing, blood pressure response s to standing and sustained handgrip) and PSA of heart rate variations. Results. Eleven patients (37%) had an abnormal response to only one parasym pathetic test. Twelve patients (40%) had a definite parasympathetic damage, as indicated by at least two abnormal heart rate tests, whereas four (13%) had combined parasympathetic and sympathetic damage. Multivariate analysis of the cardiovascular tests revealed that 19 patients (63%) had moderate-t o-severe autonomic neuropathy (AN), and 11 patients exhibited normal autono mic function. Among the symptoms suggestive of autonomic dysfunction, only impotence in males was significantly associated with test-proven AN. The PS A of the heart rate variability demonstrated a good discrimination of low-f requency (LF) and high-frequency (HF) bands (LF, 0.03 to 0.15 Hz; HF, 0.15 to 0.33 Hz) among controls, uremic patients without test-proven AN, and ure mic patients with test-proven AN. A significant reduction of the LF value o n supine uremic patients without AN suggests that an early sympathetic invo lvement exists that traditional autonomic tests were unable to detect. Conclusions. Our study indicates that the current opinion of a major parasy mpathetic damage in chronic uremic patients on hemodialysis has to be modif ied in favor of a more widespread autonomic dysfunction involving both the sympathetic and parasympathetic pathways.