AUTONOMIC NERVOUS FUNCTION DURING HEMODIALYSIS ASSESSED BY SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY

1. Short-term autonomic response to haemodialysis-induced hypovolaemia was studied in 30 patients undergoing chronic haemodialysis by analys ing power spectra of heart-period variability, Patients were classifie d as haemodynamically stable (15 patients) and unstable (15 patients) according to their past history of cardiovascular collapse during the treatment, Blood volume, systolic arterial pressure and heart period w ere measured during sessions that ended without the occurrence of coll apse. 2. No significant differences were observed when comparing blood volume, heart rate and arterial pressure of stable and unstable patie nts during the dialysis, and the two groups could not be distinguished merely on the basis of these haemodynamic parameters, Conversely, spe ctral analysis of beat-to-beat heart-period variability showed markedl y different power patterns: in stable patients power was mainly in the low-frequency (LF) band (0.06-0.15 Hz), whereas in unstable patients it was mainly in the high-frequency (HF) band (0.15-0.4 Hz). 3. The ef ficiency of the autonomic response to hypovolaemia was evaluated by th e ratio between the powers in the LF and HF bands, Stable patients exh ibited an LF/HF power ratio systematically greater than unstable patie nts during the entire dialysis, and on the basis of this index the two groups were clearly separated. 4. Results obtained with spectral anal ysis lead us to conclude that reduced efficiency in the autonomic cont rol of cardiovascular functions could be the main cause of the haemody namic instability of patients prone to collapse.