SYMPATHETIC REGULATION IN RABBITS WITH HEART-FAILURE - EXPERIENCE USING POWER SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY

1. In five intact rabbits beta-adrenoreceptor blockade (i.v. propranol ol), and combined cardiac blockade (i.v. propranolol plus i.v. methsco polamine sulphate) revealed that spectral power of heart rate (HR) var iability at low frequencies (LF: 0.0625-0.1875 Hz) was modulated predo minantly by the sympathetic nervous system and power at high frequenci es (HF: 0.4373-0.5625 Hz) by vagal influences. 2. In 16 rabbits restin g power of HR at LF and changes in LF power in response to maximal tre admill exercise were examined prior to and after 4 and 6 weeks of doxo rubicin treatment (1 mg/kg twice weekly). 3. The development of doxoru bicin-induced congestive heart failure (CHF) was accompanied by a prog ressive increase in resting LF power [control, 8.5 +/- 2.1; 4 weeks, 1 3.4 +/- 1.8; 6 weeks, 21.9 +/- 3.5 (beats/min)(2), P < 0.005]. 4. Powe r spectral analysis (PSA) of HR variability in the immediate post-exer cise period showed no change from resting values in normal rabbits [5. 3 +/- 1.4 vs 8.5 +/- 2.1 (beats/min)(2), P > 0.05] whereas CHF rabbits showed falls in LF power after 4 weeks [4.6 +/- 1.0 vs 13.4 +/- 1.8 ( beats/min)(2), P< 0.005] and 6 weeks [6.5 +/- 2.4 vs 21.9 +/- .3.5 (be ats/min)(2), P < 0.005] of doxorubicin treatment. 5. It was concluded that PSA of HR variability reflects the autonomic regulation of sinus node function in conscious rabbits. In doxorubicin-treated animals, th e rise in LF power reflects increased sympathetic activity as CHP deve lops. However, the apparent paradoxical fall in LF power with exercise in these animals underscores the need for caution in interpretation o f PSA profiles.