ABNORMAL AWAKE RESPIRATORY PATTERNS ARE COMMON IN CHRONIC HEART-FAILURE AND MAY PREVENT EVALUATION OF AUTONOMIC TONE BY MEASURES OF HEART-RATE-VARIABILITY

Background Reduced heart rate variability, particularly in the very-lo w-frequency (VLF) spectral band, has been found to be a marker for poo r prognosis in patients after myocardial infarction. but the origin of the VLF oscillations is unclear. in this study, we demonstrate that t he power of cardiovascular oscillations in the VLF band in awake patie nts with mild to severe chronic heart failure is greatly increased by the common occurrence of unrecognized irregularity of breathing, which may confound the use of heart rate variability measures as indexes of autonomic tone or prognosis. Methods and Results Among 110 consecutiv e patients referred for consideration of transplantation, 90 were in s inus rhythm. of whom 10 were excluded as unstable. The remaining 80 pa tients underwent recordings of ECG, beat-to-beat arterial oxygen satur ation (SaO(2)), and respiration during both spontaneous and controlled breathing. During spontaneous awake breathing. 64% showed periodic br eathing or Cheyne-Stokes respiration (CSR), which was associated with dominant power in the VLF band of all signals, This VLF power accounte d for 55%, 77%, and 87% of heart rate variability, respectively, in pa tients with normal breathing, periodic breathing, and CSR. It was redu ced by 48% and 67%, respectively, during controlled breathing in patie nts with periodic breathing or CSR. Controlled ventilation also improv ed oxygen saturation and markedly reduced its variability. Conclusions Breathing disorders art surprisingly common in awake patients with po or left ventricular function and produce large VLF oscillations in hea rt rate variability. If measures of heart rate variability are used fo r prognostic purposes during both short-term and long-term recordings, the confounding effects of variable respiratory patterns should be ex cluded. Respiratory rehabilitation might help control potentially haza rdous surges in sympathetic tone.