CIRCADIAN-RHYTHMS OF FREQUENCY-DOMAIN MEASURES OF HEART-RATE-VARIABILITY IN HEALTHY-SUBJECTS AND PATIENTS WITH CORONARY-ARTERY DISEASE - EFFECTS OF AROUSAL AND UPRIGHT POSTURE

Background Altered neural regulation of the cardiovascular system may be an important factor for various manifestations of ischemic heart di sease. This research was designed to compare the circadian rhythm of c ardiac neural regulation and autonomic responses to arousal and uprigh t posture between patients with uncomplicated coronary artery disease (CAD) and age-matched subjects with no evidence of heart disease. Meth ods and Results Twenty-four-hour heart rate variability (HRV) in the f requency domain was analyzed in 20 male patients (mean age, 52+/-7 yea rs) with angiographic evidence of CAD without prior myocardial infarct ion and in 20 healthy men (mean age, 51+/-8 years) with no clinical, e chocardiographic, or exercise ECG evidence of heart disease. None of t he 24-hour average frequency-domain components of HRV differed signifi cantly between the two groups. Healthy subjects had a significant circ adian rhythm of normalized units of high-frequency (HF) power of HRV w ith higher values during sleep. Normalized units of low-frequency (LF) power and the LF/HF ratio also showed a significant circadian rhythm in healthy subjects, with higher values during the daytime. No signifi cant circadian rhythms in any of the normalized spectral components of HRV were observed in patients with CAD, and the night-day difference in LF/HF ratio was smaller in the patients with CAD than in the health y subjects (0.5+/-1.4 versus 1.81+/-0.7, P<.001). Awakening when in th e supine position resulted in a significant increase in the LF/HF rati o (P<.01) in the healthy subjects, but no significant changes in HRV w ere observed after awakening in patients with CAD. Assumption of uprig ht position resulted in a comparable decrease in the components of HRV between the groups. Conclusions The circadian rhythm of cardiac neura l regulation is altered in patients with uncomplicated CAD. Reduced au tonomic responses to sleep-wake rhythm suggest that the modulation of cardiac autonomic function by stimuli from the central nervous system is impaired in CAD.