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3249598 
Journal Article 
The circadian pattern of cardiac autonomic modulation in a middle-aged population 
Li, X; Shaffer, ML; Rodriguez-Colon, Sol; He, Fan; Wolbrette, DL; Alagona, P, Jr; Wu, C; Liao, D 
2011 
Yes 
Clinical Autonomic Research
ISSN: 0959-9851
EISSN: 1619-1560 
SPRINGER HEIDELBERG 
HEIDELBERG 
21 
3 
143-150 
English 
21240538 
WOS:000290572100002 
Objectives To examine the circadian pattern of cardiac
autonomic modulation (CAM) and its attributes in general population. Methods We obtained 24-h
beat-to-beat RR data using a high resolution 12-lead Holter ECG in a community-dwelling sample of
115 non-smokers. We performed heart rate variability (HRV) analysis on the normal RRs from each
5-min segment to obtain time-specific HRV indices: high (HF; 0.15-0.40 Hz) and low (LF; 0.04-0.15
Hz) frequency powers, standard deviation of RR intervals (SDNN), and the square root of the mean
of the sum of the squared differences of the adjacent RR intervals (RMSSD). For each individual,
we fit the segment-specific HRV data to a cosine periodic function, and estimated 3 individual-
level cosine function parameters to quantify the circadian variation: the mean (M), amplitude
(A), and acrophase (theta). We then used a random-effects meta-analysis to summarize the M, A,
and theta, and their 95% confidence intervals (CI). Results The mean age was 56 (SD 8) years,
with 63% female and 76% white. The averages of M, A and theta (95%CI) of log HF were 3.59 (3.43-
3.76) ms(2), 0.61 (0.54-0.68) ms(2), and 3:10 (2:25-3:55) AM, respectively, and that of RMSSD
were 22.3 (20.5-24.1) ms, 6.5 (5.4-7.5) ms, 3:45 (2:55-4:35) AM, respectively. Older age is
associated with lower mean of HRV. Males have higher oscillation amplitude than females. The
acrophase of LF/HF was earlier in females than in males, and in younger individuals than in older
individuals. Conclusions The circadian pattern of CAM can be quantified by 3 cosine parameters of
HRV, which are correlated with age and gender. 
Autonomic modulation; Heart rate variability; Periodic rhythm; Community population