Correlation of Circadian Rhythms of Heart Rate Variability Indices with Stress, Mood, and Sleep Status in Female Medical Workers with Night Shifts

Abstract

Purpose: Heart rate variability (HRV) indices have been used as stress indicators. Rare studies investigated the associations of circadian rhythms of the HRV indices with the stress, mood, and sleep conditions in populations under stress.

Methods: In total 257 female participants (203 shift workers and 54 non-shift workers) were included. All the participants completed a structured questionnaire to assess the stress, mood, and sleep conditions and performed 24-hour Holter electrocardiogram monitoring on the day away from shifts. Using epochs of 1-min or 5-min beat-to-beat intervals, the HRV indices (SDNN, RMSSD, LF, HF, LF/HF, and LFnu, SD1, SD2, SD1/SD2) were plotted as a function of time and fitted into cosine periodic curves, respectively. Three mathematical parameters based on the cosine periodic curves were extracted, MESOR (M, overall averages of the cosine curve), amplitude (A, amplitude of the peak of the cosine curve), and acrophase (θ, latency to the peak) to quantify the circadian rhythms of the HRV indices. Multivariable linear regression models were used to reveal the associations of these parameters with the clinical assessments of stress, mood, or sleep conditions, as well as with the 24-h averages of the HRV indices.

Results: The parameters M and A of SDNN, RMSSD, LF, and HF, and θ of LF/HF and LFnu significantly differ between shift and non-shift workers. The parameter θ of LF/HF positively correlates with the severity of stress and anxiety. The parameter A of LF/HF and LFnu also positively correlates with daytime sleepiness and sleep fragmentation. In addition, the parameters M and A instead of θ of SDNN, RMSSD, LF, LF/HF, and LFnu significantly correlate with the 24-h averages of HRV indices.

Conclusion: The circadian rhythms of the HRV indices over 24 hours can, to some extent, predict the severity of stress, emotion and sleep conditions in female populations under stress.

Keywords: HRV indices; circadian rhythms; fatigue; mental health; sleep fragmentation; sleepiness; stress.

Figure 1

HRV circadian rhythm analysis. Definition of circadian rhythm parameters (A). The 1440 or 288 data points (black dots) extracted from 1-min (SDNN, RMSSD) or 5-min (LF, HF, LF/HF ratio, and LFnu) epochs of 24-hour ECG signals. The red lines are the circadian rhythm fitting curves of SDNN (B), RMSSD(C) and LF(D), HF(E), LF/HF ratio(F), LFnu(G), heart rate(H) and SD1(I) from one individual, respectively. MESOR, M, is a rhythm-adjusted mean that reflects the overall average of the HRV index; A, amplitude, the height of the maximum oscillation to the midline, and double amplitude represents the extent of rhythmic fluctuation within a cycle; θ, acrophase, is the timing of the zenith occurring in each cycle (the reference time point 12:00 AM was set as the value of 0). The significance of the cosine periodic rhythm curves was tested, indicated by the P value (All P < 0.0001).