Reduced heart rate variability predicts fatigue severity in individuals with chronic fatigue syndrome/myalgic encephalomyelitis

Abstract

Background: Heart rate variability (HRV) is an objective, non-invasive tool to assessing autonomic dysfunction in chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). People with CFS/ME tend to have lower HRV; however, in the literature there are only a few previous studies (most of them inconclusive) on their association with illness-related complaints. To address this issue, we assessed the value of different diurnal HRV parameters as potential biomarker in CFS/ME and also investigated the relationship between these HRV indices and self-reported symptoms in individuals with CFS/ME.

Methods: In this case-control study, 45 female patients who met the 1994 CDC/Fukuda definition for CFS/ME and 25 age- and gender-matched healthy controls underwent HRV recording-resting state tests. The intervals between consecutive heartbeats (RR) were continuously recorded over three 5-min periods. Time- and frequency-domain analyses were applied to estimate HRV variables. Demographic and clinical features, and self-reported symptom measures were also recorded.

Results: CFS/ME patients showed significantly higher scores in all symptom questionnaires (p < 0.001), decreased RR intervals (p < 0.01), and decreased HRV time- and frequency-domain parameters (p < 0.005), except for the LF/HF ratio than in the healthy controls. Overall, the correlation analysis reached significant associations between the questionnaires scores and HRV time- and frequency-domain measurements (p < 0.05). Furthermore, separate linear regression analyses showed significant relationships between self-reported fatigue symptoms and mean RR (p = 0.005), RMSSD (p = 0.0268) and HFnu indices (p = 0.0067) in CFS/ME patients, but not in healthy controls.

Conclusions: Our findings suggest that ANS dysfunction presenting as increased sympathetic hyperactivity may contribute to fatigue severity in individuals with ME/CFS. Further studies comparing short- and long-term HRV recording and self-reported outcome measures with previous studies in larger CFS/ME cohorts are urgently warranted.

Keywords: Autonomic dysfunction; Chronic fatigue syndrome; Fatigue; Heart rate variability; Myalgic encephalomyelitis.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Comparison of the HRV time-domain parameters among the participants. Values are shown as mean ± SEM of a mean of RR intervals (mean RR), b standard deviation of all R–R intervals (SDNN), c root mean square of successive RR intervals differences (RMSSD), and d the mean number of times in an hour in which the change in successive normal sinus R–R intervals exceeds 50 ms (pNN50). Significance level is indicated above the horizontal line in each chart

Fig. 2

Comparison of the HRV frequency-domain measures in the study participants. Values are shown as mean ± SEM of a absolute power of the low frequency band (LF), b absolute power of the high frequency band (HF), c normalized HF value (HFnu) and d ratio of LF-to-HF power (LF/HF). Significance level is indicated above the horizontal line in each chart

Fig. 3

Correlation analysis between fatigue severity perception and HRV indices among the participants. Total FIS-40 score significantly correlated with a the mean RR, b the RMSSD, and c the HFnu among CFS/ME patients (black squares, upper regression lines) but not for those healthy controls (white circles, bottom regression lines). Significant correlations were found between HRV indices and presence of perceived fatigue among CFS/ME individuals (p < 0.01 for mean RR and HFnu, and p < 0.05 for RMSSD), but not in healthy controls