Reproducibility and validity of heart rate variability and respiration rate measurements in participants with prolonged fatigue complaints

(1) To evaluate reproducibility of heart rate variability (HRV) and respiration rate (RR) measurements during reclining and cycling in participants with prolonged fatigue and (2) to assess concurrent validity between HRV and RR measurements and fatigue. Twenty-seven subjects reporting prolonged fatigue complaints resulting in functional impairments participated in the study. Fatigue complaints and functional impairments were assessed. Two to 4 days later, they underwent two repeated measurements of time-domain HRV (SDNN and RMSSD) and RR with 3-4 days between. Intra-class correlation coefficients (ICCs) and standard error of measurement (SEM) were calculated to define reproducibility and Pearson correlations were calculated to define concurrent validity. ICC means for SDNN and RMSSD during reclining and cycling ranged from 0.86 to 0.93. For RR the ICC means were 0.65 and 0.85 for reclining and cycling, respectively. The SEM values (ms) for SDNN and RMSSD ranged from 1.08 to 7.71 while the SEM values for RR were 1.82 and 1.99 for reclining and cycling, respectively. The Pearson correlations were non-significant and ranged from -0.05 to 0.15. There was good reproducibility of HRV and RR in participants with prolonged fatigue complaints. Concurrent validity between HRV and RR measurements and fatigue was low.