Detecting effects of yoga therapy on heart rate variability and autonomic nervous system functioning in adults after cancer treatment: results from a study using single-subject experimental methods.

BACKGROUND: Cancer is a source of physiological and psychological stress. Heart rate variability (HRV) is a measure of autonomic reactivity to physiological and psychological stress. For an initial proof-of-concept, we investigated the effects of a yoga therapy (YT) intervention on HRV metrics and self-reported autonomic nervous system (ANS) functioning using single-subject experimental methods. METHODS: Data from 20 adults (Mage (years) = 55.7 [SD = 8.6], 85% female, Myears from diagnosis = 2.8 [SD = 3.5]) were analyzed. Participants received an initial 90-min 1:1 YT session followed by 6 weekly 60-min small group YT sessions. Hexoskin Smart Shirts captured single lead electrocardiographic data suitable for HRV analysis, and questionnaires were used to assess self-reported state and trait ANS functioning. Data collected prior to (weeks - 6, -3, and 0a), during (immediately after the 1:1 YT session [week 0b] and before the first group session [week 1]), and after (weeks 7 and 12) the YT intervention were analyzed. Hierarchical linear modeling (HLM) was used to estimate average baseline levels (intercept), linear slopes (time), YT initiation effect on levels (phase), and YT intervention effect on linear slopes (time-by-phase) for each outcome. RESULTS: HLM yielded mixed results. Significant (p < 0.05) time, phase, and time-by-phase effects for state ANS, coefficient of variation and high frequency power, time-by-phase effect for trait ANS, and time and phase effects for sample entropy were observed. No significant effects were observed for remaining analyzed HRV metrics. CONCLUSIONS: Though mixed, results establish an initial proof-of-concept required to justify larger studies investigating the effects of YT on HRV and self-reported ANS functioning in adults after cancer treatment. TRIAL REGISTRATION NAME: ISRCTN registry. REGISTRATION NUMBER: ISRCTN64763228. DATE OF REGISTRATION: December 12, 2021. This study was retrospectively registered. URL OF TRIAL REGISTRY RECORD: https://www.isrctn.com/ISRCTN64763228 .