Key result
Higher baseline 6MWT complexity is positively linked to greater walking distance improvement after pulmonary rehabilitation.
Why the study?
The association between the complexity of bio-signals, such as R-R intervals, and an organism's capacity to adapt remained to be consolidated.
Does the complexity of R-R intervals at rest and during perturbation yield information regarding adaptive capacities in COPD patients during pulmonary rehabilitation?
Observational (n=23)
Yes
Does the complexity of R-R intervals at rest and during perturbation yield information regarding adaptive capacities in COPD patients during pulmonary rehabilitation?
Effect estimate: r = 0.47
p-value: p=<0.05
Reduced complexity of heart rate variability during acute perturbation at the beginning of pulmonary rehabilitation may predict decreased improvement in exercise capacity in COPD patients.
May identify COPD patients likely to improve with pulmonary rehabilitation; hypothesis-generating and requires prospective validation before clinical use.
INTRODUCTION: The complexity of bio-signals, like R-R intervals, is considered a reflection of the organism's capacity to adapt. However, this association still remains to be consolidated. We investigated whether the complexity of R-R intervals at rest and during perturbation [6-minute walking test (6MWT)], yielded information regarding adaptive capacities in Chronic Obstructive Pulmonary Disease (COPD) patients during pulmonary rehabilitation (PR). METHODS: In total, 23 COPD patients (64 ± 8 years, with forced expiratory volume in 1 s of 55 ± 19% predicted) were tested three times at the start (T1), middle (T2), and end (T3) of 4 weeks PR. Each time, R-R intervals were measured at rest and during 6MWT. The complexity of R-R intervals was assessed by evenly spaced Detrended Fluctuations Analysis and evaluated by the fractal exponent α and deviation from maximal complexity |1-α|. RESULTS: The 6MWT distance was significantly increased at T2 and T3 compared to T1. Neither α nor |1-α| at rest and during perturbation significantly changed throughout PR, nor were they consistently associated with 6MWT distances at each time. Throughout the PR program, complexity during the 6MWT was significantly lower compared to the rest. The level of α during 6MWT at T1 was positively correlated with the improvement of the 6MWT distance throughout the PR program. DISCUSSION: Reduced complexity in COPD patients during acute perturbation at the beginning of PR supports a decreased improvement of the 6MWT distance throughout PR. This result seems consistent with the notion that the complexity reflects the patients' adaptive capacities and could therefore become a clinical indicator in an applied perspective.
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Hognon et al. (2021) conducted an observational in Chronic Obstructive Pulmonary Disease (COPD) (n=23). Pulmonary rehabilitation (PR) vs. Baseline (T1) was evaluated on Correlation between fractal exponent α during 6MWT at T1 and improvement in 6MWT distance over PR (r = 0.47, p=<0.05). The level of complexity (fractal exponent α) during the 6-minute walking test at the start of pulmonary rehabilitation was positively correlated with the improvement in walking distance (r = 0.47).
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