Heterogenous Treatment Effects Following Inspiratory Muscle Training during Recovery from Post-Acute COVID-19 Syndrome.

ABSTRACT

PURPOSE: To investigate whether heterogeneous treatment effects occur for changes in inspiratory muscle strength, perceived dyspnoea, and health-related quality of life (QoL), following eight-weeks unsupervised home-based inspiratory muscle training (IMT) in adults with post-acute COVID-19 syndrome. METHODS: In total, 147 adults with self-reported prior COVID-19 either completed an eight-week home-based IMT intervention (n = 111; 92 females; 48 ± 11 years; 9.3 ± 3.6 months post-acute COVID-19 infection) or acted as "usual care" wait list controls (n = 36; 34 females; 49 ± 12 years; 9.4 ± 3.2 months post-acute COVID-19 infection). RESULTS: Applying a Bayesian framework, we found clear evidence of heterogeneity of treatment response for inspiratory muscle strength the estimated difference between standard deviations (SDs) of the IMT and control groups was 22.8 cmH2O (75% Credible Interval (CrI) 4.7-37.7) for changes in maximal inspiratory pressure (MIP), and 86.8 pressure time-units (PTUs; 75% CrI 55.7-116.7) for sustained MIP (SMIP). Conversely, there were minimal differences in the SDs between the IMT and the control group for changes in perceived dyspnoea and health-related QoL, providing no evidence of heterogeneous treatment effects. Higher cumulative power during the IMT intervention was related to changes in MIP (ß = 10.9 [95% CrI 5.3-16.8] cmH2O per 1SD) and SMIP (ß = 63.7 [32.2-95.3] PTUs per 1SD), clearly indicating an IMT dose response for changes in inspiratory muscle strength. Older age (>50 years), a longer time post-acute COVID-19 (>3 months), and greater severity of dyspnoea at baseline were also associated with smaller improvements in inspiratory muscle strength. CONCLUSIONS: Heterogenous individual responses occurred following an eight-week home-based IMT programme in people with post-acute COVID-19 syndrome. Consistent with standard exercise theory, larger improvements in inspiratory muscle strength are strongly related to a greater cumulative dose of IMT.