Respiratory muscle weakness after stroke: An exploratory mediation analysis of associated factors

This study had two aims: first, to compare pulmonary function and ultrasound-derived parameters between individuals with stroke and apparently healthy controls; and second, to examine whether selected pulmonary and ultrasound-derived variables mediated the association between stroke status and respiratory muscle strength.

In this cross-sectional study, 49 individuals with chronic unilateral stroke (≥6 months) and 53 apparently healthy adults were evaluated. B-mode ultrasound assessed diaphragm and transversus abdominis thickness at functional residual capacity and total lung capacity, diaphragm thickening fraction (TF_di), transversus abdominis thickening fraction, and echo intensity (EI). Pulmonary function (forced vital capacity [FVC], forced expiratory volume in 1 s [FEV₁], peak expiratory flow [PEF] % predicted and absolute values) and respiratory muscle strength (MIP and maximal expiratory pressure [MEP], % predicted) were measured according to ATS/ERS standards. Between-group differences were analyzed using t tests with Cohen d. Single-mediator models with bootstrap resampling evaluated mediation, adjusting for age and sex.

Pulmonary function was lower in the stroke group, including FVC (% predicted; d = 1.45), FEV1 (% predicted; d = 1.55), and PEF (% predicted; d = 1.53). %MIP and %MEP were reduced (both P < 0.001). Ultrasound measures showed reduced TF_di and transversus abdominis thickening fraction, along with higher echo intensity. Mediation analyses indicated that PEF (% predicted) and TF_di were significant mediators in the association between stroke status and lower %MIP. TF_di accounted for 14.2% of the total effect (β = -3.28; 95% CI, -7.45 to -0.60), whereas PEF accounted for 48.4% (β = -10.78; 95% CI, -17.57 to -5.50). For %MEP, TFdi and PEF also showed statistically significant indirect effects, whereas EITrA showed a smaller indirect effect and TrA thickness at TLC did not.

In this cross-sectional study, post-stroke inspiratory muscle weakness was associated with lower PEF and reduced diaphragmatic contractility in exploratory mediation analyses. These findings suggest that spirometric and ultrasound-derived measures capture complementary aspects of respiratory impairment.