Respiratory muscle strength and exercise tolerance in older patients with heart failure and preserved or reduced lower-extremity function

INTRODUCTION: Aside from lower-extremity function, respiratory muscle function may provide complementary information on exercise tolerance in older patients with heart failure (HF). We aimed to clarify the association between respiratory muscle strength and exercise tolerance in older patients with HF, considering the presence or absence of lower-extremity function decline. METHODS: We studied 552 patients aged ≥65 years admitted for HF medical treatment. Short Physical Performance Battery (SPPB) ≤9 and 6-min walking distance (6MWD) <300 m were defined as lower-extremity function decline and exercise intolerance, respectively. Maximal inspiratory pressure (PImax) was measured as respiratory muscle strength. We analysed the association of PImax with 6MWD in subgroups stratified by SPPB and assessed the incremental predictive value of PImax beyond SPPB for predicting 6MWD <300 m. RESULTS: After adjusting for clinical characteristics, PImax was independently associated with 6MWD (partial regression coefficient per 5 cmH₂O increase in PImax: 5.622, 95% confidence interval [CI]: 4.135-7.109, P <0.001). This association was consistent regardless of lower-extremity function decline (SPPB ≤9). While the area under the receiver operating characteristic curve of SPPB alone for 6MWD <300 m was 0.886 (95% CI: 0.858-0.915), the addition of PImax modestly increased the AUC to 0.909 (95% CI: 0.884-0.933; P = 0.005). CONCLUSIONS: Respiratory muscle strength is a relevant marker of exercise tolerance in older patients with HF, regardless of lower-extremity function decline, and provides complementary information to lower-extremity function in assessing exercise intolerance.