Analysis of respiratory muscle strength and its relationship with functional capacity between different field tests in patients with heart failure

Objective: To analyze respiratory muscle strength of patients with heart failure (HF) and correlate with functional capacity.

Methods: This cross-sectional study involved patients with compensated HF of both sexes, aged above 18 years. Respiratory muscle strength was assessed by measuring maximum inspiratory (MIP) and expiratory pressures (MEP) using a manovacuometer. Patients were randomized into two groups to assess functional capacity: six-minute walk test (6MWT) and incremental shuttle walk test (ISWT).

Results: Forty-eight patients were evaluated (23 from 6MWT and 25 from ISWT group). Most were male (67.8%), with mean age of 62.3 years and left ventricular ejection fraction of 40.8%. Mean predicted values of MIP [81.2% (74.7-87.8%)] and MEP [95.6% (88.2-103.0%)] did not indicate respiratory muscle weakness. The higher the New York Heart Association (NYHA) functional class, the lower the MIP (p = .011) and MEP (p = .016) values. Physically active patients presented higher respiratory muscle strength than those sedentary (MIP: 104.5 vs. 71.9 cmH₂O, p < .001; MEP: 120.0 vs. 91.1 cmH₂O, p = .004). Functional capacity was impaired [6MWT: 416.0 m (372.8-459.3 m); ISWT: 304 m (263.4-344.9 m)], and distance covered in the ISWT was shorter than 6MWT group (p < .001). Distance covered in the ISWT group presented a moderate positive correlation with MIP (r = 0.45; p = .022) and MEP (r = 0.41; p = .041).

Conclusion: Most patients with HF presented respiratory muscle strength close to predicted values; however, sedentary patients and those with high NYHA functional class, showed reduced MIP and MEP. Functional capacity was reduced, and MIP and MEP correlated with distance covered in the ISWT.