Heart failure (HF) is characterized by cardiac dysfunction and consequent exercise intolerance. In addition to peripheral muscle dysfunction, common in HF, diaphragmatic dysfunction may contribute to functional limitation and reduced exercise capacity. Maximal respiratory pressure measurement is widely used to identify respiratory muscle weakness, but diaphragmatic ultrasound has emerged as a promising tool for structural and functional diaphragm assessment, enabling early detection and therapeutic management of respiratory muscle dysfunction.

To evaluate diaphragmatic function using ultrasound and its relationship with exercise capacity in individuals with chronic HF.

This is an observational, analytical-descriptive, cross-sectional study conducted with individuals aged 18 to 65 years diagnosed with chronic HF and left ventricular ejection fraction (LVEF) < 50%. Participants underwent diaphragmatic ultrasound assessment, including measurements of diaphragmatic excursion (DE), thickness (Tdi), and thickening fraction (DTF), as well as maximal inspiratory and expiratory pressures (PImáx and PEmáx). Functional capacity was evaluated using the six-minute walk test (6MWT) and maximal oxygen consumption (VO2max). Statistical analysis was performed using SPSS 27.0 software, applying mean comparison tests and variable association analyses.

A total of 18 individuals were evaluated, predominantly male (66.7%), with a mean age of 54.9 ± 8.08 years and a mean LVEF of 34.7 ± 11.7%. The mean DE was 2.5 ± 1.3 cm during quiet breathing and 5.8 ± 1.9 cm during deep breathing, with 40% presenting below-normal values. The mean inspiratory Tdi was 4.6 ± 2.2 mm, reduced in 50% of cases, while DTF was decreased in 66.7% of participants. Respiratory muscle strength was relatively preserved, with 88.9% of individuals having PImáx above 70% of the predicted value (mean 86.3 ± 24.16 cmH2O) and 64.7% with PEmáx above the reference value (mean 114.8 ± 37.3 cmH2O). Functional capacity was impaired, with a mean VO2max of 16.2 ± 3.98 mL/kg/min, where 66.7% were classified as "very weak" and 33.3% as "weak." In the 6MWT, the mean distance covered was 453.8 ± 106.7 meters, with 60% exceeding 80% of the predicted distance. Despite these alterations, no statistically significant associations were found between diaphragmatic ultrasound parameters, respiratory muscle strength, and functional capacity.

The findings indicate a high prevalence of diaphragmatic dysfunction in HF patients, even in those with preserved respiratory muscle strength. The lack of significant associations between diaphragmatic function and exercise capacity may be related to the small sample size, reinforcing the need for studies with greater statistical power.

Diaphragmatic ultrasound may contribute to the clinical management of chronic HF, allowing early detection of respiratory dysfunction and personalized interventions such as respiratory rehabilitation and therapeutic adjustments. Additionally, its use in monitoring disease progression may help improve patient prognosis.