Background: Inspiratory muscle weakness is associated with the development of exercise intolerance in patients with heart failure (HF). Ultrasound assessment of the diaphragm is used to evaluate respiratory muscle function, but its application in patients with HF remains undefined. We examined the relationship of diaphragm function as assessed by ultrasonography with inspiratory muscle strength and exercise tolerance in HF.
Methods and results: Seventy-seven patients hospitalized with HF were enrolled. Impaired diaphragm muscle function was defined as a diaphragm thickness at end-inspiration of less than the median value of 4.0 mm, which represents diaphragm muscle loss and reduced contraction. Compared with patients with preserved diaphragm muscle function, those with impaired diaphragm muscle function were older; had significantly lower vital capacity, handgrip strength, and inspiratory muscle strength as assessed by the maximum inspiratory pressure; and had a significantly shorter 6-minute walk distance (6MWD; P < .05). Although low handgrip strength was also associated with a short 6MWD, the relationship between impaired diaphragm muscle function and short 6MWD was independent from age, vital capacity, and handgrip strength.
Conclusion: Diaphragm dysfunction as assessed by ultrasonography represents inspiratory muscle weakness and predicts exercise intolerance independently from comorbid pulmonary dysfunction and dynapenia in patients with HF.
Keywords: Diaphragm ultrasound; frailty; inspiratory muscle weakness.
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