Takeshi Sota

Diaphragm Muscle Dysfunction in Patients with Heart Failure

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.

Dynapenia and diaphragm muscle dysfunction in patients with heart failure

Skeletal muscle dysfunction (dynapenia) is often present in patients with heart failure. However, the association of dynapenia with diaphragm muscle dysfunction remains undefined. Sixty-two patients hospitalized for heart failure were enrolled. Diaphragm muscle function was assessed by ultrasonography, and impaired diaphragm function was defined as diaphragm muscle thickness at the end of inspiration below the median value (i.e. <4.0mm) as previously described. Dynapenia was classified into two phenotypes: muscle weakness with low muscle mass (i.e. sarcopenia) and muscle weakness despite normal muscle mass. Muscle weakness and muscle loss were defined according to the criteria of the Asian working group for sarcopenia. Dynapenia with muscle loss and dynapenia with normal muscle mass were present in 32.3% and 40.3% of patients, respectively. Compared with patients without dynapenia, patients with either type of dynapenia were older, had significantly reduced knee extensor muscle strength, impaired diaphragm muscle function and a significantly shorter six-minute walk distance (6MWD) (Figure 1(a)). Reduced diaphragm muscle function was associated with a further decrease in the 6MWD of patients with either type of dynapenia (Figure 1(b) and (c)). In multivariate analysis, increased age, reduced diaphragm muscle function and decreased knee extensor muscle strength were independent determinants of short 6MWD in heart failure patients with dynapenia. The present study demonstrated that ultrasoundproven diaphragm muscle dysfunction was often present in heart failure patients with dynapenia and was a significant determinant of exercise intolerance regardless of the dynapenia phenotype. Independent effect of diaphragm muscle dysfunction on exercise intolerance in heart failure patients with dynapenia may be partly explained by the limb muscle dysfunction induced by the inspiratory metaboreflex. Diaphragm muscle fatigue during exercise is likely to induce sympathetic activation and peripheral vasoconstriction, resulting in fatigue of peripheral skeletal muscles and an impairment of their endurance. A previous study demonstrated the beneficial effects of inspiratory muscle training on exercise capacity along with improved diaphragm muscle function and attenuated inspiratory metaboreflex in patients with heart failure. Thus, in addition to conventional rehabilitation programs, inspiratory muscle training may be a therapeutic option for heart failure patients with dynapenia.