Inspiratory muscle weakness in chronic heart failure: Role of nutrition and electrolyte status and systemic myopathy

Inspiratory muscle weakness has been demonstrated in ambulatory, stable chronic heart failure (CHF) and may contribute to dyspnea during daily living. However, the mechanisms underlying this weakness are unknown. Malnutrition and electrolyte depletion are recognized complications of CHF that may impair skeletal muscle function, and limb muscle weakness and myopathic changes have also been demonstrated in CHF. We examined whether nutrition and electrolyte status contribute to the reduced skeletal muscle strength and whether inspiratory muscle weakness in CHF is part of general skeletal muscle weakness. We measured maximum inspiratory and expiratory mouth pressures as indices of respiratory muscle strength, maximum hand-grip strength as an index of limb muscle strength, anthropometric indices, serum albumin, and total lymphocyte count as indices of nutritional status, and serum electrolytes in 15 stable patients with chronic cardiac pump failure who had no evidence of primary lung disease, and in 15 age-and-sex-matched healthy controls. As compared with the matched controls, the CHF patients had reduced inspiratory muscle strength (p < 0.0025), but their expiratory and limb muscle strength were not significantly reduced. CHF patients were not malnourished; they were heavier than matched controls because of increased body fat (p < 0.05). Serum sodium was significantly lower in the CHF patients than in the controls (p < 0.01), but was within the normal range in both groups. Inspiratory muscle strength in the CHF patients was not correlated with nutrition, electrolyte status, or limb muscle strength. These findings indicate that patients with stable CHF have inspiratory muscle weakness that is not due to readily measurable nutritional or electrolyte abnormalities, and which occurs without limb or expiratory muscle weakness, suggesting that the inspiratory muscle weakness is not simply due to generalized skeletal muscle weakness.