Respiratory muscle weakness and normal ventilatory drive in dilative cardiomyopathy.

Abstract

In dilative cardiomyopathy several factors influence dyspnoea. Patients with chronic heart failure may demonstrate impairment of breathing pattern, ventilatory drive and respiratory muscle strength, as well as reduction of ventilatory efficiency. The purpose of this study was to evaluate whether dilative cardiomyopathy is accompanied by changes in breathing pattern, respiratory muscle weakness and ventilatory neural drive. We investigated 47 patients (36 men, mean age = 47.8 +/- 11.2 years) with chronic heart failure due to dilative cardiomyopathy, and 30 healthy subjects (10 men, mean age = 35.4 +/- 11.7 years) served as controls. Patients and controls underwent evaluation of left ventricular ejection fraction by 2D echocardiography, spirometry, body plethysmography, mouth occlusion pressure and respiratory muscle strength, as well as by submaximal treadmill exercise testing with gas exchange measurements. The patients' results were compared to controls and predicted standard normal values, and evaluated for differences according to the degree of severity of functional impairment. Patients with dilative cardiomyopathy demonstrated a slight reduction in lung volumes (15% of the patients with obstructive and 15% with restrictive lung function pattern) and diffusion capacity (20.4 +/- 6.8 vs 15.4 +/- 6.7 ml.min-1.kPa-1; P < 0.01). In neural drive, as assessed by mouth occlusion pressure, there was no significant difference between patients and controls. There was a slight but significant reduction in respiratory muscle strength, as assessed by measuring maximal inspiratory pressure in patients with dilative cardiomyopathy (6.7 +/- 2.4 kPa vs 8.6 +/- 3.5 kPa; P < 0.01). The observed changes were more pronounced in the severe chronic heart failure patients (with a reduction in ventilatory efficiency) whereas no relationship among indices of cardiac or respiratory function was found. Patients with chronic heart failure due to dilative cardiomyopathy develop respiratory muscle weakness without changes in neural ventilatory drive, and slight changes in breathing pattern related to the severity of the disease.