RESPIRATORY MUSCLE WEAKNESS AND NORMAL VENTILATORY DRIVE IN DILATIVE CARDIOMYOPATHY

Background In dilative cardiomyopathy several factors influence dyspno ea. 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 st udy was to evaluate whether dilative cardiomyopathy is accompanied by changes in breathing pattern, respiratory muscle weakness and ventilat ory neural drive. Methods We investigated 47 patients (36 men, mean ag e=47.8 +/- 11.2 years) with chronic heart failure due to dilative card iomyopathy, 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, spiromet ry, body plethysmography, mouth occlusion pressure and respiratory mus cle strength, as well as by submaximal treadmill exercise testing with gas exchange measurements. The patients' results were compared to con trols and predicted standard normal values, and evaluated for differen ces according to the degree of severity of functional impairment. Resu lts Patients with dilative cardiomyopathy demonstrated a slight reduct ion 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 as sessed by mouth occlusion pressure, there was no significant differenc e between patients and controls. There was a slight but significant re duction in respiratory muscle strength, as assessed by measuring maxim al 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 mor e pronounced in the severe chronic heart failure patients (with a redu ction in ventilatory efficiency) whereas no relationship among indices of cardiac or respiratory function was found. Conclusions Patients wi th chronic heart failure due to dilative cardiomyopathy develop respir atory muscle weakness without changes in neural ventilatory drive, and slight changes in breathing pattern related to the severity of the di sease.