INSPIRATORY MUSCLE ENDURANCE IN PATIENTS WITH CHRONIC HEART-FAILURE

Objective-To assess the significance of changes in respiratory muscle endurance in relation to respiratory and limb muscle strength in patie nts with mild to moderate chronic heart failure using a threshold load ing technique. Subjects-20 patients with chronic heart failure (17 mal e) aged 63.8 (SD 7.4) years and 10 healthy men aged 63.1 (5.6) years. Heart failure severity was New York Heart Association (NYHA) grade II (n = 11) and NYHA grade III/IV (n = 9).Methods-Respiratory muscle stre ngth was measured from mouth pressures during maximum inspiratory effo rt (MIP) at functional residual capacity (FRC) and Limb muscle strengt h was measured using a hand grip dynamometer. Inspiratory muscle endur ance was measured using a threshold loading technique. The total endur ance duration, threshold pressure achieved and the inspiratory load (% ratio of P-Max/MIP) were recorded in all subjects. Results-Inspirator y muscles were weaker in patients with heart failure than in the contr ols [MIP 53.6 (16.5) v 70.9 (20.2) cm H2O, P < 0.05]. Hand grip streng th was similar in both subject groups [31.6 (SD) v 36.1 (15.9) dynes]. Total endurance duration was significantly reduced in the patient gro up [494 (223) v 996 (267) s, P < 0.01], as was the maximal threshold p ressure achieved [P-Max 18.5 (6.4) v 30.7 (6.6) cm H2O, P < 0.01]. Whe n expressed as a percentage of MIP, P-Max was also lower in the patien ts [35.2 (11.8) v 44.8 (11.4) %, P < 0.05]. There was no significant c orrelation between any measure of endurance and Limb muscle strength. Conclusions-Respiratory muscle endurance is reduced in patients chroni c heart failure. These changes probably reflect a generalised skeletal myopathy and provide further evidence of respiratory muscle dysfuncti on in patients with this disease. Respiratory muscle endurance needs n ow to be related to symptoms and the effects of treatment and respirat ory muscle training should also be explored.