Muscle Endurance In Patients Research Articles

Evidence of reduced respiratory muscle endurance in patients with heart failure

Objectives. We sought to investigate whether reduced respiratory muscle endurance contributes to increased dyspnea and decreased exercise capacity in patients with chronic heart failure.Background. In patients with heart failure, the sensation of dyspnea may be related to abnormalities of respiratory muscle function, such as diminished strength or endurance, or both.Methods. Respiratory muscle endurance was assessed by measuring maximal sustainable ventilatory capacity in 15 patients with congestive heart failure and 8 normal subjects using progressive isocapnic hyperpnea. Near-infrared spectroscopy of an accessory respiratory muscle, Borg scale recordings of perceived dyspnea, time in inspiration, time per breath and minute ventilation were measured. Exercise testing with measurement of oxygen consumption was also performed.Results. Maximal voluntary ventilation (normal subjects 167 ± 40, heart failure group 89 ± 31 liters/min) and maximal sustainable ventilatory capacity (normal subjects 90 ± 23, heart failure group 53 ± 22 liters/min) were significantly reduced in patients with heart failure (both p < 0.05). No significant accessory respiratory muscle deoxygenation was observed in either group. Borg scale recordings at maximal sustainable ventilatory capacity were comparable in both groups. At rest, the inspiratory duty cycle (i.e., time in inspiration divided by the time per breath) was comparable in the two groups (normal subjects 0.34 ± 0.09, heart failure group 0.37 ± 0.12, p = NS). However at maximal sustainable ventilatory capacity, only normal subjects had a significant increase in the inspiratory duty cycle (normal subjects 0.49 ± 0.04, heart failure group 0.36 ± 0.10, p < 0.05). This finding suggests obstruction to airflow in patients with congestive heart failure. Values for peak exercise minute ventilation did not differ significantly from values in maximal sustainable ventilatory capacity in either group and were significantly correlated (r = 0.84, p < 0.0001).Conclusion. Respiratory muscle endurance as assessed by maximal sustainable ventiiatory capacity is reduced in patients with heart failure.

Physical Training Fails to Improve Ventilatory Muscle Endurance in Patients with Chronic Obstructive Pulmonary Disease

We examined the effect of arm and leg exercise training on ventilatory muscle performance in 15 patients with symptomatic COPD. Eight patients trained their arms while seven trained their legs for six weeks. Before and after the training we measured exercise and pulmonary function including the maximal sustained ventilatory capacity (MSVC). After training there was no significant change in spirometric values and lung volumes. The mean endurance workload performed for 20 minutes increased significantly in both the arm and leg trained groups (14.4 +/- 2.4 to 24.8 +/- 2.5 W, P less than 0.01, and 26.1 +/- 2.4 to 44.4 +/- 2.5 W, P less than 0.01, respectively). Despite the increase in endurance, no significant change was noted in the MSVC (46 +/- 5 to 51 +/- 5 for the arm trainers and 36 +/- 2 to 39 +/- 1 for the leg trainers). We conclude that nonventilatory muscle exercise such as arm and leg cycling does not improve ventilatory muscle endurance, and that increased exercise endurance may occur independent of changes in ventilatory muscle endurance.