Abstract
PURPOSE: In patients with chronic obstructive pulmonary disease, pulmonary rehabilitation has been demonstrated to increase exercise capacity and reduce dyspnea. In the most disabled patients, the intensity of exercise during the training sessions is limited by ventilatory pump capacity. This study therefore evaluated the beneficial effect of noninvasive ventilation (NIV) support during the rehabilitation sessions on exercise tolerance.
METHODS: This study included 14 patients with stabilized chronic obstructive pulmonary disease, ages 63 +/- 7 years, with a forced expiratory volume in 1 second (FEV1) 31.5% +/- 9.2% of predicted value. All 14 patients participated in an outpatient pulmonary rehabilitation program. Seven of the patients trained with NIV during the exercise sessions (NIV group), whereas the remaining seven patients breathed spontaneously (control group). Exercise tolerance was evaluated during an incremental exercise test and during constant work rate exercise at 75% of peak oxygen consumption (VO2) before and after the training program.
RESULTS: The application of noninvasive ventilation increased exercise tolerance, reduced dyspnea, and prevented exercise-induced oxygen desaturation both before and after training. The pressure support was well tolerated by all the patients during the course of the training program. In the NIV group, training induced a greater improvement in peak VO2 (18% vs 2%; P < .05) and a reduced ventilatory requirement for maximal exercise, as compared with the control group. The constant work rate exercise duration increased similarly in both groups (116% vs 81%, nonsignificant difference), and posttraining blood lactate was decreased at isotime (P < .05 in both groups), but not at the end of the exercise.
CONCLUSION: In this pilot study, exercise training with noninvasive ventilation support was well tolerated and yielded further improvement in the increased exercise tolerance brought about by pulmonary rehabilitation in patients with chronic obstructive pulmonary disease. This improved exercise tolerance is partly explained by a better ventilatory adaptation during exercise.
In patients with chronic obstructive pulmonary disease (COPD), exercise tolerance is reduced dramatically, mainly by the inability of the respiratory system to sustain a high level of ventilation. Expiratory airflow limitation induces dynamic hyperinflation during exercise, causing an intrinsic positive end-expiratory pressure. 1-3 This results in an additional burden on the respiratory system, especially on the diaphragm, leading to muscle fatigue. 3-5 As a consequence, carbon dioxide (CO2) retention occurs, resulting in further deleterious effects on the respiratory muscles and limiting exercise.
Pulmonary rehabilitation improves the exercise capacity of patients with COPD by decreasing the ventilatory requirement for a given task. Muscle adaptation toward better oxidative metabolism reduces lactate formation during exercise after training and contributes to a decrease in the minute ventilation stimulation and the sensation of dyspnea. 6 In addition, exercise intensity affects the beneficial impact of such training programs because it has been demonstrated that exercising near or exceeding the ventilatory threshold induces a higher training effect. 6,7 Encouraging patients to exercise at a higher level leads to increased exercise tolerance and better ventilatory adaptation, even in the most disabled patients with COPD. 8 However, it has been emphasized that in very breathless patients, this goal is difficult to achieve, particularly when arterial partial pressure of CO2 (PCO2) rises during exercise. 9 Moreover, patients presenting with limb amyotrophy are sometimes unable to sustain any exercise, even unloaded cycling.
In the recent years, noninvasive positive pressure ventilation (NIPPV) has been proved to be an effective treatment for acute exacerbations of COPD. 10 It relieves respiratory muscle work and reduces arterial PCO2, thus preventing respiratory fatigue and improving recovery after the exacerbation. In stable patients with COPD, the use of inspiratory pressure support also has been found to increase exercise tolerance during a walking test. 11 Transdiaphragmatic pressure measurements have demonstrated that different types of NIPPV reduce diaphragmatic work at similar levels of exercise. 12-16 However, the benefit from repeated applications of NIPPV during rehabilitation sessions has not been evaluated.
The authors therefore undertook a prospective pilot study to examine the effect of ventilatory support during an exercise training program in patients with severe COPD presenting with relative hypoventilation during exercise. Looking for greater improvement in exercise tolerance through a decreased ventilatory requirement with ventilatory support, they examined the tolerance of repeated NIPPV sessions during exercise.