Chest Physiotherapy in Cystic Fibrosis: Improved Tolerance With Nasal Pressure Support Ventilation

Abstract

Objective. Chest physiotherapy (CPT) is an integral part of the treatment of patients with cystic fibrosis (CF). CPT imposes additional respiratory work that may carry a risk of respiratory muscle fatigue. Inspiratory pressure support ventilation (PSV) is a new mode of ventilatory assistance designed to maintain a constant preset positive airway pressure during spontaneous inspiration with the goal of decreasing the patient's inspiratory work. The aim of our study was 1) to evaluate respiratory muscle fatigue and oxygen desaturation during CPT and 2) to determine whether noninvasive PSV can relieve these potential adverse effects of CPT. Methods. Sixteen CF patients in stable condition with a mean age of 13 ± 4 years participated to the study. For CPT, we used the forced expiratory technique (FET), which consisted of one or more slow active expirations starting near the total lung capacity (TLC) and ending near the residual volume. After each expiration, the child was asked to perform a slow, nonmaximal, diaphragmatic inspiration. After one to four forced breathing cycles, the child was asked to cough and to expectorate. A typical 20-minute CPT session consisted of 10 to 15 FET maneuvers separated by rest periods of 10 to 20 breathing cycles each. During the study, each patient received two CPT sessions in random order on two different days, at the same time of day, with the same physiotherapist. During one of these two sessions, PSV was provided throughout the session (PSV session) via a nasal mask using the pressure support generator ARM25 designed for acute patients (TAEMA, Antony, France). The control session was performed with no nasal mask or PSV. Both CPT sessions were performed without supplemental oxygen. Lung function and maximal inspiratory pressures (Pimax) and expiratory pressures (Pemax) were recorded before and after each CPT session. Results. Mean lung function parameters were comparable before the PSV and the control sessions. Baseline pulse oximetry (Spo2) was significantly correlated with the baseline vital capacity (% predicted) and forced expiratory volume in 1 second (FEV1) (% predicted). PSV was associated with an increase in tidal volume (Vt) from 0.42 ± 0.01 liters to 1.0 ± 0.02 liters. Respiratory rate was significantly lower during PSV. Spo2 between the FET maneuvers was significantly higher during PSV as compared with the control session. Spo2 decreases after FET were significantly larger during the control session (nadir: 91.8 ± 0.7%) than during the PSV session (93.8 ± 0.6%). Maximal pressures decreased during the control session (from 71.9 ± 6.1 to 60.9 ± 5.3 cmH2O, and from 85.3 ± 7.9 to 77.5 ± 4.8 cmH2O, for Pimax and Pemax, respectively) and increased during the PSV session (from 71.6 ± 8.6 to 83.9 ± 8.7 cmH2O, and from 80.4 ± 7.8 to 88.0 ± 7.4 cmH2O, for Pimax and Pemax, respectively). The decrease in Pemax was significantly correlated with the severity of bronchial obstruction as evaluated based on baseline FEV1 (% predicted). Forced expiratory flows did not change after either CPT session. The amount of sputum expectorated was similar for the two CPT sessions (5.3 ± 5.3 g vs 4.6 ± 4.8 g after the control and PSV session, respectively; NS). Fifteen patients felt less tired after the PSV session. Ten patients reported that expectoration was easier with PSV, whereas 4 did not note any difference; 2 patients did not expectorate. Nine patients expressed a marked and 5 a small preference for PSV, and 2 patients had no preference. The physiotherapists found it easier to perform CPT with PSV in 14 patients and did not perceive any difference in 2 patients. Discussion. Our study in CF children shows that respiratory muscle performance, as evaluated based on various parameters, decreased after CPT and that significant falls in oxygen saturation occurred after the FET maneuvers despite the quiet breathing periods between each FET cycle. These unwanted effects of CPT were both reduced by noninvasive PSV delivered via a nasal mask. These data suggest that noninvasive PSV in CF patients partly compensated for the additional inspiratory overload resulting from FET, thereby decreasing the inspiratory work of breathing. This may allow the patient, assisted by a physiotherapist, to concentrate on the expiratory effort, which is the key to the efficacy of FET. In our study, Pimax and Pemax decreased significantly after the control session, indicating that CPT was associated with respiratory muscle fatigue. Pimax improved significantly after the PSV session. PSV delivers an unchanging level of positive pressure during spontaneous inspiration, acting as an additional external inspiratory muscle that reduces both the effort of breathing and the cost in oxygen in proportion to the level of pressure used. PSV has been shown to reduce diaphragmatic activity and to prevent diaphragmatic fatigue in chronic obstructive pulmonary disease patients. The improvement in Pimax after the PSV session in our study suggests that PSV may “rest” the inspiratory muscles during CPT. The improvement in Pemax after the PSV session could be explained by the increase in Vt during PSV. During PSV, the Vt tends to the TLC. This allows a larger amount of energy to accumulate, thereby facilitating expiration and decreasing the work of the expiratory muscles. The beneficial effect of PSV on Spo2 can be explained by the large Vts, which can improve ventilation-perfusion mismatching. Conclusions. Our study is the first to show that PSV performed with a nasal mask during the CPT was associated with an improvement in respiratory muscle performance and with a reduction in oxygen desaturation. The improvement in patient comfort may help to improve compliance with CPT in CF patients. respiratory muscles, lung function, children, cystic fibrosis, oxygenation, inspiratory assistance by positive airway pressure, mucus.