Chest Physiotherapy in Cystic Fibrosis: Improved Tolerance with Nasal Pressure Support Ventilation
by B. Fauroux, M. Boule, F. Lofaso, et al, Pediatrics, 1999;103:658–659.
Chest physiotherapy (CPT) is an essential component of a treatment regime for individuals with cystic fibrosis. The goal of CPT is to help improve ventilation and mucociliary clearance by removing the viscous pulmonary secretions that obstruct the airways. The accumulation of the thick secretions is one of the major limiting factors in cystic fibrosis. In this study, the authors evaluated the forced expiratory technique (FET), which is one of several CPT techniques used to treat cystic fibrosis. Pryor and Webbes 1 first described the FET. It consists of one or two forced expirations or huffs, followed by quiet breathing. The secretions that reach the upper airways can then be expectorated by one or two coughs or huffs. The FET is thought to promote movement of the secretions through changes in thoracic pressure and airways dynamics. The authors suggest that CPT, specifically FET, imposes additional respiratory work that may pose a risk of respiratory muscle fatigue in patients with severe respiratory disorders such as CF.
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 goals of this study were 1) to evaluate the respiratory muscle fatigue and oxygen desaturation during CPT and 2) to determine whether noninvasive PSV could relieve the potential adverse effects of CPT.
The study included 16 patients with cystic fibrosis (nine girls and seven boys). The patients, who were in stable condition, were 6 to 18 years of age. The subjects were included in the study if they were at their baseline status, in a clinically stable phase of their disease. The sample seems to be one of convenience obtained from the patient population at the sponsoring medical facility. Nine participants were colonized with Pseudomonas aeruginosa and seven with Burkholderia cepacia. Inhaled bronchodilators and corticosteroids had been used on a long-term basis by some of the sample. Eleven of the patients were receiving rhDNase. One patient, who was on a lung transplant list, had been receiving nocturnal nasal PSV for the last six years. None of the patients changed their usual treatment routine during the study period. The patients were divided into a “severe” group and a “moderately severe to normal” group; assignment to a group was based on whether their forced expiratory volume in one second (FEV1) was <40% (severe) or >40% (moderately severe to normal) of the predicted values. 2
For a specific method of CPT, the authors used the FET, which consisted of one or more slow, active expirations starting near total lung capacity and ending near residual volume. The physical therapist assisted the expirations by applying pressure to the child’s ribs. 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 included 10 to 15 FET maneuvers separated by rest periods of 10 to 20 breathing cycles each. All patients were familiar with this CPT technique and used it at home once or twice a day.
During the study, each participant received two CPT sessions in random order on two different days, at the same time of the day, with the same physical therapist. In one of the two daily sessions, PSV was provided. During these sessions the individuals received PSV through a nasal mask using the pressure support generator ARM25, which was designed for patients with acute conditions (TAEMA, Antony, France). The control session was conducted with no nasal mask or PSV. No supplemental oxygen was given in either CPT session. After each CPT session, the patients and the physical therapist were asked to report their subjective impressions of the CPT sessions with or without the use of nasal PSV. Lung function and maximal inspiratory pressures (PImax) and expiratory pressures (PEmax) were recorded before and after each session.
Data were analyzed using the paired t test for comparison of the parameters measured before and after each PSV or control session with each child serving as his or her own control. Student’s t test was used to compare the two disease severity groups. A one-way analysis of variance with repeated measures was used to evaluate the time-course parameters during the various periods of the PSV and control sessions. Comparisons of these parameters during the various periods of the PSV and control sessions were performed using two-way analysis of variance. Correlations between variables were analyzed using the least squares linear regression technique.
Results showed that the mean lung function parameters were comparable among all patients before the PSV and control sessions. Baseline pulse oximetry (SpO2) was significantly correlated with the baseline vital capacity (percent predicted) and FEV1 (percent predicted). PSV was associated with an increase in tidal volume from 0.42 ± 0.01 to 1.0 ± 0.02 L. Respiratory rate was significantly lower during PSV. SpO2 between the FET maneuvers was significantly higher during the PSV as compared with the control session. SpO2 decreases after FET were significantly larger during the control session than during the PSV session. Maximal pressures decreased during the control session, from 71.9 ± 6.1 to 60.9 ± 5.3 cm H2O and from 85.3 ± 7.9 to 77.5 ± 4.8 cm H2O for PImax and PEmax, respectively. These values increased during the PSV session, from 71.6 ± 8.6 to 83.9 ± 8.7 cm H2O and from 80.4 ± 7.8 to 88.0 ± 7.4 cm H2O for PImax and PEmax, respectively. The decrease in PEmax was significantly correlated with the severity of bronchial obstruction as evaluated based on baseline FEV1 (percent predicted). Forced expiratory flows did not change after either CPT session. There was no difference in the amount of sputum produced during the two sessions.
The authors of this study stated that the findings showed that respiratory muscle performance in individuals with cystic fibrosis, as measured by various parameters, decreased after CPT (FET) and that significant falls in oxygen saturation occurred after the FET maneuvers despite the quiet breathing periods between each FET cycle. The authors indicated that both of these unwanted effects of CPT were reduced by noninvasive PSV delivered by a nasal mask. The authors then concluded that the results signify that the use of noninvasive PSV in individuals with CF may partly compensate for the additional respiratory overload resulting from FET, thereby decreasing the inspiratory work of breathing. The authors stated that this would allow the patient, assisted by a physical therapist, to concentrate on the expiratory effort, which is the key to the efficacy of FET.
In this 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. The improvement in PImax after the PSV session in the study showed that the PSV may allow the inspiratory muscles to “rest” during CPT.
The authors finally concluded that PSV performed with a nasal mask during CPT (FET) was associated with an improvement in respiratory muscle performance and with a reduction in oxygen desaturation. The authors suggested that the improvement in patient comfort might help to improve compliance with CPT among individuals with cystic fibrosis.
Limitations and Implications
The authors’ purposes were 1) to evaluate respiratory muscle fatigue and oxygen desaturation during CPT and 2) to determine whether noninvasive PSV could relieve these potential adverse effects of CPT. Although the study generated data to support these purposes, there are several limitations of the study that may affect the validity of the conclusions.
The sample size for this study was small, and the sample was obtained by convenience. If the sample was larger and more data were generated, then the authors’ conclusions would be strengthened. The range of disease severity in this sample consisted mainly of “severe” to “moderately severe to normal,” as determined by FEV1 values. It would have been helpful to know the distribution of disease severity among the participants. Individuals with cystic fibrosis of a greater variety of degrees of disease severity should have been included to determine if the use of PSV and FET has the same positive effects for all patients with cystic fibrosis. If the authors want to validate the use of PSV with FET for persons with cystic fibrosis as a means to decrease respiratory muscle fatigue and oxygen desaturation, then it would seem important to examine all degrees of severity of the disease.
The authors indicated that the sample group did not change any of their medical treatments, including the use of bronchodilators and corticosteroids, during the study. No mention was made of the possibility that these individuals may have used their bronchodilators or other medication before the treatments. Use of these medicines may have enabled the individuals to demonstrate a more positive effect through the use PSV with FET than what existed as result of the PSV alone.
The precise timing of the sessions was never discussed. The individuals in this study were said to have undergone two sessions a day in random order on two different days, at the same time of the day. If the patients were receiving the session with PSV in the morning before any physical activity, then it is possible that the minimal changes recorded in oxygen desaturation and respiratory muscle fatigue could be affected by the time of day. Resting through the night allows patients to have a reserve of energy or increased tolerance for increased work. The same could be said for someone who received FET without the PSV in the afternoon, when they have gone about their daily routine and now have decreased respiratory muscle strength. The confounding factors must be considered when drawing conclusions about the effectiveness of a treatment method.
The authors use the term “chest physiotherapy” throughout their study. This is a very broad term that includes many other treatment techniques in addition to FET. It would be helpful to many therapists who use other methods, such as percussion/vibration and postural drainage, the vest, or the flutter, to know whether the use of PSV would also assist their patients. Chest physical therapy (chest physiotherapy), specifically the use of percussion/vibration and postural drainage among individuals with cystic fibrosis, is common, and future studies using these methods would be valuable. A concern that arose from reading the authors’ conclusions was that they thought that using PSV would increase compliance for CPT (specifically FET). The statement brings up the question of the availability and the feasibility of using the PSV machine at home. Also, the authors identify the need to have a physiotherapist assisting the patients. Both of these factors will impair the independence of the patient, which is important to many people with cystic fibrosis. Other methods, such as the vest or the flutter, allow for complete independence, and they are feasible in any environment. These factors are important to consider before concluding that one type of treatment and medical device will increase compliance.
This study investigated an important topic for individuals with cystic fibrosis, a severe, progressive respiratory disease. Over time patients will develop more impaired lung function with a decrease oxygen delivery and a decline in the efficiency of their respiratory muscles. Additional studies are needed to further support the use of PSV with other CPT techniques and to examine its effect in patients with all levels of disease severity.
Debra M. Murphy, MS, PT, Boston, Mass