Aug. 13, 2003 - Specific expiratory muscle training (SEMT) improves strength, endurance and distance walked in patients with chronic obstructive pulmonary disease (COPD), according to the results of a randomized trial published in the August issue of Chest.

"There are several reports showing that expiratory muscle strength and endurance can be impaired in patients with COPD," write Paltiel Weiner, MD, from Hillel Yaffe Medical Center in Hadera, Israel, and colleagues. "This muscle weakness may have clinically relevant implications. Expiratory muscle training tended to improve cough and to reduce the sensation of respiratory effort during exercise in patients other than those with COPD."

Of 26 patients with COPD in whom forced expiratory volume in 1 second (FEV1) was 38% of predicted value, 13 patients (50%) received 30 minutes of SEMT training daily, six times weekly, for three months, and 13 patients (50%) in the control group received training with very low load.

After training, the SEMT group fared better than the control group in terms of expiratory muscle strength (from 86 ±; 4.9 cm H2O, P < .005; mean difference from the control group, 24%; 95% confidence interval [CI], 18% to 32%), expiratory muscle endurance (from 57 ±; 2.9% to 76 ±; 4.0%, P < .001; mean difference from the control group, 29%; 95% CI, 21% to 39%), and in the distance walked in six minutes (from 262 ±; 38 to 312 ±; 47 m, P < .05; mean difference from the control group, 14%; 95% CI, 9% to 20%). There was also a small but insignificant increase in the dyspnea index, from 5.1 ±; 0.9 to 5.6 ±; 0.7 (P = .14).

"The expiratory muscles can be specifically trained with improvement of both strength and endurance in patients with COPD," the authors write. "This improvement is associated with increase in exercise performance and no significant change in the sensation of dyspnea in daily activities."

Chest. 2003;124:468-473

Learning Objectives

Upon completion of this activity, participants will be able to:

• Review the role of muscle weakness and muscle training in the symptoms of COPD.
• Evaluate the efficacy of specific expiratory muscle training in the treatment of COPD.

Clinical Context

Inspiratory muscle weakness is a hallmark of COPD. According to the authors of the present study, inspiratory muscle weakness is more common than expiratory muscle weakness in COPD and is thought to be secondary to the hyperinflation of the lungs, which places inspiratory muscles at a functional disadvantage. Weiner and colleagues demonstrated in a study published in Chest on September 11, 2000 that patients' sense of dyspnea was not improved with the combination of aerobic exercise and long-acting bronchodilators, but the addition of specific inspiratory muscle training did improve this outcome.

Expiratory muscle weakness is also important in the pathophysiology of COPD. These muscles are recruited to help maintain a functional reserve of lung capacity for patients. Ramirez-Sarmiento, et al, demonstrated in a paper published in the February, 2002 edition of Thorax that patients with COPD had a generally reduced endurance of expiratory muscles, and this deficit was linked to increased COPD symptoms such as shortness of breath.

The authors of the current study sought to determine if patients with COPD randomized to a specific training program for expiratory muscles had an improvement in pulmonary lab values and functional testing.

Study Highlights

• 22 men and 4 women were recruited into the study. All had an FEV1<50% of predicted value and FEV1/FVC<70% and were diagnosed previously with COPD.
• 13 subjects were randomized to a program of specific expiratory muscle training. This program consisted of 30-minute sessions six times per week for 3 months. Subjects built expiratory muscle strength by breathing through the expiratory port of a threshold muscle trainer. They started at a value of 15% of their maximal expiratory pressure (PEmax). The resistance on the machine was then increased over each session by 5 - 10% until 60% of PEmax was reached. Patients then continued at this level, and as the PEmax changed, the machine's resistance was also calibrated to maintain 60% of PEmax.
• 13 subjects were randomized into the control group, who had twice weekly sessions on the same machine for 3 months, but resistance was kept static at 7 cm H2O. They were encouraged to continue the exercises at home on off days.
• Study outcomes included blood gas analysis, spirometry, a 6-minute walk test, tests of respiratory muscle strength and endurance, and dyspnea symptom indices.
• 1 patient from the exercise group and 2 from the control group dropped out of the study, leaving 23 subjects available for analysis.
• Baseline characteristics between the two groups, including measures of pulmonary function, were similar.
• Blood gas analyses were not different between the exercise and control groups following the treatment period.
• Following the training period, PEmax increased by 21% in the exercise group compared to the control group. The maximal inspiratory pressure was not improved in the exercise group, highlighting the specific expiratory training goals of the program.
• Expiratory muscle endurance also increased by 33% in the exercise group, while the control group's endurance remained stable at the end of the trial.
• Walking distance in 6 minutes improved by 19% in the exercise group by the end of the study. This difference achieved statistical significance. The control group improved to a lesser extent, but their improvement was not significant.
• Exercise training did not improve dyspnea symptom indices compared to the control group. The exercise group's dyspnea symptoms actually grew slightly worse by the end of the study, but these values did not reach significance.
• This study was limited by the fact that it excluded patients with hypercapnea. Also, the expiratory muscle exercise training group had a more intensive training regimen than the control group, which may have prejudiced them to give more effort during pulmonary and exercise testing.

Pearls for Practice

• Inspiratory and expiratory muscle weakness both play a role in symptoms associated with COPD.
• An intensive program for expiratory muscle training can improve pulmonary function testing and exercise tolerance, but does not improve blood gas analysis or dyspnea.