Review: Respiratory muscle training does not have important benefits in chronic airflow limitation
ACP J Club. 1992 Sept-Oct;117:49. doi:10.7326/ACPJC-1992-117-2-049
Smith K, Cook D, Guyatt GH, Madhavan J, Oxman AD. Respiratory muscle training in chronic airflow limitation: a meta-analysis. Am Rev Respir Dis. 1992 Mar;145: 533-9.
To determine the effect of respiratory muscle training on the ventilatory strength and endurance, exercise capacity, and functional status of patients with chronic obstructive lung disease.
MEDLINE, SCISEARCH, and relevant reference lists were searched for randomized trials of breathing exercises or physical therapy for patients with obstructive lung disease. Authors of identified articles were approached for information on additional trials.
Articles were included if the patients had a clinical diagnosis of chronic airflow limitation, corresponding approximately to a group mean forced expiratory volume in 1 second (FEV1) < 35% of predicted; if the interventions were resistive breathing exercises or isocapneic hyperventilation; and if the end points were pulmonary function, respiratory muscle strength or endurance, exercise capacity, or functional status. Independent reviewers agreed that 73 of 1085 citations were potentially eligible. 17 articles met the selection criteria. 2 studies were unpublished.
2 independent reviewers extracted data on study quality, patients, interventions, and end points. Additional information was obtained from authors of 14 articles. The effect size of each intervention was calculated (difference of intervention group from control group divided by pooled standard deviation of the outcome measure).
Respiratory muscle strength, measured by maximum voluntary ventilation, was greater in patients receiving respiratory muscle training (8.8 L difference; 95% CI 1.2 to 14.4 L; P = 0.02). Trends in favor of respiratory training, with small effect sizes of ≤ 0.22, were found for FEV1 (41 mL); vital capacity (82 mL); maximum inspiratory pressures (3.0 cm); maximum sustained ventilatory capacity (37.3 L/min); functional exercise capacity (40.7 m); and improvement in quality of life (P for effect sizes > 0.05). In studies of resistance training in which patients were required to control their breathing patterns to achieve a specific flow rate, the effect sizes were moderate-to-large for respiratory muscle strength (effect size, 0.51) and functional status (effect size, 0.65). These effect sizes were larger than effect sizes for studies using uncontrolled air flow rates (P = 0.02 for both end points).
There is little evidence of important benefit to patients from respiratory muscle training. Resistance training that ensures adequate generation of mouth pressure may warrant further study.
Source of funding: No external funding.
Address for article reprint: Dr. K. Smith, McMaster University, Department of Medicine, Chedoke Division, Holbrook Building, Room 90, Box 2000, Hamilton, Ontario L8N 3Z5, Canada.
Exercises should be prescribed at an appropriate frequency, intensity, and duration in order to achieve a physiologic training response. 17 relevant studies of respiratory muscle training met the specific inclusion criteria of this meta-analysis. The major conclusion was "there is little evidence of clinically important benefit of respiratory muscle training in patients with chronic airflow obstruction." 12 of the 17 studies did not, however, include or ensure an appropriate training intensity in that respiratory muscle training was done without guaranteeing an adequate stimulus. It is, therefore, not surprising that improvements in physiologic or clinical outcomes did not occur.
The most important contribution of this meta-analysis deals with the examination of a subgroup of 5 studies that attempted to control or regulate training intensity. Significant improvement in functional status was observed when training intensity was controlled. A secondary conclusion was that increases in respiratory muscle strength, endurance, or both may translate into clinically important improvements with appropriate training intensity (or breathing pattern).
The major question that remains is "what effect does respiratory muscle training have on clinical outcomes?" Although respiratory muscle training cannot be routinely recommended for patients with chronic obstructive pulmonary disease, it is reasonable to consider it for patients with moderate-to-severe symptoms who remain symptomatic despite optimal bronchodilator therapy and participation in a general exercise reconditioning program or who have decreased maximal inspiratory mouth pressure (PImax) without severe hyperinflation. An approach for resistive inspiratory muscle training is as follows: frequency, at least 3 to 4 times per week; intensity, a specific percentage of PImax, for example, 30% to 40%, and duration, 15 to 30 minutes per day (1). All individual or group trials of respiratory muscle training should include measurement of dyspnea and functional status as clinically important outcomes.
Donald Mahler, MD
Dartmouth-Hitchcock Medical CenterLebanon, New Hampshire, USA