Patients with CAO attending the Department of Thoracic Medicine were invited to take part in an inspiratory muscle training program if they fulfilled the following criteria:
1. Poor exercise tolerance that had led to curtailment of usual activities.
2. The ratio of FEV, to VC was less than 40 percent, and the FEV, was less than 50 percent of predicted normal.
3. The baseline FEV, altered by less than 0.2 L after the administration of200 pig of aerosol salbutamol.
4. The CAO was demonstrated to be stable as shown by clinical assessment, FEV/VC measurement and blood gas analysis on at least two occasions four weeks apart.
5. There was no evidence of heart failure clinically on two occasions, and by chest roentgenography on one occasion.
6. Drug treatment had been stable for at least two months and was likely to remain so for at least two months. The intake of corticosteroid drugs, either systemic or topical, did not exclude patients. However, the need for supplemental oxygen therapy and digitalis or diuretic therapy did lead to exclusion.
7. The patient was able to attend the hospital three times weekly for six weeks. website
8. The patient was able to cycle on an ergometer.
Informed consent was obtained from each subject, and the project was approved by the Hospital Ethics Committee.
The breathing valve design was based on the principles described by Nickerson and Keens* but adapted for portable use. It consisted of a plastic plunger which contained lead weights seated over a circular inspiratory port (air intake) in the base of a plastic cylinder (Fig 1). As the patient inspired from the mouthpiece, negative pressure caused the plunger to rise clear of the air intake. Basic physical principles predicted that the threshold pressure would be related to the mass (m) of the plunger and the area (A) of its base by the equation P = m.g/A where g is the acceleration due to gravity.
Figure 1. Threshold pressure inspiratory valve.
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