The 12 subjects were studied over a four-day period. In this test, however, unlike the earlier test conducted by Maxwell and Redmond (1979), the subjects performed the chest therapies on themselves both with the mechanical device and using the manual procedure. The manual procedure in this test involved one or two forced expirations "from mid to low lung volume combined with periods of relaxed diaphragmatic breathing" (Pryor, Parker, & Webber, 1981, pp. 123-124).
Where all of the patients included in the Maxwell and Redomond (1979) test sample were in remission from their cystic fibrosis, however, the subjects included in the 1981 test sample were not in remission. In the Pryor, Parker, and Webber (1981) study, 13 of the 14 subjects had been admitted to hospital for acute exacerbation of their bronchopulmonary infection, while the fourteenth subject had been admitted to hospital for an initial assessment. Of the 14 subjects, two refused to participate in the test and were withdrawn from the research sample. Of the 12 subjects remaining in the test sample, nine subjects "required intravenous antibiotics and three required only oral antibiotics" (Pryor, Parker, & Webber, 1981, p. 123).
(1981) reported on a test of the Salford percussor two years subsequent to the Maxwell and Redmond (1979) study. As was true of the Equi-Med percussor tested by Maxwell and Redmond (1979), the purpose of the Salford percussor was to permit cystic fibrosis patients to perform their own chest therapies, as opposed to depending upon the manual performance of chest percussion by health care professionals. In this test of a mechanical device also, 14 subjects were included in the research sample. The 14 subjects in this test sample, however, were somewhat older than were the subjects in the earlier test sample. The subjects in the 1981 test sample ranged in age from 15 years old to 24 years old, with a mean subject age of 19 years old.