Diaphragms were dissected out intact from 29 male and 9 female cadavers at necropsy. Fifteen of the males and eight of the females were grouped as controls, having no history of chest disease. Fourteen of the males and one female gave a history of chronic bronchitis. Point-counting and other methods were employed to measure the mean area, thickness, and volume of the diaphragmatic muscle, excluding the central tendon.
The results showed that the diaphragm was reduced in area, thickness, and volume in the chronic bronchitics, the figures being 350 cm2, 0·29 cm, and 99·7 cm3 respectively in male controls, and 295 cm2, 0·23 cm, and 68·7 cm3 in the bronchitics. In the female controls, the values were significantly lower than in the male controls. The one female bronchitic had a muscle volume of only 40 cm3. The male controls were similar in height to the bronchitics, but their mean weight was higher, being 69·4 kg against 56·0 kg in male bronchitics.
It is concluded that the diaphragm is smaller in chronic bronchitics than in controls at necropsy and that while a major factor in causation is an associated low body weight, other factors such as the mechanical consequences of flattening of the diaphragm, longstanding reduction in physical activity, and other diseases such as cancer may also play a part. No histological changes by non-quantitative methods were found in the diaphragm in the chronic bronchitics, but muscle fibre shrinkage was suspected. By contrast, a few cases of asthma examined to date have shown no evidence of reduction in diaphragm size. The mechanical implications are discussed.
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