The cross sectional area of diaphragmatic muscle fibres in emphysema, measured by an automated image analysis system.

The cross-sectional area of diaphragmatic muscle fibres was measured using a Quantimet 720 image analysis system in 18 patients with emphysema and six control non-emphysematous patients. The technique proved to be an accurate method of measuring muscle fibre area and much more rapid than the previously described methods. The mean cross-sectional area of the muscle fibres in the emphysematous group was 1069-5 mum2 and this was significantly greater than the mean of the control group which was 851-0 mum2. In the emphysematous group nine patients who died from chronic airways obstruction had a larger mean muscle fibre area than the nine patients with non-fatal respiratory disease. The emphysematous patients showed a marked increase in the number of very large muscle fibres (2000-2200 mum2) in the diaphrahm and also an increased variation in size from fibre to fibre. The increase in muscle fibre size showed a positive correlation with ventricular weight but not with the amount of emphysema in the lungs. It would appear that although the excursion of the diaphragm is reduced in emphysema the muscle fibres do not atrophy but in fact undergo work hypertrophy. This is presumably due to the horizontal shortening of the muscle fibres, when the diaphragm is working at a poor mechanical advantage, because it cannot descend normally in emphysematous patients.