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

Abstract

The cross-sectional area of diaphragmatic muscle fibers was measured using a Quantimet 720 image analysis system in 18 patients with emphysema and 6 control non-emphysematous patients. The technique proved to be an accurate method of measuring muscle fiber area and much more rapid than the previously described methods. The mean cross-sectional area of the muscle fibers in the emphysematous group was 1069.5 .mu.m2 and this was significantly greater than the mean of the control group which was 851.0 .mu.m2. In the emphysematous group 9 patients who died from chronic airways obstruction had a larger mean muscle fiber area than the 9 patients with non-fatal respiratory disease. The emphysematous patients showed a marked increase in the number of very large muscle fibers (2000-2200 .mu.m2) in the diaphragm and also an increased variation in size from fiber to fiber. The increase in muscle fiber size showed a positive correlation with ventricular weight but not with the amount of emphysema in the lungs. Although the excursion of the diaphragm is reduced in emphysema the muscle fibers apparently do not atrophy but undergo work hypertrophy. This is presumably due to the horizontal shortening of the muscle fibers, when the diaphragm is working at a poor mechanical advantage, because it cannot descend normally in emphysematous patients.