Structural variation in the named bronchi of the left lung. A morphometric study.

In order to establish whether or not the named bronchi of the left lung differ structurally from each other, their proportions of cartilage, gland and muscle in normal and chronic bronchitic patients were measured. In the normal subject the lower lobe bronchus contains proportionally more muscle than either the upper lobe bronchus or the segmental bronchi. Its proportion of cartilage is less than that of the main and upper lobe bronchi, and in this respect it is similar to the segmental bronchi. The proportions of gland in the main, upper and lower lobe bronchi are the same. There is no difference between the tissue proportions of the segmental bronchi of the upper and lower lobes. In chronic bronchitics the proportion of gland is increased, and in many cases there is also an increase in muscle. The relatively high proportion of muscle in the lower lobe bronchus is no longer apparent, and its proportion of cartilage is greater than in the normal subject. The main and upper lobe bronchi contain a higher proportion of gland than the lower lobe bronchus and the segmental bronchi. The proportions of the components in the upper and lower segmental bronchi are again similar. It is concluded that in the left lung the tissue proportions of the named bronchi vary. In particular, the normal lower lobe bronchus is characterized by a relatively high percentage of muscle, and a similar cartilage content to the segmental bronchi. Care is therefore needed in selecting airways for morphometric studies.