Morphometry of muscular pulmonary arteries: with special reference to the effects of age and smoking

Structural changes in the pulmonary vessels are usually first evident in the muscular pulmonary arteries. Current methods for quantitating the media, intima and artery size are inadequate because they produce measurements that are affected by artery collapse/constriction or the irregular distribution of intimal abnormality within and between vessels, or they are unacceptably tedious. New techniques were developed in this study to overcome these problems; using a semi-automatic digitising system measurements are produced, directly from histological sections, of medial and intimal area, and artery size is defined as total length of internal elastic lamina (IEL).Technique validation was carried out on thirteen subjects with a variety of cardio-pulmonary disorders. At an appropriate magnification reproducibility of the measurements is excellent. Although only cross-sectional arteries with a well-defined IEL ('digitisable') may be measured these are representative of the total population.The relationship between medial area and artery size is a curved one, best linearised by taking the square root of medial area. This latter relationship was used to investigate the effect of different tissue preparation procedures on the measurements obtained, specifically by comparing slopes of the regression lines. Complete arterial distension by an injection medium caused the IEL to stretch, x 1.5. However, neither the pressure/method used for lung inflation/fixation nor the tissue embedding medium affected the above relationship. Tissue shrinkage was considerable with paraffin embedding/sectioning and negligible with glycol methacrylate in which more arteries were considered 'digitisable'.A new method for expressing intimal abnormality was devised, the Intima Index, namely intimal area expressed as a proportion of the area enclosed by the IEL in its theoretically unwrinkled state. Values range from >0 to ^1 indicating minimal through to total lumen occlusion. Subjects are compared by calculating mean Intima Indices for arteries sub-divided by size.The medial and intimal areas of cross-sectional but 'undigitisable' arteries may be obtained by simply delineating the boundaries of intima-media, and media-adventitia. The total length of the IEL in such arteries is readily obtained by multiplying the length of the intima-media boundary by a factor based on a by-eye estimate of the degree of lamina 'crinkling'.The effects of age and smoking on muscular pulmonary arteries were studied in thirty-two resection specimens and twenty-three autopsy specimens. The amount of medial muscle was unaffected by age, sex or smoking habit, and varied considerably between subjects. In small arteries it correlated with absolute weight of right ventricle.In the autopsy group the amount of intimal abnormality, although very varied, increased with age in all sizes of artery but was most prominent in the smaller ones; contrary to previous reports no lobar differences were evident. These trends were strongest in smokers.The resection group was unsuitable for this study, the results suggesting that superimposed on the effects of age and smoking there is a degree of intimal fibrosis which results either directly or indirectly from the presence of the bronchial carcinoma itself