Collagen and elastin fibers in human pulmonary alveolar walls.

The morphology and morphometric data of collagen and elastin fibers in the pulmonary alveolar walls are presented. Specimens were obtained from postmortem lungs quick-frozen at specified transpulmonary pressures. Collagen was stained by silver, and elastin was stained by orcein. Photomicrographs were composed by computer. Young lungs typically show small collagen fibers that radiate from the "posts," whereas larger fiber bundles traverse the septum irrespective of capillary blood vessels. In older lungs, rings of collagen around the posts appear enlarged. Elastin bundles do not show obvious variation in pattern with age and inflation pressure. Statistical frequency distributions of the fiber width and curvature are both skewed, but the square root of the width and the cube root of the curvature have approximate normal distributions. Typically, for young lungs at transpulmonary pressure of 4 cmH2O, the mean of (width)1/2 (in micron1/2) for collagen fibers is 0.952 +/- 0.242 (SD), that of (curvature)1/3 (in micron-1/3) is 0.349 +/- 0.094. The corresponding values for elastin are 0.986 +/- 0.255 and 0.395 +/- 0.094.

Changes in arteriole in acute and chronic hypoxic pulmonary hypertension and recovery in rat.

After 1 h of exposure to 0.5 atm of pressure, the electron microscopy of intra-acinar arterioles of the young female adult rat showed edema and subendothelial blebs. Pulmonary hypertension developed rapidly with an increase in hemoglobin, hematocrit, and right ventricular weight. By 24 h, there was a threefold increase in the number of fibroblasts within the arteriolar wall, followed during the next 2 days by transformation of the fibroblast through a transitional cell form to a smooth muscle cell. By 1 wk, the neomuscularization was essentially complete. There was further minor thickening and increase in density of the wall over the next 9 mo. On return to 1 atm after prolonged hypoxia, within 4 wk, the smooth muscle of neomuscularized arterioles dedifferentiated but did not disappear. There was a concurrent rapid fall in the pulmonary arterial pressure, hemoglobin, hematocrit, and right ventricular weight. Veins, capillaries, and arteries remained normal. Parallel studies in the male rat during 14 days of hypoxia demonstrated the same phenomena except slightly accelerated over the female. The rapid sequential changes in the arteriole, beginning with subendothelial blebs and wall edema, followed by fibroblast recruitment and transformation into smooth muscle through a transitional cell form, suggest a cascade. The anatomic and physiological responses to hypoxia are not sex related.

Redistribution of canine left ventricular myocardial blood flow in unloaded systole.

The left coronary arteries of dogs were cannulated and perfused with blood from support dogs. The experimental hearts were unloaded by severing the aortas to maximize strains and minimize fiber stress. In each heart we compared the transmural distribution of blood flow in two states: (1) provision of perfusion pressure (40 mm Hg) only during systole and then (2) provision of perfusion pressure throughout the cardiac cycle. The distribution of flow in each of these perfusion states was labeled with a diffusible radioisotope (42K or 86Rb, one labeling the first state; the other labeling the second). Quantitative, paired autoradiography was used to visualize the two flow distributions. The differences between the two distributions after standardization was plotted as differences between activity vs. depth in the myocardium (r = 0.91). This was fitted with a line by least squares, the slope of which was significantly different from zero at the 0.005 level. The magnitude of the gradient of the systolic flow was represented by the ratio of deep to shallow flow. The mean of these ratios was 0.54 +/- 0.12 (95% confidence interval). A graphical analysis shows that the data are consistent with a gradient of extravascular compression across the left ventricular wall.

Computer-derived image compositing.

A computer-derived composite image is obtained of the details contained in successive photomicrographs taken by optical sectioning of the collagen networks in the pulmonary interalveolar wall. Three-dimensional information is therefore contained in a two-dimensional portrayal, providing a basis for computer digital analysis otherwise not readily available.