ABSTRACTS 99

TITLE: Quantifying the Capillary Changes in Emphysema: Comparison oP Scanning Electron Microscopy Image Analysis to Linear Intercepts and PV Curves

AUTHORS: Dean Sehraufnagel, M.D. and Alice Schmid, B,S.

TITLE: Section of Respiratory and Critical Care Medicine, Department of Medicine, The University of Illinois at Chicago, ?.0. Box 6998, Chicago 60680.

INTRODUCTION. Although loss of capillaries is recognized to parallel the loss of other elements in the lung parenohyma in pulmonary emphysema, the inability to quantify and describe this damage has hampered study I~ this area. Established methods of measuring emphysema include measurement of mean linear intercepts and pressure volume curves. The former method is not sensitive, and the latter is difficult to use to compare degrees of emphysema, let alone ca~+illarity, Tranamission electron microscopy morphometry is difficult because of the relatively lOW magnifications and the need to sample large areas. We undertook a scanning elec- tron mlcrosc~py-image analysis study to quantify the chan,i~es in the lung capillaries.

polynomial pressure-volume regression and it Is more sensitive than the mean linear intercept method. Furthermore, image analysis of scanning electron micrographs is the only method which d i rec t l y measures and allows v isual izat ion o f the capillarles.

METHODS. W~+eompared 2 groups of female, Sprague- Dawley, 50 day-o ld ra ts . One group was given 42 un i t s elai~tase in 0.25 ml o f sa l i ne and the o ther group wa~ given sal ine alone endotracheally. After 30 daya,~alf the animals in each group were used for vascular casting with methacrylate and the other ~alf were used for PV curves and organ welgh~9. Pressure was regressed against volume, From paraffin sections fixed at 25 cm H20 pres- sure, mean linear intercept measurements were carried out. The scanning electron microscopy images were directly transmitted to a DEC VAX computer with Deltapro image analysis software. Each image had one o f 255 leve ls o f gray assigned to each of its 65,536 pixels. A binary file was constructed which assigned white to all pixels with a relative number on the gray scale of 80 or greater and black to all numbers 79 or less. This ratio was compared in the emphysema and saline animals, for the parenchymal and pleural surfaces. Two-hundred photos at 1200 magnification were taken.

RESULTS. The polynomial pressure-volume equation contained pressure, pressure squared, treatment and the interactive term, pressure and treatment. Each component was2signifieant at the p <0.001 level; the model R =0.78. The mean linear intercept measurement of the alveolar areas was I0.4 (SE= 0,45) for emphysema and 12.2 (SE:0.54) for saline (p=0.02). The image analysis ratio of white area to total area was 0.639 (SE=O.013) for the emphysema animals and 0.673 (SE=O.O07) for the saline animals p<0.0001,

CONCLUSION: Even though all 3 of the methods dis- tingulshed between the emphysema and normal animals, the image analysis ratio was the most sensitive. The image analysis density is more useful to compare the degree of emphysema than the

Figure 1. Scanning electron micrograph of capillary casts from emphysematous lungs at 600 magnification. Scale bar = 10 um.

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Sigure 2, Binary image of figure I at 440 magnlflcation. Scale bar = 10 urn.