Studies on Gangrene Following Cold Injury. V. The Use of Fluorescein as an Indicator of Local Blood Flow: Fluorescein Tests in Experimental Frostbite 1

Abstract

The application of the fluorescein test to the study of frostbite has been described recently by Lange and Boyd (1). In the course of studies of experimental frostbite carried on in this laboratory, certain of the results obtained with the fluorescein test have been difficult to explaih on the basis of interpretations suggested by the proposers of the method. Two groups of experiments were undertaken in order to study certain aspects of fluorescein exchange not already reported in the literature. The first group of experiments consisted of studies on normal rabbits of skin fluorescence and fluorescein distribution in body fluids: these have been presented previously (2). The present paper reports the second group of studies carried out on normal rabbits and on rabbits subjected to severe cold injury. METHODThe techniques employed in the fluorescein test, the measurement of skin fluorescence after the injection of fluorescein, and the analysis of body fluids for fluorescein were described previously (2). Skin cence was detectable in hair-free areas of the skin within a few seconds after the beginning of injection. The intensity of color became maximal in about 15 minutes. The decline of intensity was, at first, rapid and then progressively more gradual over a period of 2 to, 2Y2 hours.In the rabbit ear, the regions which glowed most intensely were those relatively free of large blood vessels. The larger blood vessels stood out as dark streaks which could be obliterated by prescure with a glass slide. The areas rendered ischemic by pressure showed no decrease of fluorescence. Fuorescence in frostbitten ears of rabbitsThe influence of injury by frostbite upon the distribution of fluorescein after intravenous injection was studied on rabbits' ears. Frostbite was produced by immersing the distal 3 to 4 cm. of the ears in a freezing mixture consisting of alcohol, ethylene glycol, and water with sufficient solid carbon dioxide added to bring the temperature between -520 C. and -70°C. The details of the method of producing standard cold injury and the general course of changes following such injuries have been described in previous reports (3,4).Abnormalities in the distribution of fluorescein in the frostbitten portion of rabbits' ears included decreased rate of entrance of dye, slower rate of removal, and lower maximum intensity of fluorescence than was observed in the normal ear. Observations made at varying intervals after injury showed that the local changes, which were responsible for the abnormalities of fluorescein distribution, undergo modification with time. The photographs in Figure 1 illustrate the delayed penetration and exit of the dye as well as the differences in results of identical tests made immediately after inquiry and repeated 268

Studies on Gangrene Following Cold Injury. Ix. The Effect of Rutin and Other Chemical Agents on the Course of Experimental Frostbite in Rabbits 12

“…In the case of frostbite, direct observations of capillaries (16), as well as indirect evidence based upon tests with fluorescein (32), indicate that the slowed rate of protein loss in the later stages of injury depends upon reduction of total area available for filtration of material from the capillaries.…”

Studies on Gangrene Following Cold Injury: Vi. Capillary Blood Flow After Cold Injury, the Effects of Rapid Warming, and Sympathetic Block 1

“…Tests of the local circulation in coldinjured regions with intravenously injected fluorescein show that the exchange of this dye between blood and interstitial fluid is impaired during the interval when the minute volume blood flow is greater than that in comparable uninjured regions (2,3). Early arrest of blood flow in regions injured by cold has been variously ascribed to "conglutination" of red-cells (4), to capillary stasis (5), and to intravascular clotting (2).…”