Definition

We characterized early blood and tissue markers predictive of DCS during the 24 hr period immediately following compression-decompression of female SpragueDawley rats (Bigley et al. 2008). Control animals were maintained at 1 atmospheres absolute pressure ATA (101 kPascal). In animals exposed to 2 (202 kPascal), 3 (303 kPascal), or 4 (404 kPascal) ATA, followed by rapid decompression, increased levels of TNF-α and interferon gamma (IFN-γ) were found in the circulation at 6 hr aft er decompression, while increased levels of only IL-6 were observed at both 6 and 24 hr following decompression. Signifi cant increases in expression of E-selectin and L-selectin as well as ICAM-1 were observed immunohistochemically in the lungs and brains of the rats 6 hr aft er decompression. Th ese levels dropped by 24 hr. Greater increases in expression of E-selectin and L-selectin around vessels and connective tissue were seen at 24 hr aft er decompression in the quadriceps of rats exposed to either 3 or 4 ATA. In cardiovascular disorders and reperfusion damage, the multistep vascular extravasation process is mediated by P-selectin, E-selectin, L-selectin, ICAM-1 and VCAM-1 (Haverslag et al. 2008). Macrophages were seen in high abundance in lung sections of experimental rats (Bigley et al. 2008), suggesting that the endothelial vasculature was activated by leukocytes and that both the macrophages and activated endothelium were sources of TNF-α and IL-6. IFN-γ-inducible proteins, IP-10 and ICAM-1, were elevated in the lungs and brains of all experimental rats at both 6 and 24 hr aft er rapid decompression, with higher expression seen at the earlier observation time. IP-10 was expressed only in the lungs of rats by 24 hr aft er decompression, with the 4 ATA rats showing the most marked expression. ICAM-1 and E-selectin, markers of endothelial activation, were observed in microvessels from the cerebral cortex within 24 hr aft er exposure of male Wistar rats to hypobaric hypoxia (Dore-Duff y et al. 1999). Increased expression of integrin αv, which activates latent transforming growth factor-β (TGF-β) on epithelium in lungs, was found only in the brains of rapidly decompressed rats (Bigley et al. 2008). Notable expression of ICAM-1 was seen only in muscle from rats 24 hr following rapid decompression aft er exposure to 3 or 4 ATA. Th is observation implied that the muscle response to the infl ammatory stimuli requires a period of time longer than 6 hr. Muscle cells present antigens, produce cytokines, and upregulate expression of ICAM-1 (Nagaraju 2001), suggesting that the infl ammatory response could be modulated locally or by immune cells directed to this site. DCS can simultaneously aff ect endothelium at multiple areas, such as the brain, lung,

liver, and skeletal muscle (Dore-Duff y et al. 1999). Lungs (the ultimate fi lter of venous blood) and the liver (the ultimate fi lter of portal blood fl ow) are especially targeted by leukocyte aggregation in severe neurological DCS in pigs (Nyquist et al. 2004). In our study, macrophages were found near vessels, suggesting the migration of immune cells to the site of infl ammation. A signifi cant increase in ICAM-1 levels by 24 hr aft er decompression may also suggest a local response by individual muscle cells. Sections of quadriceps were stained with hematoxylin and eosin (H&E). H&E-stained sections of the quadriceps of rats sacrifi ced at 24 hr post decompression showed macrophages located near blood vessels, which was not common in control slides (Fig. 1); the blood vessels appeared swollen in comparison with those seen in muscle tissue from control rats (rats held in the chamber at 1 ATA but not decompressed). Capillaries in quadriceps tissue of rats exposed to 4 ATA and rapidly decompressed appeared swollen (diameter 10 μm) at 24 hr following decompression. Th is swelling of the vessels was not observed in the vessels of control rats, which remained approximately 7 μm in diameter, or in vessels from skeletal muscle tissues from rats exposed to 2 or 3 ATA (Fig. 1). Th e Masson’s Trichrome stain used to stain sections of the lungs contains four diff erent dyes (fast green, hematoxylin, acid fuchsin and xylidine ponceau) enabling observation of specifi c cell types and organization of connective tissue. Th e trichrome stain of the lung tissues of the experimental and control rats revealed many cell types such as macrophages, neutrophils and eosinophils (Fig. 2). Th e lung tissues from control rats as well as experimental rats had many macrophages located in the alveoli. Notably the alveolar walls of rats exposed to 2 (approximately 3 μm), 3 or 4 ATA (approximately 10 μm), rapidly decompressed and sacrifi ced at 6 or 24 hr, were swollen when compared to alveoli from control rats (< 1 μm).