[abstract] SPINAL CORD BENDS, SCUBA DIVING, AND BASIC ISSUES.

Abstract

Brian Hills's expression, "relevant tissue," has gained special meaning in air-decompression studies in sheep and pygmy goats. The type of exposure greatly influences the incidence of specific types of decompression sickness (DCS) when the decompression is not greatly beyond safe limits. The most urgent implication of this finding concerns the risk of spinal cord DCS in short, relatively deep dives likely to be common with compressed-air scuba. The risk to scuba divers is confirmed by the current proportion of "cord bends" among DCS incidents. The cord itself appears to become the dominant (most relevant) tissue under these circumstances. Our findings indicate that other tissues become relevant in other dive profiles. For example, "the chokes" is associated with extraordinary numbers of venous gas bubbles and is rare except following long exposures to compressed air or when shorter exposures involve unusual pressure. The relevant tissues in chokes appear to saturate slowly with nitrogen under ordinary conditions and must have an unusual capacity for that gas. Adipose tissue meets these qualifications. Other relevant tissues can probably be characterized for limb bends (with or without increased intramedullary bone pressure) and dysbaric osteonecrosis. Such analysis should lead to increased understanding of the mechanisms of DCS, better methods of evaluating risks, and improved decompression tables. The significance of gas-elimination studies must depend upon the type of exposure and symptomatology at issue as well as upon the site of measurement. (Supported by the University of Wisconsin Sea Grant College Program.)