Decompression outcome following saturation dives with multiple inert gases in rats

Abstract

This investigation examined the question of whether gas mixtures containing multiple inert gases provide a decompression advantage over mixtures containing a single inert gas. Unanesthetized male albino rats, Rattus norvegicus, were subjected to 2-h simulated dives at depths ranging from 145 to 220 fsw. At pressure, the rats breathed various He-N2-Ar-O2 mixtures (79.1% inert gas-20.9% O2); they were then decompressed rapidly (within 10 s) to surface pressures. The probability of decompression sickness (DCS), measured either as severe bends symptoms or death, was related to the experimental variables in a Hill equation model incorporating parameters that account for differences in the potencies of the three gases and the weight of the animal. The relative potencies of the three gases, which affect the total dose of decompression stress, were determined as significantly different in the following ascending order of potency: He less than N2 less than Ar; some of these differences were small in magnitude. With mixtures, the degree of decompression stress diminished as either N2 or Ar was replaced by He. No obvious advantage or disadvantage of mixtures over the least potent pure inert gas (He) was evident, although limits to the expectation of possible advantage or disadvantage of mixtures were defined. Also, model analysis did not support the hypothesis that the outcome of decompression with multiple inert gases in rats under these experimental conditions can be explained totally by the volume of gas accumulated in the body during a dive.

Pharmacological Interventions to Decompression Sickness in Rats: Comparison of Five Agents

“…The dosage we tested was nearly double that of Popovic et aI., but we administered ASA for 3 d predive, versus 30 d predive in the Popovic et al study. Our dives saturated the rats with nitrogen (29), whereas the Popovic dives were of 30 min duration, which is subsaturated. We do not know how these differences in protocol may have contributed to the disparate results.…”

“…Dive protocols were derived from the work of Lillo et al, with pressure and duration selected for a high inci dence of DCS in untreated rats of this body mass (29). Rats were exposed in groups of 4 per dive, approxi mately 40 per experimental group, for a total of 633 ani mals for this study.…”

“…min-I results in a high incidence of pulmonary DCS in addition to neurological symp toms. A similar dive depth and duration but with a much more rapid decompression, within 30 s, is likely to induce primarily neurological DCS symptoms (29).…”

Natural history of severe decompression sickness after rapid ascent from air saturation in a porcine model

“…Although it does not achieve significance, there is a trend for increasing animal weight to increase the risk of DCS. Lillo et al (18) found a stronger weight dependence in rats, presumably because of a wider relative weight range. Neither age nor weight change during the dive (a surrogate for respiratory and urinary fluid losses) was significant here.…”

Probabilistic Modelling for Estimating Gas Kinetics and Decompression Sickness Risk in Pigs During H2 Biochemical Decompression

“…Years of experience with the maximum likelihood technique have shown that a large number of experiments are necessary to solve problems such as differences in gas potencies for inducing DCS (Lillo, 1988;Lillo and MacCallum, 1991), or asymmetrical exchange kinetics for compression and decompression (Thalmann et al, 1997;Lillo and Parker, 2000). Since large data sets are not always feasible, some studies have limited the physiological models by either restricting the complexity of the model or restricting the experiments to a small number of compression and decompression sequences (Lillo et al, 1985;Lillo, 1988). The present study likewise separated the experiments into those that featured changes in time spent at constant pressure, and those that featured changes in time spent during decompression.…”