Decompression-induced decrease in nitrogen elimination rate in awake dogs

Abstract

Formulation of safe decompression procedures still requires unproven assumptions regarding both gas equilibration rates and the associated ascent criteria. Although the assumption of symmetry of uptake and elimination rates has been suspect for several years, few data are available. Measurements of actual mixed venous blood nitrogen content [vN2] during compression and following decompression in chronically catheterized awake dogs have clearly demonstrated that desaturation is markedly slower than saturation, and that this effect can be imposed by decompression. The disappearance of arteriovenous nitrogen concentration differences during desaturation following a decompression that produced decompression sickness indicates that cardiopulmonary and cardiovascular changes induced by mechanisms associated with decompression per se can potentiate its deleterious effects. Current US practices do not provide for such asymmetry, while those used in the UK have incorporated this in their models for the last decade.

Inert Gas Exchange and Bubbles

“…Thus, the elimination of nitrogen from a bubble is slower than the elimination of nitrogen dissolved in tissue. This has been demonstrated in both animal [65][66][67] and human studies. [68][69][70] Most decompression models assume that bubbles do not form, but when bubbles are present, diffusion between bubble and tissue cannot be ignored.…”

A New Dynamical Theory of Decompression

“…The gas phase in the slowest compartments can remain several hours. All that is in good adequacy with practical rules such as "not doing efforts after a dive" and gives a quantitative justification to the well-known fact that desaturation is not symmetrical from saturation [16]. For each compartment, lower and upper limit are given for several values of the parameters Each column correspond to a pair of parameters (pressure gradient and inner halftime)…”

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

“…Therefore, Fahlman et al, (2001) used one exponential time constant to describe the kinetics, which satisfactorily explained the observed DCS incidence. However, since other DCS modelling efforts (Tikuisis et al, 1991;Himm et al, 1994;Lillo et al, 1997;Parker et al, 1998;Lillo and Parker, 2000) and studies using direct physiological or physical measurements of gas fluxes in animals (D'aoust et al, 1976;Novotny et al, 1990) suggest that the uptake and elimination of gases are asymmetrical, we wanted to perform a critical evaluation of our previous model in an attempt to gain further understanding of gas fluxes in hyperbaria. Studying gas kinetics and DCS risk in this data set is particularly interesting because of the combination of gas fluxes occurring during conventional decompression and fluxes due to active metabolism of gas during biochemical decompression.…”