Equivalent air depth: fact or fiction.

In mixed-gas diving theory, the equivalent air depth (EAD) concept suggests that oxygen does not contribute to the total tissue gas tension and can therefore be disregarded in calculations of the decompression process. The validity of this assumption has been experimentally tested by exposing 365 rats to various partial pressures of oxygen for various lengths of time. If the EAD assumption is correct, under a constant exposure pressure each incremental change in the oxygen partial pressure would produce a corresponding incremental change in pressure reduction tolerance.

Visual recognition thresholds in a compressed air environment.

An experiment was performed to determine the effects of different high-pressure air environments on human binocular visual recognition time as a function of stimulus size and type. Eight adult male volunteers were randomly exposed to high-pressure air environments in hyperbaric test chambers instrumented for visual studies. Analysis of variance for a three-factor repeated-measures design revealed significant main effects for the variables of stimulus size and pressure, indicating that recognition time (RT) increases as a function of decreasing stimulus size and increased pressure.

Use of oxygen for optimizing decompression.

For over 70 years, decompression has been facilitated by the use of elevated oxygen partial pressures. Oxygen has been administered even though little is known about the proper dosage or the way in which this benefit is derived. The historical literature indicates that there is an envelope or narrow range of oxygen partial pressures that can be used.

Species differences in decompression.

In an effort to bring together the diverse laboratory-animal decompression studies, a literature review and statistical evaluation were undertaken. Although 22 different species that had been used in decompression studies were identified, systematic data were available for only 7 of these species: man, goat, dog, guinea-pig, rat, hamster, and mouse. Mathematical functions using physiological data on these seven species were developed to estimate 1) saturation time (the time for the body to equilibrate after an increase in hydrostatic pressure), and 2) no-decompression saturation-exposure limits (the maximum saturation-exposure pressure from which an abrupt return to 1 ATA can be tolerated).