Evaluation of oxygen and pressure in treatment of decompression sickness in guinea pigs

These experiments examined whether increasing the partial pressure of oxygen (PO2), hydrostatic pressure, or both were responsible for the improvement in effectiveness of recompression treatment previously observed in guinea pigs with increasing depths of air. Unanesthetized male guinea pigs (600-700 g) were subjected to 8.6 atm abs (871 kPa) air dives for 60 min and then decompressed at 1.82 atm (184 kPa)/min to the surface. Subsequently, animals usually displayed hypotension, cardiac arrhythmia, and tachypnea, indicative of a fatal bout (> 95% death rate) of decompression sickness (DCS). Animals that developed DCS were treated by recompressing to depths ranging from 2.5 to 11.6 atm abs (253-1175 kPa), with 14, 28, 42, or 100% O2/balance N2. This design produced PO2's at treatment depth ranging from 0.4 to 3.6 atm abs (41-365 kPa). Upon recompression, recovery of blood pressure, heart rate, and breathing rate generally occurred. The area under the breathing rate vs. time curve was used to examine the effectiveness of treatment over a period of 60 min. A dramatic improvement in recovery over time was observed with increasing recompression depth for all gas mixtures. Analysis indicated that the positive response to depth was related to increasing hydrostatic pressure, increasing PO2 had no statistically significant beneficial effect.