The Effects of Gas Switching During Decompression on Decompression Sickness in a Swine Model

Abstract

Abstract : In a porcine model of neurological and cutaneous decompression sickness (DCS), the effect of switching the inert gas to nitrogen during decompression on a heliox dive was examined. Control pigs were dived in a dry chamber environment on a profile of 250 feet of seawater (fsw) for 30 min with 3 decompression stops, 10 min at 120 fsw, 20 min at 60 fsw, and 50 min at 20 fsw. The experimental group underwent the same dive except the breathing mixture was switched to air at 170 fsw. Each group comprised 32 pigs. Animals were observed postdecompression for the onset of neurological and cutaneous DCS. In the control group, 20 pigs developed neurological DCS and 12 manifested cutaneous DCS. In the experimental group, 14 pigs developed neurological DCS and 4 developed cutaneous DCS. The difference in incidence for neurological DCS (0.6 vs 0.4) was not significant using chi-square analysis with Yates' correction (chi squared=1.57; p >0.10), but was smaller than the detection limit of the study design. The difference in incidence for cutaneous DCS (0.4 vs 0.1) was significant (chi squared= 4.08; p <0.05). The results suggest a slight benefit to gas switching in pigs during decompression from a helium/oxygen (heliox) dive of this depth and duration.