Reinertsen, R. E., V. Flook, S. Koteng, and A. O. Brubakk. Effect of oxygen tension and rate of pressure reduction during decompression on central gas bubbles. J. Appl. Physiol. 84(1): 351-356, 1998.Reduction in ascent speed and an increase in the O₂ tension in the inspired air have been used to reduce the risk for decompression sickness. It has previously been reported that decompression speed and O₂ partial pressure are linearly related for human decompressions from saturation hyperbaric exposures. The constant of proportionality K (K = rate/partial pressure of inspired O₂) indicates the incidence of decompression sickness. The present study investigated the relationship among decompression rate, partial pressure of inspired O₂, and the number of central gas bubbles after a 3-h dive to 500 kPa while breathing nitrox with an O₂ content of 35 kPa. We used transesophageal ultrasonic scanning to determine the number of bubbles in the pulmonary artery of pigs. The results show that, for a given level of decompression stress, decompression rate and O₂ tension in the inspired air can be traded off against each other by using pulmonary artery bubbles as an end point. The results also seem to confirm that decompressions that have a high K value are more stressful.