Role of metabolic gases in bubble formation during hypobaric exposures

1 Universities Space Research Association, Division of Space Life Sciences, 2 Environmental Physiology Laboratory, Life Sciences Research Laboratories, National Aeronautics and Space Administration Johnson Space Center, and 3 Division of Computing and Mathematics, University of Houston Clear Lake, Houston, Texas, 77058 Our hypothesis is that metabolic gases play a role in the initial explosive growth phase of bubble formation during hypobaric exposures. Models that account for optimal internal tensions of dissolved gases to predict the probability of occurrence of venous gas emboli were statistically fitted to 426 hypobaric exposures from National Aeronautics and Space Administration tests. The presence of venous gas emboli in the pulmonary artery was detected with an ultrasound Doppler detector. The model fit and parameter estimation were done by using the statistical method of maximum likelihood. The analysis results were as follows. 1 ) For the model without an input of noninert dissolved gas tissue tension, the log likelihood (in absolute value) was 255.01. 2 ) When an additional parameter was added to the model to account for the dissolved noninert gas tissue tension, the log likelihood was 251.70. The significance of the additional parameter was established based on the likelihood ratio test ( P