New observations on pressure-induced motor disturbances in a small mammal.

New observations on pressure-induced motor disturbances in a small mammal. Undersea Biomed. Res. 4(1):1-8.-Adult and baby mice were subjected to helium pressures up to 120 atm. Pressure-induced changes in motor acitivity (tremors and convulsions) were monitored both visually and with a noninvasive mechanical transducer. A study of five rates of compression showed that adult convulsion pressure thresholds (Pc) fell from a maximum of 90 atm at 20 atm/hr to a minimum of 63 atm at 610 atm/hr, Pc for baby mice rose from 53 atm at 8 days to reach the adult value (85-90 atm) at 21 days of age. Measurements of accommodation, or the decline in motor disturbances at constant pressure, are described. Animals allowed to accommodate for five hours at a pressure 9% higher than the first Pc (85 atm) and then compressed further showed a significantly higher second Pc (114 atm) than animals allowed one hour to accommodate (100 atm). The effects on including nitrogen in the heliox compression mixture on accommodation are also described.