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A method for continuously recording the motor activity of pressurized rats was used to monitor their condition after 1) holding pressure constant after compression, 2) decompression, and 3) adding nitrogen prior to holding pressure constant. After procedures 1 and 2 the logarithm of activity plotted linearly against time in two distinct phases. A short initial decline was followed by a slower, longer decline that was incomplete after 5 h. The rate of the second, slower decline was inversely related to the holding pressure and unaffected by prior convulsions. The addition of 4.8 atm N2 was very effective at decreasing the activity at constant pressure compared to a large (43%) decompression step. The slopes obtained from plots of activity against pressure, which provide a measure of the sensitivity of the animal to compression, were unaltered by the early inclusion of 4.8 atm N2 or 0.19 atm N2O but were displaced to higher pressures. Activity appears to be the net result of activity-generating and accommodation processes, and there was no evidence that it was in equilibrium with pressure.

Regional heat flux (intensity of heat flow rate, W m-2) was measured using heat flux transducers affixed to the skin surface at 14 sites on the left arm and 15 sites on both the left leg and the trunk (total of 44 locations) of human subjects during head-out immersion in water at temperatures between 11 and 28 degrees C. The heat flux data and skin temperature data were collected continuously over a 30-min period taking approximately 2.5 min to scan through all transducers in sequence before repeating the process. There were 3 immersions per individual, monitoring the arm or the leg or the trunk. The local measurements of heat flux from each of the body segments were summated and meaned to obtain a value of overall flux for each area of the body for each 2- to 3-min interval. This mean value was taken as the optimal value (Hopt) for any particular body segment. Every permutation of the positions of any 1, 2, 3, 4, or 5 heat flux transducers from the possible 14 or 15 sites was used to obtain a mean value which could be compared to the Hopt over the total duration of each immersion. Comparisons could be made between the best individual sites (Iopt) and Hopt as well as between the overall best site for the group of 10 people (Gopt) and Hopt. All possible permutations could be ranked in ascending order of preference based on a decreasing sum of the squares of the differences between Hopt and either Iopt or Gopt. Confirmation of the validity of this simple ranking system was based on an analysis of the percentage differences between Iopt or Gopt and Hopt. Such an analysis indicated that the better choice of discs when using a small number of transducers was between 3 and 5 sites, affording both reasonable accuracy and practicality. It is recommended that between 3 and 5 discs be used per body segment at specific locations and the calculated heat loss from each segment be weighted according to its area of representation to give a value for the mean rate of total body heat loss. A reasonable level of accuracy was demonstrated using Gopt permutations for measuring both the rate of heat flow as well as the integral of the data to obtain a value of the quantity of heat (Joules) lost from the body.

An investigation into the maximum safe decompression step from oxygen nitrogen saturation to 1 bar was carried out with and without the presence of 0.02 bar carbon dioxide. The series, Islander 1, involved 13 teams of 5, fully informed, male volunteers carrying out simulated dives. One group of 6 teams carried out dives in an atmosphere of 0.4 bar oxygen, balance nitrogen (O2-N2); another group of 7 teams used an atmosphere of 0.38 bar oxygen, 0.02 bar carbon dioxide, balance nitrogen (O2-N2-CO2). The dives consisted of a 48-h stay at 1.7 or 1.8 bar to saturate the tissues, followed by decompression to 1 bar air at 0.5 bar/min. Two decompression parameters were studied; the incidence of decompression sickness (DCS) in the 24 h postdecompression, and the incidence and grade of venous gas emboli (VGE) in the first 6 h postdecompression. The grade of VGE was assessed using the Kisman-Masurel scoring system which produces a bubble grade with the subject at rest and after movement. No significant difference was found in the incidence of DCS between the two groups. Twenty subjects were decompressed from 1.7 bar using each mixture, without signs or symptoms of DCS. However, after decompression from 1.8 bar there were 2 cases of DCS in 10 subjects in the O2-N2 group and 2 cases in 15 subjects in the O2-N2-CO2 group. The incidence of detectable VGE was always lower in the O2-N2-CO2 group at both saturation pressures; at 1.7 bar the VGE incidence was lower by 40% (P less than 0.05) at rest and by 55% (P less than 0.001) after movement. At 1.8 bar the reduction was 3% (NS) at rest and 30% (NS) after movement. The results indicate that decompression from 1.8 bar to 1 bar, with or without the presence of 0.02 bar carbon dioxide, is likely to produce more than 5% DCS.