[abstract] THE KANGAROO RAT AS A MODEL FOR TYPE I DECOMPRESSION SICKNESS.

Abstract

An animal is needed for testing decompression schedules which is smaller and cleaner than the goat and yet provides a subjective display of decompression-induced distress mediated by the same mechanism as limb bends in man. Tail-biting in the kangaroo rat Dipodomys Merriami has been investigated in over 20 of these small desert rodents native to West Texas -before, during and after decompression. When the depth and time of exposure exceeded certain well defined limits, the frequency of tail-biting was found to increase from less than 10 per hour to once per second and yet returned to normal levels upon recompression. Some mature kangaroo rats (35-40 gm.) have a minimum tail-biting depth for no-stop decompression on air of 35-40 feet of sea water -comparable to 33-38 fsw for the minimum bends depth for man. For shorter exposure times, many animals could be selected with depth-time limits lying within 20% (pressure-wise) of those depicted on the standard Van der Aue curve for air diving. The correlation with man was found to extend to heliox mixtures -also over the whole range of exposure times. Examination of excised tails from "bent" rats indicated bubbles in the tendon fibres. Hence the kangaroo rat is recommended as a cheap, clean and very small animal with both a comparable inherent susceptibility to decompression sickness as man and similar time response to hyperbaric exposure. Moreover tail-biting would certainly seem more realistic as an indication of marginal symptoms than the death-or-recovery end-point often used in other small animals.