Comparative biodynamic response of two primate species to the same vibrational environment

Four Rhesus monkeys and three baboons, all young adult males of nearly the same size (8-17 kg), were implanted with an accelerometer on the upper thoracic and lower lumbar spinous process, respectively. Each animal was exposed to sinusoidal vibrations from 4 to 50 Hz at +/- 0.177 and 0.283 rms GZ acceleration levels, respectively, for approximately 30 s/frequency and to the whole vibration spectrum for about 1h X d-1 up to 4 consecutive days. The impedance magnitude, impedance phase and transmissibility between the seat and two spinal accelerometers were compared at the two acceleration levels. The resonant frequency, other impedance characteristics, and the linearity of the response were compared between the two primate species. Modeling parameters, including the damping and elastic coefficients and spring mass, were calculated from impedance data using an established two-mass model. The majority of each species showed a tendency to be less rigid at 0.283 rms Gz than the lower G level, suggesting more decoupling from the seat with higher acceleration. Over most of the frequency range tested, all the animals vibrated out of phase rather than rigidly with the seat. When the impedance and transmissibility results of the two species were plotted and compared, it raised the question of the phylogenicity and the appropriateness of selecting as a biodynamic model the baboon over the Rhesus monkey in the interspecies scaling efforts up to man.