Published in the Journal of Applied Physiology, this study examined how the canine rib cage contributes to overall chest wall elastance and hysteresis. Using an isolated rib cage preparation, the researchers applied sinusoidal forcing of the sternum in the midsagittal plane across a range of low frequencies (0.02–2.0 Hz) to characterize force–displacement relationships.
The results showed that rib cage elastance remained nearly constant with forcing frequency between 0.02 and 1.0 Hz, but decreased as the amplitude of motion increased. Hysteresis—defined as the width of the force–displacement loop at zero displacement—was also largely frequency-independent below 1.0 Hz, while increasing with larger forcing amplitudes.
Crucially, removal of respiratory muscles led to a substantial reduction in both elastance and hysteresis. This finding indicates that muscles play a dominant role in determining the mechanical behavior of the otherwise passive chest wall. The excised dog rib cage, when muscles were intact, exhibited dynamic properties closely resembling those of the intact human rib cage and chest wall.
The authors further calculated major and minor stiffnesses of the rib cage in the sagittal plane. These stiffness components differed by a factor of 3–11, with their principal directions aligning closely with the dorsoventral and cephalocaudal axes. Muscle removal reduced the magnitude of these stiffnesses but did not alter their directional orientation.
Overall, the study demonstrates that while respiratory muscles impede motion of the rib cage, they do not change the fundamental pattern of chest wall deformation. These findings provide important comparative insights into respiratory mechanics, supporting the dog as a valuable model for understanding human chest wall physiology.
Source: Kikuchi, Y., Stamenović, D., & Loring, S. (1991). Dynamic behavior of excised dog rib cage: dependence on muscle. Journal of Applied Physiology. Published March 1, 1991.
