Journal of Applied Physiology, Vol 62, Issue 2 444-450, Copyright © 1987 by American Physiological Society
Frequency-dependent effects of hypercapnia on respiratory mechanics of cats
P. D. Sly, J. H. Bates, T. Kochi, S. Okubo and J. Milic-Emili
The effect of increasing arterial partial pressure of CO2 (PaCO2) on
respiratory mechanics was investigated in six anesthetized, paralyzed cats
ventilated by constant-flow inflation. Respiratory mechanics were studied
after end-inspiratory occlusions. Zero frequency resistance (Rmax),
infinite frequency resistance (Rmin), and static elastance (Est) were
calculated for the respiratory system, lung, and chest wall. Alveolar
ventilation was manipulated by the addition of dead space to achieve a
range of PaCO2 values of 29.3-87.3 mmHg. Cats did not become hypoxic during
the experiment. Under control conditions marked frequency dependence in
Rmax, Rmin, and Est of the respiratory system, lungs, and chest wall was
demonstrated. The chest wall contributed 50% of the total resistance of the
respiratory system. With increasing PaCO2 the only resistance observed to
increase was Rmax of the lung (P less than 0.01). There were also no
changes in the static elastic properties of either the lungs or the chest
wall. These results suggest that hypercapnia increases resistance by
changes in the lung periphery and not in the conducting airways.
