Abstracts Health Sciences

Mechanical properties of the ventilatory system and their contribution to stability of ventilation.

by L. David. Pengelly

In decerebrate cats, and in consciousman, mechanical properties of the respiratory system were studied during electrical stimulation of the diaphragm. With a fixed stimulus, at constant lung volume, transdiaphragmatic pressure decreases with increasing airflow, and at constant airflow transdiaphragmatic pressure decreases with increasing lung volume. Taking into account these properties of the respiratory system observed during diaphragmatic contraction, and also the pattern and frequency of breathing, it can be predicted that during spontaneous breathing the ventila tory pump should resist changes in tidal volume brought about by mechanical loading to a degree much greater than that expected on the basis of its mechanical properties under passive conditions. Experimental elastic loading of respiration in human subjects verified this prediction, and showed also that this 'stability' to changes in mechanical load increased with increasing ventilation. Stability under these circumstances was increased partly by increased respiratory frequency, and partly by further mechanical changes.