Journal of Applied Physiology, Vol 67, Issue 3 993-1000, Copyright © 1989 by American Physiological Society
Minimization of lung pressure swings during high-frequency ventilation: a model
M. C. Khoo, S. M. Yamashiro and P. Yamashiro
Department of Biomedical Engineering, University of Southern California, Los Angeles 90089.
The goal of this theoretical study was to develop a simple computational
model for determining the lung pressure excursions that accompany the
maintenance of adequate gas transport through high-frequency airway
oscillations applied via the trachea (HFAO) and by transthoracic means
(HFTO). Respiratory mechanics and gas transport parameters estimated from
the preceding companion study (J. Appl. Physiol. 67: 985-992, 1989) were
used in the model for computing tracheal, alveolar, pleural, and
transpulmonary pressure swings. Comparison of model predictions with
corresponding data obtained in dogs showed close agreement. The
specification of eucapnia as a constraint led to results that were
significantly different from previous findings which had assumed constant
airflow. We used the model to identify "quasi-optimal" strategies for HFAO
and HFTO application in which all pressure excursions were kept below the
corresponding levels produced by conventional mechanical ventilation
operating at 15 breaths/min. The model suggests the application of both
HFAO and HFTO at frequencies substantially lower than the settings commonly
employed in high-frequency ventilation. Application of HFAO at frequencies
ranging from 1 to 4 Hz is recommended, whereas for HFTO the quasi-optimal
range lies between 1 and 1.7 Hz. In patients with chronic obstructive
pulmonary disease, pressure costs during HFAO or HFTO are minimized in the
vicinity of 1 Hz.
