Interaction between Lung Mechanics and Gas Exchange by Low Volume High Frequency Pulmonary Ventilation in Patients with Respiratory Failure. (1 Oct 84-30 Sep 85)

摘要

Flow limitation during a forced expiration was simulated by a mathematical model. This model draws upon a pressure-area law obtained in other work, and on known methods of analysis for flow in collapsible tubes. This approach represents an improvement over previous models in that 1) the effects of changing lung volume and of parenchymal/bronchial interdependence are simulated, 2) a more realistic representation of the collapsed airways is employed, 3) a solution is obtained mouthward of the flow limiting site by allowing for a smooth transition from subcritical to supercritical flow speeds, then matching mouth pressure by imposing an elastic jump (an abrupt transition from supercritical to subcritical flow speeds) at the appropriate location, and 4) the effects of levels of effort (or vacuum pressure) in excess of those required to produce incipient flow limitation are examined, including the effects of potential physiological limitation. In patients, dynamic hyperinflation of the lungs occurs during high frequency oscillatory ventilation (HFOV), and has been attributed to asymmetry of inspiratory and expiratory impedances. To identify the nature of this asymmetry, the authors compared changes in lung volume (V sub L) observed during HFOV in ventilator-dependent patients with predictions of V sub L changes from electrical analogs of 3 potential modes of impedance asymmetry.