Measurement of tidal volumes in case of high frequency oscillation ventilation

摘要

Artificial ventilation can implicate dangerous complications for patients. An increasing number of concepts for lung protective ventilation systems are being developed as a result of this knowledge. The high frequency oscillation ventilation (HFOV) is one possible implementation of such a lung protective ventilation. The physiological background of higher oxygenation is an important element of current research. We present the measurement of physiologically important gas flow and oscillatoric tidal volumes using the lung ventilation system Twinstream~R. In order to use this ventilation system the oxygenation can be optimized. Furthermore, the carbon dioxide exchange can be controlled through the possibility of superposing normo and high frequency ventilation techniques in the Twinstream~R system. The knowledge of oscillatory tidal volumes is important for optimal lung ventilation and simultaneous ventilation gas conditioning. In the area of intensive care the use of a laryngoscope is often necessary in an open set up. Hence, the flow can not be measured directly, because the laryngoscope must be open for medical uses. As a matter of fact, the flow itself can not be measured, therefore the flow has to be determined via the pressure values. The calibration of the flow-pressure-dependence has to take place near real physiological situations. The applied oscillation tidal volumes of high frequency ventilation are quite small in comparison to the volumes of normofrequent ventilation. Both signals are superposed to an additional large noise. The noise is caused by the complex, highly turbulent flow geometry. We present an algorithm for filtering the interesting oscillatory tidal volume. Measurement results are presented for open systems. Differences of oscillatory tidal volume in inspiration and expiration phase are deduced from flow theory.