AN OPTICAL TECHNIQUE FOR THE MEASUREMENT OF THORACIC WAIL MOVEMENT DURING HIGH-FREQUENCY JET VENTILATION

Instrumentation for use in high-frequency jet ventilation is not curre ntly capable of providing information suitable for predicting gas exch ange. Whilst techniques for the accurate measurement of tidal volume d uring jet ventilation are now available, the relationship between tida l volume and the efficiency of gas exchange varies with frequency and inspiratory/expiratory time (I:E) ratio. We report technical details o f a new non-invasive instrument capable of accurately measuring displa cement of the thoracic wall at high frequencies and without electrical connection to the patient. It is hoped that use of this instrument wi ll allow the calculation of an efficiency index for the transduction o f airway pressure changes into peripheral expansion. It is also hoped that this index may be of value in predicting the gas exchange respons e to changes in jet parameters.