A new sensor for monitoring chest wall motion during high-frequency oscillatory ventilation

The recently developed technique of fibre optic respiratory plethysmography (FORP) has been modified to monitor the rapid, small amplitude movements o f the chest wall during high-frequency oscillatory ventilation (HFOV). The FORP sensor is an expandable belt encircling the chest, in which is housed a fibre optic loop that alters its radius of curvature as a function of che st perimeter. These curvature changes cause variations in macrobending loss es of light transmitted through the fibre, which are proportional to the ch est perimeter. Dynamic measurement of transmitted light intensity can hence be used to monitor chest wall motion (CWM). For application to HFOV, the d esign of the FORP belt was altered to increase sensitivity and the material s were chosen to maximise macrobending effects induced by the CWM. FORP was tested in four piglets ventilated with HFOV, both in the normal and surfac tant-deficient lung. Measurement of CWM was possible over the full range of tidal volumes and ventilation frequencies used during HFOV. In all cases, the measured frequency of the CWM fell within 3% of the applied ventilation frequency. In addition, the technique was sufficiently sensitive to detect changes in the amplitude of CWM in response to changes in applied tidal vo lume. It is anticipated that application of this new non-invasive measureme nt device will lead to an increased understanding of the dynamics of chest and abdominal wall motion during HFOV. (C) 2000 IPEM. Published by Elsevier Science Ltd. All rights reserved.