Assessment of diaphragmatic contraction using a non-invasive piezoelectric contact sensor

The use of a contact piezoelectric sensor (accelerometer) to study the mechanical properties of the canine diaphragm is presented. This study determined whether it is possible to monitor the dynamic diaphragmatic function via a non-invasive sensor. For this, the contact sensor (CS) signal on the rib cage is compared with direct measurements of the diaphragmatic muscle length, made by sonomicrometry. Experiments were performed in three pentotarbital-anesthetized mongrel dogs. Length changes were measured using a pair of piezoelectric crystals implanted into the costal diaphragm. The movement of the chest wall, due to the diaphragm contraction, was measured with a piezoelectric contact sensor positioned on the costal wall. In previous works, it have been shown that beginning of inspiratory and expiratory stages were indicated with inflexion points in the contact sensor (CS) signal. Two specific algorithms have been developed to determinate the contraction and relaxation periods in the two signals. The diaphragm length (DL) algorithm has been validated, using a simple replication reliability study (SRRS), by means of manually measures done in the DL signal by a specialist. Finally, a SRRS has been applied between DL and CS signals algorithms measures. Results suggest that it would be possible to evaluate the diaphragmatic function by a non-invasive piezoelectric contact sensor.