Compartmental analysis of breathing in the supine and prone positions by optoelectronic plethysmography

Optoelectronic plethysmography (OEP) has been shown to be a reliable method for the analysis of chest wall kinematics partitioned into pulmonary rib cage, abdominal rib cage, abdomen, and right and left side in the seated and erect positions. In this paper, we extended the applicability of this method to the supine and prone positions, typically adopted in critically ill patients. For this purpose we have first developed proper geometrical and mathematical models of the chest wall which are able to provide consistent and reliable estimations of total and compartmental volume variations in these positions suitable for clinical settings. Then we compared chest wall (CW) volume changes computed from OEP(deltaVCW) with lung volume changes measured with a water seal spirometer (SP) (deltaVSP) in 10 normal subjects during quiet (QB) and deep (DB) breathing on rigid and soft supports. We found that on a rigid support the average differences between deltaVSP and deltaVCW were -4.2% +/- 6.2%, -3.0% +/- 6.1%, -1.7% +/- 7.0%, and -4.5% +/- 9.8%, respectively, during supine/QB, supine/DB, prone/QB, and prone/DB. On the soft surface we obtained -0.1% +/- 6.0%, -1.8% +/- 7.8%, 18.0% +/- 11.7%, and 10.2% +/- 9.6%, respectively. On rigid support and QB, the abdominal compartment contributed most of the deltaVCW in the supine (63.1% +/- 11.4%) and prone (53.5% +/- 13.1%) positions. deltaVCW was equally distributed between right and left sides. In the prone position we found a different chest wall volume distribution between pulmonary and abdominal rib cage (22.1% +/- 8.6% and 24.4% +/- 6.8%, respectively) compared with the supine position (23.3% +/- 9.3% and 13.6% +/- 13.0%).