Comparison of Two Methods to Compute Respiratory Volumes Using Optoelectronic Plethysmography

Plethysmography is an indispensable component of clinical lung function testing. However, lung volume measurement in the supine position using an optoelectronic system requires the placement of reflective markers on the anterior and lateral torso surface. The conventional method computes breath-by-breath changes in the volume between the markers and the bed, which serves as the reference plane. In contrast, the surface method consists of measuring the volume delineated by the surface area of the marker network at the onset and end of inspiration. We compared these 2 methods to spirometry during spontaneous breathing in 11 healthy volunteers and in 14 patients receiving routine visits for neuromuscular disease. Bland-Altman plots showed that agreement with spirometry was better for the surface method that the conventional method. Our results open up prospects for integrating these methods in the development of new devices.