ABSTRACT
Accurate measurement of pulmonary ventilation requires the use of devices such as masks or mouthpieces coupled to the airway opening. These devices may alter ventilation, and their encumbrance is frequently inconvenient. It would be desirable for some purposes to have measurements that are noninvasive and nonencumbering. Devices that sense respiratory excursions at the body surface can do this, although at some cost of accuracy. Konno and Mead (1967) extensively evaluated a "two-degree-of-freedom" model of chest wall motion. They measured anteroposterior dimensions of the rib cage and abdomen and summed the two signals to obtain tidal volume. Ventilation could be estimated to within 10% of actual ventilation during quiet breathing and exercise when a given posture was maintained. Smith and Mead (1986) later described a third degree of freedom of chest wall motion; axial displacements of the chest wall due to postural movements of the spine and pelvis could cause large displacements of the rib cage and abdomen. This third degree of freedom can be assessed from the distance between the xiphisternal junction and pubic symphysis, and this approach provides a reasonable degree of accuracy with measurements of ventilation in freely moving subjects.
