Whole-body plethysmography revisited

Whole-body plethysmography (WBP) is an established method to determine physiological parameters and pathophysiological alteration of breathing in animals and animal models of a variety of diseases, reaching from pulmonary diseases to complex neurological syndromes. Although frequently used, there is ongoing debate about what exactly is measured by whole-body-plethysmography and how reliable the data derived from this method are? Here, we designed a simple device that can serve as an artificial lung model that enables a thorough evaluation of different predictions about and around whole-body plethysmography. Using our lung model, we confirmed that during WBP two components contribute to the pressure changes detected in the chamber: 1) the increase of the pressure due to heating and moistening of the air, termed as conditioning, during inspiration; 2) changes of chamber pressure that depend on airway resistance. Both components overlap and contribute to the temporal pressure-profile measured in the chamber or across the wall of the chamber. Our data showed that a precise measurement of the breathing volume appears to be hindered by at least two factors: 1) the unknown relative contribution of each of these components; 2) not only the air in the inspired volume is conditioned during inspiration, but also air within the residual volume and death space that is recruited during inspiration. Moreover, our data suggest that the expiratory negative pressure peak that is used to determine the so called "enhanced pause" (Penh) parameter is not a measure for airway resistance as such but rather a consequence of the animals response to the airway resistance, using active expiration to overcome the resistance by a higher thoracic pressure.