In unrestrained whole body plethysmography (WBP), the spontaneously breathing subject moves freely within a small, closed plethysmograph chamber. Changes in pressure within the chamber along with the flow in and out of the box are measured using pressure transducers and pneumotachographs. Analyzers within the software (iox by emka TECHNOLOGIES) provide endpoints such as breathing frequency (f) and duration, estimates of tidal volume (TV), minute ventilation (MV) as well as a dimensionless quantity known as enhanced pause (Penh). Additional temperature and humidity sensors may be added to compensate thermodynamic effects in the chamber.
In head-out plethysmography (HOP), the subject is conscious, spontaneously breathing, and situated in a conical restraint. The conical restrainers follows the animal’s head shape and ensures that air, displaced by the chest wall motion, is isolated from the total air moving in and out of the lungs, thus permitting true flow measurements. This approach provides a true tidal volume (TV) along with measurements of breathing frequency (f) and minute ventilation (MV).
In double chamber plethysmography (DCP), the head-out set-up is complemented with a head chamber, permitting delivery and containment of aerosolized compounds. A second pneumotachograph is added to the head chamber to measure both nasal flow and thoracic flow. Time shift measurement between thoracic and nasal flow allows additional outcomes to be calculated, including specific airway resistance (sRaw) and specific airway conductance (sGaw).