Whole-Body Plethysmography

Respiratory functional analysis in conscious, freely moving, 18- and 31-week-old mice was measured using a whole-body plethysmography technique as described previously.15 The plethysmograph apparatus (emka Technologies, Falls Church, VA, USA) was connected to a ventilation pump to maintain a constant air flow, a differential pressure transducer, a usbAMP signal amplifier, and a computer running EMKA iox2 software with the respiratory flow analyzer module, which was used to detect pressure changes caused by breathing and recording the transducer signal. An initial amount of 20 mL of air was injected and withdrawn via a 20-mL syringe into the chamber for calibration. Mice were placed inside the free-moving plethysmograph chamber and allowed to acclimate for 5 min to minimize any effects of stress-related changes in ventilation. Resting ventilation was measured for a duration of 15 min after the acclimation period. Body temperatures of all mice were assumed to be 37°C and to remain constant during the ventilation protocol.