Using a closed nose chamber for airflow measurements in a transfer impedance system

A transfer impedance system has been developed for noninvasive monitoring of the respiratory mechanics in a mouse. The animal´s thorax is exposed to pressure oscillations, which induce a flow through the airway opening. By oscillating with a large range of frequencies, one can determine the frequency response from applied thoracic pressure to generated airflow through the nose. The pressure variations around the thorax can be measured using a piezoresistive transducer, but the authors have not found any flow sensor that is reliable for diminutive flow rates and frequencies up to 200 Hz. The authors´ approach has therefore been to let the mouse breathe into a dosed nose chamber (volume=36 mi). Assuming the gas compression in the nose chamber to be adiabatic, the authors then calculate the airflow from the pressure signal