End-expiratory and tidal volumes measured in conscious mice using single projection x-ray images

The evaluation of airway resistance (Raw) in conscious mice requires both end-expiratory (Ve) and tidal volumes (Vt) (Lai-Fook SJ and Lai YL. J Appl Physiol 98: 2204–2218, 2005). In anesthetized BALB/c mice we measured lung area (AL) from ventral-to-dorsal x-ray images taken at FRC (Ve) and after air inflation with 0.25 and 0.50 ml (ΔVL). Total lung volume (VL) described by equation: VL = ΔVL + VFRC = KAL1.5 assumed uniform (isotropic) inflation. Total VFRC averaged 0.55 ml, consisting of 0.10 ml tissue, 0.21 ml blood and 0.24 ml air. K averaged 1.84. In conscious mice in a sealed box, we measured the peak-to-peak box pressure excursions (ΔPb) and x-rays during several cycles. K was used to convert measured AL1.5 to VL values. We calculated Ve and Vt from the plot of VL vs. cos(α − φ). Phase angle α was the minimum point of the Pb cycle to the x-ray exposure. Phase difference between the Pb and VL cycles (φ) was measured from ΔPb values using both room- and body-temperature humidified box air. A similar a...