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 analysis was used after aerosol exposures to bronchoconstrictor methacholine (Mch), except that φ depended also on increased Raw. In conscious mice, Ve (0.24 ml) doubled after Mch (50–125 mg/ml) aerosol exposure with constant Vt, frequency (f), ΔPb, and Raw. In anesthetized mice, in addition to an increased Ve, repeated 100 mg/ml Mch exposures increased both ΔPb and Raw and decreased f to apnea in 10 min. Thus conscious mice adapted to Mch by limiting Raw, while anesthesia resulted in airway closure followed by diaphragm fatigue and failure.
Aerosol exposure during surgical tracheotomy with and without laminar air flow