Submitted on July 6, 2007
Accepted on September 12, 2007
END-EXPIRATORY AND TIDAL VOLUMES MEASURED IN CONSCIOUS MICE USING SINGLE PROJECTION X-RAY IMAGES
Stephen J. Lai-Fook1*, Pamela K. Houtz1, and Yih-Loong Lai2
1 Dept. of Biomedical Engineering, University of Kentucky, Lexington, Kentucky, United States
2 Department of Physiology, National Taiwan University College of Medicine, Taiwan - Republic of China
* To whom correspondence should be addressed. E-mail: laifook{at}email.uky.edu.
The evaluation of airway resistance (Raw) in conscious mice requires both end-expiratory (Ve) and tidal volumes (Vt) (Ref. 22). 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 (
VL). Total lung volume (VL) described by equation: VL = VL + 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 (Pb) 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 (
- 
). Phase angle was the minimum point of the Pb cycle to x-ray exposure. , phase difference between the Pb and VL cycles, was measured from Pb values using room and body temperature humidified box air. A similar analysis was used after aerosol exposures to bronchoconstrictor methacholine (Mch), except that depended also on increased Raw. In conscious mice, Ve doubled after Mch (50-125 mg/ml) exposure with constant Vt, frequency (f), Pb and Raw. In anesthetized mice, in addition to an increased Ve, repeated 100 mg/ml Mch exposures increased Pb and Raw and decreased f to apnea in 10 minutes. Thus conscious mice adapted to Mch by limiting Raw, while anesthesia resulted in airway closure followed by diaphragm fatigue and failure.
