Submitted on February 5, 2008
Accepted on June 23, 2008
AIRWAY CONSTRICTION MEASURED FROM TANTALUM BRONCHOGRAMS IN CONSCIOUS MICE IN RESPONSE TO METHACHOLINE
Stephen J. Lai-Fook1* and Pamela K. Houtz2
1 Center for Biomedical Engineering, University of Kentucky, Lexington, Kentucky, United States; United States
2 Center for Biomedical Engineering, University of Kentucky, Lexington, Kentucky, United States
* To whom correspondence should be addressed. E-mail: laifook{at}email.uky.edu.
A single projection x-ray technique showed an increase in FRC in conscious mice in response to aerosolized methacholine (Mch) with little change in airway resistance (Raw) measured using noninvasive barometric plethysmography (J. Appl. Physiol. 104: 521-533, 2007). The increase in FRC presumably prevented airway constriction by offsetting airway contractility. We sought a more direct measure of airway constriction. Anesthetized Balb/c mice were intubated with a 22G catheter, and tantalum dust was insufflated into the lungs to produce a well-defined bronchogram. After overnight recovery, the conscious mouse was placed in a sealed box and bronchograms were taken at maximum and minimum points of the box pressure cycle before (control) and after 1 min exposures to 25, 50 and 100 mg/ml Mch aerosol. After overnight recovery, each mouse was studied under room and body temperature box air conditions to correct for gas compression effects on the control tidal volume (Vt) and to determine Vt and Raw with Mch. Airway diameter (D), FRC and Vt were measured from the x-ray images. Compared to control, D decreased by 24%, frequency (f) decreased by 35%, FRC increased by 120% and Raw doubled, to reach limiting values with 100 mg/ml Mch. Vt was unchanged with Mch. The limiting D occurred near zero airway elastic recoil where maximal contractility was relatively small. The conscious mouse adapted to Mch by breathing at a higher lung volume and reduced f to reach a limit in constriction.
