Lai-Fook Stephen J, Houtz Pamela K
Center for Biomedical Engineering, Univ. of Kentucky, Lexington, KY 40506-0070, USA.
J Appl Physiol (1985). 2008 Sep;105(3):933-41. doi: 10.1152/japplphysiol.00133.2008. Epub 2008 Jun 26.
A single-projection X-ray technique showed an increase in functional residual capacity (FRC) in conscious mice in response to aerosolized methacholine (MCh) with little change in airway resistance (Raw) measured using barometric plethysmography (Lai-Fook SJ, Houtz PK, Lai Y-L. J Appl Physiol 104: 521-533, 2008). 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 22-G 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 both 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 with control, D decreased by 24%, frequency 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 the maximal contractility was relatively small. The conscious mouse adapted to MCh by breathing at a higher lung volume and reduced frequency to reach a limit in constriction.
单投影X射线技术显示，清醒小鼠吸入雾化乙酰甲胆碱（MCh）后功能残气量（FRC）增加，而使用气压体积描记法测量的气道阻力（Raw）变化不大（Lai-Fook SJ、Houtz PK、Lai Y-L.《应用生理学杂志》104: 521 - 533，2008）。FRC的增加可能通过抵消气道收缩性来防止气道收缩。我们寻求一种更直接测量气道收缩的方法。将麻醉的Balb/c小鼠用22G导管插管，向肺内吹入钽粉以产生清晰的支气管造影图像。过夜恢复后，将清醒小鼠置于密封箱中，在箱内压力循环的最大和最小点分别在接触25、50和100mg/ml MCh气雾剂1分钟之前（对照）和之后拍摄支气管造影图像。过夜恢复后，在室温和体温箱内空气条件下对每只小鼠进行研究，以校正气体压缩对对照潮气量（Vt）的影响，并确定MCh作用下的Vt和Raw。从X射线图像测量气道直径（D）、FRC和Vt。与对照相比，100mg/ml MCh时D降低24%，频率降低35%，FRC增加120%，Raw翻倍并达到极限值。MCh作用下Vt不变。极限D出现在气道弹性回缩接近零的位置，此时最大收缩性相对较小。清醒小鼠通过在更高肺容量下呼吸并降低频率来适应MCh，以达到收缩极限。
