End-expiratory and tidal volumes measured in conscious mice using single projection x-ray images.
The evaluation of airway resistance (R(aw)) in conscious mice requires both end-expiratory (V(e)) and tidal volumes (V(t)) (Lai-Fook SJ and Lai YL. J Appl Physiol 98: 2204-2218, 2005). In anesthetized BALB/c mice we measured lung area (A(L)) from ventral-to-dorsal x-ray images taken at FRC (V(e)) and after air inflation with 0.25 and 0.50 ml (DeltaV(L)). Total lung volume (V(L)) described by equation: V(L) = DeltaV(L) + V(FRC) = KA(L)(1.5) assumed uniform (isotropic) inflation. Total V(FRC) 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 (DeltaP(b)) and x-rays during several cycles. K was used to convert measured A(L)(1.5) to V(L) values. We calculated V(e) and V(t) from the plot of V(L) vs. cos(alpha - phi). Phase angle alpha was the minimum point of the P(b) cycle to the x-ray exposure. Phase difference between the P(b) and V(L) cycles (phi) was measured from DeltaP(b) values using both room- and body-temperature humidified box air. A similar analysis was used after aerosol exposures to bronchoconstrictor methacholine (Mch), except that phi depended also on increased R(aw). In conscious mice, V(e) (0.24 ml) doubled after Mch (50-125 mg/ml) aerosol exposure with constant V(t), frequency (f), DeltaP(b), and R(aw). In anesthetized mice, in addition to an increased V(e), repeated 100 mg/ml Mch exposures increased both DeltaP(b) and R(aw) and decreased f to apnea in 10 min. Thus conscious mice adapted to Mch by limiting R(aw), while anesthesia resulted in airway closure followed by diaphragm fatigue and failure.
Lai-Fook
Stephen J
SJ
Center for Biomedical Engineering, Wenner-Gren Research Laboratory, Univ. of Kentucky, Lexington, KY 40506-0070, USA. laifook@email.uky.edu
Houtz
Pamela K
PK
Lai
Yih-Loong
YL
D000280:Administration, Inhalation; D000336:Aerosols; D000403:Airway Resistance / Q000187:drug effects; D000778:Anesthetics, Dissociative / Q000008:administration & dosage; D000818:Animals; D001049:Apnea / Q000000981:diagnostic imaging / Q000503:physiopathology; D001831:Body Temperature; D001985:Bronchial Provocation Tests; D016084:Bronchoconstriction / Q000187:drug effects; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage; D002138:Calibration; D045853:Exhalation / Q000187:drug effects; D005652:Functional Residual Capacity; D006813:Humidity; D007274:Injections, Intraperitoneal; D007649:Ketamine / Q000008:administration & dosage; D008168:Lung / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000503:physiopathology; D008176:Lung Volume Measurements / Q000379:methods*; D016210:Methacholine Chloride / Q000008:administration & dosage; D051379:Mice; D008807:Mice, Inbred BALB C; D008954:Models, Biological; D011312:Pressure; D011859:Radiography; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D013990:Tidal Volume / Q000187:drug effects; D013997:Time Factors; D014965:X-Rays
D000336:Aerosols; D000778:Anesthetics, Dissociative; D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride; D007649:Ketamine