Authors
   Adler A. Cieslewicz G.  Irvin CG.
Institution
   School of Information Technology and Engineering,
   University of Ottawa, Ottawa, Ontario, Canada
Title
   Unrestrained plethysmography is an unreliable measure of airways
   responsiveness in BALB/c and C57BL6 mice
Source
   Journal of Applied Physiology, Accepted March 16, 2004
Abstract
   There has been significant utilization of the technique described
   by Hamelmann et al. (1997) in which a parameter, Penh, related to
   airways responsiveness is non-invasively measured using unrestrained
   plethysmography (UP). We investigated this technique, seeking to answer
   these questions: 1) How do changes in Penh compare with changes in
   traditional plethysmographic and lung mechanical parameters? 2) How
   do UP parameters perform in two different mouse strains? Awake immunized
   and control BALB/c (N=16) and C57BL6 (N=14) mice were placed in the UP
   chamber and exposed to doses of aerosolized methacholine, while the
   following parameters were measured at each concentration: inspiratory
   time (TI), expiratory time (TE), total time (TTot), TI/TTot, peak
   inspiratory pressure (PI), peak expiratory pressure (PE), Pause,
   Penh, tidal volume (VT), VT/TI, VT/TE, and VT/TTot. The next day,
   lung resistance and compliance (RL, CL), were invasively measured
   in the same animals. For the BALB/c, the parameters with the highest
   magnitude of correlation coefficient vs. RL are (in order): 1) CL,
   2) Pause and Penh, 3) parameters of breathing frequency (TE, TTot,
   TI) and 4) parameters related to tidal volume (PI, PE, VT). Flow
   parameters (VT/TTot, VT/TE, VT/TI) and duty cycle parameters (TI/TTot)
   had insignificant correlations. This ordering is significantly
   different in the C57BL6, where the parameters with the largest
   correlations are: 1) CL, 2) parameters of breathing frequency,
   3) flow parameters. Pause, Penh, tidal volume and duty cycle
   parameters had insignificant correlations. This data shows that
   Penh is problematic in the sense that it is strain specific; it
   behaves very differently in BALB/c and C57BL6 mice. We suggest
   that UP parameters largely originate as part of reflex control
   of breathing processes, rather than in the lung mechanics, and
   conclude that it is inappropriate to use UP parameters in general,
   and Penh specifically, as substitute variables for invasive mechanical
   indices such as RL.