Abstract
ABSTRACT: The purpose of our study was to determine the effects of insufflation time (Ti) and of tidal volume (VT) on the passive deflation time constant (τ) of juvenile rabbits. We sedated and paralyzed nine 7-wk-old New Zealand rabbits (wt 1.2 ± 0.2 SD kg) and placed them on a timecycled, pressure-limited mechanical ventilator. Measurements of τ and dynamic compliance of the respiratory system were made at nine ventilator settings. Ti was adjusted to 0.2,0.4, and 0.6 s and VT was adjusted to 10,15, and 20 mL so that the effects of Ti and VT on τ could be determined independently. Respiratory system quasi-static and static compliances were also measured and served as a basis for discussing the physiologic explanations for the effects of Ti and VT on τ. In general, increases in Ti resulted in increases in r and increases in VT also resulted in increases in τ. Increasing Ti from 0.2 to 0.6 s plus increasing Vi from 10 to 20 mL resulted in an increase in τ from 0.220 ± 0.007 to 0.282 ± 0.010 s (mean ± SEM) (p<0.05, student Newman-Kuels), which is a 28% increase. At a VT of 10 mL, dynamic compliance increased from 1.95 ± 0.10 to 2.14 ± 0.10 mL/cm H2O (p<0.05) when TIwas increased from 0.2 to 0.6 s; however, dynamic compliance decreased 19% as VT was increased from 10 to 20 mL. Quasi-static compliance increased from 2.04 ± 0.07 to 2.17 ± 0.12 mL/cm H2O (p<0.05) as deflation volume was increased from 10 to 20 mL, yet static compliance remained relatively constant at 2.6 mL/cm H2O in the volume range of 10 to 20 L. We conclude that both Ti and VT affect τ in the small, healthy rabbit and that neither the viscoelastic properties of the lung nor parallel modeling with a distribution of time constants can fully explain our observations.
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Valdes, E., Pace, W., Richardson, P. et al. Passive Deflation Time Constant of 7-Week-Old Rabbits. Pediatr Res 28, 75–76 (1990). https://doi.org/10.1203/00006450-199007000-00016
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DOI: https://doi.org/10.1203/00006450-199007000-00016
