Passive deflation time constant of 7-week-old rabbits

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 (tau) 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 time-cycled, pressure-limited mechanical ventilator. Measurements of tau 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 tau 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 tau. In general, increases in TI resulted in increases in tau and increases in VT also resulted in increases in tau. Increasing TI from 0.2 to 0.6 s plus increasing VI from 10 to 20 mL resulted in an increase in tau from 0.220 +/- 0.007 to 0.282 +/- 0.010 s (mean +/- SEM) (p less than 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 less than 0.05) when TI was increased from 0.2 to 0.6 s; however, dynamic compliance decreased 19% as VT was increased from 10 to 20 mL.(ABSTRACT TRUNCATED AT 250 WORDS)