[Relationship between measurements of tidal volume and thoracic inflating volume by pressure plethysmography in mice].

Objective: To evaluate the accordance of tidal volume (TV) with thoracic inflating volume (TIV) measured by pressure whole-body or double-chamber plethysmography in mice.

Methods: TV and TIV by double-chamber plethysmography were simultaneously measured in 6 mice with spontaneous respiratory frequencies 90 - 120/min; TV and TIV by whole-body plethysmography were measured in 8 paralyzed mice ventilated by fixed frequency.

Result: TIV value by double-chamber plethysmography was significantly higher than TV [(0.369 +/- 0.014) ml vs (0.356 +/- 0.012) ml, P < 0.01)] in 6 spontaneously breathing mice. TIV value by whole-body plethysmography was significantly lower than TV[(0.233 +/- 0.003) ml vs 0.3 ml, P < 0.001] in 8 paralyzed mice.

Conclusion: The TV value assessed by TIV measurement can not be accurate, because of the humidifying and heating of inhaled air and negative thoracic pressure during the measurement.