Measurement of tidal volume using a pneumotachometer during high-frequency oscillation

Crit Care Med. 1990 Jun;18(6):651-3. doi: 10.1097/00003246-199006000-00015.


To assess the accuracy of a pneumotachometer (PN) for tidal volume (VT) measurements during high-frequency oscillation (HFO), we determined simultaneously VT using a PN and a full body plethysmograph (PL) in 12 rabbits. HFO was delivered with an oscillator at a frequency of 10 Hz, mean airway pressure of 8 cm H2O, and inspiratory time of 50%. Pressure amplitude (delta P) was varied as follows: 40, 60, 80, 20, 100, 40 cm H2O. Finally, in ten rabbits a spacer equal in deadspace (VD) to that of the PN (15 ml) was left in-line for 5 min. Blood gases were obtained before and after the spacer was added. We found that VT-PN correlates well with VT-PL (r = .92), although the difference between VT-PN and VT-PL is greater at large VT. Significant respiratory acidosis developed with the spacer in-line. PN may be used to trend VT during HFO but PN must not be left in-line, as increased VD seriously affects ventilation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • High-Frequency Ventilation*
  • Lung Volume Measurements*
  • Plethysmography, Whole Body
  • Rabbits
  • Respiratory Function Tests / instrumentation*
  • Tidal Volume*