Measurement of tidal volume using a pneumotachometer during high-frequency oscillation.
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.
Courtney
S E
SE
Department of Pediatrics, Wright State University, Dayton, OH 45435.
Weber
K R
KR
Spohn
W A
WA
Malin
S W
SW
Bender
C V
CV
Gotshall
R W
RW
D000818:Animals; D006612:High-Frequency Ventilation; D008176:Lung Volume Measurements; D010993:Plethysmography, Whole Body; D011817:Rabbits; D012129:Respiratory Function Tests / Q000295:instrumentation*; D013990:Tidal Volume