Journal of Applied Physiology, Vol 60, Issue 3 885-892, Copyright © 1986 by American Physiological Society
Resonant amplification of delivered volume during high-frequency ventilation
V. Brusasco, K. C. Beck, M. Crawford and K. Rehder
The volume of gas delivered from a high-frequency ventilation (HFV) circuit
was measured with an ultrasonic flowmeter. The measurements were done in
vitro (20-liter air-filled glass bottle) and in vivo (9 anesthetized dogs
lying supine) at oscillation frequencies ranging from 4 to 23 Hz and stroke
volumes of the pump ranging from 36 to 150 ml. We varied the length and
diameter of the tube connecting the pump with the endotracheal tube, the
length and diameter of the bias outflow tube, the diameter of the
endotracheal tube, and the stroke volume of the pump. Both in vitro and in
vivo, there was resonant amplification of the delivered gas volume; i.e.,
the delivered gas volume exceeded the stroke volume at certain frequencies.
Altering the dimensions of connecting tube, endotracheal tube, bias outflow
tube, or stroke volume, i.e., changing the resistance to gas flow, gas
compliance, and/or gas inertance in these elements, altered the ratio of
gas delivered to stroke volume that could be predicted by an electric
analog. These data indicate that the delivered gas volume during HFV
depends critically on the configuration of the HFV circuit, the size of the
endotracheal tube, the oscillation frequency, and the pump stroke volume.
Knowledge of the delivered gas volume during HFV and appreciation of the
phenomenon of resonant amplification of the delivered gas volume will
permit a more accurate description of factors contributing to gas transport
during HFV.
