Journal of Applied Physiology, Vol 63, Issue 1 302-308, Copyright © 1987 by American Physiological Society
Effect of tracheal bias flow on gas exchange during high-frequency chest percussion
N. Gavriely and Y. Shabtai
High-frequency chest percussion (HFP) with constant fresh gas flow (VBF) at
the tracheal carina is a variant of high-frequency ventilation (HFV)
previously shown to be effective with extremely low tracheal oscillatory
volumes (approximately 0.1 ml/kg). We studied the effects of VBF on gas
exchange during HFP. In eight anesthetized and paralyzed dogs we measured
arterial and alveolar partial pressures of CO2 (PaCO2) and O2 (PaO2) during
total body vibration at a frequency of 30 Hz, amplitude of 0.17 +/- 0.019
cm, and tidal volume of 1.56 +/- 0.58 ml. VBF was incrementally varied from
0.1 to 1.2 l.kg-1.min-1. At low flows (0.1-0.4 l.kg-1.min-1), gas exchange
was strongly dependent on flow rate but became essentially flow independent
with higher VBF (i.e., hyperbolic pattern). At VBF greater than 0.4
l.kg-1.min-1, hyperventilatory blood gas levels were consistently sustained
(i.e., PaCO2 less than 20 Torr, PaO2 greater than 90 Torr). The resistance
to CO2 transport of the airways was 1.785 +/- 0.657 l-1.kg.min and was
independent of VBF. The alveolar-arterial difference of O2 was also
independent of the flow. In four of five additional dogs studied as a
control group, where constant flow of O2 was used without oscillations, the
pattern of PaCO2 vs. VBF was also hyperbolic but at substantially higher
levels of PaCO2. It is concluded that, in the range of VBF used,
intraairway gas exchange was limited by the 30-Hz vibration. The fresh gas
flow was important only to maintain near atmospheric conditions at the
tracheal carina.
