Spahn D R, Leuthold R, Schmid E R, Niederer P F
Institut für Anästhesiologie, Universitätsspital, Zürich, Switzerland.
Respir Physiol. 1991 Apr;84(1):1-11. doi: 10.1016/0034-5687(91)90015-b.
In 7 anesthetized supine dogs with an anatomic dead space of 115-162 ml, gas transport during high-frequency oscillation (HFO) was investigated at an oscillatory frequency of 15 Hz. Starting with an oscillatory volume effectively delivered to the lungs (VDEL) of 60 ml, measured on line with an ultrasonic airflow meter, VDEL was reduced in steps of 10 ml, down to a VDEL of 30 ml, whereby fresh gas flow rate, airway occlusion pressure and lung volume above functional residual capacity were kept constant. An HFO-circuit without bias tube was used. The volume of endotracheal tube and three port connector, designated as HFO-circuit related rebreathing volume, was 35 ml. PaCO2 continuously increased, when VDEL was reduced from 60 ml to 40 ml and the data fit perfectly to a reciprocal regression (1/PaCO2 = a + b.VDEL), r2 ranging from 0.95 to 1.00. Measured PaCO2 values at a VDEL of 30 ml (8.26 +/- 1.77 kPa), however, were significantly (P less than 0.025) higher than PaCO2 values predicted by the individual reciprocal regression equations (6.25 +/- 1.46 kPa). This overproportionate increase in PaCO2 due to a reduction of VDEL from 40 ml to 30 ml may be explained by the sudden drop out of bulk convection as a gas transport mechanism between central airways and the surrounding because bulk convection is only possible as long as VDEL exceeds the HFO-circuit related rebreathing volume. Bulk convection therefore is considered an essential gas transport mechanism during HFO and the efficiency of CO2 elimination during HFO is critically dependent on the net oscillatory volume, i.e. VDEL minus the HFO-circuit related rebreathing volume and not on the relationship between VDEL and anatomic dead space.
在7只麻醉仰卧的犬中，解剖无效腔为115 - 162 ml，在15 Hz的振荡频率下研究了高频振荡（HFO）期间的气体传输。从用超声气流计在线测量的有效输送到肺的振荡容积（VDEL）60 ml开始，VDEL以10 ml的步长递减，直至VDEL为30 ml，同时保持新鲜气流速、气道闭塞压和高于功能残气量的肺容积恒定。使用了无偏置管的HFO回路。气管内导管和三通接头的容积，即与HFO回路相关的重复吸入容积为35 ml。当VDEL从60 ml降至40 ml时，PaCO2持续升高，数据与倒数回归（1/PaCO2 = a + b·VDEL）完全拟合，r2范围为0.95至1.00。然而，在VDEL为30 ml时测得的PaCO2值（8.26±1.77 kPa）显著高于（P<0.025）由各个倒数回归方程预测的PaCO2值（6.25±1.46 kPa）。由于VDEL从40 ml降至30 ml导致的PaCO2过度增加可能是由于作为中央气道与周围之间气体传输机制的体对流突然消失，因为只有当VDEL超过与HFO回路相关的重复吸入容积时体对流才可能发生。因此，体对流被认为是HFO期间的一种重要气体传输机制，HFO期间CO2清除效率关键取决于净振荡容积，即VDEL减去与HFO回路相关的重复吸入容积，而不是VDEL与解剖无效腔之间的关系。
