Kurata T, Ohta Y, Kondo T, Kuwahira I, Hayashi Y
Department of Medicine, School of Medicine, Tokai University, Kanagawa, Japan.
Tokai J Exp Clin Med. 1991 Jul;16(2):133-43.
This study was intended to elucidate gas exchange in a quasi-steady state during high frequency oscillatory ventilation (HFO) in terms of arterial blood gases, tidal volume(VT) and frequency of oscillation (f). Firstly, experiments were performed on anesthetized, paralyzed and tracheostomized dogs using a piston-type oscillator with a fresh air bias flow. The f values employed in the animal experiments were 10 to 30 Hz, and VT values were 1 to 3 ml/kg of body weight. Changes in PaO2 observed during HFO could be expressed by the equation PaO2 = 125.2-60.3/(VT X f), which closely coincided with the alveolar ventilation equation for O2, i.e., PaO2 = 125-78/, VA, Where P(A-a) O2 and O2 consumption were assumed to be 25 Torr and 90 ml/min, respectively. PaCO2 during HFO deviated from the curve of the alveolar ventilation equation, PaCO2 = constant/, VA at a higher VT x f, and was distributed along the hyperbolic curve of PaCO2 = 1/, VA + 14.7. This suggested that HFO shows a certain limitation in CO2 elimination. Secondly, indicator gas transport through straight tube models for two directions, i.e., wash-in and wash-out, were observed. Wash-in of indicator gases (He, N2 and SF6) in terms of indicator appearance time at the other end of the tube changed as a function of VT x f. The effect of increasing f at a fixed VT on the wash-in was much less than that of increasing VT at a fixed f. The heavier gas (SF6) was washed in faster than the lighter gas (He) although wash-in of each indicator gas was closely related to the function VT x f. Washout in terms of the appearance time of indicators in the opposite direction was, however, strongly dependent on VT, and the effect of increasing f at a fixed VT on wash-out reached a limit beyond a certain f. It was concluded from the present study, that both convective dispersion and augmented diffusion play important roles, although they are not clearly distinguished, as gas transport mechanisms during HFO. The difference between inspiratory and expiratory gas transport modes could be explained by differences in flow profiles, relative important of convective dispersion, and/or time required for gas mixing in the airways.
本研究旨在根据动脉血气、潮气量（VT）和振荡频率（f）阐明高频振荡通气（HFO）期间准稳态下的气体交换。首先，使用带有新鲜空气偏流的活塞式振荡器对麻醉、麻痹并进行气管切开的犬进行实验。动物实验中采用的f值为10至30Hz，VT值为1至3ml/kg体重。HFO期间观察到的PaO2变化可用方程PaO2 = 125.2 - 60.3/(VT×f)表示，这与O2的肺泡通气方程即PaO2 = 125 - 78/VA非常吻合，其中假设P(A-a)O2和O2消耗量分别为25Torr和90ml/min。HFO期间的PaCO2在较高的VT×f时偏离肺泡通气方程曲线PaCO2 = 常数/VA，并沿双曲线PaCO2 = 1/VA + 14.7分布。这表明HFO在CO2清除方面存在一定局限性。其次，观察了示踪气体在直管模型中两个方向（即洗入和洗出）的传输情况。示踪气体（He、N2和SF6）的洗入情况根据示踪剂在管另一端的出现时间随VT×f而变化。在固定VT时增加f对洗入的影响远小于在固定f时增加VT的影响。较重的气体（SF6）比较轻的气体（He）洗入得更快，尽管每种示踪气体的洗入都与VT×f的函数密切相关。然而，示踪剂在相反方向的洗出强烈依赖于VT，并且在固定VT时增加f对洗出的影响在超过一定的f后达到极限。从本研究得出结论，对流扩散和增强扩散在HFO期间作为气体传输机制都起着重要作用，尽管它们没有明显区分。吸气和呼气气体传输模式的差异可以通过流型、对流扩散的相对重要性和/或气道中气体混合所需时间的差异来解释。
