Niederer P F, Leuthold R, Bush E H, Spahn D R, Schmid E R
Institute of Biomedical Engineering and Medical Informatics, Swiss Federal Institute of Technology, Zurich.
Crit Care Med. 1994 Sep;22(9 Suppl):S58-65. doi: 10.1097/00003246-199422091-00005.
To determine the influence of the dynamic properties of the oscillator on the oscillatory volume delivered through the endotracheal tube to the lung or lung surrogate (delivered volume) under conditions of high-frequency ventilation. In particular, the relation between the tidal volume of the pump (oscillator) and the delivered volume was analyzed. PaCO2 was measured further as a function of the delivered volume in a number of experiments performed with healthy dogs.
Laboratory study.
Engineering and animal laboratory.
Lung surrogates and healthy dogs.
An experimental oscillatory system was connected to various lung surrogates. In addition, six beagle dogs received high-frequency ventilation with different delivered volumes during the study. Control of the mean airway pressure was achieved by a peripheral pressure chamber located at the exhaust port of the bias flow tube.
The delivered volume, which is the quantity of interest from a physiologic point of view, can deviate considerably from the tidal volume of the pump due to dynamic (particularly resonance) effects. Because the delivered volume and the mean airway pressure have to be controlled independently, two independent quantities are necessary for control purposes (e.g., the tidal volume of the pump and the mean pressure at the exhaust port). Furthermore, it was found that a minimal condition for adequate gas exchange is a delivered volume that exceeds the machine-related deadspace. For this reason, and in order to maximize the CO2 gradient, the exhaust tube must be as short as possible.
a) The delivered volume has to be monitored under clinical conditions; b) however, because the impedance of the endotracheal tube in general considerably exceeds the impedance of the lung, the influence of the impedance of the lung on the delivered volume is generally small, and thus an in vitro calibration may serve as a useful approximation; c) at least two independent quantities are needed for an adequate oscillatory control; d) a necessary (not necessarily sufficient) condition for adequate CO2 removal is that the delivered volume must exceed the machine-related deadspace; e) in a clinical environment involving extremely pathologic lung conditions, e.g., adult respiratory distress syndrome, mechanical lung characteristics may deviate substantially from those characteristics used in this study (i.e., the results obtained may not necessarily be applicable under all clinical situations).
确定在高频通气条件下，振荡器的动态特性对通过气管导管输送到肺或肺替代物的振荡气量（输送气量）的影响。特别分析了泵（振荡器）的潮气量与输送气量之间的关系。在对健康犬进行的多项实验中，进一步测量了动脉血二氧化碳分压（PaCO2）作为输送气量的函数。
实验室研究。
工程与动物实验室。
肺替代物和健康犬。
将一个实验性振荡系统连接到各种肺替代物上。此外，在研究过程中，六只比格犬接受了不同输送气量的高频通气。通过位于偏流管排气口的外周压力室实现平均气道压力的控制。
从生理学角度来看，作为关注量的输送气量可能会因动态（特别是共振）效应而与泵的潮气量有很大偏差。由于输送气量和平均气道压力必须独立控制，因此控制目的需要两个独立的量（例如，泵的潮气量和排气口的平均压力）。此外，发现充分气体交换的一个最低条件是输送气量超过机器相关死腔。因此，为了使二氧化碳梯度最大化，排气管必须尽可能短。
a）在临床条件下必须监测输送气量；b）然而，由于气管导管的阻抗通常大大超过肺的阻抗，肺阻抗对输送气量的影响通常较小，因此体外校准可作为一种有用的近似方法；c）充分的振荡控制至少需要两个独立的量；d）充分去除二氧化碳的必要（不一定充分）条件是输送气量必须超过机器相关死腔；e）在涉及极端病理肺部状况（如成人呼吸窘迫综合征）的临床环境中，机械肺特性可能与本研究中使用的特性有很大偏差（即，所获得的结果不一定适用于所有临床情况）。
