Lutchen K R, Suki B, Zhang Q, Peták F, Daróczy B, Hantos Z
Department of Biomedical Engineering, Boston University, Massachusetts 02215.
J Appl Physiol (1985). 1994 Jul;77(1):373-85. doi: 10.1152/jappl.1994.77.1.373.
In five open-chest dogs and with four to five alveolar capsules we used an optimal ventilator waveform (OVW) to follow frequency and tidal volume (VT) dependence of lung, airway, and tissue resistance (R) and elastance (E) before and during constant infusion of histamine (16 micrograms.kg-1.min-1). OVW contains sufficient flow energy between 0.234 and 4.7 Hz, avoids nonlinear harmonic interactions, and simultaneously ventilates with physiological VT. Each OVW breath permits a smooth estimate of frequency dependence of R and E for the whole lung. A constant-phase model analysis provided estimates of purely viscous resistance (Rvis), which represents the sum of airway resistance (Raw) and any purely newtonian component of tissue resistance (Rti), and parameters G and H, which govern frequency dependence of Rti and tissue elastance (Eti), respectively. Tissue structural damping (eta) is calculated as G/H. This model was applied to the whole lung and tissue impedance as estimated from each capsule. We found a small but inconsequential purely newtonian component of Rti, even during constriction. Four dogs showed a peak response at approximately 4 min in lung Rvis coupled (in time) to initial increases in G, H, eta, and airway inhomogeneities. In two of these dogs the response was severe. Tissue properties estimated from whole lung impedance (G, H, and eta) were nearly identical to values estimated from unobstructed capsules throughout infusion. By using a technique independent of alveolar capsules, our results indicate that a major if not dominant response to a constrictive agonist occurs in lung tissues, resulting in a large increase in Rti and Eti. With severe constriction, significant increases occur in Raw and airway inhomogeneities as well. Finally, separation of airway and tissue properties using input impedance estimated from the frequency-rich OVW avoids use of alveolar capsules and may prove an effective tool for partitioning airway and tissue properties in humans.
在五只开胸犬身上，使用四到五个肺泡囊，我们采用一种最佳通气波形（OVW）来跟踪在持续输注组胺（16微克·千克⁻¹·分钟⁻¹）之前和期间肺、气道及组织阻力（R）和弹性（E）对频率和潮气量（VT）的依赖性。OVW在0.234至4.7赫兹之间包含足够的气流能量，避免非线性谐波相互作用，并同时以生理潮气量进行通气。每个OVW呼吸允许对整个肺的R和E的频率依赖性进行平滑估计。一个恒相模型分析提供了纯粘性阻力（Rvis）的估计值，它代表气道阻力（Raw）与组织阻力（Rti）的任何纯牛顿分量之和，以及参数G和H，它们分别控制Rti和组织弹性（Eti）的频率依赖性。组织结构阻尼（eta）计算为G/H。该模型应用于整个肺以及从每个囊估计的组织阻抗。我们发现即使在收缩期间，Rti也有一个小但无关紧要的纯牛顿分量。四只犬在肺Rvis中大约在4分钟时出现峰值反应，同时（在时间上）与G、H、eta和气道不均匀性的初始增加相关。其中两只犬的反应很严重。在整个输注过程中，从全肺阻抗估计的组织特性（G、H和eta）与从通畅囊估计的值几乎相同。通过使用一种独立于肺泡囊的技术，我们的结果表明，对收缩性激动剂的主要（如果不是占主导地位的）反应发生在肺组织中，导致Rti和Eti大幅增加。在严重收缩时，Raw和气道不均匀性也会显著增加。最后，使用从富含频率的OVW估计的输入阻抗来分离气道和组织特性，避免了使用肺泡囊，并且可能证明是一种在人体中划分气道和组织特性的有效工具。
