PULMONARY CAPILLARY PRESSURE IN DOGS AND HUMANS

肺循环是一个高容量系统， 血容量的五倍变化而压力变化很小。 维持肺毛细血管的恒定滤过压 对于避免肺水肿很重要， 交易所直到最近，人们还认为肺毛细血管 压力Ppc）可以通过Gaar方程近似为Ppc=Pla + .4 （Ppa-Pla）。临床上，Ppc通常被认为等于肺动脉压。 动脉闭塞或楔压Ppw）。然而，这些近似 在许多临床试验中， 条件 这些研究的目的是评估准确性、重现性 三种技术估计肺毛细血管的局限性 压力（Ppc）：目视测定法，计算机定义 肺动脉压曲线中的断点时间，以及 从计算机模拟得出的理论PPC。这些方法将 在病人和狗身上进行比较， 闭塞PpC在开胸犬肺。肺动脉的划分 前（ra）和后（rv）毛细血管的血管阻力（PVR） 组件和Ppc相比，楔压力将 在改变的生理条件下进行评估。其中包括：急性 主动脉阻断期间血容量的变化 慢性心力衰竭血管外重建 红细胞增多症后的容量保持、粘度变化以及 例如在机械通气和正压通气期间所见的气道压力 呼气末压，油酸损伤，毛细血管扩张 增加血管阻力（缺氧）， 电容和电阻可以任意改变， PPC决定。然后可以将测量的Ppc与预测的Ppc进行比较。 理论值。 在犬肺中，将使用标准实验方案。在病人身上， 肺动脉压力描记的分析不需要额外的 生理入侵

The pulmonary circulation is a high capacitance system that can adapt to a five fold variation in blood volume with little change in pressure. Maintaining a constant filtration pressure at the pulmonary capillaries is important in avoiding pulmonary edema which would impede air exchange. Until recently, it was assumed that pulmonary capillary pressure Ppc) could be approximated by the Gaar equation as Ppc=Pla + .4 (Ppa-Pla). Clinically Ppc is often assumed to be equal to the pulmonary arterial occlusion or wedge pressure Ppw). However, these approximations are not an accurate prediction of Ppc in a number of clinical conditions. The goal of these studies is to evaluate the accuracy, reproducibility and limitations of three techniques to estimate pulmonary capillary pressure (Ppc): the visual determination method, computer definition of the break point time in the pulmonary arterial pressure profile, and theoretical Ppc derived from computer simulation. These methods will be compared to one another in patients and in dogs and to the double occlusion PpC in open-chested dog lungs. The division of pulmonary vascular resistance (PVR) into pre (ra) and post (rv) capillary components and the Ppc as compared to the wedge pressure will be evaluated under altered physiological conditions. These include: acute changes in blood volume induced by aortic cross clamping during aortic reconstruction, chronic heart failure with extravascular volumeretention, viscosity changes after polycythemia, and alteration in airway pressure such as seen during mechanical ventilation and positive end expiratory pressure, oleic acid injury, increasing capillary permeability, and increasing vascular resistance (hypoxia) and capacitance and resistance can be arbitrarily changed and the resultant Ppc determined. The measured Ppc can then be compared to predicted theoretical values. In dog lungs standard experimental protocols will be used. In patients, analysis of the pulmonary artery pressure tracing requires no additional physiological trespass.