Kindig N B, Hazlett D R
Q J Exp Physiol Cogn Med Sci. 1977 Apr;62(2):121-32. doi: 10.1113/expphysiol.1977.sp002382.
Steady state estimates of the pulmonary diffusing capacity for carbon monoxide (DLCO) require measurement of the uptake and the average alveolar partial pressure of carbon monoxide (PACO). The expired alveolar sample obtained by different experimental methods and/or breathing patterns rarely represents the actual PACO. It is widely accepted that nonuniform distribution of ventilation, diffusion and perfusion causes discrepancies in the measurement of diffusing capacity. tan additional source of error in choosing PACO arises in the sampling time chosen by the experimental method. A theoretical study of a ramp-with-pause and a square breathing pattern demonstrates that the sample-time error exists even in the homogeneous lung. The study shows for the homogeneous lung that the correct fractional concentration of alveolar carbon monoxide (FAV) occurs at a time (TAV), one-half of a breathing period after the effective inspiration time (TI) for the two very different breathing patterns. TI is well-defined in relation to any breathing pattern which can be approximated by ramps and pauses. If TAV and the sample time chosen by the experimental method are known, then the measured DLCO can be corrected to the actual diffusing capacity (DL). The theory agrees with experimental results and computer simulations of inhomogeneous lungs from the literature. This agreement suggests that the theory for the homogeneous lung is also relevant to the inhomogeneous lung.
一氧化碳肺扩散容量（DLCO）的稳态估计需要测量一氧化碳的摄取量和肺泡平均分压（PACO）。通过不同实验方法和/或呼吸模式获得的呼出肺泡样本很少能代表实际的PACO。人们普遍认为，通气、扩散和灌注的不均匀分布会导致扩散容量测量出现差异。在选择PACO时，实验方法所选择的采样时间会产生另一个误差来源。对斜坡-暂停和方形呼吸模式的理论研究表明，即使在均匀肺中也存在采样时间误差。该研究表明，对于均匀肺，在两种非常不同的呼吸模式下，肺泡一氧化碳的正确分数浓度（FAV）在有效吸气时间（TI）后的半个呼吸周期时间（TAV）出现。TI相对于任何可以用斜坡和暂停近似的呼吸模式都有明确的定义。如果已知TAV和实验方法选择的采样时间，那么测量的DLCO可以校正为实际扩散容量（DL）。该理论与文献中关于非均匀肺的实验结果和计算机模拟结果一致。这种一致性表明，均匀肺的理论也适用于非均匀肺。
