Van Liew H D, Lapennas G N, Murray K R
Respir Physiol. 1986 Dec;66(3):355-66. doi: 10.1016/0034-5687(86)90086-1.
For quantitative assessment of how gas mixing in the lung compares to the ideal of perfect mixing, it is necessary to measure pre-inspiratory lung volume as well as to study the inhaled and exhaled gas. Normal young-adult persons in the seated position assumed various lung volumes and then took 1-L test breaths (11% Ar, 22% O2 in N2). Integration of concentration at the mouth against volume yielded amounts of Ar inhaled, exhaled and retained; un-exhaled concentration in the lung after the single breath was calculated from amount retained divided by lung volume (measured by rebreathing). Retention was 60% of the inhaled amount when pre-inspiratory volume was above FRC and less when it was below. Series dead space increased with lung volume. End-tidal Ar was the same as, or slightly above, the concentration predicted for perfect mixing and un-exhaled Ar was slightly below the perfect-mix concentration.
three separable influences decrease the transfer of inspirate to the resident gas. A dilution effect, predictable from the volumes involved, decreases retention at low lung volumes. An enlarged series dead space decreases retention at high volumes. In normal persons, a mixing defect that is attributable to poor distribution or incomplete gas-phase diffusion is small and can be ascribed almost completely to the part of the expirate that gives rise to the slope of the alveolar plateau, except when breaths are taken at very low lung volumes.
为了定量评估肺内气体混合与理想的完全混合相比的情况，有必要测量吸气前肺容积以及研究吸入和呼出的气体。正常的年轻成年人坐姿下采用不同的肺容积，然后进行1升的测试呼吸（氮气中11%氩气、22%氧气）。将口腔处的浓度对容积进行积分得出吸入、呼出和留存的氩气量；单次呼吸后肺内未呼出的浓度通过留存量除以肺容积（通过重复呼吸测量）来计算。当吸气前容积高于功能残气量时，留存量为吸入量的60%，低于功能残气量时则更少。串联死腔随肺容积增加。呼气末氩气浓度与完全混合预测的浓度相同或略高于该浓度，未呼出的氩气浓度略低于完全混合浓度。
三种可分离的影响因素会降低吸入气体向存留气体的转移。一种稀释效应，可根据所涉及的容积预测，在低肺容积时会降低留存量。扩大的串联死腔在高肺容积时会降低留存量。在正常人中，由于分布不佳或气相扩散不完全导致的混合缺陷较小，几乎完全可归因于产生肺泡平台斜率的呼出气体部分，除非在非常低的肺容积下呼吸。
