Sullivan K J, Mortola J P
Respir Physiol. 1987 Mar;67(3):295-309. doi: 10.1016/0034-5687(87)90060-0.
Stress relaxation within the respiratory system was examined in young rats at different ages, 0-1 day old (GPI), 4-5 days old (GPII) and 30-40 days old (GPIII). Each rat was anesthetized, tracheostomized and placed inside a saline filled plethysmograph with the tracheal cannula projecting through the wall of the plethysmograph. Volume history was standardized by three inflations to a mean transrespiratory system pressure (P) of 20-25 cm H2O, then P was set to zero and lung volume was abruptly increased by rapidly withdrawing fluid from the plethysmograph. Following the volume step, lung volume was maintained constant and changes in P due to stress relaxation were recorded for 30 sec. The rate of stress relaxation was obtained by calculating the slope (R) of the normalized change in P per unit of time on a semi-log plot. GPIII rats exhibited the slowest rate (R = 0.068 +/- 0.004 SD) whereas GPII rats demonstrated the fastest rate (R = 0.092 +/- 0.011 SD). Stress relaxation in GPI was intermediate (R = 0.076 +/- 0.005 SD). Values of dynamic (Cdyn) and static (Cstat) compliance were determined for rats similar in age to the three age groups used to determine R. The difference between Cstat and Cdyn increased with R and was greatest in rats between 0 and 6 days old. We conclude that: (1) stress relaxation within the rat respiratory system at 30-40 days is less than that found in rats during the first week after birth, and (2) changes in the viscoelastic properties of the respiratory system may contribute to age related variation in the difference between Cstat and Cdyn.
在0至1日龄（GPI）、4至5日龄（GPII）和30至40日龄（GPIII）的幼鼠中检测了呼吸系统内的应力松弛情况。每只大鼠均经麻醉、气管切开，并置于充满盐水的体积描记器内，气管插管穿过体积描记器壁伸出。通过三次充气将平均跨呼吸系统压力（P）标准化为20至25 cm H₂O，然后将P设为零，并通过迅速从体积描记器中抽出液体使肺容积突然增加。在容积阶跃后，保持肺容积恒定，并记录30秒内由于应力松弛导致的P的变化。应力松弛速率通过在半对数图上计算单位时间内P的归一化变化的斜率（R）来获得。GPIII组大鼠的应力松弛速率最慢（R = 0.068 ± 0.004标准差），而GPII组大鼠的速率最快（R = 0.092 ± 0.011标准差）。GPI组的应力松弛速率居中（R = 0.076 ± 0.005标准差）。测定了与用于确定R的三个年龄组年龄相似的大鼠的动态（Cdyn）和静态（Cstat）顺应性值。Cstat和Cdyn之间的差异随R增加，在0至6日龄的大鼠中最大。我们得出以下结论：（1）30至40日龄大鼠呼吸系统内的应力松弛小于出生后第一周大鼠的应力松弛，（2）呼吸系统粘弹性特性的变化可能导致Cstat和Cdyn之间差异的年龄相关变化。
