Ghadiali S N, Gaver D P
Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana 70118, USA.
J Appl Physiol (1985). 2000 Feb;88(2):493-506. doi: 10.1152/jappl.2000.88.2.493.
Airway reopening mechanics depend on surfactant physicochemical properties. During reopening, the progression of a finger of air down an airway creates an interface that is continually expanding into the bulk fluid. Conventional surfactometers are not capable of evaluating physicochemical behavior under these conditions. To study these aspects, we investigated the pressure required to push a semi-infinite bubble of air down a fluid-filled cylindrical capillary of radius R. The ionic surfactant SDS and pulmonary surfactant analogs L-alpha-dipalmitoylphosphatidylcholine and Infasurf were investigated. We found that the nonequilibrium adsorption of surfactant can create a large nonequilibrium normal stress and a surface shear stress (Marangoni stress) that increase the bubble pressure. The nonphysiological surfactant SDS is capable of eliminating the normal stress and partially reducing the Marangoni stress. The main component of pulmonary surfactant, L-alpha-dipalmitoylphosphatidylcholine, is not capable of reducing either stress, demonstrating slow adsorption properties. The clinically relevant surfactant Infasurf is shown to have intermediate adsorption properties, such that the nonequilibrium normal stress is reduced but the Marangoni stress remains large. Infasurf's behavior suggests that an optimal surfactant solution will have sorption properties that are fast enough to reduce the reopening pressure that may damage airway wall epithelial cells but slow enough to maintain the Marangoni stress that enhances airway stability.
气道再开放机制取决于表面活性剂的物理化学性质。在再开放过程中，一股空气在气道中向下推进时形成一个界面，该界面不断向大量液体中扩展。传统的表面张力仪无法评估这些条件下的物理化学行为。为了研究这些方面，我们研究了将一个半无限大的气泡沿半径为R的充满液体的圆柱形毛细管向下推所需的压力。研究了离子型表面活性剂十二烷基硫酸钠（SDS）以及肺表面活性剂类似物L-α-二棕榈酰磷脂酰胆碱和固尔苏。我们发现，表面活性剂的非平衡吸附会产生较大的非平衡法向应力和表面剪切应力（马兰戈尼应力），从而增加气泡压力。非生理性表面活性剂SDS能够消除法向应力并部分降低马兰戈尼应力。肺表面活性剂的主要成分L-α-二棕榈酰磷脂酰胆碱无法降低这两种应力，表明其吸附特性缓慢。临床相关的表面活性剂固尔苏表现出中等吸附特性，即非平衡法向应力降低，但马兰戈尼应力仍然很大。固尔苏的行为表明，最佳的表面活性剂溶液将具有足够快的吸附特性，以降低可能损害气道壁上皮细胞的再开放压力，但又足够慢以维持增强气道稳定性的马兰戈尼应力。
