外源界面活性劑在呼吸道黏性薄膜上傳輸之理論探討

Abstract

本研究以潤滑理論推導之運動與傳輸模式，配合數值計算，模擬外源界面活性劑在呼吸道黏性薄膜上之傳輸，以及其所造成的黏膜擾動。其研究目的為探討影響「界面活性劑療法」治療新生兒「呼吸窘迫症候群」之相關參數，包括：黏膜厚度與呼吸道半徑比、外源界面活性劑強度、原有界面活性劑、薄膜黏滯性、呼吸道氣流、以及界面活性劑之可溶性。數值模擬結果發現；外源界面活性劑在低級數呼吸道（較高之黏膜厚度與呼吸道半徑比值）中所造成之薄膜擾動幅度較高級數呼吸道中明顯，但呼吸道半徑對界面活性劑傳輸之影響極小。外源界面活性劑初始強度愈強，則所造成的薄膜擾動波與界面活性劑之傳輸速率亦愈快。原有界面活性劑的存在對薄膜擾動與外源界面活性劑傳輸皆產生極大的影響；原有界面活性劑降低薄膜之擾動幅度，然而卻提高界面活性劑波前傳播之速率。此波前傳播速率之提高乃因外源活性劑推擠原有界面活性劑，使原有界面活性劑局部濃度增加並往前推進，然而外源界面劑之傳輸速率則因此降低。呼吸道氣流在黏膜表面所造成之剪力對界面活性劑之傳輸影響極小。界面活性劑之可溶性質減緩表面界面活性劑之濃度梯度，進而減弱表面張力梯度引起的流場，降低表面界面活性劑之傳輸速率，但黏膜擾動波波高則明顯增大。

The transport of the exogenous surfactant in a pulmonary airway lining is analyzed using the theoretical model developed based on the lubrication theory. The primary objective of the model is to study the parameters involved in surfactant replacement therapy for neonatal respiratory distress syndrome, including the ratio of film thickness to airway radius, the strength of exogenous surfactant dose, the presence of preexisting surfactant, the film viscosity, the shear stress due to air flow, and the surfactant solubility. Numerical simulation of the model indicates that the film disturbance induced by the Marangoni effect in low-generation airways (larger ratio of film thickness to airway radius) is more significant than that in high-generation airways. However, the surfactant spreading is virtually unaffected. Increasing the initial local exogenous concentration enhances the surfactant transport and also accelerates the propagation of film disturbance. The presence of preexisting surfactant tends to moderate the shock-like film disturbance and also prolongs the extent of surfactant monolayer front. This, however, does not mean that the spreading of exogenous surfactant is enhanced by the presence of preexisting surfactant. The extended monolayer is attributed to the compression of the preexisting surfactant in regions ahead of the advancing exogenous surfactant front. The shear stress induced by the air flow within the airway has very little effect on the surfactant transport. If the surfactant is soluble, the gradient in the surface concentration distribution as well as the induced Marangoni effect diminish, and the surfactant transport is slowed down. The shock-like film disturbance, however, is elevated significantly.