A theoretical study of surfactant and liquid delivery into the lung

• Published in: Journal of applied physiology (1985) 1998-07, Vol.85 (1), p.333-352
• Main Authors: Halpern, D, Jensen, O. E, Grotberg, J. B
• Format: Article
• Language: English
• Subjects: Algorithms; Biological and medical sciences; Biological Transport; Humans; Infant, Newborn; Kinetics; Lung - metabolism; Lungs; Medical sciences; Models, Biological; Pharmacology. Drug treatments; Pulmonary Alveoli - physiology; Pulmonary Circulation - physiology; Pulmonary Surfactants - administration & dosage; Pulmonary Surfactants - metabolism; Respiration, Artificial; Respiratory diseases; Respiratory system; Surface Tension; Trachea - blood supply; Trachea - metabolism; Trachea - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1998.85.1.333

1  Department of Mathematics, University of Alabama, Tuscaloosa, Alabama 35487; 2  Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 9EW, United Kingdom; and 3  Department of Biomedical Engineering, Northwestern University, Evanston, 60208, and Department of Anesthesiology, Northwestern University Medical School, Chicago, Illinois 60611 A computational study is presented for the transport of liquids and insoluble surfactant through the lung airways, delivered from a source at the distal end of the trachea. Four distinct transport regimes are considered: 1 ) the instilled bolus may create a liquid plug that occludes the large airways but is forced peripherally during mechanical ventilation; 2 ) the bolus creates a deposited film on the airway walls, either from the liquid plug transport or from direct coating, that drains under the influence of gravity through the first few airway generations; 3 ) in smaller airways, surfactant species form a surface layer that spreads due to surface-tension gradients, i.e., Marangoni flows; and 4 ) the surfactant finally reaches the alveolar compartment where it is cleared according to first-order kinetics. The time required for a quasi-steady-state transport process to evolve and for the subsequent delivery of the dose is predicted. Following fairly rapid transients, on the order of seconds, steady-state transport develops and is governed by the interaction of Marangoni flow and alveolar kinetics. Total delivery time is ~24 h for a typical first dose. Numerical solutions show that both transit and delivery times are strongly influenced by the strength of the preexisting surfactant and the geometric properties of the airway network. Delivery times for follow-up doses can increase significantly as the level of preexisting surfactant rises. pulmonary surfactant; drug delivery; surfactant replacement therapy; respiratory distress syndrome; Marangoni flow; airway liquid; surface tension dynamics; pulmonary fluid mechanics