טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBen-Zaken Cohen Sigal
SubjectThe Role of Lung Surfactant in Lung Stability and Alveolar
Functioning
DepartmentDepartment of Biomedical Engineering
Supervisors Professor Emeritus Eitan Kimmel
Professor Emeritus Abraham Marmur
Mr. Zalman Weintraub


Abstract

Lung surfactant is a surface active agent found in the liquid films that coat surfaces of normal lung. It reduces surface tension (ST) forces and plays a role in stabilizing lung parenchyma. Deficiency of surfactant induces pathological functioning such as in respiratory distress syndrome. Male rats (BW=352+28gr) were anesthetized and connected to a mechanical ventilator. Lungs were exposed. Using video microscope, alveolar images and tracheal pressure were sampled simultaneously and processed. The procedure was performed in normal lungs (n=20); BAL lungs (n=15) that were washed (lavaged)  and as a result suffer from lack of surfactant; and in SRT lungs treated with surfactant replacement therapy, after BAL (n=10).  Alveoli diameter in normal lungs are small (0.11 to 0.13mm) and show marked hysteresis. In comparison, alveoli of BAL lungs are exceptionally large (0.20 to 0.35mm) and show no hysteresis, while SRT alveoli are medium (0.11 to 0.16mm) and show moderate hysteresis. Stability of lungs is studied theoretically using the dodecahedron model (DOM) where ST and stress in tissue elements are size dependent. The criterion for stability is associated with certain increasing rate of ST and tissue stress with alveolar size.  DOM is used also for ST estimation from measured data. It is found that ST increases gradually with alveolar size. In normal lung, ST is relatively small (5 to 30 dyne/cm), in BAL lung, ST is much greater (58 to 70 dyne/cm) and shows no hysteresis. The treatment by introduction of exogenous surfactant to lungs with damaged surfactant is an effective treatment as demonstrated by the considerable recovery of ST in the SRT lung.