Cross-Sectional Physiology



Cross-Sectional Physiology


Jud W. Gurney, MD, FACR



Terminology


Definitions



  • Geometry of airways and arteries is important determinant of flow distribution


  • Airway branching



    • Asymmetric dichotomous pattern (each parent divides into 2 daughter branches of unequal size)



      • Asymmetric branching follows consistent rules (has fractal geometry)


      • Diameter and length of daughter branches reduced by consistent factor


      • Approximately 17 orders (counting from peripheral to central)


      • Pathology lengths to alveolar unit varies from 7.7-22.4 cm


      • Alveoli present after 14th branch point (from 14-23 generations)


  • Vascular branching



    • Asymmetric pattern similar to airways, exception


    • Supernumerary branches distally that arise at 90° from parent vessel and supply alveoli


  • Perfusion: Nongravity



    • Normal 4x increase in flow from central to periphery of lung in isogravitational plane


    • In asymmetric branches, total flow divided unequally and when continued over several generations, results in wide dispersion of perfusion


    • 75% of blood flow may be attributable to vascular branching geometry in comparison to gravity


    • Transit time in pulmonary circulation longer in peripheral lung


  • Ventilation: Nongravity



    • Parallels perfusion, optimizes matching of ventilation and perfusion


  • Lymphatic function: Nongravity



    • Passive augmentation increased in lung periphery due to respiratory excursion


    • Experimental studies of particulate clearance show increased clearance from lung periphery as compared to more central lung


  • Secondary pulmonary lobule: Similar nongravitational gradient from core bronchovascular structures to periphery of lobule

Tags: ,
Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Cross-Sectional Physiology

Full access? Get Clinical Tree
Get Clinical Tree app for offline access