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Flashcards in Surface Tension/Airway Resistance Deck (12)
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Impacts of surface tension (of H2O) on lung function

  • ==> reduced lug compliance; surface tension produces net force that opposed exansion of alveoli
  • ==> fluid accumulation w/in alveoli; surface tension facros fluid movement inwards
  • ==> collapse of small alveoli
    • P=2T/r (P=pressure, T=surface tension, r=radius) ==> smaller alveoli have higher internal pressure
    • air flows down pressure gradient and into larger alveoli


Surfactant characterisitcs

  • =mix of lipids and proteins secreted by alveolar type II cells
  • fxn=lowers the surface tension of water via intercalation ==> decreased attractive forces
    • increased effect @ smaller radii


Respiratory distress syndrome characteristics

  • infants w/a surfactant definiciecy
  • stiff, noncompliant lungs ==> prone to collapse


Properties of air flow w/in airways (+ 3 types of flow)

  • flow is a fxn of change in pressure and airflow resistance (provided by airways)
    • Flow = (P1 - P2) / R
  • @ low flow rates ==> laminar flow
    • R(resistance)=(8nl)/(πr4)
  • increased flow ==> turbulent flow
    • occurs often @ large diamter tubes w/high flow rates
  • @ branches/irregular walls ==> transitional flow


Major site of airway resistance

  • intermediate-sized bronchi


Factors controlling airway resistance

  1. lung volume
  2. bronchial smooth muscle tone
  3. dynamic airway collapse


Lung volume impact on airway resistance

  • airways expand @ large lung volumes ==> decreased resistance
  • airways most sensitive = bronchioles (no cartilage)


Impact of bronchial smooth muscle tone on airway resistance

  • contraction of muscle ==> narrowed airway ==> increased resistance
  • bronchial smooth muscle <== vagal nerve
    • (vagal) Ach release stimulates contraction
  • adrenergic receptor stimulation (by epinephrine/norepinephrine) ==> bronchodilation via activation of ß2 receptors


Agents that cause bronchoconstriction

  • Ach release via vagal nerve
  • histamine
  • products of arachidonic acid metabolism (thromboxane A2, leukotriences)
  • low PCO2


Agents that cause bronchodilation

  • epinephrine/norepinephrine
  • isoproteranol (drug)
  • high PCO2


Dynamic Airway collapse impact on airway resistance

  • Positive PIP develops outside of airway ==> collapse of airway
  • Positive PIP develops during forced expiration
    • chest wall exerts a strong force on intrapleural space ==> positive force


Emphysema impacts on airway resistance

  • patients w/emphysema have higher tendency of airway collapse due to reduced recoil/elasticity

    • ​==> increased likelihood of compression of intrapleural space 
  • pts are more likely to use expiratory muscles during queit breathing
  • also more likely to collapse due to loss of supporting connective tissue
  • often pts expire w/pursed lips ==> maintains larger air pressure @ airways & helps keep airways open