Surface Tension/Airway Resistance

Question 1

Impacts of surface tension (of H₂O) on lung function

Answer 1

• ==> 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

Question 2

Surfactant characterisitcs

Answer 2

• =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

Question 3

Respiratory distress syndrome characteristics

Answer 3

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

Question 4

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

Answer 4

• 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

Question 5

Major site of airway resistance

Answer 5

• intermediate-sized bronchi

Question 6

Factors controlling airway resistance

Answer 6

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

Question 7

Lung volume impact on airway resistance

Answer 7

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

Question 8

Impact of bronchial smooth muscle tone on airway resistance

Answer 8

• 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

Question 9

Agents that cause bronchoconstriction

Answer 9

• Ach release via vagal nerve
• histamine
• products of arachidonic acid metabolism (thromboxane A₂, leukotriences)
• low P_CO2

Question 10

Agents that cause bronchodilation

Answer 10

• epinephrine/norepinephrine
• isoproteranol (drug)
• high P_CO2

Question 11

Dynamic Airway collapse impact on airway resistance

Answer 11

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

Question 12

Emphysema impacts on airway resistance

Answer 12

• 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