Flashcards in Surface Tension/Airway Resistance Deck (12)
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1
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
- 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
2
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
- increased effect @ smaller radii
3
Respiratory distress syndrome characteristics
- infants w/a surfactant definiciecy
- stiff, noncompliant lungs ==> prone to collapse
4
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
- Flow = (P1 - P2) / R
- R(resistance)=(8nl)/(πr4)
- occurs often @ large diamter tubes w/high flow rates
5
Major site of airway resistance
- intermediate-sized bronchi
6
Factors controlling airway resistance
- lung volume
- bronchial smooth muscle tone
- dynamic airway collapse
7
Lung volume impact on airway resistance
- airways expand @ large lung volumes ==> decreased resistance
- airways most sensitive = bronchioles (no cartilage)
8
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
- (vagal) Ach release stimulates contraction
9
Agents that cause bronchoconstriction
- Ach release via vagal nerve
- histamine
- products of arachidonic acid metabolism (thromboxane A2, leukotriences)
- low PCO2
10
Agents that cause bronchodilation
- epinephrine/norepinephrine
- isoproteranol (drug)
- high PCO2
11
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
- chest wall exerts a strong force on intrapleural space ==> positive force
12
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
patients w/emphysema have higher tendency of airway collapse due to reduced recoil/elasticity
-
==> increased likelihood of compression of intrapleural space
