Surface tension/airway resistance Flashcards
define surface tension
forces due to favorable water-water interactions and unfavorable air-water interactions
how does the alveolus form favorable interactions between air-water?
How does increased surface tension affect lung compliance
incr surface tension
decr lung compliance b/c water layer in smaller alveoli has a smaller surface area to volume ratio so surface tension prevents expansion
how does saline-filled lung differe from air-filled lung
fluid into alveoli provides alternate way to reduce liquid-air interface by creating deeper water layers
water from pulmonary capillary
how does surface tension affect small alveoli
collapse of small alveoli (high P due to P = 2T/R) and pressure gradient forces pressure into larger alveoli
What is surfactant?
What does it do?
mix of lipids + proteins iwth polar and non-polar ends
intercalates between water molec, decr attractive forces
increased effect at smaller alveoli
Effect of surfactant
1) incr lung compliance
2) prevent collapse of small alveoli
3) prevent accum of fluid inside alveoli
what is disease characterized by surfactant deficiency?
respiratory distress syndrome – stiff, noncompliant lungs prone to collapse
Respiratory airways provide ____
Flow always from __ to ___
resistance, R
high to low pressure
Flow equation for laminar flow
relationship between airway resistance to radius
Flow = (P2 - P1) / R
R proportional to 1/r^4
compare laminar to turbulent flow
most air flow in airways is ___
flow < (P2 - P1) / R
transitional (between laminar and turbulent)
Chemical factors that affect airway resistance
All act by doing what?
affecting smooth muscle tone of bronchioles
What are examples of bronchoconstrictors
Parasympathetic Nervous system (acetycholine)
Histamine (asthma)
what are examples of bronchodilators
sympathetic nervous system (epinephrine/norepinephrine via beta adrenergic receptors)
agonists for beta adrenergic receptors (isproteronol, albuterol)
CO2 in bronchioles
Mechanical factors that affect airway resistance
1) mucous (bronchitis)
2) lung volumes
3) dynamic airway collapse
how does lung volume affect airway resistance
implications for obstructive disease?
incr lung volume, decr resistance
patient with obstructive disease breath at higher lung volumes
(deleterious for muscle forces needed to inflate lungs)
Discuss dynamic airway collapse
when does it occur?
how does your body create a positive PIP
PTP = PAW -PIP
if you have positive PIP –> airway collapse
if expiratory muscles used, chest wall exert force on intrapleural space or during coughing
Airway is ___ when PAW > PIP
Airway is ___ when PAW < PIP
open
closed
Healthy person, quiet breathing
What is PIP? Open or close airway?
negative PIP pulls airway open
Healthy person, forced expiration
what happens to PIP?
Open or close airway
Chest wall exerts force on intrapleural space
–> PIP positive
positive PIP collapses airway
what happens to emphysema, quiet expiration
Primary problem
Compensation
Primary problem–> , decr tendency of lungs to deflate/recoil, employ use muscles in forced expiration, lose connective tissue supporting airway –> PIP = positive
Compensation = positive PIP collapses airway
why do emphysemic patients exhale through pursed lips?
exhaling through pursed lips incr airway pressure, decr probability of airway collapse
