Airway Resistance Flashcards
What is pressure gradient?
Difference between alveolar and atmospheric pressure
Pressure gradient = resistance X flow
What is airway resistance?
Pressure difference between atm and alv/flow rate
R = change in P/F
What are the 3 flow rates?
Laminar flow
Unsteady eddies
Turbulent
What does an increase in air viscosity cause?
increased airway resistance
What do longer airways mean for resistance?
Increased airway resistance
What flow is most common at resting flow rates?
laminar
Where is turbulent flow normally found?
Branch points and large airways
What does the probabilty of turbulence increase with?
Increasing radius and veolcity
What is Poiseuille’s law?
Flow = ∆Pπr4/8ηl
decreased radius = increased resistance
What is the resistance in smaller airways?
Overall cross sectional area is increased -> lower resistance
What are the major sites of resistance?
larger airways and medium sized bronchioles
How does lung volume affect resistance?
Total airway resistance declines with increasing lung volume
bronchiolar diameter increases with increasing lung volume
What happens at low lung volumes?
Airways close completely preventing complete deflation of isolated lungs
How does airway SM regulate resistance?
Regulates diameter by bronchoconstriction/dilation
What does cholinergic PNS stimulation cause?
Bronchoconstriction rvia M3 muscarinic cholinergic receptors
comes from vagus
What does beta adrenergic SNS stimulation cause?
Bronchodilation from circulating adrenaline
What is ventolin?
beta adrenergic agonist
What is limiting expiratory flow?
dynamic compression of airways
What is transpulmonary pressure?
Pressure that holds lungs open at 4mmHg along End expiration airways
Ptp = Palv - Pip
What is Palv, Patm and Pip?
Palv = 0mmHg
Patm = 0mmHg
Pip = -4mmHg
What happens as pressure travels towards the mouth?
As airway pressure decreases towards atmospheric pressure at mouth, collapsing pressure increases
What pressure is exerted on all airways/
Intrapleural pressure
What happens when Palv drops below Pip?
Ptp becomes negative -> equal pressure point
What is the equal pressure point?
Point at which pressure inside the airway equals pressure outside (intrapleural pressure)
What happens when Palv is above the equal pressure point?
Tendency for collapse
What prevents the tendency to collapse?
- opposed by cartiliaginous support in larger airways and traction by alveolar elastic recoil in smaller airways
What does emphysema cause?
Increased compliance
loss of elastic recoil
What happens in emphysema during expiration?
Dynamic airway collapse - increase +ve pressure as more muscles recruited to expire
contributes to hyperventilation (increased FRC)
Increased airway resistance
What happens in chronic bronchoitis?
Narrow lumen of airways from thickening of airway wall
What does asthma cause?
Increased airway resistance
Excessive bronchial SM contraction
thickened airway wall
dynamic airway collapse
Hyperinflation
How can we test for increased airway resistance?
Clincial pulmonary function testing
What is FVC?
Amount of air breathed in and out at forced expiration
What is the difference between obstructive and restrictive lung diseases?
O = airway narrowing eg asthma
R = reduced compliance eg pulmonary fibrosis
