Airway Resistance

Question 1

What is pressure gradient?

Answer 1

Difference between alveolar and atmospheric pressure
Pressure gradient = resistance X flow

Question 2

What is airway resistance?

Answer 2

Pressure difference between atm and alv/flow rate
R = change in P/F

Question 3

What are the 3 flow rates?

Answer 3

Laminar flow
Unsteady eddies
Turbulent

Question 4

What does an increase in air viscosity cause?

Answer 4

increased airway resistance

Question 5

What do longer airways mean for resistance?

Answer 5

Increased airway resistance

Question 6

What flow is most common at resting flow rates?

Answer 6

laminar

Question 7

Where is turbulent flow normally found?

Answer 7

Branch points and large airways

Question 8

What does the probabilty of turbulence increase with?

Answer 8

Increasing radius and veolcity

Question 9

What is Poiseuille’s law?

Answer 9

Flow = ∆Pπr4/8ηl
decreased radius = increased resistance

Question 10

What is the resistance in smaller airways?

Answer 10

Overall cross sectional area is increased -> lower resistance

Question 11

What are the major sites of resistance?

Answer 11

larger airways and medium sized bronchioles

Question 12

How does lung volume affect resistance?

Answer 12

Total airway resistance declines with increasing lung volume
bronchiolar diameter increases with increasing lung volume

Question 13

What happens at low lung volumes?

Answer 13

Airways close completely preventing complete deflation of isolated lungs

Question 14

How does airway SM regulate resistance?

Answer 14

Regulates diameter by bronchoconstriction/dilation

Question 15

What does cholinergic PNS stimulation cause?

Answer 15

Bronchoconstriction rvia M3 muscarinic cholinergic receptors
comes from vagus

Question 16

What does beta adrenergic SNS stimulation cause?

Answer 16

Bronchodilation from circulating adrenaline

Question 17

What is ventolin?

Answer 17

beta adrenergic agonist

Question 18

What is limiting expiratory flow?

Answer 18

dynamic compression of airways

Question 19

What is transpulmonary pressure?

Answer 19

Pressure that holds lungs open at 4mmHg along End expiration airways
Ptp = Palv - Pip

Question 20

What is Palv, Patm and Pip?

Answer 20

Palv = 0mmHg
Patm = 0mmHg
Pip = -4mmHg

Question 21

What happens as pressure travels towards the mouth?

Answer 21

As airway pressure decreases towards atmospheric pressure at mouth, collapsing pressure increases

Question 22

What pressure is exerted on all airways/

Answer 22

Intrapleural pressure

Question 23

What happens when Palv drops below Pip?

Answer 23

Ptp becomes negative -> equal pressure point

Question 24

What is the equal pressure point?

Answer 24

Point at which pressure inside the airway equals pressure outside (intrapleural pressure)

Question 25

What happens when Palv is above the equal pressure point?

Answer 25

Tendency for collapse

Question 26

What prevents the tendency to collapse?

Answer 26

- opposed by cartiliaginous support in larger airways and traction by alveolar elastic recoil in smaller airways

Question 27

What does emphysema cause?

Answer 27

Increased compliance loss of elastic recoil

Question 28

What happens in emphysema during expiration?

Answer 28

Dynamic airway collapse - increase +ve pressure as more muscles recruited to expire contributes to hyperventilation (increased FRC) Increased airway resistance

Question 29

What happens in chronic bronchoitis?

Answer 29

Narrow lumen of airways from thickening of airway wall

Question 30

What does asthma cause?

Answer 30

Increased airway resistance Excessive bronchial SM contraction thickened airway wall dynamic airway collapse Hyperinflation

Question 31

How can we test for increased airway resistance?

Answer 31

Clincial pulmonary function testing

Question 32

What is FVC?

Answer 32

Amount of air breathed in and out at forced expiration

Question 33

What is the difference between obstructive and restrictive lung diseases?

Answer 33

O = airway narrowing eg asthma R = reduced compliance eg pulmonary fibrosis