Physiological Basis of Flow-Volume Curve

Question 1

Obstructive effect

Answer 1

Peak flow reduced

RV and TLC increased

This is due to increased lung compliance and increase in air trapping

ALSO, concave shape of expiratory curve

Question 2

Restrictive effect on FVC

Answer 2

Compliance is decreased…peak flow is about the same because the increased recoil helps push air out

Much less so on inspiration

Question 3

Efffort independent portion

Answer 3

Only occurs in range of low lung volume and reflects the flow resistance of the small airways

Question 4

Mech of effort-independent

Answer 4

Forced expiratory effort generates positive intrapleural pressure

This can compress the intrathoracic small airways

Larger effort means more compression

THis means that increasing effort does not increase airflow

Compression occurs when Palv = Pip

Question 5

What happens in obstructed that allows collapsiing?

Answer 5

Radial traction by tethering bands disappears

This normally keeps the airways open

Forced expiration will further close these airways and lead to air trapping

Question 6

Equation related to air trapping

Answer 6

Change in pressure = flow times reisistance

If the resistance of small airways are increased as they are in emphysema, then pressure drops more rapidly along airways and airway closure occurs at an earlier point