Flow Volume Curves

Question 1

Flow Volume Curves Definition

Answer 1

• The flow volume curve shows the r/s b/w lung volume + airflow
• utilises Total lung capacity + Residual volume

Question 2

Expiratory airflow is affected by:

Answer 2

• Expiratory force
• Airway diameter: especially bronchioles (due to smooth muscle)
• Airway collapse

Question 3

When is peak expiratory air flow? and why?

Answer 3

• occurs early in expiration - when the lung is under the greatest stretch, + elastic recoil is greatest
• High flow rates are achieved early as gas leaves large airways
• Flow decreases later when smaller airways make greater contribution
• Expiratory airflow decreases as lung volume decreases

Question 4

Other important expiratory airflow points:

Answer 4

• During expiration, decreased effort results in decreased flow.
• However, above a threshold, the only effect is on the initial stages of the expiration → we have limited ability to regulate the expiratory flow rate.
• The closing volume is the lung volume at which small airways begin to close so flow decreases.
• Early in the forced expiration muscular effort determines the gas flow
• Later in the forced expiration closure of the small airways determines the gas flow:
  
  • Bigger expiratory effort → earlier closure of the airways
  • Smaller expiratory effort → less force pushing gas out

Question 5

During inspiration…

Answer 5

During inspiration, greater effort results in greater flows = only dependent on muscular effort

However inspiration is most difficult at:

• Low volumes (when surface tension is greatest)
• High volumes (when elastic forces are greatest)