2. Factors affecting pulmonary ventilation
1. Surface tension of alveolar fluid
2. Compliance of lungs
3. Airway resistance
3. 1. Surface tension of alveolar fluid:
• thin layer of alveolar fluid coats the luminal surface of
alveoli and exert a force known as surface tension
• It arises as liquid surround the air sphere
• It produces and inward-directed force
• Surfactant (mixture of phospholipid and lipoprotein)
present in alveolar fluid reduces the surface tension.
• Deficiency of surfactant causes respiratory distress
syndrome.
5. Cont.…
2. Compliance of the lungs
• How much effort is required to stretch the lungs and chest
wall
• Depends on elasticity and surface tension
• Present during
1. Tuberculosis
2. pulmonary edema
3. produce deficiency in surfactant
4. impede lung expansion e.g. paralysis of muscles
5. Emphysema: destruction of elastic fibers
6. Cont.…
3. Airways resistance
• Present in airways esp. bronchioles
• Rate of airflow through airways depend on both pressure
difference and the resistance
• Larger diameter airways have decreased resistance
• Signals from sympathetic divisions of autonomic nervous system
cause relaxation of smooth muscles of in the wall of airways which
result in bronchodilation and decreased resistance
• Asthma, COPD, Emphysema, chronic bronchitis
7. Spirometry
Definition:
• “The technique /process of recording the volume (amount) & speed
(flow) of air into & out of the lungs is known as Spirometry.”
• It is also known as pulmonary function test.
Apparatus:
• The apparatus use for Spirometry is known as Spirometer or
respirometer.
Graph:
• Graphical representation of changes in the lungs volumes is known as
spirogram.
8. Lung volumes and capacities
• The volume of one breath is called the tidal volume (VT).
• Minute ventilation (MV) = total volume of air inhaled and exhaled
each minute
• Normal healthy adult averages 12 breaths per minute, moving about
500 ml of air in and out of lungs (tidal volume)
• MV = 12 breaths/min x 500 ml/ breath
= 6 liters/ min
10. Pulmonary volumes
• “Amount of air present in the lungs during
inspiration & expiration”
• These are of 4 types.
1. Tidal volume
2. Inspiratory reserve volume
3. Expiratory reserve volume.
4. Residual volume.
12. Volumes of Air Exchange
Tidal volume - amount of air exhaled normally after a typical
inspiration. Normal - about 500 ml
Expiratory Reserve volume - additional amount of air forcibly
expired after tidal expiration (1000 - 1200 ml).
Inspiratory Reserve volume - (deep breath) amount of air that
can be forcibly inhaled over and above normal (1900-3100) .
Residual volume - amount of air that stays trapped in the alveoli
(about 1.2 liters).
13. Pulmonary capacities
• The combination of specific lung volumes is known as
pulmonary capacities
• These are of 4 types.
1. Inspiratory capacity
2. Functional residual capacity
3. Vital capacity
4. Total lung capacity
14. Inspiratory capacity & Functional residual
capacity
• Inspiratory capacity
• Total Inspiratory ability of lungs. Or
• Inspiratory capacity = Tidal volume + Inspiratory reserve
volume
• Value: 500+3100=3600ml in males
• 500+1900= 2400 in female
• Functional residual capacity
• Volume of air remaining in the lungs at normal expiration or
• functional residual capacity = Expiratory reserve volume+
residual volume
• Value: 1200+1200=2400ml and 110=700= 1800 in female
15. Vital capacity
• Max amount of air that a person can expel forcefully from lungs after
taking deep inspiration.
• Or
• Vital capacity = Tidal volume + Inspiratory reserve volume +
expiratory reserve volume
• Value: 4800ml in male and 3100 in female
16. Total lung capacity
• Max volume of air to which lungs can be expanded with
greatest possible Inspiratory effort
• Or
• Max volume of air present in the lungs after deep
inspiration.
• Vital capacity + residual volume
• Value:
• 4800+1200=6000ml in males
• 3100+1100=4200 in females
