The apparatus used to measure Volume of air exchanged during breathing Respiratory rate The record is called a spirogram Upward deflection inhalation Downward deflection exhalation

1. Lung Volume And Capacities

2. Spirometer
• The apparatus used to measure
– Volume of air exchanged during breathing
– Respiratory rate
• The record is called a spirogram
• Upward deflection inhalation
• Downward deflection exhalation

3. • Healthy adult averages R/R of 12 breaths/min
• Tidal Volume(VT)
– Amount of air inhaled and exhaled in and out of the
lungs is 500ml/breath
• Minute Ventilation:
– The total volume of air inhaled and exhaled each
minute
• Calculated by:
– MV = VT × R/R
= 500 breaths/ml × 12 breaths/min
= 6 litres/min

4. • In a typical adult
– 70% of the tidal volume i.e. 350ml reaches the
respiratory portion of the system
– Respiratory bronchioles, alveolar ducts, alveolar
sacs and alveoli
– 30% remains in non-respiratory passageways or
conducting airways of the system
• Anatomic Dead Space
– Nose, pharynx, larynx, trachea, bronchi,
bronchioles and terminal bronchioles

5. • Alveolar Ventilation Rate:
– Volume of air per minute that reaches the alveoli
and other respiratory portions
• 350ml/breath × 12 breaths/min = 4200ml/min

6. Lung Volumes
• 4 volumes
• Tidal Volume (VT)
• Amount of air inhaled and exhaled every breath
• Inspiratory Reserve Volume (IRV)
• The amount of air that can be forcefully inspired over
and above normal inspiration

7. • Expiratory Reserve Volume (ERV)
• The amount of air that can be forcefully exhaled after
normal exhalation
• Residual Volume (RV)
• The amount of air remaining in the lung even after
forced expiration

10. Lung Capacities
• Inspiratory capacity (IC)
– Represents the maximum volume that can be inspired
– Tidal volume plus inspiratory reserve volume
• VT + IRV
• Functional residual capacity (FRC)
– Represents the volume of air left in the lungs after normal
expiration
– Expiratory reserve volume plus the residual volume
• ERV + RV

11. • Vital capacity (VC)
– Maximum volume one can exchange in a respiratory cycle
– Sum of inspiratory reserve volume, tidal volume, and
expiratory reserve volume
• IRV + TV + ERV
• Total lung capacity (TLC)
– The air in the lungs at full inflation
– Sum of inspiratory and expiratory reserve volumes plus the
tidal volume and residual volume
• IRV + ERV + TV + RV

14. Factors That Reduce VC
• Loss of Distensible Tissue
– e.g. pneumonectomy, atelectasis.
• Decreased Compliance
– e.g. respiratory distress syndrome, alveolar
edema, or infiltrative interstitial lung diseases.
• Increased Residual Volume
– e.g. emphysema, asthma, or lung cyst

15. Extrapulmonary Factors that Reduce VC
• Limited Thoracic Expansion.
– e.g. thoracic deformities (Kyphoscoliosis) and pleural
fibrosis.
• Limited Diaphragmatic Descent.
– e.g. ascites and pregnancy.
• Nerve or Muscle Dysfunction.
– Pain (surgery, rib fracture)
– Primary neuromuscular disease.