The document discusses the use of a spirometer to measure lung volume and capacities, detailing various metrics such as tidal volume, respiratory rate, minute ventilation, and types of lung volumes and capacities. It includes definitions of anatomical structures, the concept of dead space, and factors that may reduce vital capacity, both intrapulmonary and extrapulmonary. The document emphasizes the importance of understanding these respiratory metrics for assessing lung function and health.

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.