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ALL / Respiratory Medicine
Respiratory physiology: lung volumes
Respiratory physiology: lung volumes
The diagram below demonstrates the lung volumes which may be measured:
Tidal volume (TV)
- volume inspired or expired with each breath at rest
- 500ml in males, 350ml in females
Inspiratory reserve volume (IRV) = 2-3 L
- maximum volume of air that can be inspired at the end of a normal tidal inspiration
- inspiratory capacity = TV + IRV
Expiratory reserve volume (ERV) = 750ml
- maximum volume of air that can be expired at the end of a normal tidal expiration
- significantly reduced in obesity (increased abdominal fat mass pushes up against the diaphragm, reducing the volume of air that can be expelled)
Residual volume (RV) = 1.2L
- volume of air remaining after maximal expiration
- increases with age
- RV = FRC - ERV
Functional residual capacity (FRC)
- the volume in the lungs at the end-expiratory position
- FRC = ERV + RV
Vital capacity (VC) = 5L
- maximum volume of air that can be expired after a maximal inspiration
- 4,500ml in males, 3,500 mls in females
- decreases with age
- VC = inspiratory capacity + ERV
Total lung capacity (TLC) is the sum of the vital capacity + residual volume
Physiological dead space (VD)
- VD = tidal volume * (PaCO2 - PeCO2) / PaCO2
- where PeCO2 = expired air CO2
+PassMedicine Notes
The diagram below demonstrates the lung volumes which may be measured:
swb023.jpg
Tidal volume (TV)- volume inspired or expired with each breath at rest
- 500ml in males, 350ml in females
- maximum volume of air that can be inspired at the end of a normal tidal inspiration
- inspiratory capacity = TV + IRV
- maximum volume of air that can be expired at the end of a normal tidal expiration
- significantly reduced in obesity (increased abdominal fat mass pushes up against the diaphragm, reducing the volume of air that can be expelled)
- volume of air remaining after maximal expiration
- increases with age
- RV = FRC - ERV
- the volume in the lungs at the end-expiratory position
- FRC = ERV + RV
- maximum volume of air that can be expired after a maximal inspiration
- 4,500ml in males, 3,500 mls in females
- decreases with age
- VC = inspiratory capacity + ERV
Total lung capacity (TLC) is the sum of the vital capacity + residual volume
Physiological dead space (VD)- VD = tidal volume * (PaCO2 - PeCO2) / PaCO2
- where PeCO2 = expired air CO2
