Lung Capacity

Lung capacities refer to the volumes of air associated with the different phases of the respiratory cycle:

  • Total lung capacity – Volume of air in the lungs after a maximal inhalation (~ 6 litres in a normal adult male)
  • Vital capacity – Volume of air that can be exchanged by the lungs via a maximal inhalation and exhalation
  • Residual volume – Volume of air that is always present in the lungs (~ 20% of total lung capacity)
  • Tidal volume – Volume of air that is exchanged via normal breathing (~ 500 ml per breath)

Ventilation rate (breathing frequency) at rest for a typical adult is roughly 12 – 16 breaths per minute

  • Ventilation rate can be substantially increased with physical activity (maximal increase is roughly 5 – 6 fold over normal)

A number of factors contribute to an individual’s total lung capacity and ventilation rate, including:

  • Height (taller people tend to have larger chests and hence larger total lung capacities)
  • Location (people living at high altitudes tend to have larger capacities to compensate for the lower atmospheric pressure)
  • Lifestyle (obese people and smokers tend to have lower capacities and higher rates of ventilation)

Overview of Lung Capacities

lung capacity