Lung volumes

Lung volumes refer to the amount of air that is normally exchanged by our lungs, which can be calculated as information about the health of a person. These values are different in males, females, and kids and the ones used here as reference are those corresponding to an average male.

  • Tidal Volume (TV): the amount of air taken in and out of the lungs during a normal and relaxed breath, also known as quiet breathing. A person at rest takes between 10 to 12 breaths per minute, and the amount of air inhaled and exhaled in each breath is approximately 500 mL for both males and females. This volume of air can change, especially during exercise, due to the increase in carbon dioxide production by the body. Increasing the Tidal Volume during exercise is the only way to exhale all the CO2 carbon dioxide over-produced. This does not only explain why the breathing rate increases during physical activity but also why each breath is deeper.

  • Inspiratory Reserve Volume (IRV): the maximum amount of air that can be inhaled during a deep breath, in addition to the TV. IRV in males is about 3000 mL, while it is approximately 2000 mL in females.

  • Expiratory Reserve Volume (ERV): the maximum amount of air that can be exhaled in addition to the TV during a hard expiration. In males, this volume is around 1000 mL, and in females, it is 800 mL.

  • Residual Volume (RV): quantity of air that remains in the lungs after a forced exhalation. There is always some air inside the lungs to prevent the alveoli and bronchioles from collapsing. In males, the air remaining inside the lungs is around 1200 mL, and in females, it is 1000 mL.

The Dead Space is the air volume in the respiratory tract that does not undergo gas exchange. Every time a breath is taken, only a portion of the 500 mL of air ends up in the alveoli for gas exchange. The rest is trapped within the passageways of the lungs, including the trachea, bronchi, and bronchioles. This amount of air is around 150 mL for both males and females.

These values can change depending on additional factors such as age, ethnicity, health, and temporary changes like pregnancy.

This is an image of a pair of lungs. The lungs are divided into four parts colored differently to indicate the different lung volumes. From top to bottom: the first part, which is the biggest, is labeled as 3000 milliliters and it corresponds to the inspiratory reserve volume. The second part is labeled with 500 milliliters and it refers to the tidal volume. The third part is labeled as 1000 milliliters, which would be the expiratory reserve volume. And, finally, the last part is labeled as 1200 milliliters and it refers to the residual volume. A line imitating a respirometry analysis result is also shown inside the lungs. Bellow the lungs, small colored rectangles are the legend to match the colors in the lungs with the volumes they refer to.

Figure 1. Schematic illustration of a set of lungs and their volumes and capacities.