Thoraxvolumens

Thoraxvolumes, or thoracic volumes, are the discrete quantities of air contained in the lungs and conducting airways at specific points of the respiratory cycle. The principal volumes are tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume. Tidal volume is the amount of air moved in and out with a normal breath. Inspiratory reserve volume is the extra air that can be inhaled after a normal inhalation, while expiratory reserve volume is the extra air that can be exhaled after a normal exhalation. Residual volume is the air remaining in the lungs after a maximal exhalation and cannot be measured by simple spirometry.

From these volumes, several capacities are defined. Inspiratory capacity equals tidal volume plus inspiratory reserve volume. Vital capacity equals inspiratory reserve volume plus tidal volume plus expiratory reserve volume. Functional residual capacity equals residual volume plus expiratory reserve volume. Total lung capacity equals the sum of all four volumes (tidal, inspiratory reserve, expiratory reserve, and residual).

Typical values for healthy adults at sea level, with normal body size, are approximately: tidal volume about 0.5 liters; inspiratory reserve volume around 2.5 to 3.0 liters; expiratory reserve volume around 0.8 to 1.5 liters; residual volume around 1.0 to 1.5 liters; vital capacity about 4.0 to 5.0 liters; total lung capacity about 5.5 to 6.5 liters; functional residual capacity about 2.0 to 2.5 liters. These values vary with age, sex, body size, and posture.

Measurement of thoraxvolumes is performed using spirometry for some volumes, and body plethysmography or gas dilution methods for others (notably residual volume and total lung capacity). Changes in thoraxvolumes reflect normal physiology and can indicate respiratory or systemic disease, such as obstructive or restrictive patterns.