Thoraxvolumes

Thorax volumes refer to the air-filled spaces within the thoracic cavity as the lungs expand and contract. In respiratory physiology, they are used to describe how much air the lungs hold under different conditions. The term is often used interchangeably with lung volumes, though some discussions distinguish between the two by emphasizing volumes inside the chest rather than the anatomical structures alone. These measurements help assess pulmonary function, the mechanics of breathing, and the effects of aging, sex, body size, and disease.

The major thorax volumes are tidal volume (VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), residual volume (RV), functional residual capacity (FRC), vital capacity (VC), and total lung capacity (TLC). VT is the amount of air moved in and out during a normal breath. IRV is the extra air that can be inhaled after a normal inspiration, while ERV is the extra air that can be exhaled after a normal expiration. RV is the air remaining in the lungs after a maximal exhale. FRC is the sum of ERV and RV and represents the lung volume after a normal expiration. VC is the maximum amount of air that can be exhaled after a maximum inhalation, and TLC is the sum of all lung volumes.

Measurement typically uses spirometry to quantify VT, IRV, ERV, and VC, while RV and TLC are often determined with body plethysmography or gas-dilution methods. In healthy adults, typical values are VT about 0.5 L; IRV ~2–3 L; ERV ~0.8–1.5 L; RV ~1–1.5 L; FRC ~2–3 L; VC ~3–5 L; TLC ~5–6 L, with variations by age, sex, height, and overall health. Abnormal patterns aid in diagnosing restrictive or obstructive lung conditions.