Lungvolymer

Lung volumes, or lungvolymer, describe the different amounts of air present in the lungs at various points in the breathing cycle. They are distinct from lung capacities, which are combinations of volumes used to describe overall lung size and ventilatory reserve. The main volumes are tidal volume (the regular amount of air moved during a normal breath), inspiratory reserve volume, expiratory reserve volume, and residual volume (the air remaining after a maximal exhalation).

From these volumes, several capacities are defined. Vital capacity is the total volume that can be inspired after a maximal expiration (IRV + tidal volume + ERV). Functional residual capacity is the volume remaining in the lungs after a normal exhalation (ERV + RV). Inspiratory capacity is the sum of tidal volume and inspiratory reserve volume (VT + IRV). Total lung capacity equals the sum of all volumes (IRV + VT + ERV + RV).

Typical values vary widely with age, height, sex, and body composition. As rough references for a healthy adult, tidal volume is about 0.5 liters, residual volume around 1–1.5 liters, and total lung capacity near 6 liters, with functional residual capacity often around 2.5 liters.

Measurement and interpretation: Spirometry can measure tidal volume, IRV, and ERV, but cannot directly measure residual volume or total lung capacity. These require additional methods such as body plethysmography or gas dilution techniques (helium or nitrogen).

Clinical relevance: Lung volumes and capacities help assess pulmonary function and distinguish obstructive from restrictive patterns. Obstructive diseases (for example, COPD or asthma) often show increased residual volume and functional residual capacity due to air trapping, while restrictive diseases reduce total lung capacity and vital capacity.