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Lung volumes. Functional residual capacity (FRC) is the volume of air present in the lungs at the end of passive expiration. [1] At FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm or other respiratory muscles. [1]
Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. [1] Tidal breathing is normal, resting breathing; the tidal volume is the volume of air that is inhaled or exhaled in only a single such breath.
A lung's capacity consists of two or more lung volumes. The lung volumes are tidal volume (V T), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). The four lung capacities are total lung capacity (TLC), inspiratory capacity (IC), functional residual capacity (FRC) and vital capacity (VC).
Tidal volume: that volume of air moved into or out of the lungs in 1 breath (TV indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol TV or V T is used.) RV: Residual volume: the volume of air remaining in the lungs after a maximal exhalation: ERV
Restrictive lung diseases are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, [2] resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.
COPD is defined as a forced expiratory volume in 1 second divided by the forced vital capacity (FEV1/FVC) that is less than 0.7 (or 70%). [8] The residual volume, the volume of air left in the lungs following full expiration, is often increased in COPD, as is the total lung capacity, while the vital capacity remains relatively normal.
The closing capacity is less than the Functional Residual Capacity, the amount of gas that normally remains in the lungs during respiration. This means that there is normally enough air within the lungs to keep these airways open throughout both inhalation and exhalation. As the lungs age, there is a gradual increase in the closing capacity (i.e.
TLC = IRV + Vt + ERV + RV: The volume of air contained in the lung at the end of maximal inspiration. The total volume of the lung. Values of between 80% and 120% of average value are considered normal. [3] Vital capacity (VC) = 4.6 / 3.6 L: VC = IRV + Vt + ERV: The amount of air that can be forced out of the lungs after a maximal inspiration.