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Total lung capacity: the volume in the lungs at maximal inflation, the sum of VC and RV. TV: 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
Mechanical stimulation of the lungs can trigger certain reflexes as discovered in animal studies. In humans, these seem to be more important in neonates and ventilated patients, but of little relevance in health. The tone of respiratory muscle is believed to be modulated by muscle spindles via a reflex arc involving the spinal cord.
In cases of right to left shunts more of deoxygenated blood mixes with oxygenated blood from the lungs and thus to a small extent the condition might neutralize the high A-a gradient with pure oxygen therapy. Patient with parenchymal lung diseases will have an increased A-a gradient with moderate response to oxygen therapy.
The lungs expand and contract during the breathing cycle, drawing air in and out of the lungs. The volume of air moved in or out of the lungs under normal resting circumstances (the resting tidal volume of about 500 ml), and volumes moved during maximally forced inhalation and maximally forced exhalation are measured in humans by spirometry. [12]
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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]
Vital capacity (VC) is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume. It is approximately equal to Forced Vital Capacity (FVC). [1] [2] A person's vital capacity can be measured by a wet or regular spirometer.
Tidal volume (Vt) is the volume inspired and expired with each breath. Variability in the wave form can be used to differentiate between restrictive (less) and obstructive pulmonary diseases as well as acute anxiety. Minute ventilation is equivalent to tidal volume multiplied by respiratory rate and is used to assess metabolic activity.