Tidal volume
Say it: TY-dul VOL-yoom
Tidal volume is the amount of air that moves into or out of the lungs in one normal, relaxed breath, about 500 mL in a healthy adult.
Definition
What is tidal volume?
Tidal volume is the amount of air breathed in or out in a single quiet breath, taken without extra effort. In a healthy adult it is about half a liter, a small fraction of the roughly 6 liters the lungs can hold. It is one of the standard lung volumes measured with a spirometer, alongside the inspiratory and expiratory reserve volumes, the extra air that can be forced in or out beyond a normal breath, and the residual volume, which always stays in the lungs.
Not all of each breath reaches the alveoli. Part of it fills the airways, the anatomical dead space, where no gas exchange takes place. Multiplying tidal volume by breathing rate gives minute ventilation, while subtracting the dead space first gives alveolar ventilation, the air that actually takes part in exchange. This is why rapid, shallow breathing moves fresh air into the alveoli less effectively than slower, deeper breaths.
During exercise, tidal volume rises along with breathing rate. In intensive care it is a key ventilator setting, and using smaller breaths scaled to a patient's predicted body weight helps protect injured lungs from overstretching.
Word parts
Where does the term “tidal volume” come from?
- tidal
- rising and falling like the tideOld English tid, time or season
Related
Terms that go with it
- Gas exchangeGas exchange is the movement of oxygen into the blood and carbon dioxide out of it by diffusion across thin membranes, mainly in the lungs and tissues.
- AlveolusAn alveolus is one of the tiny air sacs at the end of the lung's airways, where oxygen passes into the blood and carbon dioxide passes out.
- DiaphragmIn anatomy, the diaphragm is the dome-shaped sheet of muscle and tendon dividing the chest from the abdomen, and the main muscle of breathing.
- COPDCOPD is a long-term lung disease, usually caused by smoke or polluted air, in which damaged airways and air sacs limit the flow of air out of the lungs.
- AsthmaAsthma is a long-term lung disease in which the airways become inflamed and narrowed, causing wheezing, coughing, chest tightness and breathlessness.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 22.3 The Process of Breathing
- OpenStax Biology 2e, 39.2 Gas Exchange across Respiratory Surfaces
- OpenStax Biology 2e, 39.3 Breathing
- NCBI MeSH: Tidal Volume
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