# Ventilation (physiology)

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Christine Henen, MD

One of the primary roles of the lungs is to facilitate gas exchange between the circulatory system and the external environment. The lungs are constitute of branching airways that terminate in respiratory bronchioles and alveoli, which participate in gas exchange. The conducting zone of the lung which delivers gas to sites of gas exchange in alveoli is Mostly bronchioles and large airways. Gas exchange happens in the lungs between alveolar air and the blood of the pulmonary capillaries. For sufficient gas exchange to occur, alveoli must be ventilated and perfused. Ventilation (V) refers to the flow of air in and out of the alveoli, compared to perfusion (Q), which refers to the flow of blood to alveolar capillaries. every Individual alveoli have variable degrees of ventilation and perfusion in different regions of the lungs. The ratio of ventilation to perfusion (V/Q) is the Collective changes in ventilation and perfusion in the lungs, for which are measured clinically as V/Q ratio . Changes in the V/Q ratio can affect gas exchange and can contribute to hypoxemia [1].

In respiratory physiology, ventilation (or ventilation rate) is the rate at which gas enters or leaves the lung. It is categorised under the following definitions:

 Measurement Equation Description Minute ventilation = tidal volume * respiratory rate[1][2] the total volume of gas entering the lungs per minute. Alveolar ventilation = (tidal volume - dead space) * respiratory rate [1] the volume of gas per unit time that reaches the alveoli, the respiratory portions of the lungs where gas exchange occurs. Dead space ventilation = dead space * respiratory rate[3] is the volume of gas per unit time that does not reach these respiratory portions, but instead remains in the airways (trachea, bronchi, etc.).

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 [4]

## References

1- Wagner PD, Laravuso RB, Uhl RR, West JB. Continuous distributions of ventilation-perfusion ratios in normal subjects breathing air and 100 per cent O2. J Clin Invest. 1974 Jul;54(1):54-68. [PMC free article] [PubMed]

1. http://www.nda.ox.ac.uk/wfsa/html/u12/u1211_02.htm
2. Essentials of Human Physiology by Thomas M. Nosek. Section 4/4ch3/s4ch3_16.
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