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BriVocals
Ventilation
The tissues of the body must be continuously supplied with sufficient amounts of oxygen, and relieved of the carbon dioxide produced by them. Oxygen is taken from the air we breathe in, and carbon dioxide is carried away in the air we breathe out. The respiratory tract is composed of the nose, mouth, pharynx, larynx, trachea, bronchi, bronchiole and alveoli. The oxygen/carbon dioxide gas exchange occurs only in the alveoli.
Gas ventilation is in proportion to the amount of air reaching the alveoli: During each breath, about 150cc of fresh air never reaches the alveoli but remains in the rest of the respiratory tract, this is termed respiratory dead space. This dead space fresh air is pushed out during the following expiration and is replaced by breath containing a high amount of carbon dioxide. On the next breath this alveolar gas from the dead space is drawn back into the alveoli before the incoming fresh air.
The same total amount of air may be inspired in 32 shallow breaths or 16 deeper breaths, but there will be a considerable difference in the amount of alveolar ventilation due to breath 'lost' in respiratory dead space.
In the following examples are three types of breathing: 32 shallow breaths at 250cc per breath. 16 normal breaths at 500cc per breath. 8 deep breaths at 1000cc per breath. All producing 8000cc inspired air in one minute.
To find the amount of breath lost in respiratory dead space multiply the number of breaths by dead space volume. (150cc)
32 x 150 = 4800 lost and
3200 for gas exchange
16 x 150 = 2400 lost and
5600 for gas exchange
8 x 150 = 1200 lost and
6800 for gas exchange
These figures show that if the normal frequency is halved, the depth of respiration need only be increased by approximately 70% (not doubled) in order to obtain the same degree of alveolar ventilation.
This is of particular importance to singers, illustrating the need to carry out breathing exercises in order to increase lung capacity. Enabling the frequency of respiration to be decreased.
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