Tidal volume is a percentage of total lung capacity. It represents the amount of air inhaled or exhaled by a person at rest. You can increase tidal volume through deep breathing and through exercise. However, not all the air consumed in tidal volume actually contributes to the oxygenation of body tissues. Tidal volume should not be the single factor used to estimate the amount of oxygen your body receives with each breath.
- Skill level:
Take slow, deep breaths. The total amount of air that the lungs can hold is called "total lung capacity." Total lung capacity for men is about 6000 millilitres and for women is about 4200 millilitres. Tidal volume is a small percentage of total lung capacity--about 500 millilitres in both men and women. You can increase tidal volume to about 1000 millilitres by deep breathing, about 10 breaths per minute. Average breathing is about 12 to 20 breaths per minute.
Increase tidal volume with exercise. The body compensates for working muscles' increased oxygen use by incrementally upping tidal volume and respiratory rate. The tidal volume is boosted by taking from other respiratory volumes in the lungs. Two volumes--the expiratory reserve volume and inspiratory reserve volume--contain air that is not normally inhaled or expelled during a regular breath. These reserve volumes are drawn on during rest through forced inhalation or exhalation. Tidal volume returns to normal when exercise is complete.
Maintain even breathing. Don't hyperventilate to increase tidal volume. Hyperventilating is quick, shallow breathing. This decreases the tidal volume and can lead to inadequate gas exchange. Insufficient amounts of oxygen can lead to diminished brain function and death.
Tips and warnings
- Don't confuse tidal volume with the level of oxygenation of body tissues. Not all of the air breathed during inhalation goes deep into the alveolar sacs where gas exchange occurs. Some of the air remains in the pharynx, bronchi and trachea. This is called "anatomical dead space." Dead space accounts for about 150 millilitres of tidal volume and is constant in each individual, regardless of the rate or quality of respiration. The difference between tidal volume and dead space can provide a good estimate of how effective each breath is in oxygenating body tissues. Breathing at a normal rate and depth is only about 70 per cent effective. Deep breathing is about 85 per cent effective in providing oxygen to the body. In contrast, hyperventilating produces a tidal volume of about 250 millilitres, which is half the amount of air inhaled during restful breathing. Hyperventilation is an ineffective form of respiration and is only about 40 per cent effective at delivering oxygen to the tissues.
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