Tidal volume

As Tidal volume describes the volume of air that is normally - usually unconsciously - inhaled and exhaled per breath. At rest, the tidal volume is around 500 milliliters, but can increase to around 2.5 liters when the muscles are put to great use. The tidal volume can be significantly increased by voluntarily activating the inspiratory and expiratory reserve volumes.

What is the tidal volume?

Tidal volume (AZV) is the amount of air that is normally inhaled and exhaled per breath. This is mostly about unconscious breathing. The amount of air in one breath is approx. 0.5 liters at rest, but can increase to 2.5 liters when the performance is more demanding.

This value can be increased again by the inspiratory and expiratory reserve volumes through voluntary breathing. The inspiratory reserve volume can be used by voluntary deep inhalation including diaphragmatic breathing and the expiratory reserve volume can be activated by voluntary deep exhalation.

When the two reserve volumes are fully used, the tidal volume is then identical to the vital capacity, the maximum amount of air that can be used for breathing. The AZV can accordingly not only be controlled vegetatively on the basis of variable performance requirements, but also by consciously influencing breathing. The vital capacity of untrained people is on average 4.5 l. For trained endurance athletes, it can exceed 7 liters.

The size of the AZV does not say much about the performance of the breathing system. For this, the breathing rate is also required, which multiplied by the AZV results in the minute volume. Also known as the respiratory time volume, the respiratory minute volume gives an indication of the amount of air per unit of time that passes through the lungs during breathing.

Function & task

The tidal volume influences the air flow through the lungs and is normally adjusted by the autonomic nervous system in terms of strength (volume) and breathing rate to the requirements.

It is also possible to change both parameters willingly in order to consciously adjust the air flow even in the event of a conflict with the vegetative control or to consciously cause an over- or under-supply of oxygen.

In situations in which only a relatively low AZV is required, there are always volume reserves on both the expiratory and the inspiratory side, with the inspiratory reserves being significantly higher than the expiratory reserves. The two-sided volume reserves have the advantage that if there is a sudden demand for power, the reserves are available at all times, regardless of whether the moment of demand occurs during inhalation or exhalation.

The opinion is often expressed that the lung volume can also be increased in adults through endurance training. This is not entirely true because the size of the lungs is genetically determined and cannot change after the growth phase has ended. However, what can be changed through training is the vital capacity, i.e. the tidal volume plus the two reserve volumes. The training effect is based on the trained and strengthened chest and rib muscles, which can lift the chest better and give the lungs the opportunity to expand further. When top athletes in endurance sports have a "high lung volume", this does not mean the absolute lung volume, but the maximum tidal volume or vital capacity.

Even with trained high vital capacity and deep exhalation, a residual volume of air, the residual volume, remains in the lungs. It is approx. 1.3 liters in healthy adults of normal stature. With each deep breath, the air remaining in the lungs is largely exchanged, so that gas exchange also takes place during the pause before inhalation. In addition, the remaining air prevents the alveoli from total collapse and sticking together.

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Illnesses & ailments

Functional disorders or diseases that impair the maximum tidal volume are usually associated with ventilation disorders. In principle, the ventilation disorders can be divided into restrictive and obstructive disorders. A restrictive ventilation disorder manifests itself, among other things, in a reduction in the maximum tidal volume, i.e. a reduction in vital capacity. Symptoms can include B. caused by an impairment of the chest or rib muscles after an accident or an operation or by an impairment of the muscles involved in active breathing by diseases or toxins.

Causes for this can be neurotoxins (snake venom, box jellyfish, sea wasp, etc.) or neuromuscular diseases. Pneumonia or pulmonary edema also cause symptomatic functional limitations of the alveoli and are classified as restrictive ventilation disorders.

Increased airway resistance is usually symptomatic of an obstructive ventilation disorder. The increased resistance is caused by an increased accumulation of secretions, foreign substances such as dust or a narrowing of the airways due to inflammation. In most cases, the exhalation is more affected than the inhalation.

The most common diseases that also lead to reduced tidal volume via an obstructive ventilation disorder are bronchial asthma and chronic bronchitis as well as a group of diseases and complaints that are summarized under the term COPD (chronic obstructive pulmonary disease). This also includes the so-called smoker's lung. In the coal mining centers, until the 1960s, the miners were often diagnosed with pneumonia, which, as a recognized occupational disease, could lead to considerable restrictions in the maximum breathable volume due to bronchial obstruction.

Other disease complexes, which in the advanced course also impair the maximum tidal volume via impairment of the lung function, are different types of carcinomas of the lungs and airways.