Human respiration is physiologically characterized by different volumes. These volumes describe the respiratory air in the lungs and respiratory tract. The room sizes are known as respiratory gas volumes, respiratory volumes or lung volumes. Pneumology measures the various volumes via procedures such as spirometry.
The breathing limit is a respiratory time volume. As such, the volume of breathing air is referred to, which can be inhaled and exhaled within a certain period of time. The measurement of the respiratory limit value takes place at maximum tidal volume and maximum respiratory rate and is achieved by hyperventilation. Thus, the respiratory limit value corresponds to the respiratory time volume that a subject can reach through arbitrary breathing.
As a unit of time for the respiratory time volume usually one minute is used. Under physiological conditions, the respiratory minute volume results from the respiratory rate times the tidal volume. Under exercise or under the conditions of a breath threshold test, there is a multiplication of the physiological respiratory minute volume. For athletes a multiplication by up to 15 times is conceivable.
The lungs are a paired organ that enables active breathing in the human organism. The place of the gas exchange are the alveoli. Oxygen is drawn from the inhaled air and diffuses into the bloodstream, where a large portion of hemoglobin binds. Oxygen reaches all areas of the body via the bloodstream.
The tissue types depend on the supply of oxygen. If the organs and tissues reach little or no oxygen over a period of time, they will die irreversibly. In the lung alveoli, in addition to the absorption of oxygen, the release of carbon monoxide also takes place. If this levy is obstructed, symptoms of intoxication occur.
The human respiratory volumes ensure that sufficient gas exchange can take place and the organs and tissues are thus supplied with sufficient oxygen. An adult breathes for this purpose on average about 12 to 15 times a minute. With every breath he takes on a tidal volume of about 500 to 700 milliliters. This results in an average respiratory minute volume of about eight liters. This volume corresponds to the volume at which physiological pulmonary respiration supplies oxygen to all body tissues and organs within one minute at an ideal rate.
The respiratory limit does not result from the physiological breathing conditions, but corresponds to the maximum possible minute ventilation. For measurement, the mouthpiece of a pneumotachograph is placed in the patient's mouth. He is then instructed to hyperventilate for a maximum of ten seconds. The measured value is converted to one minute.
The standard for the breathing limit is between 120 and 170 liters per minute. Age and size-specific fluctuations can occur. If the respiratory threshold is severely reduced, it is likely that there is a ventilatory disorder that can be more closely determined through studies such as spirometry, the Tiffeneau test or body plethysmography.
Ventilation disorders worsen the ventilation of the lungs and thus the gas exchange in the alveoli. The disorders are either obstructive or restrictive. In addition to a pathological reduction, a ventilation disorder may as well be characterized by a pathological increase in lung ventilation. As a rule, however, the respiratory limit only says something about diminished values and can therefore be used as a criterion for the diagnosis of hypoventilation.
In restrictive hypoventilation, the extensibility of the lung or chest (thorax) is limited. Traumas of the thorax are also conceivable causes. The same applies to neuromuscular diseases, adhesions or pulmonary edema. Frequently, restrictive hypoventilation also corresponds to pneumonia.
Obstructive ventilation disorders are different from restrictive in their cause. In addition to an increased flow resistance, there is usually an increased resistance to breathing in these diseases. The respiratory tract is prone to collapse and patients have problems exhaling. In addition to bronchial asthma, mechanical causes such as cystic fibrosis of cystic fibrosis or chronic bronchitis can cause obstructive ventilation disorder. Also conceivable is a lack of elastic fibers, which reduces the Atemzugkräfte.
Hypoventilation limits pulmonary gas exchange. As a result, hypercapnia, hypoxaemia and respiratory acidosis occur. The CO2 exhalation of the patients is lower than the production. For this reason, there is an increased CO2 partial pressure in the blood. As causes in addition to the diseases mentioned, for example, a paresis of the respiratory muscles in question, which usually precedes a lesion of the phrenic nerve. Damage to the respiratory center in the central nervous system can also cause hypoventilation.
Sometimes, instead of damage, there is only central nervous dysregulation, such as drug-induced interference with the central nervous system. Hypoventilations also affect clinical pictures, such as the Pickwick syndrome. In order to narrow down the cause of hypoventilation and a so-called respiratory limit, the above additional examinations are necessary.