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Время эффективного сознания (Time of Useful Consciousness, TUC)

Сколько времени человек в среднем способен сохранять эффективное сознание при нехватке кислорода:

Таблица показывает время нахождения в сознании в зависимости от высоты над уровнем моря.

Например, на высоте 8500 метров (ниже вершины Эвереста) человек сохраняет работоспособное сознание до 3 минут.

В авиации эти значения показывают, в течение какого времени в состоянии гипоксии пилот способен принимать осмысленные решения. Это не время до полной потери сознания: по прошествии максимального времени человек может остаться в сознании, но потерять способность принятия решений. В том числе, не сможет принимать решения по устранению причин нехватки кислорода.

Ограничения в зависимости от условий:

The Time of Useful Conciousness (TUC) or Effective Performance Time is the period of elapsed time from the interruption of normal air supply or exposure to an oxygen-poor environment until the time when the ability to function usefully is likely to be lost at which point an affected individual would no longer be capable of taking normal corrective or protective action.
Time of useful consciousness (TUC) is not the time to total unconsciousness.

The physical condition of individuals influences the TUC. The TUC will be less for people with existing health conditions.
The TUC is less if the person is engaged in any kind of physical exercise, such as moving around the cabin.
In the case of explosive decompression, the TUC may be halved because of the effects of the sudden outflow of oxygen from the body’s tissues.

There are many individual variations of hypoxia, even within the same person. Generally, old age tends to reduce the efficiency of the pulmonary system, and can cause the onset of hypoxia symptoms sooner.[3] Smoking drastically reduces oxygen intake efficiency, and can have the effect of reducing tolerance by 1,000-2,000 meters[4] (approx. 3,000-6,000 feet). Hypoxia can be produced in an altitude chamber. This can be useful for identifying individual symptoms of hypoxia, along with rough estimates of the altitude that causes problems for each person. Identifying symptoms is often helpful for self-diagnosis in order to realize when altitude should be reduced. Although the times in the table below are often called average TUCs, an average failure is meaningless to a person who has a shorter TUC.

The table below reflects various altitudes with the corresponding average TUC for healthy, young military pilots:[5]

The Time of Useful Consciousness (TUC) is that period between an individual’s sudden deprivation of oxygen at a given altitude and the onset of physical or mental impairment which prohibits his taking rational action. It represents the time during which the individual can recognize his problem and re-establish an oxygen supply, initiate a descent to lower altitude, or take other corrective action. TUC is also referred to as effective performance time.

TUC is primarily related to altitude, but is also influenced by individual tolerances, physical activity, the way in which the hypoxia is produced, and the environmental conditions prior to the exposure. Average TUC at rest and with moderate activity at various altitudes are shown in the following table (Table — Time of Useful Consciousness). It is important to note, however, that the data present in this table are derived from a study where subjects were breathing oxygen through a mask, and that the hypoxic environment was produced by disconnecting their masks. The time of useful consciousness when hypoxic conditions are produced for an individual breathing normal air is shorter than if he had been breathing oxygen. This is because the pAO2 in his lungs drops immediately to a level dependent only on the final altitude, rather than dropping gradually with each breath of air, depending on lung volume, dilution of that volume, and altitude.