Pilot during flight are protected against the adverse effected of a drop of the atmospheric pressure by hyperbaric cabin and oxygen system and under emergency conditions by a system of positive pressure breathing. Despite this, emergency situations cannot by ruled out when pilots are exposed to a great load of hypoxic hypoxia. The authors evaluated the physiological response of the organism during high hypoxic loads –33 000 ft (10 000m) and compared it with the response to a load of the standard test of the NATO alliance (height 25 000 ft-7 500 m). The most useful investigated parameter was the saturation of functional arterial oxyhaemoglobin (SpO2) recorded by the method of pulsed oximetry. From the assembled results the following facts ensued: compensatory possibilities of the organism are at an altitude of 33 000 ft relatively ineffective and the performance of the proband declines very rapidly. The assessed values indicate a greater drop of the psychophysiological performance than would correspond only to the limit of the time of useful consciousness (TUC). At the end of the assessed interval the probands achieved the critical value of %SpO2. The time taken to achieve the liminal margin is at a load of 33 000 ft three times shorter than at a height of 25 000 ft. A safe time interval or the first affection of logical functions is at a load of 33 000 ft ca 44 seconds, while at a height of 25 000 ft it is ca 120 seconds. The time interval leading to the serious affection of logical functions is at a height of 33 000 ft ca 72 seconds while at a height of 25 000 ft it is circa 272 seconds. The onset of subjective complaints declared by the probands at an altitude of 33 000 ft correlates with the decline of saturation (complaints set in markedly more rapidly) and are a clear marker of deterioration of the psychophysiological performance. At a height of 25 000 ft the character of subjective complaints is not so marked (influence of hypoxia on self-control). Subjective sensations need not be sufficiently alarming for the inexperienced pilot.

        Key words: hypoxic hypoxia, pulse oximetry, saturation of oxyhaemoglobin, active pilots