Testing the Resistance to Large Loads of Hypoxic Hypoxia in Active Pilots of the Czech Army

Overview

Pilot during flight are protected against the adverse effected of a drop of the atmospheric pressure by hyperbaric cabin andoxygen system and under emergency conditions by a system of positive pressure breathing. Despite this, emergency situationscannot by ruled out when pilots are exposed to a great load of hypoxic hypoxia. The authors evaluated the physiological response ofthe organism during high hypoxic loads –33 000 ft (10 000m) and compared it with the response to a load of the standard test of theNATO alliance (height 25 000 ft-7 500 m). The most useful investigated parameter was the saturation of functional arterialoxyhaemoglobin (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 ftrelatively ineffective and the performance of the proband declines very rapidly. The assessed values indicate a greater drop of thepsychophysiological performance than would correspond only to the limit of the time of useful consciousness (TUC). At the end ofthe assessed interval the probands achieved the critical value of %SpO2. The time taken to achieve the liminal margin is at a loadof 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 loadof 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 oflogical 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 ofsubjective complaints declared by the probands at an altitude of 33 000 ft correlates with the decline of saturation (complaints setin markedly more rapidly) and are a clear marker of deterioration of the psychophysiological performance. At a height of 25 000 ftthe character of subjective complaints is not so marked (influence of hypoxia on self-control). Subjective sensations need not besufficiently alarming for the inexperienced pilot.

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