Despite technological advances flying is still associated with the effect of a number of stressing factors which influence the human organism. One of the most important ones is the action of the drop of the partial oxygen pressure (pO2 ) on the human organism. The cabin altitude which is ensured by the pressure cabin of army fighter planes may during flight reach values as high as 23 000 feet (7000 m). This is an altitude greatly exceeding the compensating possibilities of the unprotected organism. It is thus important to test, when selecting pilots for the Czech Army, their natural resistance to hypoxic hypoxia. Testing resistance to hypoxia is done by exposure in a hypobaric chamber at an altitude of 25 000 feet (7 600 m). The period of hypoxic exposure depends on subjective sensations of the proband and on the objective symptoms and values of the investigated physiological variables. The maximal period of exposure is 5 min. During exposure the following parameters are investigated: heart rate ECG (limb leads) and saturation values of functional arterial oxyhaemoglobin (%SpO2 ) recorded by the method of pulsed oxymetry. The control group comprised 23 pilots on active service of the Czech Army. The greatest contribution to evaluation of the tolerance to hypoxia is evaluation of changes of %SpO2. Values of %SpO2 declined in the course of hypoxic exposure and eventually reached a level of 62% in the group with an adequate tolerance, while in the group with a low tolerance they declined within the time limit beneath 60%. The differences of the two groups were statistically significant (p < 0.01) during the 3rd minute of hypoxic exposure. Values of %SpO2 after oxygen administration following the hypoxic load in both groups increased very rapidly and within 1 min. %SpO2 reached in both groups a level of 97%. In the context of changes of SpO2 during hypoxic exposure the authors recorded a statistically significant difference of values between groups only at the beginning of oxygen administration (p < 0,05). The parameters of the hypoxic load were selected correctly - the psychophysiological efficiency of all probands was influenced during exposure and the load made it possible to differentiate probands according to their performance.

        Key words: testing resistance, hypoxic hypoxia, pulse oximetry, values of %SpO2