Preliminary study of the effects of mild thalassemia on hypoxia tolerance of civil aviation student pilots

Objective To investigate the effects of mild thalassemia on hypoxia tolerance of civil aviation student pilots, and provide the basis for aviation medical identification of thalassemia in civil aviation pilots. Methods The parameters of red blood cells and hemoglobin were analyzed in 1 711 subjects including the student candidates who were checked in the physical examination for recruitment and the student pilots of flight college. The thalassemia gene tests were performed for the subjects with small cell and low pigmented anemia to diagnose if they were with thalassemia. Twenty-five mild thalassemia cases and 19 healthy cases were chosen for the comparison according to the principles of proximity and phone call reachable. The hypoxia test was conducted at 7.5 km simulated altitude by Model 2007 anti-G/anti-hypoxia Detector. SaO2, heart rate and blood pressure were respectively recorded at 20 s, 60s and 120 s of the test. In case of the test did not reach to 120 s but the SaO2 had been lower than 60% the test was terminated and the SaO2, heart rate and blood pressure were marked at the moment. The subjects were tested by writing digits with down sequence before and after hypoxia test. In 7.5 km simulated altitude test if the SaO2 level had decreased to 60% within 120 s the test would be terminated and the actual test duration was recorded. Results ①Ninety-seven cases of thalassemia were found in 1 711 students (5.67%) and all cases were mild thalassemia. The highest detection rate was found in the students of Hainan Province, accounting for 20%. ②The difference of test duration was statistically significant between mild thalassemia group and health group under simulated 7.5 km altitude hypoxia environment (Z=3.630, P 0.05), but the difference at the end of test was statistically significant (t=5.248, P 0.05). The difference of systolic pressure at 60 s and the difference of diastolic pressure at the end of test were statistically significant between two groups [(t=2.215, P=0.029) and (t=2.518, P=0.018)]. The difference on the number of correctly writing digits with down sequence was insignificant between two groups before the hypoxia test (P>0.05), but was significant after the test (t=3.489, P<0.01). Conclusions The hypoxia tolerance of the patients with mild thalassemia is lower than that of the healthy population. It is suggested that more attention should be paid to the candidates with mild thalassemia in the physical examination for recruiting student pilots. The pilots with mild thalassemia should minimize the flying on plateau. Key words: Thalassemia; Hypoxia; Oximetry; Consciousness; Student pilots