Effects of piloting supersonic aircraft on plasma corticosteroids and bicarbonate

¹ Department of Physiology-Biophysics, School of Aviation Medicine, USAF Randolph Air Force Base, Texas

While flying high-speed military aircraft, pilots frequently hyperventilate to a degree sufficient to induce marked alkalosis. Psychogenic factors are thought to be responsible for the hyperventilation. Comparison was made of pre- and postflight plasma bicarbonate (determined titrimetrically) and corticosteroid levels (Sweat's technique) for 20 instructor pilots and 47 student pilots flying F-100 aircraft for 50 minutes. No differentiation of students and instructors was possible on the basis of either pre- or postflight values; therefore, the data for the two groups were combined. The plasma bicarbonate value following the flight was 1.1 ± .24 mEq/l. (mean ± S.E.) lower than before the flight. Free 17-hydroxycorticosterone was increased 5.8 ± .70 µg/100 ml, while conjugated 17-hydroxycorticosterone increased 5.7 ± .75. The free corticosterone-like fraction increased 3.1 ± .34 µg/100 ml, while the conjugated corticosterone-like fraction increased 3.2 ± .35. Each of these changes was significantly different from zero (P < .001). No statistically significant correlation was found between the fall in bicarbonate and any of the increases in steroid fractions.