Background: The author previously reported in-flight EKG changes, Pa2, and blood chemistries in F-4 pilots during surface attack training (SAT) and aerial combat maneuvers (ACM) while breathing ambient air. Myoglobin levels were also measured to determine if rhabdomyolysis occurred during positive + Gz force expenditure. Contrary to the expected instead of rising serum myoglobins dropped precipitously during 45 min missions. EKGs revealed marked ischemic and arrhythmia changes. This study was undertaken to further evaluate these changes.
Methods: There were 22 EKG in-flight recordings made on 20 aircrew members breathing 100% oxygen during SAT and ACM and compared with previously reported results with pilots using ambient air. In six of those pilots using 100% oxygen, serum myoglobin, ACTH, and cortisol levels were determined before and after each mission and also compared with previously reported results obtained on ambient air. Of the six aircrew in the blood study, three flew similar missions the following day on ambient air as a control, with a significant decrease in serum myoglobin after each mission.
Results: While sinus arrhythmia and tachycardias persisted on 100% oxygen, ischemic changes were absent. ACTH and cortisol levels increased similarly in both studies consistent with a stress response. Serum myoglobins remained unchanged on 100% oxygen unlike the marked decrease noted on ambient air.