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An optoelectronic ear oximeter (Hewlett-Packard, model 47201A) was evaluated as a noninvasive method for determining arterial oxygen saturation (SaO2) in human subjects during exposure to various levels of accelerative forces. This physiological calibration involved exposing five subjects, while breathing air and wearing the ear oximeter for 60 s to each of three levels of accelerative forces (3, 5, and 7 G); arterial blood samples were withdrawn concurrently. SaO2 was calculated indirectly from the oxygen tensions (PaO2) measured from the sampled arterial blood with a blood gas analyzer and corrected for pH and base excess. These data were compared, as were similar data taken from the same subjects breathing three different hypoxic gas mixtures while resitng at earth's gravity (1 G). Regression analyses of these data for both experimental groups (a, G exposure, or b, hypoxic exposure), comparing the ear-oximeter SaO2 with the calculated SaO2, showed the ear oximeter to be accurate with correlation coefficients of 0.95 and 0.98, respectively.

Eight experimental subjects from the USAF Sschool of Aerospace Medicine (SAM) and four YF-16/17 test pilots were exposed to a simulated aerial combat maneuver (SACM) which included a maximum G exposure of 6 s at 8 G. The following physiologic parameters were examined relative to seatback angles of 23degrees, 28degrees, and 40degrees; heart rate and rhythm; arterial oxygen saturation; performance; intrathoracic (esophageal) pressure; arterial pressure; and subject comfort, effort, and fatigue. Relaxed and straining high sustained G (HSG) tolerances (6 G for 60 s) were also determined using only SAM subjects. The advantages of the 40 degree setback angle during the SACM included increased subject comfort, less fatigue and effort, greater pilot acceptance and a statisically significant reduction in the increased mean heart rate associated with G exposure. On the other hand, a statistically significant reduction in arterial oxygen saturation was obtained during the SACM at 40 degrees compared with the 23 degree back angle. An increase in relaxed G tolerance was found with the 40degree seatback angle--statistically significant only compared with the 28 degree seatback angle.

In aerial combat maneuvers (ACMs), at Luke AFB, Az, eight pilots flew their two F-15 aircraft against nine pilots in three F-106 aircraft. A total of nine flights, consisting of 23 ACMs, were accomplished in 5 successive days. The degrees of fatigue, stress, and sympathetic activity were quantified using both subjective analyses and the biochemical constituents in the urine of the pilots of the F-15 or F-106. Biochemical indicators, reported per 100 mg creatinine, included: epinephrine, norepinephrine, 17-OHCS, urea, inorganic phosphate, sodium, potassium, and sodium/potassium ratio. The F-106 pilots exerted more relative effort than did the F-15 pilots--effort which appeared to be associated with high-G experience. Both groups of pilots were equally fatigued following ACMs; however, only the fatigue of the F-106 pilots was directly correlated with the length of the ACM. Sympathetic and stress responses during the ACM--similar for both groups of pilots--showed postflight increases of 54% in epinephrine, 19% in norepinephrine, and 20% in 17-OHCS over preflight values, thus suggesting a moderate stress response. Resting levels of these same indicators, for days the pilots did not fly and for pre-ACM values, were similar but higher than control values previously reported for other stressful activities. By late afternoon, postflight values for these indicators had returned to near-preflight levels.

Two studies were conducted to evaluate physiological responses and possible tolerance to high sustained +Gz forces at the USAF School of Aerospace Medicine, using the 20-ft (6.10 m) radius Human Centrifuge. In the first study (A), 14 human volunteer subjects--fully protected with an anti-G suit and performing the M-1 or L-1 straining maneuver--were exposed to +Gz forces. These forces began at +6.5 Gz, and increased weekly in 0.5 G increments to +9.0 Gz, for a duration of 45 sec at each level. Physiological performance was based mostly on the subjects' ability to maintain clear vision during the 45 sec exposure. Of the 14 subjects, 9 were able to maintain vision and remain at the +9 Gz level for 45 sec. In the second study (B), 12 human volunteer subjects--also protected with anti-G suits and using the straining maneuvers--were exposed to levels of +1, 3, 6, and 8 Gz, for 60 sec at each level. Extensive physiologic parameters were recorded in order to detect objective criteria which could be used as determinants for a medical tolerance endpoint to the particular level of +Gz stress. In both studies, the reasons for stopping the runs at levels exceeding +7.5 Gz included: fatigue, cardiac arrhythmias, blackout, and one occurrence of ventricular tachycardia. Other physiological responses to the sustained +Gz stress (such as heart rate, arterial blood pressure, central venous blood pressure, arterial oxygen saturation, gastric pressure, and ankle venous pressure) did not furnish specific information that could be used as "physiological tolerance limit" criteria.