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Background: There is a need for a more operationally relevant +Gz profile for centrifuge-based research and evaluation. This article describes a simulated aerial combat maneuver (SACM) named the Tactical Aerial Combat Maneuver (TACM)., Hypothesis: A more representative centrifuge-based SACM can be devised for high-G acceleration research and evaluation., Methods: TACM consists of 9G x 5 s, 5G x 1 s, 8G x 5 s, and 4G x 2 s. TACM was compared against the widely accepted 4.5-7G and 5-9G SACMs. There were 15 centrifuge subjects used in this study., Results: TACM accounted for all four incidents of G-Induced Loss of Consciousness (G-LOC); and most incidents of blackouts (5 of 8) observed., Conclusion: TACM simulates the seesaw pattern of +Gz forces of aerial combat and retains the reproducibility needed for acceleration research and evaluation. TACM captures the high onset, high amplitude +Gz changes of aerial combat when G-LOC and blackouts are more likely to occur. TACM should be particularly useful for evaluation of G-protective equipment and maneuvers, as well as fighter aircrew medical evaluations.

Background: There is a need for evaluation of new G protection equipment., Hypothesis: There is no difference between the two anti-G ensembles on affecting subjects' ability to tolerate multiple simulated aerial combat sorties., Methods: There were 15 subjects wearing the standard CSU-13 B/P anti-G ensemble (STD) or COMBAT EDGE/ATAGS (CE/ATAGS) ensemble who were exposed to 3 centrifuge-based simulated air combat sorties during a 2-h period. Each sortie consisted of four different G-profiles: 1) a gradual onset profile; 2) simulated air combat maneuver consisting of +4.5 to +7 Gz plateaus (4.5-7 SACM); 3) simulated air combat maneuver derived from actual fighter maneuvers with peaks up to +9 Gz (TACM); 4) simulated air combat maneuver consisting of +5.0 to +9.0 Gz plateaus (5-9 SACM). Each sortie was separated by a 20-min rest period. We measured heart rate, peripheral light loss (PLL), subjective effort level, subjective fatigue level, and reported recovery time., Results: There were no incidents of unintended G-induced loss of consciousness (G-LOC) with CE/ATAGS. There were four incidents of unintended G-LOC with STD. At the end of the third sortie, with CE/ATAGS, mean heart rate was lower during the 4.5-7 SACM (p < 0.001) and the TACM (p < 0.001); PLL was less during all three rapid onset profiles (p < 0.01); subjects reported less effort during the 4.5-7 SACM (p < 0.001), the TACM and the 5-9 SACM (p < 0.01); reported fatigue was significantly lower (p < 0.001); and reported recovery times were nearly halved (p < 0.01)., Conclusion: CE/ATAGS provided significantly greater G-protection than the standard anti-G ensemble. There was no G-LOC with CE/ATAGS. This greater protection should be of significant operational value in enhancing sortie generation capability by increasing fighter aircrew G-tolerance and decreasing aircrew fatigue.

Introduction: The literature contains a paucity of information on female tolerance to high sustained acceleration. With women now flying high-performance aircraft, gender-specific factors that may affect female acceleration tolerance have become increasingly important. The purpose of this investigation was to determine how menstrual state and physical condition affect acceleration tolerance. We hypothesized the menstrual cycle would have no effect on acceleration tolerance and that a positive correlation would exist between physical fitness level and tolerance to high sustained acceleration., Methods: Centrifuge exposures on 8 female subjects consisted of a relaxed gradual-onset run (0.1 G.s-1) to the visual endpoint, a rapid-onset run (6 G.s-1) to +5 GZ for 15 s, and a +4.5 to +7 GZ simulated aerial combat maneuver (SACM) to physical exhaustion. Acceleration tolerance data were collected at onset of menstruation and 1, 2 and 3 weeks following the onset for two complete menstrual cycles. On separate days, body composition, anaerobic power output and peak oxygen uptake were determined. Retrospective data from 10 male subjects who had performed the +4.5 to +7 GZ SACM were analyzed and compared to these data., Results: Analysis of variance revealed no significant difference in relaxed tolerance or SACM duration between the four selected menstrual cycle time points. Time-to-fatigue on the +4.5 to +7 GZ SACM was positively (p < or = 0.05) correlated with absolute fat-free mass (r = 0.87) and anaerobic power production (r = 0.76) in female subjects. However, when these variables were adjusted for total body mass, the significant correlations no longer existed. No correlation was found between SACM duration and absolute (L min-1) nor relative (ml.kg-1.min-1) aerobic fitness. Time-to-fatigue during the SACM was not significantly different between male and female subjects (250 +/- 97 and 246 +/- 149 s, respectively).

It has been suggested there is a relationship between acceleration-induced loss of consciousness (G-LOC) and head/body position. A two-part investigation was conducted to determine whether head and body position affects acceleration tolerance. A retrospective analysis of high-G training data (N = 1,914) compared G-LOC occurrence during straight-ahead exposure to a "check-6" exposure [10 s at +9 Gz; 6 G/s onset rate; G-suit inflated; anti-G straining maneuver (AGSM) performed]. A prospective study (N = 12) was conducted with acceleration exposures using light loss criteria with subjects in straight-ahead, above, over-the-right shoulder, or over-the-left shoulder positions. Profiles consisted of 0.1 G/s onset-rate runs (no G-suit inflation; relaxed) to a maximum of +9 Gz and 0.5 G/s onset-rate runs (G-suit inflated; AGSM performed) to +9 Gz for up to 26 s. In the retrospective study, no significant difference existed between G-LOC occurrence during straight-ahead (22/1914) and check-6 (32/1914) positions. During the prospective study with AGSM runs, there was no significant difference in the time at maximum G among any of the positions. During the relaxed runs, several comparisons yielded significant differences in peak G attained. These results indicate there may be an underlying physiologic effect of head and body position on acceleration tolerance; however, the AGSM and the G-suit overcame this effect. Although task saturation and distraction may compromise performance of the AGSM and subsequently predispose acceleration-related hazards, a proper AGSM, combined with effective protective systems, remains essential components of a protection strategy.

Goats (N = 7) were decompressed from 1,500 m to 9,150, 9,750, or 10,400 m simulated altitude while breathing CO2 tensions of 0, 15, 30, or 46 mm Hg in O2 during 15-min prebreathing and 30-min peak altitude exposures. Risk of decompression sickness was determined by detecting venous gas emboli (VGE) in the pulmonary artery with an implanted Doppler cuff. VGE scores were calculated using the ratio of cardiac cycles containing VGE to total cardiac cycles. The VGE scoring methodology proved sensitive to standard treatment effects (air versus O2 prebreathing). No significant change in VGE scores as a result of varying the inspired CO2 level was detected. Further, no significant change in cardiac index occurred during the various CO2 exposures, and VGE scores were not correlated with cardiac index. Ground-level studies revealed the tension of end-tidal CO2 was significantly elevated at all three levels of inspired CO2, but no change in cardiac index was observed. Short-duration breathing of CO2 in oxygen failed to significantly reduce the risk of decompression sickness as assessed by VGE production.

In-flight canopy loss in high-speed fighter or trainer aircraft poses serious aeromedical problems for the crew-members. To assess these problems in the TF-15, a series of canopy-off tests were conducted. Preliminary phases of the test consisted of a taxi and a flight test up to 485 knots with pilot in the front seat and an instrumented dummy in the back seat. Upon evaluation of these results, a taxi phase and a flight phase were conducted with a pilot in the front seat and a live subject in the back seat. Maximum air-speed attained was 410 knots. The front crewmember experienced no serious control or medical problems during all phases. The back crewmember did experience problems such as loss of communications, loss of vision, helmet lift, high frequency head buffet, and exhalation difficulties. Airspeed, seat height, and body position had the greatest effect on the severity of the windblast. Angle of bank, angle of attack, and acceleration had little effect. The aft crewmember was able to significantly decrease windblast effects by leaning forward and pulling his head and helmet forward and down with his hand.