Human tolerance to aerial combat maneuvers.

An acceleration profile was developed on the USAF School of Aerospace Medicine's 6.1-m radius centrifuge to measure human tolerance to the Aerial Combat Maneuver (ACM). The ACM profile is a continuous repetitive, 4.5 G for 15 s to 7 G for 15 s, cyclic G exposure which is terminated by the subject at his fatigue endpoint. ACM tolerances using this type of G profile were determined for seven subjects at four different seatback angles; i.e. 13 degrees, 30 degrees, 55 degrees, and 65 degrees from the vertical. Group (mean +/- S.E.) tolerances for the ACM were 170 +/- 17 s at 13 degrees and 541 +/- 48 s at 65 degrees. These tolerances were not usually correlated with relaxed gradual onset G tolerances. The subjective fatigue endpoint was physiologically verified using heart rate, heart rhythm, and performance criteria at the four seatback angles. The potential value of the ACM profile is considered as a measure of the effectiveness of anti-G equipment and methods in the aerial combat environment.

Evaluation of assisted positive pressure breathing on +Gz tolerance.

The effect of both assisted and unassisted positive pressure (PPB) breathing on +Gz tolerance was evaluated. A GOR (gradual onset rate = 0.1 G/s) acceleration profile was used to evaluate five different experimental conditions: 1) G-suit-only, 2) G suit + unassisted PPB, 3) G suit + PPB assisted by the English jerkin, 4) G suit + PPB assisted by the Canadian waistcoat, and 5) the Swedish counterpressure garment G suit combination. Acceleration tolerances for these experimental conditions (excluding the Swedish garment) with the subjects performing M-1 maneuvers were measured using an exhaustive ACM (Aerial Combat Maneuvers) acceleration profile. GOR tolerances were similar for both assisted and unassisted PPB with the pressure breathing experimental conditions providing a significant GOR tolerance increase over the G suit only condition. Assisted PPB increased ACM tolerances over both unassisted PPB and G suit only conditions. It appears that assisted PPB may offer a practical method for reducing the fatigue associated with exposure to high G.

Pressurized sleeves and gloves for protection against acceleration-induced arm pain.

BACKGROUND: Acceleration (or G) induced arm pain may develop in centrifuge runs and in flight with low arm position and assisted pressure breathing during G (PBG) in combination with an extended coverage anti-G suit. To decrease this arm pain, pressurized sleeves and gloves were developed. METHODS: Eight subjects who earlier exhibited G-induced arm pain were tested on the centrifuge. The G-exposures consisted of a gradual onset run up to a maximum of +9 G2, rapid onset runs to +3, +4, +5, +6, +7, +8, and +9 Gz and a simulated aerial combat maneuver (SACM) with peaks up to +9 Gz. On separate days, the subjects were tested without the sleeves and gloves, and with the sleeves and gloves pressurized to a maximum of 40, 60, or 80 mmHg at +9 Gz. The subjects reported their left and right arm pain on a subjective rating scale. RESULTS: G-induced arm pain, usually starting above +6 Gz, was often the reason for termination of the G-exposure without the pressurized sleeves and gloves. The pressurized sleeves and gloves significantly (p < 0.001) decreased arm pain, put no significant difference was found among the different pressures used. Heart rate was not different with and without the pressurized sleeves and gloves. CONCLUSIONS: The pressurized sleeves and gloves are an effective method to alleviate and sometimes eliminate G-induced arm pain.

Accommodation of females in the high-G environment: the USAF Female Acceleration Tolerance Enhancement (FATE) Project.

BACKGROUND: In 1993, the U.S. Secretary of Defense opened combat aircraft assignments to women. To verify the adequacy of acceleration (+Gz) protection for female high-G aircrew, USAF investigators conducted fit tests of standard and developmental G-protective equipment and determined the effectiveness of a unique laboratory modification (AL Mod) of the standard (CSU-13B/P) anti-G suit during gender-comparative centrifuge evaluations. METHODS: Investigators determined relaxed +Gz tolerance and straining endurance to +4.5 to +7 Gz and +5 to +9 Gz simulated aerial combat maneuver (SACM) centrifuge profiles (4.5-7 SACM: 8 females and 10 males; and 5-9 SACM: 6 females and 8 males, respectively). Additionally, in the 5-9 SACM study, between and within gender SACM endurance differences were assessed before and after female subjects' use of the AL Mod. Ten female subjects also were fit tested in extended coverage, developmental G-protective equipment. RESULTS: There was no gender difference in 4.5-7 SACM endurance. Male 5-9 SACM endurance exceeded that of females in the unmodified CSU-13B/P (p < 0.05), but gender parity was achieved when females wore the AL Mod. Fit modifications of developmental G-protective equipment were not required, but smaller sizes of the standard CSU-13B/P and a developmental anti-G suit were indicated and developed. CONCLUSION: In properly fitted anti-G suits, gender parity in SACM endurance is achievable; however, full accommodation of female aircrew in the high-G environment will require the AL Mod and/or smaller sized anti-G suits.

Differences between syncope resulting from rapid onset acceleration and orthostatic stress.

BACKGROUND AND HYPOTHESIS: Orthostatically-induced syncope is accompanied by venous pooling and vasodilatation. Loss of consciousness during head-to-foot acceleration (G-LOC) in aviators may be caused by a different mechanism, as venous pooling should be prevented through the use of an anti-G suit. This research was conducted to test the hypothesis that in individuals wearing a well-fitted anti-G garment, no important changes occur in the volume of dependent regions during loss of consciousness resulting from rapid onset acceleration stress. Further, this work compares venous pooling patterns in G-LOC subjects to patterns seen during syncope in volunteers and patients subjected to orthostatic stress. We conducted the tilt/LBNP tests to establish what level of venous pooling was required to induce syncope in the absence of a hydrostatic component (other than 1 G) and to confirm that our equipment was sensitive enough to detect volume changes large enough to cause syncope. METHODS: Shifts in blood volume to the calf, thigh and abdominal segments were compared in subjects with G-LOC to those in subjects taken to presyncope with orthostatic stress created by upright tilt and lower body negative pressure (LBNP). Centrifuge subjects were exposed to a 15 s rapid onset (6 G.s-1) + 5 Gz exposure on the centrifuge while remaining relaxed and wearing a well-fitting anti-G suit, but with the anti-G suit pressure inactivated. RESULTS: Blood volume decreased an average of 14.9 +/- 22.1 ml in the calf segment; increased an average of 64.1 +/- 7.9 ml in the thigh segment, and decreased an average of 80.1 +/- 29.7 ml in the abdominal segment. The mean net change in volume of the three combined regions was not significantly different from zero. Presyncope was induced in subjects by a progressive exposure to upright tilt, and then addition of LBNP at -20 mm Hg and -40 mm Hg. In the tilt/LBNP group, there was a net increase of 1022 +/- 269.8 ml for the combined segments. Changes in all three segments were significantly different than the mean segmental volume changes seen in centrifuge subjects at G-LOC endpoints. Significant changes from baseline mean arterial pressure, but not heart rate were also seen within, but not between the 2 groups, with mean eye level blood pressures (ELBP) falling an average of 45.6 +/- 7.7 mm Hg in the tilt/LBNP group at syncope and 105.1 +/- 15.5 mm Hg in the centrifuge subjects at G-LOC. CONCLUSIONS: These differences suggest that G-LOC may be due entirely to hydrostatic effects, with venous pooling being prevented by the wearing of an ant-G garment, even when it remains uninflated.