Echocardiographic evaluation of female centrifuge subjects for chronic changes in cardiac function.

BACKGROUND: High sustained G exposure as experienced in flying high performance aircraft can affect cardiac function. Numerous studies, mostly on male pilots, have evaluated the chronic effects of exposure to high G. To date, none of these studies has revealed significant positive findings in cardiac function as a result of long-term high G exposure. METHODS: A longitudinal study was conducted on six female centrifuge panel members who did not have a history of significant high +Gz exposure. Baseline echocardiographic studies were conducted prior to any +Gz exposure on the Dynamic Environment Simulator (DES) centrifuge. The echocardiograms were repeated after each panel member completed approximately 100 3-min high G (up to 9 G) exposures over the period of 7 mo. These follow-up echos were performed after all six subjects had been exposed to at least 6 h (cumulative) of sustained acceleration > 3 G. The women were protected with the COMBAT EDGE positive pressure breathing G protection ensemble. Each subject served as her own control. All studies were evaluated independently by a cardiologist who was blinded to the order in which the echos were performed. Although complete echocardiographic studies were performed, only the parameters identified as significant in prior studies were evaluated. RESULTS: No significant differences were found between the initial and follow-up echo parameters. CONCLUSIONS: We found no significant differences in cardiac function after at least 6 and up to 17 h (cumulative) of exposure to G > 3 in women. These subjects will be monitored during a longitudinal study throughout their centrifuge subject career.

Female exposure to high G: echocardiographic evaluation for chronic changes in cardiac function.

BACKGROUND: Significant changes in cardiac preload and afterload are generated by a number of factors present during the operation of high performance aircraft. These include high levels of +Gz, positive pressure breathing and anti-G straining maneuvers. Centrifuge subjects are exposed to these same factors in doses that are comparable to their operational counterparts. The question of whether such exposures produce long-term adverse effects on the heart has not been definitively answered. METHODS: In an effort to further address this issue, a longitudinal study was conducted on 18 newly recruited centrifuge panel members (7 males and 11 females) who did not have a previous history of significant high +Gz exposure. In order to document the cumulative long-term effects of high +Gz exposure and G protection measures, baseline echocardiographic studies were conducted prior to any +Gz exposure on the Dynamic Environment Simulator (DES) centrifuge. The echocardiograms were repeated after each panel member completed eight sessions of indoctrination. These follow-up echos were performed after all 18 subjects had been exposed to over 45 min (cumulative) of sustained acceleration > or = 2 G. Each subject served as his/her own control. All studies were evaluated independently by a cardiologist who was blinded to the order in which the studies were performed. Although complete echocardiographic studies were performed, only the parameters identified as significant in prior studies were evaluated. RESULTS: No significant differences were found between the initial and follow-up echo parameters. No significant differences were found between male and female responses. CONCLUSIONS: We found no significant differences in cardiac function after 45 min (cumulative) of exposure to G > or = 2 in men or women. These subjects will be monitored during a longitudinal study throughout their centrifuge subject career.

Female exposure to high G: performance of simulated flight after 24 hours of sleep deprivation.

BACKGROUND: Ground-based research has investigated the loss of cognitive function in the extreme conditions of G-induced loss of consciousness, however, little is known about pilots' abilities to maintain cognitive performance throughout prolonged conscious exposure in the high-G environment. The effects of fatigue and G layoff on performance during exposure to high G are mostly unknown for the female population. METHODS: This research was conducted on the centrifuge Dynamic Environment Simulator. Active-duty personnel (8 male and 8 female) were trained to fly the F-16 simulation while 30 performance measures were recorded. Performance was re-evaluated after 24 h of sleep deprivation. RESULTS: Neither male nor female overall performance was affected significantly by sleep status, although individual tasks showed sensitivity; call-sign reaction time was longer by 33%, and missile survival was less likely. Also, when sleep deprived, perceived effort and physical demand were higher while perceived performance was lower. No differences in performance were found in either gender due to lay-off, although some physiologic deconditioning was apparent. Women commanded and endured the same amount of G load as men, however, on average they could not perform the tracking task quite as well. CONCLUSIONS: Sleep deprivation (24 h) produced sensations of fatigue and frustration, but overall performance was not reduced. The ability of personnel to complete a complex defensive maneuver was reduced when they were sleep deprived. The women that we tested apparently could not optimize the tracking task as well as their male counterparts when Gz was in the simulation. None of these results were sufficient to suggest that women should not be allowed to compete for flying assignments in high-performance aircraft.

Effect of G suit type on cognitive performance.

BACKGROUND: Sustained acceleration protection ensembles are being developed to help pilots of high performance aircraft endure high G exposures for longer periods of time. It has been assumed that better G endurance confers better pilot task performance. This premise was studied on the Armstrong Laboratory Dynamic Environment Simulator centrifuge. METHOD: Human subjects repeatedly endured prolonged high-G simulated aerial combat on a centrifuge to the point of loss of vision or physical exhaustion. Some profiles included over 20 exposures to +9 Gz. While enduring the G exposures, subjects tracked a simulated "bogey" aircraft on a visual display and performed a secondary task. Measures of cognitive function and physiologic status were taken throughout the exposures. G protection ensembles included the standard CSU 13 B/P anti-G suit, the Advanced Technology Anti-G Suit (ATAGS), COMBAT EDGE positive pressure breathing system with the CSU 13 B/P, COMBAT EDGE with ATAGS, and the Northrop Advanced Protection System (APS). RESULTS: More advanced protective systems not only allow longer G endurance, but provide adequate support for maintained cognitive performance throughout the extended exposure. Although measures were affected by the type of protective system the subject was wearing, as well as individual ability and coping strategies, consistent target tracking task performance, rapid choice reaction time, and sufficient arterial oxygen saturation were maintained throughout extended exposures to a point preceding termination by only a second or two. CONCLUSIONS: Those anti-G protection ensembles that cover and protect the body and which employ positive pressure breathing allow longer high G exposures which provide support for maintained cognitive performance.

The effect of brief headward acceleration on human G tolerance.

OBJECTIVE: To generate, on a multi-axial centrifuge, a negative to positive acceleration profile that reproduces the physiological reaction and subjective symptoms experienced by agile aircraft pilots. Previous research will be summarized and current status of research described. METHODS: Experiments have been accomplished with the Dynamic Environment Simulator (DES) using different profile generating techniques. The DES was programmed with a set of open-loop profiles that provided five second duration baseline exposures ranging from +1.4 Gz down to -2 Gz followed by rapid transition to positive G levels up 2 to 8 +Gz. Volunteer subjects were instrumented and trained to report visual symptoms. RESULTS: Both profile generation approaches produce the reduced cardiovascular and subjective tolerance in a subset of subjects tested. Accumulated stress and motion sickness are factors in quantitative measures. Use of the anti-G straining maneuver may only temporarily alleviate the symptoms with a second period of visual symptoms even as the G load is removed. Positive pressure breathing for G (PBG) does not appear to exacerbate the effect, but the advantages gained from PBG may be lost when a sustained G pull is preceded by a negative G push. CONCLUSIONS: The utility and limitations of using a multi-axial centrifuge for the study of negative to positive G transitions have been described. Greater study is necessary on multiple factors affecting the effect and large numbers of volunteer subjects are needed.

Development of space motion sickness in a ground-based human centrifuge.

Adaptation of the vestibular system, specifically the otolith organs, to a non-terrestrial environment can result in space motion sickness-like symptoms when the human is reintroduced to the normal, 1 Gz, terrestrial environment. This premise was investigated by exposing nine subjects to 90 min of sustained 2 Gz acceleration in a human centrifuge and then observing and evaluating them at 1 Gz. Five of the subjects developed slight SMS symptoms, three developed moderate, and one developed frank sickness. Postural instabilities in two of the most affected subjects were also observed using the Equitest System post exposure. Long duration exposure to a non-terrestrial G(2Gz) appears to be a potential means for developing SMS-like symptoms in a ground-based human centrifuge.

The effect of head tilt on perception of self-orientation while in a greater than one G environment.

The effect of head tilt on the perception of self-orientation while in a greater than one G environment was studied in nine subjects using the Armstrong Laboratory Dynamic Environment Simulator. After a 12-s stabilization period at a constant head tilt and G level, subjects reported their perception of the horizon by placing their right hand in a position they believed to be horizontal. Head tilt conditions ranged from -30 degrees to +45 degrees pitch over each of three head yaw positions. G levels ranged from one to four and were in the longitudinal axis of the body (Gz). Hand position was recorded in both the pitch and roll body axes. A function of head tilt did improve the fit of a multiple regression model to the collected data in both the pitch and roll axes (P < .05). The best fit was accomplished with a nonlinear function of G and head pitch. When the head remained level but the environment tilted with respect to the G vector (at angles similar to those perceived during head tilt), subjects accurately reported the environmental tilt. Head tilt under G can result in vestibular-based illusionary perception of environmental tilt. Actual environmental tilt is accurately perceived due to added channels of haptic information.

Non-invasive sensing systems for acceleration-induced physiologic changes.

The status of a system under development for detection of gravity-induced loss of consciousness (G-LOC) and subsequent recovery is presented. The physiological factors under investigation for use in the loss-of-consciousness monitoring system (LOCOMS) effort are eye blink rate, head slumping, head-level arterial pulsations, and spectral shift in EEG frequency. Also being studied for inclusion in the LOCOMS are a means of detecting the presence/quality of the anti-G straining maneuver and anti-G suit functions, and a system for voice-synthesized query for interrogating the pilot prior to intervention in aircraft control. The possibility of reducing the length of the period of relative incapacitation that occurs after the pilot regains consciousness is considered.

The effect of sustained acceleration and noise on workload in human operators.

Biodynamic stressors such as acceleration, vibration, heat, and cold can affect pilot performance. The objective of this research was to determine the individual effect of two of these stressors, sustained acceleration or high intensity pink noise, on workload in human operators. Combined stressors were not investigated. A total of 13 workload measures, including 1 subjective, 4 performance, and 8 physiological, were recorded on subjects (N = 9) performing a dual psychomotor task in the human centrifuge. Increasing noise stress (max 100 dB-A weighted) had a significant effect on the Subjective Workload Assessment Technique or SWAT scores (p = 0.0001) and reaction times (p = 0.0189); acceleration stress (average peak, 3.75 Gz) had a significant effect on SWAT (p = 0.0001), heart rate (p = 0.0001), total eye blinks (p = 0.0184), blink duration (p = 0.0017), and the standard deviation of the EMG on the tracking forearm (p = 0.0452). Although many of the workload measures were affected by the noise or acceleration, subjects were able to maintain their performance on the primary tracking task. It is concluded that biodynamic stressors, such as noise and acceleration can adversely affect subjective operator workload without affecting objective task performance.