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PubMed2003

Color vision with rapid-onset acceleration.

INTRODUCTION: Only sporadic information exists concerning perceived color shifts at increased G-loads. The purpose of this study was to investigate whether or not color vision is affected by rapid onset high G7-loads up to +9 Gz, and specifically whether perception of hue changes. METHODS: There were 10 male subjects, 9 with normal color vision and 1 with red-green protanomaly, all accustomed to Gz-loads in a human centrifuge. Each subject was tested on a total of 60 Gz-exposures with 10 s periods at +3, +5, +7, and +9 Gz in the centrifuge on three different days. G-onset rate was 6 G x s(-1). The subjects wore an anti-G suit and performed straining maneuvers if necessary to maintain vision. Five square color stimuli of medium saturation (yellow, red, blue, green, and gray) were projected one at a time on a screen in front of the subject, who gave his hue response orally. RESULTS: In 96.6% of exposures to various Gz-loads, the subjects responded by correctly naming colors. (The statistical analyses of the results were done for the subjects with normal color vision, with the protanomalous subject excluded.) Hue shifts occurred at the higher +Gz-levels, including 7.7% of the +9 Gz exposures. Yellow was the hue most frequently perceived as changed. Hue shifts were reported for yellow in 11% and 16% of the +7 and +9 Gz exposures, respectively. Hue shifts at +9 Gz occurred as frequently as blackout and G-LOC together. However, statistical analyses showed no significant effects for +Gz-load. CONCLUSIONS: Absolute identification of the color stimuli of medium saturation was stable and was not significantly affected by the rapid onset +Gz-loads up to and including +9 Gz.

Acceleration↗
PubMed2003

The effect of posture and positive pressure breathing on the hemodynamics of the internal jugular vein.

BACKGROUND: Mathematical and mechanical models of cerebral circulation indicate that the resistance of the collapsed internal jugular veins limits cerebral blood flow during high acceleration (+Gz) and that positive pressure breathing (PPB) restores cerebral blood flow by elevating blood pressure and preventing collapse of the vein. The effect of acceleration and PPB on the jugular resistance and flow can be estimated by documenting changes in the lumen area and blood velocity. METHODS: The right internal jugular vein was imaged with vascular ultrasound in supine and seated human subjects exposed to 0-50 mm Hg of PPB. For each of the PPB posture combinations the vein was imaged at four locations along the length; resistance and flow were calculated using Poiseuille flow approximation. RESULTS: For the supine subjects, the lumen area, just above the inferior bulb, was 1.0 +/- 0.49 cm2, the estimated resistance was 0.13 +/- 0.07 x 10(-3) mm Hg x cm(-3) x min(-1), and the estimated blood flow was 931 +/- 477 cm3 x min(-1). In the sitting position, the lumen narrowed to 0.11 +/- 0.07 cm2, the resistance increased to 6.3 +/- 4.9 x 10(-3) mm Hg x cm(-3) x min(-1), and the blood flow dropped to 372 +/- 194 cm3 x min(-1). However, the vessel of a sitting subject can be completely reopened with PPB of 30 mm Hg or higher, and the resistance can be brought to supine levels. CONCLUSIONS: The results demonstrate that the internal jugular vein collapses with transition from supine to sitting position. This implies a significant increase in resistance which is inversely proportional to the square of the lumen area. However, the collapse can be prevented with sufficiently high PPB.

Adult↗
PubMed2003

Acceleration effects on neck muscle strength: pilots vs. non-pilots.

BACKGROUND: Conditioning of neck muscles, if any, due to repeated exposures to +Gz forces has received little research attention. OBJECTIVE: This study was conducted to evaluate and compare the neck muscle strength of test volunteers representative of the general populations of fighter aircraft pilots and non-pilots. METHODS: The tests were performed using a special attachment device on a computerized dynamometer. Ten pilots and ten non-pilots volunteered as test subjects. Each individual's maximal isometric neck muscle strength was evaluated in the extension, flexion, and left and right lateral bending directions in a single day. Peak values from the measurements were used for data analysis. Overall neck strength was calculated as the mean values for the four directions in each group. RESULTS: The overall muscular strength of the necks of pilots did not differ significantly from that of non-pilots, nor did exposure to +Gz forces lead to specific changes in isometric muscle strength across any of the four principal directions. Neck muscle strength in the four measured directions pooled across the two subgroups were statistically significant. The widespread practice of adopting protective head-positioning strategies to minimize neck strains, coupled with results from this research study, suggest that the neck muscles are subjected to reduced in-flight strengthening workouts during exposures to +Gz forces. CONCLUSIONS: To maximize in-flight performance and minimize +Gz-induced neck injuries, fighter pilots should be encouraged to perform on-land neck muscle strengthening exercise and in-flight head-positioning techniques. More research is needed to fine-tune this countermeasure strategy against cervical spine injury.

Adult↗
PubMed2002

Expression of heat shock protein after +Gz exposure and its protective effects on +Gz-induced brain injury.

Objective. To investigate the rule of intensity and duration of HSP70 expression in rat brain and its relationship with brain injury after repeated +Gz exposures. Method. SD male rats were arranged into control group, +2 Gz, +4 Gz, +6 Gz, and +10 Gz exposure groups. Rat brains were taken 6 h, 10 h, 1 d, 2 d, 4 d or 6 d after +Gz exposure for histopathologic and immunohistochemic or in situ hybridization studies. The expression of HSP70 and HSP70 mRNA or morphology of neurons were observed. Result. The intensity and duration of HSP70 expression were weak and brief at +2 Gz exposure, but was relatively extensive. There was a middling reaction of HSP70 only in hippocampal area after +10 Gz exposure. The duration, extension and intensity of HSP70 expression were wide, long and strong after +4 Gz and +6 Gz exposures. After 1 or 3-5 times exposures, the HSP70 expression reached its peak on the first day after +4 Gz exposures, and dropped obviously on the second day. However the expression of HSP70 maintained a high level after 2 d and was still higher than normal on the 6 d after 3-5 times repeated +4 Gz exposures. The distribution of HSP70 mRNA expression was as same as that of the HSP70 expression but the peak appeared much earlier (10 h) and its duration was shorter. After +10 Gz/5 min exposure, degenerated neurons were found in cortex, hippocampus and thalamus regions while the number of degenerated neurons were obviously decreased in such areas in pre-exposure groups with repeated +4 Gz/3 min for 3-5 times. Conclusion. The intensity and duration of HSP70 and HSP70 mRNA expression after +4 Gz and +6 Gz exposure were stronger and longer than +2 Gz and +10 Gz exposure. The degree of neuron damage after +10 Gz/5 min exposure in pre-exposure groups with repeated +4 Gz/3 min 3-5 times was obviously slight comparing with that of single +10 Gz exposure group.

Animals↗
PubMed2002

[Study on anti +Gx respiratory maneuver and its training method].

Objective. To study the anti +Gx respiratory maneuver and its training method. Method. Seven young male subjects undertook the anti +Gx respiratory maneuver training. Their +Gx tolerances were examined on human centrifuge before and after training. The change of respiratory type, breath rate, electrocardiogram, heart rate, arterial oxygen saturation (SaO2), subjective symptom and vision were real-time monitored during the +Gx tolerance examination. Result. Compared with pre-training, the +Gx tolerance increased after training (P<0.05). Dyspnea and chest pain disappeared or obviously lightened and the magnitude of decrease of SaO2 decreased significantly (P<0.05). Conclusion. The above results suggested that the anti +Gx respiratory maneuver can effectively eliminate or alleviate dyspnea and chest pain induced by +Gx stress and increase human +Gx tolerance.

Adaptation, Physiological↗