Repetitive high-sustained gravitoinertial stress does not modulate pressure responsiveness to peripheral sympathetic stimulation.

PURPOSE: We evaluated the hypothesis that repetitive gravitoinertial stress would augment the arterial-pressure response to peripheral sympathetic stimulation. METHODS: Before and after a 5-weeks G-training regimen conducted in a human-use centrifuge, twenty healthy men performed a hand cold-pressor test, and nine of them also a foot cold-pressor test (4 min; 4 °C water). Arterial pressures and total peripheral resistance were monitored. RESULTS: The cold-induced elevation (P ≤ 0.002) in arterial pressures and total peripheral resistance did not vary between testing periods, either in the hand [mean arterial pressure: Before = + 16% vs. After = + 17% and total peripheral resistance: Before = + 13% vs. After = + 15%], or in the foot [mean arterial pressure: Before = + 19% vs. After = + 21% and total peripheral resistance: Before = + 16% vs. After = + 16%] cold-pressor tests (P > 0.05). CONCLUSION: Present results demonstrate that 5 weeks of prolonged iterative exposure to hypergravity does not alter the responsiveness of sympathetically mediated circulatory reflexes.

In vivo pressure-flow relation of human cutaneous vessels following prolonged iterative exposures to hypergravity.

The study examined intra- and interlimb variations in cutaneous vessel responsiveness to acute and repeated transmural pressure elevations. In 11 healthy men, red blood cell flux was assessed via laser-Doppler flowmetry on both glabrous and nonglabrous skin regions of an arm (finger and forearm) and leg (toe and lower leg), across a wide range of stepwise increasing distending pressures imposed in the vessels of each limb separately. The pressure-flux cutaneous responses were evaluated before and after 5 wk of intermittent (40 min, 3 sessions per week) exposures to hypergravity (∼2.6-3.3 G; G training). Before and after G training, forearm and lower leg blood flux were relatively stable up to ∼210 and ∼240 mmHg distending pressures, respectively; and then they increased two- to threefold (P < 0.001). Finger blood flux dropped promptly (P < 0.001), regardless of the G training (P = 0.64). At ≤120-mmHg distending pressures, toe blood flux enhanced by ∼40% (P ≤ 0.05); the increase was augmented after the G training (P = 0.01). At high distending pressures, toe blood flux dropped by ∼70% in both trials (P < 0.001). The present results demonstrate that circulatory autoregulation is more pronounced in glabrous skin than in nonglabrous skin, and in nonglabrous sites of the leg than in those of the arm. Repetitive high-sustained gravitoinertial stress does not modify the pressure-flow relationship in the dependent skin vessels of the arm nor in the nonglabrous sites of the lower leg. Yet it may partly inhibit the myogenic responsiveness of the toe's glabrous skin.

ANALYSIS OF ECG. MONITORING DURING CENTRIFUGE TRAINING IN PILOTS, ROKAF (Dysrhythmia and G-LOC)

The ROKAF(Republic of Korea Air Force ) has been conducting high G-training with new centrifuge training equipment at Aeromedical Research and Training Center(AMRTC) to enhance G-tolerance since July 1995. All trainees routinely have received ECG monitoring during High G training, both for safety and medical evaluation. The purpose of this study was to estimate the incidence of cardiac dysrhythmia among the fighter pilots of ROKAF and other countries and to investigate the relationship between G-induced loss of consciousness (G-LOC) and the presence of dysrhythmia during High-G training. The electrocardiographic responses of 417 fighter pilots exposed to the standard centrifuge high-G training profile were analysed. Dysrhythmias were observed in 204(42.7%) of the sessions, Ventricular ectopy occurred In 143(29.9% ) and supraventricular ectopy showed in 56(11.7%) of the sessions. G-induced loss of consciousness(G-LOC) occurred in 15%(62 pilots) of the trainees. Dysrhythmias associated with G-LOC were recorded In 23(37%), however, aeromedically serious arrhythmias were not observed. 41%(25/61) of dysrhythmias appeared in ROR(Rapid Onset Rate), whereas 27.9%(17/61) of them in GOR (Gradual Onset Rate). Although riding the centrifuge is a stressful experience in aircrews, the presence of the serious arrhythmias could potentially result in sudden incapacitation during flight. Therefore, ECG monitoring of aircrews during centrifuge training is hlghly recommended for their safety as well as aeromedical policy.

Analysis of Risk Factors on the G-induced Loss of Conscious in ROKAF Pilots / 항공우주의학회지

Of all the aeromedical treats to flying safety, G-induced loss of consciousness (G-LOC) must be one of the most important. The present study is undertaken to acquire the physiological normative data (including lifestyle and physical fitness) of KAF pilots and to investigate the factors that will be related with G-LOC. From 15 May through 27 Nov 2000, 464 KAF pilots underwent high G training and flight performance tests at the Aeromedical Research and Training Center are checked CBC, total cholesterol, PFT, physical fitness battery tests-muscular strength, muscular endurance, power, and flexibility. High G training and 2 kinds (before and after the G-training) of questionnaire were tried. Pilot's attitude for health promotion was relatively passive and the proportions as of high and borderline risk for atherosclerosis in total cholesterol level were 4.98% and 22.1%, respectively. 17.6% of the pilots had G-LOC and three quarters of them fell into G-LOC within the first 5 seconds. Variables showing significant correlation (p<0.05) with G-LOC were as follows; height, age, total flying time, and high G-training times. Trunk extension had positive correlation and curls ups had negative correlation, but the reasons are needed more following study. Also, the judgments of pilots and a supervisor in skillfulness of L1 maneuver were significant with G-LOC.

Changes in Urinary Excretion of Epinephrine, Norepinephrine and Dopamine after Gravitional Acceleration Training

Urinary excretion of catecholamines (epinephrine, norepinephrine and dopamine) was determined in student pilots during high gravitational acceleration training. A total of 20 student pilots were exposed to +6GZ for 30 seconds using human centrifuge without anti-G suit and urine samples were collected before and after +GZ load. Each urine sample was adjusted to pH 2 with hydrochloric acid and stored at -20degreeC. Urine samples were derivatized with fluorescence using Toyopak SP cartridge and concentration of urinary catecholamines was determined by high-performance liquid chromatography (HPLC) with fluorescence detection. The amount of urinary excretion of catecholamines after exposure to +6GZ was significantly increased in comparison with pre-exposure level (epinephrine, 3.02+/-1.66 to 7.62+/-3.97; norepinephrine, 1.10+/-0.36 to 2.03+/-1.09; dopamine, 3.49+/-1.76 to 5.33+/-3.21 ng/100 mg creatinine). But, there was no difference in catecholamine excretion pattern between passed trainees and failed ones who experienced G-induced loss of consciousness (G-LOC). These data suggest that high +GZ stress was a powerful physical and mental stimuli to all student pilots and resulted in increased excretion of catecholamines. And the cartridge derivatization method was very useful in catecholamine measurement.