A new evaluation method for +Gz tolerance with loratadine by using a near-infrared spectroscopy.

BACKGROUND: Loratadine (Claritin), an over-the-counter antihistamine in U.S. and UK, is acceptable for use without adverse side effects by aircrew with mild or moderate allergic or other situations requiring an antihistamine. Although +Gz (head to foot direction) tolerance testing for aircrew with loratadine has not been documented in the published literature, it is commonly accepted that loratadine dose not effect +Gz tolerance. The purpose of this study was to offer and validate a new evaluation method for +Gz tolerance testing with loratadine by using a near-infrared spectroscopy (NIRS). METHODS: A double-blind, placebo-controlled, randomized, crossover protocol was used to administer 10 mg of loratadine or placebo in nine healthy subjects. The subjects didn't wear anti-G suit. The +Gz exposure profiles consisted of, in series, a gradual onset ran (0.1 G.sec-1) to the subject's visual end-point (peripheral light loss) or loss of consciousness (GLOC), and rapid onset run (1.0 G.sec-1) to the subject's same end-point. In this study, G-level tolerance was defined as the +Gz level at visual end-point and/or at GLOC. As a subject's G-duration tolerance, we measured the total time (seconds) during rapid onset run. Otherwise, to confirm the effect of loratadine on +Gz tolerance, we measured the cerebral NIRS variables (hemoglobin concentration changes and tissue oxygenation index) as a new quantitative method for +Gz tolerance during a centrifuge experiments. RESULTS: No significant differences were observed in +Gz tolerance (+Gz level, duration time and NIRS variables) between subjects taking loratadine and placebo. CONCLUSION: Our results demonstrate that loratadine has no detectable effect on +Gz tolerance by using a new method with cerebral NIRS variables and the traditional method with +Gz level and duration time. This study represents the first use of a quantitative parameter such as cerebral NIRS variables to assess the effects of a drug on acceleration tolerance.

Effects of flight workload on urinary catecholamine responses in experienced military pilots.

This study investigated the flight responses induced by strenuous aerobatic demonstration flight and an air-to-air combat maneuvering flight in experienced pilots. Subjects were 54 military male pilots on a volunteer basis: 8 T-4 pilots (M= 35.8 yr., SD=4.9), 15 F-4 pilots (M=32.6 yr., SD=5.1), 13 F-15 pilots (M=33.8 yr., SD=1.0), and 18 F-2 pilots (M=33.7 yr., SD=3.9). Samples of urine were collected approximately 30 min. before and 20 min. after the flights. The postflight adrenaline in all pilots was significantly higher than at preflight, while a significant increase in noradrenaline at postflight was not observed. The post-/preflight ratio of adrenaline in all pilots was relatively similar and high. These findings might be regarded as a result of autonomic nervous system response to the flight workload of military pilots. Especially is increment in sympathetic activity considered to play an important part in psychological adaptation to flight.

Hormonal responses of pilots to training flights: the effects of experience on apparent stress.

INTRODUCTION: The levels of urinary noradrenaline (NAd), adrenaline (Ad) and salivary cortisol (Cor) were determined in student and instructor pilots during Phase 1 (training with propeller engine; PH1), and Phase 2 (training with jet engine; PH2) flight training. METHODS: The subjects in PH1 were 30 students and 33 instructors, and in PH2 were 17 students and 15 instructors. Urine and saliva were collected approximately 30 min before and 20 min after the flights. The ratio (post/preflight) of the hormonal levels was calculated to compare the students with the instructors and/or PH1 with PH2. RESULTS: In PH1, the levels of all three hormones for postflight were significantly higher than for preflight in students, and the ratios of all three hormones in students were significantly higher than in instructors. In PH2, the ratios of all three hormones for students and instructors did not differ significantly, and the ratios of Ad and Cor levels in students for PH2 were significantly lower than for PH1 (Ad: 1.64 +/- 0.10 vs. 2.23 +/- 0.14; Cor: 0.86 +/- 0.16 vs. 1.68 +/- 0.11, respectively). CONCLUSIONS: The results from PH1 clearly demonstrated that flight stress for students was significantly higher than for instructors. The ratios might be regarded as result of adaptation to flight stress in students. We conclude that the ratios of Ad and Cor levels are a good indicator of stress coping in student pilots.

Effect of muscle tensing on cerebral oxygen status during sustained high +Gz.

BACKGROUND: Successful monitoring of oxyhemoglobin during +Gz exposure was recently achieved using near-infrared spectroscopy (NIRS). To assess the effects of muscle tensing on sustained +Gz tolerance, we measured muscle activity and cerebral oxygen status (COS) during anti-G straining maneuvers at sustained high +Gz. METHOD: We exposed 21 male pilots wearing CSU-13/P anti-G suit to two different centrifuge profiles: 1) short-term repeated exposure (5 to 20 s) at 4, 5, 6, 5.5, or 7 Gz; 2) sustained exposure to a + 7Gz plateau for 30 s. During the Gz exposures, surface electromyographic (EMG) measurements were taken from the vastus medialis (VM) and rectus abdominis (RA) muscles. At the same time, the COS was recorded from the left forehead area using a commercial NIRS system. Mean muscular tensing for each muscle was calculated as a percentage of maximal voluntary contraction (% MVC). RESULTS: Oxyhemoglobin (O2Hb) and total hemoglobin (sum of O2Hb and deoxyhemoglobin) were decreased during both short-term and sustained +Gz exposure. RA muscle tensing was positively correlated with changes in the concentration of O2Hb during sustained + 7Gz exposure (r = 0.540, p < 0.05). RA tensing ranged from 6.2 to 36.8%MVC, and O2Hb ranged from -41.3 to -7.28 micromol x L(-1) during the exposures. No significant correlation was observed between VM tensing and O2Hb. CONCLUSION: NIRS measurements confirmed that a muscle straining maneuver increases G tolerance. Higher RA muscle tensing helps preserve brain blood volume during sustained high +Gz.