Reversal of triazolam- and zolpidem-induced memory impairment by flumazenil.

The effects of flumazenil, a benzodiazepine receptor antagonist, on triazolam- and zolpidem-induced memory impairment were investigated. Sixty subjects received oral triazolam 0.5 mg, zolpidem 20.0 mg, or placebo at 10 a.m. (n = 20 per drug). Ninety minutes later, half of the subjects (n = 10) in each oral drug group were administered flumazenil 1.0 mg, while the remaining half received placebo (normal saline), through indwelling venous catheters. Learning/memory tests (including Simulated Escape, Restricted Reminding, Paired-Associates, and Repeated Acquisition) were administered at that time, and at 1.5-h intervals over the next 6 h. Triazolam/placebo and zolpidem/placebo drug combinations impaired memory on all tests (all Ps < 0.05). However, the triazolam/flumazenil and zolpidem/flumazenil groups showed no evidence of impairment during any test session. These results demonstrate that flumazenil 1.0 mg rapidly and lastingly reverses memory impairment caused by agonists of the benzodiazepine receptor. Furthermore, nonsignificant trends suggested that performance of the placebo/flumazenil group was consistently better than that of the placebo/placebo group, denoting a possible role of endogenous benzodiazepine agonists in natural sleep/wake processes.

Improvement in hypoxemia at 4600 meters of simulated altitude with carbohydrate ingestion.

BACKGROUND: Carbohydrate ingestion increases the relative production of carbon dioxide which results in an increase in ventilation in normal individuals. An increase in ventilation at altitude can result in improvement of altitude-induced hypoxemia. HYPOTHESIS: Carbohydrate ingestion will increase the arterial blood oxygen tension and oxyhemoglobin saturation during acute high altitude simulation. METHODS: There were 15 healthy volunteers, aged 18-33 yr, who were given a 4 kcal x kg(-1) oral carbohydrate beverage administered 2.5 h into an exposure to 15,000 ft (4600 m) of simulated altitude (5.5 h after the last meal). Altitude was simulated by having subjects breath a 12% oxygen/balance nitrogen mixture while remaining at sea level. Arterial blood gas samples were drawn at baseline and at regular intervals up to 210 min after carbohydrate ingestion. Subjects were evaluated for AMS by use of the Environmental Symptoms Questionnaire (ESQ) and a weighted average of cerebral symptom score (AMS-C). RESULTS: Baseline PaO2 increased significantly (p < 0.01) from 43.0 +/- 3.0 mmHg at 4600 m before carbohydrate ingestion to 46.8 +/- 6.2 mmHg at 60 min after carbohydrate ingestion. Arterial oxygen saturation rose significantly (p < 0.01) from a baseline of 79.5% +/- 5.1 to 83.8% +/- 6.42 at 60 min. CONCLUSIONS: Carbohydrate consumption significantly increased oxygen tension and oxyhemoglobin saturation in arterial blood of normal subjects during simulated altitude. Effects reached statistical significance across all subjects at 60 min. There was no significant difference in arterial oxygen levels or arterial oxygen saturation in subjects who developed AMS vs. those who did not develop AMS.

Visual performance with the Aviator Night Vision Imaging System (ANVIS) at a simulated altitude of 4300 meters.

This study determined if visual performance with Aviator Night Vision Imaging System (ANVIS) was degraded by the degree of hypoxia experienced at the maximum flight altitude currently authorized (U.S. Army regulations) without supplemental oxygen. Visual acuity and contrast sensitivity with ANVIS were tested under simulated starlight and full moonlight illumination in a hypobaric chamber: at ground level (93 m), 5 min and 30 min after ascent to 4300 m, and 10 min after return to ground level. Visual acuity was significantly (p < 0.05) degraded by a small amount (0.05 log minimal angle resolvable) after 30 min at 4300 m. Contrast sensitivity was not significantly degraded at any time. No significant difference between males (n = 11) and females (n = 6) on any measure of visual performance was detected. Females did have a significantly lower percent oxygen saturation of hemoglobin compared with males at altitude (72% versus 80% after 30 min). The results suggests that visual acuity ANVIS is degraded slightly after 30 min of exposure to 4300 m, although less than what would be expected with unaided night vision under these conditions.