Cognition Effects of Low-Grade Hypoxia.

INTRODUCTION: The effects of low-grade hypoxia on cognitive function are reported in this paper. The study compared cognitive function during short exposures at four different altitudes. METHODS: Ninety-one subjects were exposed to simulated altitudes of ground level, 1524, 2438, and 3658 m (5000, 8000, and 12,000 ft) in the Brooks City-Base altitude pressure chamber in a balanced design. Oxygen saturation, heart rate, and cognitive performance on seven different cognitive tasks were measured. In addition, subjects indicated their symptoms from a 33-item subjective symptom survey. RESULTS: As designed, oxygen saturation decreased and heart rate increased with higher altitudes. Very small degradations in performance were found at the two highest altitudes for only two of the cognitive tasks (continuous performance and grammatical reasoning). In the subjective symptom survey, 18 of the 33 possible symptoms were more common at 3658 m (12,000 ft) than at ground level. CONCLUSIONS: The findings indicated a minimal influence of low-grade hypoxia on cognitive performance in contrast to some existing classic symptoms of hypoxia. Pilmanis AA, Balldin UI, Fischer JR. Cognition effects of low-grade hypoxia. Aerosp Med Hum Perform. 2016; 87(7):596-603.

G Protection When Adding Pressurized Sleeves and Gloves to a Representative G-Suit Ensemble.

BACKGROUND: In a previous study, pressurized sleeves and gloves were found to substantially diminish or eliminate G-induced arm pain. Since this equipment presumably acts similarly to a G suit for the arms and hands, it was hypothesized that higher inflation pressures might provide an additional increment of G protection. METHODS: In a human-rated centrifuge, 15 well trained subjects using Combat Edge and ATAGS G-protective equipment were exposed to gradual and rapid onset relaxed G exposures as well as rapid onset straining and simulated aerial combat maneuver G exposures up to + 9 Gz with and without pressurized sleeves and gloves. RESULTS: The pressurized sleeves and gloves did not show any improvement in G tolerance or endurance compared to the control. However, significantly lower heart rates (6-12%) and subjective effort (11%), along with slightly less peripheral vision loss, suggest a decreased work load when wearing the pressurized sleeves and gloves. A trend to shorter time on target in a tracking task was found with the pressurized sleeves and gloves, likely due to decreased mobility of the hands, thus affecting control stick input. CONCLUSIONS: G tolerance and endurance were not improved by the pressurized sleeves and gloves. However, a lower heart rate and a decreased subjective effort level and peripheral vision loss indicated that the subjects did not have to work as hard with this equipment.

Air break during preoxygenation and risk of altitude decompression sickness.

INTRODUCTION: To reduce the risk of decompression sickness (DCS), current USAF U-2 operations require a 1-h preoxygenation (PreOx). An interruption of oxygen breathing with air breathing currently requires significant extension of the PreOx time. The purpose of this study was to evaluate the relationship between air breaks during PreOx and subsequent DCS and venous gas emboli (VGE) incidence, and to determine safe air break limits for operational activities. METHODS: Volunteers performed 30 min of PreOx, followed by either a 10-min, 20-min, or 60-min air break, then completed another 30 min of PreOx, and began a 4-h altitude chamber exposure to 9144 m (30,000 ft). Subjects were monitored for VGE using echocardiography. Altitude exposure was terminated if DCS symptoms developed. Control data (uninterrupted 60-min PreOx) to compare against air break data were taken from the AFRL DCS database. RESULTS: At 1 h of altitude exposure, DCS rates were significantly higher in all three break in prebreathe (BiP) profiles compared to control (40%, 45%, and 47% vs. 24%). At 2 h, the 20-min and 60-min BiP DCS rates remained higher than control (70% and 69% vs. 52%), but no differences were found at 4 h. No differences in VGE rates were found between the BiP profiles and control. DISCUSSION: Increased DCS risk in the BiP profiles is likely due to tissue renitrogenation during air breaks not totally compensated for by the remaining PreOx following the air breaks. Air breaks of 10 min or more occurring in the middle of 1 h of PreOx may significantly increase DCS risk during the first 2 h of exposure to 9144 m when compared to uninterrupted PreOx exposures.

Caffeinated tube food effect on pilot performance during a 9-hour, simulated nighttime U-2 mission.

INTRODUCTION: Interventions to maintain performance are necessary to meet demanding mission requirements during sustained and surge aviation operations. Tube foods are the only foods that can be consumed during a U-2 mission due to the confining and encapsulating nature of required support equipment. Caffeine is a safe and effective strategy to enhance cognitive performance and is an ingredient in some tube foods. The objective of this study was to determine whether moderate doses of caffeinated tube foods would enhance performance in a simulated U-2 mission. METHODS: Volunteers were 12 healthy USAF male pilots. The study used a double blind, placebo-controlled, two-factor, repeated-measures (five iterations per night) design. Caffeinated (200 mg each) or placebo tube food was consumed at 00:00 and 04:00. Dependent measures assessed included standardized tests of cognitive performance, vigilance, and mood designed to simulate the demands of a nighttime U-2 mission. RESULTS: Statistically significant (p < 0.05) improvements in performance due to caffeine administration compared with placebo were present in all five cognitive tasks either as main effects, interactions, or absence of significant degradation in the caffeine treatment condition compared with the placebo condition. A majority of sleep deprivation-induced performance decrements were attenuated by 200 mg of caffeine in tube food consumed every 4 h, and in some cases, performance was improved beyond baseline levels. CONCLUSIONS: Caffeinated tube food maintained cognitive performance representative of U-2 long-duration mission tasks at or near baseline levels for a 9-h overnight period in qualified USAF pilots. Side effects were minor and did not differ between placebo and caffeine conditions.

Altitude decompression sickness susceptibility: influence of anthropometric and physiologic variables.

INTRODUCTION: There is considerable variability in individual susceptibility to altitude decompression sickness (DCS). The Air Force Research Laboratory Altitude DCS Research Database consists of extensive information on 2980 altitude exposures conducted with consistent procedures and endpoint criteria. We used this database to quantify the variation in susceptibility and determine if anthropometric and/or physiologic variables could be used to predict DCS risk. METHODS: There were 240 subjects who participated in at least 4 of 70 exposure profiles in which between 5 and 95% of all subjects tested developed DCS symptoms. A subject/study ratio (SSR) was calculated by dividing the DCS experienced by a subject during all their exposures by the DCS incidence for all subjects who participated in the identical exposures. The SSR was used to identify the relative susceptibility of subjects for use in analyzing possible relationships between DCS susceptibility and the variables of height, weight, body mass index, age, percent body fat, and aerobic capacity. RESULTS: The DCS incidence was 46.5% during 1879 subject-exposures by subjects exposed at least 4 times. A significant relationship existed between higher DCS susceptibility and the combination of lower aerobic capacity and greater weight (p < 0.05). DISCUSSION: Despite a correlation, less than 13% of the variation in DCS susceptibility was accounted for by the best combination of variables, weight and VO2max. CONCLUSION: Differences in DCS susceptibility cover a wide range and appear to be related to some anthropometric and physiologic variables. However, there was insufficient correlation to allow prediction of an individual's susceptibility.

Hypnotic efficacy of zaleplon for daytime sleep in rested individuals.

STUDY OBJECTIVES: The primary objective of this study was to determine whether zaleplon (10 mg) effectively promoted sleep during the daytime in well-rested individuals when compared to placebo. A secondary objective was to see if, while not expected, the use of zaleplon impacted the performance of well-rested individuals upon awakening. DESIGN: Repeated measures with 2 within-subject factors: drug (placebo/zaleplon) and trial (hourly testing during waking hours). Polysomnographic variables were recorded during a 3.5-hour nap following drug administration. Performance measures and subjective reports were collected during every waking trial of each session. SETTING: The study was conducted at the Chronobiology and Sleep Laboratory located at Brooks Air Force Base. PARTICIPANTS: Twelve participants, 6 men and 6 women. INTERVENTIONS: 10-mg zaleplon or placebo capsules, single afternoon dose. Drug administration was counterbalanced and double-blinded. MEASUREMENTS AND RESULTS: Zaleplon allowed participants to obtain significantly more slow-wave sleep than under placebo. There was also a trend for participants under zaleplon to accomplish a greater amount of sleep than under placebo. Performance was not adversely impacted following a 3.5-hour daytime sleep under zaleplon, nor were any undesirable symptoms induced. CONCLUSIONS: Zaleplon improves sleep quality when used by rested individuals to accomplish daytime sleep.

Dextroamphetamine use during B-2 combat missions.

INTRODUCTION: Fatigue among warriors can jeopardize mission success. Prescribed stimulant medications, in-flight sleep, and self-medication with caffeine can mitigate fatigue. During Operation Iraqi Freedom, pilots flew the B-2 bomber to targets in Iraq from one of two airfields. Sortie durations were long (16.9 h) from one field and very long (35.3 h) from the other. Controversy exists concerning the use of stimulant medication, in part because of a paucity of combat data. METHODS: A retrospective analysis of 75 pilots who performed 94 combat sorties was performed. We examined the prevalence of the pilot's decision to use dextroamphetamine, caffeine, and in-flight sleep during combat. We compared demographic factors, the impact of one anti-fatigue tool on the use of others, stimulant benefit, and adverse effects. RESULTS: Pilots on shorter missions used dextroamphetamine for 97% and in-flight naps for 13% of sorties. Those on longer missions used dextroamphetamine on 58% and naps on 94% of sorties. Stimulant use was not affected by pilot age, bomber experience, or long-duration experience. The opportunity to obtain in-flight sleep was limited by certain mission profiles, which influenced the decision to use dextroamphetamine. Among pilots who used the medication, 97% noted a benefit. Side effects and failure to observe benefits were uncommon. CONCLUSIONS: B-2 pilots in long-duration combat flight selectively employ dextroamphetamine, naps, and other fatigue countermeasures. Major determinants of these decisions are mission requirements and the pilot's experience with each measure and its effect.

Performance following a sudden awakening from daytime nap induced by zaleplon.

BACKGROUND: Zaleplon appears to be a prime candidate for assisting individuals in obtaining sleep in situations not conducive to rest (i.e., a short period during the day). However, should an early unexpected awakening and return to duty be required, the effect on performance is not known. HYPOTHESIS: Zaleplon (10 mg) would negatively affect human performance for some duration, compared with placebo, after a sudden awakening from a short period (1 h) of daytime sleep. METHODS: There were 16 participants, 8 men and 8 women, who volunteered to participate in this study. The study was conducted using a counterbalanced, double-blind, repeated measures design. At 1 h prior to drug administration, and at each of 7 h postdrug, performance measures (cognition, memory, balance, and strength) and subjective symptom reports were recorded. RESULTS: Zaleplon had a statistically significant (p < 0.05) negative impact on balance through the first 2 h postdose when compared with placebo. In addition, symptoms related to "drowsiness" were statistically more prevalent under zaleplon than under placebo through the first 3 h postdrug. Of the eight measures of cognitive performance, six were significantly negatively impacted in the zaleplon condition through 2 h postdose when compared with placebo, with one remaining significantly degraded through 3 h postdose. Zaleplon also had a significantly negative impact on memory at 1 h and 4 h postdose. CONCLUSIONS: Zaleplon (10 mg), when used as a daytime sleep aid, causes drowsiness (and related symptoms) up to 3 h postdose, and may impact task performance, especially more complex tasks, for at least 2-3 h postdose.

Prevalence of proximal adenomas after an adenoma is found on flexible sigmoidoscopy.

BACKGROUND: Adenomatous polyps are a precursor of colorectal cancer and a frequent finding on screening flexible sigmoidoscopy (FS). Performance of colonoscopy when a diminutive (<6mm) adenoma is found on FS has been the subject of considerable debate. METHODS: We retrospectively reviewed the data from our colorectal cancer screening program for patients with adenoma(s) found on FS. Patients were divided into three groups based on FS findings: (1) an adenoma <6mm in size, (2) multiple non-advanced adenomas or an adenoma 6-10mm in size, or (3) advanced adenoma defined as an adenoma >10mm or with villous histology or high-grade dysplasia or cancer. A comparison of the proximal findings was then made. RESULTS: 5291 FS reports were reviewed with 606 (12%) patients having at least one adenoma. Colonoscopy reports were available in 550 patients. Of the 258 patients with a diminutive distal adenoma, 69 (27%) had a proximal adenoma and 13 (5%) had an advanced proximal adenoma on colonoscopy. Of the 164 patients with an adenoma 6-10mm or multiple non-advanced adenomas, 59 (36%) had a proximal adenoma and 13 (8%) had an advanced proximal adenoma. Of the 128 patients with a distal advanced adenoma, 58 (45%) had a proximal adenoma and 15 (12%) had an advanced proximal adenoma. The increase in proximal adenomas across the three groups was significant (P=0.001), and there was a trend for increased prevalence of advanced adenomas (P=0.061). CONCLUSIONS: The prevalence of proximal adenomas increased significantly with more advanced lesions found distally at FS, and there was a trend towards a higher prevalence of advanced proximal adenomas. Based on current guidelines, flexible sigmoidoscopy is a screening option that can be used to identify average-risk patients at increased risk of proximal neoplasia.

Effect of a physician-directed educational campaign on performance of proper diabetic foot exams in an outpatient setting.

BACKGROUND: The established guidelines for a diabetes foot examination include assessing circulatory, skin, and neurological status to detect problems early and reduce the likelihood of amputation. Physician adherence to the guidelines for proper examination is less than optimal. OBJECTIVE: Our objective was to increase compliance with the performance of a proper foot examination through a predominantly physician-directed interventional campaign. METHODS: The study consisted of 3 parts: a retrospective chart review to estimate background compliance, an educational intervention, and prospective chart review at 3 and 6 months. A properly documented foot examination was defined as assessing at least 2 of the 3 necessary components. The educational intervention consisted of 2 lectures directed at resident physicians and a quality assurance announcement at a general internal medicine staff meeting. Clinic support staff were instructed to remove the shoes and socks of all diabetic patients when they were placed in exam rooms, and signs reminding diabetics were placed in each exam room. RESULTS: There was a significant increase in the performance of proper foot examination over the course of the study (baseline 14.0%, 3 months 58.0%, 6 months 62.1%; P <.001). Documentation of any component of a proper foot examination also increased substantially (32.6%, 67.3%, 72.5%; P <.001). Additionally, performance of each component of a proper exam increased dramatically during the study: neurological (13.5%, 35.8%, 38.5%; P <.001), skin (23.0%, 64.2%, 69.2%; P <.001), and vascular (14.0%, 51.2%, 50.5%; P <.001). CONCLUSIONS: Patients with diabetes are unlikely to have foot examinations in their primary medical care. A simple, low-cost educational intervention significantly improved the adherence to foot examination guidelines for patients with diabetes.

Asian-Pacific Islander race independently predicts poor outcome in patients with endometrial cancer.

OBJECTIVE: The Department of Defense health care system provides access to care without respect to age, race, or socioeconomic status. We sought to determine the effect of race as a predictor of survival in patients with endometrial cancer treated in the Department of Defense medical system. METHODS: Information on patients with endometrial carcinoma was extracted from the Department of Defense centralized tumor registry for the period 1988 to 1995. Data included age at diagnosis, military status, race, tumor histology, grade, FIGO surgical stage, adjuvant therapies, and disease-free survival. The chi(2) test was used for analysis of prognostic factors and adjuvant treatments between racial groups. Actuarial survival curves were calculated by using the method of Kaplan and Meier and compared by the log-rank test. Variables found to be significant on univariate analysis (P < 0.05) were entered into a multivariate Cox regression analysis. RESULTS: Of 1811 patients meeting criteria for the study, racial distribution was 90% Caucasian, 4.4% African-American, and 5.5% Asian-Pacific Islander. African-Americans had more advanced stages of disease compared to Caucasians (P < 0.001). Both African-Americans and Asian-Pacific Islanders had higher grade tumors and less favorable histologic types than Caucasians (P < 0.05). The extent of adjuvant therapies was similar for racial groups. African-Americans and Asian-Pacific Islanders had significantly worse 5-year disease-free survivals than Caucasians (P = 0.007). Additional poor prognostic factors included age >60 years, grade, unfavorable histology, and stage. On multivariate analysis age >60 years, stage, and Asian-Pacific Islander race remained significant prognostic factors. CONCLUSION: African-Americans and Asian-Pacific Islanders had worse survivals than Caucasians. After controlling for imbalances in clinicopathologic factors, Asian-Pacific Islander race was found to be a newly identified poor prognostic factor.