Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans.

Acutely stressful situations can disrupt behavior and deplete brain norepinephrine and dopamine, catecholaminergic neurotransmitters. In animals, administration of tyrosine, a food constituent and precursor of the catecholamines, reduces these behavioral and neurochemical deficits. Using a double-blind, placebo-controlled crossover design we investigated whether tyrosine (100 mg/kg) would protect humans from some of the adverse consequences of a 4.5 hour exposure to cold and hypoxia. Tyrosine significantly decreased symptoms, adverse moods, and performance impairments in subjects who exhibited average or greater responses to these environmental conditions. These results suggest that tyrosine should be evaluated in a variety of acutely stressful situations.

Self-rated moods of humans at 4300 m pretreated with placebo or acetazolamide plus staging.

Self-rated moods were determined twice daily with the Clyde Mood Scale on 35 human subjects at 200 m (baseline) during a study concerned with evaluating the efficacy of staging plus acetazolamide (treatment) for the prevention of acute mountain sickness (AMS). Mood states also were determined on all subjects at 4300 m (Pikes Peak, Co) and on 18 of these subjects at 1600 m (staging site). Mood state changes were not observed at 1600 m, but four of the six mood factors were sensitive to the 4300 m altitude. At 4300 m, all subjects, treatment and control, rated themselves as less friendly and clear thinking and more sleepy and dizzy. At 4300 m, the treatment strategy resulted in an improved mood on the friendly, sleepy, and dizzy factors. Altitude-induced changes in clear thinking were not altered by the treatment strategy.

Mood states at 1600 and 4300 meters terrestrial altitude.

Personal anecdotes suggest that ascent to high altitude can cause mood changes such as depression, apathy, and drowsiness. Observed behaviors at high altitude indicate that people can become more euphoric, irritable, or argumentative. Since there are few systematic and quantitative studies assessing the effects of altitude on mood, this study compared moods measured at two different altitudes and times of day (morning-evening) using a standardized scale. Self-rated moods were determined twice daily in 19 males and 16 females with the Clyde Mood Scale. Baseline values were determined at 200 m; moods were then assessed at 4300 m with one group and at 1600 m with a second group. Friendliness, clear thinking, dizziness, sleepiness, and unhappiness were affected at 4300 m but only sleepiness changed at 1600 m. At 4300 m, the altered moods differed from baseline on the day of arrival (1-4 hours), differed even more after one day (18-28 hours), and returned to baseline by day 2 (42-52 hours). Morning and evening values were similar at each altitude. Therefore, changes in mood states at altitude have a distinct and measurable time course.

Relationships between symptoms, moods, performance, and acute mountain sickness at 4,700 meters.

Ascents above 4,000 m adversely affect symptoms, moods, and performance and cause acute mountain sickness (AMS). It is assumed that individuals afflicted with AMS will be more susceptible to changes in these other parameters; however, previous studies have suggested that their time courses are different. This investigation analyzed the relationships between symptoms, moods, and performance and a measure of altitude sickness, the AMS-cerebral (AMS-C) factor of the environmental Symptoms Questionnaire (ESQ). We evaluated 20 male soldiers on 11 symptom, 13 mood, and 14 cognitive/motor performance measures after exposure to altitudes of 550 and 4,700 m for 5-7 h and a difference score was calculated for each measure. The difference scores for 70% of the symptom, 46.2% of the mood, and 28.6% of the performance measures were significantly correlated with the AMS-C difference score. The difference scores for each measure were then rank ordered (to standardize for differences across measures) and the sum of the ranks was calculated for each subject's symptoms, moods, and performance. The AMS-C factor score correlated significantly 0.90, 0.77, and 0.59 with these composite measures of symptoms, moods, and performance, respectively. Changes in AMS after 5-7 at 4,700 m were correlated best with changes in symptoms, then moods, and finally performance, suggesting that these parameters may be differentially affected at this point in time.

Effects of chemical defense clothing and individual equipment on ventilatory function and subjective reactions.

BACKGROUND: We hypothesized that the multiple layers of protective clothing (PC) of a Chemical Defense Uniform (CDU) with body armor (BA), and load bearing equipment (LBE) impose an external impedance on breathing mechanics in addition to that caused by the chemical-biological protective mask (CB mask). METHODS: We measured the effects of wearing the CDU with BA + LBE on the mechanics and pattern of breathing and subjective reactions in 15 male soldiers during rest and sustained exercise (600 W). Heat strain on each soldier was made minimal and equivalent between the battle dress uniform (BDU) and CDU configurations. RESULTS: Results from wearing the CDU were contrasted with data from wearing a physical training uniform (PTU), or BDU. At rest, the CDU decreased maximal voluntary ventilation (MVV) by 25% (p < 0.05) compared with the PTU. The CB mask alone reduced MVV 20% (p < 0.05), and the PC + BA + LBE components of the CDU contributed an additional 5% decrement (p = 0.059). The CB mask decreased maximal respiratory flows (p < 0.05), whereas the PC + BA + LBE components decreased lung volumes (p < 0.05), and potentiated the decrement of respiratory flows. Total respiratory system elastance (Ers) was increased by 16% (p < 0.05) in the CDU. During exercise, VE was comparable for both the CDU and BDU, but VT was smaller (p < 0.01) and fR greater (p < 0.05) in the CDU; a breathing pattern consistent with the increased Ers. Perceptions of anxiety, not getting enough air, not breathing the way one usually does, and not being relaxed were greater (p < 0.05) during exercise in the CDU than in the BDU. CONCLUSIONS: This study shows that some of the respiratory impairment associated with the wearing of CDU is created by the PC, BA and LBE which present a unique external constraint on the chest wall. These impairments to ventilation may provoke more aversive effects than the larger resistive loads imposed by the CB mask.

The Environmental Symptoms Questionnaire: corrected computational procedures for the alertness factor.

The Environmental Symptoms Questionnaire (ESQ) provides a systematic and quantitative measurement of acute mountain sickness (AMS) as well as other symptoms resulting from exposure to various climatic or stressful conditions. The questionnaire yields factor scores for nine distinct symptom groups. The computational procedures for one of the factors, Alertness, were incorrect as reported in the original manuscript (2). This paper gives the correct procedures and their rationale.

Effects of dexamethasone and high terrestrial altitude on cognitive performance and affect.

This study examined the effects of dexamethasone and exposure to high terrestrial altitude on cognitive performance, affect, and personality. Cognitive performance was evaluated by five cognitive tasks, affect was evaluated by the Clyde Mood Scale and the Multiple Affect Adjective Check List, and personality was examined using the Minnesota Multiphasic Personality Inventory. Sixteen healthy young men received either dexamethasone (4 mg every 6 h) (n = 7) or placebo (n = 9) for 34 h prior to and 52 h after ascent to 4,300 m. Subjects treated with dexamethasone correctly performed more computer interaction and addition problems than did placebo-treated subjects. They also were less sleepy, dizzy, depressed, and anxious than placebo-treated subjects at altitude. No adverse effects on cognitive performance, affect, or personality were noted after dexamethasone was discontinued on the third day at altitude. Results indicate that dexamethasone at the present dose positively influences cognitive performance and mood states at altitude, but has no residual effect on personality.

Cognitive performance deficits in a simulated climb of Mount Everest: Operation Everest II.

Cognitive function at simulated altitude was investigated in a repeated-measures, within-subject study of performance by seven volunteers in a hypobaric chamber, in which atmospheric pressure was systematically lowered over a period of 40 d to finally reach a pressure equivalent to 8,845 m, the approximate height of Mount Everest. The portable cognitive test battery used, Automated Performance Test System (APTS), was specifically designed for field research under adverse environmental conditions as evidenced by compact computer design; automated test administrations, data storage, and retrieval; psychometric properties of stability and reliability; and factorial richness. Significant impairments of cognitive function were seen for three of the five tests in the battery; on two tests, grammatical reasoning and pattern comparison, every subject showed a substantial decrement. The results are discussed in terms of the impact of altitude on specific aspects of cognitive function and the importance of having sensitive and reliable instruments to monitor such effects.

Psychological factors that influence traumatic injury occurrence and physical performance.

This 9 month prospective study, conducted at the US Army Sergeants Major Academy (USASGMA), examined the association of selected psychological variables (e.g., measures of tension/anxiety, sleep disturbance, Type A behavior pattern) with injury occurrence and physical performance in 126 soldiers. ANOVA and logistic regression analyses revealed significant relationships between: 1) Traumatic injury occurrence and mean tension/anxiety scores, 2) Mean self-reported sleep disturbance scores and traumatic injury occurrence, 3) The Type A behavior pattern (abbreviated Jenkins Activity Survey) and number of sit-ups repetitions completed in 2 minutes, one component of the Army Physical Fitness Test (APFT), 4) The Type A behavior pattern and total score APFT. No significant associations were found for mean tension/anxiety scores and overuse injuries, or Type A behavior pattern and two mile run time or number of push-up repetitions completed in 2 minutes. These data suggest traumatic injury occurrence is influenced by tension/anxiety and disturbances in sleep habits. Additionally, individuals with higher Jenkins Activity scores (characteristic of the Type A behavior pattern) perform better physically.

Hypoxia-induced metabolic and core temperature changes in the squirrel monkey.

To identify components of reduced core temperature (Tre) with exposure to hypoxia, oxygen uptake (VO2) and skin temperatures were measured in chair-restrained squirrel monkeys during conditions of 21% O2, 11% O2, and 11% O2 + 5% CO2. Exposure to 11% O2 resulted in a 20% decrease in VO2 and a 1.8 degrees C reduction of Tre with skin temperatures closely paralleling Tre. The addition of 5% CO2 to 11% O2 effectively blocked the decrease of both VO2 and Tre. The responses of one monkey (LD) exhibiting decreased Tre (greater than 2.0 degrees C) and 20% decrease in VO2 were compared to those of another (SD) exhibiting decreased Tre (less than 0.5 degrees C) and little change of VO2 under the same experimental conditions. Increased mean arterial blood pressure (BPa) and heart rate (HR) occurred for monkey SD, while for monkey LD BPa decreased and HR increased slightly. Arterial pressure of oxygen (PaO2) and calculated arterial saturation of oxygen (SaO2) were higher, while PaCO2 was lower for monkey SD than for monkey LD. When 5% CO2 was added to 11% O2 both animals exhibited decreased PaO2, little change of Tre, VO2, PaCO2, arterial pH, and calculated SaO2, and increased BPa and HR. These data suggest that decreased Tre resulted from reduced heat production and reduced oxygen transport was primarily responsible for reduction of heat production.

Normal acid-base status of arterial blood from the conscious, chair-restrained squirrel monkey.

Normal acid-base status of arterial blood (pHa =7.40, PaCO2=38.1 Torr) was demonstrated for conscious, restrained squirrel monkeys when environmental stimuli were minimized and monkeys are habituated to experimental procedures. These results indicate the potential for using squirrel monkeys in experiments in which normal acid-base status is a significant factor.

Elevation-dependent symptom, mood, and performance changes produced by exposure to hypobaric hypoxia.

Altitude exposures above 3,000 m produce changes in symptoms, moods, and cognitive/motor performance of unacclimatized individuals and should produce graded effects on these parameters as elevation and duration are increased. This study examined effects on these parameters as a function of altitude level and duration of exposure by administering standardized tests from 1 to 3 times to 23 males in an altitude chamber during 4.5-hour exposures to 3 levels of hypobaric hypoxia: 500 m, 4,200 m, and 4,700 m. Exposure to altitude significantly affected symptoms, moods, and performance in an elevation-dependent fashion. Adverse changes increased with higher altitudes (all measures were affected at 4,700 m, whereas only some were at 4,200 m) and usually with longer durations. Therefore, specific aspects of symptoms, moods, and performance are significantly degraded after only a few hours of exposure to hypobaric hypoxia, and the severity of the effects dramatically increases when testing is conducted at 4,700 m compared to 4,200 m.

Influence of age and physical training on measures of cardiorespiratory and muscle endurance.

This study describes associations between age, physical training and measures of muscle and cardiorespiratory endurance. The subjects were 5079 healthy male soldiers aged 18-53 years from 14 Army installations in the United States. The subjects completed as many push-ups as possible in 2 min, as many sit-ups as possible in 2 min, and performed a timed 3.2-km run. The training level was assessed by asking the subjects two questions about the frequency (times each week) and duration (hours each week) of their physical training. For all three performance events there were significant declines with age, but at a given age, groups that trained more demonstrated higher performance levels than groups that trained less. For the 3.2-km run, the age-associated rate of performance decline was less in the groups that trained more, and greater amounts of training resulted in progressively less performance decline with age. For push-ups and sit-ups, the training level did not systematically influence the age-related rate of performance decline. The results suggest that tasks involving different physiological systems may be influenced differentially by age and training. Training may slow age-associated performance declines in tasks requiring cardiorespiratory endurance but not in tasks requiring muscle endurance.