New metric of hypoxic dose predicts altitude acclimatization status following various ascent profiles.

Medical personnel need practical guidelines on how to construct high altitude ascents to induce altitude acclimatization and avoid acute mountain sickness (AMS) following the first night of sleep at high altitude. Using multiple logistic regression and a comprehensive database, we developed a quantitative prediction model using ascent profile as the independent variable and altitude acclimatization status as the dependent variable from 188 volunteers (147 men, 41 women) who underwent various ascent profiles to 4 km. The accumulated altitude exposure (AAE), a new metric of hypoxic dose, was defined as the ascent profile and was calculated by multiplying the altitude elevation (km) by the number of days (d) at that altitude prior to ascent to 4 km.

Acute Mountain Sickness is Reduced Following 2 Days of Staging During Subsequent Ascent to 4300 m.

Objective: To determine whether 2 days of staging at 2500-3500 m, combined with either high or low physical activity, reduces acute mountain sickness (AMS) during subsequent ascent to 4300 m.

Methods: Three independent groups of unacclimatized men and women were staged for 2 days at either 2500 m (n = 18), 3000 m (n = 16), or 3500 m (n = 15) before ascending and living for 2 days at 4300 m and compared with a control group that directly ascended to 4300 m (n = 12). All individuals departed to the staging altitudes or 4300 m after spending one night at 2000 m during which they breathed supplemental oxygen to simulate sea level conditions.

Is normobaric hypoxia an effective treatment for sustaining previously acquired altitude acclimatization?

This study examined whether normobaric hypoxia (NH) treatment is more efficacious for sustaining high-altitude (HA) acclimatization-induced improvements in ventilatory and hematologic responses, acute mountain sickness (AMS), and cognitive function during reintroduction to altitude (RA) than no treatment at all. Seventeen sea-level (SL) residents (age = 23 ± 6 yr; means ± SE) completed in the following order: ) 4 days of SL testing; ) 12 days of HA acclimatization at 4,300 m; ) 12 days at SL post-HA acclimatization (Post) where each received either NH ( = 9, [Formula: see text] = 0.122) or Sham ( = 8; [Formula: see text] = 0.

Efficacy of residence at moderate versus low altitude on reducing acute mountain sickness in men following rapid ascent to 4300 m.

To determine if residence at moderate (~2000 m) compared to low (<50 m) altitude reduces acute mountain sickness (AMS) in men during subsequent rapid ascent to a higher altitude. Nine moderate-altitude residents (MAR) and 18 sea-level residents (SLR) completed the Environmental Symptoms Questionnaire (ESQ) at their respective baseline residence and again at 12, 24, 48, and 72 h at 4300 m to assess the severity and prevalence of AMS. AMS cerebral factor score (AMS-C) was calculated from the ESQ at each time point.

United States Army Research Institute of Environmental Medicine: Warfighter research focusing on the past 25 years.

The United States Army Research Institute of Environmental Medicine (USARIEM) celebrated its 50th anniversary on July 1, 2011. This article reviews its history, evolution, and transition of its research programs as well as its scientific and military accomplishments, emphasizing the past 25 yr. During the 1990s, USARIEM published a series of pocket guides providing guidance for sustaining Warfighter health and performance in Southwest Asia, Somalia, the former Republic of Yugoslavia, Rwanda, and Haiti.

Effect of repeated normobaric hypoxia exposures during sleep on acute mountain sickness, exercise performance, and sleep during exposure to terrestrial altitude.

There is an expectation that repeated daily exposures to normobaric hypoxia (NH) will induce ventilatory acclimatization and lessen acute mountain sickness (AMS) and the exercise performance decrement during subsequent hypobaric hypoxia (HH) exposure. However, this notion has not been tested objectively. Healthy, unacclimatized sea-level (SL) residents slept for 7.

The impact of moderate-altitude staging on pulmonary arterial hemodynamics after ascent to high altitude.

Staged ascent (SA), temporary residence at moderate altitude en route to high altitude, reduces the incidence and severity of noncardiopulmonary altitude illness such as acute mountain sickness. To date, the impact of SA on pulmonary arterial pressure (PAP) is unknown. We tested the hypothesis that SA would attenuate the PAP increase that occurs during rapid, direct ascent (DA).

Exercise performance of sea-level residents at 4300 m after 6 days at 2200 m.

Unlabelled: Partial acclimatization resulting from staging at moderate altitude reduces acute mountain sickness during rapid exposure to higher altitudes (e.g., 4300 m).

Intermittent hypoxic exposure does not improve endurance performance at altitude.

Purpose: This study examined the effect of 1 wk of normobaric intermittent hypoxic exposure (IHE) combined with exercise training on endurance performance at a 4300-m altitude (HA).

Methods: Seventeen male lowlanders were divided into an IHE (n = 11) or SHAM (n = 6) group. Each completed cycle endurance testing consisting of two 20-min steady state (SS) exercise bouts (at 40% and 60% V O2peak) followed by a 10-min break and then a 720-kJ cycle time trial at HA before IHE or SHAM treatment (Pre-T).

Intermittent hypoxic exposure does not improve sleep at 4300 m.

The purpose of this study was to determine in sea-level residents if 6 to 7 consecutive days of normobaric intermittent hypoxic exposure (IHE) (hypoxia room: 2-h ambient PO2=90 mmHg sedentary and 1-h ambient PO2=110 mmHg exercising at 80+/-5% of maximum heart rate) improved sleep quality (awakenings per hour) and quantity at altitude (4300 m). We hypothesized that IHE would improve sleep arterial oxygen saturation (SaO2) levels and decrease desaturation events, thereby contributing to improvements in sleep quality and quantity during subsequent exposure to high altitude. Ten sea-level residents (mean+/-SE: 22+/-1 yr, 179+/-2 cm, 79+/-3 kg) were assigned to an IHE group and six to a SHAM group (20+/-0.

Seven intermittent exposures to altitude improves exercise performance at 4300 m.

Purpose: The purpose of this study was to determine whether seven intermittent altitude exposures (IAE), in combination with either rest or exercise training, improves time-trial exercise performance and induces physiologic adaptations consistent with chronic altitude adaptation at 4300 m.

Methods: Ten adult lowlanders (26 +/- 2 yr; 78 +/- 4 kg; means +/- SE) completed cycle endurance testing during an acute exposure to a 4300-m-altitude equivalent (446 mm Hg) once before (pre-IAE) and once after (post-IAE) 7 d of IAE (4h x d(-1), 5 d x wk(-1), 4300 m). Cycle endurance testing consisted of two consecutive 15-min constant-work rate exercise bouts followed immediately by a time-trial exercise performance test.

Validation of a shortened electronic version of the environmental symptoms questionnaire.

The purpose of this study was to validate a shortened (11-item) electronic version of the 67-item paper and pencil Environmental Symptoms Questionnaire (ESQ-III) to assess acute mountain sickness (AMS). Thirty-three volunteers (means +/- SE; 28 +/- 1 yr; 74 +/- 2 kg) were given both the paper and pencil and electronic versions of the ESQ (IPAQ 5550, Hewlett Packard, Palo Alto, CA) to complete one after the other at residence altitude (RA) and after 24-h (PP24), 48-h (PP48), and 72-h (PP72) exposure to 4300 m on the summit of Pikes Peak (PP). The AMS-Cerebral (AMS-C) weighted factor score was calculated from responses to the same 11 items for each version of the ESQ.

Hemoglobin P(50) during a simulated ascent of Mt. Everest, Operation Everest II.

The amount of O(2) available to tissues is essentially the product of cardiac output, [Hb], and O(2) saturation. Saturation depends on P(O2) and the O(2)Hb dissociation curve. With altitude, increased [2,3-DPG] shifts the dissociation curve rightward, but hypocapnia and alkalosis move it leftward.

Changes in ventilatory threshold at high altitude: effect of antioxidants.

Purpose: To investigate the effects of prolonged hypoxia and antioxidant supplementation on ventilatory threshold (VT) during high-altitude (HA) exposure (4300 m).

Methods: Sixteen physically fit males (25 +/- 5 yr; 77.8 +/- 8.

Negative energy balance in male and female rangers: effects of 7 d of sustained exercise and food deprivation.

Background: A challenging 7-d ranger field exercise (FEX) by cadets in the Norwegian Military Academy provided a venue in which to study the effects of negative energy balance.

Objective: We quantified total energy expenditure (TEE), food intake, and changes in body composition in male and female cadets.

Design: TEE (measured by doubly labeled water), food intake, activity patterns (measured by accelerometry), and body composition (measured by dual-energy X-ray absorptiometry) were measured in 16 cadets (10 men and 6 women aged 21-27 y).

White blood cell and hormonal responses to 4300 m altitude before and after intermittent altitude exposure.

Recent studies have demonstrated that brief daily IAE (intermittent altitude exposure) was equally as effective as continuous altitude residence in inducing physiological adaptations consistent with altitude acclimatization. Although the positive benefits of IAE have been clearly defined, the potential negative consequences of IAE on health, specifically the immune system, remain undefined. The present study determined the effects of IAE on WBC (white blood cell) and hormonal responses during rest and exercise at 4300 m altitude.

Cytokine responses at high altitude: effects of exercise and antioxidants at 4300 m.

Purpose: This study tested the hypothesis that antioxidant supplementation would attenuate plasma cytokine (IL-6, tumor necrosis factor (TNF)-alpha), and C-reactive protein (CRP) concentrations at rest and in response to exercise at 4300-m elevation.

Methods: A total of 17 recreationally trained men were matched and assigned to an antioxidant (N = 9) or placebo (N = 8) group in a double-blinded fashion. At sea level (SL), energy expenditure was controlled and subjects were weight stable.

Effect of acetazolamide on leg endurance exercise at sea level and simulated altitude.

Acetazolamide can be taken at sea level to prevent acute mountain sickness during subsequent altitude exposure. Acetazolamide causes metabolic acidosis at sea level and altitude, and increases SaO2 (arterial oxygen saturation) at altitude. The aim of the present study was to determine whether acetazolamide impairs muscle endurance at sea level but not simulated altitude (4300 m for <3 h).

Endocrine responses to acute and chronic high-altitude exposure (4,300 meters): modulating effects of caloric restriction.

High-altitude anorexia leads to a hormonal response pattern modulated by both hypoxia and caloric restriction (CR). The purpose of this study was to compare altitude-induced neuroendocrine changes with or without energy imbalance and to explore how energy sufficiency alters the endocrine acclimatization process. Twenty-six normal-weight, young men were studied for 3 wk.

Saccadic velocity and pupillary reflexes during acclimatization to altitude (4300 m).

Introduction: Oculometrics have been shown to be responsive to acute hypoxemia. We investigated whether oculometrics could be used as an objective index of a hypoxic effect on the central nervous system (CNS) during altitude acclimatization. We hypothesized that oculomotor reflexes [pupil diameter (PD), constriction amplitude (CA), constriction latency (CL), and saccadic velocity (SV)] changed in concert with a select number of accepted acclimatization variables and that these changes correlated with the severity of acute mountain sickness (AMS).

Three weeks of caloric restriction alters protein metabolism in normal-weight, young men.

The effects of prolonged caloric restriction (CR) on protein kinetics in lean subjects has not been investigated previously. The purpose of this study was to test the hypotheses that 21 days of CR in lean subjects would 1) result in significant losses of lean mass despite a suppression in leucine turnover and oxidation and 2) negatively impact exercise performance. Nine young, normal-weight men [23 +/- 5 y, 78.

Residence at moderate altitude improves ventilatory response to high altitude.

Background: This study compared the distribution of arterial oxygen saturation (SaO2) and susceptibility to Acute Mountain Sickness (AMS) in moderate altitude residents (MAR) and low altitude residents (LAR) following rapid ascent to 4056 m.

Methods: Resting PETCO2 and SaO2 were measured in 38 subjects residing for > 3 mo near Colorado Springs, CO (MAR group), at 1940 m (USAF Academy), and after approximately 1 h at 4056 m on the summit of Pikes Peak, CO, following ascent by car. SaO2 was also measured at 610-m elevation intervals during the ascent.

Antioxidant supplementation does not attenuate oxidative stress at high altitude.

Introduction: Hypobaric hypoxia and heightened metabolic rate increase free radical production.

Purpose: We tested the hypothesis that antioxidant supplementation would reduce oxidative stress associated with increased energy expenditure (negative energy balance) at high altitude (HA 4300 m).

Methods: For 12 d at sea level (SL), 18 active men were fed a weight-stabilizing diet.

Cysteinyl leukotriene blockade does not prevent acute mountain sickness.

Background: Acute Mountain Sickness (AMS) is a multi-system disorder that is characterized by headache, anorexia, nausea, vomiting, insomnia, lassitude, and malaise. The syndrome is common in unacclimatized low altitude residents who rapidly ascend to terrestrial elevations exceeding 2,500 m. AMS may be a manifestation of hypoxia-induced cerebral edema resulting, in part, from increased capillary permeability.