Distribution of magnetic remanence carriers in the human brain.

That the human brain contains magnetite is well established; however, its spatial distribution in the brain has remained unknown. We present room temperature, remanent magnetization measurements on 822 specimens from seven dissected whole human brains in order to systematically map concentrations of magnetic remanence carriers. Median saturation remanent magnetizations from the cerebellum were approximately twice as high as those from the cerebral cortex in all seven cases (statistically significantly distinct, p = 0.016). Brain stems were over two times higher in magnetization on average than the cerebral cortex. The ventral (lowermost) horizontal layer of the cerebral cortex was consistently more magnetic than the average cerebral cortex in each of the seven studied cases. Although exceptions existed, the reproducible magnetization patterns lead us to conclude that magnetite is preferentially partitioned in the human brain, specifically in the cerebellum and brain stem.

Prevention of acute mountain sickness by acetazolamide in Nepali porters: a double-blind controlled trial.

OBJECTIVE: This study aimed to determine the efficacy, tolerability, and practicality of acetazolamide for the prevention of acute mountain sickness (AMS) in Nepali trekking porters early in the trekking season. METHODS: This study was a randomized, double-blind controlled trial with 400 male Nepali porters in the Mount Everest region of Nepal, trekking from Namche Bazaar (3440 m) to Lobuche (4930 m), the study endpoint. Participants were randomized to receive 250 mg acetazolamide daily or placebo, and AMS symptom scores (Lake Louise) were compared in highlanders vs lowlanders. RESULTS: Only 109 (27.2%) of the 400 porters completed the trial (28 highlanders, 81 lowlanders). The rest either dropped out (275/400 porters, 68.8%) or were excluded (16/400 porters, 4%). Acute mountain sickness occurred in 13 (11.9%) of 109 porters; all were lowlanders; 7 were taking acetazolamide, 6 taking placebo. Birthplace, acclimatization in the week before the trial, ascent rate, and rest days were the most important variables affecting the incidence of AMS. No highlanders, but 13 (16.1%) of 81 lowlanders had AMS (P = .016). Acclimatization in the pretrial week reduced AMS incidence (P = .013), as did a slower ascent rate (P = .0126), but rest days were the most potent prophylactic variable (P = .0001). Side effects were more frequent in porters taking acetazolamide than in the placebo group (P = .0001), but there were no serious side effects. CONCLUSIONS: Acetazolamide was tolerable, but impractical for the routine prevention of AMS in Nepali porters. A good trekking schedule and adequate acclimatization remain the most effective preventive measures. This study identified lowland porters as a high-risk group for developing AMS.

The sharpened Romberg test for assessing ataxia in mild acute mountain sickness.

OBJECTIVE: To evaluate the Sharpened Romberg Test (SRT) as a measure of ataxia in subjects with mild acute mountain sickness in order to determine its sensitivity and specificity. METHODS: The SRT was performed in 23 subjects during ascent to 5260 m. RESULTS: The SRT was more often abnormal than the traditional heel-to-toe test, and at the highest altitude it was related to higher median Lake Louise symptom scores with predictive values of 60% sensitivity and 89% specificity. Our evaluation of the SRT appears to agree with similar studies on ataxia showing a lack of correlation between ataxia and symptoms of acute mountain sickness at altitudes below 5260 m. CONCLUSION: The SRT was easy to perform and provided a quantitative assessment of truncal ataxia in the field without the need for specialized equipment.

Ataxia at altitude measured on a wobble board.

OBJECTIVE: To establish a simple measure of ataxia for use at high altitude. METHODS: Twenty healthy subjects took part in a trek to 5005 m. At 5 different altitudes on the route, they undertook a balance test using a wobble board. The primary objectives were to investigate disturbances of ataxia at altitude and to correlate any observed disturbances with acute mountain sickness (AMS) scores. Secondary outcomes were correlations with cerebral regional oxygenation, pulse oximetry, and age. RESULTS: After a short learning curve, the wobble board test was found to be reproducible. Subjects over 31 years of age were significantly less steady than younger subjects. Subjects suffering acute mountain sickness scored significantly worse on the wobble board test, although scores did not correlate with a specific question on unsteadiness. A positive test defined as equal to or more than 2.5 contacts over 2 minutes gave a predictive value for acute mountain sickness of 66.7% at 4650 m and 100% at 5005 m. Cerebral regional oxygenation in 9 subjects at 5005 m correlated with the wobble board test (r = 0.73; p < .05), whereas pulse oximetry did not. CONCLUSIONS: The wobble board may be a useful adjunct in quantitating ataxia in the field. A positive result may indicate the presence of AMS and may be a useful clinical measure of cerebral hypoxia but should be correlated with other clinical features.

Medroxyprogesterone at high altitude. The effects on blood gases, cerebral regional oxygenation, and acute mountain sickness.

OBJECTIVE: To study the effect of medroxyprogesterone on blood gases and cerebral regional oxygenation at high altitude, alone and in conjunction with acetazolamide, and to assess the effect on acute mountain sickness (AMS). DESIGN: Two placebo-controlled trials during rapid ascent to high altitude. PARTICIPANTS: In the first trial, 20 participants, and in the second trial, 24 participants. SETTING: During rapid ascent to 4680 m and on rapid ascent to 5200 m. INTERVENTION: In the first trial, participants were randomized to receive medroxyprogesterone 30 mg or a placebo twice a day. In the second trial, participants were randomly assigned to one of 4 groups: a placebo twice daily, medroxyprogesterone 30 mg twice daily, acetazolamide 250 mg plus a placebo twice daily, or acetazolamide 250 mg plus medroxyprogesterone 30 mg twice daily. MAIN OUTCOME MEASURES: Blood gas changes and symptom scores of AMS in both trials and cerebral regional oxygen saturations in the first trial only. RESULTS: Medroxyprogesterone improved peripheral oxygen saturations in both trials and improved PaO2 in combination with acetazolamide. Cerebral regional oxygen saturation was not altered by medroxyprogesterone. The reduction in symptom scores and in the extent of AMS was not significant in this limited study. CONCLUSIONS: Medroxyprogesterone acts as a respiratory stimulant, but the clinical benefit regarding the development of AMS was unproven at high altitude. Combined medroxyprogesterone and acetazolamide gave the best PaO2.