Acute mountain sickness: increased severity during  simulated altitude compared with normobaric hypoxia

Roach, Robert C., Jack A. Loeppky, and Milton V. Icenogle.Acute mountain sickness: increased severity during simulated altitude compared with normobaric hypoxia. J. Appl. Physiol. 81(5): 1908–1910, 1996.—Acute mountain sickness (AMS) strikes those in the mountains who go too high too fast. Although AMS has been long assumed to be due solely to the hypoxia of high altitude, recent evidence suggests that hypobaria may also make a significant contribution to the pathophysiology of AMS. We studied nine healthy men exposed to simulated altitude, normobaric hypoxia, and normoxic hypobaria in an environmental chamber for 9 h on separate occasions. To simulate altitude, the barometric pressure was lowered to 432 ± 2 (SE) mmHg (simulated terrestrial altitude 4,564 m). Normobaric hypoxia resulted from adding nitrogen to the chamber (maintained near normobaric conditions) to match the inspired[Formula: see text] of the altitude exposure. By lowering the barometric pressure and adding oxygen, we achieved normoxic hypobaria with the same inspired[Formula: see text] as in our laboratory at normal pressure. AMS symptom scores (average scores from 6 and 9 h of exposure) were higher during simulated altitude (3.7 ± 0.8) compared with either normobaric hypoxia (2.0 ± 0.8; P < 0.01) or normoxic hypobaria (0.4 ± 0.2; P < 0.01). In conclusion, simulated altitude induces AMS to a greater extent than does either normobaric hypoxia or normoxic hypobaria, although normobaric hypoxia induced some AMS.

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Intermittent altitude exposures reduce acute mountain sickness at 4300 m

Clinical Science ◽

10.1042/cs20030161 ◽

2004 ◽

Vol 106 (3) ◽

pp. 321-328 ◽

Cited By ~ 63

Author(s):

Beth A. BEIDLEMAN ◽

Stephen R. MUZA ◽

Charles S. FULCO ◽

Allen CYMERMAN ◽

Dan DITZLER ◽

...

Keyword(s):

Acute Mountain Sickness ◽

Urine Volume ◽

Barometric Pressure ◽

Self Report ◽

Altitude Exposure ◽

Cerebral Symptom ◽

Cycle Training ◽

Mountain Sickness ◽

End Tidal ◽

Rest And Exercise

Acute mountain sickness (AMS) commonly occurs at altitudes exceeding 2000–2500 m and usually resolves after acclimatization induced by a few days of chronic residence at the same altitude. Increased ventilation and diuresis may contribute to the reduction in AMS with altitude acclimatization. The aim of the present study was to examine the effects of intermittent altitude exposures (IAE), in combination with rest and exercise training, on the incidence and severity of AMS, resting ventilation and 24-h urine volume at 4300 m. Six lowlanders (age, 23±2 years; body weight, 77±6 kg; values are means±S.E.M.) completed an Environmental Symptoms Questionnaire (ESQ) and Lake Louise AMS Scoring System (LLS), a resting end-tidal partial pressure of CO2 (PETCO2) test and a 24-h urine volume collection at sea level (SL) and during a 30 h exposure to 4300 m altitude-equivalent (barometric pressure=446 mmHg) once before (PreIAE) and once after (PostIAE) a 3-week period of IAE (4 h·day-1, 5 days·week-1, 4300 m). The previously validated factor score, AMS cerebral score, was calculated from the ESQ and the self-report score was calculated from the LLS at 24 h of altitude exposure to assess the incidence and severity of AMS. During each IAE, three subjects cycled for 45–60 min·day-1 at 60–70% of maximal O2 uptake (VO2 max) and three subjects rested. Cycle training during each IAE did not affect any of the measured variables, so data from all six subjects were combined. The results showed that the incidence of AMS (%), determined from both the ESQ and LLS, increased (P<0.05) from SL (0±0) to PreIAE (50±22) at 24 h of altitude exposure and decreased (P<0.05) from PreIAE to PostIAE (0±0). The severity of AMS (i.e. AMS cerebral symptom and LLS self-report scores) increased (P<0.05) from SL (0.02±0.02 and 0.17±0.17 respectively) to PreIAE (0.49±0.18 and 4.17±0.94 respectively) at 24 h of altitude exposure, and decreased (P<0.05) from PreIAE to PostIAE (0.03±0.02 and 0.83±0.31 respectively). Resting PETCO2 (mmHg) decreased (i.e. increase in ventilation; P<0.05) from SL (38±1) to PreIAE (32±1) at 24 h of altitude exposure and decreased further (P<0.05) from PreIAE to PostIAE (28±1). In addition, 24-h urine volumes were similar at SL, PreIAE and PostIAE. In conclusion, our findings suggest that 3 weeks of IAE provide an effective alternative to chronic altitude residence for increasing resting ventilation and reducing the incidence and severity of AMS.

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Postural Instability and Acute Mountain Sickness During Exposure to 24 Hours of Simulated Altitude (4300 m)

High Altitude Medicine & Biology ◽

10.1089/152702901753397072 ◽

2001 ◽

Vol 2 (4) ◽

pp. 509-514 ◽

Cited By ~ 18

Author(s):

Allen Cymerman ◽

Stephen R. Muza ◽

Beth A. Beidleman ◽

Dan T. Ditzler ◽

Charles S. Fulco

Keyword(s):

Acute Mountain Sickness ◽

Postural Instability ◽

Simulated Altitude ◽

Mountain Sickness

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No effect of patent foramen ovale on acute mountain sickness and pulmonary pressure in normobaric hypoxia

Experimental Physiology ◽

10.1113/ep089948 ◽

2021 ◽

Author(s):

Kaitlyn G. DiMarco ◽

Kara M. Beasley ◽

Karina Shah ◽

Julia P. Speros ◽

Jonathan E. Elliott ◽

...

Keyword(s):

Patent Foramen Ovale ◽

Acute Mountain Sickness ◽

Normobaric Hypoxia ◽

Foramen Ovale ◽

Pulmonary Pressure ◽

Mountain Sickness

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Atrial Natriuretic Peptide, Altitude and Acute Mountain Sickness

Clinical Science ◽

10.1042/cs0770509 ◽

1989 ◽

Vol 77 (5) ◽

pp. 509-514 ◽

Cited By ~ 25

Author(s):

J. S. Milledge ◽

J. M. Beeley ◽

S. McArthur ◽

A. H. Morice

Keyword(s):

Body Weight ◽

Atrial Natriuretic Peptide ◽

Natriuretic Peptide ◽

Packed Cell Volume ◽

Sodium Excretion ◽

Acute Mountain Sickness ◽

Urine Volume ◽

Symptom Scores ◽

Mountain Sickness ◽

Atrial Natriuretic

1. To investigate the mechanisms of acute mountain sickness, 22 subjects travelled to 3100 m by road and the following day walked to 4300 m on Mount Kenya. Control measurements were made over 2 days at 1300 m before ascent and for 2 days after arrival at 4300 m. These included body weight, 24 h urine volume, 24 h sodium and potassium excretion, blood haemoglobin, packed cell volume, and symptom score for acute mountain sickness. In 15 subjects blood samples were taken for assay of plasma aldosterone and atrial natriuretic peptide. 2. Altitude and the exercise in ascent resulted in a marked decrease in 24 h urine volume and sodium excretion. Aldosterone levels were elevated on the first day and atrial natriuretic peptide levels were higher on both altitude days compared with control. 3. Acute mountain sickness symptom scores showed a significant negative correlation with 24 h urinary sodium excretion on the first altitude day. Aldosterone levels tended to be lowest in subjects with low symptom scores and higher sodium excretion. No correlation was found between changes in haemoglobin concentration, packed cell volume, 24 h urine volume or body weight and acute mountain sickness symptom score. 4. Atrial natriuretic peptide levels at low altitude showed a significant inverse correlation with acute mountain sickness symptom scores on ascent.

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The Effect of an Expiratory Resistance Mask with Dead Space on Sleep, Acute Mountain Sickness, Cognition, and Ventilatory Acclimatization in Normobaric Hypoxia

High Altitude Medicine & Biology ◽

10.1089/ham.2018.0074 ◽

2019 ◽

Vol 20 (1) ◽

pp. 61-70 ◽

Cited By ~ 3

Author(s):

Alexander Patrician ◽

Michael M. Tymko ◽

Hannah G. Caldwell ◽

Connor A. Howe ◽

Geoff B. Coombs ◽

...

Keyword(s):

Dead Space ◽

Acute Mountain Sickness ◽

Normobaric Hypoxia ◽

Expiratory Resistance ◽

Mountain Sickness

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

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00633.2010 ◽

2011 ◽

Vol 300 (2) ◽

pp. R428-R436 ◽

Cited By ~ 55

Author(s):

Charles S. Fulco ◽

Stephen R. Muza ◽

Beth A. Beidleman ◽

Robby Demes ◽

Janet E. Staab ◽

...

Keyword(s):

Heart Rate ◽

Exercise Performance ◽

Hypobaric Hypoxia ◽

Sham Group ◽

Acute Mountain Sickness ◽

Time Trial ◽

Normobaric Hypoxia ◽

Performance Decrement ◽

Mountain Sickness ◽

End Tidal

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 7.5 h each night for 7 consecutive nights in hypoxia rooms under NH [ n = 14, 24 ± 5 (SD) yr] or “sham” ( n = 9, 25 ± 6 yr) conditions. The ambient percent O2 for the NH group was progressively reduced by 0.3% [150 m equivalent (equiv)] each night from 16.2% (2,200 m equiv) on night 1 to 14.4% (3,100 m equiv) on night 7, while that for the ventilatory- and exercise-matched sham group remained at 20.9%. Beginning at 25 h after sham or NH treatment, all subjects ascended and lived for 5 days at HH (4,300 m). End-tidal Pco2, O2 saturation (SaO2), AMS, and heart rate were measured repeatedly during daytime rest, sleep, or exercise (11.3-km treadmill time trial). From pre- to posttreatment at SL, resting end-tidal Pco2 decreased ( P < 0.01) for the NH (from 39 ± 3 to 35 ± 3 mmHg), but not for the sham (from 39 ± 2 to 38 ± 3 mmHg), group. Throughout HH, only sleep SaO2 was higher (80 ± 1 vs. 76 ± 1%, P < 0.05) and only AMS upon awakening was lower (0.34 ± 0.12 vs. 0.83 ± 0.14, P < 0.02) in the NH than the sham group; no other between-group rest, sleep, or exercise differences were observed at HH. These results indicate that the ventilatory acclimatization induced by NH sleep was primarily expressed during HH sleep. Under HH conditions, the higher sleep SaO2 may have contributed to a lessening of AMS upon awakening but had no impact on AMS or exercise performance for the remainder of each day.

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