Salt and water control at altitude.

Area of Science:

• Physiology
• Environmental Medicine
• Altitude Physiology

Background:

• Altitude hypoxia typically causes sodium and water loss, reducing plasma and extracellular volumes.
• Conversely, exercise at low altitude leads to fluid retention and expanded volumes.
• Acute mountain sickness (AMS) presents a pathological response to hypoxia, differing from the typical physiological response.

Purpose of the Study:

• To compare the fluid balance and hormonal responses to altitude hypoxia, exercise, and acute mountain sickness.
• To investigate the role of plasma aldosterone concentrations (PAC) and atrial natriuretic peptide (ANP) in these conditions.

Main Methods:

• Observational study comparing physiological responses to altitude, exercise, and AMS.
• Measurement of fluid balance parameters (diuresis, sodium retention).
• Assay of plasma hormone levels, including PAC and ANP.

Main Results:

• Physiological altitude hypoxia results in diuresis and volume contraction, with decreased PAC and increased ANP.
• Exercise causes anti-diuresis, sodium retention, and volume expansion, with elevated PAC and ANP.
• AMS subjects exhibit anti-diuresis, sodium retention, and increased volumes, with elevated PAC compared to AMS-resistant individuals.

Conclusions:

• The pathological response in AMS parallels exercise effects, contrasting with the physiological response to hypoxia.
• Both exercise and the pathological response to hypoxia contribute to edema formation and are implicated in AMS development.