Beyond Hemoglobin Concentration: How Intravascular Volume Measurements Can Advance Our Understanding of High-Altitude...

Area of Science:

• Physiology
• Altitude Adaptation
• Human Evolution

Background:

• Hemoglobin concentration is commonly used to assess hemoglobin mass in high-altitude adaptation studies.
• However, hemoglobin concentration is influenced by both plasma volume and total hemoglobin mass.
• This can lead to misinterpretations of physiological responses and adaptation.

Purpose of the Study:

• To highlight the limitations of using hemoglobin concentration as a sole marker for hemoglobin mass.
• To demonstrate how plasma volume and total hemoglobin mass provide more accurate physiological insights.
• To advocate for improved methodologies in high-altitude adaptation research.

Main Methods:

• Review of existing literature and data from athletic, clinical, and high-altitude populations.
• Analysis of physiological responses to environmental stressors.
• Discussion of the carbon monoxide rebreathing technique for measuring plasma volume and total hemoglobin mass.

Main Results:

• Examples show dissociation between plasma volume and hemoglobin concentration across various populations and conditions.
• Reliance on hemoglobin concentration may incorrectly suggest blunted erythropoiesis in Tibetan and Ethiopian highlanders.
• Total hemoglobin mass and plasma volume are more physiologically relevant phenotypes.

Conclusions:

• Hemoglobin concentration is an inadequate measure for assessing hemoglobin mass and adaptation.
• Plasma volume and total hemoglobin mass measurements are crucial for accurate physiological interpretation.
• Future high-altitude adaptation studies should prioritize these more comprehensive measurements over hemoglobin concentration.