Variability in human plasma volume responses during high-altitude sojourn

Area of Science:

• Physiology
• Altitude Medicine
• Cardiovascular Research

Background:

• Ascent to high altitude (HA) causes a decrease in plasma volume (PV) in sea-level (SL) residents.
• A quantitative model exists to predict %∆PV within the first 7 days at HA, based on previous measurements.

Purpose of the Study:

• To compare measured %∆PV with model-predicted %∆PV in individuals residing at HA for 21 days.
• To assess the accuracy of an existing quantitative model in predicting individual plasma volume changes at high altitude.

Main Methods:

• Seventeen SL natives lived at 4300m for 21 days.
• Fasting hematocrit, hemoglobin, and total circulating protein were measured at SL and on days 2, 7, 13, and 19 at HA.
• %∆PV and %∆TCP were calculated, and measured %∆PV was compared to model predictions.

Main Results:

• Measured %∆PV showed significant decreases at HA2, 7, 13, and 19 days (-2.5%, -11.0%, -11.7%, -16.8% respectively).
• The model overpredicted PV decrease at HA2 and HA7, accurately predicted at HA13, and predicted an increase at HA19.
• Individual %∆PV measurements were poorly predicted by the model, with only a small percentage falling within the predicted confidence intervals.

Conclusions:

• Plasma volume regulation at HA is significantly influenced by oncotic pressure and exhibits substantial inter-individual variability.
• Current quantitative models require substantial refinement to accurately predict individual plasma volume changes during high-altitude sojourns.
• Further research is needed to improve predictive models for individual physiological responses to high altitude.