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Plasma volume changes with movement to supine and standing positions
Summary
Posture significantly impacts plasma volume, affecting blood composition. Hematocrit, hemoglobin, and plasma proteins reliably indicate these fluid shifts, crucial for understanding physiological responses to stress.
Area of Science:
- Physiology
- Cardiovascular System
- Fluid Balance
Background:
- Understanding fluid shifts is critical for interpreting physiological data.
- Posture changes are known to influence blood volume and composition.
Purpose of the Study:
- To determine the chronology of hemoconcentration and hemodilution due to posture changes.
- To assess the reliability of hematocrit, hemoglobin, and plasma proteins as indicators of plasma volume changes.
Main Methods:
- Seven male subjects were studied in supine and erect positions.
- Venous hematocrit (Hct), hemoglobin (Hb), and plasma proteins (PP) were measured.
- Red cell mass was determined using the carbon monoxide (CO) method.
Main Results:
- Posture changes induced rapid and progressive alterations in Hct, Hb, and PP.
- Supine posture led to a 440-ml plasma volume expansion.
- Erect posture caused significant increases in Hct (10.3%), Hb (10.8%), and PP (20.8%), with a 593-ml fluid efflux.
Conclusions:
- Hematocrit, hemoglobin, and plasma proteins are reliable indicators of posture-induced plasma volume changes.
- Red cell mass remains unaffected by postural shifts.
- These findings are significant for interpreting plasma volume alterations under various physiological stresses.