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Biphasic blood volume changes with lower body suction in humans
H Hinghofer-Szalkay1, E M König, G Sauseng-Fellegger
1Department of Physiology, Karl-Franzens-University, Graz, Austria.
The American Journal of Physiology
|October 1, 1992
Summary
Lower body subatmospheric pressure (LBNP) causes a transient blood volume gain followed by fluid loss. This hemoconcentration and subsequent hemodilution during recovery can be precisely measured using mass densitometry.
Area of Science:
- Physiology
- Cardiovascular Research
Background:
- Understanding fluid shifts in the body is crucial for cardiovascular health.
- Lower body subatmospheric pressure (LBNP) is a model for simulating hypovolemia and studying cardiovascular responses.
Purpose of the Study:
- To investigate the transient fluid shifts and hemoconcentration during and after lower body subatmospheric pressure (LBNP) exposure.
- To quantify microvascular fluid exchange using precise mass densitometry.
Main Methods:
- Measurement of blood and plasma mass density and hematocrit in 12 subjects under LBNP (-35 mmHg).
- Utilized the mechanical oscillator technique for high-precision mass densitometry.
- Data collected in supine position before, during, and after LBNP exposure (20-40 min).
Main Results:
- Blood mass density initially decreased, indicating a transient 2.8% blood volume gain.
- Density then increased during LBNP, signifying a 1.5% hemoconcentration.
- Post-LBNP showed further hemoconcentration before returning to baseline, suggesting reflex-driven filtration effects.
Conclusions:
- LBNP induces an initial microvascular fluid gain followed by fluid loss (hemoconcentration).
- Receptor unloading and subsequent loading during LBNP and recovery cause distinct fluid shifts.
- Mass densitometry is a valuable tool for quantifying these dynamic fluid exchanges.