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Transcapillary fluid responses to lower body negative pressure
M Aratow1, S M Fortney, D E Watenpaugh
1Life Science Division, National Aeronautics and Space Administration-Ames Research Center, Moffett Field, California 94035-1000.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 1, 1993
Summary
Lower body negative pressure (LBNP) shifts fluid to the legs, decreasing plasma volume. Ingesting saline during LBNP causes significant fluid to move from the vascular space.
Area of Science:
- Physiology
- Cardiovascular Research
- Fluid Balance
Background:
- The impact of lower body negative pressure (LBNP) on transcapillary fluid balance remains unclear.
- Understanding fluid shifts is crucial for managing physiological stress.
Purpose of the Study:
- To assess leg interstitial fluid pressures (IFP), leg circumference, plasma volume (PV), and transcapillary fluid transport (TFT) during and after LBNP.
- To evaluate the effect of oral saline ingestion on transcapillary exchange during LBNP.
Main Methods:
- Six healthy males underwent 4 hours of 30 mmHg LBNP with and without 1 liter of isotonic saline ingestion.
- Continuous IFP measurement in leg tissues using slit catheters.
- Plasma volume changes and leg circumference were monitored.
Main Results:
- LBNP caused leg circumference to increase and plasma volume to decrease.
- LBNP alone resulted in fluid movement into the legs but no net whole-body transcapillary fluid transport.
- During LBNP with saline ingestion, 72% of ingested fluid moved into the interstitial space, indicating significant transcapillary filtration.
Conclusions:
- Lower body negative pressure induces fluid sequestration in the legs.
- Oral saline ingestion during LBNP significantly increases transcapillary filtration, moving fluid out of the vascular space.