GLOSSARY

Fluid Volume is fluid volume within a specified space, requiring the space to distinguish total water, plasma and urine.

Circulating volume, total body water and effective perfusion are different concepts. Bleeding or abnormal distribution can reduce effective circulation without inadequate drinking being the explanation. Excess body fluid can even coexist with inadequate effective perfusion. Severe dizziness, collapse or shock signs require urgent assessment rather than a self-selected drinking volume. Volume terminology should not be reduced to a simple tally of water bottles.

Plasma volume describes the liquid blood component; plasma water is its water content, while blood volume also includes cells. Exercise, posture, heat and fluid shifts affect hemoglobin concentration and hematocrit. Concentration or dilution alone does not demonstrate a real change in red-cell mass or establish its cause. Standardized sampling and appropriate context are needed when comparing athlete blood results.

Total body water is distributed within cells and outside them. Extracellular fluid includes plasma and interstitial fluid, whereas whole blood also contains cells. Barriers between compartments differ in permeability, and water and solute movements change distribution. Drinking a glass does not permanently add that entire volume exclusively to blood. Compartment terminology identifies location rather than a separate dietary kind of water.