Mass of components of fluid in the human body
After pumping these substances into the blood, after a few hours, they will dissolve in the whole body, then using the dilution principle, we can calculate the volume of water.
Measure total body water
3H2O, 2H2O are used to measure the total amount of water in the body. After pumping these substances into the blood, after a few hours, they will dissolve in the whole body, then using the dilution principle, we can calculate the volume of water. Another substance used is antipyrine, a lipid-soluble and able to rapidly cross membranes to reach extracellular and intracellular fluids.
Board. Measure the volume of fluid in the body
Measure extracellular fluid volume
The extracellular fluid volume is measured using indicators that only enter the plasma and intercellular fluid but not the intracellular fluid, including radioactive sodium, radioactive chlorine, radioactive iodine, thiosulfate, inulin although there are some substances such as radioactive Na or inulin still enter the cell in a small amount.
Measure the volume of intracellular fluid
Intracellular fluid is not measured directly but is measured by subtracting the amount of extracellular fluid from the total body fluid.
Measurement of plasma volume
To measure plasma volume, the indicator must not pass through the holes in the capillary wall but must be retained in the blood. The most commonly used substance is plasma albumin conjugated with radioactive iodine (125I-albumin), in addition, T-1824, a substance bound to plasma proteins, can be used.
Measure the volume of intercellular fluid
Measured indirectly by subtracting plasma fluid from the extracellular fluid.
Measure blood volume
Once the plasma volume is known, the blood volume in haematocrit can be calculated using the formula:
Total blood volume = Plasma volume / (1 - Haematocrit)
Another way is to inject into the blood a mass of red blood cells with a radioactive isotope, usually 51Cr, and wait until this red blood cell is completely dissolved in the blood, then the volume of blood can be calculated using the principle of side dilution. on.