Topic 2: Volume Quantification of Fluid Compartments

Question 1

What should be mentioned in this topic?

Answer 1

• Measuring the EC compartment using the dilution principle. - Stewart principle in the living organism. - Assessment of TBW. - Quantification of the EC Compartment - Quantification of the Intravascular Compartment. - Quantification of the Intracellular Compartment. - Quantification of the Interstitial Fluid Compartment.

Question 2

Measuring the EC compartment using the dilution principle:

Answer 2

2 phases are observed - Quickly equilibriating space: Substance flow is fast, equilibriates within the 0.5- 1hour -Blood plasma -Interstitium of soft tissues -Lymph - Slowly equilibriating space: Completely uniform distribution develops only 8-10 hours later -Bone -Transcellular space

Question 3

Stewart dilution principle:

Answer 3

It is used to quantify volume: V= S/C S - indicator After waiting for equal distribution of the indicator you will see a slight increase on a graph until it is stable.

Question 4

Stewart principle in the living organism:

Answer 4

In the living organism the concentration of the indicator decreases constantly: - Permeates barriers - Metabolised - Excreted by the kidney, lung or skin The calculation should be modified: - Decrease in indicator concentration should be considered - Indicator concentration should be calculated: V=S/C0 C0 ? supposed original concentration at administration. Extrapolation graph should be used.

Question 5

Assessmeent of TBW:

Answer 5

• Based on dilution principle: o 3H2O o 2H2O o Antipirin o Urea o Tiourea - Excsiccation: Desiccation till constant mass at a temperature of 105C - Quantifying density in vivo (Exciccation: to dry or remove the moisture from, as a substance.)

Question 6

Quantification of the EC Compartment: - suitable substances: - In the EC space fluid distributes at different rates:

Answer 6

• The substances can diffuse across the capillary wall, but not cross the cell membrane. Suitable substances: Inulin, Mannitol, Sacharose. - In the EC space fluid distributes at different rates: Stewart-principle -Fast Distribution: Shows the volume of soft tissues -Slow Distribution: Volume of the soft tissues and fibrous tissues -Late Distribution Volume of bone tissues, fibrous tissues and soft tissues

Question 7

Quantification of the Intravascular Compartment: - Suitable substances:

Answer 7

The substances can not cross the capillary wall nor the cell membrane. - Suitable substances: - Plasma: Evans blue, 131-I or 125-I labelled albumin, globuline ir fibrinogen.

Question 8

Intracellular Compartment

Answer 8

IC = TBW – EC

Question 9

Interstitial Fluid Compartment

Answer 9

ISF = EC – Intravasal volume

Question 10

what is an extrapolation graph?

Answer 10

The indicator starts to dissociate and to eliminate from the given compartment right after its administration. After the first bigger changes (fast outflow and backflow to other compartments) it is only the continuous dissociation and excretion that decreases the concentration. In this phase by extrapolating (see red line) we can estimate the initial concentration (Co) that would have been present at the time of indicator administration (S), if some dissociation and elimination had not ocured.

Question 11

TBW-assessing density

Answer 11

-Weigh the mass (m) - Quatify volume (V) - Calculate density (m/V) -Bone: 1.56 -Soft Tissue: 1.06 -Fat:0.94 - Lean Body Mass has a constant 73% water content while fat has a 10% water content - Calculating density: Suitable for estimating the composition of the body - New method: Total Body Electrical Conductance: (TOBEC) measures the fat content of the body with high precision.

Question 12

Major rules of the compartments:

Answer 12

-The primary aim is to keep the IC compartment isoosmotic and isovolemic. -The osmolality of the EC and IC compartment equalizes in few minutes - Water is moved by osmotic (and hydrostatic) forces; the cell membrane is the main barrier of substance movement

Question 13

Hyperhydration (hypervolemia)

Answer 13

Isoosmotic hypervolemia – oedema; overdosed physiological saline: per os or parenterally • Hyperosmotic hypervolemia – hyperosmotic fluid intake per os or parenterally • Hypoosmotic hypervolemia – exaggerated water uptake; water retention in the kidney (ADH overproduction)

Question 14

Time factors of the regulation:

Answer 14

IC and EC osmolality returns to balance – in a few minutes – by the movement of fluids and osmotically active substances • IC and EC isoosomosis is formed – in half an hour • Isovolemia is restored – takes a couple of days – volume shifts can be tolerated much better than shits in osmolality

Question 15

Extrapolation graph: picture

Answer 15