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 is used to quantify volume:

Answer 3

V=S/C

S - indicator

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 hence be modified:
- Decrease in indicator concentration should be considered
- Indicator concentration should be calculated at administration:
o V=S/C0

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
  o Weigh the mass (m)
  o Quatify volume (V)
  o 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 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:
  
  • 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

Quantification of the Intracellular Compartment

Answer 8

IC = TBW – EC

Question 9

Quantification of the Interstitial Fluid Compartment

Answer 9

ISF = EC – Intravasal volume