4. Measurement of Fluid Volumes

• What principle is the indicator-dilution method based on?

  Conservation of mass principle
• How is the volume of a fluid compartment measured?

  By analyzing the dilution of an indicator substance
• What must be done after injecting the indicator substance?

  Allow it to disperse evenly throughout the compartment
• What does the total mass of a substance after dispersion equal?

  Total mass injected into the compartment
• What is the formula to calculate the unknown volume of chamber B?

  Volume B = Volume A × Concentration A / Concentration B
• What two pieces of information are needed for the volume calculation?

  Total amount of substance injected and concentration after dispersion
• If 1 ml of dye solution with 10 mg/ml is used, what is the volume of chamber B if the final concentration is 0.01 mg/ml?

  1000 ml
• What conditions must be met for the indicator to measure the volume accurately?

  Indicator must disperse evenly, stay in the compartment, and not be metabolized
• What must be done if the indicator is metabolized or excreted?

  Correction must be made for loss of the indicator
• What substances can be used to measure body fluid volumes?

  • Various indicator substances
  • Must disperse evenly
  • Must not be metabolized or excreted