Air displacement plethysmography

Air Displacement Plethysmography

Adult body composition through air displacement plethysmography

Air displacement plethysmography (ADP) is a method used to measure human body composition. It is a non-invasive technique that estimates body volume and density, which can then be used to calculate body fat percentage. This method is based on the principle of plethysmography, which involves measuring changes in volume within an organ or whole body.

Principles of Operation

Air displacement plethysmography operates on the principle of Boyle's law, which states that the pressure and volume of a gas are inversely proportional at a constant temperature. In ADP, the subject is placed inside a sealed chamber, and the volume of air displaced by the subject's body is measured. This is achieved by comparing the pressure changes in the chamber with and without the subject inside.

The process involves two chambers: a test chamber where the subject sits, and a reference chamber. The system measures the pressure changes in both chambers to determine the volume of air displaced by the subject. The body volume is then used to calculate body density, which is further used to estimate body fat percentage using established equations.

Procedure

The procedure for air displacement plethysmography is straightforward and typically involves the following steps:

1. Preparation: The subject wears minimal clothing, usually a swimsuit, and a swim cap to minimize air trapped in hair and clothing. 2. Calibration: The system is calibrated to ensure accurate measurements. 3. Measurement: The subject sits inside the chamber, and the door is closed. The system measures the air displacement to calculate body volume. 4. Calculation: Body density is calculated from the body volume and mass, and body fat percentage is estimated using formulas such as the Siri or Brozek equations.

Advantages and Limitations

Air displacement plethysmography offers several advantages:

- Non-invasive: The method does not require any invasive procedures, making it comfortable for the subject. - Quick and Easy: The measurement process is quick, typically taking about 5-10 minutes. - Accurate: ADP provides reliable estimates of body composition, comparable to other methods like dual-energy X-ray absorptiometry (DEXA).

However, there are some limitations:

- Cost: The equipment can be expensive, limiting its availability to specialized facilities. - Sensitivity to Clothing and Hair: The accuracy can be affected by the amount of air trapped in clothing and hair, requiring careful preparation.

Applications

Air displacement plethysmography is widely used in various fields, including:

- Clinical Settings: For assessing body composition in patients, particularly in weight management and nutritional assessment. - Sports Science: To monitor athletes' body composition as part of training and performance optimization. - Research: In studies investigating the relationship between body composition and health outcomes.

Infant Body Composition

Infant body composition through air displacement plethysmography

ADP is also adapted for use in infants, providing valuable data on infant growth and development. The procedure is similar but uses a smaller chamber designed for infants. This adaptation allows for the assessment of body composition in early life, which is crucial for understanding growth patterns and nutritional status.

Related Pages

• Body composition
• Plethysmography
• Boyle's law
• Dual-energy X-ray absorptiometry