Can We Measure Visceral Fat With Air Displacement Plethysmography?

INTRO

Measurement of body fat percentage with air displacement plethysmography method. The process of air displacement and body plethysmography.

What is Air displacement plethysmography?

Determination of body fat percentage u density measurement via volume determination.

Air Displacement Plethysmography (ADP; Greek. plethore = fullness, graphein = write) is a technique to determine body composition. In particular body fat percentage. Using density measurement (densitometry) via volume determination (plethysmography).

The technique is based on the same principles as hydro densitometry. Underwater weighing, see also pycnometer. But uses air displacement instead of water displacement.

Air displacement plethysmography has some advantages. Compared to other established reference methods for determining body composition. Such as the short duration of the examination. Non-invasiveness and feasibility for many groups of subjects. Children, overweight, elderly, or disabled people.

Body composition for adults using whole-body air displacement plethysmography (ADP)
Body composition for infants using whole-body air displacement plethysmography (ADP)

History of air displacement plethysmography

The principle of plethysmography was already used. At the beginning of the 20th century. To survey the body volume and body composition of young children. Until the 1960s, however, no reliable measurement methods were available. The systems required strict maintenance of the environmental conditions.

The technical difficulties in standardizing the temperature. And humidity of the air at the surface of the body limited the study of humans. Due to the multitude of technological difficulties. None of the early air displacement plethysmographs were further developed for everyday use.

The development approach of later. More technologically advanced systems from the 1980s were also discontinued. In the mid-1990s. The first commercially available air displacement plethysmograph for adults came. At the beginning of 2000. A system for small children followed.

Air displacement plethysmography basics

In air displacement plethysmography. The density of a subject’s body is determined by the determination of the body volume. And the mass of his subject. From this, in turn, conclusions are drawn about the body composition. In particular the fat percentage.

In air displacement plethysmography. A person’s volume is determined indirectly. By measuring the volume of air displaced. Within a closed chamber (plethysmography).

The person’s body inside the chamber displaces a volume of air that is equal to the volume of the body. To calculate the body volume. The remaining chamber volume is subtracted from the volume of the empty chamber. When the subject is in the chamber.

The amount of air inside the chamber is calculated by slightly changing the volume of the chamber. E.g. by means of a sliding membrane. And then the amount of air in the chamber can be calculated by means of physical gas laws.

Isothermal measurement

Boyle’s law states. That s is the pressure of a gas. Is inversely proportional to its volume at a constant temperature. If a constant temperature can be guaranteed (isothermal change of state). Boyle’s law can be applied.

Early plethysmography systems attempted to create isothermal conditions. In the test chamber and were therefore impractical. This problem could only be solved with the development of systems. That no longer required isothermal test conditions.

Adiabatic measurement

Systems available since the end of the 1990s dispense. With the production of isothermal conditions. And choose an approach in which no thermal energy is exchanged. Between the measuring room and the environment. Adiabatic change of state. And determine on this basis the volume of the displaced air.

And thus the body volume of the test person with the help of Poisson’s equation. The fact that (also) these conditions cannot be fully established. Is compensated for with the help of corrections. Which in turn takes into account the isothermal approach.

Validation

Air displacement plethysmography has been validated. Against the main methods of body composition analysis:

Hydrodensitometry (underwater weighing)
The main reference methods are underwater weighing,
Dual X-ray absorptiometry,
Measurement of total body water (TBW) by isotope dilution analysis,
Measurement of total body potassium and multi-compartment models
Deuterium Method (in infants)
Whole-body magnetic resonance imaging.

Body plethysmography

Body plethysmography, is often also referred to as whole-body plethysmography. Or large lung function. Is a pneumology procedure for measuring lung and respiratory parameters.

A large number of respiratory parameters are measured in body plethysmography. Such as respiratory resistance, residual volume, or total lung capacity. Are not accessible with other measurement techniques, such as spirometry.

Modern body plethysmograph

The method of body plethysmography used today dates back. The introduction of the method by DuBois in 1956. Body plethysmography is the diagnostic method of choice in the clinical field. And in the practices of established pneumologists.

Body plethysmograph test method

The examination using a body plethysmograph is the ideal lung function test method. Since it can calculate the specific airway resistance. Including the breathing loop. The thoracic gas volume and all parameters that can be derived from it. In the same examination in addition to the measured variables of spirometry.

This method is less dependent on cooperation. Then with spirometry and the additional time required is low. However, the high level of equipment complexity. And the high acquisition costs. Explain why body plethysmographs are practically only found in clinics and with specialists.

Body plethysmograph contents

1 measurement principle
1.1 Determination of breathing resistance
1.2 Determination of the thoracic gas volume
2 indication
3 web links
4 individual proofs

Measuring principle

Determination of respiratory resistance

The body plethysmograph is designed as a cabin. With a (largely) closed volume of air. It looks like a small telephone booth. The cabin has a minimal leak. To compensate for an increase in cabin pressure. Caused by the patient’s body heat.

Body plethysmograph examination

During the examination, the patient breathes through a spirometer to determine flow characteristics. For inhalation, the patient’s chest rises. Which minimally reduces the air volume in the cabin. And thus increases the pressure.

Breathing loop

When breathing at rest, you can now observe what pressure change is necessary. To generate a certain flow. The analysis of this so-called breathing loop. Allows conclusions to be drawn about the resistance of the lungs. And can thus quickly and easily reveal clinical pictures. Such as a simple obstruction (flatter breathing loop). Or COPD (triangular protuberance in the expiratory part of the breathing loop).

Airway resistance

The specific airway resistance sRAW. Then corresponds to the slope of the breathing loop. The thoracic gas volume (TGV) is also required to determine the total respiratory resistance:

Determination of the thoracic gas volume

The measurement of the thoracic. Often also: intrathoracic gas volume is based on the physical law of Boyle and Mariotte. According to this the product of pressure. And volume remains constant at a constant temperature.

Breathing movements result

As described, the breathing movements result in compression. Or the expansion of the gas volume enclosed in the thorax. While the air pressure in the lungs corresponds to the external pressure in the breathing rest position.

I.e. at the end of an exhalation, the volume of the lungs increases. During inhalation due to the lifting of the chest. Which in turn causes the air pressure to drop. Therefore, Boyle and Mariotte’s law can be applied.

Respiratory flow

A shutter briefly closes the mouthpiece. This is why no more respiratory flow can be measured for a short moment. And therefore there is no pressure drop across the airway resistance. The pressure measured then corresponds solely to the pressure in the pulmonary alveoli. The intrapulmonary pressure.

With further parameters determined by simple spirometry. The total lung capacity and the residual volume can now also be deduced.

Body plethysmographs manufacturers

Although the physics of this method does not seem too complex. Only a few manufacturers have mastered this technique. Only about a dozen companies worldwide offer body plethysmographs. On the one hand, this is due to the extremely small pressure differences.

That occurs during inspiration. But also to the major disruptive influences. Such as cabin heating and phase shift of the pressure. Or susceptibility to external pressure influences the sensitive sensors.

Spirometry indication

Spirometry provides initial indications of the presence of lung disease. And is suitable for observing the course of the disease and treatment. However, body plethysmography is essential for a definitive diagnosis.

In addition to the basic distinction of z. Asthma and COPD allow a body plethysmograph a quick classification of the obstruction. In z.B. Homogeneous obstruction, COPD, or extrathoracic stenosis. Body plethysmography is also required for the reliable diagnosis of restrictions. Pulmonary emphysema or pulmonary fibrosis.

CONTENT:

• What is air displacement plethysmography?
• History of air displacement plethysmography
• Air displacement plethysmography basics
• Isothermal measurement
• Adiabatic measurement
• Validation
• Body plethysmography
• Modern body plethysmograph
• Body plethysmograph test method
• Body plethysmograph contents
• Determination of respiratory resistance
• Body plethysmograph examination
• Breathing loop
• Airway resistance
• Determination of the thoracic gas volume
• Breathing movements result
• Respiratory flow
• Body plethysmographs manufacturers
• Spirometry indication