What is the purpose of doubly labeled water?
What is the purpose of doubly labeled water?
The doubly labelled water (DLW) technique measures total carbon dioxide production by observing the differential rates of elimination of a bolus dose of the stable isotope tracers, 2H (deuterium) and 18O. Combined with an estimate of the respiratory quotient, this yields an estimate of total energy expenditure.
What is the main advantage of the doubly Labelled water technique?
Of these, doubly labeled water, the most accurate method, has the advantage of measuring energy consumption in a free-living individual over a prolonged period of time. Its disadvantages are expense and lack of availability.
How much is doubly labeled water?
b. Advantages and Disadvantages of Doubly Labeled Water.
| Advantages | Disadvantages |
|---|---|
| Noninvasive, unobstrusive, and easily administered | Availability and expense of oxygen-18 (approximately $900 for 70-kg adult) |
What is DLW method?
The DLW method is based on the premise that after a dose of doubly labeled water, 2H2 18O, the two isotopes equilibrate with total body water (TBW) and then are eliminated differentially from the body (Figure 12-1). Deuterium (2H) leaves the body as water, while 18O leaves as water (H2O) and carbon dioxide (CO2).
How accurate is doubly labeled water?
Later, validation studies, comparing doubly labelled water-assessed energy expenditure with simultaneously measured energy expenditure in a respiration chamber, showed that the method is accurate and has a precision of 2–8% (Schoeller 1988).
What is direct and indirect calorimetry?
Direct calorimetry measures the heat output by the subject, through direct observation inside a calorimeter. Indirect calorimetry measure heat by using the variable of O2 consumption and manufactured CO2. Indirect calorimetry gives a more feasible and accurate measure of heat or energy, compared to direct calorimetry.
How is indirect calorimetry performed?
Indirect calorimetry is the method by which measurements of respiratory gas exchange (oxygen consumption, V O 2 and carbon dioxide production, V CO 2 ) are used to estimate the type and amount of substrate oxidized and the amount of energy produced by biological oxidation.
Is doubly Labelled water indirect calorimetry?
Measurement of energy expenditure with doubly labelled water is an innovative variant on indirect calorimetry, where energy expenditure is derived from the measurement of carbon dioxide production.
How is doubly labeled water made?
In practice, doses of doubly labeled water for metabolic work are prepared by simply mixing a dose of deuterium oxide (heavy water) (90 to 99%) with a second dose of H218O, which is water which has been separately enriched with 18O (though usually not to a high level, since doing this would be expensive, and …
Is doubly labeled water indirect calorimetry?
What is direct calorimetry?
Direct calorimetry obtains a direct measurement of the amount of heat generated by the body within a structure large enough to permit moderate amounts of activity. These structures are called whole-room calorimeters. Direct calorimetry provides a measure of energy expended in the form of heat.
What is the difference between direct and indirect calorimetry What does each actually measure and how?
Indirect calorimetry is a measure of the heat produced by oxidative processes. Direct calorimetry measures the rate of dissipation of heat from the body. An increase in the rate of heat production, as with exercise, may not always result in an immediate, measurable increase in heat released by the body (from the skin).
What is the doubly-labelled water method?
What is the Doubly-Labelled Water Method? The doubly labelled water (DLW) method is an isotope-based technique for the assessment of energy expenditure. The method is based on the difference between the turnover rates of the hydrogen and oxygen of body water as a function of carbon dioxide (CO 2) production.
What are the limitations of doubly labeled water?
The doubly labeled water method, however, does not provide any information on the pattern or intensity of any one activity during that time but the overall average energy expenditure. This method is also expensive due to the cost of the 18 O and it does require sophisticated mass spectrometric analyses.
What is the double labeled water method for estimating energy expenditure?
The scientific basis that underlies the doubly labeled water method for estimating energy expenditure relies on the differential rates of loss of hydrogen and oxygen from the body at different levels of energy expenditure. Hydrogen is lost primarily in water, whereas oxygen is lost in both water and carbon dioxide.
What is deuterium and heavy oxygen labeled water (DLW)?
This is an isotope dilution technique wherein deuterium and heavy oxygen-labeled water (doubly labeled water, DLW) are given to individuals and timed urine samples are collected to measure the elimination rates of 2 H and 18 O in the urine. 2 H label from DLW mixes with the body water and is eliminated as water in the urine.
