Assessment of Total Energy Expenditure by Stable Isotopes

Stable isotopes of hydrogen and oxygen have been recently used to measure energy expenditure in free-living humans. The doubly labeled water method using these isotopes is a form of indirect calorimetry which has been extensively validated in animals and humans. The method is completely safe, requires only periodic sampling of body fluids, and is ideally suited for measurement of energy expenditure in free-living or hospitalized patients.

After the administration of doubly labeled water (D₂¹⁸O), the labeled hydrogen (D₂) would be eliminated as water (D₂O), corresponding to water output, whereas the oxygen isotope would be eliminated as water (H₂¹⁸O) and as expired carbon dioxide (C¹⁸O₂). By measuring the difference between the elimination rates of labeled oxygen and hydrogen, the carbon dioxide production rate can be calculated. The carbon dioxide production rate is converted into energy expenditure by knowing the respiratory quotient of the food ingested during the observation period.

The advantage of this technique is that sample collection only involves urine collection at timed intervals following initial dosing. These samples are then analyzed using isotope ratio mass spectrometry (IRMS) to determine the stable isotope remaining in the body.

 

Reference:

Measuring Energy Expenditure Using the Doubly Labeled Water Method Technical Paper 905.

Stable Isotopes in Oil Industry

Mud tracing is utilized in a variety of drilling fluid systems to help define the amount of filtrate invasion throughout coring operations. It is used to achieve more accurate oil and water saturations during the formation evaluation.

D₂O is a water-soluble tracer used to treat the water phase of the drilling fluid. As it is non-radioactive and harmless to the environment, it will not hinder disposal or recycling of the drilling fluid. D₂O is used to elevate the natural background level of deuterium, which generally ranges from 130 - 150 ppm throughout the world. D₂O found in the core during analysis is easily distinguished by its mass from any other water extracted from the sample. The amount introduced to the drilling mud can be manipulated to reflect certain concentrations targeted for the determination of fluid saturations.

 

Reference:

Weatherford Laboratories, well site services brochure.

stable isotope info

Isotopes are variants of a particular chemical element such that, while all isotopes of a given element have the same number of protons in each atom, they differ in neutron number.

• The short relaxation time of deuterium of the spin 1 (quadrupole) provides substantial sensitivity for nuclear magnetic resonance spectroscopy (MRS).

• When D2O is administered in a bolus fashion to a specific tissue or organ in vivo, the deuterium MRS intensity time course can be analyzed to measure the rate of blood flow and tissue perfusion.

•FDA responds to Teva’s NDA with complete response letter for Huntington’s chorea drug

•SD-809 is the first deuterated product that the FDA has reviewed.

•FDA just asked Teva to analyze blood levels of certain metabolites, which are not novel and are similar in subjects who take either tetrabenazine or deutetrabenazine.

•The FDA has requested no further clinical trials.

•Teva will continue to work closely with the FDA to bring SD-809 to the market as quickly as possible,” said Michael Hayden, M.D., Ph.D., Teva’s president of global research and development and CSO