Direct and Indirect Calorimetry Flashcards
Why is direct calorimetry not the preferred type to use by nutritionists?
Direct calorimetry is expensive between the cost of the flooring needed to be installed, the chamber structure and the weight of the water. Likewise, it is lengthy in order to determine significant changes in water. Only really measures the heat that is given off and water vapour needs to be quantified.
What is the basis for indirect calorimetry?
The basis for indirect calorimetry is that all energy releasing reactions in the body will depend on the usage of oxygen and the production of carbon dioxide.
How does indirect calorimetry measure the amount of energy that is produced by food in the body?
Indirect calorimetry is able to measure the amount of energy produced by food by measuring the amount of oxygen that is used in litres, the amount of carbon dioxide that is released in litres and the amount of nitrogen that is present in the urine as urea. (When amino acids go into the citric acid cycle they remove the nitrogen group through deamination so that can indicate how much energy was produced as for oxidation reactions to occur it happens through glycolysis or the citric acid cycle)
What are the known and unknown values in indirect calorimetry?
The known values are the amount of oxygen used (L), the amount of carbon dioxide released (L) and the amount of nitrogen released in the urine (g).
The unknown values are the amount of oxidation of each macronutrients.
How is the crude protein value determined?
The amount of nitrogen in the urine is collected during the period of interest and is multiplied by 6.25.
In indirect calorimetry some individuals are required to wear a mask. What can this cause and why is that bad?
Wearing a mask can cause some individuals to hyperventilate and can lead to artifacts being in the O2 and CO2 measurements. Likewise, masks can be uncomfortable and can cause discomfort and stress to the subject.
Does both direct and indirect calorimetry yield the same results?
Yes both direct and indirect calorimetry yield comparable results. With the difference typically being less then 1%. for the daily caloric output.
What does indirect calorimetry measure to determine energy production? What do they compare these values with?
Indirect calorimetry measures the flow rate of O2 and CO2 in comparison to the known concentrations of O2 and CO2 in the air.
What does RQ stand for and how is the RQ determined?
RQ = respiratory quotient RQ = CO2 produced (L) / O2 consumed (L)
What does RQ assume?
RQ assumes the exchange of O2 and CO2 at the lungs the gas exchange from nutrient metabolism at cellular level.
What does the gross metabolic RQ not included unless a truly RQ is needed to be calculated?
The gross metabolic RQ will ignore nitrogen in the urine as this value is typically very small and will look more at fats and carbohydrates.
What can RQ (respiratory quotient) measure?
The RQ can measure
- the amount of energy that is expended.
- the portion of the amount of each macronutrients that is oxidized (usually fats and carbohydrates).
When would urinary nitrogen be measured?
Urinary nitrogen would be measured to determine the amount of lean muscle (protein is in muscle as the amino acids are there) lost.
The difference between the respiratory quotient values for Fats and Carbs is the same properties which cause the difference between their gross energy and metabolized energy? True or false
True. The difference in RQ values for fats and carbs is that fats have less inherent oxidation so they will require more oxygen for oxidation and release more energy. Whereas, carbohydrates already have parts of their structures that were oxidized and can’t be oxidized further so as a result they require less oxygen to produce the similar amount of carbon dioxide. The fact fats have less inherent oxidation is the same property as to why they produce more energy than carbohydrates, as energy again is produced through the breaking of the bonds (mostly H-C) in macronutrients to release energy as heat (60%) and store the rest as ATP (40%).
What does the thermal equivalent allow you to determine?
The amount of energy expenditure.
