Energy Expenditure Flashcards
what is the first law of thermodynamics
energy is neither created nor destroyed, but instead, transformed from one form to another
what is a kilocalorie?
the amount of heat required to raise the temperature of 1 kg (liter) 1 degree C
what is a joule?
energy expended (work done) in applying a force of one newton through a distance of one meter
explain how direct calorimetry works
water (of a known constant temperature) passes from one ends of a jacket to the other; the temp of the water leaving the jacket is used to calculate energy expended
why don’t we use direct calorimetry
expensive
takes a lot of time to ensure there are no leaks/everything works properly
where do we still use direct calorimetry?
in bomb calorimetry with food
- food is lit on fire, the amount of heat it produces changes the temperature of the water
- nitrogen ash can be used to determine protein in food
direct calorimetry measures …
heat production
explain how indirect calorimetry works
O2 is needed to metabolize macronutrients and produce energy
the amount of energy released per liter of O2 consumed is specific for each substrate
if we can can accurately measure O2 consumption and CO2 production, we can estimate EE (we must know the substrate mix and RQ)
indirect calorimetry measures …
O2 consumption and CO2 production
RQ = __ / __
CO2 production / O2 production
RQ of carbs, fat, protein
carbs: 1.0
fat: ~0.7
protein: ~0.8
if we don’t have RQ, we would use ___
*5 kcal/liter O2 consumed
explain how doubly labled water works
a free living technique where the loss from the body of two isotopes reflects the CO2 production during the period
three other techniques for measuring energy expenditure (that are less accurate)
- heart rate
- accelerometer
- pedometer
define: RMR
the amount of energy required to keep the body functioning at rest plus the cost of arousal (i.e. breathing, blood circulation, body temp control, cell growth, brain/nerve function, heart function)
what factors influence REE
- FFM/FM
- sex
- age
- genetics
- body tmp
- menstural cycle (highest during leutal phase)
- certain hormones/medications
- fasting/severe dieting
- overeating
- exercise training
- smoking
- caffeine
- extreme temperatures
- injury/illness
- growth
define: thermic effect of food
obligatory: the amount of energy needed to digest, absorb, metabolize, and store nutrients (and non-nutrients) following a meal
facultative: loss of heat due to SNS activity
higher with protein, lower with fat
explain the thermic effect of protein
the body has no storage capacity for protein and thus it needs to be metabolically processed immediately
specific metabolic costs
- high cost of urea production
- high ATP cost of peptide bond synthesis as proteins are synthesized
- high cost of gluconeogenesis
define: adapative thermogenesis
change in MR leading to increased heat production vs. ATP coupling
can be as a result of environment such as cold acclimation, response to drugs/hormones, overeating
explain how shivering/nonshivering contribute to EE
shivering: heat generation through muscle contraction (glycolysis)
non shivering: generation of heat in cold/metabolic processes other than muscle contraction
- brown adipose tissue provides heat to vital organs (mostly in small animals with high demands for maintenance of body temp)
- diet induced thermogenesis: assimilation of meal accompained by metabolic cost over and above TEF
outpatient protocol for REE
- overnight (12h) fast
- no caffeine or ice water
- no exercise for 24-48 hours
- in energy balance (often assumed)
- rest on bed w/ 30 degree elevation at head
- 30 min collection - first 10 min thrown out
- pt cannot fall asleep
inpatient protocol for REE
- must be hemodynamically stable
- no overnight fasting necessary
- no caffeine
- rest on bed
- 10 min collection - first 5 min thrown out
- UUN may be measured to account for protein metabolism
don’t perform REE on pts …
with chest tubes or air fistuals
receiving nitric oxide
ventilated with positive end-expiratory pressure >12
measuring TEF protocol
- standarized meal
- measure increase in O2 consumption (+RQ) above rest for as long as 4-6 hours post meal
- TEF typically peaks 1 hour after meals – may be higher at breakfast vs. lunch or dinner
in the ICU EE can be influenced by
- body temperature
- healing + recovery
- feeding (level + formula)
- precense of spepsis
- level of sedation
- medications (adrenergic blockers, muscle relaxants, opiates, barbiturates)
- therapy
- family members
why bother measuring indirect calorimetry?
- gold standard in critical care
- over 200 equations developed to predict REE
- equation determined by regression analysis (wt, ht, age, sex)
- large errors of estimation
- critical to be accurate if feeding pt (EN/PN) and/or critically ill and/or on ventilator
