Slide 3 - BIA Flashcards
What is bioelectrical impedance Analysis
Technique to estimate body composition based on the difference in electrical conductive properties of various tissues
What does BIA do
What does it measure
Low level electrical current passed through body
Measures impedance/opposition to current flow
What does BIA estimate
Total body water from impedance measurement
Fat free mass
BIA is able to work because of the
Conductivity properties of muscle and fat
What is conductance
The ability of an electrical current to pass through a medium (body tissues)
What is impedance
The degree to which a current is slowed down or stopped when an electrical current is applied
Adipose tissue is made up of:
20% water
80% adipose cells
Adipose tissues are
Therefore it
As a result there is a
Resistant to electricity
Does not conduct electricity well = majority of current is stopped
High impedance
Muscle tissue is made up of:
75% water
25% muscle cells
Muscle tissues are
As a result there is a
Conductive = conduct electricity very well
Low impedance
When there is a large total water volume in the body this means
The current flows more easily through the body (with less resistance
What assumptions are made for BIA measurement
Fluids conduct electricity
Approx 73% of body water is contained in FAT FREE BODY MASS - better conductivity
Fat cells contain little water - higher resistance, lower conductivity
Your body is a perfect cylinder - uniform length and cross sectional area
What do the assumptions cause to happen
Errors
What are the Pre test precautions when doing a BIA test
Avoid exercise = 12 hours
Avoid liquids that dehydrate = 12 hours
Avoid alcohol = 48 hours
Avoid eating or drinking = 4 hours
Void completely before the test
Menstural cycle phase should be noted
What are the sources of error in BIA test
What does each cause to happen on resistance and effect on body fat
Cool skin =
Higher resistance
Higher effect on body fat
Warm Temp =
Lower resistance
Lower effect on body fat
Meal within 4 hours =
Lower resistance
Lower effect on body fat
Drinking 1 litre of water within 90 mins =
Lower resistance
Lower effect on body fat
Dehydration =
Higher resistance
Higher effect on body fat
Exercise =
Lower resistance
Lower effect on body fat
What may cause these possible sources of error
Equipment
Technician - body position and electrode placement
Client - Hydration and pre test intructions
Prediction equations
What is the advantage of the BIA test
Little technician skill required
Comfortable for clients
Can be used for obese individuals
What equipment did we use for Upper body
What does it determine
OMRON
Body fat based on impedance in upper body only
What equipment did we use for Lower body
What does it determine
Where is the current applied
Tanita Scale
Body fat based on impedance in lower body only
Current is applied to balls of feet, impedance measured at heels
What measure upper and lower body
Tetrapolar
SECA
What happens for tetrapolar
Current applied at distal electrodes in hand and fat
Impedance measured by proximal electrodes in wrist and ankle
Exercising prior to BIA testing may decrease level of resistance; thus, the percent body fat can be estimated lower (underestimate) than what it actually is
True
There are high variabilities between BIA analyzers
True
Even though technician’s skill is not a major source of error for the BIA method, it could be possible to have a source of error from misplacement of electrodes especially for 4-electrode unit BIA
True
