LAB7- Air Plethysmography Body Composition Analysis Flashcards
plethysmography
a measure in the change of volume
air plethysmography
an assessment of the change in volume of air
BODPOD
the brand name of a device that measures air plethysmography
-a large egg-shaped fiberglass chamber that is capable of measuring pressure changes
-accurate method of body composition measurement that is fast (after calibration), requires minimal client compliance + minimal technician skill
the general premise of BODPOD works the same as ____
hydrostatic weighing
how does BODPOD work in simple terms
-a client’s weight is measured on a scale
-their volume is measured in the BODPOD
-using a 2-compartment model their body fat is estimated
describe chambers of BODPOD
has a reference chamber + a measurement chamber
volume of reference chamber
300L
volume of measurement chamber
450L
what is found in between the reference chamber + measurement chamber
a diaphragm
what does the diaphragm do during a measurement
oscillates back + forth to create sinusoidal volume changes (of roughly 350 mL) that are equal in magnitude but opposite in sign
sinusoidal volume change created by the oscillation of the diaphragm
350 mL
volume changes created by diaphragm lead to what in the 2 chambers
small + complementary pressure changes in the 2 chambers
how does the BODPOD computer calculate volume
uses the changes of volume + pressure between the reference chamber + the testing chamber to calculate volume
known volume inside the testing chamber
450L
what is the major problem in measuring volume changes of air in a closed system
depending on the conditions of the environment, the relationship between pressure, volume, + temperature changes
density formula
m / v
isothermal conditions
the temperature of the system stays constant because there is a transfer of heat between the system + the surroundings
when air is in isothermal conditions, the relationship of pressure + volume of a gas can be explained by
Boyle’s law (Boyle-Mariotte law)
Boyle’s law equation
P1 / P2 = V2 / V1
adiabatic conditions
the temperature of the system is not constant + there is no transfer of heat between the system + the surroundings
when air is in adiabatic conditions, the relationship of the pressure + volume of a gas can be explained by
Poisson’s equation
what is ɣ in Poisson’s equation
the ratio of specific heat of the gas
Poisson’s equation
P1 / P2 = (V2 / V1)^ ɣ
Boyle’s law = isothermal/adiabatic
isothermal
Poisson’s equation = isothermal/adiabatic
adiabatic
when air is inside the BODPOD chamber does the air act uniformly
no
air near the body surface in clothing + hair reacts like isothermal/adiabatic conditions
isothermal
air away from the body surface reacts like isothermal/adiabatic conditions
adiabatic
we will assume we are in isothermal/adiabatic
adiabatic
-assume things are not constant
**air whose volume is compressed under isothermal conditions changes its pressure ____ % less than air compressed under adiabatic conditions
40% less
air whose volume is compressed under isothermal conditions changes its pressure 40% less than air compressed under adiabatic conditions
^^what does this mean
means air under isothermal conditions is 40% more compressible than under adiabatic conditions
throughout the measurement in a BODPOD, it’s assumed that the air is acting under isothermal/adiabatic conditions
adiabatic
-for this to be the case, several things must be controlled for + ultimately assumed
we assume adiabatic conditions- for this to be true what must we do to ɣ
there must be a constant ɣ
how do we achieve a constant ɣ
there must be the same composition of air in the reference chamber that’s in the testing chamber
-to achieve this an air circulation system is used to mix the air between the 2 chambers throughout measurement
to assume adiabatic conditions, what must we eliminate
anything that increases air under isothermal conditions (excess hair, baggy clothing, etc.)
regardless of how many items are eliminated like exccess hair + clothing…
air that is in contact with the skin is going to act under isothermal conditions
-this needs to be considered
what equation estimates body surface area
Dubois formula
how do we use body surface area
BSA is multiplied by a constant k to yield the surface area artifact which is automatically computed + used to correct the isothermal air that can’t be eliminated
what else must we consider to assume adiabatic conditions
average thoracic gas volume (V of TG)
BODPOD predicts V of TG (average thoracic gas volume) based on what 2 things
height + weight
individuals with lower average V of TG will be over/underpredicted by the BODPOD
underpredicted
individuals with a higher average V of TG will be over/underpredicted by the BODPOD
overpredicted
it is recommended that average V of TG is measured or predicted
measured
-more precision
in this lab, average V of TG will be measured or predicted
predicted
most people’s V of TG falls within what values
3-4.5 L
ultimately what does the BODPOD do
takes a measurement of volume change inside the measurement chamber by comparison of the reference chamber with air under adiabatic conditions + then factors in the surface area artifact + V of TG
**formula to solve for final body volume
final body volume = raw body volume - surface area artifact + 40% V of TG
why do we multiply V of TG by 40% in the equation for final body volume
the lung volume appears 40% larger than it is because the air in the lungs is acting under isothermal conditions
what is final body volume used to calculate
density
because density is used to estimate body composition…
the estimations of 2-compartment model are still assumed
fat mass has a density of
0.9 g/cm^3
fat-free mass has a density of
1.1 g/cm^3
equipment- scale
-highly accurate
-10kg weights for calibration beside scale
**for calibration what is used
two 10kg weights beside scale
testing chamber is able to accomodate up to ____ lb clients
550 lb
testing chamber is able to accomodate up to ____ tall clients
7’ tall
testing chamber has a safety button inside
**volume of calibration cylinder in testing chamber
50.118 L
the volume of the cylinder in the testing chamber varies around ____ L
50L
diaphragm
creates the changes in pressure + volume that allow for precise measurement
clothing requirements- women
-form fitting
-spandex-type swimwear or single layer compression shorts (no padding) + single layer (not padded) sports bra
-remove all jewelry
clothing requirements- men
-form fitting spandex-type swimwear or single layer compression shorts (no padding) + no shirt
-remove all jewelry
clothing requirements- both gender
-a swim cap will be required to be worn during testing
-the swim cap will be provided or you can bring your own
-use disinfectant spray between participants
prior to testing- exercise
do not exercise for at least 2 hours prior to testing
prior to testing- eat/drink
do not eat/drink for at least 2 hours prior to test
prior to testing- caffeine
avoid caffeine or thermogenic supplements prior to testing
prior to testing- bladder
void bladder prior to testing
prior to testing- skin creams/lotion
do not apply skin creams/lotions before test
prior to testing- shaving
if you shave any part of your body, do so the day of the test if possible
during testing
there is a blue emergency button inside the BODPOD behind the left leg to unlock the magnetic door
normative data for % body fat- men
20-29: 14.8%
30-39: 18.4%
40-49: 20.8%
50-59: 22.3%
60-69: 23%
70-79: 22.9%
normative data for % body fat- women
20-29: 20%
30-39: 21%
40-49: 23.6%
50-59: 26.6%
60-69: 27.5%
70-79: 26.3%
