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29 Cards in this Set
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- Back
- 3rd side (hint)
Cadaveric Dissection Studies |
- Only direct measure of body composition. - Used to validate many in vivo methods. - Fat (skinfolds and chemical analysis), muscle (ptn), K, water? |
Gold Standard |
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Pros and Cons of Cadaveric Dissection |
ADVANTAGES - most direct measure available
DISADVANTAGES - limited # of studies (ages, weights etc) - assume cadavers have similar characteristics to living subjects (cause of death is usually illness....so is this really a representative sample?) |
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Pros and Cons |
ADVANTAGES
- measurements are precise (repeatable and reliable)
DISADVANTAGES
- subject cooperation is necessary - not practical for large groups - unsuitable for young children, elderly etc (underwater weighing) - accuracy ↓ due to "lung residual volume" (estimate using nitrogen washout method m) - density in fat-free component ***(bone & muscle) |
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Hydrostatic Weighing |
Errors – Equations – Residual lung volume – Water density - Consistency of tissues across races, gender, age
Recommended Techniques – Water tank – Nitrogen wash out • Residual volume – Weight belt – Maximal exhalation – Repeat 8-12 times
• r = 0.94 |
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Dilution Technique |
- TBW measured in FFM by dilution with D, O, or T.(FFM because there is no water in fat, only fat free mass)
- ECW measured by dilution of NaBr (Br does not enter cell) • a known amount of isotope is given (C and V), steady state reached, biological fluid sampled (e.g., blood, urine, or saliva)
C1V1 x C2V2
solve for V |
Deuterium Oxygen-18 Tritium
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Dilution: Pros and Cons |
DISADVANTAGES - difficult procedure with limited precision (unreliable and not repeatable) - isotopes are expensive
ADVANTAGES - gives TOTAL BODY WT, EXTRA CELLULAR WATER (and therefore ICW) - stable isotopes can now be used |
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Total Body Potassium |
• 40^K is found in a known amount (0.012%) in ICW and not present in stored triglycerides • therefore, FFM is estimated by external counting of gamma rays emitted by 40K |
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TBK Pros and Cons |
ADVANTAGES - very precise (repeatable, reliable)
DISADVANTAGES - assumes FF tissue has (differs gender, obesity, age) a known and constant Potassium content e.g., older and obese overestimate fat
- accuracy ???
- high cost & limited locations |
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Absorptiometry |
- body (region) is scanned transversely in small steps by radiation from gadolinium-153
• 153Gd emits 2 gamma rays of different energies for quantitation of bone mineral/soft tissue (FFM/LBM) |
Single-photon Dual-photon DEXA [dual energy X- ray absorptiometry] or DEXA) |
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Absorptiometry Pros and Cons |
ADVANTAGES - DEXA allows for regional body composition (body sections differences) measurements - small error = ±1-5% - quick, subject friendly
DISADVANTAGES - expensive equipment & limited locations - calibration and mathematical treatment of data is complicated - x-ray (😐radiation exposure) |
Single photon Dual-photon |
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Ultrasound |
- electrical energy is converted to high-frequency ultrasonic energy in a probe - transmission of sounds waves through various tissues (fat and muscle tissue have differing densities) can be used to calculate tissue thickness (e.g., subcutaneous fat) |
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Pros and Cons |
ADVANTAGES - portable equipment available -safe & non-invasive - compares well with skinfolds
DISADVANTAGES - validity for wide range of body fatness levels is unknown - constant pressure of probe is difficult, thus prejudicing determination of fat thickness i.e., resolution not as good as with Computerized Tomography |
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Computerized Tomography |
• Method measures attenuation (consistency) of X-rays as they pass through tissues • degree of attenuation is related to density of tissue • an image is generated by computerized processing of density-frequency distribution data • regional body composition (fat, lean tissue, bone) |
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CT Pros and Cons |
ADVANTAGES additional use, organ size (liver, spleen, kidneys) can be measured
DISADVANTAGES - exposure risk (X-rays), limits use for whole-body and multiple scans - no chemical composition information - expensive & limited location |
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Magnetic Image Resonance |
• based on the fact that atomic nuclei can behave like magnets • external magnetic field is applied across body and nuclei attempt to align with the external field • radio-frequency is directed into the body & nuclei absorb energy (change in positioning of magnetic field) • radio-frequency turned off (return to orginal state) • emit signal which is imaged by computer (level of hydration and fat content) |
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MRI Pros and Cons |
ADVANTAGES - safe (e.g., children etc, multiple studies) -non-invasive - both amount and distribution of body fat obtained - high quality images of the body (better than CT) - can currently image hydrogen and phosphorous (will soon image C, N, Na, Cl)
DISADVANTAGES -limited locations -high cost |
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Neutron Activated Analysis |
- radioisotopes of N, P, Na, Cl, Ca are created by irradiating the subject - radioactivity of element is measure using a whole body counter and is related to content |
Na P Ca N Cl |
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NAN Pros and Cons |
ADVANTAGES - only technique currently available for measurement of multielemental composition of the human body (Ca P Mg Na Cl) in addition to muscle mass (N)
DISADVANTAGES - subjects exposed to radioactivity - elements not uniformly activated, thus sensitivity varies - expensive & limited locations |
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Anthropometric Measurements |
Examples - some will differ for infants, children, nonambulatory persons
• Weight - electronic or balance-beam scale - calibrated
• Height - stadiometer - technique - e.g., Frankfort horizontal plane
• Circumferences - landmarking, tape measure - placement, two people
• Skinfolds m - landmarking, equipment, technique (skill) |
Weight is useful for extremes • Monitoring change – sudden gains or losses in weight
Height is useful for “stunting” – indicator for undernutrition – nutrient deficiencies e.g., Zn |
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Anthro Pros and Cons |
SOME ADVANTAGES measurements (for fat etc) can be made in field but require skilled technicians for accuracy
SOME DISADVANTAGES -dependence on technicians skill - not applicable to all population groups |
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Electrical Conductance
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- based on the difference in electrolyte content between fat and fat-free tissue
- electrolytes in water are capable of conducting electricity better than its fat mass
- determinations of resistance and reactance are made, and used to calculate conductance and to predict LBM/FFM, TBW, ECW from "various" equations |
TOBEC- total body electric conductivity
BIA- bioelectrical impedance analysis
BIS-bioelectric impedance spectroscopy
BE |
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Electrical Conductance Pros and Cons |
ADVANTAGES - safe, convenient to use, portable, rapid, and non-invasive - BIA (measures extremities) less expensive than TOBEC (whole body)
DISADVANTAGES - affected by conditions (fed, fasted, edema, dehydration etc.) - extent to which variation in body shape and size affects readings not yet known |
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Infrared Interactance |
• recently developed to estimate fat • measurement of body fat is made at various sites on the extremities through use of short wavelengths of infrared light • fat is calculated from the absorption spectra • predictive equations used to estimate total fat |
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Infrared Interactance Pros and Cons |
ADVANTAGES - safe, non-invasive, rapid, convenient (used in health clubs and weight loss clinics)
DISADVANTAGES - validation studies (comparing with other techniques) have not been favourable depends upon regional fat distribution to predict TBF - believed to be inferior to skin-folds - not a recommended approach for determining body composition |
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Biochemical Parameters |
Urinary creatinine excretion – muscle mass
Total plasma creatinine – skeletal mass (muscle) 3-methylhistidine – muscle mass
***major problem is accounting for amounts found in diet
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Accuracy |
Being accurate means close to what you are going for. Imagine a target with a bullseye in the center. Accurate shots would be those close to the bullseye while not accurate shots would be farther away from the bullseye. In science accurate results would be results that are close to the expected outcome.
It is possible to be accurate and precise at the same time if you get the same result over and over and that result is close to the expected result. |
Validity- how well it measures what it's supposed to measure |
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Precision |
Precise means being able to get the same thing over and over. In the bullseye target example you are precise if you shoot the same area again and again no matter how close or far from the bullseye you are. As long as you are in the same area again and again it is considered precise. In science results are precise if you get the same result over and over again.
High accuracy (valid) but low precision is not bad because it is measuring what is needed but it could be better if the results were more precise repeatable (reliable) |
Reliable -consistency of results (repeatable) |
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Coefficient of Determination |
square of the correlation coefficient represents the proportion of variance in one variable accounted for by the other |
Estimating shared variance R squared R2 |
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Correlation Coefficient (r) |
Correlation does not mean causation Use correlations as a source for subsequent hypotheses |
From +1 to -1 The closer to zero, less correlation Closer to one, higher correlation |
