Full implementation of all the colleges of the block Non-invasive metabolic diagnostics (BGK) of year 3. I myself have to achieve the basis of this summary, the block with an 8.
Ectopic is fat stored in non-adipose tissue, e.g. muscle, heart, liver.
Ectopic is a possible link between obesity and insulin resistance and diabetes, and cardiovascular
complications.
The lipotoxicity hypothesis:
Lipid ‘overflow’ to non-adipocytes may lead to cellular dysfunction and cell-death.
Ectopic fatty acid accumulation occurs in muscles, liver, heart and pancreas.
A high fat content in muscles is related
with insulin resistance.
IMCL = intramyocellular lipid
The higher the IMCL, the lower the insulin
sensitivity. Thus, high fat content in the
muscle leads to insulin resistance.
Hepatic fat accumulation correlates with all the components of the metabolic syndrome. When the
number of hepatic lipids increases, the insulin sensitivity decreases.
The prevalence of NAFLD (Non-Alcoholic Fatty Liver Disease) is high: 24%
NAFLD > 5% by wet weight (fatty liver disease, aka steatosis, when lipid content in the liver is
more than 5%).
The more weight, the higher the risk on steatosis. This is not a very strong relation.
Steatohepatitis is
reversible. It is very
important to treat patients
when diagnosed. Without
treatment the disease can
progress to cirrhosis.
A fatty liver causes
cardiovascular disease and
diabetes.
Lipid accumulation in the heart can lead to apoptosis of cardiomyocytes. This leads to impairment of
heart function.
Diagnosis of liver steatosis
Ultrasound
Ultrasound = echo-imaging
A transducer generates and detects the sound wave. The distance between generation and detection
of the wave indicates the different structures.
𝑡𝑖𝑚𝑒 ×𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑢𝑛𝑑
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 2
velocity of sound = 331 m/s
A sound wave with a high frequency is produced
(>20kHz)
2
, Ultrasonic transducers: made of piezo electric crystals
When the voltage is changes,
the proton lining can be
changed. Depending on the
change of the voltage, the
protons are compressed or
expanded.
Next, when the protons
compress or expand, they
also change the voltage. The
effect works in two ways:
1) Shape changes by
applying voltage
2) Changing shape
generates voltage
Velocity of sound: Air: 331 m/s
Human soft tissue: 1540 m/s
Imaging: line by line
2 MHz < ultrasound frequency < 20 MHz
At transitions between different tissues, sound waves can be reflected. The tissues differ mainly on
the acoustic impedance (key parameter).
Organ Acoustic impedance
The acoustic impedance Z = ρ • c Kidney 1.63 kg/(m2sec)
ρ = density (kg/m3) Blood 1.65 kg/(m2sec)
c = velocity of sound (m/s) Liver 1.65 kg/(m2sec)
Muscle 1.71 kg/(m2sec)
At transitions of tissues with different impedance (Z):
Fat 1.34 kg/(m2sec)
1) Reflection at mirroring surface
Bone 7.8 kg/(m2sec)
2) Scattering (at small irregularities)
Lung 0.18 kg/(m2sec)
Water 1.48 kg/(m2sec)
The fat content causes scattering.
Fatty tissue contains ‘water’ and fat-spheres. Therefore, the Z is
very different, which leads to scattering. This gives a bright image.
A fatty liver gives a high intensity on the ultrasound image. Liver
fat is only detected with ultrasound when the liver fat content is
more than 30%. This method is less reliable in obese people
because fat causes scattering.
3
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