Physics of-human-body pressure of-human-body
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Transcript of Physics of-human-body pressure of-human-body
Pressure in the Body
Physics of Human Body
Pressure
Pressure is defined as the force per unit area in a gas or liquid.
In solid it is referred to as Stress.
2
F NP
A m
SI unit is Pascal. 1 Pa = 1 N/m2
Standard atmospheric pressure at sea level, 1 atm = 101.3 kPa
Many different units are used to measure pressure:
mm Hg (millimeters of mercury) for blood pressure
psi (pounds per square inch) for tire pressure
Pa (Pascals) for scientists and engineers
Pressure
Pressure under a column of liquid
of height h is-
Where ρ is density of liquid and g is
the acceleration due to gravity.
ρhP gh
Pressure
We measure pressure in reference with atmospheric pressure ( 1 atm),
which is Gauge pressure.
True or absolute pressure will be -
1
101
abs atm gauge
abs gauge
abs gauge
P P P
P atm P
P kPa P
atm Pa cm H2O mm Hg
atm 1 1.01*10e5 1033 760
Pa 0987*10e-5 1 0.0102 0.0075
cm H2O 9.68*10e-4 98.1 1 0.735
mm Hg 0.00132 133 1.36 1
Pressure
When you inhale, air is pulled into your lungs, not pushed.
The volume of the lungs is expanded, and the pressure in the alveoli
decreases.
Pressure in the lungs are lower than atmospheric or negative, when we
breathe in.
Measurement of Pressure Classical Method:
• Determine the height of a column of liquid that produces a pressure equal to pressure
being measured.
Manometer: Pressure measuring instruments. (e.g. Sphygmomanometer)
The oldest method of measuring low pressures, simple U tube method.
If a U shaped glass tube is half filled with a liquid, e.g. mercury, and a pressure is applied to one
end of the limb, the other being open to atmosphere, the liquid will move to balance the
pressure.
The weight of liquid so displaced will be proportional to the pressure applied.
As the difference in height of the two columns of liquid and the density are known the pressure
can be calculated.
Measurement of Pressure
A m m atmP gh P
Pressure of the fluid A,
Pressure inside the Skull
Hydrocephalus (Waterhead)
Commonly referred to as "water on the brain." The
so-called "water" is actually cerebrospinal fluid
(CSF), a clear liquid that looks like water and is
produced in the 4 ventricles (cavities) of the brain,
connected by narrow pathways.
It is an abnormal buildup of cerebrospinal fluid
(CSF) in the ventricles of the brain. The fluid is often
under increased pressure and can compress and
damage the brain.
If detected early can be corrected by surgically
installing a by-pass drainage system for the CSF.
Pressure in the Eye
Glaucoma
A disease that damages eye's optic nerve. Usually happens when fluid builds
up in the front part of the eye. That extra fluid increases the pressure in eye,
damaging the optic nerve.
Pressure increases when either too much fluid is produced in the eye or the
drainage or outflow channels (trabecular meshwork) of the eye become
blocked.
In severe cases can cause blindness.
Instruments used in measuring pressure in the eye, called Tonometer.
Pressure in the Skeleton
Highest pressures in the body (stresses) are in the bone joints.
Force reduces when area increases.
Area of bone joints are relatively large, so we feel less stress.
Finger bones are flat, which makes force spread over a larger
surface. This reduces stress in the tissues over the finger bones.
Pressure Effects While Diving
Pressure changes can cause severe effects in the gas cavities of
the body.
Boyle’s law – For a fixed quantity of gas at a constant
temperature, the product of absolute pressure and volume is
constant.
PV = Constant
Pressure Effects While Diving
Eardrum rupture
Pressure in the middle air should be equal to atmospheric pressure
outside eardrum.
While diving equalization can be hampered causing increased ear
pressure, which can make the eardrum to rupture.
Rupture can affect vestibular or balance mechanism and cause
nausea and dizziness.
Diver should raise the pressure in the mouth by holding the nose
and try to blow out.
Pressure Effects While Diving
Other effects-
Sinus Squeeze.
Eye Squeeze
Pressure rise due to holding breath
Pressure in the lungs (Oxygen poisoning)
Breathing air at a depth below 30m
Nitrogen narcosis
The bends or decompression sickness
Air Embolism
Pneumothorax
Hyperbaric Oxygen Therapy (HBOT)
Our body lives in an atmosphere, where one-fifth Oxygen and four-fifth
Nitrogen.
HBOT involves breathing pure O2 in a pressurized room or tube.
HBOT is a medical treatment process, which enhances the body’s natural
healing by inhalation of 100% oxygen in a total body chamber, where
atmospheric pressure is increased (2-3 atm) and controlled.
It can treat serious infections, bubbles of air in blood vessels and wounds that
won’t heal as a result of diabetes or radiation injury.
HBOT
Under normal circumstances, oxygen is transported throughout the
body only by red blood cells. With HBOT, oxygen is dissolved into all
of the body's fluids, the plasma, the central nervous system fluids, the
lymph, and the bone and can be carried to areas where circulation is
diminished or blocked. In this way, extra oxygen can reach all of the
damaged tissues and the body can support its own healing
process. The increased oxygen greatly enhances the ability of white
blood cells to kill bacteria, reduces swelling and allows new blood
vessels to grow more rapidly into the affected areas. It is a simple,
non-invasive and painless treatment.
Hyperbaric oxygen therapy improves the quality of life of the patient
in many areas when standard medicine is not working. Many
conditions such as stroke, cerebral palsy, head injuries, and chronic
fatigue have responded favorably to HBOT.
Problems
1. Positive pressure is used in blood transfusions. A container of blood is
placed 1 m above a vein where the venous pressure is 0.3 kPa, if the
density of blood is 1.04*10e3, what is the net pressure acing to transfer
the blood into the vein?
2. Approximately 50% of your body weight lies above the fifth lumber
vertebra. If the cross-sectional area of that vertebra is take to be about
3*10e-3 m2, what is the stress at that point in your spinal column?
3. What volume of air an atmospheric pressure of 100 kPa is needed to fill
a 1.42*10e-2 m3 scuba tank to a pressure of 1.4*10e4 kPa?
4. If you are a deep-sea diver in a dive to 30 m, what absolute and gauge
pressures will you experience?