Physics of-human-body pressure of-human-body

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Pressure in the Body Physics of Human Body

Transcript of Physics of-human-body pressure of-human-body

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Pressure in the Body

Physics of Human Body

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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

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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

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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

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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.

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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.

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Measurement of Pressure

A m m atmP gh P

Pressure of the fluid A,

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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.

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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.

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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.

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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

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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.

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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

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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.

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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.

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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?