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  1. 1. Pressure in the Body Physics of Human Body
  2. 2. 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 N P 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
  3. 3. Pressure Pressure under a column of liquid of height h is- Where is density of liquid and g is the acceleration due to gravity. hP gh
  4. 4. 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
  5. 5. 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.
  6. 6. 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.
  7. 7. Measurement of Pressure A m m atmP gh P Pressure of the fluid A,
  8. 8. 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.
  9. 9. 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.
  10. 10. 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.
  11. 11. Pressure Effects While Diving Pressure changes can cause severe effects in the gas cavities of the body. Boyles law For a fixed quantity of gas at a constant temperature, the product of absolute pressure and volume is constant. PV = Constant
  12. 12. 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.
  13. 13. 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
  14. 14. 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 bodys 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 wont heal as a result of diabetes or radiation injury.
  15. 15. 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.
  16. 16. 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?