Lecture 11

• oxygen constant = 21%

  atmospheric pressure @ sea level = 100kPa

  so pressure oxygen = 21kPa

  therefore alevolar gas = 13.3kPa
• atmoshpheric pressure at 5800m is half that at sea level = 9.3kPa

  on summit of everest = 5kPa
• 60,000 feet, atmoshperic pressure 6.3kPa = same as SVP water
• Response to altitude and acclimatisation:

  1. hyperventilation & respiratory alkalosis
  2. increased 2,3-DPG causes better unloading of oxygen
  3. polycythaemia, slow to develop
  4. bicarbonate excretion from CSF and kidneys
  5. diuresis, hyponatraemia
  6. acetazolamide used to treat acute mountain sickness
• acute mountain sickness:

  breathless at > 2000m

  headache

  nausea

  loss apeptite

  difficulty sleeping/exercising

  amnesia/dizziness
• severe mountain sickness

  cheyn stokes resp

  cerebral/pulmonary oedema
• every 10m depth, pressure increases by 1atm = 100kPa
• boyle's law = lung volume 6L compressed to 1L (residual volume) at this depth
• deep diving:

  air supplied at environmental pressure

  helium oxygen used = 2% oxygen sufficient as gives pressure of alveolar oxygen 20kPa at 90m

  enables removal of Nitrogen
• dive reflex:

  innate

  many mammals

  vasoconstriction so oxygen conserved to heart, lungs, brain

  reflex vagal bradycardia

  suppressed ventilation drive
• hyperoxia = cellular oxygen toxicity