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  <head>
    <title>104-03 Heat, cold, altitude, diving, and microgravity</title>
    <ownerName>Integrated Medical Foundations</ownerName>
  </head>
  <body>
    <outline text="Heat, cold, altitude, diving, and microgravity">
      <outline text="Environmental stress principles">
        <outline text="Exchange of heat, gas, fluid, load"/>
        <outline text="Stress depends on intensity, duration, equipment"/>
        <outline text="Exercise raises heat and oxygen demand"/>
        <outline text="Adaptation extends range, not physical limits"/>
      </outline>
      <outline text="Heat exchange and acclimation">
        <outline text="Core temperature balances production and exchange">
          <outline text="Radiation, convection, conduction, evaporation"/>
        </outline>
        <outline text="Radiation and convection add heat when hotter"/>
        <outline text="Evaporation needs favourable vapour pressure">
          <outline text="Humidity, impermeable clothing, dripping sweat"/>
        </outline>
        <outline text="Skin and core sensors to hypothalamus, brainstem"/>
        <outline text="Skin flow competes with muscle, central volume">
          <outline text="Plasma loss raises heart rate"/>
        </outline>
        <outline text="Forced drinking risks dilutional hyponatraemia"/>
        <outline text="Heat acclimation with repeated exposure">
          <outline text="Plasma volume expands"/>
          <outline text="Earlier, dilute sweat via aldosterone"/>
          <outline text="Days to begin, one to two weeks, decays"/>
        </outline>
      </outline>
      <outline text="Heat illness">
        <outline text="Heat exhaustion: cannot continue, no severe CNS injury"/>
        <outline text="Heat stroke: hyperthermia with CNS dysfunction">
          <outline text="Liver, kidney, muscle, coagulation injury"/>
          <outline text="Sweating does not exclude it"/>
        </outline>
        <outline text="Exertional in active, classic in vulnerable"/>
        <outline text="Medicines impair sweating or judgement"/>
        <outline text="Cool rapidly without delaying care"/>
        <outline text="Antipyretics fail: set point not raised"/>
      </outline>
      <outline text="Cold exposure and injury">
        <outline text="Vasoconstriction and behaviour conserve heat"/>
        <outline text="Shivering and non-shivering thermogenesis"/>
        <outline text="Water removes heat faster than still air"/>
        <outline text="Alcohol accelerates heat loss"/>
        <outline text="Hypothermia slows metabolism and conduction">
          <outline text="Confusion to arrhythmia and arrest"/>
          <outline text="Irritable myocardium: move with care"/>
        </outline>
        <outline text="Passive, active external, internal rewarming"/>
        <outline text="Frostbite: ice, endothelium, thrombosis">
          <outline text="Refreezing after thaw worsens injury"/>
          <outline text="Rubbing adds mechanical injury"/>
        </outline>
        <outline text="Non-freezing injury from wet cold"/>
      </outline>
      <outline text="Altitude physiology">
        <outline text="Pressure falls, oxygen fraction constant"/>
        <outline text="Hypoxic ventilatory response">
          <outline text="Respiratory alkalosis restrains ventilation"/>
          <outline text="Renal bicarbonate loss permits hyperventilation"/>
        </outline>
        <outline text="Maximal aerobic performance falls"/>
        <outline text="Erythropoietin raises red cells over weeks">
          <outline text="Plasma contraction raises concentration first"/>
          <outline text="Excess viscosity impedes flow"/>
        </outline>
        <outline text="Acclimatisation differs from evolutionary adaptation"/>
      </outline>
      <outline text="Altitude illness">
        <outline text="Acute mountain sickness: headache after ascent">
          <outline text="Ascent rate, sleeping altitude, susceptibility"/>
        </outline>
        <outline text="Cerebral oedema: ataxia, altered mental state"/>
        <outline text="Pulmonary oedema: breathlessness, hypoxaemia">
          <outline text="Widespread hypoxic vasoconstriction"/>
          <outline text="Uneven constriction and high flow"/>
        </outline>
        <outline text="Descent and oxygen are central"/>
        <outline text="Acetazolamide aids acclimatisation"/>
        <outline text="Glucocorticoids ease cerebral symptoms only"/>
      </outline>
      <outline text="Diving and immersion">
        <outline text="One atmosphere per ten metres of seawater"/>
        <outline text="Boyle&#x27;s law: gas compresses and expands">
          <outline text="Unequalised ears, sinuses, mask, lungs"/>
          <outline text="Breath-hold ascent: barotrauma, gas embolism"/>
        </outline>
        <outline text="Henry&#x27;s law: more gas dissolves at depth">
          <outline text="Fast ascent: bubbles, decompression sickness"/>
          <outline text="Oxygen and urgent recompression assessment"/>
        </outline>
        <outline text="Nitrogen narcosis impairs cognition"/>
        <outline text="Oxygen toxicity: seizures, lung injury"/>
        <outline text="Carbon dioxide retention worsens both"/>
        <outline text="Immersion shifts blood centrally, diuresis"/>
        <outline text="Cold immersion: gasping before hypothermia"/>
        <outline text="Pre-dive hyperventilation risks blackout"/>
      </outline>
      <outline text="Microgravity">
        <outline text="Fluid shifts toward chest and head">
          <outline text="Diuresis lowers plasma volume"/>
        </outline>
        <outline text="Deconditioning, bone loss, muscle atrophy"/>
        <outline text="Orthostatic intolerance on return"/>
        <outline text="Urinary calcium raises stone risk"/>
        <outline text="Vestibular reinterpretation, motion sickness"/>
        <outline text="Radiation risk with dose and duration"/>
        <outline text="Countermeasures reduce, do not eliminate"/>
      </outline>
      <outline text="Integrated prevention">
        <outline text="Identify the governing physical exposure"/>
        <outline text="Match work and equipment to reserve"/>
        <outline text="Allow graded adaptation"/>
        <outline text="Recognise early failure before injury"/>
      </outline>
    </outline>
  </body>
</opml>
