Altitude illnesses
1. Mountain sickness
- Transient syndrome on first arriving at a high altitude
- Starts 8 – 24 hrs after arrival, lasts 4 – 8 days
- Headache, irritability, insomnia, breathlessness, vomiting
- Cause – unknown
- Maybe associated with more serious altitude illnesses – cerebral & pulmonary oedema
2. High altitude cerebral oedema
- Cause – unknown
- Assumed – low PO2 causes cerebral arteriolar dilatation
- Increased capillary pressure (if cerebral autoregulation does not compensate)
- Increased transudation
- Leads to cerebral oedema
- May give rise to: ataxia, disorientation, coma, death due to herniation of the brain through the tentorium
3. High altitude pulmonary oedema
- Marked pulmonary hypertension leading to patchy oedema of the lungs
- Real cause – unknown
- ? Because some pulmonary arteries do not have enough smooth muscles to constrict in response to hypoxia
- In capillaries supplied by those arteries – increase in pressure
At high altitude…
Those who do not develop mountain sickness – have diuresis
Those who develop mountain sickness – decrease in urine output
Treatment of altitude illnesses
- Descent to a lower altitude
- Diuretic Acetazolamide
-Inhibits carbonic anhydrase enzyme, increase HCO3– excretion in the urine
- Glucocorticoides to reduce cerebral oedema
- In high altitude pulmonary oedema – O2 therapy (If available – hyperbaric chamber)
- Nifedipine (a Ca2+ channel blocker)
-Lowers pulmonary arterial pressure
Some facts…
- Highest permanent human habitation: above 5500 m
- If breathing atmospheric air – highest altitude possible to reach without loss of consciousness (if unacclimatized): 6000m
- Peak of mount Everest: 8854 m
How do people climb mount Everest without dying in the effort?
Acclimatization
Acclimatization
- Increased altitude tolerance
- Due to a number of compensatory mechanisms operating over a period of time
1. Right shift of O2 – Hb dissociation curve
- Respiratory alkalosis – shifts the curve to left
- Increase in RBC 2,3-BPG – shifts the curve to right
- Net effect – slight shift to the right
- Small increase in P50
- Decrease in O2 affinity of Hb, increase in O2 availability for tissues
- Increase in P50 is limited; a very low O2 affinity may interfere with O2 uptake by Hb at the lungs
- Acclimatization cont.
2. Increased pulmonary ventilation
- Initial ventilatory response at high altitude – small (alkalosis counteracts stimulating effects of hypoxia)
- Next 4 days – ventilation steadily increases (b/c active transport of H+ into CSF & lactic acidosis in brain)
- Reduced CSF pH increases the response to hypoxia
- After 4 days – ventilation declines slowly
- After years – ventilation declines to initial level
- Person desensitized to stimulatory effects of hypoxia
3. Polycythemia
- Erythropoietin secretion increases soon after ascent to high altitude
- Falls a little over the next 4 days
- Increase in the number of circulating RBC begins in 2 – 3 days
- Remains elevated as long as the individual remains in the high altitude
4. Other changes
- Mitochondria – increase in number
- Myoglobin – increases
- Tissue cytochrome oxidase content – increases
- Capillaries – increase in number
- Maximum breathing capacity – increases
Natives living in high altitudes..
- Permanent human habitations in Himalayas and Andes – above 5500 m (18,000 ft)
- Natives living in these villages show:
-Increased chest size, barrel chested
-Increased pulmonary ventilation capacity
-Markedly polycythemic
-Low alveolar PO2 values
-Decreased body size, stocky build
-Decreased work capacity
When breathing 100% oxygen –
- The total atmospheric pressure becomes the limiting factor in altitude tolerance
- The lowest barometric pressure at which the normal alveolar PO2 of 100 mmHg is possible = 187 mmHg (= 10,400 m or 34,000 ft)
-Water vapour: 47 mmHg (constant)
-Alveolar CO2: 40 mmHg
-Total barometric pressure: 100 mmHg
-Alveolar PO2: 40 mmHg
-Consciousness lost in spite of administration of 100% O2
-Total barometric pressure: 47 mmHg
-Body fluids boil at body temperature
How is it possible to travel in interplanetary space which is devoid of oxygen?
- Artificial atmosphere created around individual
- Pressurized suit or cabin
- O2 supplied, CO2 removed