Climbing is the commonest natural cause of hypoxia: as you go up, the partial pressure of inspired O₂ falls, and the body answers with hyperventilation, more red cells, a faster heart and remodelled tissues. Examiners rarely set a long essay here, but “physiological changes at high altitude”, “acclimatization” and “Monge’s disease” are standing short questions, and the viva goes system by system through the adaptive changes and then asks the basis of treatment.
Topics, in the book’s order
- Acclimatization to high altitude · pp. 947–949 · asked once
- High altitude illness · p. 949 · asked once
When you’ve read them: Quiz 109 · Physiological Changes at High Altitude, 15 questions.
After this chapter you should be able to
- say at what altitude hypoxia becomes significant, and the greatest height to which a person can adapt
- explain how ventilation adapts at high altitude, in its two stages and by its two mechanisms
- list the respiratory, hematological, cardiovascular and tissue changes of acclimatization
- name the high altitude illnesses, and give the physiological reasoning behind each treatment
Viva checklist
- The altitude at which alveolar PO₂ reaches 60 mmHg, and why that number matters
- Maximum height of adaptation, and what is needed above it
- The two stages of hypoxic hyperventilation, and why the first one is small
- The two mechanisms of ventilatory acclimatization: chemoreceptor and renal
- Why urine becomes alkaline at high altitude
- Ventilatory equivalent: what it is and how altitude changes it
- Hematological changes: erythropoietin, and how soon erythropoiesis starts
- What 2,3-DPG does to the O₂–Hb curve, and the initial shift the other way
- Cardiovascular changes, early and late; why the heart hypertrophies
- The tissue changes, especially in skeletal muscle
- Features of acute mountain sickness, and when they appear
- Features of chronic mountain sickness (Monge’s disease)
- Mechanism of high altitude pulmonary hypertension and edema
- Mechanism of cerebral edema, and why coma occurs
- Why acetazolamide is the diuretic of choice