Acclimitisation Part 1 Flashcards
What is acclimitisation?
Compensatory changes observed when a native sea-level dweller moves to high altitude
What happens to VO2 max at high altitude?
VO2 max decreases at high altitude, resulting in decreased exercise tolerance
What happens O2 gradient at high altitude?
Lower PO2 at high altitude reduces gradient and impairs tissue function
What happens O2 transfer at high altitude?
Gradient reduced and therefore rate of diffusion is slower and longer time needed for equilibrium
What are the processes involved in O2 delivery?
Ventilation
Transfer to blood
Carriage in blood (Hb)
Transport in blood
Transfer to tissues (mitochondria)
Oxidative metabolism (use of O2)
What does reduced PIO2 do to ventilation?
Reduction of inspired oxygen leads to reduced arterial partial pressure and hyperventilation caused by activation of carotid chemoreceptors
What does hyperventilation do at high altitude?
Reduces PACO2 and increases PAO2
Increases gradient for diffusion
Promotes O2 uptake
Increased rate of exchange
Is hyperventilation effective during hypoxia?
Increases oxygen saturation and Hb saturation to carry more oxygen in blood
What is the effect of hypocapnia on ventilation?
Hypocapnia (decreased carbon dioxide) inhibits ventilation through elevated pH (alkalosis) centrally and peripherally
What is the effect of renal compensation on hypoxia?
At moderate altitudes, significant renal compensation is nearly 100%
As alkalosis corrected, ventilation increases
When is renal compensation less effective?
At extreme altitudes renal compensation much less effective due to persistent alkalosis
What are the phases of acclimitisation (prolonged hypoxia)?
> initial hypocapnia and respiratory alkalosis
> increased pH acts on chemoreceptors
> attenuates hypoxia induced hyperventilation
> renal and CSF compensation (by HCO excretion)
> pH correction over 3-7 days removes ventilation inhibition
> increases in ventilation to stable plateau
> further reductions in PACO2 and increases in PAO2
What is the limit of tolerated hypoxia in arterial blood?
At PO2 of approx. 35mmHg the PO2 remains constant due to increasing hyperventilation
What changes occur to the gas exchange membrane during hypoxia?
Increased area of perfused pulmonary capillaries, reduced membrane thickness and capillary angiogenesis
What are the advantages of capillary angiogenesis during hypoxia?
Increased RBC time in capillary at fixed cardiac output means more time for equilibrium to be reached
