Acclimatization 2 Flashcards
What is an advantage at high altitude with total hypoxic vasoconstriction?
V/Q is more matched -> vessels at apex dilate
What are 2 mechanisms that PAP and vascular reistance is increased due to?
Diffuse hypoxic vasoconstriction
Pulmonary arteriolar remodelling
What happens to vascular remodelling in 1-5% of the population?
Endothelium hypertrophies and encroaches into lumen increasing vascular resistance and right ventricle begins to fail
What did Wagner prove in 1987?
V-Q mismatch increases during acclimatisation
What inhibitors can reduce pulmonary vascular resistance?
IV rhi kinase inhibitor
What type of response is the increase in PVR in response to high altitude?
maladaptive response
What causes an increased in RBC at high altitude?
Low PaO2 triggers kidneys to make more erythropoietin to increase O2 carrying capacity
What does increased RBC content cause?
increased viscosity -> increased resistance
What is haematocrit?
Proportion of blood that is occupied by RBCs
What causes an increase in haematocrit?
Reduction in plasma volume
increase in RBC
What are 2 disadvantages of increasing haematocrit
Reduced blood volume - affects CO
Increased viscosity
What is the optimum Hb level?
around 60/70
What way does the Hb O2 dissociation curve shift to at respiratory alkalosis at high altitudes?
Left ward shift -> more O2 loaded by Hb
What receptors are involved in the integrated response to hypoxia?
Chemoreceptor
Pulmonary stretch
What 3 things happen in the CVS in response to hypoxia?
Tachycardia
Increased CO
Reduced total PVR
How is blood pressure maintained at normoxic values?
Direct vasodilator action on systemic blood vessels
Partially antagonized by increased SNS activity
directs blood flow to active tissues
What receptors drive SNS activity?
Peripheral chemoreceptors
pulmonary arterial baroreceptors
What do the arterial baroreceptors do to high SNS?
Seek to maintain systemic pressue by reducing SNS
What happens to CO after acclimatization?
Returns to sea level values
HR increased & SV reduced
What happens to the systemic capillaries at high altitude?
Increased capillary density in brain, retina, liver, skeletal muscle
What is the increase of capillary density achieved by?
Angiogensis
What are 3 advantages of capillary angiogenesis?
Increased SA
Reduced diffusing distance - speeds up O2 transfer
Slowed blood velocity at constant total flow rate
What happens in muscle at high altitude?
Muscle atrophies -> muscle fibres shrink -> capillaries are closer together
What are 2 other adaptations?
Optimise ATP production
Reduce O2 requirement
What are tissue changes that occur in skeletal muscle?
Increased myoglobin
Increased enzymes of glycolytic pathway, tricarboxylic acid cycle and electron transport chain
increased mitochondrial density
What is myoglobin’s role in hypoxia?
Increase O2 solubility in cytosol of cell -> diffuse into mitochondria
What are 3 ways oxygen requirement is reduced?
Reduce activity
Weight reduction
Reduced workrate
What happens to enzymes of tricarboxylic acid cycle and electron transport chain at extreme altitudes?
No increase
