Exercise and high altitude Flashcards
What affect does exercise have on ventilation?
It increases tidal volume
Increases ventilation rate
Increases diffusion capacity due to increasing the BP
What happens to arterial PO2 during exercise?
Stays constant
What happens to venous PO2 during exercise?
Decreases
What happens to PCO2 during exercise?
Stays constant until 70% of oxygen has been used and then it decreases
What happens to pH during exercise?
It decreases after 70% oxygen consumption because oxygen is low and glycolysis begins this forms lactic acid which decreases pH
What is the rate limiting step of ventilation increase during exercise?
The transport of fully oxygenated blood from the heart to the tissue as you can push lungs harder than the heart
What type of response is the initial response of pulmonary ventilation during exercise?
Neural or metabolic?
Neural
Describe the initial pulmonary ventilation response during exercise?
Stimulation from the motor cortex transmitted tot he peripheral receptors which are transmitted to the lung stretch receptors, there is an increase in potassium concentration and this increases sensitivity of respiratory centres
What happens to PO2, pH and PCO2 at high altitudes?
PO2 decreases which means PCO2 decreases which increases pH
Why does low O2 at sea level not cause a ventilatory drive?
It is not low enough and peripheral chemoreceptors are not sensitive enough
What detects low oxygen levels and what do they cause?
Peripheral chemoreceptors mainly carotid bodies - causing hyperventilation
What are the consequences of hyperventilation?
There is only a small increase in Hb saturation but a lot of extra CO2 is blown off so there is an increase in pH. The decrease in CO2 reduces the ventilatory drive (mediated by central chemoreceptors)
The decrease in protons caused by decrease in CO2 increases Hb’s affinity to oxygen small amount
How is ventilation and perfusion matched at high altitude?
Low O2 in the lungs causes redistribution of blood flow around the alveolar capillaries.
Alveoli with poor ventilation become constricted to divert the blood to well ventilated areas (hypoxic vasoconstriction)
Why can hypoxic vasoconstriction cause pulmonary oedema?
Vasoconstriction increases BP in pulmonary artery which can cause fluid to escape from capillaries and leak into lungs
Describe the adaptation to altitude? (after 3 days)
HCO3- is transported out of the CSF causing a decrease in pH. The central chemoreceptors are then rest.
This increases the ventilatory drive and sensitivity of the peripheral chemoreceptors.
pH is normalised by renal HCO3- excretion
Describe the adaptive response to altitude after a few hours?
Hypoxia causes glycolysis to take place and release 2,3DPG, this shifts the oxygen dissociation curve to the right, so Hb has a lower affinity for oxygen and will release more to the tissues
What is the disadvantage to the short term adaptive response to high altitude? What is the solution?
Oxygen dissociation curve is shifted tot he right so it is harder for Hb to bind oxygen at the lungs (alveolar capillaries).
Solution- increase in oxygen carrying capacity
How does hypoxia stimulate an increase in oxygen carrying capacity? When does this occur?
It stimulates formation of RBCs by releasing EPO from the kidneys. After 2-3 days
RBC production increases fro 2-3 weeks
By how much does hypoxia increase oxygen carrying capacity?
50%
What are the consequences of increasing RBC?
Increases the viscosity of the blood so the heart has to work harder.
Peripheral vasoconstriction at low temperatures may cause viscous blood to stop flowing causing frostbite
What is the effect of increasing pulmonary pressure int he short term?
It recruits more capillaries
What short term physiological and morphological changes occur at high altitude?
Increased BP uses more capillaries
Number and size of mitochondria increases to enhance the efficiency of aerobic metabolism
What long term physiological and morphological changes occur at high altitude?
More capillaries develop to improve the diffusion of O2 by shortening the distance
