Exercise and high altitude

Question 1

What affect does exercise have on ventilation?

Answer 1

It increases tidal volume
Increases ventilation rate
Increases diffusion capacity due to increasing the BP

Question 2

What happens to arterial PO2 during exercise?

Answer 2

Stays constant

Question 3

What happens to venous PO2 during exercise?

Answer 3

Decreases

Question 4

What happens to PCO2 during exercise?

Answer 4

Stays constant until 70% of oxygen has been used and then it decreases

Question 5

What happens to pH during exercise?

Answer 5

It decreases after 70% oxygen consumption because oxygen is low and glycolysis begins this forms lactic acid which decreases pH

Question 6

What is the rate limiting step of ventilation increase during exercise?

Answer 6

The transport of fully oxygenated blood from the heart to the tissue as you can push lungs harder than the heart

Question 7

What type of response is the initial response of pulmonary ventilation during exercise?
Neural or metabolic?

Answer 7

Neural

Question 8

Describe the initial pulmonary ventilation response during exercise?

Answer 8

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

Question 9

What happens to PO2, pH and PCO2 at high altitudes?

Answer 9

PO2 decreases which means PCO2 decreases which increases pH

Question 10

Why does low O2 at sea level not cause a ventilatory drive?

Answer 10

It is not low enough and peripheral chemoreceptors are not sensitive enough

Question 11

What detects low oxygen levels and what do they cause?

Answer 11

Peripheral chemoreceptors mainly carotid bodies - causing hyperventilation

Question 12

What are the consequences of hyperventilation?

Answer 12

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

Question 13

How is ventilation and perfusion matched at high altitude?

Answer 13

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)

Question 14

Why can hypoxic vasoconstriction cause pulmonary oedema?

Answer 14

Vasoconstriction increases BP in pulmonary artery which can cause fluid to escape from capillaries and leak into lungs

Question 15

Describe the adaptation to altitude? (after 3 days)

Answer 15

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

Question 16

Describe the adaptive response to altitude after a few hours?

Answer 16

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

Question 17

What is the disadvantage to the short term adaptive response to high altitude? What is the solution?

Answer 17

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

Question 18

How does hypoxia stimulate an increase in oxygen carrying capacity? When does this occur?

Answer 18

It stimulates formation of RBCs by releasing EPO from the kidneys. After 2-3 days
RBC production increases fro 2-3 weeks

Question 19

By how much does hypoxia increase oxygen carrying capacity?

Answer 19

50%

Question 20

What are the consequences of increasing RBC?

Answer 20

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

Question 21

What is the effect of increasing pulmonary pressure int he short term?

Answer 21

It recruits more capillaries

Question 22

What short term physiological and morphological changes occur at high altitude?

Answer 22

Increased BP uses more capillaries

Number and size of mitochondria increases to enhance the efficiency of aerobic metabolism

Question 23

What long term physiological and morphological changes occur at high altitude?

Answer 23

More capillaries develop to improve the diffusion of O2 by shortening the distance