Control of respiration during exercise

Question 1

how much does alveolar ventilation increase during respiration?

Answer 1

can increase up to 20fold

Question 2

increased CO2?

Answer 2

as exercising muscles produce more CO2, systemic venous blood increases in blood CO2, but not systemic arterial blood.

Question 3

why does arterial CO2 not increase due to exercise? (2 factors)

Answer 3

arterial CO2 is determined by alveolar CO2

alveolar CO2 is determined by ratio of co2 production to alveolar ventilation

Question 4

why doesn’t alveolar and arterial CO2 change?

Answer 4

during moderate exercise, alveolar ventilation increases in exact proportion to increased co2 production

Question 5

strenuous exercise

Answer 5

alveolar ventilation increases more than co2 production, so hyperventilation may decrease arterial co2

Question 6

decreased o2 as the stimulus?

Answer 6

systemic venous o2 decreases, but alveolar and arterial o2 are unchanged
increased consumption of o2 in the tissues and alveolar ventilation increase in exact proportions to each other

Question 7

what is the limiting factor in strenuous exercise?

Answer 7

cardiac output, not ventilation

Question 8

increased [H+] as the stimulus?

Answer 8

no accumulation of excess H+ due to CO2 accumulation.
increased arterial H+, due to generation and release of lactic acid into the blood
partly responsible for stimulating hyperventilation

Question 9

other factors affecting ventilation during exercise

Answer 9

reflex input from mechanoreceptors in joints and muscles
increased body temperature
inputs to respiratory neurons via branches from axons descending from the brain to motor neurons supplying muscles
increased plasma epinephrine conc
increased plasma potassium conc from muscles
conditioned response mediated by neural input to respiratory centres