Lecture 12 - Respiratory responses to exercise

Question 1

Breathing frequency and tidal volume _____ during exercise

Answer 1

increase

Question 2

What are the major functions of the respiratory system during exercise?

Answer 2

Maintain arterial O2 saturation

CO2 removal

Acid-Base balance

Fluid and temperature balance

Question 3

VO2 is primarily determined by ..

Answer 3

exercise intensity

Question 4

Most of the increase in ventilation, from incremental exercise, is from…

Answer 4

the increase in CO2 production in aerobic metabolism

Question 5

What the main chemical controllers of respiration?

Answer 5

CO2

H+

Oxygen levels

Question 6

Hyperventilation will do what to PCO2?

Answer 6

decrease

Question 7

Explain Ventilatory drift

Answer 7

Breathing more often, resp muscles need more oxygen that this contributes to an increase in VO2

Question 8

Alveolar PO2 is about…

Answer 8

100mmHg

Question 9

Alveolar PCO2 is about..

Answer 9

46 mmHg

Question 10

During exercise your mixed venous PO2 will be lower (about 25mmHg). The incerase in HR will mean the transit time through the gas exchange aveolar will decrease.

Is the diffusion gradient affected in healthy individuals?

What about at high altitudes?

Answer 10

not really - Arterial PO2 is well maintained even in high levels of exercise

If you’re at altitude - the diffusion gradient is much less. The inspired Oxygen is not high enough. Harder to exercise.

Question 11

Is the low transit time a problem for really well trained individuals with a high CO?

Answer 11

Can be - there may not time for full equilibration.

Lungs don’t adapt to exercise training. Lung volume is just due to body size - they don’t get bigger

Question 12

What is exercise-induced arterial hypoxemia?

Answer 12

difference between the alveolar O2 and arterial O2 due to DIFFUSION LIMITATION (same lung morphology but increase cardiac output = a mismatch)

could also be expiratory flow limitations at high levels of ventilation.
Could also be a slight shift in the O2 dissociation curve so it’s harder for the haem to load up with oxygen.

Question 13

Respiratory muscles are ____ and can fatigue

Answer 13

voluntary

Question 14

Diaphragm fatigue can limit performance as it is…

Answer 14

important to maintain arterial saturation.

can load it with intense exercise and ‘train’to reduce fatigue

Question 15

Respiratory muscle work may increase to as much as __% VO2 and CO during strenuous exercise

Answer 15

15% VO2 and CO

Question 16

How is the diaphragm blood flow maintained at high intensities?

Answer 16

results in reduced active muscle blood flow due to sympathetically mediated vasocontriction arising from respiratory muscle chemoflexors

type 3/4 afferent fibres - tell brain that more oxygen is needed at diaphragm.

Question 17

How is ventilation controlled

Answer 17

group of respiratory neurons in the hindbrain.

Subject to cortical control (higher centres)

Feedback - central chemoreceptors and peripheral chemoreceptors

stretch receptors in the lung

type 3/4 afferents in limb and diaphragm muscles

Question 18

What are the major factors driving ventilation during exercise?

Answer 18

Motor cortical activation - central command

the limb skeletal muscles - Muscle afferents (spindles, type 3/4 afferents) sending signals to the brain

CO2 flux to the lung - remember PCO2 is maintained

Increased K+, H+, lactate - drives the hyperventilation of intense exercise

Elevated catecholamines and temperature

No role for O2 - no hypoxic drive for ventilation during exercise

Question 19

What are the adaptations from untrained - trained individuals

Answer 19

right-shift in the ventilation curve - ventilation is lower in the trained individual, along with lactate curve]

There’s a lower K+ response - after training your muscles there are more Na/K pumps so the K concentration is able to be protected better. –> lower arterial K+

Question 20

Why is ventilation lower following training?

Answer 20

reduced blood lactate / H+

Lower plasma K+

Lower plasma catecholamines

reduced activation of muscle afferents?

reduced central drive? The exercise is more relaxed