Lecture 33

Question 1

How does minute ventilation (VE) increase during exercise?

Answer 1

By increasing tidal volume and breathing frequency.

Question 2

Breathing pattern in mild exercise?

Answer 2

Tidal volume increases first with small increases in frequency.

Question 3

Breathing pattern in heavy exercise?

Answer 3

Tidal volume plateaus at ~50–60% VC; increases in VE come from frequency.

Question 4

How is the initial increase in tidal volume achieved?

Answer 4

By lowering end-expiratory lung volume via activation of expiratory muscles.

Question 5

How is further increase in tidal volume achieved?

Answer 5

By raising end-inspiratory lung volume via accessory inspiratory muscles.

Question 6

Why increase tidal volume first?

Answer 6

Reduces dead space ventilation → improves alveolar ventilation (Vd/Vt falls).

Question 7

Why is tidal volume limited to 50–60% of VC?

Answer 7

This range minimizes work of breathing and elastic load.

Question 8

Why is reducing end-expiratory lung volume beneficial?

Answer 8

Lengthens diaphragm → allows optimal force generation; stores elastic energy.

Question 9

What are the three phases of VE during submaximal exercise?

Answer 9

Phase 1 rapid rise, Phase 2 slow rise (~2–3 min), Phase 3 steady-state.

Question 10

What is exercise hyperpnea?

Answer 10

Matched increase in ventilation proportional to metabolic rate in submaximal exercise.

Question 11

Two major control theories for exercise breathing?

Answer 11

Feedforward (central command) and feedback mechanisms.

Question 12

What supports feedforward control?

Answer 12

Initial rapid ventilation rise (Phase 1) is too fast for peripheral feedback.

Question 13

Evidence from decorticate cat studies?

Answer 13

Respiration increases before locomotion → central command contributes to drive.

Question 14

Key feedback mechanisms during exercise?

Answer 14

CO₂ production, chemoreceptors, Type III/IV afferents.

Question 15

What do chemoreceptors sense?

Answer 15

CO₂, pH, and low O₂ (peripheral only).

Question 16

Why are blood gases stable in submaximal exercise?

Answer 16

Ventilation closely matches metabolic demands.

Question 17

What are Type III & IV afferents?

Answer 17

Group III (mechanical) and IV (chemical) muscle afferents influencing breathing.

Question 18

Evidence for Type III/IV afferents?

Answer 18

Fentanyl blocking reduced VE, HR, and BP.

Question 19

Ventilation pattern summary for submaximal exercise?

Answer 19

Phase 1 neural, Phase 2 combined neural & feedback, Phase 3 steady-state matching metabolic rate.

Question 20

What is exercise hyperventilation?

Answer 20

Ventilation rises disproportionately above ~60–70% VO₂max.

Question 21

Why does hyperventilation occur above VT1?

Answer 21

Large CO₂ production from muscles triggers ventilatory drive.

Question 22

During heavy exercise, what happens to PaCO₂?

Answer 22

Falls 5–15+ mmHg below rest due to hyperventilation.

Question 23

Why does pH fall during maximal exercise?

Answer 23

ATP hydrolysis during cross-bridge cycling, NOT lactic acid.

Question 24

How does hyperventilation affect pH?

Answer 24

Reduces CO₂ → slows pH decline.

Question 25

Does physical training increase lung structure?

Answer 25

Generally no; heart and muscles adapt more than lungs.

Question 26

Which athletes may show lung adaptation?

Answer 26

Swimmers—repeated forced inspirations to TLC may increase lung volumes.

Question 27

What airway adaptations may occur with training?

Answer 27

Repeated stretch may improve airway smooth muscle function.

Question 28

Do children show respiratory adaptations?

Answer 28

Yes—high activity may accelerate lung growth pre‑puberty.

Question 29

Why is the lung considered ‘overbuilt’?

Answer 29

Large diffusion surface and short diffusion distance allow adequate gas exchange even in exercise.

Question 30

What is expiratory flow limitation?

Answer 30

When tidal expiratory flow reaches maximal flow-volume loop boundary.

Question 31

What is dynamic hyperinflation?

Answer 31

End-expiratory lung volumes rise toward/above rest due to shortened expiration.

Question 32

Consequences of dynamic hyperinflation?

Answer 32

Increases elastic work and fatigues inspiratory muscles by shortening them.

Question 33

Sex differences in ventilatory constraints?

Answer 33

Women have ~17% smaller airway diameters → higher resistance and earlier limitations.