Respiration during Exercise (2)

Question 1

What are the 3 phases in the ventilatory response to constant load steady-state exercise?

Answer 1

o Phase 1: Immediate increase in VE
o Phase 2: Exponential increase in VE
o Phase 3: Plateau

Question 2

What is hyperpnoea?

Answer 2

Hyperpnoea - PaCO2 regulation due to proportional changes in alveolar ventilation (VA) and metabolic rate (VCO2)

Question 3

How does ventilation increase during incremental exercise? When does this stop?

Answer 3

Linearly - until a point commonly referred to as the ventilatory threshold (lactate/anaerobic threshold)

• this occurs at 50-75% of peak workload (VO2 peak).

Question 4

What happens after ventilatory threshold is reached?

Answer 4

VE increases exponentially, resulting in hyperventilation (decreases PaCO2)

Question 5

What is exercise-induced arterial hypoxaemia (EIAH)?

Answer 5

The reduction in Pa02 of ≥10 mmHg from rest
- Occurs in highly trained males (50%) during heavy exercise and the majority of females regardless of fitness or exercise intensity.

Question 6

Why is EIAH theorised to occur?

Answer 6

Because ventilatory demand exceeds capacity (demand vs capacity theory)

Question 7

Although not fully understood, what are understood to be the 3 causes of EIAH?

Answer 7

1. Diffusion limitation
2. V/Q mismatch
3. Relative hypoventilation

Question 8

What are changes in VE achieved by at the onset of exericse?

Answer 8

Increasing tidal volume

Question 9

During heavy exercise, tidal volume plateaus and further increases in VE are achieved by..?

Answer 9

Increased breathing frequency

Question 10

Tidal volume does not exceed ? of vital capacity?

Answer 10

60%

Question 11

Work = ? x ?

Answer 11

Work = force x volume
Applied to breathing: work = pressure x volume

Total work is the sum of elastic, flow-resistive, and inertial forces

Question 12

How do you work out mechanical work of breathing during exercise?

Answer 12

By using oesophageal pressure (Poes)
- an estimate of pleural pressure

Question 13

Where are respiratory central patterns located?

Answer 13

Within the brainstem (pons and medulla)

Question 14

What are the 3 main groups of neurons?

Answer 14

o Ventral respiratory group (inspiratory and expiratory)
o Dorsal respiratory group (inspiratory)
o Pontine respiratory group (modulatory)

Question 15

The control of ventilation has a 3-compartmental model. What are the 3 compartments of this model?

Answer 15

• Central controlled (pons, medulla, other parts of brain)
• Effectors (respiratory muscles)
• Sensors (chemoreceptors, lung, + others)

Question 16

Where are peripheral chemoreceptors located?

Answer 16

Aortic arch + carotid body
- These detect changes in P02 of blood perfusing systemic and cerebral circulation

Relays sensory info to the medulla via vagus and glossopharyngeal nerves

Other stimuli also activate peripheral
chemoreceptors, such as temperature,
adrenaline and CO2

Question 17

Where are central chemoreceptors located?

Answer 17

Central chemoreceptors are located primarily in the ventral surface of the medulla, known as the retrotrapezoid nucleus (RTN).

The RTN is sensitive to change in PaCO2/H+
o Many other brain sites are also sensitive to CO2, such as the NTS, locus coeruleus, raphe, and cerebellum

Question 18

Describe the chemoreceptor feedback

Answer 18

1. Chemoreceptors detect error signals (disturbances to blood gas homeostasis)
2. Central and peripheral chemoreceptors increase afferent
   input to the brainstem in response to increasing PaCO2or decreasing PaO2or pH
3. Premotor neurons in the dorsal respiratory group are activated
4. Inspiratory muscle contract, increasing VE
5. Changes in VE elicit changes in PaO2, PaCO2and pH, thus restoring blood-gas balance

Question 19

How does the ventilatory response to O2 and CO2 different?

Answer 19

O2 - curvilinear
CO2 - linear

Question 20

Is there a change in PaCo2 during moderate exercise?

Answer 20

No change in mean PaCO2 during moderate exercise, primary exercise stimulus must be feedforward in origin.

Question 21

What fine-tunes breathing during mod-intensity exercise?

Answer 21

Peripheral chemoreceptors

Question 22

What happens to PaCO2 during severe exercise?

Answer 22

Falls and inhibits breathing
- additional sources of ventilatory stimulus come from increased body temp and augmented muscle afferent input.

Question 23

What is the difference in ventilation during submaximal exercise between trn and untrn individuals?

Answer 23

Ventilation is 20-30% lower during submaximal exercise in trained versus untrained individuals.

Question 24

What are 3 chronic training adaptations that improve aerobic capacity?

Answer 24

• decreased metabolite accumulation
• decreased afferent feedback
• decreased ventilatory drive

Question 25

DO the lungs adapt to exercise training?

Answer 25

With few exceptions, the lungs and airways don’t adapt to physical training
- airways and lungs do not get bigger
- diffusing capacities are unchanged

Respiratory muscles may becomes stronger and more fatigue resistant.

Question 26

What are 5 examples of how the pulmonary system may limit exercise performance?

Answer 26

1. Exercise-induced arterial hypoxaemia (EIAH)
2. Exercise-induced laryngeal obstruction (EILO)
3. Expiratory flow limitation
4. Respiratory muscle fatigue
5. Intrathoracic pressure effects on cardiac output