Week 7 - Respiration During Exercise (Part 2)

Question 1

Explain the ventilatory response to constant load steady-state exercise
(ON SHEET)

Answer 1

Phase 1 - Immediate increase in expiratory volume per unit of time expired
Phase 2 - exponential increase in expiratory volume per unit of time expired
Phase 3 - Plateau

Question 2

Explain exercise hyperpnoea
(ON SHEET)

Answer 2

Hyperpnoea is defined as PaCo2 regulation due to proportional changes in alveolar ventilation and metabolic rate

Question 3

Whats the effect of increased exercise intensity on ventilation

Answer 3

Ventilation increases linearly with exercise
intensity/workload until a point commonly referred to as the ‘ventilatory threshold’

Question 4

What happens when ventilatory threshold is reached

Answer 4

Expiratory volume increases exponentially resulting in hyperventilation (decrease PaCo2)

Question 5

What is exercise induced arterial hypoxaemia (EIAH)

Answer 5

EIAH is defined as a reduction in PaCo2 of >10mmHg from rest

Question 6

When does EIAH occur

Answer 6

EIAH occurs in highly trained males (50%) during heavy exercise and the majority of females regardless of fitness or exercise intensity

Question 7

What are the causes of EIAH

Answer 7

Causes are not fully understood but are generally believed to be due to:
1. Diffusion limitation
2. V/Q mismatch
3. Relative hypoventilation

Question 8

What are the changes in breathing pattern at the onset of exercise

Answer 8

At onset of exercise changes in expiratory volume are achieved by increasing tidal volume

Question 9

What are the changes in breathing pattern during heavy exercise

Answer 9

Tidal volume plateaus and further increases in expiratory volume are achieved by increased breathing frequency

Answer 10

Tidal volume does not exceed 60% of vital capacity

Question 11

What is the formula for work applied to breathing

Answer 11

Work = pressure x volume

Question 12

How do you work out total work

Answer 12

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

Question 13

What are the measurements of work and o2 cost of breathing for respiratory muscle

Answer 13

Respiratory muscle can exceed 500J/min and up to 500ml o2/min

Question 14

What does oesophageal pressure tells you
(ON SHEET)

Answer 14

It is an estimate of pleural pressure and can be used to calculate the mechanical work of breathing during exercise

Question 15

Where are the respiratory central brain generators located
(ON SHEET)

Answer 15

In the brainstem (pons and medulla)

Question 16

What are the 3 main neuron groups for the control of breathing

Answer 16

Ventral respiratory group - inspiratory and expiratory
Dorsal respiratory group - inspiratory
Pontine respiratory group - modulatory

Question 17

Where are the peripheral chemoreceptors located

Answer 17

aortic arch and carotid body

Question 18

Whats the function of peripheral chemoreceptors

Answer 18

Detect changes in Po2 of blood perfusing systematic and cerebral circulation

Question 19

What is the role of peripheral chemoreceptors

Answer 19

Relay information to the medulla via the vagus and glossopharangeal nerves

Question 20

Whats the effect of a decreased Pao2

Answer 20

Increased expiratory volume

Question 21

Where are central chemoreceptors located

Answer 21

They are primarily located on the ventral surface of the medulla also known as the retrotrapezoid nucleus (RTN)

Question 22

Whats the role of central chemoreceptors

Answer 22

To detect changes in PaCo2 and h+

Question 23

What are the other brain sites senstive to Co2

Answer 23

NTS, locus coeruleus,
raphe, and cerebellum

Question 24

Explain the process of chemoreceptor feedback
(ON SHEET)

Answer 24

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 Paco2, decreasing pao2 or pH
3. Premotor neurons in the dorsi respiratory group are activated
4. Inspiratory muscles contract, increasing expiratory volume
5. Changes in expiratory volume elicit changes in PaO2, PaCO2 and pH, thus
   restoring blood-gas balance

Question 24

What are the ventilatory responses to O2

Answer 24

They are curvilinear (-65mmHg) whereas the response to Co2 is linear

Question 24

Whats the effect of increase Paco2

Answer 24

Increased expiratory volume

Question 25

Why are the ventilatory responses to o2 and Co2 different (ON SHEET)

Answer 25

Small changes in PaCO2 elicit much greater changes in ሶ VE versus PaO2

Question 26

How is mean Paco2 effected during moderate exercise (ON SHEET)

Answer 26

There is no change during moderate exercise, the primary exercise stimulus must be feedforward in origin Both central and peripheral neurogenic stimuli play a major role in the exercise hyperpnoea Peripheral chemoreceptors ‘fine-tune’ breathing

Question 27

How is ventilatory control effected during exercise (ON SHEET)

Answer 27

During exercise above ventilatory threshold, metabolites accumulate, including H+ and K+, which can stimulate breathing—remember that PaCO2 falls and therefore actually inhibits breathing

Question 28

How does expiratory volume differ between trained and untrained athletes

Answer 28

Expiratory volume is 20-30% lower in trained athletes than untrained

Question 29

What are some chronic adaptations that improve aerobic capacity (ON SHEET)

Answer 29

Decreased metabolite accumulation Decreased afferent feedback Decreased Ventilatory drive

Question 30

Do the lungs adapt to exercise training

Answer 30

With few exceptions the lungs and airway do not adapt to physcial training. Airways and lungs do not get bigger Diffusing capacities are unchanged However Respiratory muscles may become stronger and more fatigue resistant

Question 31

What are 5 ways that the pulmonary system may limit maximal exercise performance

Answer 31

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