Week 7 - Respiration During Exercise (Part 2) Flashcards
Explain the ventilatory response to constant load steady-state exercise
(ON SHEET)
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
Explain exercise hyperpnoea
(ON SHEET)
Hyperpnoea is defined as PaCo2 regulation due to proportional changes in alveolar ventilation and metabolic rate
Whats the effect of increased exercise intensity on ventilation
Ventilation increases linearly with exercise
intensity/workload until a point commonly referred to as the ‘ventilatory threshold’
What happens when ventilatory threshold is reached
Expiratory volume increases exponentially resulting in hyperventilation (decrease PaCo2)
What is exercise induced arterial hypoxaemia (EIAH)
EIAH is defined as a reduction in PaCo2 of >10mmHg from rest
When does EIAH occur
EIAH occurs in highly trained males (50%) during heavy exercise and the majority of females regardless of fitness or exercise intensity
What are the causes of EIAH
Causes are not fully understood but are generally believed to be due to:
1. Diffusion limitation
2. V/Q mismatch
3. Relative hypoventilation
What are the changes in breathing pattern at the onset of exercise
At onset of exercise changes in expiratory volume are achieved by increasing tidal volume
What are the changes in breathing pattern during heavy exercise
Tidal volume plateaus and further increases in expiratory volume are achieved by increased breathing frequency
Tidal volume does not exceed 60% of vital capacity
What is the formula for work applied to breathing
Work = pressure x volume
How do you work out total work
Total work is the sum of elastic, flow-resistive and inertial forces
What are the measurements of work and o2 cost of breathing for respiratory muscle
Respiratory muscle can exceed 500J/min and up to 500ml o2/min
What does oesophageal pressure tells you
(ON SHEET)
It is an estimate of pleural pressure and can be used to calculate the mechanical work of breathing during exercise
Where are the respiratory central brain generators located
(ON SHEET)
In the brainstem (pons and medulla)
What are the 3 main neuron groups for the control of breathing
Ventral respiratory group - inspiratory and expiratory
Dorsal respiratory group - inspiratory
Pontine respiratory group - modulatory
Where are the peripheral chemoreceptors located
aortic arch and carotid body
Whats the function of peripheral chemoreceptors
Detect changes in Po2 of blood perfusing systematic and cerebral circulation
What is the role of peripheral chemoreceptors
Relay information to the medulla via the vagus and glossopharangeal nerves
Whats the effect of a decreased Pao2
Increased expiratory volume
Where are central chemoreceptors located
They are primarily located on the ventral surface of the medulla also known as the retrotrapezoid nucleus (RTN)
Whats the role of central chemoreceptors
To detect changes in PaCo2 and h+
What are the other brain sites senstive to Co2
NTS, locus coeruleus,
raphe, and cerebellum
Explain the process of chemoreceptor feedback
(ON SHEET)
- Chemoreceptors detect error signals (disturbances to blood gas homeostasis)
- Central and Peripheral chemoreceptors increase afferent input to the brainstem in response to increasing Paco2, decreasing pao2 or pH
- Premotor neurons in the dorsi respiratory group are activated
- Inspiratory muscles contract, increasing expiratory volume
- Changes in expiratory volume elicit changes in PaO2, PaCO2 and pH, thus
restoring blood-gas balance
What are the ventilatory responses to O2
They are curvilinear (-65mmHg) whereas the response to Co2 is linear
Whats the effect of increase Paco2
Increased expiratory volume
Why are the ventilatory responses to o2 and Co2 different
(ON SHEET)
Small changes in PaCO2 elicit much greater changes in ሶ VE versus PaO2
How is mean Paco2 effected during moderate exercise
(ON SHEET)
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
How is ventilatory control effected during exercise
(ON SHEET)
During exercise above ventilatory threshold, metabolites accumulate, including H+ and K+, which can
stimulate breathing—remember that PaCO2 falls and therefore actually inhibits breathing
How does expiratory volume differ between trained and untrained athletes
Expiratory volume is 20-30% lower in trained athletes than untrained
What are some chronic adaptations that improve aerobic capacity
(ON SHEET)
Decreased metabolite accumulation
Decreased afferent feedback
Decreased Ventilatory drive
Do the lungs adapt to exercise training
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
What are 5 ways that the pulmonary system may limit maximal exercise performance
- Exercise-induced arterial hypoxaemia (EIAH)
- Exercise induced laryngeal obstruction (EILO)
- Expiratory flow limitation
- Respiatory muscle fatigue
- Intrathoracic pressure effects on cardiac output
