Respiration during Exercise (2) Flashcards
What are the 3 phases in the ventilatory response to constant load steady-state exercise?
o Phase 1: Immediate increase in VE
o Phase 2: Exponential increase in VE
o Phase 3: Plateau
What is hyperpnoea?
Hyperpnoea - PaCO2 regulation due to proportional changes in alveolar ventilation (VA) and metabolic rate (VCO2)
How does ventilation increase during incremental exercise? When does this stop?
Linearly - until a point commonly referred to as the ventilatory threshold (lactate/anaerobic threshold)
- this occurs at 50-75% of peak workload (VO2 peak).
What happens after ventilatory threshold is reached?
VE increases exponentially, resulting in hyperventilation (decreases PaCO2)
What is exercise-induced arterial hypoxaemia (EIAH)?
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.
Why is EIAH theorised to occur?
Because ventilatory demand exceeds capacity (demand vs capacity theory)
Although not fully understood, what are understood to be the 3 causes of EIAH?
- Diffusion limitation
- V/Q mismatch
- Relative hypoventilation
What are changes in VE achieved by at the onset of exericse?
Increasing tidal volume
During heavy exercise, tidal volume plateaus and further increases in VE are achieved by..?
Increased breathing frequency
Tidal volume does not exceed ? of vital capacity?
60%
Work = ? x ?
Work = force x volume
Applied to breathing: work = pressure x volume
Total work is the sum of elastic, flow-resistive, and inertial forces
How do you work out mechanical work of breathing during exercise?
By using oesophageal pressure (Poes)
- an estimate of pleural pressure
Where are respiratory central patterns located?
Within the brainstem (pons and medulla)
What are the 3 main groups of neurons?
o Ventral respiratory group (inspiratory and expiratory)
o Dorsal respiratory group (inspiratory)
o Pontine respiratory group (modulatory)
The control of ventilation has a 3-compartmental model. What are the 3 compartments of this model?
- Central controlled (pons, medulla, other parts of brain)
- Effectors (respiratory muscles)
- Sensors (chemoreceptors, lung, + others)
Where are peripheral chemoreceptors located?
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
Where are central chemoreceptors located?
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
Describe the chemoreceptor feedback
- Chemoreceptors detect error signals (disturbances to blood gas homeostasis)
- Central and peripheral chemoreceptors increase afferent
input to the brainstem in response to increasing PaCO2or decreasing PaO2or pH - Premotor neurons in the dorsal respiratory group are activated
- Inspiratory muscle contract, increasing VE
- Changes in VE elicit changes in PaO2, PaCO2and pH, thus restoring blood-gas balance
How does the ventilatory response to O2 and CO2 different?
O2 - curvilinear
CO2 - linear
Is there a change in PaCo2 during moderate exercise?
No change in mean PaCO2 during moderate exercise, primary exercise stimulus must be feedforward in origin.
What fine-tunes breathing during mod-intensity exercise?
Peripheral chemoreceptors
What happens to PaCO2 during severe exercise?
Falls and inhibits breathing
- additional sources of ventilatory stimulus come from increased body temp and augmented muscle afferent input.
What is the difference in ventilation during submaximal exercise between trn and untrn individuals?
Ventilation is 20-30% lower during submaximal exercise in trained versus untrained individuals.
What are 3 chronic training adaptations that improve aerobic capacity?
- decreased metabolite accumulation
- decreased afferent feedback
- decreased ventilatory drive
