L4.3 Respiratory Systems

Question 1

What are the respiratory responses to exercise?

Answer 1

• Maintain CaO2 saturation
• Remove CO2
• Acid-base balance (by↓CO2)
• Fluid & temp balance (air breathed out = hot & humid → slight heat loss and fluid loss)
  
  • Problem at high altitudes, ↑ventilations ∴ ↑water loss

Question 2

What is ventilation?

Answer 2

Ventilation = frequency (main determinant) x TV

Question 3

How does ventilation vary according to exercise intensity?

Answer 3

• ↑exercise → ↑ventilation (↑exponentially → plateaus)
• Stop exercise → rapid ↓ventilation (implies neural control) followed by slow decline (chem – CO2, O2, pH – control)
  
  • ↑aerobic exercise → ↑CO2 production
• At ↑↑VO2 → ↓PCO2 due to ↑↑ventilation (ventilation also ↑ by ↓pH, ↑lactic acid, glycolysis)

Question 4

What is the basal gas exchange pressures?

And in high altitudes?

Answer 4

• Basal rates:
  
  • Inspired O2 : 150mHg
  • PAO2: 100mmHg
  • PVO2 : 40mmHg
  • PACO2: 46mmHg
• Difference in O2 pressures → allows diffusion at arterial end and equilibrates
• High altitude:
  
  • Inspired O2: ~50mmHg → limited diffusion
  • Causes hypoxemia → harder to exercise

Question 5

What is the gas exchange pressure during exercise?

Answer 5

• PvO2: ~20-25mmHg → ↑diffusion gradient and equilibrates
• Lungs don’t get bigger when trained, but heart does (↑output)
  
  • ∴↑training → ↑Q → blood perfusion → ↓transit time → hard to diffuse and equilibrate, CaO2 desaturated
    
    • Results in exercise-induced arterial hypoxemia (EIAH)

Question 6

What are the characteristics of EIAH?

Answer 6

• Alveolar-arterial O2 difference
• VA/Q inequality
• Diffusion limitations (↓transit time) due to ↑↑Q but same morphology in lungs (Major limitation)
• Expiratory flow limitation
• Shift in O2 dissociation curve – harder to load haemoglobin
• Contributes to significant muscle fatigue (not enough O2 to muscles)

Question 7

Can exercise induce diaphragmatic fatigue?

Answer 7

• Diaphragm stimulated through phrenic nerve
  
  • Contracts to create pressure difference
• Trans-diaphragmatic pressure (pressure difference btw thorax & abdomen)
• Diaphragm fatigues post exercise

Question 8

Respiratory muscles can consume up to 15% of VO2 max and Q, this results in a muscle metaboreflex.

What is the muscle metaboreflex?

Answer 8

• Type 3 & 4 afferent fibres → from fatiguing diaphragm → brain → inhibits blood flow to locomotive muscles → muscles fatigue → Q supply brain & prevent hypoxemia

Question 9

How is respiration controlled?

Answer 9

• Mainly in pons, some medullary and central command roles
• Chemoreceptors (central & peripheral)
• Lung stretch receptors
• Type 3 & 4 afferent fibres in muscles & diaphragm
• Mechanoreceptors

Question 10

What drives ventilation (exercise hyperpnea) during exercise?

Answer 10

• Activate motor cortical
• Limb muscle afferents (type 3 & 4 – important during med intensity → makes sure O2 supply and demands are aligned,↓during high intensity, spindles)
• Venous CO2 flux to lungs (major determinant)
• ↑K+, H+, lactate → drives hyperventilation
• O2 has no role controlling ventilation during exercise

Question 11

What is the effect of training on the respiratory system?

Answer 11

• Right shift in ventilation curve
• Not much difference in max ventilation
• Lower lactate (Spare glycogen)
• Lower K+ responses – protect K+ levels (↑Na+/K+ pumps from training)
• Delayed ↓pH

Question 12

How is the effect of training achieved?

Answer 12

• ↓blood lactate/H+
• ↓plasma K+, plasma catecholamines
  
  • ∴muscles afferents
• ↓central drive