S1, L9: Ventilation and ventilatory thresholds

Describe how respiration is controlled

• Central chemoreceptors - stimulated by carbon dioxide increases in cerebrospinal fluid, cause the rate and depth of breathing to increase to remove excess carbon dioxide from the body

• Peripheral chemoreceptors - in aortic and carotid bodies, sensitive to blood partial pressure of oxygen and carbon dioxide, and protons, protect against reduced oxygen pressure in inspired air

How does coordination between the respiratory and cardiovascular systems occur?

Involuntary regulation of pulmonary ventilation

How are protons (H⁺) removed from the body by ventilation?

Bicarbonate buffers protons to form carbonic acid, which splits into carbon dioxide and water to be expelled in exhalation

What other buffers are there for protons, other than bicarbonate? (3)

• Phosphocreatine

• Proteins

• Phosphate

How does ventilation influence blood pH?

• Increased ventilation results in greater carbon dioxide expiration, reducing blood PCO₂ and H⁺ concentration, increasing pH

• Decreased ventilation results in less carbon dioxide expiration, increasing blood PCO₂ and H⁺ concentration, decreasing pH

What are ventilatory thresholds?

Points during progressive exercise intensity when ventilation increases disproportionately to oxygen consumption

What is the aerobic ventilatory threshold (VT1)?

There is more carbon dioxide relative to oxygen from this point onwards

What method is used to determine VT1?

The slope method

What is the respiratory compensation point (RCP/VT2)?

• A further increase in ventilation at intensities higher than maximal lactate steady state (MLSS)

• There is even more pronounced hyperventilation from this point onwards

What does the ventilatory equivalent for oxygen show?

The volume of air that needs to be inhaled to absorb 1L of oxygen

How is the ventilatory equivalent for oxygen calculated?

V_E/VO₂

Why may ventilatory thresholds not occur at their corresponding lactate thresholds?

Ventilation could be affected by increases in core temperature, potassium, or mechanical receptors in muscles

How are blood lactate and ventilatory thresholds linked?

When lactate increases, proton concentration increases, so PCO₂ increases, therefore ventilation needs to increase to remove excess carbon dioxide

What is the advantage of using ventilatory thresholds?

Non-invasive method - no blood sampling required

What are the disadvantages of using ventilatory thresholds? (3)

• Expensive equipment - breath by breath analysis

• Mask or mouthpiece may not be tolerated well by participants - can be annoying or cause hyperventilation

• Needs to be done in a lab setting

How does training influence ventilatory thresholds?

Both absolute (L/min) and relative (% VO_{2 max}) ventilatory thresholds increase following training

Why are ventilatory thresholds a better predictor of performance than VO_{2 max}?

VO_{2 max} may remain constant throughout the season whereas VT1 and VT2 could increase during the season (+8% and +6% respectively in world class cyclists)