How does the ventilatory equivalent for oxygen (VE/VO2) change across exercise intensities, and what does an increasing value indicate?

How does the ventilatory equivalent for oxygen (VE/VO2) change across exercise intensities, and what does an increasing value indicate?

• A. VE/VO2 remains constant across intensities
• B. VE/VO2 decreases at lower intensities and rises at higher intensities; an increase indicates less efficient oxygen use and ventilatory compensation due to metabolic acidosis
• C. VE/VO2 decreases as intensity increases
• D. VE/VO2 increases at all intensities

Answer: (B)

The key idea is that the ventilatory equivalent for oxygen (VE/VO2) tells us how much air we have to breathe to use a given amount of oxygen. If this ratio is low, oxygen use is more efficient—you’re getting O2 with less ventilation. If the ratio rises, you’re ventilating more air for each liter of O2 consumed, meaning oxygen use is less efficient. Early in exercise, breathing becomes more efficient as you move from rest to light/moderate work: VO2 increases with workload, but ventilation increases in a way that doesn’t require a proportional jump in air to deliver that oxygen, so VE/VO2 tends to fall. As exercise intensity climbs further, lactate starts to accumulate and the body buffers hydrogen ions, producing CO2. The drive to blow off this excess CO2 causes ventilation to rise disproportionately to VO2, so VE/VO2 increases. This rise reflects ventilatory compensation for metabolic acidosis and indicates less efficient oxygen use at high intensities.

The key idea is that the ventilatory equivalent for oxygen (VE/VO2) tells us how much air we have to breathe to use a given amount of oxygen. If this ratio is low, oxygen use is more efficient—you’re getting O2 with less ventilation. If the ratio rises, you’re ventilating more air for each liter of O2 consumed, meaning oxygen use is less efficient.

Early in exercise, breathing becomes more efficient as you move from rest to light/moderate work: VO2 increases with workload, but ventilation increases in a way that doesn’t require a proportional jump in air to deliver that oxygen, so VE/VO2 tends to fall. As exercise intensity climbs further, lactate starts to accumulate and the body buffers hydrogen ions, producing CO2. The drive to blow off this excess CO2 causes ventilation to rise disproportionately to VO2, so VE/VO2 increases. This rise reflects ventilatory compensation for metabolic acidosis and indicates less efficient oxygen use at high intensities.