Enhanced cerebral CO2 reactivity during strenuous exercise in man

Area of Science:

• Physiology
• Neuroscience
• Exercise Science

Background:

• Light to moderate exercise increases cerebral blood flow (CBF) by ~20% (middle cerebral artery mean flow velocity; MCA V(mean)).
• Strenuous exercise, especially with hyperthermia, shows a greater reduction in MCA V(mean) than explained by arterial CO2 tension (PaCO2) changes alone.

Purpose of the Study:

• To investigate if enhanced cerebrovascular CO2 reactivity contributes to the observed reduction in MCA V(mean) during exhaustive exercise.
• To evaluate the relationship between PaCO2 and MCA V(mean) under resting, exercise, and exercise with hyperthermia conditions.

Main Methods:

• Six healthy young males underwent CO2 administration and voluntary ventilation changes at rest and during exercise.
• Exercise was performed with and without induced hyperthermia.
• Cerebral CO2 reactivity was assessed by measuring MCA V(mean) using ultrasound Doppler sonography.

Main Results:

• The relationship between MCA V(mean) and PaCO2 shifted from linear at rest to curvilinear during exercise and exercise with hyperthermia.
• Cerebral CO2 reactivity significantly increased during exercise with hyperthermia compared to rest.
• A decrease in PaCO2 at exhaustion during exercise with hyperthermia, coupled with heightened CO2 reactivity, explained the observed reduction in MCA V(mean).

Conclusions:

• Cerebrovascular CO2 reactivity is enhanced during strenuous exercise, particularly under hyperthermic conditions.
• Changes in cerebral blood flow during exercise are predominantly influenced by alterations in arterial carbon dioxide tension.