Panting and Selective brain cooling

Question 1

Define thermal panting

Answer 1

Increased respiratory evaporative heat loss due to increased respiratory minute volume

Question 2

Define first phase panting; what happens to PETCO2/PaCO2

Answer 2

AKA thermal tachypnea: A rapid respiratory frequency accompanied by an increased respiratory minute volume and decreased tidal volume
- PETCO2/PaCO2 is maintained

Question 3

Define second phase panting

Answer 3

AKA thermal hyperpnea: An increased tidal volume, increased alveolar ventilation
- PETCO2/PaCO2 is decreased

Question 4

How does ventilation change relative to core temperature

Answer 4

• Ventilation increases proportionally to core temperature in humans
• i.e. as core temperature increases, ventilation increases (and PaCO2 decreases)
• Potential influence in brain to thorax temperature

Question 5

What happens to blood flow as temperature increases; how can this be measured

Answer 5

• As temperature increases, blood flow increases (to brain and working muscles)
• This can be measured with intravenous 133Xe clearance and scintillation detectors

Question 6

What is the relationship between core temperature, CO2 and phrenic nerve activity

Answer 6

• As Tc increases and PACO2 increases, phrenic nerve activity increases therefore increasing the depth of breathing

Question 7

What does selective brain cooling mean

Answer 7

• Brain and body temperature are separated during exercise/body warming, meaning the brain stays cooler than the body

Question 8

How do animals carry out selective brain cooling

Answer 8

• Countercurrent exchange via the nose and carotid rete

- Longer snout = greater SA for exchange

Question 9

what is a countercurrent heat exchange

Answer 9

• crossover of heat between two opposing flows
• Gradual decline in the temperature differential
• the once hot and cold streams exit at the reversed temperature difference

Question 10

Due to the absence of the carotid rete, what mechanisms might selective brain cooling occur in humans

Answer 10

• ventilation of the upper airways, surface cooling of sweat of the head

Question 11

What is the importance of the cavernous sinuses

Answer 11

• The only anatomical location in which an artery travels completely through a venous structure
• Located at the base of the skull

Question 12

Describe what may happen in animals when sympathetic activity is turned down/up in response to activity levels to facilitate SBC

Answer 12

• Down: Rest decreases SA, Angular oculi sphincter is relaxed via alpha R, while the facial vein sphincter is contracted via beta R. resulting in increased BF to the cavernous sinus promoting brain cooling
• Up: Exercise increases SA, angularis oculi sphincter contracts while the facial vein sphincter contracts therefore BF bypasses the cavernous sinus and inhibiting SBC

Question 13

Where are the emissary veins located; In which direction do the emissary veins drain in hyperthermia vs hypothermia

Answer 13

Connect drainage from scalp to brain
Hyperthermia: inwards
Hypothermia: Outwards

Question 14

What are three mechanisms in humans through which selective brain cooling might occur

Answer 14

• Cooling of venous blood by the skin which in turn cools the internal carotid blood supply to the brain
• Heat loss through the skull via emissary veins
• Heat loss via the upper/lower airways