Integration

Question 1

Normal values

• HR
• Respiratory rate
• BP
• Temp
• Blood glucose

Answer 1

• HR = 60 - 80 beats/min
• Respiratory rate = 12 breaths/min
• BP = 120/80 mmHg
• Temp = 36.5 -37oC
• Blood glucose = 4 - 5.5 mM

Question 2

Dehydration and resting blood volume

Answer 2

Dehydration reduces resting blood volume

• Blood volume is 15% lower in dehydrated state

Question 3

Dehydration and body temperature

Answer 3

Dehydration increases body temperature more rapidly during exercise in the heat

Question 4

Dehydration and skin blood flow and heat loss

Answer 4

Dehydration dampens the rise in skin blood flow and heat loss

• Dehydration reduces the increase in skin blood flow
• Lower skin blood flow leads to lower rate of heat loss, greater gain in body heat content and a faster increase in body temperature.

Question 5

Fluid restriction during exercise and the effects on temperature

Answer 5

• Fluid restriction leads to dehydration and fall in blood volume
• Results in faster rise in body temperature

Question 6

Why is the rise of skin blood flow dampened when we are dehydrated during exercise

Answer 6

So the increase in vascular resistance – partly in the skin – and fall in MAP contribute to the fall in skin blood flow, reduction in heat loss and increase in body temperature.

Question 7

A fall in stroke volume contributes to the decline in cardiac output

Answer 7

• To maintain CO, heart rate increases

- The fall in stroke volume is linked to reductions in blood volume and filling of the heart (preload).

Question 8

Ventilation and cerebral blood flow

Answer 8

• Alveolar PCO2 is proportional to arterial PCO2
• Excessive breathing blows off CO2 and lowers arterial PCO2
• CO2 alters cerebral vascular tone: decrease arterial CO2 levels (PCO2 ) leads to vasoconstriction and lowers cerebral blood flow.
• Therefore, hyperventilation can reduce cerebral blood flow.

Question 9

ventilation is increased by hyperthermia

Answer 9

• A rise in body temperature of 1oC or more results in an increase in ventilation
• And MAP falls, due to a fall in stroke volume and cardiac output

Question 10

Fall in MAP and increase in ventilation cause cerebral blood flow to fall

Answer 10

• Cerebral blood flow falls progressively during ‘hyperthermia’ test by ~25 %, enough to cause symptoms (e.g., dizziness and nausea).
• Approximately half of the fall in cerebral blood flow (“MCA Vmean”) is due to the fall in MAP.
• The remainder of the fall is attributed to the fall in arterial PCO2 induced by hyperventilation