Lecture 11: Cardiorespiratory Physiology of Exercise

Question 1

How is the body able to maintain relatively constant levels of oxygen and
carbon dioxide when metabolic rate is increased during exercise?

Answer 1

By:
-precisely controlling the blood flow (perfusion) to a tissue
-ensuring that minute ventilation (the volume of air breathed per minute)
increases almost exactly in step

Question 2

Describe the mechanisms whereby blood flow to a tissue can vary according to
metabolic need.

Answer 2

Cardiac output can increase up to 4 - 7 fold.
Shunting blood flow towards the active tissue (vasodilation of exercising muscle’s vascular beds) and away from other tissues (vasoconstriction of some other vascular beds (e.g. gut).

Question 3

Describe the relative importance of increased heart rate and increased stroke volume when cardiac output increases at different exercise intensities.

Answer 3

• Heart rate progressively increases as exercise workload (and metabolic rate) increase
• Cardiac stroke volume becomes maximal during moderate intensity exercise workloads.

Question 4

How are heart rate measurements useful in determining energy

expenditure?

Answer 4

Noninvasive and nonintrusive.
• Some devices (e.g. the Actiheart system) are remarkably accurate over a
wide range of activities.
• Can monitor and record energy expenditure every minute continuously for
days or weeks.

Question 5

Why doesn’t systemic arterial blood pressure normally reach dangerously high levels during intense exercise?

Answer 5

PVR decreases markedly during exercise as a result of widespread vasodilation in the exercising muscles.
Ohm’s law:
Mean arterial blood pressure = cardiac output x PVR

Question 6

Perfusion to a tissue and metabolic needs is:

a. precisely matched
b. increased by up to 100 fold
c. Not aligned without training
d. Insufficient in individuals who are not athletes

Answer 6

a. precisely matched

Question 7

At rest, what proportion of cardiac output is received by the brain?

Answer 7

15%

Question 8

During moderate intensity exercise workloads, heart rate is:

a. maximal
b. increased to match
c. decreased

Answer 8

b. increased to match (linear relationship between exercise and heart rate)

Question 9

Work involving a relatively small muscle mass will evoke a(n) ______ blood
pressure and heart rate response than an equivalent workload involving a
large muscle mass.

a. equivalent
b. greater
c. smaller

Answer 9

b. greater

Question 10

What happens to minute ventilation at workloads above the anaerobic threshold (lactate inflection point)?

a. It decreases
b. It increases disproportionately
c. It increases steadily
d. It demonstrates a linear increase

Answer 10

b. It increases disproportionately
Because accumulation of lactic acid results in acidosis and the increased concentration
of H+ stimulates the respiratory center

Question 11

What is tidal volume?

Answer 11

The lung volume representing the normal volume of air displaced between normal inhalation and exhalation (amount of air breathed in).

Question 12

State Ohm’s law as it applies to blood pressure.

Answer 12

Mean arterial blood pressure = cardiac output x PVR
where
PVR is peripheral vascular resistance (the total resistance to blood flow in the
systemic circulation.

Question 13

True or false: respiratory frequency contributes more than tidal volume at higher levels of
minute ventilation

Answer 13

True: respiratory frequency contributes more than tidal volume at higher levels of
minute ventilation

Question 14

Define minute ventilation.

Answer 14

Minute ventilation (or respiratory minute volume or minute volume) is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person’s lungs per minute.