Cardiovascular Exercise Physiology – Lecture Review

These flashcards cover the acute cardiovascular responses to exercise, including the Fick equation, heart rate and stroke volume behavior, blood pressure dynamics, cardiovascular drift, thermoregulatory effects, autonomic control, and vascular adaptations discussed in the lecture.

What equation relates VO₂ to cardiac output and oxygen extraction during exercise?

The Fick equation: VO₂ = Cardiac Output (Q) × (arterial-venous) O₂ difference.

What does the (a-v)O₂ difference represent?

The amount of oxygen extracted by the tissues – the O₂ content difference between arterial and venous blood.

Which two variables determine cardiac output (Q)?

Heart rate (HR) and stroke volume (SV).

Which branch of the autonomic nervous system increases HR and contractility during exercise?

The sympathetic nervous system via epinephrine and norepinephrine acting on β₁ receptors.

How does heart rate respond to rising exercise intensity?

It increases linearly until near maximal effort.

At about what percentage of VO₂max does stroke volume usually plateau in untrained people?

Around 50 % VO₂max (≈40–60 %).

Why can cardiac output still rise after stroke volume plateaus?

Because heart rate continues to climb.

What formula is commonly used to estimate maximal heart rate?

Tanaka formula: HRmax ≈ 208 − (0.7 × age in years).

How much does endurance training affect maximal heart rate?

Very little; HRmax is largely age-determined.

How does endurance training affect maximal stroke volume?

Training increases SV, allowing a higher maximal cardiac output.

What is preload?

The end-diastolic volume or stretch on the ventricular walls before contraction.

What is afterload?

The resistance the heart must overcome to eject blood (arterial pressure).

State the Frank-Starling mechanism.

Greater ventricular stretch (higher preload) increases force of contraction, raising stroke volume.

What are mechanoreceptors and how do they influence HR?

Muscle receptors sensing length/tension changes; they trigger sympathetic activation to raise HR when muscles contract.

What do muscle chemoreceptors detect during exercise?

Accumulation of metabolic by-products (CO₂, H⁺, lactate) that stimulate sympathetic drive.

Define steady-state exercise.

A constant submaximal workload where VO₂, HR, SV, and Q reach plateaus.

What is cardiovascular drift?

A gradual rise in HR and fall in SV during prolonged (>40 min) steady-state exercise while Q remains stable.

Explain the traditional cause of cardiovascular drift.

Increased core temperature → more sweating & skin blood flow → reduced plasma volume & venous return → lower SV → HR rises to keep Q constant.

What is the alternative theory for cardiovascular drift?

Greater sympathetic outflow and reduced filling time elevate HR first, leading to a compensatory drop in SV.

During aerobic exercise, how is blood flow redistributed?

Vasodilation directs more blood to working muscles and skin, while vasoconstriction limits flow to GI tract, kidneys, and liver.

Does the proportion of Q reaching the heart itself change during exercise?

No; the percentage stays the same, but absolute coronary flow rises because Q is higher.

What happens to total peripheral resistance (TPR) during dynamic aerobic exercise?

TPR decreases due to widespread vasodilation in active tissues and skin.

Write the relationship between mean arterial pressure (MAP), cardiac output, and TPR.

MAP = Cardiac Output × Total Peripheral Resistance (MAP = Q × TPR).

How does systolic blood pressure respond to increasing aerobic intensity?

It rises proportionally with cardiac output and then plateaus near maximal work.

How does diastolic blood pressure usually respond to dynamic aerobic exercise?

It remains unchanged or changes minimally because vasodilation and vasoconstriction balance each other.

Why does MAP rise only modestly during aerobic exercise?

The fall in TPR offsets the rise in Q, and DBP stays fairly constant.

What is exercise hyperemia?

The large increase in skeletal-muscle blood flow during exercise due to metabolic vasodilation and the muscle pump.

Name three local vasodilators released during exercise.

Nitric oxide, adenosine, and prostaglandins.

How does exercising in a hot environment affect stroke volume?

SV falls because plasma volume drops and more blood is sent to the skin.

How is cardiac output maintained when stroke volume falls in the heat?

Heart rate rises further (higher cardiovascular strain).

Why may arterial blood pressure decline slightly during prolonged exercise in the heat?

Extensive skin vasodilation lowers TPR, sometimes outpacing the rise in Q.

Define flow-mediated vasodilation.

Dilation that occurs after transient flow reduction; restored flow stimulates endothelial NO release, enlarging the vessel.

Give typical resting and maximal cardiac output values for a trained athlete.

Rest ≈ 5 L·min⁻¹; maximal exercise ≥ 25 L·min⁻¹ (five-fold or more increase).

Why does very high HR limit stroke volume?

Shortened diastolic filling time reduces preload, lowering SV.

Which autonomic change causes the initial rapid HR rise at exercise onset?

Withdrawal of parasympathetic (vagal) tone, followed by sympathetic activation.