Cardiovascular Exercise Physiology – Acute & Prolonged Responses

A set of question-and-answer flashcards reviewing key concepts on cardiovascular responses to acute, prolonged, and heat-stressed exercise.

What equation relates VO₂ to cardiac output and a-vO₂ difference during exercise?

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

During incremental aerobic exercise, how does whole-body oxygen consumption change relative to intensity?

It increases proportionally to exercise intensity.

Which two variables increase to raise cardiac output during exercise?

Heart rate and stroke volume.

Which branch of the autonomic nervous system primarily elevates heart rate and contractility during exercise?

The sympathetic nervous system.

Which adrenergic receptor subtype on the heart mediates the sympathetic increase in heart rate and force?

β₁ (beta-1) receptors.

How does heart rate respond to increasing exercise intensity?

It rises linearly with intensity until maximal effort.

At approximately what percentage of VO₂max does stroke volume plateau in untrained individuals?

Around 50 % VO₂max (≈40–60 % range).

Why can cardiac output continue to rise after stroke volume plateaus?

Because heart rate continues to increase.

Which formula is commonly used to estimate maximal heart rate?

An age-predicted equation, e.g., HRmax ≈ 208 – 0.7 × age (Tanaka formula).

How does training status affect maximal heart rate?

Training has little to no effect; max HR is largely age-dependent.

What are mechanoreceptors and how do they influence cardiovascular responses to exercise?

Stretch/tension receptors in muscle that signal the brain to increase sympathetic activity, raising heart rate when muscles contract.

Which metabolic by-products stimulate muscle chemoreceptors during exercise?

CO₂, H⁺ (lower pH), lactate and other metabolites.

Define steady-state exercise.

Constant sub-maximal intensity where HR, SV, and cardiac output reach plateaus.

What is cardiovascular drift?

A gradual rise in heart rate and fall in stroke volume during prolonged (> ≈45 min) steady-state exercise while cardiac output stays constant.

Identify two proposed mechanisms behind cardiovascular drift.

1) Fluid loss & peripheral vasodilation reduce preload → ↓SV → ↑HR; 2) Rising sympathetic drive shortens filling time → ↑HR, forcing ↓SV.

What is typical resting cardiac output and how much can it increase in endurance-trained athletes?

~5 L·min⁻¹ at rest, rising to ≥25 L·min⁻¹ at maximal exercise.

List the three primary determinants of stroke volume.

Preload, afterload, and myocardial contractility.

At low exercise intensities, which mechanism mainly augments stroke volume?

The Frank-Starling mechanism (greater preload/stretch increases force of contraction).

How is blood flow redistributed during dynamic exercise?

Increased to skin and active skeletal muscles; decreased to GI tract, kidneys, and liver.

Express mean arterial pressure (MAP) in terms of systemic variables.

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

Why does systolic blood pressure rise during exercise?

Because cardiac output increases with intensity.

Why does diastolic blood pressure usually remain unchanged during aerobic exercise?

Balanced vasoconstriction in inactive beds and vasodilation in active beds keeps total peripheral resistance relatively stable.

What happens to total peripheral resistance during aerobic exercise and why?

It decreases due to widespread vasodilation in active muscle and skin.

Name three local vasodilators released in exercising muscle.

Nitric oxide, adenosine, and prostaglandins.

What term describes the large increase in muscle blood flow during exercise?

Exercise hyperemia.

Describe flow-mediated vasodilation.

Vessel dilation that occurs after temporary occlusion; when flow resumes, endothelial signals cause marked dilation.

How does exercising in the heat affect stroke volume and heart rate?

Heat-induced fluid loss lowers stroke volume, so heart rate rises further to maintain cardiac output.

Which two adrenergic receptor subtypes regulate vascular tone during exercise?

α₁ receptors cause vasoconstriction in inactive tissue; β₂ receptors cause vasodilation in active muscle.

What is the typical time frame when cardiovascular drift becomes evident?

After roughly 45 minutes of steady-state exercise (sometimes as early as 15–20 min).

Why can prolonged, intense endurance events lead to a "physiological wall"?

Combined fuel depletion and cardiovascular limits (dehydration, HR/SV alterations) eventually reduce the ability to sustain required cardiac output.