Cardiovascular Exercise Physiology Lecture Review

A set of question-and-answer flashcards covering key cardiovascular responses and mechanisms discussed in the lecture, including VO₂ relationships, autonomic control, stroke volume, blood pressure, cardiovascular drift, vascular regulation, and the impact of heat on exercise physiology.

What equation relates whole-body VO₂ to cardiac output and the a-vO₂ difference?

The Fick equation: VO₂ = Q × (a-vO₂ difference).

In the Fick equation, what does the a-vO₂ difference represent?

The difference in oxygen content between arterial and venous blood, i.e., oxygen extracted by tissues.

During dynamic exercise, how do heart rate and stroke volume change?

Both increase, raising cardiac output.

Which branch of the autonomic nervous system primarily raises heart rate during exercise?

The sympathetic nervous system via β₁-adrenergic stimulation.

How is maximal heart rate commonly estimated?

By age using the Tanaka formula (HRmax ≈ 208 − 0.7×age).

Does endurance training significantly alter maximal heart rate?

No; HRmax is largely age-dependent.

Up to about what % of VO₂max does stroke volume rise before plateauing in untrained adults?

~50 % VO₂max (≈40–60 %).

Why can cardiac output still rise after stroke volume plateaus?

Heart rate continues to increase.

What are mechanoreceptors and how do they influence HR?

Muscle sensors detecting length/tension changes; they trigger sympathetic activation, raising HR.

What do muscle chemoreceptors detect and how do they affect cardiovascular responses?

Accumulation of metabolic by-products (CO₂, H⁺, lactate); they increase sympathetic outflow to elevate HR.

Define steady-state exercise.

Continuous, unchanging intensity where physiological variables plateau.

During steady-state submax exercise, what happens to cardiac output over time?

It rises quickly then plateaus to match O₂ demand.

What is cardiovascular drift?

Gradual ↑HR and ↓SV during prolonged (>~45 min) steady-state exercise while cardiac output stays constant.

List two primary factors in the traditional theory of cardiovascular drift.

1) Rising core temperature → sweating → plasma-volume loss; 2) Blood redistribution to skin.

According to the alternate theory, what initiates cardiovascular drift?

Increased HR from higher sympathetic drive and reduced filling time, leading to lower SV.

How does exercising in the heat influence cardiovascular drift?

It accelerates and magnifies drift due to higher sweat rates and greater skin vasodilation.

How is blood flow redistributed during exercise?

Sympathetic vasoconstriction in inactive organs plus vasodilation in active muscles and skin.

Does the proportion of cardiac output going to the heart change during exercise?

No; the fraction stays similar, but absolute flow increases.

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

It generally decreases because of widespread vasodilation.

Give the equation for mean arterial pressure (MAP).

MAP = (SBP − DBP)/3 + DBP = Q × TPR.

How does systolic blood pressure respond to increasing exercise intensity?

It rises linearly with cardiac output.

Should diastolic blood pressure change markedly during aerobic exercise?

Usually remains unchanged (±10 mmHg) because vasodilation and constriction balance.

Why does MAP rise modestly with intensity despite falling TPR?

The increase in cardiac output (and SBP) outweighs the drop in resistance.

What limits further rises in cardiac output at very high intensities?

Stroke volume plateau combined with maximal heart rate.

Define exercise hyperemia.

The exercise-induced increase in skeletal-muscle blood flow.

Name three local vasodilators that contribute to exercise hyperemia.

Nitric oxide, adenosine, prostaglandins.

What is flow-mediated vasodilation?

Vessel dilation triggered by increased shear stress or temporary occlusion to restore flow.

How does plasma volume change during prolonged exercise, especially in heat?

It decreases due to sweat loss and fluid shifts out of the vasculature.

When plasma volume falls, how is cardiac output maintained?

Heart rate increases to compensate for lower stroke volume.

During incremental exercise to max, what happens to plasma volume after the first 5–10 min?

It continues to decline with ongoing fluid loss.

Why can trained endurance athletes reach higher maximal cardiac output than untrained peers?

They have higher maximal stroke volume; HRmax is similar.

How does greater venous return enhance stroke volume via the Frank-Starling mechanism?

Increased end-diastolic volume stretches myocardium, boosting contractile force and SV.

Which receptors mediate sympathetic increases in HR and contractility?

β₁-adrenergic receptors.

What is the muscle pump and its cardiovascular effect?

Rhythmic muscle contractions compress veins, enhancing venous return and preload.

Why does very high heart rate reduce stroke volume?

Shorter diastole leaves less time for ventricular filling.

How does parasympathetic withdrawal affect HR at exercise onset?

Causes the initial rapid rise in HR up to ~100 bpm.

What is a typical resting cardiac output for an average adult?

≈5 L · min⁻¹.

By how much can cardiac output increase during maximal exercise in trained individuals?

Approximately five-fold or more (25–35 L · min⁻¹).

What is the most efficient avenue of heat loss during exercise?

Evaporation of sweat from the skin.

Around which marathon mile is the physiological “wall” commonly encountered?

Approximately mile 20, when energy stores become critically low.