Circulatory Responses to Exercise: Chapter 9

Comprehensive vocabulary flashcards covering the circulatory system anatomy, cardiac cycle, electrocardiography, hemodynamic regulation, and exercise-induced cardiovascular adjustments from Chapter 9 of SPE 325.

Cardiorespiratory System

The integrated physiological system formed by the heart, blood vessels, and lungs that works to deliver $O_2$ and nutrients to active tissues, remove $CO_2$ and metabolic waste products, and assist in regulating body temperature.

Major Blood Flow Adjustments During Exercise

The two primary cardiovascular mechanisms ensuring adequate oxygenation to working muscles during exercise: increased cardiac output (amount of blood pumped per minute) and the redistribution of blood flow from inactive viscera to active skeletal muscle.

Arteries and Arterioles

High-pressure, muscular blood vessels that transport oxygenated blood away from the heart toward systemic tissues (and deoxygenated blood to the lungs via pulmonary arteries).

Capillaries

Microscopic blood vessels that provide the site for gas exchange ($O_2$ and $CO_2$) and nutrient/waste transfer between circulating blood and surrounding tissues.

Veins and Venules

Capacitance blood vessels that collect blood from capillaries and transport it back toward the heart.

Pulmonary Circuit

The circulatory pathway powered by the right side of the heart that pumps deoxygenated blood to the lungs via pulmonary arteries and returns oxygenated blood to the left atrium via pulmonary veins.

Systemic Circuit

The circulatory pathway powered by the left side of the heart that ejects oxygenated blood to all peripheral organs and tissues via systemic arteries and returns deoxygenated blood to the right atrium via systemic veins.

Circulatory Circuits

The dual-loop vascular system consisting of the pulmonary circuit (oxygenating blood via the lungs) and the systemic circuit (delivering oxygen and nutrients to working organs and skeletal muscle).

Heart Wall Layers

The three anatomical layers enclosing the heart: the outer epicardium (visceral pericardium), the middle muscular myocardium, and the inner endothelial endocardium.

Epicardium

The serous outer protective membrane of the heart wall (visceral pericardium) containing blood capillaries, lymph capillaries, and nerve fibers that serves as a lubricative covering.

Myocardium

The muscular middle layer of the heart wall composed of cardiac muscle fibers separated by connective tissues that generates the force needed to eject blood from cardiac chambers.

Endocardium

The internal protective layer of the heart wall comprised of endothelial tissue and a thick subendothelial layer of elastic and collagenous fibers lining the heart chambers and valves.

Myocardial Infarction (MI)

Ischemic cardiac injury and myocardial cell death caused by a sudden interruption or severe blockage of blood and oxygen flow through the coronary arteries.

Intercalated Discs

Specialized cellular junctions between cardiac muscle fibers containing gap junctions that permit free ionic movement, allowing electrical action potentials to propagate across all cells simultaneously so they contract as a functional unit.

Exercise-Induced Cardioprotection

The cellular resistance to ischemia-reperfusion injury resulting from regular aerobic exercise training, which reduces myocardial infarct size by $60\%$ to $20\%$ through improved myocardial antioxidant capacity and enhanced function of ATP-sensitive potassium channels.

Systole

The contraction and ejection phase of the cardiac cycle, during which ventricular pressure exceeds arterial pressure and approximately two-thirds of the ventricular blood volume is ejected.

Diastole

The relaxation and filling phase of the cardiac cycle, during which intraventricular pressure falls below atrial pressure and the ventricles fill with blood.

Cardiac Cycle Timing (Rest vs. Heavy Exercise)

At rest ($75\,\text{beats/min}$), systole lasts $0.3\,\text{second}$ and diastole lasts $0.5\,\text{second}$; during heavy exercise ($180\,\text{beats/min}$), systole shortens to $0.2\,\text{second}$ while diastole drops disproportionately to $0.13\,\text{second}$.

First Heart Sound

The initial sound heard during cardiac auscultation ('lub'), produced by the closure of the atrioventricular (AV) valves at the onset of ventricular systole.

Second Heart Sound

The second sound heard during cardiac auscultation ('dub'), produced by the closure of the aortic and pulmonary semilunar valves at the initiation of ventricular diastole.

Systolic Blood Pressure (SBP)

The maximal arterial pressure generated during ventricular contraction and blood ejection into the aorta (normal value: $120\,\text{mmHg}$).

Diastolic Blood Pressure (DBP)

The minimal pressure maintained within systemic arteries during ventricular relaxation and cardiac diastole (normal value: $80\,\text{mmHg}$).

Pulse Pressure

The arithmetic difference between systolic and diastolic arterial blood pressure: $\text{Pulse Pressure} = \text{SBP} - \text{DBP}$.

Mean Arterial Pressure (MAP)

The time-weighted average pressure in the systemic arterial system over a complete cardiac cycle, calculated at rest as: $\text{MAP} = \text{DBP} + 0.33(\text{SBP} - \text{DBP})$.

Determinants of Mean Arterial Pressure

The physiological variables determining arterial pressure, represented by the product: $\text{MAP} = \text{Cardiac Output} \times \text{Total Vascular Resistance}$.

Primary (Essential) Hypertension

Chronic systemic hypertension with no identifiable single medical cause, attributed to multifactorial genetic and lifestyle factors, comprising approximately $90\%$ of all diagnosed cases.

Secondary Hypertension

High arterial blood pressure that arises directly as a consequence of another specific underlying medical condition or disease process, such as renal or endocrine disease.

Baroreceptor Reflex (Short-Term BP Control)

The rapid neural regulatory mechanism mediated by pressure sensors in the carotid sinus and aortic arch that modulate sympathetic and parasympathetic outflow to maintain acute blood pressure homeostasis.

Long-Term Blood Pressure Regulation

The endocrine and renal mechanism controlling arterial pressure over extended periods by adjusting blood volume through urinary fluid excretion or retention.

Sinoatrial (SA) Node

The primary intrinsic pacemaker of the heart, located in the superior-posterior wall of the right atrium, that exhibits spontaneous diastolic depolarization to initiate cardiac impulses.

Atrioventricular (AV) Node

A cluster of specialized conductive cells located in the interatrial septum that relays depolarization to the ventricles while introducing a $0.1\,\text{second}$ delay to allow complete ventricular filling.

Purkinje Fibers

The terminal arborization of the specialized ventricular conduction system that conducts action potentials rapidly through the ventricular walls to stimulate synchronized ventricular contraction.

Cardiac Conduction System

The specialized neuromuscular pathway coordinating cardiac depolarization: SA node $\rightarrow$ internodal pathways $\rightarrow$ AV node (delay) $\rightarrow$ AV bundle $\rightarrow$ bundle branches $\rightarrow$ Purkinje fibers.

Electrocardiogram (ECG)

A graphic recording of the surface electrical currents generated during atrial and ventricular depolarization and repolarization cycles of the myocardium.

P Wave

The electrocardiographic deflection produced by electrical depolarization of the atria, preceding atrial contraction.

QRS Complex

The prominent electrocardiographic waveform corresponding to ventricular depolarization, which simultaneously conceals atrial repolarization.

T Wave

The electrocardiographic deflection that represents the repolarization of the ventricles at the completion of ventricular systole.

ST-Segment Depression

A clinical abnormality on an exercise ECG where the ST segment drops below the baseline, serving as a diagnostic hallmark of exercise-induced myocardial ischemia.

Atherosclerosis

A progressive vascular pathology characterized by fibrofatty plaque buildup inside coronary arteries, which narrows the lumen, restricts myocardial blood flow, and predisposes to myocardial ischemia.

Cardiac Output ($Q$)

The total volume of blood pumped by the left ventricle into systemic circulation per minute, calculated as the product of heart rate and stroke volume: $Q = \text{HR} \times \text{SV}$.

Stroke Volume (SV)

The absolute volume of blood ejected from the left ventricle into the arterial tree with each individual cardiac contraction, measured in milliliters per beat ($\text{ml/beat}$).

Parasympathetic Withdrawal

The initial mechanism of heart rate increase at the onset of exercise (raising HR up to approximately $100\,\text{beats/min}$) through reduced vagal tone on the SA and AV nodes, before sympathetic excitation dominates.

Beta-Blockers

Antihypertensive and cardioprotective medications that competitively bind to $\beta_1$-adrenergic receptors on myocardial cells, preventing catecholamine binding and attenuating heart rate, contractility, and myocardial metabolic demand during exercise.

Heart Rate Variability (HRV)

The rhythmic variation in time intervals between successive heartbeats (standard deviation of R–R intervals), serving as an index of autonomic sympathovagal balance, where high variability indicates cardiovascular health.

End-Diastolic Volume (EDV / Preload)

The volume of blood collected inside the ventricles at the completion of ventricular diastole just prior to contraction, representing myocardial preload.

Afterload

The vascular resistance or mean arterial pressure against which the left ventricle must generate intraventricular pressure to open the aortic valve and eject blood.

Frank-Starling Mechanism

The intrinsic law of the heart stating that increased end-diastolic filling stretches the ventricular myocardium, optimizing actin-myosin overlap and triggering a more forceful contraction that elevates stroke volume.

Venoconstriction

Sympathetic constriction of the systemic venous reservoir, decreasing venous capacitance and driving an increased volume of venous blood back to the heart.

Skeletal Muscle Pump

A mechanical circulatory mechanism where rhythmic contractions of skeletal muscle compress deep veins, propelling blood toward the heart past one-way venous valves that prevent retrograde flow.

Respiratory Pump

A ventilatory mechanism that enhances venous return through inspiratory decreases in intrathoracic pressure and concurrent increases in intra-abdominal pressure that pull blood toward the right atrium.

Vascular Resistance Determinants

Physical parameters that oppose systemic blood flow, including vessel length, blood viscosity, and blood vessel radius, where radius/diameter exerts the greatest regulatory influence.

Stroke Volume Plateau

The leveling off of stroke volume at $40\%$ to $60\%$ of $\dot{V}O_2\,\text{max}$ observed in untrained individuals; by contrast, highly trained endurance athletes exhibit no plateau due to enhanced diastolic ventricular filling at high heart rates.

Skeletal Muscle Vasodilation

Local metabolic autoregulation that relaxes vascular smooth muscle in active muscle beds during maximal exercise, shifting muscle blood flow from $15\text{–}20\%$ of cardiac output at rest to $80\text{–}85\%$ at peak effort.

Double Product (Rate-Pressure Product)

A validated physiological index reflecting myocardial oxygen uptake and workload, computed as: $\text{Double Product} = \text{Heart Rate} \times \text{Systolic BP}$.

Hemodynamic Differences (Arm vs. Leg Exercise)

At any identical submaximal oxygen uptake ($\dot{V}O_2$), upper-body arm work elicits higher heart rate (due to elevated sympathetic tone) and higher arterial blood pressure (due to intense vasoconstriction across inactive lower-body muscle mass).

Cardiovascular Drift

The continuous cardiovascular response observed during prolonged submaximal steady-state exercise in warm environments, marked by a progressive drop in stroke volume (from sweat-induced dehydration) coupled with a compensatory increase in heart rate to maintain cardiac output.

Sudden Cardiac Death in Exercise

A rare exercise-related fatal event occurring in approximately $1\text{ in }200{,}000$ youth athletes, triggered by lethal arrhythmias stemming from congenital coronary anomalies, cardiomyopathies, or myocarditis in youth, and advanced coronary artery disease in adults.

Central Command Theory

The neuromuscular motor control model proposing that initial cardiovascular control signals originate from higher brain motor centers at exercise onset, with real-time modifications provided by afferent signals from arterial baroreceptors and muscle mechanoreceptors and chemoreceptors.