Cardiovascular control during exercise
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Cardiovascular Control During Exercise. Learning Objectives. Review the structure and function of the heart, vascular system and blood. How the cardiovascular system responds to increased demands during exercise.

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Learning objectives
Learning Objectives

  • Review the structure and function of the heart, vascular system and blood.

  • How the cardiovascular system responds to increased demands during exercise.

  • Explore the role of the CV system in delivering oxygen and nutrients to active body tissue.

Major cv function
Major CV Function

  • Delivery of oxygen and other nutrients

  • Removal of CO2 and other metabolic waste

  • Transport of hormones

  • Thermoregulation

  • Maintenance of acid-base balance and overall body fluid balance

  • Immune function

Components of cv system
Components of CV system

  • Heart (the pump)

  • Blood vessels (system of channels or tubes)

  • Blood (a fluid medium)


To body

From body

To lungs

From lungs

Myocardium cardiac muscle
Myocardium- Cardiac Muscle

  • Myocardial thickness varies according to amount of stress placed on it

  • Cardiac muscle fibers interconnected by intercalated disks

    • Allows for rapid transmission of action potentials for uniform contractions

  • Myocardial fibers are homogenous and contain only one fiber type (similar to type I)

Left ventricle
Left Ventricle

  • Most powerful of the four chambers

  • Must contract to pump blood through entire body (to the systemic circulation)

  • Higher the intensity of exercise, working muscles require more blood, increase need in LV to deliver blood to exercising muscles, therefore, LV will hypertrophy

Skeletal Muscle

Heart Muscle

Intercalated Discs

  • Cardiac muscle contraction occurs by “calcium-induced calcium release”

  • Calcium enters cell

  • Calcium released from SR

  • Primary blood supply to heart provided by right and left coronary arteries

  • Ability of myocardium to contract as a single unit depends on cardiac conduction system

Coronary circulation
Coronary Circulation calcium release”

Cardiac conduction system
Cardiac Conduction System calcium release”

  • Cardiac muscle is able to generate own electrical signal-spontaneous rhythmicity

  • With no neural or hormonal stimulation, intrinsic HR is ~100 bpm

  • Four main components:

    • Sinoatrial (SA) node

    • Atrioventricular (AV) node

    • AV bundle (bundle of His)

    • Purkinje fibers (terminal branches of AV bundle)

Intrinsic conduction system
Intrinsic Conduction System calcium release”

Sa node
SA Node calcium release”

  • Group of specialized cardiac muscle fibers located in upper posterior wall of right atrium

  • Where impulse for normal heart contractions is initiated

  • Known as heart’s pacemaker because generates electrical impulse at ~100 bpm

Av node
AV Node calcium release”

  • Conducts electrical impulse from atria to ventricles

  • Delayed by ~0.13 s as it passes through AV node and into AV bundle

    • Delay allows blood from atria to empty into ventricles to maximize ventricular filling before ventricles contract

Av bundle
AV bundle calcium release”

  • Runs along ventricular septum and sends right and left bundle branches into both ventricles

    • Branches send impulse toward apex then outward

  • Purkinje Fibers

    • Transmit impulse 6x faster than through rest of cardiac conduction system

Extrinsic control of the heart
Extrinsic Control of The Heart calcium release”

  • Parasympathetic nervous system (PNS)

  • Sympathetic nervous system

  • Endocrine system (hormones)

Parasympathetic nervous system
Parasympathetic Nervous System calcium release”

  • Originates in medulla oblongata and reaches heart through vagus nerve

  • Vagus nerve carries impulses to SA and AV nodes

    • when stimulated, releases acetylcholine hyperpolarization of conduction cells decrease in HR

  • Predominates at rest: “vagal tone”

  • Able to decrease HR to 20-30 bpm

Sympathetic nervous system
Sympathetic Nervous System calcium release”

  • Increases HR and contraction force of the ventricles

  • Allows HR to increase to 250 bpm

  • Predominate during physical or emotional stress (when HR >100 bpm)

  • When exercise begins, HR first increases due to withdrawal of vagal tone, then later due to SNS

Powers and Howley, calcium release”Exercise Physiology, 2004

Endocrine system
Endocrine System calcium release”

  • Catecholamines: norepinephrine and epinephrine

    • Released from adrenal medulla

  • Stimulate heart and increase its rate and contractility

  • Triggered by sympathetic nervous system during times of stress

    • Actions prolong sympathetic response

Exercise training affects on hr
Exercise Training Affects on HR calcium release”

  • Normal RHR: 60-100 bpm

  • RHR can decrease to 35 bpm with training

  • Increase parasympathetic stimulation (vagal tone) and decrease sympathetic activity

Electrocardiogram ecg
Electrocardiogram (ECG) calcium release”

  • Electrical activity of the heart can be recorded to monitor cardiac changes or diagnose potential cardiac problems

  • Electrical impulses generated in heart conducted through body fluids to skin

  • Three basic components:

    • The P wave

    • The QRS complex

    • The T wave

The p wave
The P Wave calcium release”

  • Represents atrial depolarization

  • Occurs when electrical impulse travels from SA node through atria to AV node

The qrs complex
The QRS Complex calcium release”

  • Represents ventricular depolarization

  • Occurs as impulse spreads from AV bundle to Purkinje fibers and through the ventricles

The t wave
The T Wave calcium release”

  • Represents ventricular repolarization

    • Atrial repolarization cannot be seen because it occurs during QRS complex

Phases of a resting ecg
Phases of a Resting ECG calcium release”

Cardiac arrhythmias
Cardiac Arrhythmias calcium release”

  • Disturbances in the normal sequence of cardiac events can lead to an irregular heart beat-arrhythmia

  • Bradycardia

    • RHR lower than 60 bpm

  • Tachycardia

    • RHR >100 bpm

  • In both, rhythm is normal but rate is altered

Other arrhythmias
Other Arrhythmias calcium release”

  • Premature ventricular contractions (PVCs)

    • Feeling of skipped or extra beats

    • Relatively common

    • Result from impulses originating outside of SA node

Other arrhythmias1
Other Arrhythmias calcium release”

  • Atrial flutter- atria contracts 200-400 bpm

  • Atrial fibrillation- atria contracts in rapid and uncoordinated manner

    • Both are more serious arrhythmias that cause ventricular filling problems

Other arrhythmias2
Other Arrhythmias calcium release”

  • Ventricular tachycardia- ≥3 consecutive premature ventricular contractions

    • Very serious

    • Can lead to ventricular fibrillation-contraction of ventricular tissue is uncoordinated

      • little to no blood pumped out of heart

      • cause of most cardiac deaths

Cardiac cycle
Cardiac Cycle calcium release”

  • Includes all mechanical and electrical events that occur during one heartbeat

  • Consists of chambers that undergo diastole (relaxation phase) and systole (contraction phase)

  • Diastole-chambers fill with blood, ventricles contract and send blood into aorta and pulmonary veins

Cardiac cycle1
Cardiac Cycle calcium release”

  • One cardiac spans the time between one systole to another

  • Systole (ventricular contraction) starts during the QRS complex and ends in the T wave

  • Diastole (ventricular relaxation) occurs during T wave and to next contraction

    • Heart spends more time in diastole (~2/3 of time) than in systole (~1/3 of time)

Stroke volume sv edv esv
Stroke Volume (SV=EDV-ESV) calcium release”

  • Volume of blood pumped per beat (contraction)

  • End-diastolic volume (EDV)-volume of blood in ventricle before contraction

  • End-systolic volume (ESV)-volume of blood in ventricle after contraction

  • i.e.) SV= 100ml-40ml= 60ml

Ejection fraction
Ejection Fraction calcium release”

  • Fraction of blood pumped out of left ventricle in relation to the amount of blood present before the contraction

  • EF=SV/EDV x 100

  • i.e.) EF=60ml/100ml x 100 = 60%

Cardiac output q
Cardiac Output (Q) calcium release”

  • Total volume of blood pumped by the ventricle per minute

  • Q=HR x SV

  • i.e.) Q= 60 beats/min x 70 ml/min = 4,200ml/min or 4.2L/min

Vascular system closed system
Vascular System: Closed System calcium release”

  • Arteries: transport blood away from heart to arterioles

  • Arterioles: site of greatest control of circulation by SNS (resistance vessels)

  • Capillaries: where exchange between blood and tissues occur

  • Venules

  • Veins: transport blood back to heart

Blood pressure
Blood Pressure calcium release”

  • Pressure exerted by blood on vessel walls

  • Systolic blood pressure (SBP)-highest pressure in the artery

  • Diastolic blood pressure (DBP)-lowest pressure in the artery

Blood pressure1
Blood Pressure calcium release”

  • Mean arterial pressure (MAP): average pressure

  • MAP=2/3 DBP + 1/3 SBP

  • MAP=DBP + [0.333 x (SBP-DBP)]

  • i.e.) MAP=80 + [0.333 x (120-80)] = 93mmHg

General hemodynamics
General Hemodynamics calcium release”

  • Blood flows in closed-system because of pressure gradient between arterial and venous sides

  • Pressure, Flow and Resistance

  • Blood flows from high pressure to low pressure

  • MAP in aorta = ~100 mmHg

  • MAP in right atrium = ~0 mmHg

General hemodynamics1
General Hemodynamics calcium release”

  • Blood flow is proportional to pressure difference across system and inversely proportional to resistance

  • Blood flow = ∆pressure/resistance

  • Regulation of blood flow to organs accomplished by vasoconstriction and vasodilation

Distribution of blood
Distribution of Blood calcium release”

  • Varies depending on immediate needs of a specific tissue

  • Skeletal muscle receives ~15% of blood flow at rest and up to 80% during heavy endurance exercise

  • Changes in distribution in Q controlled by SNS mainly by arteriolar diameter

Intrinsic control of blood flow
Intrinsic Control of Blood Flow calcium release”

  • Ability of local tissues to vasodilate or vasoconstrict arterioles and alter regional blood flow depending on tissue need

  • Metabolic-increased O2 demand, decreases in other nutrients, increases in by-products (CO2, K+, H+, lactic acid)

  • Endothelium mediated vasodilation: NO

Intrinsic control of blood flow1
Intrinsic Control of Blood Flow calcium release”

  • Myogenic contraction:

    • Muscle contracts in response to an increase in pressure

    • Relaxes in response to a decrease in pressure

Extrinsic neural control
Extrinsic Neural Control calcium release”

  • Redistribution at the system or body level controlled by sympathetic nerves

    • Increase in sympathetic nerve activity muscle cells contractconstricts blood vesselsdecreases blood flow

  • Sympathetic nerves keep vessels moderately constricted (vasomotor tone)

    • Redirects blood flow from areas of low need to areas of high need

Distribution of venous blood
Distribution of Venous Blood calcium release”

Most of the blood volume is in the veins at rest, particularly in the viscera

Integrative control of bp
Integrative Control of BP calcium release”

  • Normally maintained by reflexes from ANS

  • Baroreceptors: pressure sensors in aortic arch and carotid arteries

  • Chemoreceptors

  • Mechanoreceptors

Return of blood to the heart
Return of Blood to the Heart calcium release”

  • CV system requires mechanical assistance to overcome force of gravity for venous return

  • Three basic mechanisms:

    • Valves in the veins: enables unidirectional blood flow, prevents backflow and pooling of blood

    • The muscle pump

    • The respiratory pump

Muscle pump
Muscle Pump calcium release”

  • Mechanical compression of veins from skeletal muscle contraction pushes blood volume back toward heart

Blood calcium release”

  • Three most important functions to exercise and sport:

    • Transportation

    • Temperature regulation: transports heat from exercising muscle to skin to be dissipated

    • Acid-base (pH) balance

Blood volume and composition
Blood Volume and Composition calcium release”

  • Hermatocrit is the ratio of the formed elements in blood (red cells, white cells, and platelets) to total blood volume.

Red blood cells
Red Blood Cells calcium release”

  • Erythrocytes have no nucleus-cannot reproduce

  • Hematopoiesis-process of replacing red blood cells with new ones

  • Life span about 4 months

  • Transport O2 mainly bound to hemoglobin

    • Hemoglobin contains iron which binds to O2

Blood viscosity
Blood Viscosity calcium release”

  • Refers to thickness of the blood

  • The more viscous, the more resistant to flow

  • For optimal performance, a low hematocrit with normal or slightly elevated RBC count is desirable

    • Facilitates O2 transport