Cardiovascular Regulation
Exercise Physiology
McArdle, Katch, and Katch, 4th ed.
Regulation of the
Cardiovascular System
Heart Rate Regulation
Blood Flow Regulation
Heart Rate Regulation
• The heart has both intrinsic (situated within
the heart) and extrinsic (originating outside
the heart) regulation.
• Many myocardial cells have unique
potential for spontaneous electrical activity
(intrinsic rhythm).
• In normal heart, spontaneous electrical
activity is limited to special region.
• Sinoatrial node serves as pacemaker.
Intrinsic Regulation of HR
• Sino atrial node: pacemaker
Intrinsic Regulation
• Depolarization muscle membrane creates an
action potential or electrical impulse
• Impulse travels through the heart in an
established pathway
– SA node →across atria →AV node →AV
bundle →left & right bundle branches →
Purkinjie fibers → Ventricles
Normal Route of Depolarization
S-A Node

Atria

A-V Node

Bundle of His

Purkinje Fibers

Ventricles
Intrinsic Heart Rate
• SA node rate approximately 90 bpm
• Parasympathetic innervation slows rate
– referred to as parasympathetic tone
– training increases parasympathetic tone
Electrocardiogram
• The ECG is recorded by placing electrodes
on the surface of the body that are
connected to an amplifier and recorder.
• Each wave in the shape of the ECG is
related to specific electrical change in heart.
• Purposes of ECG to monitor heart rate and
diagnose rhythm.
Electrocardiogram
Each wave of ECG related to specific
electrical change in the heart
• P wave - atrial depolarization
• QRS complex - ventricular depolarization
– masks atrial repolarization
• T wave - ventricular repolarization
ECG Arrhythmias
• PACs- premature
atrial contraction
• PVCs- premature
ventricular
contraction
• Ventricular
fibrillation- cardiovert
Extrinsic Regulation of HR
• Neural Influences override intrinsic rhythm
– Sympathetic: catecholamines
• Epinephrine
• Norepinephrine
– Parasympathetic
• Acetylcholine
• Cortical Input
• Peripheral Input
Neural Regulation of HR
• Sympathetic influence
– Epinephrine  ↑HR
(tachycardia) and ↑
contractility
– Norepinephrine  general
vasoconstrictor
• Parasympathetic influence
– Acetylcholine→↓HR
(bradycardia)
– Endurance (aerobic) trg.
increases vagal dominance
Cardiac Accelerator Nerves
Sympathetic Fibers
•
•
•
•
Innervate SA node & ventricles
Increase heart rate
Increase contractility
Increase pressure
Vagus Nerve
Parasympathetic Nerve
• Innervates SA node & AV node
• Releases acetylcholine
• Slows heart rate
• Lowers pressure
Cortical Influences on Heart Rate
• Cerebral cortex impulses pass through
cardiovascular control center in medulla oblongata.
– Emotional state affects cardiovascular response
– Cause heart rate to increase in anticipation of exercise
Peripheral Influences on HR
Peripheral receptors monitor state of active
muscle; modify vagal or sympathetic
• Chemoreceptors
– Monitor pCO2, H+, pO2
• Mechanoreceptors
– Heart and skeletal muscle mechanical receptors
• Baroreceptors
Peripheral Influence on HR
• Baroreceptors in
carotid sinus and
aortic arch.
– ↑ pressure → ? HR
& contractility
– ↓ pressure → ? HR
& contractility
Blood Flow Regulation
• During exercise, local
arterioles dilate and
venous capacitance
vessels constrict.
• Blood flow is regulated
according to Poiseuille’s
Law: Flow = pressure 
resistance.
Blood Flow Regulation
• Flow = pressure gradient x vessel radius4
vessel length x viscosity
• Blood flow Resistance Factors
1. Viscosity or blood thickness
2. Length of conducting tube
3. Radius of blood vessel
Blood Flow Regulation
• 1 of every 30 or 40 capillaries is open in
muscle at rest
• Opening “dormant” capillaries during
exercise
– Increases blood flow to muscle
– Reduces speed of blood flow
– Increases surface area for gas exchange
Local Factors Resulting in
Dilation
• ↓ tissue O2 produces
potent vasodilation in
skeletal and cardiac
muscle
•
•
•
•
•
•
•
Increased temperature
Elevated CO2
Lowered pH
Increased ADP
Nitric Oxide (NO)
Ions of Mg+2 and K+
Acetylcholine
Blood Flow Neural Factors
• Sympathetic nerves (adrenergic):
norepinephrine general vasoconstrictor
• Sympathetic nerves (cholingergic):
acetylcholine vasodilation in skeletal and
cardiac muscle.
Blood Flow Humoral Factors
• Sympathetic nerves
to adrenal medulla
causes release of
epinephrine &
norepinephrine into
blood (humor).
Blood Flow Humoral Factors
Sympathetic Nerves
to
Adrenal Medulla

epi & norepi in blood

vasoconstriction
except in skeletal muscle
Neural Factors of Flow Control
Neural
Factors
Sympathetic:
norepinephrine
(adrenergic)
vasoconstrictor
Sympathetic
acetylcholine
(cholinergic)
vasodilation in muscle
Local Metabolites
more powerful than
sympathetic
vasoconstrictors
Integrated Response
Regulation from Rest to Exercise
• Rapid increase in heart rate, SV, cardiac output
– due to withdrawal of parasympathetic stimuli
– increased input from sympathetic nerves
• Continued increase in heart rate
– temperature increases
– feedback from proprioceptors
– accumulation of metabolites
Integrated Response in Exercise
Conditions
Preexercise
“anticipatory”
response
Exercise
Activator
Response
Activation of motor  HR, myocardial
cortex & higher
contractility; vasobrain.
dilation in muscle
Continued sympathetic cholinergic
outflow; alterations
in local metabolic
conditions
Continued sympathetic adrenergic
outflow
Further dilations of
muscle vasculature
Concomitant constriction of vasculature in inactive
tissues