Cardiovascular Regulation

Exercise PhysiologyMcArdle, Katch, and Katch, 4th ed.

Regulation of theCardiovascular 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 Factors1. 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

S ym p ath e tic :n o rep in ep h rin e

(ad ren erg ic )vasocon s tric to r

S ym p ath e ticace tylch o lin e(ch o lin e rg ic )

vasod ila tion in m u sc le

L oca l M etab o litesm ore p ow erfu l th an

sym p ath e ticvasocon s tric to rs

N eu ra lF ac to rs

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 ExerciseConditions Activator ResponsePreexercise

“anticipatory”response

Activation of motorcortex & higherbrain.

HR, myocardialcontractility; vaso-dilation in muscle

Exercise

Continued sympa-thetic cholinergicoutflow; alterationsin local metabolicconditions

Further dilations ofmuscle vasculature

Continued sympa-thetic adrenergicoutflow

Concomitant con-striction of vascula-ture in inactivetissues