Cardiovascular Cardiovascular PhysiologyPhysiology

Blood PressureBlood Pressure

=force exerted by the blood against =force exerted by the blood against the walls of the blood vessel; the walls of the blood vessel; Changes throughout cardiac cycleChanges throughout cardiac cycle– Systolic Blood pressure=maximal Systolic Blood pressure=maximal

pressure achieved by ventricular pressure achieved by ventricular contractioncontraction

– Diastolic Blood pressure=lowest Diastolic Blood pressure=lowest pressure remaining in blood vessels pressure remaining in blood vessels after ventricle contractsafter ventricle contracts

Blood flow - amount of blood flowing at Blood flow - amount of blood flowing at any given time. Dependent on Cardiac any given time. Dependent on Cardiac output (CO).output (CO).

Blood pressure - force per unit area Blood pressure - force per unit area exerted on wall of blood vesselexerted on wall of blood vessel

Autonomic Nervous System Autonomic Nervous System – Sympathetic – causes Sympathetic – causes

vasoconstriction of arteriolesvasoconstriction of arterioles Increases blood pressureIncreases blood pressure

– Parasympathetic – causes Parasympathetic – causes vasodilationvasodilationDecreases blood pressureDecreases blood pressure

Blood PressureBlood Pressure

Systolic pressureSystolic pressure Diastolic pressureDiastolic pressure Pulse pressure = systolic - diastolicPulse pressure = systolic - diastolic MAP = Diastolic + (Pulse pressure/3)MAP = Diastolic + (Pulse pressure/3) Hypotension - Low blood pressure Hypotension - Low blood pressure

(Nutritional, anesthesia)(Nutritional, anesthesia) Hypertension - High blood pressure Hypertension - High blood pressure

(increased peripheral resistance, high (increased peripheral resistance, high blood viscosity)blood viscosity)

Blood PressureBlood Pressure

PressurePressure

Systemic circulation-high hydraulic Systemic circulation-high hydraulic pressure required to overcome pressure required to overcome gravitational forces and resistance gravitational forces and resistance

Arteriole-vessels with high resistance Arteriole-vessels with high resistance to reduce pressure before reaching to reduce pressure before reaching capillary bedscapillary beds

Pulmonary Circulation-low pressure, Pulmonary Circulation-low pressure, due to low resistance to blood flowdue to low resistance to blood flow

Effects of High Blood PressureEffects of High Blood Pressure

Abnormally high blood pressure Abnormally high blood pressure within veins-can cause leaking of within veins-can cause leaking of fluid from blood vesselsfluid from blood vessels– Result-edemaResult-edema– Congestive heart failureCongestive heart failure

Right heart failure-leaking of fluid from vena Right heart failure-leaking of fluid from vena cavacava

– Pleural effusionPleural effusionLeft heart failure-leaking of fluid within lungs Left heart failure-leaking of fluid within lungs

– Pulmonary edemaPulmonary edema

Distribution of Blood FlowDistribution of Blood Flow

Pulmonary Circulation – 15%Pulmonary Circulation – 15% Systemic Circulation – 80%Systemic Circulation – 80%

– 65% in veins65% in veins– 10% in arteries and arterioles10% in arteries and arterioles– 5% in capillary beds5% in capillary beds

Heart – 5%Heart – 5%

Functions of the CV SystemFunctions of the CV System

Maintain blood pressure within the Maintain blood pressure within the arteriesarteries

Maintain blood flow to the tissuesMaintain blood flow to the tissues Maintain normal blood pressures Maintain normal blood pressures

within the capillaries and veinswithin the capillaries and veins

=Perfusion=Perfusion

PerfusionPerfusion

Allows delivery of oxygen and Allows delivery of oxygen and nutrients (i.e. glucose)nutrients (i.e. glucose)

Removal of waste productsRemoval of waste products– Carbon dioxideCarbon dioxide

Transport of hormonal messages Transport of hormonal messages from one part of the body to anotherfrom one part of the body to another

Forces Forces

Heart must adjust contractility Heart must adjust contractility (inotropic state) based on forces (inotropic state) based on forces working on the heart.working on the heart.– PreloadPreload– AfterloadAfterload

AfterloadAfterload

=Sum of forces the ventricles must =Sum of forces the ventricles must contract against to make blood flow contract against to make blood flow forwardforward

Increased systemic blood pressureIncreased systemic blood pressure– Increases or Decreases Afterload????Increases or Decreases Afterload????– Chronic blood pressure-increases the Chronic blood pressure-increases the

work of the heart-heart enlarges!work of the heart-heart enlarges!

PreloadPreload

=Amount of blood in the heart just =Amount of blood in the heart just prior to contraction of the ventricleprior to contraction of the ventricle

=Venous Return or amount of blood =Venous Return or amount of blood returning to the heartreturning to the heart– Leaky valves-regurgitate blood back into Leaky valves-regurgitate blood back into

the atriumthe atrium Increases or Decreases Preload??Increases or Decreases Preload??

Inotropic StateInotropic State

Adjustments in contractility based on Adjustments in contractility based on Calcium and contractile protein Calcium and contractile protein interactionsinteractions– Sympathetic tone (norepinephrine-Sympathetic tone (norepinephrine-

neurotransmitter)neurotransmitter)– Increases heart rate and contractility by Increases heart rate and contractility by

increasing Calcium availabilityincreasing Calcium availability– Starling’s law-increased contractility Starling’s law-increased contractility

with stretching of sarcomerewith stretching of sarcomere

The Cardiac CycleThe Cardiac Cycle

““Pacemakers” of the heart-send Pacemakers” of the heart-send electrical signal through heart electrical signal through heart – Systole-ventricular contractionSystole-ventricular contraction– Diastole-Heart is relaxed allowing filling Diastole-Heart is relaxed allowing filling

of the heartof the heart

**Based on Ventricle, although atria also **Based on Ventricle, although atria also contract and relax contract and relax

The Cardiac CycleThe Cardiac Cycle

End of Diastole-maximal ventricular End of Diastole-maximal ventricular fillingfilling

Electrical signal-triggers ventricular Electrical signal-triggers ventricular contraction.contraction.

Pressure in Ventricle > Atria = closes Pressure in Ventricle > Atria = closes AV valves; semilunar valves not open AV valves; semilunar valves not open yetyet

The Cardiac CycleThe Cardiac Cycle First Heart SoundFirst Heart Sound =closure of AV valves =closure of AV valves

Semilunar Valves open once pressure in Semilunar Valves open once pressure in ventricle is greater than aorta or ventricle is greater than aorta or pulmonary arterypulmonary artery

Stroke Volume = amount of blood ejected Stroke Volume = amount of blood ejected (end diastolic volume-end systolic volume)(end diastolic volume-end systolic volume)

Second Heart SoundSecond Heart Sound= Closure of the = Closure of the Semilunar valvesSemilunar valves

The Cardiac CycleThe Cardiac Cycle

Semilunar Valve-openSemilunar Valve-open AV valves-closedAV valves-closed Ventricle RelaxesVentricle Relaxes Once pressure in the ventricle is less than Once pressure in the ventricle is less than

the atrium-AV valves open allowing filling the atrium-AV valves open allowing filling of ventricleof ventricle

Third heart soundThird heart sound =passive filling of the =passive filling of the ventricleventricle– Normal to hear in horses and ruminants-not Normal to hear in horses and ruminants-not

carnivorescarnivores

Ventricular FillingVentricular Filling

Initial, rapid filling phase-passiveInitial, rapid filling phase-passive Slow-filling phase-atrial contractionSlow-filling phase-atrial contraction

Fourth heart soundFourth heart sound =atrial =atrial contractioncontraction– Normal in ruminants and equine, not in Normal in ruminants and equine, not in

carnivorescarnivores

Cardiac MuscleCardiac Muscle

Striated muscleStriated muscle Impulse from cell to cellImpulse from cell to cell Automaticity-cells can become self-Automaticity-cells can become self-

excitableexcitable– Small portion of the muscle cellsSmall portion of the muscle cells

Activation of cellActivation of cell

Depolarization=Opening of fast Depolarization=Opening of fast sodium channelssodium channels

Wave of depolarizations travels down Wave of depolarizations travels down myocardium-Ca++ channels open in myocardium-Ca++ channels open in sarcoplasmic reticulumsarcoplasmic reticulum– Crosslink of myocardiumCrosslink of myocardium

Refractory Period-resting between Refractory Period-resting between depolarization, unable to contractdepolarization, unable to contract

Cardiac Impulse PropagationCardiac Impulse Propagation

Automatic Tissues-generate action Automatic Tissues-generate action potentialspotentials

Sequence of activationSequence of activation– Sinoatrial (SA) node-fastest rate!Sinoatrial (SA) node-fastest rate!

Atrial ContractionAtrial Contraction

– AV nodeAV node– Bundle of HisBundle of His– Rt. And Lt. Bundle Branch to v. apexRt. And Lt. Bundle Branch to v. apex– Purkinje fibers to myocardiumPurkinje fibers to myocardium

Conduction PropagationConduction Propagation

Action PotentialAction Potential

THE WHOLE THE WHOLE PICTUREPICTURE

CHARGE

INSIDE CELL

TIME

Na + influx creates (+) internal charge

+

0

-

0

12

3

4Resting

cell

Depolarization

Repolarization K+ leaves

cell and cell

returns to it’s resting

or repolarized

state

**Purple numbers indicate phase numbers

Action PotentialAction Potential

0-Sodium enters cell 0-Sodium enters cell via fast channelsvia fast channels

1-fast sodium 1-fast sodium channels closechannels close

2-Ca and Na enter cell 2-Ca and Na enter cell via slow channelsvia slow channels

3-K exits cells 3-K exits cells 4- Na and K 4- Na and K

equilibriumequilibrium

Intrinsic RateIntrinsic Rate

SA node-fastestSA node-fastest AV note-40-60 bpmAV note-40-60 bpm Sympathetic and Parasympathetic Sympathetic and Parasympathetic

Nervous System-alter the intrinsic Nervous System-alter the intrinsic raterate– SNS-increase rate of depolarizationSNS-increase rate of depolarization– PNS-decrease rate of depolarizationPNS-decrease rate of depolarization

Heart Rate RegulationHeart Rate Regulation

Baroreceptors-in blood vessels and Baroreceptors-in blood vessels and heart chamberheart chamber– If blood pressure decreasesIf blood pressure decreases

Brain>>Increased Sympathetic nervous Brain>>Increased Sympathetic nervous systemsystem

Increases Heart rate and vasoconstricts to Increases Heart rate and vasoconstricts to increase blood pressureincrease blood pressure

– If blood pressure increases?If blood pressure increases?

Excitation-Contraction CouplingExcitation-Contraction Coupling

See muscle physiology!!See muscle physiology!! Ca++ influxCa++ influx Myofibrils couple via Myofibrils couple via

troponin/tropomysin complextroponin/tropomysin complex

The Electrocardiogram (ECG)The Electrocardiogram (ECG)

Recording of electrical activity of the Recording of electrical activity of the heartheart

Waves-positive vs. negative Waves-positive vs. negative depending on the direction the depending on the direction the impulse is travelingimpulse is traveling

P wave-P wave-– Atrial depolarizationAtrial depolarization

QRS complexQRS complex– Ventricular Ventricular

depolarizationdepolarization T wave-ventricular T wave-ventricular

repolarizationrepolarization

ECGECG

ConductionConduction

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