1PULSE AND BLOOD PRESSURE

Rhythmic expansion and recoil of an arterial wall can be felt as a pulse in an artery close to the bodys surface.

Blood pressure is the pressure of blood against the wall of a blood vessel (The force exerted by the blood against the blood vessels wall with unit area (in mmHg))

P [1mm Hg] = 133,3 Pa

Highest pressure, systolic pressure, is reached when blood ejects from the heart.

Lowest pressure, diastolic pressure is reached when the ventricles are relaxing.

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MAP and pulse pressure decrease with distance from heart Blood pressure decreases with frictionPulse pressure decreases due to elastic rebound

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Pulse Pressure: the difference between systolic and diastolic pressure (40 mmHg)

Mean arterial pressure: the arterial pressure averaged over the cardiac cycle (90-95 mmHg)

P P +13

P - P )a d s d (

Pulse Pressure & Mean Arterial Pressure

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Blood pressure = Cardiac output x Peripheral resistance

BP = CO x PR

HEMODYNAMICS

5Cardiac output (CO) is the amount of blood pumped by each ventricle per minute

CO is the product of heart rate (HR = number of heart beats per minute) times the stroke volume (SV= amount of blood pumped out by a ventricle with each beat)

CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)

CO = 5250 ml/min (5.25 L/min)

Cardiac output

BP = HR x SV x PR6

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Stroke Volume (SV)Volume of blood pumped per contraction (per heart beat)

SV = EDV ESVNormal Value60-70 mLEnd-diastolic volume (EDV)

volume of blood in ventricle before contraction

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

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Ejection Fraction (EF)

A parameter related to SV is Ejection Fraction (EF) EF is the fraction of blood ejected by the Left Ventricle (LV) during the contraction or ejection phase of the cardiac cycle

Ejection Fraction (EF) = (SV / EDV) 100%

Cardiovascular disease can be associated with increased Q as occurs during infection and sepsis, or decreased Q, as in cardiomyopathy and heart failure

Normal range 60-75% of EDV

9Cardiac Output (CO) = SV HR

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DefinitionVolume in ventricle at the end of diastole.

ORPressure exerted on walls of ventricle at the end of diastole.

Represents fluid returning to heartAlso known as filling pressure

Preload

Right ventricle preload CVP(Central Venous Pressure)

Left ventricle preload PAOP(Pulmonary Artery Occlusion Pressure)

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DefinitionAmount of pressure the ventricle must work against duringsystole to open the valve.

Afterload

Factors that increase afterload:VasoconstrictionValvular stenosis blood volumeFactors that decrease afterloadVasodilation

Right ventricle afterload PVR(Pulmonary Vascular Resistance)

Left ventricle afterload SVR(Systemic Vascular Resistance)

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Definition The resistance the left ventricle must pump against to eject its volume This resistance is created by the systemic arteries and arterioles

Systemic Vascular Resistance (SVR)

SVR => Cardiac Output SVR => Cardiac Output

Systemic Vascular Resistance (SVR) - Causes:VasoconstrictionCatacholamine releaseHypertensionCardiogenic shockCardiac tamponade

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Systemic Vascular Resistance (SVR)

Systemic Vascular Resistance (SVR) Causes:VasodilationVasodilator therapySeptic shock (hyperdynamic)

Definition The resistance the right ventricle must pump against to eject its volume This resistance is created by the pulmonary arteries and arterioles

Pulmonary Vascular Resistance (PVR)

Causes of PVRPulmonary vessel constriction due to PaO2 PaCO2Pulmonary embolus

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Definition The hearts contractile force or muscle strength

Contractility

Factors that influence contractility:Starlings LawSympathetic nervous systemPharmacologic agents

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ContractilityStarlings LawThe force of ventricular ejection is related to:The volume in the ventricle at enddiastolic (preload).The amount of myocardial stretch placed on the ventricle.

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SNS fibers are found throughout the atria and ventricles The most important regulatory factor for myocardial contractility

Sympathetic Nervous System

Cardiac plexuses:innervate heart

Vagus nerves (X):carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus

Cardiac centers of medulla oblongata:

cardioacceleratorycenter:

controls sympathetic neurons (increase heart rate)

cardioinhibitory center: controls parasympathetic neurons (slow heart rate)

Cardiac centers monitor:baroreceptors (blood pressure)chemoreceptors (arterial oxygen and carbon dioxide levels)

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Baroreceptor reflexes-Carotid sinus reflex

Receptors in carotid artery wallSensory input to cardiovascular center in medullaMaintains normal BP in the brain

-Aortic reflexReceptors in wall of ascending aortaSensory input to cardiovascular center in medullaMaintains general systemic BP

Carotid bodies and aortic bodies Detect changes in blood levels of O2, CO2, and H+ (hypoxia, hypercapnia

or acidosis ) Causes stimulation of cardiovascular center Increases sympathetic stimulation to heart & vessels Cardiac output and increase in blood pressure

Also change breathing rates

Chemoreceptor reflexes

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Factors Involved in Regulation of Cardiac Output(Blood pressure)

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Factors Affecting Stroke Volume

Changes in EDV or ESV

SV = EDV ESV

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Venous pressure and venous return

Venous pressure is very low and can not account for return of blood to heart

Factors that aid in venous return

- Venous valves prevent backflow of blood once it is squeezed past them

- Contraction of skeletal muscles squeeze Veins and push blood toward heart

- Breathing squeeze pulmonary vessels

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Peripheral Resistance

Amount of friction blood encounters through vessels (all vascular resistance within the systemic circulation)

Depends on:

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Resistance directly proportional to length of vessel and to the viscosity of the blood

Inversely proportional to 4th power of the radius of the vessel

Peripheral Resistance

Poiseulles LawR = r4

8L

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Peripheral Resistance

Total peripheral resistance is mainly determined by arterioles (6070%)Resistance and arterial blood pressure affect blood flow of organs

Poiseulles Law

R = r48L Adult vessel length is constant

Vessel diameter varies by vasodilation and vasoconstriction

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RESISTANCE TO FLOW IN THE CARDIOVASCULAR SYSTEM

Rt = R1 + R2 + R3. SERIES RESISTANCE

1/Rt = 1/R1 + 1/R2 + 1/R3 PARALLEL RES.

ARTERIOLES CAPILLARIES

LOWER R HIGHER R LOWER R

R1 R2 R3

R1

R3R2

ARTERY

Greatest R is in arterioles... ...peripheral resistance

Advantages of Parallel CircuitryIndependence of local flow control

increase/decrease flow to tissues independentlyMinimizes total peripheral resistance (TPR)Oxygen rich blood supply to every tissue

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Blood Flow & Resistance

Blood flow (Q)amount of blood flowing through organ, tissue per given time (ml/min)

Q = Volume / Time

Combination of pressure & resistance

analogy with Ohms law I =

Increased resistance decreases blood flow

VR

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Blood Flow & Poiseuilles Law

Blood flow = P/resistance = Pr48L

But vessel length (L) and blood viscosity () do not vary significantly

describe blood flow in arteries

Viscosity Viscosity reflects a resistance to flow caused by the internal friction between layers of a fluid.

The greater the viscosity, the greater the stress required to get the layers of the liquid to slide past each other and the slower the liquid will move.

Whole blood viscosity is about 4 times that of water

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Systemic circuit blood flowAortafastest flow due to

Large blood volume and close to pressure source

Capillaries low velocity flow due to Blood traveled great distance and friction slowed it down Smaller diameter increased resistance More vessels going into larger area away from the heart

(fast river, flows into lake)

Small artery and arteriole - resistance vessels are regulatedby neurohumoral factors

Veinshigh velocity Large diameter with less resistance Many capillaries converge on a vein (lake into stream) Never reach artery pressure

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Compliance

is the ability of a vessel to stretch and hold volume

Compliance = Volume / PressureIn systemic arteries a small volume is associated with a large pressure In systemic veins a large volume is associated with a small pressure

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Cardiovascular Physiology

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Hypertension can be defined as the level of blood pressure at which there is risk to the organs or vasculature.

Hypertension - Definition

Category Systolic (mmHg) Diastolic (mm Hg)optimal 180_ >110_

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Primary Hypertension - Definition

The category of hypertension when the cause is unknown.

There are probably several different genetic causes as well as a complex interplay of polygenetic and environmental factors.

Includes approximately 90% of cases.

Also referred to as essential hypertension.

Approximately 20% of all adults are affected.

Even though the underlying cause usually is not known, hypertension can usually be very effectively treated.

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Secondary Hypertension - Definition

The category of hypertension when the cause is secondaryto renal, endocrine, anatomic disorders etc.

Includes approximately 10% of cases.

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Factors that influence mean arterial pressure