Pulse and Blood Pressure
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Transcript of Pulse and Blood Pressure
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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
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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
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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