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BLOOD PRESSURE

Lecture – 10Dr. Zahoor Ali Shaikh

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ARTERIAL BLOOD PRESSURE

What is Blood Pressure?• It is the pressure or force exerted by the blood against

the vessel wall.Systolic Pressure - It is maximum pressure exerted in the

arteries during systole of ventricle. Average 120mm Hg.

Diastolic Pressure – Minimum pressure within the arteries during the diastole of ventricle. Average 80mm Hg.

• Unit of Measurement of BP is mm Hg.

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ARTERIAL BLOOD PRESSURE

Normal BP• Systolic - 120 (100 —140 mmHg)• Diastolic - 80 (60 – 90 mmHg)

What is Pulse Pressure ?• Difference between systolic and diastolic

blood pressure.• Normal Range - 30 to 60 mm Hg

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ARTERIAL BLOOD PRESSURE

What is Mean Arterial Blood Pressure ?• It is the average pressure which keeps blood flowing

through blood vessels throughout the cardiac cycle.• Normal B.P – 120/80 mmHg• Mean Arterial B.P = DiastolicB.P+1/3Pulse pressure = 80 + 1/3 × 40 = 93.3mmHg• It is Mean Arterial Blood Pressure that is regulated

in the body.

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BLOOD PRESSURE [BP]

• Routine BP measurements record systolic and diastolic blood pressure, which is used to assess the Mean Arterial Blood Pressure.

• We use instrument Sphygmomanometer to take the blood pressure.

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DETERMINANTS OF MEAN ARTERIAL PRESSURE

Mean Arterial Pressure = Cardiac Output × Total Peripheral Resistance• Cardiac Output depends on Stroke Volume

and Heart Rate. CO = SV × HR

• We have discussed the Cardiac Output.

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PERIPHERAL RESISTANCE

• Total Peripheral Resistance depends on Radius of all arterioles and blood viscosity.

• Arteriolar radius is more important and influenced by intrinsic metabolic factors which control blood flow.

• It is also influenced by extrinsic control that is sympathetic activity, vasopressin and angiotensin II, which are vasoconstrictors.

• We have discussed factors affecting the Radius of arteriole.

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REGULATION OF BLOOD PRESSURE1. Short Term {Operates in seconds} – Baroreceptors – Chemoreceptors – CNS Ischemic Response

2. Intermediate {Operates in Minutes} – Renin-Angiotensin-Aldosterone Mechanism

3. Long Term {Operates in few hours to days} – Kidney- Regulation of Na+ and H2O

Two Important Mechanisms are: 1- Baroreceptor Reflex 2- Renin-Angiotensin Mechanism

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MECHANISM FOR REGULATION OF ARTERIAL PRESSURE

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BLOOD PRESSURE REGULATION

• We will discuss Short Term Mechanisms:

BARORECEPTORS Baroreceptors are stretch receptors present in

the walls of blood vessels—CAROTID SINUS and AORTIC ARCH, for short term regulation of B.P.

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BLOOD PRESSURE REGULATION

BARORECEPTORS• If blood pressure changes that is, increases or

decreases Baroreceptors try to bring it back to normal value by adjusting cardiac output and peripheral resistance by working through ANS influences on heart, veins and arterioles.

• They work in seconds.• Baroreceptors reflex is very important for

regulation of Mean Arterial Pressure.

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BLOOD PRESSURE REGULATIONBARORECEPTOR REFLEX

• It has following components: Receptors Afferent Pathway Center Efferent Pathway Effector Organ

RECEPTORS – Carotid Sinus and Aortic Arch, they are nerve endings and generate action potential in response to pressure present in the arteries.

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BARORECEPTOR REFLEXAfferent Pathway – Afferent nerve which carry impulse from carotid

sinus is IX [Glassophyrangeal] and from aortic arch is X [Vagus].Center – Cardiac Center is located in medulla [brain stem].

Efferent Pathway – From Cardiac center, we get Efferent ANS, Sympathetic and Parasympathetic fibers to heart and blood vessels.

Effector Organ – Sympathetic causes increase heart rate and force of contraction of heart, vasoconstriction, therefore, increase CO and BP.

Parasympathetic causes decrease heart rate, decrease force of contraction of heart, therefore, decreased cardiac output

and decreased BP.

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CHEMORECEPTORS

• They are located in the carotid artery and aorta.• They are called Carotid body and Aortic body.• They are sensitive to low O2 and increased CO2

and increased H+ ion in blood.• They are mainly for the regulation of respiration

but reflexly increase blood pressure by sending excitatory impulses to cardio vascular center in medulla.

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CNS ISCHEMIC RESPONSE

• CNS Ischemia occurs when blood pressure is very low [below 60 mmHg], there is increased sympathetic discharge from cardiac center in medulla to increase blood pressure.

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RENIN-ANGIOTENSIN SYSTEM

• It works in minutes and fully active in 20mins.• Renin is enzyme released by kidneys when

arterial blood pressure becomes low.• Renin is synthesized by Juxta glomerular [JG

cells] of the kidneys.• Renin enters the blood and acts on

Angiotensinogin.

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FACTORS AFFECTING BLOOD PRESSURE

• BLOOD PRESSURE is affected by the following factors: - Age – BP increases with age - Sex - Height, Weight - Posture—Supine, Standing - Emotions - Exercise – there is increased cardiac output and decrease in

peripheral resistance, {due to vasodilation in skeletal muscle}, therefore systolic BP increases and diastolic BP decreases. Pulse pressure is increased.

- Ethnic Background

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APPLIEDHypertension [High BP]

• Mild — 140-160/90-100mmHg• Moderate — 160-180/100-110mmHg• Severe — 180-200/110-120mmHg• Malignant — When Diastolic BP > 140mmHg• Blood Pressure should be measured on more

than Two occasions to make high blood pressure.

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HYPERTENSION

• Primary or Essential Hypertension—90% Cause is Not known.

• Secondary Hypertension—10% Renal Cause—80% Endocrine Cause—5%

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PRIMARY HYPERTENSION• Life Long Drugs are advised.Aetiology – although cause is NOT known, but Genetic Factors, Positive Family History may be there.

Factors which worsen the Hypertension: - Obesity - Increased Sodium Intake - Smoking - Stress - Increased Alcohol Intake

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SECONDARY HYPERTENSION

• When increased B.P is due to other known problem.Causes Of Secondary Hypertension1. RENAL DISEASES• E.g. Diabetic Nephropathy• Adult Polycystic Kidney Disease• Renal Artery Stenosis

2. CARDIOVASCULAR CAUSE• E.g. Coarctation Of Aorta

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Causes Of Secondary Hypertension

3. ENDOCRINE CAUSES• E.g. Pheochromocytoma• Conn Syndrome• Cushing Syndrome

4. DRUGS• E.g. Oral Contraceptive Pill

5. PREGNANCY• PRE-ECLAMSIA - Increased BP during 2nd half of pregnancy

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Hypertension Complications

• Eye -- Retinal Changes• Chronic Renal Failure• Heart Failure• C V A (Cerebro Vascular Accidents)

IMPORTANT Hypertension may be detected on routine examination. WHY? Because Hypertension may be symptomless, until complication occur.

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PRE-HYPERTENSION• Normal BP 120/80• Hypertension 140/90• Now we use the word Pre-Hypertension when systolic is between 120

to 140 and diastolic is between 80 to 90.Advice for Pre-Hypertension• Diet • ExerciseAdvice for Hypertension• Diet • Exercise• Medication – Angiotensin Converting Enzyme Inhibitors, Vasodilator,

Diuretic, Beta-blocker, Calcium blocker

BLOOD PRESSURE PRACTICAL

• Normal BP = 120/80 mmHg (In Adults)• Range Systolic = 100-140 mmHg Diastolic = 60-90 mmHg• Equipment Stethoscope Sphygmomanometer A Bicycle ergometer and/or a treadmill

• Methods Of Measurement BP 1-Palpatory Method 2-Ausculatatory Method Note: Palpatory method gives estimate of Systolic BP only• Ausculatory method allows Both Systolic and Diastolic BP to be measured.• KOROTKOFF Sounds• Laminar Flow, Turbulent Flow

We will discuss in Practical.

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WHAT YOU SHOULD KNOW FROM THIS LECTURE

• Definition of Blood Pressure• Normal Value for Blood Pressure• Pulse Pressure• Mean Arterial Blood Pressure• Factors which determine Blood Pressure {CO × Peripheral Resistors}• Factors which regulate Blood Pressure• Baroreceptor, Renin-Angiotensin Mechanism• Hypertension – Primary & Secondary

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