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Blood PressureClinical Science Applied to Nursing

Copyright CSAN 2011 Cardiff University1Why is theory and practice of Blood Pressure important?

How can we relate it to clinical practice?ARTERIAL BLOOD PRESSURE-Too low a value of arterial blood pressure

hypotension

blood flow to the tissues will be reduced(for example to the brain and induce a faintToo high a value of arterial blood pressure

hypertension

this may cause excessive capillary pressures and damagee.g heart (myocardial infarction) kidneys, brain (stroke) and eyes

Effects of High Blood Pressure on Your BodyArtery Damage

Food for thought

4 Effects of High Blood Pressure on BodyHardening of the arteriesStrokeHeart attackKidney damageBlindness

Food for thought

5Blood Pressure and Pregnancy Gestational hypertensionThe effects of high blood pressure for mother and foetus can be dangerous.High blood pressure can: harm the mother's kidneys and other organscause low birth weight and early deliverySome mothers can develops preeclampsia which can threaten the lives of both the mother and the foetusFood for thought

Blood Pressure and ChildrenOne in three children in Wales are above a healthy weight (WAG, 2010)The Health Behaviour in School-Aged Children (HBSC) Survey found that among 13-year-olds 22% of boys and 17% of girls are classed as overweight, and 4% of boys and 2% of girls classed as obeseObese children have approximately a 3-fold higher risk for hypertension than non obese children (Sorof and Daniels, 2002).Hypertension in childhood is due to renal causes and only occasionally drug treatment (eg steroids)Food for thought

An adults blood pressure is considered high when the readings are greater than 140 mm Hg systolic or 90 mm Hg diastolic (BHS, 2004)Non-modifiable Risk Factors:Age male sex family historyPrimary cause of raised cholesterol (genetic)diabetes mellitus (autoimmune)

Modifiable Risk FactorsExcess alcohol (43 units/day)Excess salt intakeLack of exerciseEnvironmental stresssmokingOverweight (obesity) Type II -Diabetes (Type II can often coexists with obesity, dyslipidaemia, hypertension)

Food for thought

Learning OutcomesDefine blood pressureState why its important to study normal mechanism of blood pressure for example what is the effect of hypertensionState the function of blood pressureExplain how blood pressure is commonly measuredName factors that influence blood pressure.Define cardiac output and state how it is calculatedDiscuss the factors that are involved in cardiac output Describe the main control mechanism for regulation of the blood pressure

9What is Blood PressureThe blood pressure is the force that causes blood to flow through the arteries, capillaries, and finally veins back to the heart What is Blood Pressure?Blood pressure is the amount of force exerted by the blood against the walls of the blood vesselArterial Blood pressure

Blood must circulate through the body and organs to maintain lifeE.G.To carry oxygen and nutrients to the cells To remove waste products from the cellsThe Heart is the pump that circulates the blood

Pressure difference in the vascular system ensures that blood flows around the bodyThat is why pressure varies in arteries, veins and capillaries

11Arterial Blood PressureExpressed as systolic/diastolicAdultNormal 120/80 mmHgHigh 140/90 mmHgSystolic pressure (top number)Pressure generated during ventricular contractionDiastolic pressurePressure during cardiac relaxation

http://www.bhsoc.org/

12Blood PressureEach blood vessel has a blood pressure value e.g. arterial blood pressure 120 mm Hg systolic

Capillary blood pressure averages 25 mm Hg

The pressures in the pulmonary system are much lower than systemic circulation

Blood flows from an area of high to an area of low blood pressure - there must be a difference in pressure for the blood to flow.

Blood PressurePulse Pressure (PP)Difference between systolic and diastolicPP = systolic - diastolicMean Arterial Pressure (MAP)Average pressure in arteriesMAP = diastolic + 1/3 (systolic diastolic)

Blood Pressure is generated by Ventricular Contraction

Blood pressure

Blood pressure is different in blood vessels and varies from minute to minute dependant on factors such as stress

19Blood Pressure A blood pressure reading consists of two numbers:

Systolic pressure - the first, highest numberIndicates pressure when the ventricles contract to push blood out to the body

Diastolic pressure- the second, lower numberIndicates when the heart relaxes between beats

20How can we measure Blood Pressure?Blood Pressure can be measured in two ways:

Indirectly, using a sphygmomanometer and ausculating (listening) with a stethoscope, the sounds you hear are called Korotkoff sounds

Directly, using an arterial cannula (only used in Critical Care Areas, Operating Theatres).

(l00k up this reference: British Hypertension Society http://www.bhsoc.org/bp_monitors/BLOOD_PRESSURE_1784b.pdf )

21Measuring BLOOD PRESSURE External blood pressure measurements: We apply a cuff to the arm & apply pressure to the cuff to form a constricting band around the arm and around internal arteries.

The pressure in the cuff is initially above Blood pressure in the arteries as the cuff pressure falls, it meets the blood pressure & 1st Korotkof sound is heard.

When the cuff pressure falls below the blood pressure, the Korotkof sound disappears22Blood Pressure

24Making sense of what we hear

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Function of blood pressureSystemic BP maintains the essential flow of substances into and out of organs

27Function of blood pressureSystemic blood pressure maintains the essential flow of the substance into and out of the organs

Control of blood pressure especially to the vital organs is essential for the maintenance of homeostasis

Control of BP is essential for the maintenance of homeostasis

Blood flow through the vessels Blood flow through vessels is directlyproportional to thedifference in pressurebetween the endsof the tube

29Arterial Blood Pressure the driving force for blood in the circulatory systemHealthy young adults: Resting Systolic pressure = 120 mmHg Diastolic is about 80 mmHgHealthy children values vary (see Whaley & Wong 2000): Rough GuideSystolic pressure 1 7years: age in years + 90: 8-18 (2 x age in years) + 83 &

Diastolic pressure: 1-5 years 56mmHg,6-8years: age in years + 52

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Blood Pressure measurement in adultBlood Pressure in PregnancyBlood pressure during pregnancy is checked at every antenatal appointment

Blood pressure change a little over whole pregnancy. This is perfectly normal.

The pregnancy hormone progesterone relaxes the walls of blood vessels.

This causes blood pressure fall during first and second trimesters

This lower blood pressure may cause a woman to faint if they stand for too long or when getting up too quickly

Blood pressure is at its lowest between 18 and 20 weeks of pregnancy

In that period a woman will have produced an extra 1 to 2.5 litres of blood, which your heart has to pump around your body

Blood pressure returns to its pre-pregnancy levels in the last few weeks before baby is born.

What are the reasons for monitoring BP during Pregnancy

May help to identify:

High blood PressurePre-eclampsia, gestational hypertension

Blood pressure change in pregnancy?

The effects of high blood pressure range from mild to severe. High blood pressure can:

In the most serious cases, the mother develops preeclampsia which can threaten the lives of both the mother and the foetus.

Factors to consider when taking BP measurementsCold ExposureBowel/Bladder DistensionCaffeinePhysical ActivityStressMaking sense of what we hear

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36Factors which influence BPCardiac output (and venous return)Blood volume and viscosityPeripheral resistanceElasticity of the blood vessels37Cardiac Output = circulating blood volumeBlood Pressure = Blood Volume Peripheral ResistanceFactors influencing blood pressureCardiac Output = Heart Rate Stroke Volume38Cardiac output affects circulating blood volume. * Any increase in circulating blood volume * will cause a corresponding increase in cardiac output. * The increased cardiac output * will increase blood volume * causing an increase in the blood pressure. As cardiac output is determined by multiplying the heart rate times the stroke volume, * any increase in either of them * * will increase cardiac output * and effect an increase in blood pressure.* For instance, an increased heart rate due to the release of epinephrine by the adrenal glands into the blood during an emergency, * will increase blood pressure. *Factors which influence blood pressureCardiac output (CO) Total Peripheral Resistance (TPR)

Or BP = CO x TPR

39Cardiac outputCardiac Output = Heart Rate x Stroke Volume l/min bpm mL

In a healthy adult this is 70 bpm x 75mL= 5L/min 40Terms, Definitions & UnitsBP = CO x TPRCardiac Output (CO) - the amount of blood pumped by a ventricle per minute. Units may be in Liters per minute

Heart Rate (HR)- number of cardiac cycles per minute. Normal 60-100 beat per minute

Stroke Volume (mls) amount of blood pumped out of a ventricle each beat.Average resting stroke volume = 70 ml.

41Cardiac output * refers to the amount of blood pumped by a single ventricle per minute. It may be reported in milliliters or Liters per minute.Heart rate * is the number of cardiac cycles per minute. The average heart rate for adult males is from 64-72 beats/minute. The average heart rate for adult females varies from 72-80/minute.Stroke volume * refers to the amount of blood pumped out of a ventricle with each beat (contraction). The average stroke volume for an adult is around 70 ml.Knowing the heart rate and the stroke volume, one can calculate the cardiac output by simply multiplying the two. For instance, if the heart rate is 70/minute and the stroke volume is 70 ml, what would be the cardiac output?70/minute x 70ml = 4,900 ml (4.9 L.) *Factors that influence cardiac outputStroke volume the amount of blood ejected from each ventricle at each heartbeat.Heart Rate regulated by the autonomic nervous system (ANS)

Increased heart rate caused by the release of epinephrine into blood by the adrenal glands = increased cardiac output, which increases circulating blood volume, to increase blood pressure.42Stroke VolumeStroke volume is determined by three factors: PreloadAfterloadContractility 43Preload - related to the volume of blood in the ventricle at the end of diastole: - End Diastolic Volume

Factors affecting preload are:Blood volumeVenous returnThe vasomotor tone 44Factors Aiding Venous Return

Venous blood pressure alone is too low to promote adequate blood return and is aided by the:

Respiratory pump pressure changes created during breathing suck blood toward the heart by squeezing local veins

Muscular pump contraction of skeletal muscles moves blood toward heartValves prevent backflow during venous returnPreload: Factors which influence Venous return to the heartMuscle pump

Respiratory Pump

Valves in the vein 46AfterloadDescribed as the resistance against which the ventricle must work.Whilst Preload is a major determinant of myocardial contractile powerAfterload is mainly mechanical factor that affects performance 47Total Peripheral Resistance (TPR)Peripheral Vascular Resistance resistance exerted by the action of the walls of the resistance vessels impeding blood flow

most resistance is provided systemically by the arterioles,and small and medium sized arteries exert a powerful influence in the control of blood pressure.

48Factors which influence TPRThe length of the vessel the blood

The diameter of the lumen of the vessel

The viscosity of the blood 49Pulse and Mean Arterial PressuresMean arterial pressure (MAP) = Diastolic + 1/3 pulse pressureMAP is considered to be the perfusion pressure seen by organs in the body.It is believed that a MAP that is greater than 60 mm Hg is enough to sustain the organs of the average person. MAP is normally between 70 to 110 mm HgIf the MAP falls significantly below this number for an appreciable time, the end organ will not get enough blood flow, and will become ischaemicThe difference between the systolic and diastolic pressure is known as pulse pressure Pulse pressure = SystolicDiastolic

Control of Blood PressureShort term control - mainly involves: First Response by:Autonomic Nervous System. The receptors which monitors changes in BP are:Baroreceptor reflex Chemoreceptor reflexCirculating hormones(They are Responsible for maintaining BP homeostasis)Second or Indirect Adaptive Response by : Renin-angiotensin Mechanism

Long term control involves regulation of Blood Pressure by the kidneys.51

MECHANISMS OF B/P CONTROL

Higher brain stimulus

Baroreceptors

Chemoreceptors53Control of Blood PressureShort term control - mainly involves:Baroreceptor reflex Chemoreceptor reflexCirculating hormonesLong term control involves regulation Of blood Pressure by the kidneys.54

Control of the HeartVasoconstrictors and VasodilatorsVasoconstrictorsEpinephrine and NorepinephrineAngiotensin IIVasopressinVasodilatorsEDRF (NO) endothelium derived relaxing factor- is produced and released by the endothelium to promote smooth muscle relaxationCardiovascular centers of the brainstem Medulla oblongata is essential to Cardiovascular centers.

When BP Renin is released by the kidney into the blood

Renin stimulates Angiotensinogen (in lungs) to convert to Angiotensin I (mild constrictive hormone)

Angiotensin I is then converted by (ACE) Angiotensin Converting Enzyme to Angiotensin IIWhen Angiotensin II causes

1 Vasoconstriction2. Release of aldosterone from the adrenal cortex.

Prevents excretion of Na+ water in kidneys reduce water loss from circulation and this increases Blood Volume which in turn increases Blood Pressure

Second or Indirect Adaptive Response by Renin-angiotensin Mechanism BP* - Stimulates Cardioinhibitory center to heart rate & Vasomotor center to diameter. Homeostatic Blood Pressure Regulation MechanismsReflex Centers in Medulla Cardioacceleratory - increases heart rateCardioinhibitory - decreases heart rateVasomotor - changes diameter of vessels BP* - Stimulates Cardioacceleratory center to heart rate & Vasomotor center to diameter.

Baroreceptors * in aortic arch & carotid sinuses: sensitive to changes in blood pressure.

61Homeostatic mechanisms for the regulation of blood pressure include the following reflex centers in the medulla oblongata: ** the Cardioacceleratory center, which increases heart rate, * the Cardioinhibitory center, which decreases heart rate, and * the vasomotor center in the aortic arch and the carotid sinuses, which can change the diameter of the arteries and arterioles causing vasoconstriction or vasodilation.In addition to the reflex centers in the medulla, there are peripheral baroreceptors * in the walls of the aortic arch , the carotid sinuses and nearly every other elastic artery in the heck and thorax which are sensitive to changes in blood pressure. * * A sudden increase in blood pressure * will cause the Cardioinhibitory center * to decrease heart rate * and will stimulate the vasomotor center * to increase the diameter of arterioles, thus reducing the blood pressure.* A sudden drop in blood pressure noted by the baroreceptors * will stimulate the Cardioacceleratory center to increase heart rate * while stimulating the vasomotor center to decrease * the diameter of arterioles to increase blood pressure. *Anti Diuretic Hormone (ADH) Released from Posterior Pituitary gland in response to low blood volume and low BP

conserves body water by reducing the loss of water in urine

vasoconstriction of mainly Splanchnic circulation & fluid retention62WHAT is the Splanchnic circulation?Atrial Natriuretic Peptide (ANP)- released from the atria by large atrial stretchProduces diuretic responses from kidney, also vasodilation and decrease in renin release.

Fluid Exchange85% of fluid that leaves blood is returned at venous endWhat about the other 15%?

ReferencesFox S. (2009) Human Physiology, (11th Ed), McGraw-Hill International EditionSaladin K. (2010) Anatomy & Physiology, (5th Ed) McGraw-Hill International Edition Sorof J and Daniels S (2002), Hypertension. 2002;40:441

Useful website:http://www.bhsoc.org/how_to_measure_blood_pressure.stm