Transcript Blood Pressure - Learning Central

Clinical Science Applied to Nursing
Copyright CSAN 2011 Cardiff University
 Why is theory and practice of Blood Pressure
important?
 How can we relate it to clinical practice?
ARTERIAL BLOOD PRESSUREToo low a value of
arterial blood
pressure
hypotension
blood flow to the
tissues will be
reduced
(for example to the
brain and induce a
faint
Too high a value of arterial
blood pressure
hypertension
this may cause excessive
capillary pressures and
damage
e.g heart (myocardial
infarction) kidneys, brain
(stroke) and eyes
Food
for
thought
Effects of High Blood Pressure on Your Body
 Artery Damage
Food for
thought
Effects of High Blood Pressure on Body
 Hardening of the
arteries
 Stroke
 Heart attack
 Kidney damage
 Blindness
Food for
thought
Blood Pressure and Pregnancy
 Gestational hypertension
 The effects of high blood pressure for mother and
foetus can be dangerous.
 High blood pressure can:
 harm the mother's kidneys and other organs
 cause low birth weight and early delivery
 Some mothers can develops preeclampsia which
can threaten the lives of both the mother and the
foetus
Food
for
thought
Blood Pressure and Children
 One 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 obese
 Obese 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 adult’s 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 history
 Primary cause of raised
cholesterol (genetic)
 diabetes mellitus
(autoimmune)
Modifiable Risk Factors
 Excess alcohol (43
units/day)
 Excess salt intake
 Lack of exercise
 Environmental stress
 smoking
 Overweight (obesity)
 Type II -Diabetes
(Type II can often coexists with
obesity, dyslipidaemia,
hypertension)
Learning Outcomes
 Define blood pressure
 State why its important to study normal mechanism of blood
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pressure – for example what is the effect of hypertension
State the function of blood pressure
Explain how blood pressure is commonly measured
Name factors that influence blood pressure.
Define cardiac output and state how it is calculated
Discuss the factors that are involved in cardiac output
Describe the main control mechanism for regulation of the blood
pressure
What is Blood Pressure
 The 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 vessel
 Arterial Blood pressure
 Blood must circulate through the body and organs to maintain life
E.G.
To carry oxygen and nutrients to the cells
To remove waste products from the cells
 The Heart is the pump that circulates the blood
 Pressure difference in the vascular system ensures that blood
flows around the body
That is why pressure varies in arteries, veins and capillaries
Arterial Blood Pressure
 Expressed as systolic/diastolic
 Adult
 Normal – 120/80 mmHg
 High – 140/90 mmHg
 Systolic pressure (top number)
 Pressure generated during ventricular contraction
 Diastolic pressure
 Pressure during cardiac relaxation
http://www.bhsoc.org/
Blood Pressure
 Each 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 Pressure
 Pulse Pressure (PP)
 Difference between systolic and diastolic
 PP = systolic - diastolic
 Mean Arterial Pressure (MAP)
 Average pressure in arteries
 MAP = 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
Blood Pressure
 A blood pressure reading consists of two numbers:
 Systolic pressure - the first, highest number
 Indicates pressure when the ventricles contract to push blood
out to the body
 Diastolic pressure- the second, lower number
 Indicates when the heart relaxes between beats
How can we measure Blood Pressure?
Blood Pressure can be measured in two ways:
1.
Indirectly, using a sphygmomanometer and
ausculating (listening) with a stethoscope, the sounds
you hear are called Korotkoff sounds
1.
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 )
Measuring 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 disappears
Blood Pressure
Making sense of what we hear
Function of blood pressure
 Systemic BP maintains the essential flow of substances into and
out of organs
Function of blood pressure
 Systemic 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 directly
proportional to the
difference in pressure
between the ends
of the tube
Arterial Blood Pressure the driving force for blood in the circulatory
system
Healthy young adults: Resting
Systolic pressure = 120 mmHg
Diastolic is about 80 mmHg
Healthy children values vary (see Whaley & Wong 2000):
Rough Guide
Systolic pressure
 1 –7years: age in years + 90:
 8-18 (2 x age in years) + 83 &
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Diastolic pressure:
1-5 years 56mmHg,
6-8years: age in years + 52
Blood Pressure measurement in adult
Blood Pressure in Pregnancy
 Blood 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 Pressure
 Pre-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 measurements
Cold Exposure
Bowel/Bladder Distension
Caffeine
Physical Activity
Stress
Making sense of what we hear
Factors which influence BP
Cardiac output (and venous
return)
Blood volume and viscosity
Peripheral resistance
Elasticity of the blood vessels
Factors influencing blood pressure
Blood Pressure = Blood Volume × Peripheral Resistance
Cardiac Output = circulating blood volume
Cardiac Output = Heart Rate × Stroke Volume
Factors which influence blood pressure
 Cardiac output (CO)
 Total Peripheral Resistance (TPR)
Or
BP = CO x TPR
Cardiac output
Cardiac Output = Heart Rate x Stroke Volume
l/min
bpm
mL
In a healthy adult this is 70 bpm x 75mL= 5L/min
Terms, Definitions & Units
BP = CO x TPR
 Cardiac 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.
Factors that influence cardiac output
 Stroke 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.
Stroke Volume
Stroke volume is determined by
three factors:
Preload
Afterload
Contractility
Preload
- related to the volume of blood in the ventricle
at the end of diastole:
- End
Diastolic Volume
Factors affecting preload are:
•
•
•
Blood volume
Venous return
The vasomotor tone
Factors 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 heart

Valves prevent backflow during
venous return
Preload: Factors which influence Venous
return to the heart

Muscle pump

Respiratory Pump

Valves in the vein
Afterload
 Described as the resistance against which
the ventricle must work.
 Whilst Preload is a major determinant of
myocardial contractile power
 Afterload is mainly mechanical factor
that affects performance
Total 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.
Factors which influence TPR
The length of the vessel the blood
The diameter of the lumen of the vessel
The viscosity of the blood
Pulse and Mean Arterial Pressures
 Mean arterial pressure (MAP) = Diastolic + 1/3 pulse
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pressure
MAP 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 Hg
If the MAP falls significantly below this number for an
appreciable time, the end organ will not get enough blood
flow, and will become ischaemic
The difference between the systolic and diastolic pressure
is known as pulse pressure
Pulse pressure = Systolic–Diastolic
Control of Blood Pressure
Short term control - mainly
involves:
First Response by:
Autonomic Nervous System.
The receptors which monitors
changes in BP are:
 Baroreceptor reflex
 Chemoreceptor reflex
 Circulating 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.
MECHANISMS OF B/P CONTROL
Higher brain stimulus
Baroreceptors
Chemoreceptors
Control of Blood Pressure
Short term control - mainly involves:
 Baroreceptor reflex
 Chemoreceptor reflex
 Circulating hormones
Long term control involves regulation
Of blood Pressure by the kidneys.
Control of the Heart
Vasoconstrictors and Vasodilators

Vasoconstrictors
 Epinephrine and Norepinephrine
 Angiotensin II
 Vasopressin
 Vasodilators
 EDRF (NO) endothelium derived relaxing factor- is
produced and released by the
endothelium to promote smooth muscle
relaxation
Cardiovascular centers of the brainstem
 Medulla oblongata
is essential to
Cardiovascular
centers.
Second or Indirect Adaptive Response by Renin-angiotensin
Mechanism
 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 II

When Angiotensin II causes
1 Vasoconstriction
2. 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 
Homeostatic Blood Pressure
Regulation Mechanisms
•
Baroreceptors * in aortic arch & carotid sinuses:
– sensitive to changes in blood pressure.
Reflex Centers in Medulla
 Cardioacceleratory - increases heart rate
 Cardioinhibitory - decreases heart rate
 Vasomotor - changes diameter of vessels
BP* - Stimulates Cardioinhibitory center to heart rate &
Vasomotor center to diameter.
BP* - Stimulates Cardioacceleratory center to
Vasomotor center to diameter.
heart rate &
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 retention
Atrial Natriuretic Peptide (ANP)

released from the atria by large atrial stretch
Produces diuretic responses from kidney, also
vasodilation and decrease in renin release.
Fluid Exchange
 85% of fluid that leaves blood is returned at venous
end
 What about the other 15%?
References
 Fox S. (2009) Human Physiology, (11th Ed), McGraw-
Hill International Edition
 Saladin 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