BLOOD PRESSURE

DR. SHEHRINA NAZMIN

 PERIPHERAL RESISTANCE (CC)
• It is the resistance which blood has to
overcome while passing through the
periphery
 PERIPHERAL RESISTANCE DEPENDS
UPON
I. Velocity of blood – PR is directly proportional
to velocity of blood
II. Viscosity of blood – PR is directly
proportional to viscosity of blood
III. Elasticity of arterial walls - PR is inversely
proportional to elasticity of arterial walls
IV. Lumen of the blood vessel - PR is inversely
proportional to lumen of the blood vessel
 BLOOD PRESSURE (CC)

• Blood pressure is the lateral pressure exerted by

blood on a unit area of vessel wall while flowing
through it
• Determinant factors for BP:
BP= CO x TPR
 LATERAL PRESSURE

• Lateral pressure is that pressure when force

is exerted at right angles to the direction of
flow at any point within a tube filled with
circulating fluid
TYPES OF BLOOD PRESSURE

1. Systolic pressure
2. Diastolic pressure
3. Pulse pressure
4. Mean pressure
 SYSTOLIC PRESSURE
• It is the maximum pressure during systole
• Range: 100-140 mm of Hg
• Average: 120 mm of Hg
 DIASTOLIC PRESSURE
• It is the minimum pressure during diastole
• Range: 60-90 mm of Hg
• Average: 80 mm of Hg
 PULSE PRESSURE

• It is the difference between systolic and

diastolic pressure
• Range: 30-50 mm of Hg
 MEAN PRESSURE
• It is average pressure throughout cardiac
cycle
• Range: 78-98 mm of Hg
• Mean pressure = Diastole pressure + 1/3 pulse
pressure
 SIGNIFICANCE OF BP
• Systolic Blood Pressure- it indicates-
I. The extent of work done by the heart
II. The force with which heart is working
III. The degree of pressure which the arterial
walls have to withstand
IV. It increases during excitement, exercise,
meals etc.
V. It decreases during sleep, rest etc.
• Diastolic pressure-
I. It indicates the constant load against which
the heart works
II. Increased diastolic pressure indicates that the
heart is approaching to failure
III. It is the index of peripheral resistance
FACTORS CONTROLLING ARTERIAL
BLOOD PRESSURE
• Pumping action of the heart
• Cardiac output
• Peripheral resistance
• Elasticity of arterial walls
• Blood volume
• Viscosity of blood
 FACTORS THAT INFLUENCE BP
• Age- BP rises with age.
• Sex – In females both systolic and diastolic
pressure are slightly lower than in male up to
age 45- 50 years.
• Built – The systolic pressure is usually high in
obese person.
• Exercise – Mild to moderate exercise systolic
pressure but diastolic pressure remain constant.
• In Severe exercise- systolic pressure , diastolic
pressure .
• Posture – The diastolic pressure is slightly
higher in the standing position. In the recumbent
position the diastolic pressure is lower than in
the standing or in the sitting position.
• Sleep – Systolic pressure falls by about 15- 20
mm of Hg during sleep.
• Race – SP and DP in black are higher than
those in white.
• After ingestion of meal- slight rise of systolic
pressure
• Emotion or excitement- systolic pressure
increases
 MEASUREMENT OF BP (CC)

• Direct method
• Indirect method
1. Palpatory method
2. Auscultatory method

*Korotkoff sound
 VASOMOTOR CENTER

• Located bilaterally in the reticular substance of

medulla and of the lower third of pons.
• This center transmit parasympathetic impulse
through vagus nerves to the heart and
sympathetic impulse through spinal cord and
peripheral sympathetic nerve to arteries,
arterioles and veins of the body.
 VASOMOTOR CENTER CONTD..

There are certain important areas-

1. Vasoconstrictor area: Located bilaterally in
anterolateral portion of upper medulla. They
excite the vasoconstrictor neuron of
sympathetic nervous system.
2. Vasodilator area: Located bilaterally in
anterolateral portions of lower half of medulla.
They inhibit the vasoconstrictor activity
 VASOMOTOR CENTER CONTD..

• A sensory area: Located bilaterally in the

tractus solitarius in the posterolateral portion of
the medulla and lower pons. They control
activities of both the vasoconstrictor and
vasodilator area of VMC.
VASOMOTOR CENTER
 REGULATION OF BLOOD
PRESSURE
1. Rapidly acting pressure control
mechanism
I. Baroreceptor feedback mechanism
II. Chemoreceptor mechanism
III. Central nervous system ischemic
mechanism
 REGULATION OF BLOOD PRESSURE
CONTD..

2. Intermediate acting pressure control

mechanism
I. Renin angiotensin vasoconstrictor mechanism
II. Stress relaxation of vasculature
III. Shift of fluid through the tissue capillary wall in
and out of circulation
 REGULATION OF BLOOD PRESSURE
CONTD..

3. Long term pressure control mechanism

I. Renin- angiotensin-aldosterone mechanism
II. Renal body fluid pressure control
mechanism
 BARORECEPTORS
• Baroreceptors are spray type nerve endings that
lie in the wall of arteries, they are stimulated
when stretched
• Location-
I. Baroreceptors are extremely abundant in the
walls of each internal carotid artery just above
the bifurcation of carotid artery an area known
as carotid sinus
II. Wall of aortic arch
III. Few are located in the walls of almost every
large artery of thoracic and neck region
 BARORECEPTORS CONTD..

• Pressure range-
1. Carotid sinus baroreceptor: 60-180 mm Hg
2. Aortic arch baroreceptor: 90-180 mm Hg
Baroreceptor feedback
mechanism
 ↑mean arterial pressure

Carotid
(+) Baroreceptor Aortic
baroreceptor baroreceptor

Hering’s nerve

Vagus nerve
Glossopharyngeal nerve

Nucleus of tractor solitarus in medulla

(-) Vasoconstrictor center

(+) Vagal parasympathetic center

Vasodilation ↓ Heart rate

↓ Force of contraction
↓ total peripheral
resistance ↓ Cardiac output

↓Arterial pressure
 BARORECEPTOR FEEDBACK
MECHANISM

• Low pressure has opposite effects, reflexly

causing the pressure to rise back towards the
normal
• Because the baroreceptor system opposes
either increases or decreases in arterial
pressure it is called a pressure buffer
system and the nerves from the
baroreceptors are called buffer nerves
 THE BARORECEPTOR SYSTEM FOR
CONTROLLING ARTERIAL PRESSURE
 CHEMORECEPTORS

• Chemosensitive cells, sensitive to O2 lack, CO2

and H+ excess
• They are located in the -
• Two carotid bodies (one of which lies in the
bifurcation of each common carotid artery)
• One to three aortic bodies (adjacent to aorta)
 CHEMORECEPTOR MECHANISM
Arterial pressure falls below critical level (80mm Hg)
↓
↓ blood flow
↓
O2 and ↑ CO2 and H+ concentration
↓
(+) chemoreceptors

Send signals to vasomotor center via Hering’s nerve and

Vagus nerve
↓
(+) Vasomotor center
↓
↑ Arterial pressure
 BAINBRIDGE REFLEX
• An increase in arterial pressure also causes an
increase in heart rate
• The stretch receptors of the atria transmit their
afferent signals through the vagus nerves to
the medulla of the brain
• Then efferent signals are transmitted back
through vagal and sympathetic nerves to
increase heart rate and strength of heart
contraction
• Thus, this reflex helps to prevent damming of
blood in the veins, atria and pulmonary
circulation
 CNS ISCHEMIC RESPONSE
• When blood flow to the vasomotor center in the
lower brain stem become severely decreased it
causes nutritional deficiency and cerebral
ischemia
• The vasoconstrictor and cardio accelerator
neurons in the VMC respond directly to the
ischemia and become strongly excited and
arterial pressure raises
 CNS ISCHEMIC RESPONSE CONTD..

• This arterial pressure elevation in response to

cerebral ischemia is known as the central
nervous system ischemic response
• It does not become significant until the arterial
pressure falls 60mm Hg or below
RENIN ANGIOTENSIN VASOCONSTRICTOR
MECHANISM
↓Arterial pressure
↓
↓Blood flow to juxtaglomerular apparatus of kidneys
↓
↑ Renin secretion from JG cells
↓
Angiotensinogen → Angiotensin I
↓ACE
Angiotensin II
↓
Vasoconstriction ( direct effect)
↓
↑TPR
↓
↑ Blood pressure
 STRESS RELAXATION OF VASCULATURES

When pressure on the blood vessels become too

high
↓
Vessels become stretched
↓
Stretched more for minutes to hour
↓
Pressure in the vessels fall towards normal
 Capillary fluid shift mechanism

↓BP
↓ ↑BP
↓Capillary pressure ↓
↓ ↑Capillary pressure
↑Fluid absorption from ↓
tissues through capillary ↑Fluid loss out of
membranes into circulation into the
circulation tissues
↓ ↓
↑Blood volume ↓Blood volume
↓ ↓
↑Pressure in circulation ↓Pressure in circulation
RENAL BODY FLUID MECHANISM
Renin-angiotensin-aldosterone mechanism
↓BP
↓
Renin (kidney)
↓
Angiotensinogen → Angiotensin I
↓ACE
Angiotensin II

Aldosterone Renal tubule Vasoconstriction

↓ ↓
Na+ & H2O Excretion of Na+ &
Reabsorption H2 O
↓ ↓

↑Blood
volume
↓ ↑TRP
↑CO ↑BP