Blood Pressure - Copy

8/2/2019 Blood Pressure - Copy

http://slidepdf.com/reader/full/blood-pressure-copy 1/92

Click to edit Master subtitle style

3/19/12



3/19/12

Arterialblood

pressure



3/19/12

Arterial Blood PressureIt is the force exerted by the blood

against any unit area of the vesselwall. It is always measured inmillimeter of mercury (mmHg).

If the pressure in a vessel is 100mmHg, this means that the force

exerted is sufficient to push acolumn of mercury up to a level100 mm high.

varies between a maximum



3/19/12



3/19/12

Systolic Blood Pressure

Systolic blood pressure is themaximum pressure that bloodexerts on vessels during systole

Range = 90-140 mmHg.

Average = 120 mmHg



3/19/12

Diastolic blood pressuremeasures the minimum pressurein the systemic arteries during

diastole)

Range = 60-90 mmHg.

Average = 80 mmHg

Diastolic Blood Pressure



3/19/12

Normal Blood Pressure

120/80

Note: it is not adivision



3/19/12

Pulse Pressure

ü It is the difference betweensystolic and diastolicpressures

ü The average value is 40mmHg.



3/19/12

Mean Blood Pressure

It is the averagepressure

throughout thecardiac cycle.

MAP= Pdiastole + 1/3 (Psystole -Pdiastole )

= 80 mmHg + 1/3 (40

mmHg) = mmH



3/19/12

PhysiologicalVariations



3/19/12

v

Correspondingarteries of both sideof body may differby 5-10mmHg

v in the femoral artery

is 10-15 mmHghigher than in thebrachial and 15-20mmHg higher thanin the popliteal



3/19/12

Age

At birth the ABP isvery low (50/30mmHg).

Thereafter, it rapidlyrises during the firstfew weeks to 90/60

mmHg.

The pressure

increases gradually





3/19/12

Sex



3/19/12

Exercise

• Moderateexercise

→

mild in systolic↑pr.

→ little or no changein diastolic pr.



3/19/12

Exercise

• Severe exercise

→ severe in systolic↑pr.

→ ↓ in diastolic pr.



3/19/12

Emotions



3/19/12

Build



3/19/12

Meals



3/19/12

Sleep



Pressures in the systemic

circulation•

The decrease in thearterial pressure atthe end of each part

of the systemiccirculation is directly

proportional to thevascular resistance



3/19/12

Aorta(93 mmHg)

Largearteries (90-93 mm Hg)

v. Smallarteries (85mm Hg)

largeveins (8-10mm Hg)

Venularend (15mm Hg)

Arteriolarend (35

mm Hg)

Rightatrium (O-2 mm Hg)



Pressures in the systemic

circulation



3/19/12



3/19/12



3/19/12

Blood pressure =COP X total peripheral

resistance



3/19/12



3/19/12

1- cardiac output



3/19/12

1- cardiac output



3/19/12

it is the resistance which the

blood has to overcome while

passing through the peripheralvessels

Affected by

1. Diameter of vessels

2. Viscosity

2- Peripheral resistance



3/19/12

4r

8VL

(r)Radius

(L)Length(V)ViscosityαR

4 π

=×

(r 4)



3/19/12

a)Diameter of vessels

• The resistance is inversely proportional to

the fourth power of the radius of the vessel1

•

R α

R 4



3/19/12


diameter resistance



3/19/12


• The peripheralresistance in thesystemic circulation

is chiefly in thearterioles becausearterioles are narrowvessels connected in

series, while thecapillaries form anetwork of vessels

connected in parallel



3/19/12



3/19/12

b) Blood Viscosity

Depends on:

• hematocrit



3/19/12

The the length

of the vessel, theis the

resistance due tofriction betweenthe blood and

vessel walls

c) Length of the vessel



3/19/12

Increase in theperipheral resistance

raises the diastolicpressure



3/19/12

• Systole→→→ Distend

• Diastole→→→ Recoil

• Prevents a greatrise in the systolicpressure and agreat drop in thediastolic pressure.

• transfer the

3-Elasticity of aorta and arteries



3/19/12

Arteriosclerosis

• The elastic and muscular tissuesare replaced by fibrous tissue).

• Accumulation of plaque in thearteries

• Flow of blood faces more resistance

• Blood pressure is altered.HOW???



3/19/12

Arteriosclerosisreduces the elasticity

of the circulatorysystem Therefore, thesystolic pressure ismuch increased,

while the diastolicpressure is slightly

reduced (high

pulse pressure )↑↑Systolic bloodpressure

↓ diastolic pressure



3/19/12

With advancedarteriosclerosis, more

cholesterol isdeposited in thearterioles narrowingtheir diameter.

Therefore, thediastolic pressure increased because of

the increased in theperipheral resistance..↑↑Systolic bloodpressure

↑↑ diastolic pressure



3/19/12

4- blood volume

decrease in the bloodvolume decreases both

the systolic and diastolic

pressure



3/19/12

Ø

The systemic circulation has manyregulatory mechanisms whichmaintain the normal mean arterialpressure between 90 mmHg and 110mmHg

Control of the arterial blood

pressure



3/19/12



3/19/12

Nervous pressurecontrol

mechanismsbegin to reactwithin seconds

and become fullyactive within a

minute



3/19/12

Intermediately actingpressurecontrol

mechanisms

come intoplay withinminutes,

then becomefully active

within 30minutes to

severalhours.



3/19/12

(high pressure

receptors)

carotid sinus and

aortic archreceptors

1- arterial Baroreceptors



3/19/12

B a r o r

e c e p t o

r s

Stimulus

The baroreceptors arestimulated by distentionof the structures in whichthey are located, and so

they discharge at anincreased rate when thepressure in thesestructures rises



3/19/12

B a r o r

e c e p t o

r s

The threshold for eliciting activity inthe carotid sinus nerve is about 50

mm Hg; maximal activity occurs atabout 200 mm Hg.

At normal blood pressure levels (about100 mm Hg mean pressure), someactivity in the baroreceptors(responsible for the vagal tone)



3/19/12

MECHANISM OF baroreceptorREFLEX

PRESSURE BETWEEN

0-50mmHg

NOTSTIMULATED

AT ALL

>50

mmHg

RESPOND MORE ANDMORE UNTIL REACHMAX AT 200mmHg



3/19/12

Baroreceptors

Baroreceptors are more sensitive to

variable pressure than to constantpressure. they respond much more toa rapidly changing pressure thanto a stationary pressure.



3/19/12

B a r o r

e c e p t o

r s

Afferent (buffer

nerves) The afferent nerve fibers fromthe carotid sinus form adistinct branch of theglossopharyngeal nerve, thecarotid sinus nerve(Herings nerve). The fibersfrom the aortic arch form abranch of the vagus nerve,

the aortic depressor nerve.



3/19/12

B a r o r

e c e p t o

r s





Arterial Baroreflex Responses



3/19/12

Arterial Baroreflex Responses

Arterialbaroreceptor

activityCardiovascular centers in

medulla

Sympathetic

nerveactivity

Vagalnerve

activity

Vascul

Strok

evolum

e

Hear

trate

Cardia

Arterial pressureAffere

ntarm

Efferentarm

Functions of baroreceptors



3/19/12

To stabilize blood pressure andheart rate if they increases ordecreases above or below theirnormal levels.

To reduce the daily variation inthe arterial pressure (from

moment to moment), e.g. changesin body posture

They also have an important role in

Functions of baroreceptors



3/19/12

B t



3/19/12

Baroreceptors

Baroreceptors resettingBaroreceptors are of NO importancein long-term regulation of arterial

pressure. They adapt in one to twodays to whatever pressure level theyare exposed to i.e. they stop theirdischarge despite the presence of the

stimulus because they get used to it;thus they lose their responsiveness.

B t



3/19/12

Baroreceptors

Baroreceptors resetting

In chronic hypertension, the

baroreceptor reflex mechanism is"reset" to maintain an elevated ratherthan a normal blood pressure.

3- Arterial Chemoreceptors



3/19/12

p

Arterial Chemoreceptor Reflex



3/19/12

Arterial Chemoreceptor Reflex

Chemorecept or

afferent

nerves

Stimulus:Changes

inarterial

P O2,

PCO2, pH, BP<80mmHg

Response: changes in pulmonary

ventilation & vascular

Brainstemrespiratory

&vasomotor centers

Sympatheti c

nerves Mot or neuron

s

Arterialchemoreceptor

activity

Vasoconstriction↑ heart rate

BPback to

normal

Ventilati

on

BP<80mmHg

++

Respirator y

centers

+

+Cardiovascular

centers

é heart rate

Ch t



3/19/12

Chemoreceptors

This reflex helps to return the arterialpressure back toward the normal

level whenever it falls too low.However, it is not a powerful arterial

pressure controller in a normal

arterial pressure range, because itdoes not respond strongly untilthe arterial pressure falls below

80 mmHg.

2- Atrial stretch receptors



p



3/19/12

Bainbridge Reflex

Atrial Stretch Receptors

Medullary cardiovascular centersActivation

IncreasedHeart Rate

andcontractility

IncreasedSympatheticActivity to SA

Node

Increased IntravascularVolume

DirectStretchingof SA Node

I d bl d



3/19/12

Increased bloodvolume causing atrial

stretch

Atrial Stretchreceptors stimulation

• Decreasedperipheral resistance• Increased venous

capacity• VD of the afferentrenal arterioles →increasedUrine Output

Generalizedvasodilatation

• Increased UrineOutput• Decreased Water

and Na+ Reabsorption• vasodilatation

DecreasedVasopressin

IncreasedAtrial Natriuretic

Peptide

• Increased

Natriuresis• Increased urineOutput• vasodilation

Decreased blood volume and blood pressure

Atrial reflexes



3/19/12

Atrial reflexes

Atrial reflexes are pressure

controllers as well as volumecontrollers.

Central ischemic response



3/19/12

Central ischemic response

4- Central ischemic response



3/19/12

4 Central ischemic response

The CIR is stimulated by cerebral ischemia.Blood pressures bellow 50-60 mmHg will

initiate this response.The CIR is extremely powerful; it can

elevate blood pressure to 200 mmHg.Blood flow through peripheral organs is

stopped or greatly reduced as a result of

generalized vasoconstriction. (exceptbrain ,heart and lungs)

The CIR maintains brain blood flow whenarterial pressure falls to critically low levels.

4- Central ischemic response



3/19/12

4 Central ischemic response

Despite the extremely powerful nature of thecentral ischemic response, it does not becomevery active until the arterial pressure falls farbelow normal, down to levels below 50 mmHg,reaching its greatest degree of stimulation at apressure of 15 to 20 mmHg.

Therefore, it is not one of themechanisms for regulatingnormal arterial pressure.



3/19/12

Intermediately actingpressurecontrol

mechanisms

come intoplay withinminutes,

then becomefully active

within 30minutes toseveralhours.

Epinephrine



3/19/12

Sympatheticstimulation

Ø These hormones can reach some parts of the circulation that haveno sympathetic nervous supply at all, including the very minutevessels such as the metarterioles.

Ø

They have especially potent actions on some vascular beds,

EpinephrineNorepinephrine

Renin-Ang II system



3/19/12

Increased

BP

Decreased extracellular fluid volume

Renin-Ang II system

Renin-Ang II system



3/19/12

• It requires approximately 20 minutesbecoming fully active.

• However, it has a correspondingly

longer duration of action.

Renin-Ang II system

Vasopressin



3/19/12

stimulation of atrial B receptorsis reduced (e.g.hypovolemia).

Ang II

(ADH)

Vasopressin



3/19/12

• The vasopressin (ADH) system wasshown to return the blood pressureabout 75% of the way back toward

normal within a few minutes afteracute hemorrhage has decreased thearterial pressure to as low as50mm.Hg.

• It is the most potent vasoconstrictor.

(ADH)

The intrinsic mechanism



3/19/12

The intrinsic mechanism

Capillary fluid shift

Long term Renal-body



3/19/12

gregulation

of bloodpressure

HOW KIDNEYREGULATS

ABP???

yfluid-

pressurecontrolmechanismHormonal

controlmechanism

(vasopressin,AngII and

aldosterone)erythropoiesi

s



3/19/12

The special value of thismechanism is that it will notstop increasing the blood

volume until the pressure rises

B l o o d S u p p l y

• A p p r o x im a t e l y o n e-f o u r th ( 1 2 0 0 m l ) o f s y s t e m i c c a r d i a co u t p u t f lo w s t h r o u g ht h e k i d n e y s e a c hm i n u t e

• A r t e r i a l fl o w i n t oa n d v e n o u s f l o w o u to f t h e k i d n e y s f o l l o ws i m i l a r p a t h s



3/19/12

Thank you for yourattention!



3/19/12

Bloodpressuresand the

vascularsystem



Capillary Network:



p y

• Blood flows from

arterioles throughmetarterioles, thenthrough capillarynetwork

• Venules drainnetwork

• Smooth muscle inarterioles,metarterioles,precapillarysphincters





3/19/12



Cross-Sectional Area



Cross Sectional Area

• As diameter of vesselsdecreases, thetotal cross-

sectional areaincreases andvelocity of bloodflow decreases

• Much like astream that flowsrapidly through anarrow gorge but

flows slowl





Blood Vessel Comparison:



3/19/12

p



Date post:	06-Apr-2018
Category:	Documents
Upload:	fazira-ekma
View:	222 times
Download:	0 times

Blood Pressure - Copy

Documents