Blood pressure

Blood pressure (BP)

Blood pressure

• is the lateral pressure exerted by circulating blood on the vessel wall

• the term blood pressure usually refers to the arterial pressure

in the brachial artery measured at a person's upper arm

Systolic blood pressure (SBP)

• maximal blood pressure within cardiac cycle

(which is during systole)

Diastolic blood pressure (DBP)

• minimal blood pressure within cardiac cycle

(which is at the end of diastole)

SBP

DBP

• during the cardiac cycle the arterial BP oscillates in the range of

Pulse pressure = SBP - DBP

• difference between systolic and diastolic pressure

Mean arterial pressure (MP) = 1/3 SBP + 2/3 DBP

- weighed mean - because systole lasts 1/3 of the cardiac cycle, diastole only 2/3

SBP

DBP

MP

pulse pressure

SBP

DBP

Elastic arteries and BP

• elastic arterial wall expands during systole

(due to ejected blood volume/pressure)

• in diastole the vessel wall returns to initial

diameter (due to its elasticity) - this results in

- a continuous blood flow without stopping

- maintenance of BP during diastole

(diastolic pressure in the venticles = 0)

Flow of blood in the cardiovascular system is

• directly proportional to the pressure gradient

- blood flows down the pressure gradient (from higher pressure to lower pressure)

- heart systole creates high pressure

Higher P1 Lower P2

Flow

P1 P2 P

• inversely proportional to

the resistance (R) to flow

• resistance (R) is

– proportional to length (L) of the tube (blood vessel)

– proportional to viscosity () of the fluid (blood)

– inversely proportional to the fourth power of the tube radius (r4)

• small changes in the vessel diameter cause major changes in blood flow

• blood flow (Q) – amount of blood passing a given point in a circulation

8L____r4

R

r4

____

8LQ Hagen-Poiseuille’s Law

Blood pressure – driving force of the blood flow

Blood flow in the vessels

Laminar

- streamline movement of blood.

- blood flows in layers which move parallel to the long

axis of the blood vessel

- velocity is highest for the layer at the center of the

vessel lumen

- blood flow in most vessels of the body is laminar

Turbulent

- non-layered flow, turbulences

- increases the energy required to drive blood

(turbulence - loss of energy in the form of friction,

which generates heat)

- occurs

- normally in large arteries at branch points,

- diseased and narrowed arteries

Reynolds number – if < 2000, the blood flow is laminar , if >4000 blod flow turbulent

blood density X velocity of blood flow X vessel diameter____________________________________________

blood viscosity

Re= https://simplemed.co.uk/images/Cardiovascular/Blood_flow_in_

blood_vessels_-_Laminar_and_Turbulent_flow_SimpleMed.jpg

Figure 15.6

SYSTEMIC CIRCULATION PRESSURES

Pressure waves created by ventricular contraction travel into the

blood vessels. Pressure in the arterial side of the circulation cycles

but the pressure waves diminish in amplitude with distance and

disappear at the capillaries.

Systolic pressure

Pulse

pressure

Mean arterial

pressureDiastolic

pressure

Pre

ssu

re (

mm

Hg

)120

100

80

60

40

20

Left

ventricleArteries Arterioles Capillaries Venules,

veinsRight

atrium

• the mean systemic BP due to resistance in blood vessels decreases as the blood

moves away from the heart through arteries

• large areries – oscilations of

– BP(systole/diastole)

– velocity of the blood flow

Pressure gradient across systemic circulation

• from small arterioles

onwards

• constant BP

• constant blood

flow velocity

1. Cardiac output (L/min)

= the volume of blood that is ejected from the heart into aorta / minute

(the more blood enters aorta, the higher the BP)

= stroke volume x frequency

Stroke volume is influenced by:

Preload

- initial stretching of the cardiac myocytes prior to contraction

(Frank-Starling mechanism)

- depends on the amount of ventricular filling

- the greater the stretch (within certain limits), the greater the

force of contraction

Contractility

- increased contractility – increased CO

Afterload

- the pressure against which the heart must work to eject blood

during systole (as afterload increases, the CO decreases)- resistence to systolic ejection- depends on elasticity of aorta, peripheral resistance, etc.

Factors determining blood pressure

https://image.slidesharecdn.com/vtonetpfsn-nw2012-130701061807-

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2.Peripheral resistance

- is determined by the smooth muscle tone in vessels (arterioles)

- determines blood outflow to the periphery

- influences the BP

- low resistance – more blood flows to the periphery – a larger decrease in DBP

- high resistance – less blood flows to the periphery, smaller decrease in DBP

- impacts the afterload

3. Blood volume

- normal volume - normal pressure

- low volume - low pressure (e.g. hemorrhagia)

- high volume - high pressure

https://image.slidesharecdn.com/vtonetpfsn-nw2012-130701061807-

phpapp02/95/vascular-tone-and-tissue-perfusion-21-638.jpg?cb=1372660004

high volume -high pressure

low volume -

low pressure

Measurement of arterial blood pressure

• measurement of BP - routine clinical examination

• the term blood pressure usually refers to the arterial pressure in the brachial

artery measured at a person's upper arm

• simple and useful indicator of cardiovascular status

Classification of blood pressure for adults (European Society of Cariology)

SBP mmHg DBP mmHg

Hypotension < 90 < 60

Optimum 90 – 120 and 60 – 80

Normal 120 – 129 or 80 – 84

Higher normal 130 – 139 or 85 – 89

Hypertension* ≥ 140 or ≥ 90

• hypertension is classified as mild, moderate, or severe depending on the BP values

• about 30- 45% of adult population have hypertension, prevalence is rising with age

• high BP – risk factor of stroke, myocardial infarction

1. Age

- children – lower values, increase with age

- from puberty onwards – normal „adult“ values

- elderly– increase in BP (atherosclerosis - loss of arterial elasticity/ increase of stiffness)

BP is not static - undergoes natural variations due to:

2. Gender

– mean BP in males is slightly higher on average

3. Respiration

– respiratory arrthymia inspiration – a mild increase of BP

expiration – a mild decrease of BP

4. Circadian rhythm

- in sleep the BP drops down

(mainly in non-REM sleep)

Non-dipper

- a person in whom there is an absence

of the normal nocturnal fall (dip) in blood

pressure

- an additional risk factor for the

development of adverse cardiovascular

events

Dipper

- a person with normal nocturnal drop in BP

5. Stress, physical activity – increase in BP

Measurement of the arterial

blood pressure

- Indirect method – with sphygmomanometer

• a cuff that is placed on the arm

• attached mercury manometer indicates values of blood pressure (BP)

- Direct method – canulla is inserted into an artery and connected to a monitor

Procedure

- before the measurement the patient should be

in rest for about 15 minutes (avoiding physical

activity or stress)

- patient is in sitting or lying position,

forearm/hand is on a table

- the cuff is wrapped around the arm 2 cm above

fossa cubiti

- stethoscope bell is placed below the cuff

/partially under

- the bag inside the cuff is inflated by a repeated squeezing a rubber bulb

- the pressure in bag is indicated by the attached manometer

- inflate to approx by 20 mm Hg higher value than the predicted value of BP

in subjects with normal BP to approx to 150

in hypertension approx to 180-200 or even more

http://www.jagranjosh.com/imported/images/E/Articles/measuring-blood-pressure.jpg

slowly release the screw of the pump and listen carefully

the pressure in the cuff will decrease

when you start hearing a sound of heart beat - read the pressure = SBP

- at the beginning the sound is like a murmur

- read the value when you hear clear heartbeat

continue releasing the screw – the pressure in manometer will be further

decreasing

the sound (heartbeat) will remain for some time audible – the sound will

undergo changes in loudness

the pressure at which the sounds disappear read the diastolic pressure

sound disappears

- silence

sound appears

„hearbeats“silence

- when it falls just below the SBP a small

spurt of blood escapes through the artery

- blood flows through a narrow space -

the blood flow is turbulent (loud)

- slight tapping sounds occur with each

heartbeat (Korotkoff sounds) – indicate

the value of SBP

- when the pressure in the cuff is equal to

the diastolic pressure, the blood flow

becomes laminar (silent) and the sound

disappears

Principle of the measurement :

- sufficiently inflated cuff – the pressure in bag exceeds blood pressure in brachial

artery – artery occluded (no blood flow)

- as the screw is released, the pressure in bag falls

Task:

- measure the blood pressure in 2 people

- repeat the measurement in each subject 3 times

Result and conclusion

- record and evaluate the values – compare the 3 measurements

- calculate the mean pressure and the pulse pressure

White-coat hypertension (WCH)

• for some patients the measurement taken in a doctor's office is higher than their

typical BP

• can result from anxiety related to an examination by a health care professional.

• A 24 h ABPM – ambulatory blood pressure monitorng monitoring is recommended

to determine valid values

Control of the cardiovascular system

Control of the cardiac function

- Frank-Starling mechanism

- Nervous regulation (sympathetic, parasympathetic)

- Humoral regulation (hormones, other humoral factors)

Regulation of the circulation

- Systemic nervous regulation (vasomotor centre)

- mainly sympathetic regulation (higher/lower tone)

- parasympathetic only in some organs (glands, genitals)

- Systemic humoral regulation (hormones, other humoral factors)

- Vasodilating agents: natriuretic peptides, epinephrine (b - receptors)

- Vasoconstricting agents: ADH, angiotensin II, epinephrine (a - receptors)

- Regulation of the blood volume

- Increase: ADH, aldosterone

- Decrease: atrial natriuretic peptide

- Local regulatory factors

A/ short-term – aimed at suffcient blood supply

B/ long-term – aimed at the maintenance of the BP

Baroreflex (baroreceptor reflex)

• one of the body's homeostatic mechanisms that helps to maintain blood

pressure at nearly constant levels

• provides a rapid negative feedback loop in which

– an elevated blood pressure reflexively

• inhibits the heart rate heart rate (via parasympathetic) and

• causes vascular dilation (inhibition of sympathetic) –

• as a result the blood pressure to decreases

– decreased blood pressure causes

• heart rate to increase

• vascular constriction to restore blood pressure levels

• very rapid - can begin to act in fractions of a second (short-term regulation)

• baroreflex adjustments are key factors in dealing with postural hypotension, the

tendency for blood pressure to decrease on standing due to gravity

This map shows the reflex

response to an increase in

mean arterial pressure.

Bloodpressure

Sensory neurons

Firing of baroreceptors incarotid arteries and aorta

Cardiovascularcontrol center

in medullaoblongata

Sympathetic output Parasympathetic output

less NE released

a-receptor b1-receptor b1-receptor

more ACh onmuscarinic receptor

Arteriolar smooth muscle

Vasodilation

Bloodpressure

Peripheral resistance Cardiac output

Heart rate

SA nodeVentricular myocardium

Force of contraction

Negativefeedback

KEY

Stimulus

Sensor

Afferent pathway

Integrating center

Output signal

Target

Tissue response

Systemic response

Cardiovascular Control

KEY

Stimulus

Sensor

Integrating center

Output signal

Target

Medullarycardiovascular

controlcenter

Parasympatheticneurons

Changein bloodpressure

Carotid and aorticbaroreceptors

Sympatheticneurons SA node

Ventricles

Veins

Arterioles

FIGURE QUESTION

Name the neurotransmitters

and receptors for each of

the target tissues.

© 2013 Pearson Education, Inc.

Orthostatic test

Principle

- reaction of CVS to a load represented by a change of position

- can be used as a screening method

Procedure

• stay in lying position for 5 minutes (resting peacefully, fully relaxed)

• measure your heart rate (HR 1) and blood pressure (BP1)

• stand up and immediately after change of position measure

– the heart rate (HR 2)

– the blood pressure (BP2)

- change from lying to standing position

- redistribution of blood volume

- systolic blood pressure decreases and heart rate increases

- the peak heart rate is found approximately 15 sec after standing up

Result

difference in heart rate = HR 2 – HR 1

Evaluation

• 6 – 12 beats per minute: adequate reaction

• 13 – 19 beats per minute: acceptable reaction

• 20 and more beats per minute: inadequate reaction

A few notes to the orthostatic test.....

• heart rate reactions are very individual - individual baseline measurement is needed

• may be used in sports medicine

• previous orthostatic test results are always the best reference for each person

Orthostatic hypotension

- defined as a decrease

- in systolic blood pressure of 20 mm Hg

- or a decrease in diastolic blood pressure of 10 mm Hg

- within three minutes of standing when compared with blood pressure from the

sitting or supine position

- results from an inadequate physiologic response to postural changes in blood

pressure

- may be acute or chronic, as well as symptomatic or asymptomatic

Case

- every time when Mary stands up, she feels dizziness, she has blurred vision,

weakness, nausea, palpitations

- It takes about half a minute until she feels good again

The Ruffier test

- in a simple way and with sufficient rate of reliability sets the functional

state of the cardiovascular system and readiness of organism for load

1. rest in sitting position for 5 minutes

• measure your heart rate per minute (HR 1)

2. do 30 squats in 30 seconds (terminate the exercise even if you do not succeed

to do 30 sqats)

• immediately after exercise measure HR 2

– measure HR over six seconds and multiply by 10 to get the number of

beats per minute

3. sit down

• one minute after the end of the effort, measure HR 3

– measure HR over six seconds and multiply by 10 to get the number of

beats per minute

Result:

calculate your index:

Index of physical fitness = [ (HR1 + HR2 + HR3)-200 ] /10

Conclusion

• 0 excellent

• up to 5 very good

• up to 10 good

• up to 15 average

• over 15 poor

Local control of the blood flow

Myogenic theory of autoregulation

- Increased blood pressure – dilation of the vessel wall – reflex contraction

Metabolic autoregulation - tissue metabolic products with vasodilating effect

- Increase in: H+, CO2, K+, lactate, histamine, adenosine, decrease in O2

Endothelium derived vasoactive substances

- endothelial cells - active tissue, cells respond according to their needs by production of

- vasodilating agents: NO, prostacyclins (PGI2), prostaglandins (PGE2)

- vasoconstricting agents: endothelines, trhomboxane A2, prostaglandines (PGH2)

Autoregulation - the tissues are able to control their blood flow

Reactive hyperemia

Hyperaemia

- an increase of blood flow to a part of the body

- hyperemia in the skin capillaries – red colour

a/ Active

b/ Reactive

Active hyperemia matches blood flow to increased metabolism.

Mechanism

Tissue

metabolism

Release of metabolic vasodilators into ECF

Arterioles dilate.

Resistance creates

blood flow.

O2 and nutrient supply to tissue

increases as long as metabolism

is increased.

Tissue

blood flow due

to occlusion

Metabolic vasodilators accumulate in ECF.

Arterioles dilate, but occlusion prevents blood flow.

Resistance creates

blood flow.

As vasodilators wash away, arterioles constrict

and blood flow returns to normal.

Remove

occlusion

Reactive hyperemia follows a period of decreased blood flow

Mechanism

Task: Observe reactive hyperaemia

Procedure:

- observe the colour of the examinee's skin on both hands, it should be

light pink

- attach the tourniquet of a manometer to the left arm

- the examinee lifts his hand above his head

- the cuff of the manometer is inflated up to approx. 165 mm Hg

- this procedure decreases the blood flow into the area below

- the examinee puts the hand on the table

• observe the colour of the hands

expected: (right – normal, left – pale to purple - hypoxia)

• after the tourniquet is removed, observe again the colour of the hands

expected: right normal, left – red for transient time

Result and conclusion:

describe the observations, explain the changes in colour of the arm

Figure 15.21

Normal arterial wall

Fatty streak

Stable fibrous plaque

Vulnerable plaque

Endothelial cells

Elastic connective tissue

Smooth muscle cells

LDL-cholesterol accumulates between the

endothelium and connective tissue and is

oxidized.

Macrophages ingest cholesterol and

become foam cells.

Smooth muscle cells, attracted by

macrophage cytokines, begin to divide

and take up cholesterol.

A lipid core accumulates beneath

the endothelium.

Fibrous scar tissue forms to wall off

the lipid core.

Smooth muscle cells divide and

contribute to thickening of the intima.

Calcifications are deposited within

the plaque.

Macrophages may release enzymes that

dissolve collagen and convert stable

plaques to unstable plaques.

Platelets that are exposed to collagen

activate and initiate a blood clot.

Atherosclerosis – underlying process of many cardiovascular diseases

Cardiovascular Disease: Risk Factors

• Not controllable

– Gender

– Age

– Family history

Some risk factors can be modified by lifestyle

- healthy diet - physical activity

Together with

- control of BP - control of blood lipid levels

• Controllable- Smoking

- Obesity

- Bad diet

- Sedentary lifestyle

- Untreated hypertension

- Dyslipidaemia

- a heart attack occurs when the flow of blood to the heart is

blocked,

- the interrupted blood flow can damage or destroy part of the

heart muscle

- mostly due to atherosclerosis

Risk Factors