ARTERIAL BLOOD PRESSURE

INTRODUCTION

-Arterial blood pressure is a lateral pressure exerted by blood on the wall of the arteries.
-Blood pressure is measured indirectly by using sphygmomanometer.
• Types of blood pressure ;
1) Systolic blood pressure
2) Diastolic blood pressure
3) Pulse pressure
4) Mean arterial blood pressure.
Normally blood pressure is denoted as Systolic blood pressure over diastolic blood pressure.

•Systolic blood pressure :

-It is the maximum pressure exerted during ventricular systole .
– Average systolic blood pressure is 120mmHg.
-Normal range is 110-140.

 

•Diastolic blood pressure :

– It is the Minimum pressure exerted during ventricular diastole .
-Average is 80mmHg.
-Normal range is 60-80mmHg.

•Pulse pressure :

-It is calculated by the difference between systolic blood pressure and diastolic blood pressure.
-Average is about 40mmHg .

•Mean arterial pressure:

-It is the average pressure through out arterial system during cardiac cycle.
-It is calculated as diastolic blood pressure + 1/3 rd of pulse pressure .
-Average mean arterial pressure is about 93mmHg.

•Physiological variations :

1) Age : In children blood pressure is low as compared to adults.
2)Gender : Female has low blood pressure then male before menopause.
3)Body built : Increase in obese person.
4)After meal : Increase due to increase in cardiac output.
5)Sleep :Decrease due to decrease in cardiac output.
6) Exercise : Systolic pressure increases but diastolic pressure remains same.

•Regulation of Blood pressure:

-It includes short term regulatory mechanism and long term regulatory mechanism.

Short term regulation of blood pressure :

– It includes,
(a) Neural mechanisms – sympathetic and parasympathetic regulation via vasomotor center.
(b) Reflex regulation
(c) hormonal regulation

*Neural mechanism :

– Vasomotor center consists of 1) Vasoconstrictor area and 2)Vasodilator area.

√ Vasoconstrictor area ;

-When the vasoconstrictor area stimulated causes intense vasoconstriction which increases heart rate , increase in contraction of heart and there by increases the blood pressure.
-They exerts effect via sympathetic neurons.

√ Vasodilator area ;

– It is present in the nucleus tractus solitarius and dorsal nucleus.
– When stimulated it inhibits Vasoconstrictor area producing vasodilation, decrease in heart rate , decrease in cardiac output , and there by decreases blood pressure.
-It exerts it’s effect either through parasympathetic neurons ( vagus nerve ) or by inhibition of Vasoconstrictor area.

* Reflex regulation :

– It includes baroreceptor mechanism and chemoreceptor mechanism.

Baroreceptor mechanism :

-It  acts when the pressure , volume changes.
– When the arterial blood pressure rises rapidly , Baroreceptors are activated and send stimulated impulses to nucleus of tractus solitarius through glossopharyngeal and vagus nerve.
-It inhibits the area of vasoconstrictor and excites the area of Vasodilator .
This decrease Cardiac output and heart rate and there by it decreases blood pressure.
– The fall in arterial blood pressure or the occlusion of common carotid arteries decrease the pressure in carotid sinus.
-This causes inactivation of Baroreceptors.
-Now there is no inhibition of Vasoconstrictor center or excition of Vasodilator center.
-Therefore it increase the cardiac output and heart rate, there by it increases blood pressure.

√ Chemoreceptor mechanism:

-It acts on the peripheral Chemoreceptor.
These Chemoreceptors sends the impulse to the Vasomotor center via glossopharyngeal and vagus nerve.
– Whenever the  blood pressure decreases, the flow of blood to the Chemoreceptors get reduced, which result in reduction of oxygen content and excess of carbon dioxide and hydrogen ion .
These exites the Chemoreceptors , which send the impulses to stimulation the vasoconstrictor center, which increases the cardiac output and heart rate, there by it increases blood pressure.

*Hormonal regulation

-When the blood pressure decreases, it decrease the GFR , which in turn decreases NaCl.
– NaCl is resistive to macula densa cell.
– Macula densa cell activates JG cells to secrete renin.
-Renin combines with angiotensin to form angiotensin 1
– Angiotensin 1 goes to lung and converted into angiotensin 2 by ACE.
-Angiotensin goes to kidney and regulates ADH.
– ADH increases the absorption of water and salt.
-There by it maintains the blood pressure .

• Long term regulation of blood pressure :

– Kidney plays the main role in long term regulation of blood pressure.
-As blood pressure slowly alters within week / years the nervous mechanism adapts to change.
– Nervous mechanism cannot regulate the pressure again.
– It is done by two ways ;
(1) By regulation of ECF
(2) Through renin- angiotensin mechanism

√ By regulation of ECF volume :

– When blood pressure increases , kidney secrets large amount of water and salt by means of diuresis and natriuresis.
-Diuresis excretes large quantity of water in urine because of increased blood pressure.
– Natriuresis excretes a large quantity of sodium (NA) in urine.
-due to diuresis and natriuresis, there is a  gradual decrease in ECF volume and blood volume which brings the arterial blood pressure back to normal.

√ Through renin- angiotensin mechanism:

– this mechanism is same as hormonal regulation .

• Measurement of Blood pressure: 

– There are 2 methods of measurement of blood pressure ,
(1) Palpatory method
(2) Auscultatory method.
– There is one more method which is not clinically used because of its inaccuracy  i.e., ascultatory method.

1) Palpatory method :

– In this method only systolic blood pressure can be measured.
– Procedure :
✓BP apparatus consists of arm cuff which is tied around the upper arm.
✓Screw in the ripper pump is tightened and examiner should palpate the radial artery .
✓ Then the pressure in the cuff is increased till the radial pulse disappears.
✓ Again the pressure js raised in 10-15mmHg .
✓ Then the hand pump is slowly released, and the mercury column slowly comes down.
✓ The reading at which the radial pulse is reappears is noted down which is called as systolic blood pressure.
– Significance : By doing Palpatory method, oscillatory gap which can be s end in hypertensive patients is avoided.

2) Auscultatory  method :

– In this method both systolic and diastolic blood pressure are recorded.
– This method requires sphygmomanometer and stethoscope.

– Procedure :

✓The cuff is tied around the upper arm and the brachial artery is felt on the medial aspect of cuboital fossa and the ear piece of the stethoscope is placed in the ears.
✓ Pressure in the cuff is increased about 20 mmHg more than Palpatory method.
✓ Then the pressure is slowly released.
✓ Now the examiner should concentrate on the brachial artery.
✓ When the pressure is decreased slowly , there is sudden tapping sound appears.
✓This is recorded as systolic blood pressure.
✓ When the pressure is further reduced the quality of sound changes.
✓Sequentially the sounds are known as – murmur sound , gong sound , muffled sound , and disappearence of sound.
✓ The disappearance of sound is considered as diastolic blood pressure.
✓ These five different qualities of sound are known as KOROTKOFF sounds.

– Advantages : By this method both systolic and diastolic blood pressure can be measured accurately.

 

• Applied physiology :

– Pathological variations of arterial blood pressure ;
(1) Hypertension 
(2) Hypotension
 

1) Hypertension :

– It is refered to continued increase in blood pressure over a period of weeks or months .
– Here systolic blood pressure is more than 140mmHg and diastolic blood pressure is more than 90mmHg.
– Types of hypertension : 1)primary and 2)secondary Hypertension .

2) Hypotension :

– It is refered to decrease in blood pressure especially systolic blood pressure is less than 90mmHg.
– There are 2 types : primary and secondary hypotension.

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