BLOOD PRESSURE REGULATION AND ITS DISORDERS

BY:---UMA KUWAR

INTRODUCTION

• DEFINITION:- THE ARTERIAL BLOOD PRESSURE (B.P) IS THE

PRESSURE OF THE COLUMN OF BLOOD IN THE ARTERIAL SYSTEM.

• FUNCTIONS:-I. TO MAINTAIN SUFFICIENT PRESSURE.II. TO KEEP THE BLOOD FLOWING THROUGHLY.III. PROVIDE MOTIVE FORCE FOR FILTRATION.

FACTORS EFFECTING ARTERIAL B.P

AGE:-BOTH SBP AND DBP INCREASE WITH AGE;SBP INCREASES MORE THAN DBP.

SEX:-SBP INCREASES IN FEMALES AFTER MENOPAUSE.

BODY BUILT:-IN OBESE INDIVIDUALS,ARTERIAL BP GIVES HIGH READINGS.

CLIMATE:-COLD AND HOT CLIMATE INCREASE AND DECREASE ARTERIAL B.P RESPECTIVELY.

DIURNAL VARIATION:-PEAK VALUES ARE OBSERVED IN AFTERNOONS AND LEAST IN MORNINGS.

EXERCISES:-B.P COMES BACK TO NORMAL WITHIN 5 MINS. OF STOPPAGE OF EXERCISE.

EMOTIONS:-EXCITEMENT,FEAR,WORRY ETC. INCREASE SBP.

GRAVITY:-B.P INCREASES IN VESSELS BELOW HEART LEVEL AND DECREASES ABOVE IT DUE TO GRAVITY.

HEREDITARY:-FAMILIAL TENDENCIES OF HYPO/HYPERTENSION WITH SBP ARE COMMON.

MEALS:-SBP INCREASES UPTO 1 HOUR AFTER MEALS.DBP REMAINS SAME.

SLEEP:-SBP FALLS IN EARLY HOURS OF SLEEP.HOWEVER,IT MAY INCREASE DUE TO DISTURBED SLEEP.

POSTURE:-DBP INCREASES WHEN STANDING,NORMAL WHEN SITTING,AND DECREASES WHEN LYING.

REGULATION OF BLOOD PRESSURE:THE VARIOUS MECHANISMS EXIST WITHIN THE BODY TO REGULATE THE SYSTEMIC ARTERIAL BLOOD PRESSURE.THEIR AIM IS TO MAINTIAN THE BLOOD PRESSURE WITHIN THE NORMAL

LIMITS.THE DIFFERENT MECHANISMS AVAILABLE ARE:

RAPIDLY ACTING REGULATORY MECHANISMSBARORECEPTOR REFLEXESCHEMORECEPTOR REFLEXESCNS ISCHAEMIC RESPONSE

INTERMEDIATE ACTING REGULATORY MECHANISMSCAPILLARY FLUID SHIFT MECHANISMSTRESS RELAXATION AND REVERSE STRESS RELAXATION

LONG TERM ACTING REGULATORY MECHANISMSDIRECT MECHANISM ALSO KNOWN AS RENAL MECHANISMINDIRECT MECHANISM

ALDOSTERONE SYSTEMRENIN ANGIOTENSIN SYSTEM

MISCELLANEOUSROLE OF SYMPATHETIC NERVESROLE OF ADH

A. RAPIDLY ACTING MECHANISMSCHARACTERISTIC FEATURES:

BEGING TO ACT WITHIN SECONDS TO MINUTES

MOST OF THESE MECHANISMS LOSE THEIR CAPABILTY AFTER FEW HOURS OR FEW DAYS.

NONE OF THESE EVER SUCCEED IN BRINGING THE ARTERIAL B.P WAY BACK TO NORMAL

THESE REFLEXES ACT UNDER FOLLOWING CONDITIONS:DURING SUDDEN CHANGE IN BODY POSTUREPROFUSELY BLEEDING PERSONS

THE CIRCULATORY REFLEXES OF THESE MECHANISMS INCLUDEBARORECEPTOR REFLEXESCHEMOREPTOR REFLEXESCNS ISCHAEMIC RESPONSE

1. BARORECEPTOR REFLEXESFALL IN ARTERIAL B.P DECREASES THE INHIBITORY DISCHARGES

FROM BARORECPTORS TO CAUSE:LESS INHIBITION OF VASOMOTOR CENTERLESS STIMULATION OF CARDIAC VAGAL CENTER

2. CHEMORECEPTOR REFLEXESIT OPERATES BETWEEN 40-100 MM HG RANGE OF MEAN BLOOD PRESSUREIT CAN CORRECT APPROX 2/3 OF THE FURTHER FALL IN B.P

3. CNS ISCHAEMIC RESPONSEIT OPERATES BETWEEN 15-50 MM HG RANGE OF MEAN BLOOD PRESSUREIT DOES NOT OPERATE UNTIL ARTERIAL B.P FALLS TO 50 MM HG

FALL IN ARTERIAL B.P CAUSES CNS ISCHAEMIA WHICH DIRECTLY STIMULATES THE VASOMOTOR CENTER, PRESSOR AREA.

THIS CAUSES A TREMENDOUS POWERFUL SYMPATHETIC DISCHARGE THROUGHOUT THE BODY.

THUS HEART RATE AND B.P INCREASE TO MAINTAIN NORMAL SUPPLY OF BLOOD TO THE BRAIN.

B. INTERMEDIATE ACTING MECHANISMS

THEY BEGIN TO ACT WITHIN FEW MINUTES AND REACH FULL FUNCTION WITHIN FEW HOURS.

THESE MECHANISM REMAIN FUNCTIONAL FROM FEW DAYS TO A MONTH ONLY.

THEY PRIMARILY CORRECT ANY ALTERATION IN B.P BY ALTERING THE BLOOD VOLUME.

THE MECHANISM INCLUDES:CAPILARRY FLUID SHIFT MECHANISMSTRESS RELAXATION AND REVERSE RELAXATION

1. CAPILLAR FLUID SHIFT MECHANISM

AS MEAN CAPILLARY PRESSURE IS DIRECTLY PROPORTIONAL TO ARTERIAL B.P, THEREFORE RISE IN ARTERIAL B.P INCREASES THE HYDROSTATIC PRESSUREAT ARTERIAL END.

BECAUSE OF INCREASE IN HYDROSTATIC PRESSURE AT ARTERIAL END THE FLUID SHIFTS OUT OF CAPILLARIES TO THE INTERSTIAL FLUID COMPARTMENTS.

THUS BLOOD VOLUME DECREASES AND THE B.P IS RESTORED

2. STRESS RELAXATION AND REVERSE STRESS RELAXATIONRISE IN ARTERIAL B.P EG. FOLLOWING

MASSIVE SLOW IV TRANFUSION, INCREASES PERFUSION PRESSURE IN

BLOOD STORAGE ORGANS.

THIS CAUSES RELAXATION OF BLOOD VESSELS SIMPLY BY LOCAL VASCULAR

TONE ADJUSTMENT.

THEREFORE B.P RETURNS TO NORMAL.THIS IS KNOWN AS STRESS

RELAXATION MECHANISM.

FALL IN ARTERIAL B.P EG. PROLONGED SLOW BLEEDING, DECREASES THE PERFUSION PRESSURE IN BLOOD

STORAGE ORGANS.

THIS CAUSES TIGHTENING OF BLOOD VESSELS .

THEREFORE B.P RETURNS TO NORMAL.THIS IS KNOWN AS REVERSE

STRESS RELAXATION MECHANISM

C.LONG TERM MECHANISMSTHESE MECHA ISMS ALMOST INVARIABLY ARE SLOW TO BEGIN ACTING. GENERALLY THEY TAKE 3-10 DAYS TO COME INTO COMPLETE EQUILIBRIUM.

THEIR FUNCTION IS TO CONTROL THE ARTERIAL B.POVER A PERIOD OF DAYS TO YEARS.

THESE MECHANISMS HAVE THE ABILITY TO BRING THE ARTERIAL B.P ALL THE WAY BACK TO NORMAL

THESE MECHANISMS OPERATE IN TWO WAYS:

DIRECT MECHANISM ALSO CALLED AS RENAL FLUID MECHANISM OR ECFV MECHANISM

INDIRECT MECHANISM

ALDOSTERONE SYSTEM RENIN ANGIOTENSIN SYSTEM

Renin – angiotensin system

Components of this system are:Renin: a. Form in JG cells of kidneys as proenzyme activated by low arterial blood pressure b. Cause activation of another substance called ANGIOTENSINOGEN present in bloodAngiotensinogen: Is present in blood , activated by renin to form ANGIOTENSIN IAngiotensin I: This is converted to ANGIOTENSIN II in lungs by an enzyme called Angiotensin converting enzyme (ACE) Angiotensin II: Is a powerful vasoconstrictor , but remains for 1-2 minutes in blood as it is rapidly degraded by angiotensinases

Angiotensin II

Elevate the blood pressure by two means:

Direct vasoconstrictive effects on the arterioles all over the body , thus increasing the total peripheral resistance , thus causing an increases in blood pressure

Decreases the excretion of both salt and water by the kidneys (more powerful effect as compared to vasoconstrictive effect)

Actions of angiotensin II

Angiotensin decreases the excretion of salt and water by the kidneys by two processes:

Direct effect on kidneys

Stimulating aldosterone secretion so as to reabsorb more sodium and water from the renal tubules

D.MISCELLANEOUS MECHANISMS

THEY ARE:

ROLE OF SYMPATHETIC NERVES

ROLE OF ADH

DIRECT EFFECTINDIRECT EFFECT

1.ROLE OF SYMPATHETIC NERVES

KIDNEYS ARE STRONGLY SUPPLIED BY SYMPATHETIC NERVESAND THE DEGREE OF SYMPATHETIC STIMULATION CAN ALTER THE RENAL FUNCTIONS.

FOR EG WHEN SYMPATHETIC NERVES TO KIDNEY ARE STIMULATED FOR SEVERAL WEEKS CONTINOUSLY, RENAL RETENTION OF FLUID OCCURS TO CAUSE CHRONICALLY ELEVATED B.P AS LONG AS THE SYMPATHETIC STIMULATION CONTINUES.

THEREFORE IT IS POSSIBLEFOR NERVOUS REGULATION OF KIDNEY TO CAUSE CHRONIC ELEVATION OF ARTERIAL B.P

2.ROLE OF ADH

DIRECT EFFECT:

IN LARGE DOSAGE IT PRODUCES:

ARTERIOLAR CONSTRICTION TO INCREASE PERIPHERAL RESISTANCEVENULAR CONSTRICTION TO INCREASE VENOUS RETURN

THESE BOTH FINALLY INCREASE THE B.P

INDIRECCT EFFECT:

RISE IN B.P INCREASE THE RIGHT ATRIUM PRESSURE AND ADH SECRETION GETS INHIBITED RESULTING IN FALL OF B.P

SIMILARLY FALL IN B.P DECREASES RIGHT ATRIUM PRESSURE, THIS PROMOTES ADH SECRETION FOR THE POSTERIOR PITIUTARY.

MEASUREMENT OF BLOOD PRESSUREThe doctor measures the maximum pressure (systolic) and the lowest pressure (diastolic) made

by the beating of the heart.

The systolic pressure is the maximum pressure in an artery at the moment when the heart is beating and pumping blood through the body.

The diastolic pressure is the lowest pressure in an artery in the moments between beats when the heart is resting.

CLINICAL METHOD OF TAKING BLOOD PRESSURE

Manual non-invasive blood pressure measurement

This requires, at the very least, an inflatable cuff with a pressure gauge (sphygmomanometer). Wind the cuff round the arm (which should be at about heart level) and inflate it to a pressure

higher than the expected blood pressure. Then deflate the cuff slowly. With a stethoscope, listen over the brachial artery. When the cuff reaches systolic pressure, a clear tapping sound is heard

in time with the heart beat. As the cuff deflates further, the sounds become quieter, but become louder again before disappearing altogether. The point at which the sounds disappear is the diastolic pressure. If you have no stethoscope, the systolic blood pressure can be found by

palpating the brachial artery and noting the pressure in the cuff at which it returns.

The sounds heard while measuring blood pressure in this way are called the Korotkoff sounds, and undergo 5 phases:

initial 'tapping' sound (cuff pressure = systolic pressure) sounds increase in intensity

sounds at maximum intensity sounds become muffled

sounds disappear

DISORDERS OF BLOOD PRESSURE:

BLOOD PRESSURE DISORDERS ACCOUNT A LARGE NUMBER OF CASES BOTH IN CLINICAL OR SUBCLINICAL.THE DISORDERS OF BLOOD PRESSURE IS GROUPED UNDER TWO BROAD GROUPS:

THOSE WHICH CAUSE INCREASE IN BLOOD PRESSURE ALSO KNOWN AS HYPERTENSION

THOSE WHICH CAUSE DECREASE IN BLOOD PRESSURE ALO KNOWN AS HYPOTENSION.

HYPERTENSION