In certain pathological states the blood pressure rises above the normal figure sometimes reaching such heights as to become a source of imminent danger to life.This raised blood pressure is not a disease by
t a sign or manifestation of a pathological process,just as fever is not a disease but a measurable external index of an internal malady.It might be said in consonance both with reason and science,that the rise of blood pressure is a CONSERVATIVE or COMPENSATORY process by which adequate circulation of blood is maintained in the tissues in spite of increased resistance or obstruction to the flow of blood. If the blood pressure would fail to rise while the obstruction to the flow of blood be increasing, the inevitable result would be death from failure of circulation.To bring the analogy closer between fever and increased blood pressure,it may be asserted that a rise of blood pressure is a necessary evil to support life in adverse circumstances of blood-flow as much as fever is an unpleasant reaction but,nevertheless,conductive to the body to fight out the invading disease.But both fever and blood pressure should remain within safe limits,and every effort should be made to reduce them when they assume alarming proportions.It must be borne in mind that a drastic reduction of fever or blood pressure by drugs is fraught with grave consequences,and should by no means be attempted.Removal of the cause to which the body reacts by fever or increased blood pressure is the ideal method of treatment.
High blood pressure,which is also known as HYPERTENSION,seems to be commoner in modern times than is the good old days,It cannot be denied that the modern civilization has brought in its trail a great deal of adverse factors tending to raise blood pressure.Intensive struggle for existence associated with continual anxiety,greedy,ambition,artificial methods of living,want of faith in religion,intemperance,irregular hours,adulterated and unwholesome food,and many vices peculiar to modern civilization do undoubtedly play important parts in its causation.Moreover,with the discovery of the Sphygmomanometer,the detection of raised blood pressure has become an easy affair and.therefore,more cases are brought to the notice of the profession today than before.However,it cannot be contended that Hypertension was a rarity in the good old days.since Apoplexy has been dealt with in the medical treaties of Ayurvedic System of Medicine.
CIRCULATION
In order to appreciate the importance of blood pressure a thorough understanding of the CIRCULATION is requisite.Circulation means a continual out-flow of blood from the heart along certain channels called the arteries and the capillaries and then back to the heart itself through the veins.Or,in other words,the blood-stream flows round and round the same course in a cyclic fashion,without pause or intermission.
The POWER,which keeps the blood moving continually,is jointly supplied by the heart and the elasticity of the arterial wall.This power is needed to push the blood forward by overcoming the resistance to the flow of blood as given by the small arteries called the arterioles and the capillaries.For the circulation to the continual,both the power and the resistance are essential.This will be explained later in this treaties.
THE HEART
The heart is a muscular pump,situated obliquely in the chest-cavity between the lungs,so that the major part of it lies to the left of the mid-sternal line.It is divided by a musculo-membranous partition into the RIGHT and the LEFT sides.Each side presents an upper small chamber called the AURICLE.and a lower larger chamber known as the VENTRICLE.The right chambers are concerned entirely with VENOUS blood,whereas the left ones are to deal with ARTERIAL or pure oxygenated blood.The phase of contraction of the heart is called the SYSTOLE,while the phase of relaxation and rest is known as the DIASTOLE.
Venous or impure blood is poured into the right auricle by the Superior and Inferior Venae Cavae-the two venous terminal trunks-the former bringing the impure blood from the head,neck and upper limbs,while the latter draining the impure blood from the rest of the body.The filling of the auricle is helped by the suction-action of the expanding auricle after contraction,as well as by the increased negative pressure produced inside the chest during inspiration.
The right auricle communicates with the right ventricle by means of a door guarded by a valve(TRICUSPID),which would allow only a one-way traffic,permitting the flow of blood from the auricle into the ventricle,and not in the opposite direction.When the ventricles relax the A.V valves(auriculo-ventricular valves)open,and by contraction of the auricles,the auricular blood rapidly rushes into the ventricles completing the ventricular filling.Here the auricular systole ends and is followed by the ventricular systole.When the auricular systole occurs the mouths of the Superior and the Inferior Vena Cava are shut by the contraction of the circular muscular fibres enriching their mouths.so that the blood cannot flow back into them.
The right ventricle,having received venous blood from the right auricle,pumps it through the PULMONARY ARTERY into the lungs for oxygenation of the blood and for washing out its carbon dioxide in the breath.When the right ventricle contracts to drive the blood into the lungs,the tricupsid valve closes to prevent its backward flow,while the SEMLUNAR valve,guarding the mouth of the pulmonary artery,is forced open to allow the passage of blood to the right and the left lungs via the right and the left branches of the pulmonary artery.
In the lungs the pulmonary arteries divide and subdivide into smaller and smaller branches till a network of very fine vessels(CAPILLARIES)is produced,their walls being so thin as to allow gaseous exchanges,the haemoglobin of the blood combines with the oxygen from the inspired air,and the carbon dioxide of the blood is got rid of in the expired air.These capillaries unite with each other and make the fine veins,which in turn unite with each other make bigger veins.Thus the process goes on till four PULMONARY VEINS are formed two for each lung.These veins open into the left auricle by separate openings,through which the oxygenated blood from the lungs is received into the left auricle.
The left auricle,like the right one,communicate with the left ventricle by means of a door guarded by a valve BICUSPID OR MITRAL,to allow a one-way traffic.
The left ventricle receives the oxygenated blood from the left auricle,exactly in the same way as the right ventricle receives its blood from the right auricle.When the left ventricle contracts,the mitral valve closes and the AORTIC VALVE,guarding the mouth of the aorta,opens and blood flows forwards into the aorta.
The auricles contract together just before the simultaneous contraction of both the ventricles.After the simultaneous contractions of both ventricles. After the auricular systole the auricles relax and continue in that state of diastole during ventricular contraction,as well as for most of the period of ventricular rest(diastole).The events from the beginning of one auricular systole to the beginning of the next constitute the CARDIAC CYCLE.
The heart beats 72 times per minute in the average in healthy young man at rest.On that basis each cardiac cycle take 0.8 second
Auricular Systole-0.05 sec
Auricular Diastole-0.75 sec
Ventricular Systole-0.3 sec
Ventricular Diastole 0.3 sec
Any increase of the heart rate is always at the expense of the rest period of the heart,that is,the diastole.
THE ARTERIAL SYSTEM
The system of tubes through which the blood flows away from the heart to the tissues is known as the
ARTERIAL SYSTEM.There is a parent trunk called the AORTA,which rises from the left ventricle.From the Aorta big branches are given off.From these big branches further branches arise.This branching process goes on till very small arteries called the ARTERIOLES are produced.Beyond these arterioles capillary networks are formed,through which gaseous and other exchanges take place between the blood and the tissues.The whole arterial system bears a close resemblance to a tree with its trunk,branches,twigs and leaves.
The arteries are not rigid tubes,The elastic tissue preponderates in the large arteries,while the muscular tissue is developed in the medium and small arteries.The capillaries have very thin transparent walls made of a singular layer of endothelial cells which are capable of contraction.On the walls of the capillaries are found a peculiar type of cells the ROUGET CELLS having thread like branching processes forming a network around the capillaries.There cells,by their contraction and relaxation,bring about alterations of the size of the capillaries.
The muscular tissue of the arteries and the arterioles,which is of the plain or involuntary variety,as well as the capillaries are under the control of the autonomic nervous systems,comprising of VASO-CONSTRICTOR and VASO-DILATOR mechanisms.The vaso-constrictor mechanism is in constant mild action or tone,there-by preventing dilation of the vessels.The vaso-dilator mechanism comes into play to dilate the arterioles and the capillaries according to requirements.Therefore,the peripheral resistance to blood-flow may increase or decrease according to the degree of vaso-constriction or vaso-dilatation,which is determined by the autonomic nervous system.
The velocity of the flow of blood is not the same in all tubes of the arterial system.The bigger the artery the faster is the flow.In the Aorta the blood flows at the rate of A FOOT PER SECOND,while in the capillaries the flow is AN INCH PER MINUTE,or,in order words,the arterioles and the capillaries constitute the peripheral resistance,which increase or decrease according to the state and degree of contraction or relaxation of the arterioles and the capillaries.
THE VENOUS SYSTEM
The capillaries unite to from small veins,which unite again to form larger ones.The process of forming larger and larger veins continue till two large venous trunks come into existence,namely,the Superior and the Inferior Venae Cava,Except in very minute veins and in those veins which are not subjected to muscular pressure,there are veins,usually found in pairs,to guide the flow of blood,by preventing its back-ward flow,from the periphery towards the heart.
BLOOD PRESSURE
The pressure which the blood exerts on the wall of the vessel is called BLOOD PRESSURE.During the contraction of the ventricle systole it is maximum,while when the ventricle is filling diastole it is the minimum.The maximum pressure of blood in an artery is called SYSTOLIC PRESSURE,as it coincides with the systole of the ventricle.The minimum pressure of blood in an artery is called the DIASTOLIC PRESSURE,as it coincides with the diastole of the ventricle.The difference between the maximum and minimum pressure is known as the PULSE PRESSURE.It is the Pulse Pressure which keeps the blood moving constantly.
The blood pressure is not the same degree in all the vessels.It is much more in those arteries which are nearer to the heart than in those which are further away from the heart.
In the BRANCHIAL ARTERY the artery of choice for taking blood pressure reading - the systolic pressure in a healthy young man at rest is about 120 mm,of mercury,while the blood pressure in the capillaries is between 20 to 10 mm.In the veins the blood pressure is lower;the venous pressure in a vein at the bend of elbow held at the level of the right auricle is only between 2 to 10 mm of Hg.
| Systolic | Diastolic | |
| Left Ventricle | 150 | |
| Aorta | 150 | |
| Branchial Artery | 120 | |
| Radial Artery | 100 | |
| Arterioles | 80 | |
| Capillaries | 20 | |
| Small Veins | 15 | |
| Femoral Veins | 20 | |
| Inferior Vena Cava | 3 |
HOW TO CHECK BLOOD PRESSURE
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