Blood Pressure: From 4 Different Sources
The cardio-vascular vessels may be compared with a central heating system in which a volume of water is forced through a network of pipes by a pump in a closed circuit, over and over again. Our heart and circulatory system operate in the same way.
Blood pressure is recorded by two readings on a sphygmomanometer with the aid of the traditional inflatable cuff. The top pressure is known as the systolic, the bottom as the diastolic. The systolic pressure occurs when the heart contracts, the diastolic when the heart relaxes and the volume of blood is at its lowest. A practitioner interprets the pressure of blood against the wall of the brachial artery in terms of millimetres.
In a healthy young person or middle-aged adult, average systolic pressure is 120, diastolic 80. They are recorded as 120/80. A pressure of 140/90 requires investigation while one of 160/95 is high and demands treatment. Average pressure at 50 is 135/80, over 65 – 165/85. Defined hypertension is a raised pressure on three consecutive readings.
The highest pressure peak is reached in the evening after a day’s work and the lowest, at night. Pressure may rise with stress when the heart responds by beating faster, or fall with physical or mental exhaustion when the heart slows down. Persistent high or low pressure is usually associated with other conditions which may require their own specific treatments: i.e. low – anaemia, high – kidney disease. See: HYPERTENSION. HYPOTENSION.
The pressure exerted by the flow of blood through the main arteries. The pressure at 2 different phases is measured. Systolic, the higher pressure, is created by the contraction of the heart. Diastolic, the lower, is recorded during relaxation of the ventricles between heartbeats; it reflects the resistance of all the small arteries in the body and the load against which the heart must work. The pressure wave that is transmitted along the arteries with each heartbeat is easily felt as the pulse.
Blood pressure is measured using a sphygmomanometer and is expressed as millimetres of mercury (mmHg).
Blood pressure varies with age, between individuals, and at different times in the same individual but a healthy young adult usually has a blood pressure reading, at rest, of about 120/80 (that is 120 mmHg systolic and 80 mmHg diastolic).
Abnormally high blood pressure is called hypertension; abnormally low pressure is termed hypotension.
Blood pressure is that pressure which must be applied to an artery in order to stop the pulse beyond the point of pressure. It may be roughly estimated by feeling the pulse at the wrist, or accurately measured using a SPHYGMOMANOMETER. It is dependent on the pumping force of the heart, together with the volume of blood, and on the elasticity of the blood vessels.
The blood pressure is biphasic, being greatest (systolic pressure) at each heartbeat and falling (diastolic pressure) between beats. The average systolic pressure is around 100 mm Hg in children and 120 mm Hg in young adults, generally rising with age as the arteries get thicker and harder. Diastolic pressure in a healthy young adult is about 80 mm Hg, and a rise in diastolic pressure is often a surer indicator of HYPERTENSION than is a rise in systolic pressure; the latter is more sensitive to changes of body position and emotional mood. Hypertension has various causes, the most important of which are kidney disease (see KIDNEYS, DISEASES OF), genetic predisposition and, to some extent, mental stress. Systolic pressure may well be over 200 mm Hg. Abnormal hypertension is often accompanied by arterial disease (see ARTERIES, DISEASES OF) with an increased risk of STROKE, heart attack and heart failure (see HEART, DISEASES OF). Various ANTIHYPERTENSIVE DRUGS are available; these should be carefully evaluated, considering the patient’s full clinical history, before use.
HYPOTENSION may result from super?cial vasodilation (for example, after a bath, in fevers or as a side-e?ect of medication, particularly that prescribed for high blood pressure) and occur in weakening diseases or heart failure. The blood pressure generally falls on standing, leading to temporary postural hypotension – a particular danger in elderly people.
the pressure of blood against the walls of the main arteries. Pressure is highest during *systole, when the ventricles are contracting (systolic pressure), and lowest during *diastole, when the ventricles are relaxing and refilling (diastolic pressure). Blood pressure is measured – in millimetres of mercury (mmHg) – by means of a *sphygmomanometer at the brachial artery of the arm, where the pressure is most similar to that of blood leaving the heart. The normal range varies with age, but a young adult would be expected to have a systolic pressure of around 120 mmHg and a diastolic pressure of 80 mmHg at rest. These are recorded as 120/80 mmHg.
Individual variations are common. Muscular exertion and emotional factors, such as fear, stress, and excitement, all raise systolic blood pressure (see hypertension). Systolic blood pressure is normally at its lowest during sleep. Severe shock may lead to an abnormally low blood pressure and possible circulatory failure (see hypotension). Blood pressure is adjusted to its normal level by the *sympathetic nervous system and hormonal controls.
A blood clot arises when blood comes into contact with a foreign surface – for example, damaged blood vessels – or when tissue factors are released from damaged tissue. An initial plug of PLATELETS is converted to a de?nitive clot by the deposition of FIBRIN, which is formed by the clotting cascade and erythrocytes. (See COAGULATION.)... blood clot
The number of each of the cellular components per litre of blood. It may be calculated using a microscope or by an automated process.... blood count
See TRANSFUSION – Transfusion of blood.... blood transfusion
See SEPTICAEMIA.... blood-poisoning
The pressure exerted by the blood against the arterial wall during DIASTOLE. This is the lowest blood pressure in the cardiac cycle. A normal reading of diastolic pressure in a healthy adult at rest is 70 mm Hg. (See HEART.)... diastolic pressure
See BLOOD GROUPS.... abo blood groups
A department in which blood products are prepared, stored, and tested prior to transfusion into patients.... blood bank
A functional, semi-permeable membrane separating the brain and cerebrospinal ?uid from the blood. It allows small and lipid-soluble molecules to pass freely but is impermeable to large or ionised molecules and cells.... blood brain barrier
See ERYTHROCYTES and LEUCOCYTES.... blood corpuscle
An individual who donates his or her own blood for use in patients of compatible blood group who require transfusion.... blood donor
Speci?cally, this describes the measurement of the tensions of oxygen and carbon dioxide in blood. However, it is commonly used to describe the analysis of a sample of heparinised arterial blood for measurement of oxygen, carbon dioxide, oxygen saturation, pH, bicarbonate, and base excess (the amount of acid required to return a unit volume of the blood to normal pH). These values are vital in monitoring the severity of illness in patients receiving intensive care or who have severe respiratory illness, as they provide a guide to the e?ectiveness of oxygen transport between the outside air and the body tissues. Thus they are both a guide to whether the patient is being optimally ventilated, and also a general guide to the severity of their illness.... blood gases
Removal of venous, capillary or arterial blood for haematological, microbiological or biochemical laboratory investigations.... blood test
Tube through which blood is conducted from or to the heart. Blood from the heart is conducted via arteries and arterioles through capillaries and back to the heart via venules and then veins. (See ARTERIES and VEINS.)... blood vessel
The pressure of blood within the right atrium of the HEART as measured by a catheter and manometer.... central venous pressure
A method for treating babies who suffer from alveolar collapse in the lung as a result of HYALINE MEMBRANE DISEASE (see also RESPIRATORY DISTRESS SYNDROME).... continuous positive airways pressure
People are divided into four main groups in respect of a certain reaction of the blood. This depends upon the capacity of the serum of one person’s blood to cause the red cells of another’s to stick together (agglutinate). The reaction depends on antigens (see ANTIGEN), known as agglutinogens, in the erythrocytes and on ANTIBODIES, known as agglutinins, in the serum. There are two of each, the agglutinogens being known as A and B. A person’s erythrocytes may have (1) no agglutinogens, (2) agglutinogen A, (3) agglutinogen B, (4) agglutinogens A and B: these are the four groups. Since the identi?cation of the ABO and Rhesus factors (see below), around 400 other antigens have been discovered, but they cause few problems over transfusions.
In blood transfusion, the person giving and the person receiving the blood must belong to the same blood group, or a dangerous reaction will take place from the agglutination that occurs when blood of a di?erent group is present. One exception is that group O Rhesus-negative blood can be used in an emergency for anybody.
| Agglutinogens | Agglutinins | Frequency |
| in the | in the | in Great |
| Group | erythrocytes | plasma | Britain |
| AB | A and B | None | 2 per cent |
| A | A | Anti-B | 46 per cent |
| B | B | Anti-A | 8 per cent |
| O | Neither | Anti-A and | 44 per cent |
| A nor B | Anti-B | |
| | | |
Rhesus factor In addition to the A and B agglutinogens (or antigens), there is another one known as the Rhesus (or Rh) factor – so named because there is a similar antigen in the red blood corpuscles of the Rhesus monkey. About 84 per cent of the population have this Rh factor in their blood and are therefore known as ‘Rh-positive’. The remaining 16 per cent who do not possess the factor are known as ‘Rh-negative’.
The practical importance of the Rh factor is that, unlike the A and B agglutinogens, there are no naturally occurring Rh antibodies. However, such antibodies may develop in a Rh-negative person if the Rh antigen is introduced into his or her circulation. This can occur (a) if a Rh-negative person is given a transfusion of Rh-positive blood, and (b) if a Rh-negative mother married to a Rh-positive husband becomes pregnant and the fetus is Rh-positive. If the latter happens, the mother develops Rh antibodies which can pass into the fetal circulation, where they react with the baby’s Rh antigen and cause HAEMOLYTIC DISEASE of the fetus and newborn. This means that, untreated, the child may be stillborn or become jaundiced shortly after birth.
As about one in six expectant mothers is Rh-negative, a blood-group examination is now considered an essential part of the antenatal examination of a pregnant woman. All such Rh-negative expectant mothers are now given a ‘Rhesus card’ showing that they belong to the rhesus-negative blood group. This card should always be carried with them. Rh-positive blood should never be transfused to a Rh-negative girl or woman.... blood groups
A procedure performed during a mother’s labour in which a blood sample is taken from a vein in the scalp of the FETUS. This enables tests to be performed that indicate whether the fetus is, for example, suffering from a shortage of oxygen (HYPOXIA). If so, the obstetrician will usually accelerate the baby’s birth.... fetal blood sampling
See ULCER – Decubitus ulcer.... pressure sores
See ERYTHROCYTES; BLOOD.... red blood cell
See BLOOD PRESSURE.... systolic pressure
See LEUCOCYTES.... white blood cell
See blood glucose.... blood sugar
See TRANSFUSION – Transfusion of blood.... autologous blood transfusion
See VENESECTION.... blood-letting
See ANAEMIA; LEUKAEMIA; LYMPHOMA; MYELOMATOSIS; THROMBOSIS.... blood, diseases of
Love, Protection, Exorcism, Potency... dragons blood
This body manages regional TRANSFUSION centres. Among its aims are the maintenance and promotion of blood and blood products based on a system of voluntary donors; implementing a cost-e?ective national strategy for ensuring adequate supplies of blood and its products to meet national needs; and ensuring high standards of safety and quality.... national blood authority
See: BLEEDING (haemoptysis). ... coughing of blood
Popular blood tonic of the 1930s, 1940s and 1950s. Ingredients: Liquid Extract Liquorice 5 per cent, Infusion Gentian Co Conc 10 per cent, Infusion Senna Conc 5 per cent. And 25 per cent alcoholic extractive from Burdock 5 per cent, Red Clover 5 per cent, Queen’s root 2.5 per cent, Yellow Dock root 1.25 per cent, Poke root 2.5 per cent, Sarsaparilla 2.5 per cent. (Carter Bros) ... glentona herbal blood purifier
The course of the circulation is as follows: the veins pour their blood, coming from the head, trunk, limbs and abdominal organs, into the right atrium of the HEART. This contracts and drives the blood into the right ventricle, which then forces the blood into the LUNGS by way of the pulmonary artery. Here it is contained in thin-walled capillaries, over which the air plays freely, and through which gases pass readily out and in. The blood gives o? carbon dioxide (CO2) and takes up oxygen (see RESPIRATION), and passes on by the pulmonary veins to the left atrium of the heart. The left atrium expels it into the left ventricle, which forces it on into the aorta, by which it is distributed all over the body. Passing through capillaries in the various tissues, it enters venules, then veins, which ultimately unite into two great veins, the superior and the inferior vena cava, these emptying into the right atrium. This complete circle is accomplished by any particular drop of blood in about half a minute.
In one part of the body there is a further complication. The veins coming from the bowels, charged with food material and other products, split up, and their blood undergoes a second capillary circulation through the liver. Here it is relieved of some food material and puri?ed, and then passes into the inferior vena cava, and so to the right atrium. This is known as the portal circulation.
The circle is maintained always in one direction by four valves, situated one at the outlet from each cavity of the heart.
The blood in the arteries going to the body generally is bright red, that in the veins dull red in colour, owing to the former being charged with oxygen and the latter with carbon dioxide (see RESPIRATION). For the same reason the blood in the pulmonary artery is dark, that in the pulmonary veins is bright. There is no direct communication between the right and left sides of the heart, the blood passing from the right ventricle to the left atrium through the lungs.
In the embryo, before birth, the course of circulation is somewhat di?erent, owing to the fact that no nourishment comes from the bowels nor air into the lungs. Accordingly, two large arteries pass out of the navel, and convey blood to be changed by contact with maternal blood (see PLACENTA), while a large vein brings this blood back again. There are also communications between the right and left atria, and between pulmonary artery and aorta. The latter is known as the ductus arteriosus. At birth all these extra vessels and connections close and rapidly shrivel up.... circulatory system of the blood
This is the pressure that is maintained by the brain tissue, intracellular and extracellular ?uid, cerebrospinal ?uid and blood. An increase in intracranial pressure may occur as a result of in?ammation, injury, haemorrhage, or tumour in the brain tissue as well as of some congenital conditions. The pressure is measured by lumbar puncture in which a syringe attached to a mamometer (pressure-measuring device) is inserted into the cerebrospinal ?uid surrounding the lower part of the spinal cord. Where continuous pressure monitoring is necessary, an in-dwelling device can be implanted into a cerebral ventricle. Normal pressure is around 10 mm of mercury (Hg), with the acceptable upper limit being 25 mm Hg.... intracranial pressure
These have almost completely replaced BONE MARROW TRANSPLANT, used to treat malignancies such as LEUKAEMIA and LYMPHOMA for the past 20 years. The high doses of CHEMOTHERAPY or RADIOTHERAPY used to treat these diseases destroy the bone marrow which contains stem cells from which all the blood cells derive. In 1989 stem cells were found in the blood during recovery from chemotherapy. By giving growth factors (cytokines), the number of stem cells in the blood increased for about three to four days. In a peripheral-blood stem-cell transplant, these cells can be separated from the peripheral blood, without a general anaesthetic. The cells taken by either method are then frozen and returned intravenously after the chemotherapy or radiotherapy is completed. Once transplanted, the stem cells usually take less than three weeks to repopulate the blood, compared to a month or more for a bone marrow transplant. This means that there is less risk of infection or bleeding during the recovery from the transplant. The whole procedure has a mortality risk of less than 5 per cent – half the risk of a bone marrow transplant.... peripheral-blood stem-cell transplants
Tests to screen for and diagnose bleeding disorders, usually resulting from deficiencies or abnormalities of blood coagulation factors or of platelets (see blood clotting). Tests are also used to monitor treatment with anticoagulant drugs.... blood-clotting tests
See culture.... blood culture
The level of glucose in the blood. Abnormally high blood glucose (sometimes called sugar) levels are an indication of diabetes mellitus. (See also hyperglycaemia; hypoglycaemia.)... blood glucose
See blood film.... blood smear
The use of a person’s own blood, donated earlier, for blood transfusion. Autologous transfusion eliminates the slight but serious risk of contracting a serious infectious illness from contaminated blood. There is no risk of a transfusion reaction occurring as a result of incompatibility between donor and recipient blood. Up to 3.5 litres of blood can be removed and stored in several sessions at least 4 days apart and up to 3 days before planned surgery. Blood may be salvaged during surgery, filtered and returned to the circulation, reducing the need for transfusion of donated blood.... blood transfusion, autologous
The simplest form of intermittent positive-pressure ventilation is mouth-to-mouth resuscitation (see APPENDIX 1: BASIC FIRST AID) where an individual blows his or her own expired gases into the lungs of a non-breathing person via the mouth or nose. Similarly gas may be blown into the lungs via a face mask (or down an endotracheal tube) and a self-in?ating bag or an anaesthetic circuit containing a bag which is in?ated by the ?ow of fresh gas from an anaesthetic machine, gas cylinder, or piped supply. In all these examples expiration is passive.
For more prolonged arti?cial ventilation it is usual to use a specially designed machine or ventilator to perform the task. The ventilators used in operating theatres when patients are anaesthetised and paralysed are relatively simple devices.They often consist of bellows which ?ll with fresh gas and which are then mechanically emptied (by means of a weight, piston, or compressed gas) via a circuit or tubes attached to an endotracheal tube into the patient’s lungs. Adjustments can be made to the volume of fresh gas given with each breath and to the length of inspiration and expiration. Expiration is usually passive back to the atmosphere of the room via a scavenging system to avoid pollution.
In intensive-care units, where patients are not usually paralysed, the ventilators are more complex. They have electronic controls which allow the user to programme a variety of pressure waveforms for inspiration and expiration. There are also programmes that allow the patient to breathe between ventilated breaths or to trigger ventilated breaths, or inhibit ventilation when the patient is breathing.
Indications for arti?cial ventilation are when patients are unable to achieve adequate respiratory function even if they can still breathe on their own. This may be due to injury or disease of the central nervous, cardiovascular, or respiratory systems, or to drug overdose. Arti?cial ventilation is performed to allow time for healing and recovery. Sometimes the patient is able to breathe but it is considered advisable to control ventilation – for example, in severe head injury. Some operations require the patient to be paralysed for better or safer surgical access and this may require ventilation. With lung operations or very unwell patients, ventilation is also indicated.
Arti?cial ventilation usually bypasses the physiological mechanisms for humidi?cation of inspired air, so care must be taken to humidify inspired gases. It is important to monitor the e?cacy of ventilation – for example, by using blood gas measurement, pulse oximetry, and tidal carbon dioxide, and airways pressures.
Arti?cial ventilation is not without its hazards. The use of positive pressure raises the mean intrathoracic pressure. This can decrease venous return to the heart and cause a fall in CARDIAC OUTPUT and blood pressure. Positive-pressure ventilation may also cause PNEUMOTHORAX, but this is rare. While patients are ventilated, they are unable to breathe and so accidental disconnection from the ventilator may cause HYPOXIA and death.
Negative-pressure ventilation is seldom used nowadays. The chest or whole body, apart from the head, is placed inside an airtight box. A vacuum lowers the pressure within the box, causing the chest to expand. Air is drawn into the lungs through the mouth and nose. At the end of inspiration the vacuum is stopped, the pressure in the box returns to atmospheric, and the patient exhales passively. This is the principle of the ‘iron lung’ which saved many lives during the polio epidemics of the 1950s. These machines are cumbersome and make access to the patient di?cult. In addition, complex manipulation of ventilation is impossible.
Jet ventilation is a relatively modern form of ventilation which utilises very small tidal volumes (see LUNGS) from a high-pressure source at high frequencies (20–200/min). First developed by physiologists to produce low stable intrathoracic pressures whilst studying CAROTID BODY re?exes, it is sometimes now used in intensive-therapy units for patients who do not achieve adequate gas exchange with conventional ventilation. Its advantages are lower intrathoracic pressures (and therefore less risk of pneumothorax and impaired venous return) and better gas mixing within the lungs.... intermittent positive pressure (ipp)
As a natural beverage, a cup of tea brings you many health benefits. One of them is related to blood pressure. Based on the type of tea you drink, it can help lower your blood pressure. Find out more about teas for blood pressure!
Problems with blood pressure
Blood pressure represents the pressure made by the circulating blood on the walls of the blood vessels. However, problems appear in the case of hypertension and hypotension.
Hypertension is a medical condition caused by a high blood pressure, while hypotension is caused by a low blood pressure. Both can be treated with one of the various types of tea for blood pressure.
Tea for high blood pressure
If you’ve got problems with hypertension (high blood pressure), hibiscus tea can help, as it is known to lower blood pressure. You can also pick one of these herbal teas: chrysanthemum tea, flax tea, periwinkle tea, red root tea, self-heal tea, white peony root tea, valerian tea, or wild cherry bark tea.
You can also drink hyssop tea, barberry tea, and rosemary tea, regardless of the blood pressure problem. These three teas will help regulate your blood pressure and reduce the risk of getting either high or low blood pressure problems.
Tea for low blood pressure
In the case of hypotension (low blood pressure), some of the teas you can try include lovage tea, ephedra tea, wu yi tea, cat’s claw tea, vervain tea, or wheatgrass tea. Black tea can help too, though you have to be careful with it as it has a high content of caffeine.
Forbidden teas for blood pressure problems
There are several teas which you should avoid drinking, no matter if you’ve got problems with high blood pressure or low blood pressure. The list of teas you shouldn’t drink includes arnica tea, black cohosh tea, gentian tea, juniper tea, lobelia tea, red ginseng tea, sage tea, stone root tea, and yohimbe tea.
Also, generally it isn’t recommended to drink tea that lowers blood pressure if you’ve got hypotension, or tea that leads to high blood pressure if you’ve got hypertension.
Whether you’ve got problems with high blood pressure or low blood pressure, try a more natural treatment: choose one of the many teas for blood pressure!... tea for blood pressure
Cells, also called blood corpuscles, present in blood for most or part of their lifespan. They include red blood cells, which make up about 45 per cent by volume of normal blood, white blood cells, and platelets. Blood cells are made in the bone marrow by a series of divisions from stem cells.
Red blood cells (also known as RBCs, red blood corpuscles, or erythrocytes) transport oxygen from the lungs to the tissues (see respiration). Each is packed with haemoglobin, enzymes, minerals, and sugars. Abnormalities can occur in the rate at which RBCs are either produced or destroyed, in their numbers, and in their shape, size, and haemoglobin content, causing forms of
anaemia and polycythaemia (see blood, disorders of).
White blood cells (also called WBCs, white blood corpuscles, or leukocytes) protect the body against infection and fight infection when it occurs. The 3 main types of are granulocytes (also called polymorphonuclear leukocytes), monocytes, and lymphocytes. Granulocytes are further classified as neutrophils, eosinophils, or basophils, and each type of granulocyte has a role in either fighting infection or in inflammatory or allergic reactions. Monocytes and lymphocytes also play an important part in the immune system. Lymphocytes are usually formed in the lymph nodes. One type, a T-lymphocyte, is responsible for the delayed hypersensitivity reactions
White (see allergy) and Red blood blood cell is also involved in cell (neutrophil) protection against cancer. T-lymphocytes manufacture chemicals, known as lymphokines, which affect the function of other cells. In addition, the T-cells moderate the activity of B-lymphocytes, which form the antibodies that can prevent a second attack of certain infectious diseases. Platelets (also known as thrombocytes), are the smallest blood cells and are important in blood clotting.
The numbers, shapes, and appearance of the various types of blood cell are of great value in the diagnosis of disease (see blood count; blood film).... blood cells
Disorders resulting from abnormalities in any of the components of blood or from infection. Disorders include types of anaemia, polycythaemia, bleeding disorders, and unwanted clot formation (thrombosis), hypoalbuminaemia (albumin deficiency) and agammaglobulinaemia (deficiency of gamma-globulin). Blood disorders such as sickle cell anaemia, thalassaemia, and haemophilia are inherited. Bone marrow cancers that affect production of blood components include leukaemia, polycythaemia vera, and multiple myeloma. Blood poisoning is usually due to septicaemia or a toxin such as carbon monoxide. Some drugs can cause blood abnormalities as a side effect. (See also anaemia, haemolytic; anaemia, iron-deficiency; anaemia, megaloblastic; malaria; hyperbilirubinaemia.)... blood, disorders of
A general term given to arteries, veins, and capillaries (see circulatory system).... blood vessels
The main mechanism by which blood clots are formed, involving a complex series of reactions in the blood plasma (see blood clotting).... coagulation, blood
See faeces, abnormal; rectal bleeding.... faeces, blood in the
The presence in the faeces of blood that cannot be seen by the naked eye, but can be detected by chemical tests. Such tests are widely used in screening for cancer of the colon (see colon, cancer of). Faecal occult blood may also be a sign of a gastrointestinal disorder such as oesophagitis, gastritis, or stomach cancer; cancer of the intestine (see intestine, cancer of); rectal cancer (see rectum, cancer of); diverticular disease; polyps in the colon; ulcerative colitis; or irritation of the stomach or intestine by drugs such as aspirin. (See also rectal bleeding.)... occult blood, faecal
Places on the body where arteries lie near the surface and pressure can be applied by hand to limit severe arterial bleeding (in which bright red blood is pumped out in regular spurts with the heartbeat). Major pressure points of the body include the brachial pressure point in the middle part of the upper arm and the carotid pressure point at the side of the neck, below the jaw.... pressure points
Analysis of a sample of blood to give information on its cells and proteins and any of the chemicals, antigens, antibodies, and gases that it carries. Such tests can be used to check on the health of major organs, as well as on respiratory function, hormonal balance, the immune system, and metabolism. Blood tests may look at numbers, shape, size, and appearance of blood cells and assess the function of clotting factors. The most important tests are blood count and blood group tests if transfusion is needed. Biochemical tests measure chemicals in the blood (see acid–base balance; kidney function tests; liver function tests). Microbiological tests (see immunoassay) look for microorganisms that are in the blood, as
in septicaemia. Microbiology also looks for antibodies in the blood, which may confirm immunity to an infection. blood transfusion The infusion of large volumes of blood or blood products directly into the bloodstream to remedy severe blood loss or to correct chronic anaemia. In an exchange transfusion, nearly all of the recipient’s blood is replaced by donor blood. Before a transfusion, a sample of the recipient’s blood is taken to identify the blood groups, and it is matched with suitable donor blood. The donor blood is transfused into an arm vein through a plastic cannula. Usually, each unit (about 500 ml) of blood is given over 1–4 hours; in an emergency, 500 ml may be given in a couple of minutes. The blood pressure, temperature, and pulse are monitored during the procedure.
If mismatched blood is accidentally introduced into the circulation, antibodies in the recipient’s blood may cause donor cells to burst, leading to shock or kidney failure. Less severe reactions can produce fever, chills, or a rash. Reactions can also occur as a result of an allergy to transfused blood components. All
blood used for transfusion is carefully screened for a number of infectious agents, including HIV (the AIDS virus) and hepatitis B and hepatitis C.
In elderly or severely anaemic patients, transfusion can overload the circulation, leading to heart failure.
In patients with chronic anaemia who need regular transfusion over many years, excess iron may accumulate (haemosiderosis) and damage organs such as the heart, liver, and pancreas.
Treatment with desferrioxamine to remove excess iron may be needed.... blood tests
see BiPAP.... bi-level positive airways pressure
a combined X-ray and manometry examination of the bladder to look for abnormal function. The bladder is filled slowly with contrast medium using a small urinary catheter and the pressure is monitored during filling and voiding (micturition). X-ray images of the bladder and urethra (see urethrography) are taken. The test is used to differentiate between obstruction to bladder outflow and abnormal involuntary contractions of the muscle in the bladder wall.... bladder pressure study
(blood corpuscle) any of the cells that are present in the blood in health or disease. The cells may be subclassified into three major categories, namely red cells (*erythrocytes); white cells (*leucocytes), which include granulocytes, lymphocytes, and monocytes; and *platelets (see illustration). The blood cells account for approximately 40% of the total volume of the blood in health; red cells comprise the vast majority.... blood cell
(blood clotting) the process whereby blood is converted from a liquid to a solid state. The process may be initiated by contact of blood with a foreign surface (intrinsic system) or with damaged tissue (extrinsic system). These systems involve the interaction of a variety of substances (*coagulation factors) and lead to the production of the enzyme thrombin, which converts the soluble blood protein *fibrinogen to the insoluble protein *fibrin, forming the blood clot. Finally, fibrin is broken down by the action of *plasmin. Anticoagulants and tissue plasminogen activators act by inhibiting or activating various pathways in this cascade (see illustration). Blood coagulation is an essential mechanism for the arrest of bleeding (*haemostasis). See also platelet activation.... blood coagulation
Blood group of people donor can receive blood from... donor’s blood group
... blood plasma see plasma.
see serum.... blood serum
a technique in which a trained assistant presses downwards on the *cricoid cartilage of a supine patient to aid endotracheal *intubation.... cricoid pressure
(FOBT) a noninvasive test used to identify microscopic blood (see occult) in faeces. It is widely used as a screening test for colorectal cancer.... faecal occult blood test
see Guthrie test.... heel-prick blood test
(JVP) the pressure in the internal jugular vein, which is an indirect measurement of *central venous pressure (CVP) in the right atrium. In clinical practice the JVP is estimated by visual inspection at the bedside with the patient reclining at 45 degrees.... jugular venous pressure
a pressure represented by the pressure difference that exists between the osmotic pressure of blood and that of the lymph or tissue fluid. Oncotic pressure is important for regulating the flow of water between blood and tissue fluid. See also osmosis.... oncotic pressure
see noninvasive ventilation.... positive-pressure ventilation
(PI) the ratio of the pressure in the posterior tibial artery to that in the brachial artery, which reflects the degree of arterial obstruction in the artery of the lower limb.... pressure index
a point at which an artery lies over a bone on which it may be compressed by finger pressure, to arrest haemorrhage beyond. For example, the femoral artery may be compressed against the pelvic bone in the groin.... pressure point
(bedsore, decubitus ulcer) an ulcerated area of skin caused by continuous pressure on part of the body: a hazard to be guarded against in all bedridden (especially unconscious) patients. Healing is hindered by the reduced blood supply to the area, and careful nursing is necessary to prevent local gangrene. The patient’s position should be changed frequently (pressure-relieving mattresses are extremely helpful), and the buttocks, heels, elbows, and other regions at risk kept dry and clean.... pressure sore
(PCWP) an indirect measurement of the pressure of blood in the left atrium of the heart, which indicates the adequacy of left heart function. It is measured using a catheter wedged in the most distal segment of the pulmonary artery. See also Swan-Ganz catheter.... pulmonary capillary wedge pressure
haemopoietic *stem cells collected from umbilical cord blood donated at birth, which can be stored indefinitely and used if a sibling or any other blood-compatible baby develops an illness (such as leukaemia) that could only be treated by cord-blood stem-cell transplantation. This facility is now available in the UK and the USA.... umbilical cord blood banked stem cells
see BiPAP.... variable positive airways pressure
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