Positive-pressure ventilation Health Dictionary

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.... blood pressure

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

(1) Passage of air into and out of the RESPIRATORY SYSTEM.

(2) The process by which air is puri?ed and circulated in domestic, occupational, industrial, and other settings. Ideally, the air we breathe should be of the right temperature and humidity, and free of dust, smoke, pollen, and other contaminants. Ventilation aims to produce such an atmosphere. Air-conditioning is frequently used in hospitals, o?ces, and other

public places. Special ?lters may be used to reduce the risk of airborne infections and allergies (see ALLERGY), but poorly maintained and contaminated systems may result in outbreaks of serious disorders, such as LEGIONNAIRE’S DISEASE. Sterilisation of air is rarely required, but ultraviolet light is sometimes used to kill pathogenic organisms. (See also ASTHMA; BRONCHITIS; HUMIDIFICATION.)... ventilation

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

A positive test result for a condition that is not, in fact, present.... false positive

Gram’s Method is a staining procedure that separates bacteria into those that stain (positive) and those that don’t (negative). Gram-positive bugs cause such lovely things as scarlet fever, tetanus, and anthrax, while some of the gram negs can give you cholera, plague, and the clap. This is significant to the microbiologist and the pathologist; otherwise I wouldn’t worry. Still, knowing the specifics (toss in anaerobes and aerobes as well), you can impress real medical professionals with your knowledge of the secret, arcane language of medicine.... gram-positive/negative

See ULCER – Decubitus ulcer.... pressure sores

See BLOOD PRESSURE.... systolic pressure

When we breathe in, the outward movement of the chest increases the volume of the lungs and the pressure in them falls below that of the outside world. Therefore, air is drawn in automatically. When we breathe out, some air exits because of the normal elastic recoil of the lungs, but we also force air out by using the muscles of the chest and the DIAPHRAGM. Replicating this arti?cially involves using a device to produce intermittent positive or negative pressure ventilation as described below.... artificial ventilation of the lungs

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

See “healthy ageing”.... positive ageing

A state of health beyond an asymptomatic state. It usually includes the quality of life and the potential of the human condition. It may also include self-fulfilment, vitality for living and creativity. It is concerned with thriving rather than merely coping. See also “health”.... positive health

The probability that a person with a reactive test has the disease and is not a false reaction.... predictive value positive

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

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

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

The procedure, usually carried out in an operating theatre or intensive-care unit, in which a device called a VENTILATOR takes over a person’s breathing. This is done for someone who is unable to breathe normally. Damage to the respiratory centre of the brain as a result of head injury, disease of the brain, or an overdose of sedative or narcotic drugs may affect the respiratory centre. Chest injuries, disease of the lungs, nerve or muscle disorders or surgery of the chest or abdomen can also affect breathing and require the use of a ventilator to maintain normal breathing. Arti?cial ventilation can also be carried out as an emergency by mouth-to-mouth resuscitation. (See also ANAESTHESIA; ARTIFICIAL VENTILATION OF THE LUNGS.)... ventilation, artificial

The pressure within the eye that helps to maintain the shape of the eyeball, due to the balance between the rate of production and removal of aqueous humour. Aqueous humour is continually produced from the ciliary body and exits from the drainage angle (a network of tissue between the iris and cornea). If drainage is impeded, intraocular pressure builds up (a condition known as glaucoma). If the ciliary body is damaged (as a result of prolonged inflammation), ultrasound scanning may be performed to assess the problem. The underlying cause is treated, if possible. If the baby’s growth is slowing, induction of labour or a caesarean section may be necessary. Most babies whose growth was retarded in the uterus gain weight rapidly after delivery. However, if an intrauterine infection or genetic disorder was the cause, poor growth may continue.

less fluid is produced and the eye becomes soft.... intraocular pressure

a technique in which a trained assistant presses downwards on the *cricoid cartilage of a supine patient to aid endotracheal *intubation.... cricoid pressure

(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

(NIV) mechanical assistance with breathing that does not require the insertion of an endotracheal tube (see intubation). In noninvasive intermittent positive-pressure ventilation (NIPPV) air is blown into the lungs through a close-fitting mask: designs range from helmet-like devices to nasal cushions and full-face or nasal masks (see also Nippy). A ventilator then applies positive pressure to the mask in a cyclical fashion. The technique simplifies the process of ventilation in respiratory failure and reduces or eliminates the need for paralysis and anaesthesia, which are required for endotracheal intubation. See also BiPAP; continuous positive airways pressure.

Negative-pressure ventilation involves the use of devices that draw air into and out of the lungs noninvasively by applying negative pressure in a cyclical way (see ventilator).... noninvasive ventilation

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

adj. see normative.... positive

(in psychiatry) symptoms of schizophrenia characterized by a distortion of some aspect of functioning, such as delusions, hallucinations, or disordered speech. Compare negative symptoms.... positive symptoms

(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

see BiPAP.... variable positive airways pressure

(V/Q scanning) a nuclear medicine technique in which two different isotopes are used, one inhaled (usually *xenon-133 or *krypton-81m), to examine lung ventilation, and the other injected into a vein, to examine lung perfusion. In *pulmonary embolism, the area of lung supplied by the blocked artery is not being perfused with blood – which gives a perfusion defect on the film – but has normal ventilation. This technique is highly sensitive for pulmonary embolism.... ventilation-perfusion scanning