Blood pressure (BP) Blood Pressure is the pressure exerted by circulating blood upon the walls of blood vessels and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation, usually measured at a person's upper arm.
A person’s blood pressure is usually expressed in terms of the systolic (maximum) pressure over diastolic(minimum) pressure and is measured in millimeters of mercury (mm Hg). Normal resting blood pressure for an adult is approximately 120/80 mm Hg.
Blood pressure varies depending on situation, activity, and disease states, and is regulated by the nervous and endocrine systems. Blood pressure that is pathologically low is called hypotension, and pressure that is pathologically high is hypertension. Both have many causes and can range from mild to severe, with both acute and chronic forms. Chronic hypertension is a risk factor for many diseases, including kidney failure, heart attack, and stroke. Chronic hypertension is more common than chronic hypotension in Western countries. Chronic hypertension often goes undetected because of infrequent monitoring and the absence of obvious symptoms. Blood pressure fluctuates from minute to minute and normally shows a circadian rhythm over a 24-hour period, with highest readings in the afternoons and lowest readings at night.Loss of the normal fall in blood pressure at night is associated with a greater future risk of cardiovascular disease and there is evidence that night-time blood pressure is a stronger predictor of cardiovascular events than day-time blood pressure.
Various factors, such as age and sex, influence a person's blood pressure and variations in it. In children, the normal ranges are lower than for adults and depend on height. Reference blood pressure values have been developed for children in different countries, based on the distribution of blood pressure in children of these countries.
As adults age, systolic pressure tends to rise and diastolic tends to fall. In the elderly, blood pressure tends to be above the normal adult range,largely because of reduced flexibility of the arteries. Also, an individual's blood pressure varies with exercise, emotional reactions, sleep, digestion, time of day and circadian rhythm.
Differences between left and right arm blood pressure measurements tend to be random and average to nearly zero if enough measurements are taken. However, in a small percentage of cases there is a consistent difference greater than 10 mm Hg which may need further investigation, e.g. for obstructive arterial disease.
The risk of cardiovascular disease increases progressively above 115/75 mm Hg.In the past, hypertension was only diagnosed if secondary signs of high arterial pressure were present, along with a prolonged high systolic pressure reading over several visits. Regarding hypotension, in practice blood pressure is considered too low only if noticeable symptoms are present.
Clinical trials demonstrate that people who maintain arterial pressures at the low end of these pressure ranges have much better long term cardiovascular health. The principal medical debate concerns the aggressiveness and relative value of methods used to lower pressures into this range for those who do not maintain such pressure on their own.
Elevations, more commonly seen in older people, though often considered normal, are associated with increased morbidity and mortality. Pulse pressure is determined by the interaction of the stroke volume of the heart, the compliance (ability to expand) of the arterial system— largely attributable to the aorta and large elastic arteries—, and the resistance to flow in the arterial tree.
By expanding under pressure, the aorta absorbs some of the force of the blood surge from the heart during a heartbeat. In this way, the pulse pressure is reduced from what it would be if the aorta were not compliant. The loss of arterial compliance that occurs with aging explains the elevated pulse pressures found in elderly patients.
Blood pressure generally refers to the arterial pressure in the systemic circulation. However, measurement of pressures in the venous system and the pulmonary vessels plays an important role in intensive care medicine but requires invasive measurement of pressure using a catheter.
Venous pressure is the vascular pressure in a vein or in the atria of the heart. It is much less than arterial pressure, with common values of 5 mm Hg in the right atrium and 8 mm Hg in the left atrium.
Variants of venous pressure include: Central venous pressure, which is a good approximation of right atrial pressure, which is a major determinant of right ventricular end diastolic volume. (However, there can be exceptions in some cases.)
The jugular venous pressure (JVP) is the indirectly observed pressure over the venous system. It can be useful in the differentiation of different forms of heart and lung disease.
The portal venous pressure is the blood pressure in the portal vein. It is normally 5–10 mm Hg Pulmonary pressure/ Pulmonary artery pressure.Normally, the pressure in the pulmonary artery is about 15 mm Hg at rest.
Increased blood pressure in the capillaries of the lung cause pulmonary hypertension, with interstitial edema if the pressure increases to above 20 mm Hg, and to pulmonary edema at pressures above 25 mm Hg. Disorders of blood pressure control include: high blood pressure, low blood pressure, and blood pressure that shows excessive or maladaptive fluctuation. Hypertension (High): Overview of main complications of persistent high blood pressure. Arterial hypertension can be an indicator of other problems and may have long-term adverse effects. Sometimes it can be an acute problem, for example hypertensive emergency.
Levels of arterial pressure put mechanical stress on the arterial walls. Higher pressures increase heart workload and progression of unhealthy tissue growth (atheroma) that develops within the walls of arteries. The higher the pressure, the more stress that is present and the more atheroma tend to progress and the heart muscle tends to thicken, enlarge and become weaker over time.
Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysms, and is the leading cause of chronic kidney failure. Even moderate elevation of arterial pressure leads to shortened life expectancy. At severely high pressures, mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.
In the past, most attention was paid to diastolic pressure; but nowadays it is recognised that both high systolic pressure and high pulse pressure (the numerical difference between systolic and diastolic pressures) are also risk factors. In some cases, it appears that a decrease in excessive diastolic pressure can actually increase risk, due probably to the increased difference between systolic and diastolic pressures (see the article on pulse pressure).
If systolic blood pressure is elevated (>140) with a normal diastolic blood pressure (<90), it is called "isolated systolic hypertension" and may present a health concern.
For those with heart valve regurgitation, a change in its severity may be associated with a change in diastolic pressure. In a study of people with heart valve regurgitation that compared measurements 2 weeks apart for each person, there was an increased severity of aortic and mitral regurgitation when diastolic blood pressure increased, whereas when diastolic blood pressure decreased, there was a decreased severity.
Low: Hypotension: Blood pressure that is too low is known as hypotension. Hypotension is a medical concern if it causes signs or symptoms, such as dizziness, fainting, or in extreme cases.
When arterial pressure and blood flow decrease beyond a certain point, the perfusion of the brain becomes critically decreased (i.e., the blood supply is not sufficient), causing light headedness, dizziness, weakness or fainting.
Sometimes the arterial pressure drops significantly when a patient stands up from sitting. This is known as orthostatic hypotension (postural hypotension); gravity reduces the rate of blood return from the body veins below the heart back to the heart, thus reducing stroke volume and cardiac output.
When people are healthy, the veins below their heart quickly constrict and the heart rate increases to minimize and compensate for the gravity effect. This is carried out involuntarily by the autonomic nervous system. The system usually requires a few seconds to fully adjust and if the compensations are too slow or inadequate, the individual will suffer reduced blood flow to the brain, dizziness and potential blackout. Increases in G-loading, such as routinely experienced by aerobatic or combat pilots 'pulling Gs', greatly increases this effect.
Repositioning the body perpendicular to gravity largely eliminates the problem.
Other causes of low arterial pressure include:
Hemorrhage – blood loss
Toxins including toxic doses of blood pressure medicine
Hormonal abnormalities, such as Addison's disease
Eating disorders, particularly anorexia nervosa and bulimia
Shock is a complex condition which leads to critically decreased perfusion. The usual mechanisms are loss of blood volume, pooling of blood within the veins reducing adequate return to the heart and/or low effective heart pumping. Low arterial pressure, especially low pulse pressure, is a sign of shock and contributes to and reflects decreased perfusion.
If there is a significant difference in the pressure from one arm to the other, that may indicate a narrowing (for example, due to aortic coarctation, aortic dissection, thrombosis or embolism) of an artery.
Fluctuating blood pressure-Normal fluctuation in blood pressure is adaptive and necessary. Fluctuations in pressure that are significantly greater than the norm are associated with greater white matter hyperintensity, a finding consistent with reduced local cerebral blood flow and a heightened risk of cerebrovascular disease.
Within both high and low blood pressure groups, a greater degree of fluctuation was found to correlate with an increase in cerebrovascular disease compared to those with less variability, suggesting the consideration of the clinical management of blood pressure fluctuations, even among normotensive older adults.
Older individuals and those who had received blood pressure medications were more likely to exhibit larger fluctuations in pressure. (ADH/Vasopressin), renin and aldosterone is the resultant increase in blood volume results in an increased blood pressure.
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