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The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from the tissues. Blood vessels are needed to sustain life, because all of the body's tissues rely on their functionality.
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" refers to the pressure in the large arteries. Blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure in the cardiac cycle. It is measured in millimeters of mercury (mmHg) above the surrounding atmospheric pressure.
Hypertension, also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high blood pressure, however, is a major risk factor for stroke, coronary artery disease, heart failure, atrial fibrillation, peripheral arterial disease, vision loss, chronic kidney disease, and dementia. Hypertension is a major cause of premature death worldwide.
Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure drops when standing up or sitting down. Primary orthostatic hypertension is also often referred to as neurogenic orthostatic hypotension. The drop in blood pressure may be sudden, within 3 minutes or gradual. It is defined as a fall in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg when a person assumes a standing position. It occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain adequate blood pressure when changing the position to standing. As a result, blood pools in the blood vessels of the legs for a longer period, and less is returned to the heart, thereby leading to a reduced cardiac output and inadequate blood flow to the brain.
Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease there may be red blood cell breakdown, a low blood platelet count, impaired liver function, kidney dysfunction, swelling, shortness of breath due to fluid in the lungs, or visual disturbances. Pre-eclampsia increases the risk of undesirable outcomes for both the mother and the fetus. If left untreated, it may result in seizures at which point it is known as eclampsia.
Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure and the diastolic blood pressure, which are the maximum and minimum blood pressures, respectively. A systolic blood pressure of less than 90 millimeters of mercury (mmHg) or diastolic of less than 60 mmHg is generally considered to be hypotension. Different numbers apply to children. However, in practice, blood pressure is considered too low only if noticeable symptoms are present. Primary symptoms generally include dizziness and lightheadedness. Other symptoms include fatigue, shortness of breath, headaches, shakiness, increased thirst, irregular heartbeat, chest pain, confusion.
Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. Resting blood pressure is normally approximately 120/80 mmHg, which yields a pulse pressure of approximately 40 mmHg.
The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels, and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall. Endothelial cells form the barrier between vessels and tissue and control the flow of substances and fluid into and out of a tissue.
Pulmonary hypertension is a condition of increased blood pressure in the arteries of the lungs. Symptoms include shortness of breath, fainting, tiredness, chest pain, swelling of the legs, and a fast heartbeat. The condition may make it difficult to exercise. Onset is typically gradual.
Essential hypertension is the form of hypertension that by definition has no identifiable secondary cause. It is the most common type affecting 85% of those with high blood pressure. The remaining 15% is accounted for by various causes of secondary hypertension. Primary hypertension tends to be familial and is likely to be the consequence of an interaction between environmental and genetic factors. Prevalence of essential hypertension increases with age, and individuals with relatively high blood pressure at younger ages are at increased risk for the subsequent development of hypertension. Hypertension can increase the risk of cerebral, cardiac, and renal events.
Compliance is the ability of a hollow organ (vessel) to distend and increase volume with increasing transmural pressure or the tendency of a hollow organ to resist recoil toward its original dimensions on application of a distending or compressing force. It is the reciprocal of "elastance", hence elastance is a measure of the tendency of a hollow organ to recoil toward its original dimensions upon removal of a distending or compressing force.
Cushing reflex is a physiological nervous system response to increased intracranial pressure (ICP) that results in Cushing's triad of increased blood pressure, irregular breathing, and bradycardia. It is usually seen in the terminal stages of acute head injury and may indicate imminent brain herniation. It can also be seen after the intravenous administration of epinephrine and similar drugs. It was first described in detail by American neurosurgeon Harvey Cushing in 1901.
A hypertensive emergency is very high blood pressure with potentially life-threatening symptoms and signs of acute damage to one or more organ systems. It is different from a hypertensive urgency by this additional evidence for impending irreversible hypertension-mediated organ damage (HMOD). Blood pressure is often above 200/120 mmHg, however there are no universally accepted cutoff values. Signs of organ damage will be discussed below.
Hypertensive encephalopathy (HE) is general brain dysfunction due to significantly high blood pressure. Symptoms may include headache, vomiting, trouble with balance, and confusion. Onset is generally sudden. Complications can include seizures, posterior reversible encephalopathy syndrome, and bleeding in the back of the eye.
In medicine, systolic hypertension is defined as an elevated systolic blood pressure (SBP). If the systolic blood pressure is elevated (>140) with a normal (<90) diastolic blood pressure (DBP), it is called isolated systolic hypertension.
Heart failure with preserved ejection fraction (HFpEF) is a form of heart failure in which the ejection fraction – the percentage of the volume of blood ejected from the left ventricle with each heartbeat divided by the volume of blood when the left ventricle is maximally filled – is normal, defined as greater than 50%; this may be measured by echocardiography or cardiac catheterization. Approximately half of people with heart failure have preserved ejection fraction, while the other half have a reduction in ejection fraction, called heart failure with reduced ejection fraction (HFrEF).
Spaceflight-associated neuro-ocular syndrome (SANS), previously known as Spaceflight-induced visual impairment, is hypothesized to be a result of increased intracranial pressure. The study of visual changes and intracranial pressure (ICP) in astronauts on long-duration flights is a relatively recent topic of interest to Space Medicine professionals. Although reported signs and symptoms have not appeared to be severe enough to cause blindness in the near term, long term consequences of chronically elevated intracranial pressure is unknown.
The main pathophysiology of heart failure is a reduction in the efficiency of the heart muscle, through damage or overloading. As such, it can be caused by a wide number of conditions, including myocardial infarction, hypertension and amyloidosis. Over time these increases in workload will produce changes to the heart itself:
Labile hypertension occurs when there are unexpected changes in blood pressure. The term can be used to describe when people have blood pressure measurements that abruptly fluctuates from being abnormally high, approximately 130/80mm Hg or over and returns to its normal range.
Hypertension is a condition characterized by an elevated blood pressure in which the long term consequences include cardiovascular disease, kidney disease, adrenal gland tumors, vision impairment, memory loss, metabolic syndrome, stroke and dementia. It affects nearly 1 in 2 Americans and remains as a contributing cause of death in the United States. There are many genetic and environmental factors involved with the development of hypertension including genetics, diet, and stress.
References
- ↑ Klaus, D. (February 1989). "Management of Hypertension in Actively Exercising Patients: Implications for Drug Selection". Drugs. 37 (2): 212–8. doi:10.2165/00003495-198937020-00008. PMID 2649357. S2CID 46963184.
- ↑ Stewart, Kerry; et al. (April 2004). "Exaggerated Exercise Blood Pressure is Related to Impaired Endothelial Vasodilatory Function". Am. J. Hypertens. 17 (4): 314–320. doi: 10.1016/S0895-7061(03)01003-3 . PMID 15062884.
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