医学英語のリーディングとリスニング

Blood is carried from the heart to all parts of your body in vessels called arteries. Blood pressure is the force of the blood pushing against the walls of these arteries. Blood pressure is at its highest when the heart beats, pumping the blood out. The value measured at this high point is called the systolic pressure. When the heart is at rest, between beats, blood pressure falls. The value measured at this low point is called the diastolic pressure.

Blood pressure is always recorded as two numbers, representing first the systolic pressure and then the diastolic pressure, and said, for example, as 120/80 mmHg or more often simply 120/80. An individual's blood pressure is not static and fluctuates throughout the day. Blood pressure is generally lowest when a person is asleep and it rises when he or she wakes up. The body itself does strive to maintain a steady state and special cells in the arteries called baroreceptors can sense when blood pressure goes up or down. These baroreceptors react to changes in blood pressure by triggering responses designed to bring the blood pressure levels back to normal.

Blood pressure readings can be broadly classified into three categories: normotension, hypertension or hypotension. Normotension, as you might guess, refers to normal blood pressure readings. The normal range for blood pressure is generally defined as a reading of lower than 120/80 and higher than 90/60.

Hypertension refers to abnormally high blood pressure readings. The cutoff point for hypertension is generally considered to be 140/90. Hypertension, or simply high blood pressure, is a serious cause for concern, particularly because the individual often exhibits no symptoms and is unaware that he or she has a problem. Hypertension has been dubbed the "silent killer" because of this lack of symptoms.

Untreated hypertension can cause a myriad of potentially fatal conditions including: enlargement of the heart leading to heart failure; the formation of small bulges in blood vessels known as aneurysms; narrowing of blood vessels in the kidneys leading to kidney failure; hardening of the arteries leading to heart attack, stroke or kidney failure; and bursting or hemorrhaging of blood vessels in the eyes leading to vision problems or even blindness. Many times patients do not realize that they have hypertension until they are hit by one of these medical emergencies when it may be too late. Thus, early diagnosis, prevention and treatment of hypertension is critical to general well-being and long-term health.

The third category, hypotension, refers to abnormally low blood pressure readings and it is usually defined as a reading of lower than 90/60. Hypotension, by itself, is not necessarily a pathological condition, rather simply a physiological state. Some people naturally have blood pressure readings that fall within the range of hypotension but exhibit no other signs or symptoms and usually require no medical treatment. Such individuals have what is technically called chronic asymptomatic hypotension, and hypotension is normal for them.

Other types of hypotension happen only sometimes, when the blood pressure suddenly drops too low. The three main types of this kind of hypotension are: (1) orthostatic hypotension which occurs when a person stands up suddenly or stands still for a long period; (2) neurally mediated hypotension, also known as NMH, which occurs when the body has difficulty regulating blood pressure; and (3) severe hypotension associated with shock. The symptoms and effects on the body of these types of hypotension range from mild to severe.

Blood pressure is an important aspect of overall health and well-being. Since abnormal or sudden changes in blood pressure readings can be a harbinger of health problems, everyone should know their own readings and have readings taken regularly as part of their overall health care plan.