Hormones are also produced by the kidney, such as renin and angiotensin, which affect blood pressure. Other factors which can alter blood pressure are the force and rate of the heart contractions, the volume of blood pumped with each beat, the muscle tone in the arteries, the general condition of the arteries, and the total volume of blood in the circulatory system. All these factors, and others both known and unknown, normally work automatically and simultaneously. These mechanisms allow the blood pressure to vary throughout the day in a "normal range". Blood pressure is a dynamic and constantly changing value; it may differ considerably between two consecutive readings, depending on conditions.

Diagnosis and Treatment of Essential Hypertension
To diagnose high blood pressure as the disease called hypertension, a series of blood pressure readings must be obtained several days or weeks apart. Hypertension, the disease, may be defined as a medical condition in which several blood pressure readings show a pattern of high readings. Since blood pressure is so variable, standards are necessary to decide how high is "too high", and how many readings are necessary to establish the diagnosis. Since hypertension is a condition causing no symptoms in most cases, how would one decide when to treat the blood pressure? What blood pressure value should determine initiation of treatment? How long can one have an elevated blood pressure before treatment is necessary?
The answer to the question "what constitutes the diagnosis of hypertension requiring treatment?" is still being researched, studied, and debated. However, guidelines have been established as indicators for treatment. The latest guideline in the United States for diagnosis, evaluation and treatment of high blood pressure is the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) published in May 2003. The most important findings of this report are:

• In persons older than 50 years, systolic blood pressure greater than 140 mmHg is a much more important cardiovascular disease (CVD) risk factor than diastolic blood pressure.
• The risk of CVD beginning at 115/75 mmHg doubles with each increment of 20/10 mmHg; individuals who have normal blood pressure at age 55 have a 90% lifetime risk for developing hypertension.
• Individuals with a systolic blood pressure of 120-139 mmHg or a diasolic blood pressure of 80-89 mmHg should be considered as prehypertensive and require health-promoting lifestyle modifications to prevent CVD.
• Thiazide-type diuretics should be used in drug treatment for most patients with uncomplicated hypertension, either alone or combined with drugs from other classes. Certain high-risk conditions are compleeling indications for the initial use of other antihypertensive drug classes (angiotensin converting enzyme inhibitors, angiotensin receptor blockers, beta-blocker, calcium channel blockers).
• Most patients with hypertension will require two or amore antihypertensive medications to achiweve goal blood pressure (<140/90 mmHg, or <130/80 mmHg for patients with diabetes or chronic hidney disease).
• If initial blood pressure is >20/10 mmHg above goal blood pressure, consideration should be given to initiating therapy with two agents, one of which usually should be a thiazide-type diuretic.

The JNC 7 notes that the most effective therapy prescribed by the most careful clinician will control hypertension only if patients are motivated. Motivation improves when patients have positive experiences with, and trust in, the clinician. Empathy builds trust and is a potent motivator. In presenting these guidelines, the committee recognized that the responsible physician's judgment remains paramount.
For those who would like to read a detailed synopsis of the JNC 7 Report, your can download an Adobe .pdf file from the National Institutes of Health at this link: http://www.nhlbi.nih.gov/guidelines/hypertension/express.pdf.
The JNC 7 provided a classification of blood pressure (BP) for adults ages 18 and older. The classification is based on the average of two or more properly measured, seated BP readings on each of two or more office visits. In contrast to previous classification in the JNC 6 report, a new category called "prehypertension" has been added, and stage 2 and 3 have been combined as a new Stage 2. Patients with what is now called "prehypertension". The old term was "high normal". Patients with blood pressure in the 130 - 139/80 - 98 mmHg range are at twice the risk to develop hypertension as those with lower values, and the old terminology "high normal" did not adequately express this risk. There was a tendency of patients, and perhaps physicians, to see only the "normal" in the terminology and not the "high" requiring action.
These categories are shown in Table 1. below:

The drug code abbreviations refer to the following classes of antihypertensive drugs: ACEI = angiotensin converting enzyme inhibitor; ARB = angiotensin receptor blocker; BB = beta blocker; CCB = calciuim channel blocker