Understanding a Blood Pressure Reading: Systolic and Diastolic

As a health care provider I am always asked about blood pressures and the significance of "the numbers" used in obtaining a blood pressure. I have found a vast variety in how individuals correlate and interpret "these numbers." An understanding of what and how a blood pressure is obtained may help to clarify that.

Accurate measurement of blood pressure is crucial to classify individuals with certain health risks and to also guide in correct management of other disease processes. There are several types of devices used in measuring blood pressure. The auscultatory (listening) technique with a trained professional and a mercury sphygmomanometer (an instrument used to measure blood pressure in an artery that consists of a pressure gauge, an inflatable cuff placed around the upper arm, and an inflator bulb or pressure pump) is still considered to be the method of choice in assessing a blood pressure according to the American Heart Association Journals. However, we know that there are a variety of different devices found today such as electronic ones.

Regardless, of which method is used the way a blood pressure is measured is done the same. A cuff is wrapped around the upper arm which occludes the brachial artery it is then inflated to above systolic pressure (the contraction of the heart, during which blood is pumped into the arteries), then it is gradually deflated as the blood flow is re-established giving a tapping noise. This measurement is then taken when accompanied by a sound detected or felt by the stethoscope or other various devices that may have been used. The first sound is then recorded and this is your systolic pressure or the top number as you may know it. Soon after, the tapping noise should start to fade and when it has disappeared completely this recording is documented as your diastolic pressure (the rhythmic expansion of the chambers of the heart at each heartbeat, during which they fill with blood) or the bottom number.

This blood pressure measurement is then evaluated by a health care professional and a diagnosis of high blood pressure or low blood pressure can be determined. This is determined when the systolic and diastolic pressures fall into different categories.

The categories as listed by the American Heart Association are as follows:

Normal - Systolic reading (top number) is less than 120 or the Diastolic reading (bottom number) is less than 80

Pre-hypertension (high blood pressure) - Systolic reading 120-139 or the Diastolic reading of 80-89

Hypertension is then classified into two stages:

Stage 1 - Systolic reading of 140-159 or the Diastolic reading of 90-99

Stage 2 - Systolic reading of 160 or higher or the Diastolic reading of 100 or higher

Diagnosing high blood pressure is based on the average of two or more readings taken at each of two or more visits after an initial screening. Unusually low blood pressure readings need further evaluating by a health care provider based on symptoms and clinical findings.

Based on these categories a decision will be determined by the health care provider. And at the time of diagnosis whether it is low blood pressure, pre-hypertension or hypertension, recommendations will be given. These recommendations and treatment may include medications, diet and exercise.

Remember that blood pressure determination continues to be one of the most important measurements in all of medicine. Hypertension is a major risk factor for heart disease, stroke, and kidney failure. And if caught early and treated it can prevent further damaging results in the end.

Resources:

http://www.americanheart.org/presenter.jhtml?identifier=4450

http://hyper.ahajournals.org/cgi/content/full/45/1/142

http://encarta.msn.com/