Blood pressure: what do we measure and what do the numbers really mean?

By October 23, 2008 December 14th, 2011 No Comments

Blood pressure is commonly measured by wrapping an inflatable cuff around the upper arm. Air is pumped into the cuff until the blood vessels in the arm get so squeezed that the circulation is cut off; when a stethoscope is then placed just under the cuff there should be relative silence. As the air is slowly let out of the cuff the squeezing eases, blood begins to flow again and can be heard through the stethoscope. This is the point of greatest pressure (called Systolic), and is usually expressed as how high it forces a column of mercury to rise in a tube. At its highest normal pressure, the heart would send a column of mercury to a height of about 120 millimeters. At some point, as more and more air is let out of the cuff, the pressure exerted by the cuff is so little that the sound of the blood pulsing against the artery walls subsides and there is silence again. The last audible beat heard through the stethoscope is the point of lowest pressure (called Diastolic), which normally raises the mercury to about 80 millimeters. Systolic and Diastolic readings are both important but it must always be remembered that lots of things will cause fluctuations in BP. Exercise will make the systolic leap up, while the lower reading (the diastolic) will usually stay fairly constant. Simply having your BP taken can cause an elevation in BP (white coat syndrome – the nerves you feel make your BP go up!). Diastolic pressure has traditionally been emphasized because it is less subject to fluctuations. However, recent studies have revealed that systolic pressure may be as significant a heart attack predictor as diastolic pressure.

Normal blood pressure is thus usually said to be 120/80 (systolic/diastolic),  measured in millimeters of mercury (abbreviated as mm Hg). What do blood pressure numbers indicate?  The first is the big push from the larger left ventricle (the heart is lopsided, one side being stronger than the other.) The second reading is the relaxation of the heart between beats as the right atrium pulls blood into the heart. The higher (systolic) number represents the pressure while the heart is beating, or on the push. The lower (diastolic) number represents the pressure when the heart is resting between beats, creating lower pressure and sucking blood in. A good way of imagining this is to look at the heart as your central heating pump – the pipes and radiators are your blood vessels. The clearer the pipes (blood vessels) the less pressure will be exerted on the system by the pump. But if the pipes are clogged (with fatty deposits!!) then the pressure in the system will be higher and the pump will have to work harder to force circulation through the narrower pipes (or blood vessels), eventually to breaking point. The systolic pressure is always stated first and the diastolic pressure second. For example: 122/76 (122 over 76); systolic = 122, diastolic = 76. Blood pressure of less than 140 over 90 is considered a normal reading for adults. A systolic pressure of 130 to 139 or a diastolic pressure of 85 to 89 needs to be watched carefully. A blood pressure reading equal to or greater than 140 (systolic) over 90 (diastolic) is considered elevated (high).

A good test of your personal trainer is to see is he/she understands this. A personal trainer worth his salt and at REPS level 3 will have an in depth knowledge of BP and the ways to help it.

Leave a Reply