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Authors: Obika, Leonard F. O
Issue Date: 15-Jun-2006
Series/Report no.: Inaugural Lecture Series 83;
Abstract: BLOOD PRESSURE: WHAT IS NORMAL Blood is a liquid and as such cannot be compressed. Since it is enclosed in a series of vessels (blood vessels), the force that it exerts per unit area against these vessels is referred to as blood pressure. These vessels are of different sizes, different shapes and of different make-ups. This means that blood pressures differ from one type of blood vessel to another: arterial blood pressure, venous blood pressure, arteriolar blood pressure, etc. My emphasis for this lecture will be on arterial blood pressure. This is only for convenience as all the vessels are linked. 7 Majority of the vessels are also elastic so that with each pump of the heart, a pulse can be felt. The surge (which can be felt) is the systolic blood pressure, while the diastolic blood pressure cannot be felt. In systemic circulation, systolic blood pressure results from the volume of blood ejected into the aorta by the left ventricle as it contracts; while the diastolic blood pressure is when the heart is at ‘rest’. Numerically, blood pressure can be expressed as a force equal to that exerted by a column of mercury of a given height as measured in millimeters (mmHg). Mathematically, blood pressure (BP) is related by the following equation: BP (mmHg) = CO x TPR (where CO is the cardiac output and it is the quantity of blood pumped by the heart in one minute; and TPR is the total peripheral resistance to flow through the blood vessels). The CO is equal to the number of times the heart beats per minute (heart rate, HR) multiplied by the quantity of blood pumped out per beat (stroke volume, SV). Therefore, BP (mmHg) = HR x SV x TPR This means that any change in blood pressure will be dependent on how those three variables change. The total amount of blood in the adult body is relatively constant, and it is enclosed in the blood vessels which are ‘closed’. This means that changes in the ‘quantity of blood’ or ‘amount of blood pumped out by the heart per minute’ or a ‘change in the diameter of the blood vessels’ will directly affect the blood pressure. The ultimate aim of nature is to maintain the status quo, so that increase in cardiac output (CO) will through some sensors (baroreceptors) affect the total peripheral resistance (and vice versa), so as to maintain a constant blood pressure. It is obvious therefore that if the sensing mechanism(s) of the body is unable to detect
Appears in Collections:University of Benin Inaugural lectures

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