Blood Pressure
<p ><b>Blood pressure</b> (<b>BP</b>), sometimes it is called <b>arterial blood pressure</b>, is the <a href="http://en.wikipedia.org/wiki/Pressure" title="Pressure" >pressure</a> exerted by circulating <a href="http://en.wikipedia.org/wiki/Blood" title="Blood" >blood</a> upon the walls of <a href="http://en.wikipedia.org/wiki/Blood_vessel" title="Blood vessel" >blood vessels</a>, and is one of the principal<a href="http://en.wikipedia.org/wiki/Vital_signs" title="Vital signs" >vital signs</a>. </p>
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When used without further specification, "blood pressure" usually refers to the <a href="http://en.wikipedia.org/wiki/Arterial" title="Arterial" class="mw-redirect" >arterial</a> pressure of the <a href="http://en.wikipedia.org/wiki/Systemic_circulation" title="Systemic circulation" >systemic circulation</a>. </p>
<p>
During each heartbeat, blood pressure varies between a maximum (<a href="http://en.wikipedia.org/wiki/Systole_(medicine)" title="Systole (medicine)" >systolic</a>) and a minimum (<a href="http://en.wikipedia.org/wiki/Diastolic" title="Diastolic" class="mw-redirect" >diastolic</a>) pressure.<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Blood_pressure#cite_note-0" >[1]</a></sup> The blood pressure in the circulation is principally due to the pumping action of the heart.<sup id="cite_ref-Caro_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Blood_pressure#cite_note-Caro-1" >[2]</a></sup> </p>
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Differences in mean blood pressure are responsible for blood flow from one location to another in the circulation. </p>
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The rate of mean blood flow depends on the resistance to flow presented by the blood vessels. Mean blood pressure decreases as the <a href="http://en.wikipedia.org/wiki/Circulatory_system" title="Circulatory system" >circulating blood</a> moves away from the <a href="http://en.wikipedia.org/wiki/Heart" title="Heart" >heart</a> through <a href="http://en.wikipedia.org/wiki/Artery" title="Artery" >arteries</a>, <a href="http://en.wikipedia.org/wiki/Capillaries" title="Capillaries" class="mw-redirect" >capillaries</a> and <a href="http://en.wikipedia.org/wiki/Veins" title="Veins" class="mw-redirect" >veins</a> due to <a href="http://en.wikipedia.org/wiki/Viscosity" title="Viscosity" >viscous</a> losses of energy. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and <a href="http://en.wikipedia.org/wiki/Arterioles" title="Arterioles" class="mw-redirect" >arterioles</a>.<sup id="cite_ref-Klabunde2005p93-4_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Blood_pressure#cite_note-Klabunde2005p93-4-2" >[3]</a></sup> </p>
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Gravity affects blood pressure via <a href="http://en.wikipedia.org/wiki/Fluid_statics" title="Fluid statics" >hydrostatic</a>forces (e.g., during standing) and valves in veins, <a href="http://en.wikipedia.org/wiki/Breathing" title="Breathing" >breathing</a>, and pumping from contraction of skeletal muscles also influence blood pressure in veins.<sup id="cite_ref-Caro_1-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Blood_pressure#cite_note-Caro-1" >[2]</a></sup></p>
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The measurement <i>blood pressure</i> without further specification usually refers to the systemic arterial pressure measured at a person's <a href="http://en.wikipedia.org/wiki/Arm" title="Arm" >upper arm</a>
and is a measure of the pressure in the <a href="http://en.wikipedia.org/wiki/Brachial_artery" title="Brachial artery" >brachial artery</a>, major <a href="http://en.wikipedia.org/wiki/Artery" title="Artery" >artery</a> in the upper arm. </p>
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A person’s blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure and is measured in millimetres of mercury (<a href="http://en.wikipedia.org/wiki/Torr" title="Torr" >mmHg</a>), for example 140/90.</p>