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The reference pressure level , termed zero, is considered to be at heart level, i.e. towards the middle of the chest and level with the right atrium.
Actually the barometric pressure around the body, about 760 mmHg, is called zero. Blood pressure is read as the number of mmHg above atmospheric pressure, which is used as the zero reference.
Venous pressure is the blood pressure in a vein. It is much less than arterial blood pressure. e.g. typically about 5 mmHg in the right atrium, 8 mmHg in the left atrium.
Measurement of pressures in the venous system and the pulmonary vessels plays an important role in intensive care medicine but requires invasive techniques.
Arterial blood pressure is usually measured in millimeters of mercury (mm Hg) using a sphygmomanometer. This is an inflatable cuff placed around the upper arm, at roughly the same vertical height as the heart in a sitting person, attached to a manometer. The cuff is inflated until the artery is completely occluded. Listening with a stethoscopeThe stethoscope is an acoustic medical device for auscultation i. listening to internal sounds in the human body. It is most often used to listen to heart sounds and breathing, though it is also used to listen to intestines and to blood flow in arteries a to the brachial arteryThe brachial artery is a blood vessel of the upper arm. It is a continuation of the axillary artery, and it starts and the lower margin of teres major and continues down the arm, until it reaches the cubital fossa at the elbow. It then ends by dividing in at the elbow, the examiner slowly releases the pressure in the cuff. When blood flow barely begins again in the artery, a "whooshing" or pounding sound is heard. The pressure is noted at which this sound began. This is the systolic blood pressure. The cuff pressure is further released until the sound can no longer be heard. This is the diastolic blood pressure. The peak pressure in the arteries during the cardiac cycle is the systolic pressure, and the lowest pressure (at the resting phase of the cardiac cycle) is the diastolic pressure.
Normal ranges for blood pressure in adult humans are:
In children the observed normal ranges are lower, in the elderly, they are more often higher. Clinical trials demonstrate that people who maintain blood pressures in low end of these pressure ranges have much better long term cardiovascular health and are considered optimal. The principal medical debate is the aggressiveness and relative value of methods used to lower pressures into this range for those who don't maintain such pressure on their own. Elevations, more commonly seen in older people, though often considered normal, are not healthy. The clear trend from double blind clinical trials (for the better strategies and agents) has increasingly been that lower ends up being demonstrated to result in less disease/better outcomes long term.
The mean blood pressureBlood pressure or arterial blood pressure is the pressure (force per unit area) exerted by the blood on the walls of the blood vessels. Unless indicated otherwise, blood pressure refers to the pressure in the large arteries, such as the brachial artery (i in the arteries supplying the body is a result of the heart pumping blood from the veins back into the arteries.
The meanThe mean arterial pressure MAP is a term used in medicine to describe an average blood pressure in an individual. The mean arterial pressure is calculated as the diastolic pressure plus 1/3 of the pulse pressure. The MAP is considered the perfusion pressu blood pressure value is determined by the volume of blood the heart is pumping per minute, termed Cardiac Output, versus the resistance of the 20,000 to 30,000 arterioleAn arteriole is a blood vessel that extends and branchs out from an artery and leads to capillaries. Arterioles have thick muscularized walls and are the primary site of vascular resistance''. The mean blood pressure in the arteries supplying the body iss, termed total peripheral resistanceTotal peripheral resistance refers the cumulative resistance of the thousands of arterioles in the body, or the lungs, respectively. See Arteriole. The total peripheral resistance of healthy lung arterioles is typically about 0. 20 that of the body, so pu, through which the blood must flow to reach the capillariesCapillaries are the smallest of the body's blood vessels. They connect arteries and veins. Capillaries have walls composed of a single layer of cells, the endothelium. This layer is so thin that molecules such as oxygen, water and lipids can pass through and then veins.
The up and down fluctuation of the arterial blood pressure, termed Systolic (the top number) and the Diastolic (the bottom number) result from the pulsatile nature of the Cardiac Output. The pulse pressure is determined by the interaction of the Stroke Volume versus the volume and elasticity of the major arteries.
The larger arteries, including all large enough to see without magnification, are low resistance (assuming no advanced atherosclerotic changes) conduit vessels with high flow rates but producing very little pressure drop. For instance, about 5 mmHg mean pressure decrease in the blood flow traveling from the heart all the way to the toes is typical, assuming the individual is supine (horizontal with respect to gravity).
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