blood pressure is the actual pressure of the blood flowing inside body or the diff of atm pressure?

Question

and the pressure of the bloodflow? Why its unit is different than ordinary pressure unit ie bar or N/mm2 or dyne/cm2 etc? again,why the units are different in higher bp and lower bp? what is meant by those unit? (diahstolic or so is the name of one of the units).Only serious answers please

Answer 1

Blood pressure is the pressure exerted by the blood on the walls of the blood vessels usually the Brachial Artery. It is the actual pressure generated by the blood in the vessels.

Blood pressure values have traditionally been measured in millimetres of mercury (mm Hg) as what is conventionally measured is the amount of pressure transmitted to a vertical column of mercury. The blood pressure is not constant. It is a dynamic value that fluctuates throughout the cardiac cycle. The two values measured by physicians is the peak (systolic) and the lowest (diastolic) blood pressure during the cardiac cycle. The systolic pressure is defined as the peak pressure in the arteries during the cardiac cycle; the diastolic pressure is the lowest pressure (at the resting phase of the cardiac cycle).

Normal blood pressure is 120 mm Hg systolic and 80 mm Hg diastolic (written as 120/80 mm Hg). However these values can differ slightly according to age, race, sex etc…
In addition natural variations throughout the day can occur in response to stress, exercise,drugs, or disease.

Answer 2

Blood pressure, although thought of as a property of a patient's entire bodily system, is a number which cycles high and low with each heart beat, it changes over the course of the day, and it's actually different in different parts of the body. That's just in the normal state of health. In disease, it becomes complicated!

The heart is a pump, and the blood vessels are flexible hoses with stretchy walls. When the heart contracts, it forces out blood into the blood vessels, and while the heart valves are open and the blood is flowing out, blood pressure (measured with a blood pressure cuff on the arm) is approximately a hydraulic measurement of the contractile force of the heart. This is called the "systolic pressure".

Next, the heart relaxes and refills with blood entering from the venous system. As it relaxes, the valves of the heart snap shut so that the arterial blood doesn't back-flow into the heart ineffectively. The remaining pressure in the arterial blood vessel system comes from the hydraulic loading of stretchy elastic blood vessels, much like the pressure of water in a water balloon. The pressure doesn't completely bottom out, but it hits a "low" called the "diastolic pressure".

The measurement of blood pressure is typically performed by an indirect experiment which has changed little in a hundred years. An air bag with a hand pump is wrapped around the upper arm snugly and then inflated. This part is termed the "cuff". The cuff becomes very snug and eventually cuts off blood flow down the arm through the brachial artery.

A stethescope is used to listen to the blood flow downstream of the cuff. The pressure in the cuff is slowly released. As the pressure in the cuff falls to a point just below the systolic pressure maximum, small amounts of blood are able to squirt past the cuff as the pressure lifts it. The tiny jet of flow in the blood vessel is turbulent and makes a swishing sound. The sound is picked up by the stethoscope and the pressure is noted at that point. The pressure in the cuff continues to be slowly released. During this phase, the pressure in the cuff is less than the systolic pressure but greater than the diastolic. Dynamically, during the cardiac cycle, then, the cuff is deforming the blood vessel by compressing it externally, and flow is being impeded. Because blood flow continues to nozzle past the cuff, turbulent sounds can still be heard. Eventually the pressure in the cuff reaches a point just below the low point pressure or "diastolic" pressure, at which point the blood vessel is no longer deformed and the sounds stop. The pressure measurement where the sounds stop is noted and this is taken to be the diastolic pressure.

Because this experiment occurs with atmospheric pressure acting on both the human body and the blood pressure cuff, the pressure measurements are in units above atmospheric pressure.

The reason that units of "millimeters of mercury" are the standard, is because blood pressure measuring devices (sphygmomanometers) were originally made with a glass U-tube filled with mercury. The air filled cuff was connected by a hose to one end of the U-tube and pressure was measured by literally seeing the deflection of the mercury column in millimeters. This is still a very useful scale because this unit is well sized to detect the magnitude of changes in humans which are clinically significant. Ultimately, however, units are just units, and the only reason that people stick with one unit over another is because of tradition. Medicine is a world which is strongly influenced by tradition.


... I hope that helps!

Answer 3

Nope blood pressure is not the difference of atmospheric pressure. Blood pressure in effect the measurement of firstly, the pumping effect of the heart and secondly the recoil pressure induced by arteries when the heart relaxes. In medicine, when the heart contracts, its called systole..this is measured as the higher systolic pressure. When the heart relaxes, its called diastole. When this happens, the arteries recoil as they are elastic and the pressure created by this is called diastolic pressure.

There are a few ways that we can measure this. One is by placing a cuff around the arm and increasing the pressure around it by using a sphygamomanometer. The pressure should be increased to above systolic pressure. Then the perssure is slowly released. A stethescope is placed on the below the cuff somewhere along the path of the axiallary artery just before it splits into the radial and ulnar artery. The moment the first click sound is heard, that is the systolic pressure. As more pressure is released, the moment the sounds disappear, that is diastolic pressure.

Another more accurate way in which this can be done is be placing an arterial line. That is a catheter is inserted into the radial artery in the wrist and the pressure of blood is measured using an input device. This is more accurate as compared to using the cuff.

Answer 4

Blood pressure (BP) is measures in mm Hg as this was what was traditionlay used as a measure of how much pressure is needed to be exerted on the artery to stop the blood flow.
The units used for systolic (first number) is the same as the for the diastolic (second number).

The first number represents the pressure exerted by the blood flow when the heart contracts (this is when you can feel the pulse) and the second number represents the pressure of the blood when the heart is relaxed, and is sort of taken to represent the state of the blood vesels (whenther they are constricted innapropriatly).

Answer 5

There are 2 ways to measure pressure, absolute and gauge. In absolute you would add atmoshperic pressure to the reading, in gauge the atmospheric is subtracted out by the measuring instrument. The mmhg or millimeters of mercury is a very old scale to measure pressure. It really means the pressure of actual elemental mercury in a calibrated glass tube so it is accurate by definition. It is not really a pressure scale but it has been adopted by the medical community, and I believe that is the only place you will see it used. The higher reading is when the heart is contracting and that is the systolic reading the lower reading is when the heart is relaxing and that is the diastolic reading. Oh and the reading is gauge.

Answer 6

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Answer 7

To answer your first query:
Blood pressure as given by a blood-pressure monitor is the pressure in excess of atmospheric. To use engineers terms, it is a 'gauge' pressure.
I think the other aspects of your question have been covered by other answers.