What is the physics involved in the blood pressure cuff used by doctors ?

Question

Even in big shopping places free blood pressure systems take your pressure in a cuff which slowly squeezes around your arm and within a minute the numbers show out stating the low and high blood pressure at the time . What is the Physics involved ?

Answer 1

f the cuff of a sphygmomanometer is placed around a patient's upper arm and inflated to a pressure above the patient's systolic blood pressure, there will similarly be no sound audible. This is because the pressure in the cuff is high enough such that it completely occludes the blood flow. It is similar to a flexible tube or pipe with fluid in it that is being pinched shut.

If the pressure is dropped to just slightly below the patient's systolic blood pressure, the first Korotkoff sound will be heard. As the pressure in the cuff is slightly below the pressure produced by the heart, some blood will be able to pass through the upper arm when the pressure in the artery rises during systole. This blood flows in spurts as the pressure in the artery rises above the pressure in the cuff and then drops back down, resulting in turbulence that results in audible sound.

As the pressure in the cuff is allowed to fall further, thumping sounds continue to be heard as long as the pressure in the cuff is between the systolic and diastolic pressures, as the arterial pressure keeps on rising above and dropping back below the pressure in the cuff.

Eventually, as the pressure in the cuff drops further, the sounds change in quality, then become muted, then disappear altogether. As the pressure in the cuff drops below the diastolic blood pressure, the cuff no longer provides any restriction to blood flow allowing the blood flow to become smooth again with no turbulence and thus produce no further audible sound.

Korotkoff actually described 5 types of Korotkoff sounds:

1. The first Korotkoff sound is the snapping sound first heard at the systolic pressure.
2. The second sounds are the murmurs heard for most of the area between the systolic and diastolic pressures.
3. The third and-
4. the fourth sound, at pressures within 10 mmHg above the diastolic blood pressure were described as "thumping" and "muting".
5. The fifth Korotkoff sound is silence as the cuff pressure drops below the diastolic blood pressure.

Traditionally, the systolic blood pressure is taken to be the pressure at which the first Korotkoff sound is first heard and the diastolic blood pressure is the pressure at which the fourth Korotkoff sound is just barely audible. However, there has recently (2000 onwards) been a move towards the use of the 5th Korotkoff sound (i.e. silence) as the diastolic blood pressure, as this has been felt to be more reproducible. In pregnancy a fifth phase may not be identifiable, in which case the fourth is used. This change, and associated uncertainty adds to the difficulties in interpreting clinical studies of hypertension although modern trials will specify the method used.

Answer 2

Your heart is an amazing pump. It works reliably for decades, and it safely pumps blood -- one of the trickiest liquids around. In the same way, your blood vessels are pipes. They take the output from the pump and distribute it throughout the body. A blood pressure gauge is simply a way to measure the performance of the pump and the pipes.
There are two numbers in a blood pressure reading: systolic and diastolic. For example, a typical reading might be 120/80. When the doctor puts the cuff around your arm and pumps it up, what he/she is doing is cutting off the blood flow with the pressure exerted by the cuff. As the pressure in the cuff is released, blood starts flowing again and the doctor can hear the flow in the stethoscope. The number at which blood starts flowing (120) is the measure of the maximum output pressure of the heart (systolic reading). The doctor continues releasing the pressure on the cuff and listens until there is no sound. That number (80) indicates the pressure in the system when the heart is relaxed (diastolic reading).

If the numbers are too high, it means that the heart is having to work too hard because of restrictions in the pipes. Certain hormones, like adrenaline (which is released when you are under stress) cause certain blood vessels to constrict, and this raises your blood pressure -- if you are under constant stress, your blood pressure goes up, and it means that your heart has to work too hard. Other things that can increase the blood pressure include deposits in the pipes and a loss of elasticity as the blood vessels age.

High blood pressure can cause the heart to fail (from working too hard), or it can cause kidney failure (from too much pressure).

Answer 3

Sphygnomanometers (blood pressure cuffs) work by pressure differences. When the cuff is filled with air, it soon cuts off circulation in the arm. As the pressure is slowly released, the blood pressure will eventually equal the cuff pressure.It will do so in 2 stages. In both cases, the sound the doctor or nurse hears would correspond to the time the pressures equalized, and a reading taken.

Answer 4

It cuts off your circulation by applying a pressure. It then measures when blood starts flowing again. That point is when the pressure in your bloodstream is greater than the pressure exerted by the Sphygmomanometer (technical term for the 'cuff').

Here's a website that explains it in more detail, and the difference between systolic and diastolic blood pressure.

Answer 5

3 years ago, I was diagnosed - hypertension with a reading of 160/100. I used to feel dizzy a lot, my legs had awful cramps, and levels were very low in my potassium, causing my fingers and toes to always cramp together. One day I started to feel really faint while I was driving with my daughter in the back seat and I passed out, hitting 3 cars and ending up in a ditch. That moment,I knew I had to do something because my meds weren't working. I heard about this diet from a friend and thought I'd give it a shot. The results have been remarkable. In just 21 days, I honestly can't remember feeling this good, my blood pressure went from 175/110 to 125/70.