Blood pressure machine

You might have seen the manual blood pressure measuring device at your doctor's office: it consists of a cuff that goes around your arm, a reading scale or gauge and an inflation bulb that the doctor pumps to make the cuff tight for measuring BP. The doctor also uses a stethoscope along with this machine, placing it on your upper arm below the cuff. 

The cuff contains an inflatable bladder which swells up to constrict the blood vessels to measure blood pressure. The size of the cuff should be accurate or else it can give incorrect blood pressure readings.

The different sizes of cuffs are "small adult" cuff (8.7 to 10.2 inches), "adult" cuff (10.6 to 13.4 inches), "large" cuff (13.8 to 17.3 inches) and "adult thigh" cuff (17.7 to 20.5 inches).

There are two types of manual sphygmomanometers:

• Mercury sphygmomanometer: The mercury sphygmomanometer is the gold standard for measuring blood pressure clinically. It comprises a machine box, a cuff, a rubber inflation bulb, a scaling board with a glass body in the middle filled with mercury.
• Aneroid sphygmomanometer: This device was introduced to reduce the use of mercury, which has harmful effects (mercury toxicity) on the environment. The aneroid sphygmomanometer does not have a scaling board with the mercury - instead, it has a round gauge which has markings written over it. Though these devices do not have mercury, they are less accurate than the conventional mercury sphygmomanometers.

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These devices were introduced in the medical field so that people could monitor their blood pressure on their own. These devices consist of a cuff and a digital monitor. You do not require a prescription to buy a digital sphygmomanometer. They are also used to measure ambulatory blood pressure. 

Ambulatory monitoring involves measuring blood pressure every 30 minutes with the help of a cuff (which is wrapped around the arm) and a small, portable, programmable monitor, which can be carried everywhere. The benefits of ambulatory monitoring are:

• Convenience: The monitor is smaller than the usual digital device, so you can carry it around easily.
• Separate white coat hypertension from high BP: Some people are a little stressed when they visit the doctor’s clinic, which spikes their blood pressure momentarily - this is known as white coat hypertension. Ambulatory monitoring helps to distinguish between white coat hypertension and actual high blood pressure in such cases.
• Diagnose masked hypertension: In the case of masked hypertension, it is difficult to diagnose hypertension as the blood pressure is normal at the doctor’s clinic but elevates at home. Ambulatory monitoring helps in the diagnosis of this condition.

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You will need assistance to measure your blood pressure if you are using a manual blood pressure machine. You will also need a stethoscope in addition to the blood pressure machine. If you are using a manual sphygmomanometer to take a loved one’s blood pressure, follow these steps:

• Ask the patient to rest their arm on a flat surface - their arm should be supported on a height, at the level of their heart.
• Now place the portion of the cuff that contains the inflatable bladder directly over the crook (inside crease of the elbow) of the left arm. This is where the brachial artery is located which helps in measuring the blood pressure.
• While wrapping the cuff around the arm, make sure that the lower edge of the cuff stays one-inch above the crook of the elbow (antecubital fossa). Fasten the cuff snugly but make sure there is a “two-finger” gap between the cuff and the arm.
• Now take up the stethoscope, and place the chest piece (the part which is placed on the chest) of your stethoscope between the cuff and the arm. Make sure that the chest piece is located slightly inside to the centre of the antecubital fossa (crook of the elbow). 
• Put the earpieces of the stethoscope in your ears with the tips directed forward.
• Now, close the valve needle (also known as an airlock) attached to the hand control rubber bulb firmly by turning it clockwise. Do not close it too tight as it will get difficult to release it later.
• Pump the rubber bulb to inflate to 20-30 mm Hg above the normal systolic pressure - inflate the cuff till or beyond 180 mm Hg. 
• Then slowly release the airlock counterclockwise 2-3 mm per second. 
• Listen to the sounds of the blood flow, called the Korotkoff sounds, in the earpiece. The Korotkoff sounds are clear and loud “tap; tap” sounds which denote the systolic and diastolic blood pressure.
• Note the first number at which the sounds start, which would be the systolic blood pressure and then continue to release the airlock slowly. 
• Mark the last number at which you could hear clear “tap” sounds as this would be your diastolic blood pressure.
• Let the rest of the air out rapidly and let the patient relax for a while. 
• If you need to confirm the measurements, wait for 5 minutes before checking the readings again.

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A digital sphygmomanometer is easier to use, and you can take your blood pressure without the assistance of another person. You also don’t need a stethoscope for this. 

Digital BP devices just have a cuff and a monitor. These devices not only measure blood pressure but also determine the heart rate. This is how you can use the digital sphygmomanometer:

• Place the portion of the cuff that contains the inflatable bladder directly over the crook (inside crease of the elbow) of the left arm. This is where the brachial artery is located which helps in measuring the blood pressure.
• While wrapping the cuff around the arm, make sure that the lower edge of the cuff stays one-inch above the crook of the elbow (antecubital fossa). Fasten the cuff snugly.
• Then press the start button. The cuff starts inflating on its own to reach a pressure about 20 mm Hg above systolic pressure for any individual. 
• When the cuff is fully inflated, no blood flows through the brachial artery. After the highest systolic pressure is achieved, the cuff starts to deflate on its own at a slow pace.
• As the cuff deflates, the pressure over the constricted artery reduces and blood slowly starts passing through it. This creates a detectable vibration in the arterial wall.
• This is transferred from the arterial wall to the air inside the cuff. Then the vibration travels to the transducer present in the monitor which converts the measurements into electrical signals. 
• Thus the measurements of the blood pressure show up on the screen.

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