Automatic blood pressure (bp) monitors are an integral part of any vital signs monitor used in hospitals, critical care units, emergency rooms, and even homes. The reason is quite simple – While an EKG can give the representation of the electric signals in the heart muscle, the oximeter can give the oxygen content of the blood in the body, only the bp monitor is actually capable of measuring the actual effectiveness of the heart pumping blood into the system.
The importance of blood pressure measurement
In other words, both the EKG and the oximeter could be showing normal values, yet, without the proper blood pressure sensor reading, the patient’s body cells would still not be receiving an amount of oxygen sufficient for normal functioning. Which means, the life of a patient would be endangered without us knowing.
Manual blood pressure meter
Before we look into the workings of an automatic meter, let’s investigate how a manual blood pressure monitor, or NIBP monitor, or high blood pressure bp monitor works. The meter consists of the bp cuff that is filled with air gradually and presses on the main artery in the upper arm. The basic physics of the pressure meter reflects the interplay between the air pressure in the cuff and the air pressure in the artery. There are two principal pressures, the systolic, and the diastolic in the artery. The systolic is the maximal pressure in the artery, and the diastolic is the minimal pressure.
The simple principle of operation is this: When the cuff air pressure is higher than the systolic pressure, the cuff continually squeezes the artery until the blood flow into the lower arm is stopped, and there is no pulsation audible in the stethoscope. When the cuff air pressure is less than the diastolic pressure, the artery pressure always maintains the artery at its full size. In between these two pressures, the expansion and contraction of the artery follows the varying bp in the artery, and the pulsation is audible in the stethoscope attached to the arm.
So, in manual bp monitors, as the manual blood pressure cuff the air pressure is gradually increased up to the diastolic pressure, we begin to hear pulsation, and by further increasing the cuff air pressure we come to the higher, systolic pressure point, where the pulsation disappears again.
How does an automatic blood pressure (bp) monitor work?
The action of an automatic digital bp monitor is quite analogous to the operation of the manual pressure meter with a couple of differences:
- First, for speed, automatic digital bp monitor will measure the diastolic pressure and the systolic pressure already on the first pass, while increasing the air pressure in the cuff.
- Second, the air will be provided to the digital bp cuff by an electric pump instead of the manual pump.
- Third, the pulsation will not be observed by hearing but rather by the built in microphones or other sensor types.