Blood pressure: standard unit and measurement of blood pressure

2021-05-31 04:30 PM

Blood pressure has always been measured in millimetres of mercury because the standard reference for measuring pressure has been since Poiseuille's invention of the mercury barometer.

The function of the circulatory system is to provide the blood needed for tissues - transport nutrients to organ tissues, and at the same time transport substances, transport hormones from some organs in the body to other places, keep stable The concentration of substances in the homeostasis in the body helps cells survive and perform their functions well.

Standard units of blood pressure

Blood pressure has always been measured in millimeters of mercury (mmHg) because the standard reference for measuring pressure has been since Poiseuille's invention of the mercury barometer in 1846. Currently, blood pressure means the force of blood acting on 1 unit charge of the vessel wall. When we say the pressure of the blood vessel wall is 50 mmHg, that is enough force to push the column of mercury up to a height of 50mm. If the pressure is 100 mm Hg, it will push the column of mercury up 100 mm.

Sometimes the unit of pressure is cm H2O. A pressure unit of 10 cm H2O means that the force exerted is enough to push the water column 10 cm high. One mm of mercury blood pressure is equal to 1.36 cm of blood pressure using a water column because the specific gravity of mercury is 13.6 times that of water and 1 cm is equal to 1 mm.

An accurate method of measuring blood pressure

Mercury in a barometer is too slow for it to go up or down. For these reasons, mercury sphygmomanometers used to measure steady pressures cannot respond to rapidly changing blood pressures within a 2-3 second period. Whenever rapid recording of pressure changes is required, a different type of manometer is required. Figure 14-7 clarifies the basic principles of a common electronic blood pressure monitor used to convert blood pressure or rapid changes in pressure into an electrical signal and to record the electrical signals. in a high-speed electric recorder.

Figure. The operating principle of three types of electronic probes for blood pressure recording changes rapidly.

Each transducer uses a very thin and stretched metal film that forms a wall of liquid wall. The fluid wall is continuously contacted through a needle or tube inserted into the wall of the blood vessel where rhythmic pressure is applied. When the pressure is high, the film swells, and when the pressure is low, the film returns to its resting position.

In Figure A, a sheet of metal wrap is typically a few hundredths of a piece thin. As the film swells, the film proceeds to close the cover, increasing capacitance, and changes in capacitance can be recorded using a suitable electrical device.

In Figure B, a small iron tip is in the membrane, and the iron tip can travel upward a space center into an electrical coil. Dynamic calibration of the iron in the coil increases the inductance of the coil and this can also be recorded by the machine.

Finally, in figure C, a very thin stretched resistance wire is connected to the screen. When the wire is stretched excessively, the resistance increases; when it is stretched less, the resistance will drop. But this change can be recorded by the electrical system.

The electrical signals from the transducer are sent to the appropriate amplification and recording. With the high precision of the logger, pressure cycles can be recorded up to 500 cycles/second. It is common to use a recording cycle of 20 to 100 cycles/second, as shown in the recorder shown in Figure C.