Measurement of Blood Pressure(part 1):
Sphygmomanometer classic stethoscope.
Automatic Digital Blood Pressure Wrist indicating systolic and diastolic.
It is typically made by a circular inflatable cuff connected to a gauge called sphygmomanometer or blood pressure cuff. The first aircraft of this type has been described by Dr. Scipione Riva-Rocci December 10 1896 in the Medical Gazette of Turin.
The current instrument is placed in the arm. A stethoscope is placed at the elbow to listen to the brachial artery. By inflating the cuff to a pressure higher than the maximum pressure, the artery of the arm is then occluded. It then deflates it very gradually and when the inflation pressure equals the systolic pressure (and maximum), the artery opens intermittently as manifested by the appearance of a knocking noise in the stethoscope; these sounds, called "sounds of Korotkoff, are due to turbulent blood flow, hampered by the cuff pressure. Pulses are also important perceptible by the patient and the examiner. When cuff pressure falls below the minimum pressure (diastolic), the artery is then permanently open: the laminar flow becomes turbulent and the auscultatory sounds disappear.
This is the method "counterpulsation.
You can also feel the pressure without a stethoscope, but less precise:
- pulsation of the artery are reflected in the cuff, the cuff pressure oscillates between systolic and diastolic pressure, when the cuff deflates, it is therefore the pressure at which the gauge starts to oscillate (systolic pressure) and one to which the needle stops oscillating (diastolic pressure);
- taking the pulse of the radial arm compressed when the cuff is compressed, it does not receive the pulse, when the cuff deflates, the pressure at which the pulse appears is the systolic pressure (this method does not d having diastolic pressure).
The association manual sphygmomanometer and stethoscope is increasingly being replaced by automatic equipment (electronic blood pressure) cuff inflated and engine noise is detected by a microphone (auscultatory method), or amplitude variations of 'wave pulse (oscillometric method). These devices allow repeated measurements and monitoring in near real time blood pressure.
One can also measure blood pressure by the same techniques but this time in the same wrist and finger. This is not however the reference method.
When a couple electronic sphygmomanometer to a battery and a memory, we can then take the blood pressure repeatedly during 24 h: the MAPA (= monitoring ambulatory blood pressure also falsely called Holter blood pressure).
In some cases, blood pressure is measured by inserting into the artery, a catheter filled with liquid and connected to a pressure sensor. This more invasive (and therefore riskier) gives more accurate measurements and gives the blood pressure dynamics. Thus, the pressure at each moment of each cardiac cycle the patient is measured, not only the systolic and diastolic blood pressure over time.
Continued... Part 2.