This effect is called auscultatory failure. It was noticed over a hundred years ago. If you measure blood pressure with a mechanical tonometer, then at some point the same knocks in the phonendoscope may disappear, and then, as if by magic, reappear.
Because of such a failure, you can make a mistake and miss the high blood pressure.
Let's say that a person has a real upper pressure of about 180 millimeters of mercury. Due to the auscultatory failure, his knocks disappear at the level of 165 millimeters of mercury, appear at 140 millimeters and then disappear at 90 millimeters of mercury. If measured correctly, the pressure will be 180/90 millimeters of mercury. With such pressure, you cannot go in for sports and work.
There is a chance that this person's blood pressure will not be measured correctly. He sits so happy and does not complain about anything. No one would ever suspect that he has high blood pressure. They will pump a man's cuff of a tonometer to 160 millimeters of mercury, but nothing is heard there, because it is in this place that he has a failure.
Then, air is vented from the tonometer cuff and gradually reaches 140 millimeters of mercury. At this point, the failure ends, and knocks appear. Then, at 90 millimeters of mercury, the knocks disappear and we get a blood pressure of 140/90. Quite decent pressure, which does not look threatening. But in fact there will be 180/90 millimeters of mercury.
How to prevent this
It must be measured correctly. To do this, you need to measure the pressure with your fingers. They find a person's pulse on the wrist and begin to pump up the tonometer's cuff.
At some point, the pulse will disappear. It is necessary to notice on the pressure gauge at what pressure this happened, and pump another 30 millimeters of mercury. That is, if the pulse has disappeared by 150, then you need to pump up to 180.
And only after that you can grab the phonendoscope and gradually bleed the air out of the tonometer cuff. The air is released slowly, at a rate of about 2 to 3 millimeters per second.
Typically, an auscultatory dip results in errors in upper pressure measurements. But if the cuff was inflated with all the foolishness, then this very failure can be mistaken for lower pressure. Therefore, do not give up ahead of time, but deflate the cuff completely and listen to the very end.
Who has it
Well, this usually happens in hypertensive patients. All constantly refer to the same scientific study, in which about one in five people with persistent high blood pressure found an auscultatory failure.
Why does it happen
Here it is interesting. The auscultatory failure was discovered more than a hundred years ago, but its mechanism has not yet been understood. It seems to be due to stiff arteries and atherosclerosis. Somehow, the stiff arteries affect the acoustics of the Korotkoff tones we hear in the phonendoscope. The mystery of nature.
Did you have that?
