Sunday, February 22, 2009

Automatic Blood Pressure Monitors

You might have thought of owning one of those automatic blood pressure monitors to conveniently take readings of your blood pressure at home. It is nice to have such a device at home so that you don't have to wait till you see your doctor just to know what your blood pressure is. That is why I bought one of those small compact automatic monitors. The one I bought was a generic, relatively cheap monitor ($50 or so), and it is easy to use. Just wrap the cuff around your arm, press the button and it pumps air into the cuff and displays your diastolic and systolic pressures on the LCD screen.
I used my monitor for over a year and was happy to see my blood pressure close to 120/80. However, I was not sure how accurate those readings were, especially when I found discrepancies between the readings I got at home and readings I got elsewhere. I am not talking big discrepancies, only a few points. I wanted to know how accurate were the readings I took at home, because although I knew that blood pressure varied all over the place within minutes, I also knew that there was a big difference between 126/76 and say 134/84. All I wanted to know was the accuracy window of my monitor. I surfed the internet looking for how accurate those monitors were but I did not find the information I was looking for. I found warnings about the necessity of calibrating the monitor periodically to ensure accurate readings, but of course you couldn't calibrate it yourself, you had to send it to a special lab to do that for you, for a fee of course. I was frustrated about all this, and was coming to the conclusion that the only accurate blood pressure reading was the manual one where the nurse had to listen to the turbulence in your blood with a stethoscope while pumping air into the cuff.
Lately, I found a brand called Omron that had a reputation of being accurate, so I bought one the other day. The specifications sheet inside the box said it was calibrated to be accurate within 2% of the actual pressure. Now that was impressive. I tried it instantly, and I got a reading of 126/76 the first time I used it. Within minutes, I used my old generic monitor to compare the two, and I got a reading of 134/84. OK, so which one could I believe now. Then after a few more attempts, it occurred to me that in order to have a fair comparison I had to have the same position in both measurements. Reading the booklet that came with the Omron monitor it said to sit on a chair and lay your arm on a table so that it was about the same level as your heart, and to keep your feet flat on the floor. So I sat in that position and used my old monitor again. I got a reading of 127/76. Then I used the Omron monitor in that same setting and I got 126/76! Bingo! Almost exactly the same reading. I made two more measurements with each monitor in that position and I got similar readings again. I was thrilled. This meant that what was important was the position in which you measured your blood pressure not the monitor itself. It seemed that both monitors read the same pressure when the conditions were similar. To make sure that was the case I tried both monitors again the next morning, and again I got very similar readings. So I returned the new expensive Omron monitor and decided to continue using my old one. All I had to do was to make sure that each time I used it I sat in that position on the table, laying my arm at the same level as my heart, and keeping my feet flat on the floor. That position always gave a consistent accurate measurement of my blood pressure.
So now I know that I have a means of telling within reasonable accuracy what my blood pressure is at the convenience of my home.

1 comment:

Kawthar Hegazi said...

Wow baba, this is a very nice peice of work. I never knew that Automatic Blood Pressure Monitors could be a topic to write about. Great job!
Salam