My Sphygmomanometer

 

 This is it !

I've been "under the weather" for quite a few weeks and Mrs EP decided that I should go and visit the doctor. I have a new GP, the previous one having decided to retire at 60 because under the new NHS he felt that he was doing more paperwork than doctoring. The new lady doctor is very young, and doesn't look old enough to have gone through university, let alone qualified as a GP.  Mrs EP's comment was "She's very sweet, but does she know what she's doing!".

Anyway, she went through all the usual tests, decided that I wasn't yet senile, and all that seemed wrong was that my blood pressure was a bit on the high side. Hence the machine above, which I have on loan with instructions to take my blood pressure two or three times a day for the next couple of weeks.

Now being a (retired) engineer, things like this device are interesting in the technical sense. When my old GP took my blood pressure he used the old fashioned method which balanced the pressure against a mercury column and listened my pulse with a stethoscope to determine the reading. All that has gone now in favour of this machine. What puzzles me is that there is no apparent way that it listens to my pulse, so how does it know when to record the values? Then the next questions, which any researcher asks about instrumentation is "How accurate is it?" and "Does it give reproducible results?"

Having found the specification on the web, the accuracy is quoted as + or - 3 mm Hg but I'm unable to confirm that without a "Standard arm" to check it against. I did some tests on reproducibility. My method was to put the cuff on my arm, sit in a comfortable chair and continue with a book I'm reading (not the newspaper, that would certainly raise my blood pressure). I took a reading every few minutes for twenty minutes or so and no two were the same varying from a high of 177/87 to a low of 143/73 which is considerably more variance than might be expected from the quoted accuracy figure. So did my blood pressure vary by + or - 10% from the centre value of 160/80 or is the meter faulty?

I will repeat my experiment sometime, taking care not to move between readings, but somehow I suspect that discussing instrumentation accuracy and reproducibility will not be within my lady doctor's abilities.

As most of the figures were on the high side, I suspect that I will be issued with some pills to get it down. Just as long as she doesn't expect me to give up my nightly tot, I'm not too concerned !