Dear Jim,
Thank you for your thoughtful consideration of this issue; I think that it
is very important as the medical profession should be among the first to
benefit from the simplicity of SI and subsequently be metric leaders in the
community.
I agree completely that a wide numerical margin is needed so that there can
be no confusion between the old ways and the new ways, so I am inclined to
agree with your suggestion that to use kilopascals is probably the best
choice of unit.
However, it might not give enough (illusion of) precision for the
physicians. Remember that you are reducing them from an apparent* range of
50 numbers (90 to 140) to a set of six numbers {9, 10, 11, 12, 13, 14}. This
may be too much of a change for their self esteem to bear.
* this is an apparent range because the real range is current only a set of
6 numbers {90, 100, 110, 120, 130, 140} or 11 numbers {90, 95, 100, 105,
110, 115, 120, 125, 130, 135, 140} depending on whether the physician uses
rounding to 5mmHg or 10mmHg.
Another option is that physicians might simply use pascals as the unit of
choice for all pressures. This would give a range from 9000 pascals
diastolic to 14�000 systolic with plenty of numbers to discriminate small
differences in between. This approach might especially suit medical
researchers who could appreciate the finer discrimination possible.
I agree that there should be no need to add a tenths digit to blood pressure
measurements in kPa, because, as you say, blood pressure readings 'are
neither that accurate nor that precise when taken by most common means'.
However, I believe that many medical workers would feel a need for more
numbers than the set {9, 10, 11, 12, 13, 14}. I suspect that they would feel
a need for at least one decimal point to give the illusion of accuracy and
precision. This would increase the range from 6 numbers to a set of 60
numbers {9, 9.1, .9.2, 9.3, ... 14.8, 14.9}. However, given the deserved
fame given to physician's handwriting, I don't much like the chances of the
smooth communication of the decimal point in life-and-death situations.
Cheers,
Pat Naughtin CAMS
Geelong, Australia
on 2002-11-18 09.19, James R. Frysinger at [EMAIL PROTECTED] wrote:
> Pat Naughtin wrote:
>>
>> Dear All,
>>
>> Over the last few weeks, I have had a chance to see various medical offices
>> and hospitals in action.
> .....
>> I believe that use of the unit mmHg is holding back progress in this area,
>> and causing the medical profession to cling to old and dangerous technology
>> because they have yet to find a way to change to the pascal, the SI unit for
>> pressure, including blood pressure.
> ....
>
> So, what new numbers should we get used to? Taking the commonly used
> threshold of 120 mmHg for a systolic pressure that is too high, that
> would come out to 160 hPa or 16.0 kPa. And a respectable diastolic value
> of 60 mmHg corresponds to 80 hPa or 8.0 kPa. I don't know what diastolic
> value gets the medicos concerned.
>
> But, I can see a dangerous situation arising if a transition is made
> from mmHg to hPa. The numbers are too close. A pressure reading of
> 150/90 is dangerous if the units are mmHg but OK if they are hPa. On the
> other hand, if a patient's blood pressure were measured in hPa and
> charted without units, then a dangerously low 100/60 (in hPa) would
> appear "normal" in mmHg and thus be overlooked. Thus, I suggest it safer
> to train people to work in kilopascals here. A charted 15/9 BP would
> call attention to the fact that it is not in mmHg.
>
> So, I suggest that we think of "normal blood pressures" as being
> roughly "14/9", short for 14 kPa systolic and 9 kPa diastolic. (Charts
> normally provide very little space to be explicit, hence the
> "shorthand".) No need to add a tenths digit; blood pressure measurements
> are neither that accurate nor that precise when taken by most common
> means. In fact, I think that most doctors and nurses round those values
> off to the nearest 5 or 10 mmHg.
>
> I just checked my wife's Omron automatic sphygmomanometer. It reads out
> in mmHg and there is no apparent way to change the units.
>
> Oh, to save anyone from having to look it up,...
> 1 mmHg = 0.133 322 4 kPa or 15.00 mmHg = 2.000 kPa
>
> Jim
