Thu, 10 Jun 2004
Your heart as a squirming bag of worms
In response to my
about the kludgy body, Pete TerMaat sent me
some entertaining notes about how complex even a straightforward bodily
function is. I'm really repeating these because
they're cool, but I suppose I need some Grand Metaphorical Lesson,
that being my schtick. How about "think of these next time you're
tempted to whine about complex business rules"?
Even though it's simple in purpose, the heart is integrated in ways that
are tough to duplicate.
Medtronic spends millions trying to come up with a hunk of metal that
can replace just the electrical (pacemaking) aspects of the heart.
The company's first pacemaker came about when the founder, Earl
Bakken, grabbed a metronome circuit from a Popular Electronics
magazine, and hooked it up to some leads so that the circuit would
provide pacing pulses to the heart. Simple enough...
But not as sophisticated as the heart, which has some tight
integration with the rest of the body. For example, when you
merely *think* about running, your pulse starts to quicken in
anticipation of greater demands on the heart. Also, when you go to
sleep, your heart slows down.
How do pacemakers handle the problem of ramping up the pulse in
reponse to exercise? They have motion detectors in them. One of the
early models was fooled by a woman who knitted a lot. When she sat in
her rocking chair and bobbed forward/backward, the motion detector
figured she was out for a jog, and ramped up her heart rate.
There's another story about a rock climber. During an ascent he'd
stop for a breather. As soon as he started climbing again, he needed
his heart rate to increase. But the pacemaker lagged his needs.
His solution was to pound his chest repeatedly, causing vibrations
that were picked up by the pacemaker and interpreted as motion caused
by exercise. This technique was a crude "remote control" for his
How do pacemakers know when you're sleeping? They check the time of
day and compare it against the bedtime that your doc has programmed in
for you. Again, not as nicely integrated as the real heart.
Another tidbit: the "rate response" feature of modern pacemakers, where they
detect a person exercising and respond with a faster heart rate, was
discovered by accident. Medtronic engineers put a vibration sensor in a
pacemaker, hoping to to detect a particular condition--possibly ventricular
fibrillation (where the heart quivers like a bag of worms), or ventricular
tachychardia (an overly fast heartbeat). When they put the device in a
canine for testing, it picked up a lot of "noise". They figured out that
the "noise" happened when the dog moved. From that came the idea of
interpreting the vibrations as body movement, corresponding to
## Posted at 09:47 in category /misc
Apropos of my posting mentioning
Steve Freeman points to Joe Walnes's
Development Practices Map workshop at
Development Conference. Sounds rather like what I was asking
for (depending on the granularity of the practices they consider).
## Posted at 08:14 in category /misc