By Leta Currie Marshall
You know by now not to judge a book by its cover. You should also know not to judge a heart by its visible mechanical support system.
I may not look like your idea of a heart patient, but I am one. In the spring of 1981, when I was nearly nine months pregnant, I had a sort of cardiac short-circuit. As I lay on a cold table under the combined heaviness of a full-term baby and the weight of a lead blanket, a surgeon with hairy arms, a thick accent and an unsayable name sewed a pacemaker into my chest.
I went home the following day to finish being pregnant. I spent the next couple of weeks knitting a powder blue baby sweater and taking leisurely walks through my neighborhood. Right on schedule, I went into a labor almost embarrassing in its ease. Just before dawn on a beautiful May morning, nobody was more astonished than I when after a few hours of deep concentration I brought forth a robust infant daughter.
Powder blue is still her favorite color.
At nearly eight and a half pounds, my baby was not exactly small, but a pacemaker is. The early models were the size of a hockey puck and lasted less than a year. Nowadays they’re about the size of a cookie–an old-fashioned Granny-made cookie, not the gigantic shrink-wrapped kind you can buy at the mall.
This little medical miracle has kept my heart waltzing along, day in, day out, for 21 years. I just got my third pacemaker, much fancier than the first. It responds to my heart’s own rhythm and speeds up when I speed up, so I can do just about anything except play racquetball or run a marathon.
When I got that first unit I could feel the little electric impulse going tick, tick, tick in my chest muscle. It was kind of unnerving to be made aware of my own mortality with every heartbeat. But modern pacemakers are programmable from the outside by a combination of computers, magnets and magic. Without doing surgery the doctor or a technologist can tinker with the settings and turn down the output. This makes the lithium battery last as long as possible, and I no longer feel the tiny jolt of electricity so I can more or less forget about the whole thing. More or less.
I have some idea of how a pacemaker works but I’ve always wondered just how much juice it takes to jump-start my heart. I know that we pacemaker people have to be careful around airport and department store security gates, cell phones, computer monitors, and wrecking yards because electromagnets can mess with our machinery. I began to worry: what about vice versa? Am I a source of electromagnetic frequencies that could endanger my family and friends, or mess up my computer (Heaven forbid–I have newspaper deadlines to meet)?
I logged onto the internet, and found the web site of St. Jude Medical, a leading company in cardiac rhythm technology and manufacturers of my new pacemaker. I sent them an e-mail and received a prompt reply from Senior Technical Specialist Jerry Hadduck. Jerry wrote:
“The pacemaker will deliver between 1.0 to 5.0 volts for .5 milliseconds on average to the heart muscle for each pacemaker pulse depending on the programmed settings. This amount of current is very small and the energy would be between 6.3 and 25 microjoules. I have never seen in pacemaker journals any studies that show any increase in electromagnetic field strength in patients with pacemakers.”
Well, that last part eased my mind, even though I speculated whether the reason there were no studies on electromagnetic field strength in pacemaker patients was that nobody else ever bothered to wonder about it, given the more pressing problems we have to deal with, like Life, Death, Deadlines, and What’s For Dinner.
The technical language of Jerry’s message threw me a little. I’d heard of volts and milliseconds. But microjoules? No idea.
Back for more research.
Pay attention. This will be on your final exam:
A microjoule is the basic unit of electrical energy used in pacemaker technology. One microjoule equals one millionth of a joule. Microjoule is abbreviated using the Greek letter Mu (µ), which means the same as “micro”-one millionth-and a capital J for Joules. Moo Jay.
I think µJ would look cool on a tee shirt.
The Joule is the standard international unit for measuring electrical energy, and is equal to one watt-second, or ten million ergs. What’s an erg? Even smaller than a microJoule: an erg is one ten-millionth of a Joule. You write it like this: .0000001. Pretty small.
The Joule was named after James Prescott Joule, an English physicist who co-discovered the Law of the Conservation of Energy. The Law says that energy used up in one form reappears in another, and is never lost. I think people have instinctively known this all along. Some of us call it “eternal life.” The Universe is big, but it’s a closed system: nothing gets in or out, nothing is ever really new, or ever really gone. I like thinking that when I die, I’ll just transmogrify into something else. Where would I go?
A Joule also equals about one-fourth of a calorie. What’s a calorie? Well, an average chocolate chip cookie is a pacemaker-sized and, to my mind, ideal calorie-delivery system. One cookie can truck a bazillion calories straight to my hips, which are not particularly small.
If you look at it the other way around, a calorie is about four Joules, or four million microJoules. If a chocolate chip cookie actually has, say, 100 calories, it would provide enough energy to keep my heart going for a long, long time. Too bad scientists haven’t figured out a way to make that connection.
A Joule is also the amount of work done by one newton acting through a distance of one meter. My husband loves fig Newtons, and can easily reach a package a meter away…but that’s another story.
As my robust 21-year-old daughter the geophysics major can tell you, when you start talking microjoules, you are entering the land o’physics, where you’ll learn words like femtoseconds and picomoles and zeptograms. It’s a small, small world, and the trail of nanocrumbs leads ever deeper into the mystical forest of quantum physics, populated by itty bitty, jiggling wave-particles with silly names.
Sometimes I wonder whether, if I concentrated hard enough, I could get my body, my hips, and even my pacemaker to dissolve into jiggling wave-particles. I feel lighter just thinking about it, all that beautiful sparkling clean space like cosmic fresh air blowing through my molecules.
Well, class is almost over. Time to wrap up that question of how much power it takes to keep me going. According to Jerry the Senior Technical Specialist, it takes between one and five volts. If nine of them fit into a nine-volt battery, a volt must be about the size of a chocolate chip. When my pacemaker, like a power pea shooter, pops a volt per second down the wire into my heart, I can’t even feel it. I’m just glad somebody invented the thing so I can enjoy a full lifetime of cookie eating.
So now you know the facts. If you’re worried about being slammed by a direct blast of a baker’s dozen microjoules, don’t hug me. On the other hand, if you’re in a slump and need a little extra energy, I can always spare a few ergs.
©2002 Leta Currie Marshall