SCUBA

Have a Medtronic Model 5076-58.
Interested in the depth I can dive.
Medtronic says 2.5 atm (absoute) or about 49 ft.

Has anyone dove with a pacemaker?

Does anyone know the safety limits built into the device?

Any reaction on the case other than compression of the case?

5 Comments

What's magic about 49 feet?

by donr - 2011-12-10 08:12:23

Why not 50 ft? Let's make it a number that makes sense!!!! What is the pressure difference between 49 & 50 ft? Does it really make sense to cap the limit at such a whacky number? Who the heck can control the depth of a dive that precisely? Hmmmmm? Fer cryin' out loud - if there are 1 ft waves at the surface, the pressure where you are will vary by that 1 ft, anyway!

I remember the conversation I had w/ my cardio after getting my PM. Don, you cannot lift any more than 5 lbs. Doc, can you allow me 8 lbs? Don, why such a whacky number as 8 lbs. Doc, that's how much a gallon of milk weighs. I know that number - I haven't the foggiest idea what 5 lbs is, cause I rarely lift 5 lb weights, but I lift gallons of milk all the time. Don, if 8 lbs makes you happier, you can lift 8 lbs. (At this point, Doc exits the room, once more shaking his head in bewilderment, having once again given in to common sense.) After he left, the conversation continues w/ his head nurse, Martha. Martha, is there any limit as to what I can lift in the curl mode w/ my elbow held at my waist? Don, yes, the 8 lbs, just like Dr. H said. Martha, why do you care how much I curl, since the problem is restricting the stress on shoulder & chest muscles. Don, well uhhhhhh... Martha, it seems that I should be able to lift anything in curl that is comfortable & easy; all I would use is biceps - no pecs, etc. Don, well, uhhhhh... go ahead, whatever is comfortable & easy in curl.

Personally, I'm not sure that Medtronic REALLY knows what the safe depth for a SCUBA dive is, they are just grabbing a number that they KNOW is safe. They oughta get John Cameron Swazey & Timex to figure it out - after all it took a lickin' & kept on tickin'!!

Don

Reaction on pacer

by ElectricFrank - 2011-12-10 12:12:21

Probably the most vulnerable part of the pacer is the lead connection area. The wires have to come through the metal case while remaining insulated. Also, the leads to the heart insert into small holes with some sort of O-ring seals. Since the leads are coaxial any fluid that gets between the shield and center conductor is a partial short circuit. Since the pacer is inside the body the fluid would be slightly saline which is more conductive.

Maintaining a hermetic seal under much worse conditions is done regularly. It's just a matter of what Medtronic specified. So that's where the 2.5 atm comes from. They have tested and FDA certified it to that dept. I don't know what the safety limits are

The result of a failure could be serious even if you aren't dependent on it. Body fluid plus pressure inside the pacer body would have an unknown effects on the circuitry. The full battery voltage could short circuit to one of the leads and apply it as a continuous current to the heart. The battery if short circuited could leak or burst releasing unknown (at least to us) chemicals into your body. And more likely your insurance would not be happy campers at the thought of replacing an expensive pacer destroyed by your knowingly exceeding the specified depth. You might wind up paying for the next one.

So that's my pessimistic reply. Of course I don't know how I get off with all these warnings after some of my antics. I wonder what the upper altitude limit would be. I've been up around 13,000' with no problem.

best,

frank

don

by ElectricFrank - 2011-12-11 02:12:49

It's common practice in underwater work to specify pressure in absolute atmospheres (atm). So the 49 ft is just a conversion to pressure. Like most conversions the ratio isn't a whole number and Ton was just giving us the equivalent for convenience.

Another way to look at it is that 1 atm=14.7psi abs. So 2.5 atm= approx 37 psi.

In this case since specifications have to be cleared with the FDA I suspect each finished pacer is tested in a pressure chamber at 37 psi plus some sizable safety margin. This isn't some cya number that doctors are famous for.

As an example power line operated monitoring equipment like an ECG needs to provide 170 volts isolation for safety purposes. However it is required and each unit is tested at 4000 volts. The tests must be traceable to the serial number of the unit. Again I suspect the same is true of the pacemaker depth rating.

I agree with what you said about your cardio's instructions on lifting etc. Keep in mind these come under the ability for a doctor to say whatever he/she likes without being held to account. It's in the same category as prescribing meds "off label". The doc can do it, but the drug manufacturer is required to limit what they put on the label. It's a crazy system.

frank

Frank, I understand...

by donr - 2011-12-11 08:12:12

...about depth & pressure. My point is that how many depth gauges carried by a diver are precise to that point? All you need is a sea state that gives you 2 ft waves & cruising along at "49 ft" will periodically put you at either 47 or 51 ft. Let's work backwards from the 49 ft: 1 atmosphere is about 34 ft of water, if my memory from 1959 still holds. Therefore, 1 ft of water is about 1/34 of an atmosphere. Now, I ask you, is a diver's depth gauge that precise that it can measure 1/34 of an atmosphere? That would make the 2.5 criteria far more precise than it really is. So why not say "...or about 50 ft?" That falls into my 5 lb vs 8 lbs criteria.

Being somewhat of an engineer of some sort, myself, I look at the safety factors we pile on to criteria & look at a HUGE CYA blanket. If we were confident in our engineering, would we slap such huge safety factors on? The answer is buried in the Tacoma Narrows where the bridge collapsed in about 1940. I'm sure that the engineers that designed that structure were confident in their work - they were just plain wrong & the wind down that narrow proved once again that Mother Nature sides w/ the hidden flaw. BTW, every engineer I've ever met, world-wide knows about that bridge, & brings it up, given a chance!

I remember very vividly the assinine requirements placed on environmental issues we were facing in the Army back in the 70's & 80's. We were being required to meet standards that we were hard-pressed to measure w/ lab grade equipment, let alone field type instruments. MOF, some of the standards were beyond the capability of even existing lab grade gear. All because of the monster safety factors used by EPA & OSHA. Not only that, but we would meet the safety requirements & STILL have to dump our waste in a hazardous waste site. WE come up w/ some number for a criteria that is precise to several decimal places; then we throw on a safety factor of, say ten, & we keep the SAME stupid precision of several decimal places. That gives the criteria a validity that is unwarranted.

From my experience w/ such issues, I came up w/ my law of testing which stated "...never perform a test that is not necessary just because you are curious." That maxim was violated by Uncle Sam's Navy on a weapon called the Bigeye (maybe you remember that beast from your China Lake days). They found that the system very handily met its design parameters, but the results came back to haunt them in the form of politics in the Congress. The system's opponents seized on that one test to force a total redesign & safety program that was unnecessary.

Science, emotions, politics, & profit

by ElectricFrank - 2011-12-12 03:12:44

The key to it all.

frank

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A pacemaker completely solved my problem. In fact, it was implanted just 7 weeks ago and I ran a race today, placed first in my age group.