5 ms·

Easier to replace the whole pacemaker than the battery, for a couple of reasons: * Pacemakers are hermetically sealed, usually laser-welded in a titanium case.

by Kelbit 9y ago

Easier to replace the whole pacemaker than the battery, for a couple of reasons: * Pacemakers are hermetically sealed, usually laser-welded in a titanium case. Adding a replaceable battery with seals would complicate this arrangement. * By the time the battery winds down, there may be a newer, better pacemaker on the market that fits the patient's needs. * Since a battery replacement necessitates surgery, you might as well replace the whole unit and get all new parts rather than put an old one back in that may be reaching MTTF. As for how long the cells last, modern Lithium Thionyl Chloride cells last 5-10 years depending on the pacemaker. They probably actually last longer, manufacturers are pretty conservative with lifetime estimates. As for plutonium supplies like those in the article, they don't really die since they're thermoelectric. The amount of current you can draw will be proportional to the amount of heat generated by the isotope and the temperature gradient. Since the heat is related to the amount of isotope remaining, the power available will follow an exponential decay. The half-life of Pu-238 is about 88 years, so the battery will last a very long time. The exact lifetime depends on how much current the pacemaker takes to operate. Most people had these devices replaced with more modern versions, but there are still a few people who have the old plutonium devices which were implanted decades ago.

bigiain 9y ago
> The exact lifetime depends on how much current the pacemaker takes to operate. Not so sure. I don't think the plutonium decay is affected by the current drawn via the thermocouple - it'll just keep putting out the same power (well, the same decaying power curve anyway) no matter how much current you try and draw. I suspect the thermocouple's voltage will just sag so the maximum drawn power will be the thermal output less the efficiency of the conversion (which, I guess, might be non-linear with current?). But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right?
- perlgeek 9y ago
  > But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right? True. The power requirements can still vary between patients (due to varying quality of the electrical contacts, which tends to deteriorate over time), so there is an individual component, it's just not based on the power drawn from the battery.
- Kelbit 9y ago
  Correct, the decay is not affected by the amount of charge you've pulled out of the cell. What I meant (and should have expressed more clearly) is that the pacemaker will have some minimum current it needs to be able to draw from the TEG to operate, and after the plutonium has decayed to a certain point it won't be able to source enough current to operate, so the pacemaker will brown out.
perlgeek 9y ago
Somebody in my family has a pacemaker, and is fully dependent on it. I can confirm this part: > Easier to replace the whole pacemaker than the battery unfortunately, this statement: > As for how long the cells last, modern Lithium Thionyl Chloride cells last 5-10 years depending on the pacemaker. They probably actually last longer, manufacturers are pretty conservative with lifetime estimates. only partially applies in this case. That pacemaker has a lot of work to do (stimulate every single heart beat), and depending on the quality of the electrodes on the heart, and the cables that lead to them, some needed to be replaced after two or three years. If one lasts 7 years, that is a very welcome respite, but quite the exception. That said, pacemakers have come a long way. The first on that this person had implanted had a fixed beat. The current generation has sensors for oxygen saturation and movement, and be configured and maintained through a wireless interface, they log unusual events etc.
- ctdonath 9y ago
  I have one. 100% dependent, dynamic rate, wireless interface, logging, runs about 7 years. "Battery low" state is addressed with progressively more annoying behavior (fixed 60 bpm, beat skipping, etc) that both saves power and urges patient to doctor. Whole unit indeed gets replaced (yes, the hard way), no point in fiddling with maintaining old tech and increased point-of-failure interfaces. And with it, I'm likely healthier than without it & the underlying issue.
rplnt 9y ago
Wouldn't wireless charging pad work well for this? Or is it unnecessary complicated considering how long batteries last?
- joshschreuder 9y ago
  I think the main problem is the giant meat sack sitting between the charging pad and battery :)
  - rplnt 9y ago
    The main problem might be patents :) Samsung includes charging of medical device[1] in their wireless charging patent. Although the patent[2] seems to focus on the charging method/devices, rather than where they are located. 1. http://patentimages.storage.googleapis.com/US20140084858A1/US20140084858A1-20140327-D00014.png http://patentimages.storage.googleapis.com/US20140084858A1/U... 2. http://www.google.com/patents/US20140084858 http://www.google.com/patents/US20140084858
- ianhowson 9y ago
  Chest cavities aren't especially space-constrained, and another commenter mentioned that electrodes wear out fairly quickly (single-digit years), so it appears that a fixed non-rechargeable battery has enough capacity to last the lifetime of the device. Wireless charging (for a pacemaker) has the issue that you've got to push the energy through quite a lot of flesh, with consequent efficiency and heat issues. Wireless charging is absolutely an option for other devices implanted closer to the skin, though.
- ctdonath 9y ago
  The issue being rather close to my heart, I'd rather have a single-use 7-year battery + full modern replacement of unit, than have to fiddle with periodic recharging just to prolong use of aging technology. Nobody much wants their life relying on >10 year old computers. (Remember: it's already "old technology" when you first get it implanted.)
  - 9y ago

by Kelbit 9y ago

bigiain 9y ago

> The exact lifetime depends on how much current the pacemaker takes to operate. Not so sure. I don't think the plutonium decay is affected by the current drawn via the thermocouple - it'll just keep putting out the same power (well, the same decaying power curve anyway) no matter how much current you try and draw. I suspect the thermocouple's voltage will just sag so the maximum drawn power will be the thermal output less the efficiency of the conversion (which, I guess, might be non-linear with current?). But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right?

perlgeek 9y ago
> But I'm pretty sure whether you draw zero Amps or short circuit the output, you'll still have precisely 50% of your plutonium left after 88 years, right? True. The power requirements can still vary between patients (due to varying quality of the electrical contacts, which tends to deteriorate over time), so there is an individual component, it's just not based on the power drawn from the battery.
Kelbit 9y ago
Correct, the decay is not affected by the amount of charge you've pulled out of the cell. What I meant (and should have expressed more clearly) is that the pacemaker will have some minimum current it needs to be able to draw from the TEG to operate, and after the plutonium has decayed to a certain point it won't be able to source enough current to operate, so the pacemaker will brown out.

perlgeek 9y ago

Somebody in my family has a pacemaker, and is fully dependent on it. I can confirm this part: > Easier to replace the whole pacemaker than the battery unfortunately, this statement: > As for how long the cells last, modern Lithium Thionyl Chloride cells last 5-10 years depending on the pacemaker. They probably actually last longer, manufacturers are pretty conservative with lifetime estimates. only partially applies in this case. That pacemaker has a lot of work to do (stimulate every single heart beat), and depending on the quality of the electrodes on the heart, and the cables that lead to them, some needed to be replaced after two or three years. If one lasts 7 years, that is a very welcome respite, but quite the exception. That said, pacemakers have come a long way. The first on that this person had implanted had a fixed beat. The current generation has sensors for oxygen saturation and movement, and be configured and maintained through a wireless interface, they log unusual events etc.

ctdonath 9y ago
I have one. 100% dependent, dynamic rate, wireless interface, logging, runs about 7 years. "Battery low" state is addressed with progressively more annoying behavior (fixed 60 bpm, beat skipping, etc) that both saves power and urges patient to doctor. Whole unit indeed gets replaced (yes, the hard way), no point in fiddling with maintaining old tech and increased point-of-failure interfaces. And with it, I'm likely healthier than without it & the underlying issue.

rplnt 9y ago

Wouldn't wireless charging pad work well for this? Or is it unnecessary complicated considering how long batteries last?

joshschreuder 9y ago
I think the main problem is the giant meat sack sitting between the charging pad and battery :)
- rplnt 9y ago
  The main problem might be patents :) Samsung includes charging of medical device[1] in their wireless charging patent. Although the patent[2] seems to focus on the charging method/devices, rather than where they are located. 1. http://patentimages.storage.googleapis.com/US20140084858A1/US20140084858A1-20140327-D00014.png http://patentimages.storage.googleapis.com/US20140084858A1/U... 2. http://www.google.com/patents/US20140084858 http://www.google.com/patents/US20140084858
ianhowson 9y ago
Chest cavities aren't especially space-constrained, and another commenter mentioned that electrodes wear out fairly quickly (single-digit years), so it appears that a fixed non-rechargeable battery has enough capacity to last the lifetime of the device. Wireless charging (for a pacemaker) has the issue that you've got to push the energy through quite a lot of flesh, with consequent efficiency and heat issues. Wireless charging is absolutely an option for other devices implanted closer to the skin, though.
ctdonath 9y ago
The issue being rather close to my heart, I'd rather have a single-use 7-year battery + full modern replacement of unit, than have to fiddle with periodic recharging just to prolong use of aging technology. Nobody much wants their life relying on >10 year old computers. (Remember: it's already "old technology" when you first get it implanted.)
- 9y ago