Pacemakers, Deep Brain Stimulation

[Stiganator]

I'm doing a theoretical design for an implantable epilepsy control device. It will be pretty similar to a cardiac pacemaker. I've been trying to find some power specs about pacemaker batteries, but I've been coming up empty handed.

My design for the epilepsy control device consists of a wearable control unit which communicates via RF with a unit that is implanted in the skull and that unit records the EEG and streams it via RF to the control unit (1 minute of EEG every 10 minutes) and when the control unit decides it should stimulate is sends the signal to the implanted unit.

What do you think?

Feasible or is power the reason most Deep Brain Stims have a module implanted in the chest an run leads up to the brain.

 

[CycloWizard]

A quick check gave me a ton of info on pacemaker batteries. Some give you a lot more useful information than others, but this onepopped out at me right away.

 

[QuixoticOne]

"(1 minute of EEG every 10 minutes)" -- so 9 minutes after you have a seizure it'll sense danger get you back into sync? Ok, pardon the silliness, I just had no idea that the signals precursor to an event were very detectable 10 minutes in advance. Interesting.

Anyway, I'm sure you've found all you need to know about pacemaker batteries. They're probably almost state of the medical art. If you want to extrapolate you can start to look at just the theoretical energy density of lithium ion batteries per cubic centimeter or per gram or whatever and realize that you'll always get a bit less in a practical design. Also look at some of the technology reports of net rechargeable lithium polymer or other sorts of batteries, though keep in mind that state of the medical art is often about 15 or more years behind the engineering state of the art due to the slow process of research / studies / trials / certifications et. al.

I'd think that a rechargeable solution would be preferable all things considered, possibly with a non-rechargeable backup if desired. Though the thought of rechargeable batteries in this application immediately brought thoughts of people climbing into borg recharging stations for a top-up.

The RF emitter is probably the weak link, you can run a data collection CPU on microwatts of energy, though when you start actively emitting RF you're probably going to be consuming at least 100uW to 1mW of energy doing so. ~ 100,000 seconds / day, 1 milliwatt = 100 Joules / day, or 3.6J/hour power consumption which is pretty much out of the question for any non-rechargeable battery consideration.
Indeed at even 1 microwatt power consumption that'd be 86mJ/day, 32J/year, a significant long term figure, but not unthinkable if one could get the battery replaced every so often.

So you'd basically have to communicate passively like most cheap RFID tags do, though that limits your data rate a bit, and requires an active scanner device to read the data and energize the readout process, though 0-10 micro-watt level data collection could still occur absent that power source given a good rechargeable battery.

 

[SsupernovaE]

I don't know, but my sister has pretty severe epilepsy (grand mal seizures, petite mal, and absence). So whatever you can do to further the technology, thanks!

 

[Modelworks]

There is already one such device called a vagal nerve stimulator.
Its not attached in the brain itself but on the vagal nerve.
The device is implanted under the skin in the chest.
http://www.vnstherapy.com/

I would think the reason for not implanting the device totally in the brain would be due to lack of access to the device should something go wrong.
The chances that the device would fail are much higher than the chances a lead at the end of a wire would fail.

 

[Stiganator]

Brian Litt had a paper from 2004 about how frequencies in 94Hz range increase up to 1 hour before seizures occurred. All patients who exhibited increased 94 Hz activity at 20 min prior would have a seizure.

 

[Stiganator]

I suggested we include an induction coil type recharging mechanism so we could recharge without another surgery.

 

[Mark R]

Pacemaker batteries tend to be good for around 10-15 years - and those are primary cells.

Presumably, there are some very high tech low power techinques used in the electronics, as well as top quality batteries in order to achieve that type of battery life., Modern pacemakers are quite sophisticated in the signal processing that they perform, so I would presume that this is quite a challenge, but even then it is going to be trivial compared to EEG processing.

Brain stimulators need very little processing power, as they are virtually 'dumb' devices, they just stimulate at the programmed frequency and voltage, and collect diagnostic data for transmission to a programming device.

What is the power budget for your device, and how would it compare to a pacemaker? It may be that the degree of DSP of you need exceeds that available in a completely self contained unit?

Are you proposing that the wearable processor recharge the implanted unit? In that case, does the internal unit even need much of a battery at all, if it can't treat without command of the processing unit?

 

[firewolfsm]

I don't think the remote is the best idea, it's cumbersome, prone to damage or loss. Also, there are other nerves that could be used to detect the signal, areas where size constraints aren't so tight and surgeries aren't as invasive.

and...is there a good way to charge off body heat yet?