Jump to content


E-Newsletter Signup Like us on Facebook Sign Up For Our e-Newsletter
Photo

DBS long term impedance testing


  • Please log in to reply
5 replies to this topic

#1 am0665

am0665

    Member

  • Members
  • PipPip
  • 26 posts

Posted 20 January 2012 - 03:18 PM

This is a question, from a long-time PD biDBS STN patient, is meant for your programming experts with hands-on experience of impedance fluctuations in Medtronic or St. Jude devices.
Please feel free to reply on- or off- line.

Given Dr. Okun's chapter in the William Marks book on DBS Management, I'd be interested in experiences with your tracking and interpreting impedance and current fluctuations over time.
Not just:
- immediately post-operative changes while the brain tissue heals
- or out-of-range values possibly indicating a short or a break in the the wire loops or leads

To more subtle causes of such variations, which put into doubt a statement like " after the first few weeks post-op the impedance doesn't show any change"; whether the brain is receiving a consistent neuro-modulation, like maybe:
- slow fluid penetration at connectors
- IPG degradation
- effect of testing impedance at therapeutic, not unit, amplitudes

Thank you

#2 Dr. Okun

Dr. Okun

    Advanced Member

  • Ask the Doctor Moderators
  • PipPipPip
  • 4,299 posts
  • LocationUniversity of Florida

Posted 22 January 2012 - 08:54 AM

To more subtle causes of such variations, which put into doubt a statement like " after the first few weeks post-op the impedance doesn't show any change"; whether the brain is receiving a consistent neuro-modulation, like maybe:
- slow fluid penetration at connectors
- IPG degradation
- effect of testing impedance at therapeutic, not unit, amplitudes

I will post this for you. I think more research needs to be done in this area to understand changes in impedance in tissue over time. These changes in the human have been thought to be less with constant current, however some have argued that with voltage driven devices a capsule forms around the lead and that may stabilize impedence of the tissue.

Interesting conversation and I will post for comment.

Michael S. Okun, M.D.
Author of the Amazon Bestseller Parkinson's Treatment: 10 Secrets to a Happier Life
National Medical Director | NPF
UF Center for Movement Disorders & Neurorestoration
Read More about Dr. Okun at: http://movementdisor...hael-s-okun-md/
or Visit Parkinson's Disease treatment and research blogs at:
NPF's What's Hot in Parkinson's disease
or his parkinsonsecrets.com blog for treatment tips


#3 am0665

am0665

    Member

  • Members
  • PipPip
  • 26 posts

Posted 23 January 2012 - 12:16 AM

Dear Dr. Okun,

My delving deeper into this question has to do with a patient becoming very worried after a few months of consistently low impedance... whereby getting some insight may be more helpful than chasing after the medical team.
Like flying in an airplane, one can combine the low frequency occurrence with the high risk consequence toward a measure of System Safety and Reliability.
I see such anecdotal possibilities appear in the published literature on long term DBS management.

I was hoping that my description and question above was detailed enough that your team could address it beyond generalities.
Maybe some specifics could help. Let me try some definitions before asking the question again:

Impedance of an alternating or time-varying current loop: it is a system response function, a relationship between voltage and current. If the current flow were steady in a resistive path, or static, it would be close to the Resistance of the current loop, and it could even be constant. For an implanted DBS, it can only be measured inside the IPG, so it is an indirect estimate of what gets to and from the brain, via the lead, wiring, and connectors.

The Medtronic IPG clinician's manuals, if I may paraphrase in simpler terms, strongly recommends that this integrity test be performed upon every recalibration visit, for unit test voltages applied to each possible electrical loop. The Impedance should be in the range 500 - 1500 Ohm; out-of-range results indicate something abnormal... maybe requiring an expensive CT or MRI test.

Given that you just authored a report for 136 PD DBS biSTN patients implanted with St Jude Libra leads and IPGs in the period 2005 - 2009, including an instance of an IPG battery needing premature replacement (a few St Jude patients have reported on another DBS forum), what can you tell us about out-of-range impedance situations (dx, cause, fix) among these patients:

- how often did below-range impedances come up for the constant current mode? I am talking about consistently low for repeated measurements over time
- does the fact that it is a quick "therapeutic impedance measure" make any difference? in other words it is measured at production current levels
- to my basic understanding, short of published information, it involves using just the currently active loop and sending a short test current through it; so would such a transient procedure affect the measurement?
- is a bi-polar setting more likely to produce an aberrant impedance (smaller and more concentrated path through the brain tissue) than a mono-polar setting?
- St. Jude advertizes their IPGs even being usable with an already implanted Medtronic lead, through a connector + adaptor. Would this choice change the impedance story?

Forgive me if I wrapped the question into technical jargon. I believe that, for patients worried about the electrical field in their brain being correct, it is an important question to formulate properly and to answer.

Thank you.

#4 Dr. Okun

Dr. Okun

    Advanced Member

  • Ask the Doctor Moderators
  • PipPipPip
  • 4,299 posts
  • LocationUniversity of Florida

Posted 23 January 2012 - 07:52 AM

I will post these for you as I cannot tell you any more answers from a neurologist's perspective. I may suggest a device engineer could help you.

Michael S. Okun, M.D.
Author of the Amazon Bestseller Parkinson's Treatment: 10 Secrets to a Happier Life
National Medical Director | NPF
UF Center for Movement Disorders & Neurorestoration
Read More about Dr. Okun at: http://movementdisor...hael-s-okun-md/
or Visit Parkinson's Disease treatment and research blogs at:
NPF's What's Hot in Parkinson's disease
or his parkinsonsecrets.com blog for treatment tips


#5 KLH

KLH

    Newbie

  • Members
  • Pip
  • 1 posts

Posted 25 February 2012 - 11:56 PM

Hi Dr. Okun,

Greetings from a PD DBS patient with St. Jude implant, who seems to have impedance measurement concerns. A Google search led to two relevant threads on your NPF forum.

May I contribute a bit to the topic, then follow-up with questions.
I also found two recent publications, addressing long term IPG hardware problems:
1. Essential Neuromodulation, by JE Arle & JL Shils (editors): (Academic Press 2011), Chap 15 on DBS Circuit Fault-testing
2. Electrode dysfunctions in patients with DBS: a clinical retrospective study, by Niels Allert & M Markou & AA Miskiewicz & L Nolden & H Karbe, Acta Neurochir (2011) … mentions a 3% statistic of occurrence of IPG to extension wire faults: fluid penetration shorts, disconnects. I note that in translation from the original German, “electrode” probably means anywhere in the implanted system.
I don’t mean to make this issue controversial… only to couple it with a measure of medical severity (like possible loss of stimulation), toward a measure of patient Safety.

Reading your multi-patient reports, hearing of your reported experiences and access to a database of patients, would your team have some information on such impedance aspects for the newer Medtronic and St. Jude models? Both device developers provide upgraded IPGs, compatible via a Pocket Adaptor with an already implanted Medtronic extension wiring upon battery exhaustion.

More specific qns:
- what would you know about therapeutic-level impedance and current not indicating properly whether the design stimulation field is reaching the mid-brain nuclei (in some cases)?
- diagnosis: beyond impedance, what can the patient test (away from a distant hospital), or once he / she sees a more or less hardware savvy programming nurse, to confirm proper flow intensity in the wiring? Is any EM-detection device available, better than the old transistor radio … while we wait for what Boston Scientific is working on?
- certification of system interfaces: when St. Jude advertises on the web that it has CE Mark Approval for Brio and / or Libra device, including its IPG driving a Medtronic lead, what assurance does that imply on the level of system testing applied to the Pocket Adaptor, i.e. the interface between two manufacturers? Cumulating a combination of factors possible during the 9 year rechargeable battery life: like connector seals holding up to electrical, thermal (during recharge), mechanical, or chemical factors?

Thank you.

#6 Dr. Okun

Dr. Okun

    Advanced Member

  • Ask the Doctor Moderators
  • PipPipPip
  • 4,299 posts
  • LocationUniversity of Florida

Posted 03 March 2012 - 05:03 PM

I will post your questions as they are beyond my expertise. The Parkinson Alliance will be sponsoring a meeting soon on some of these issues.

One suggestion may be to touch base with the engineers at each manufacturer's factories. They can probably tell you the most about the device.

Head to head trials, and trials on some of the information you want I would imagine will be published as the technology evolves.

I will post and hope some people on the forum will weigh in.

Michael S. Okun, M.D.
Author of the Amazon Bestseller Parkinson's Treatment: 10 Secrets to a Happier Life
National Medical Director | NPF
UF Center for Movement Disorders & Neurorestoration
Read More about Dr. Okun at: http://movementdisor...hael-s-okun-md/
or Visit Parkinson's Disease treatment and research blogs at:
NPF's What's Hot in Parkinson's disease
or his parkinsonsecrets.com blog for treatment tips





0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users