Performance Testing and Tuning for the Human Brain

The neurostimulator (aka implanted pulse generator)
and lead extensions were implanted and
connected last week to the leads previously
implanted two weeks ago.

One of my occupational passions for the past 20 years has been to improve the performance of large computer systems using data-driven scientific methods.   "Scientific" means measuring stuff.  It always pains me to quote "Mythbusters" but in this case they have a point: "Remember kids, the only difference between screwing around and science is writing it down."  Whether you're testing the stability of a system, how fast it can complete an individual task, or how many tasks it can process in an hour, you have to be able to describe how the system behaves before AND after you make a change. You need DATA.  "Otherwise," said one of my mentors, "we might as well just go play football."  Indeed.


Programming a neurostimulator for Deep Brain Stimulation (DBS) looks a lot like setting up and tuning other complex technology systems.  I've been studying medical texts and the Medtronic programming manuals for months.  And I told everyone I'd met in the Neurology and Neurosurgery units at Mayo that I wanted to have an active role in the programming and management of the neurostimulator.  I have to be careful here, because I could easily take this off the rails and into techno-babble.  For now, I will resist the urge to pontificate and otherwise make this boring.  Though I am a self-proclaimed scientist, computer scientists rarely get the kind rave reviews for the writing that theoretical physicists get.  So let's start with a few facts: first, I've learned that it takes quite a while to get pain under control on oral medication after I have a surgical procedure.  Next, once it's controlled, I feel better very quickly.  I was able to sleep several hours Wednesday night following surgery.  Mobility in my left arm increased rapidly, despite the deep incision just under the left collar bone where the neurostimulator was implanted.  Any movement of the upper part of the left arm disturbs this site.

The surgical sites where the neurostimulator was
implanted, and second site where the extensions were
conneccted to the previously implanted leads.  The
extension wires run behind my ear and down my neck.

On Thursday morning, the teenagers were not happy about being rousted from slumber in their adjoining room, but we wanted to get over to the Mayo Clinic's subway tunnels for breakfast.  The subway under this part of downtown Rochester allows year-round walking access between buildings without the need to bundle up against the harsh Minnesota winters.  The tunnels are also home to several important establishments, such as Brueger's Bagels, Cinnabon, and Caribou Coffee.

Just before 10 AM, we made our way up to the familiar waiting area for the Neurology Clinic.  I checked in.  In a few more minutes, I was called back.  Lynette came with me so she could watch the fun.  Initial programming is done by the experienced nurses in the Neurology unit, then reviewed by a neurologist.  The nurse doing the initial DBS evaluation and programming had also done some of my earlier testing, so we were already familiar with each other.  We picked up just like we left off, jumping back into a UPDRS (Universal Parkinson's Disease Rating Scale) evaluation to use as a baseline.

Photo of the four contacts on the
DBS lead.  One of these is implanted
in each side of my brain.

Each DBS lead implanted in my head has 4 separate contacts that can be used alone or in combination with other contacts on a given side.  My research led me to understand that the initial programming appointment would mostly consist of testing all 8 of these contacts (4 per side).  There are 3 goals for this testing:

1. Ensure that the contact is functioning
2. Find the voltage for each contact where negative side effects start, establishing an upper threshold
3. Hopefully identify a voltage range where some some beneficial therapeutic effects are noted for each contact.

The Medtronic manual for the Clinician Programmer device says to begin and end every programming session by checking the impedance values for the contacts.  This measures how much opposition there is to the flow of electrical current from that contact or pair of contacts.  It's a sanity check to ensure that there aren't any broken or shorted wires or other problems with the electrical element.  And we did start this way, after I reminded her that I was going to be asking a lot of questions, actively participating.  Unfortunately, this didn't go over well.  I asked if I could see the measured impedance values and was essentially ignored because she was busy transcribing the values from the handheld programmer into the computer.  She also did not offer to show me before proceeding to the next step.  I was disappointed, but not surprised (experts don't like "amateurs" questioning their work or disrupting their routine.)

I'll sum up most of the next two hours by saying that when voltages got too high, one of the following happened:

• I felt a tingling or buzzing sensation in my hand
• the muscles in my arm would tighten
• my eye would start pulling or closing
• my hand and fingers would curl up

In most cases, higher voltage also resulted in a "cognitive impairment."  In some cases, I just felt slower, like I'd had too much to drink.  In other cases, I felt "stuck," as if I couldn't assemble a thought or make my mouth move to produce words, or even find the words I wanted to use.  It makes a certain amount of sense to me.  The ultimate goal of DBS is to disrupt signal patterns and oscillations in the brain that are causing some of the physical symptoms of Parkinson's Disease.  Too much voltage could, perhaps, disrupt things to the point where it becomes difficult to think normally.  Lynette says she could tell by looking at me and watching that something just wasn't right.  She actually came to my rescue later in the session.  She said my eyes looked "lost," which is a great description, because I did feel lost in my head.  I couldn't think straight.  Fortunately, the haze faded within seconds of the stimulation being turned off.

The nurse said that they try to get to 4 Volts on each contact during an initial session.  Here's how I did:

Contact	Voltage
0 (left bottom)	4.0 V
1	3.3 V
2	3.8 V
3 (left top)	4.0 V
8 (right bottom)	2.0 V
9	2.0 V
10	2.4 V
11 (right top)	2.5 V

So, on the left side of the brain (controlling movement on my right),  I nearly met their expectations.  The right hemisphere was much more sensitive.  This mirrored the results I remember from placement testing in the O.R.  I was glad that Lynette had the opportunity to see, at least once, my mouth pulling to the left like it did during testing in surgery.  The good news is that nearly every contact had some therapeutic effect before reaching the adverse effects threshold.  The bad news is that whole ordeal left me feeling very out of sorts.  Imagine you've just had your brain repeatedly exposed to unnatural electric current and brought to the threshold of physical twitching.  You might feel a little funny, and no doubt tired.

With the survey of individual contacts completed, they try to start the therapy with the simplest possible program: 1 active contact per hemisphere configured as an anode (negative) and the neurostimulator case set as the cathode (positive) for the system.  (Remember, electrons flow from negative to positive.)  Much more complex arrangements are possible, but again, this takes time to tease out.  We tested one initial setting with contact #1 at 1.5 V.  I took a walk down the hallway and felt as if I were walking like a robot.  My muscles on my right side were more relaxed, but something was interfering with my movement (I wonder what that could be?)  Lynette says I didn't look right in the slightest.  Like I was walking like a marionette with someone else pulling the strings.  The nurse switched from contact #1 to contact #2 at 1.5 volts.  The Tin Man walk went away and my right leg actually lifted when I'd take a step.  She added contact #10 for my left side at 1.5 volts.

Somewhere in here, I asked for the ability to adjust, within separate program groups, the voltage, pulse width, and pulse frequency.  I was told that they only allow patients to change the voltage setting.  I didn't realize it at the time, but I was mentally stuck, having difficulty expressing my thoughts.  This probably worked out for the best, because I might have lost my patience with that answer.  Lynette, being much sharper than me at that point, inquired what was necessary to get an exception to that policy.  Well, we'd have to talk to Dr. Klassen, and she'd just paged him.  I was expecting Dr. Klassen to be in the clinic that morning, and hoping to have a chance to review everything with him.  When the nurse finally returned with him, I was mentally fogged in.  Lynette asked if they could reduce the voltage setting, they said, "Sure," and kept talk to us.  Lynette told them, "Chris looks like he's not thinking clearly right now, so I'd appreciate it if you could change the voltage before we continue."  My Hero!  As the voltage dropped from 1.5 V to 1.3V, the "electric fence" inhibiting my mind faded.  I could finally join the conversation, thought I'm not sure how much mental energy I had left to give.

Dr. Klassen described how they typically proceed: for the next two weeks, keep the settings steady, if possible.  After that, I could attempt 0.1 V per day increase.  Then we talked medication.  It immediately became apparent that I had TWO variables (Voltage and medication) to optimize within the next 2 -3 months.  So, at this point, I decided to back down from my righteous indignation at not being allowed access to more settings.  I'll save that for a future visit, and instead demonstrate that I know how to properly document and propose adjustments to test parameters.

This is your brain, overstimulated by DBS testing.
Any questions?
(That, or surgery gone terribly wrong.)

Shortly after leaving the appointment, my head was still feeling scrambled.  I was too tired and my brain was too "frazzled" from testing.   I needed a break to let things settle.  I turned the system off with my patient programmer.  I immediately felt better.    I turned it on at 1.2 V later that evening.

Since Thursday, I've alternated between 1.2 V and 1.3 V.  The higher setting provides a little more therapeutic benefit, but also seems to be inducing a mild "headache," for lack of a better description.  After everything it took to get here, I was actually hopeful that this part might be easy.  Expecting?  No. But Hopeful.

Okay folks, I've been working on this half the day, and I've put what I can into it.  I'm now turning keyboard over to Lynette for her to enhance, beyond the great editing she's already done.  Take it away...!
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I don't have much to add, but...here goes.  One thing that Chris didn't say when he was describing the testing of the leads is that whenever he started to get to a higher voltage, his voice would get "gravel-y-er".  Beyond him talking slower and looking like it took more effort to talk, his voice would change, and keep getting deeper and more gravel-y.  Once the stimulation was turned off, it went back to normal immediately.

And, BTW, I'm still puzzled and astonished by the lack of reaction to Chris asking for them to turn down his stimulator in the appointment.  You could clearly tell he was struggling (or at least I could), he asked to be turned down, they responded "yes", and then kept talking about the process.  Huh?  Did I miss something?  I had to have had the dumbest look on my face before I spoke up to ask again for them to turn it down...

Also, (and this is a "cool" effect in my opinion) is that the next morning after a night's sleep at home and without his morning meds, Chris was able to walk normal (no right leg stiffness and not bending like it has been - his Parkinson's walk).  His leg was bending at the knee and ankle and his walk was just smoother.  His right arm was swinging instead of being straight down not moving and his wrist was straight, not bent.  All more typical instead of Parkinson's.  Very cool!
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