Category Archives: pacemakers

Be gentle to the heart, otherwise you’ll lose it

Researchers at the Max Planck Institute and Cornell University have come up with a low-energy pulse sequence to
restart hearts and make implants last longer is what we can read in IEEE Spectrum today. Other advantages of using a train (a burst) of pulses instead of using a single (tonic) pulse are that defibrillation becomes less painful to the patient and is less likely to evoke fibrillation elsewhere in the heart. The new therapy still has to be tested on patients, though. 

From this, it is only a small step towards realizing that other types of tissue should be stimulated with burst-like or even more exotic yet gentle pulses, too. In the Biomedical Electronics Group of Delft University of Technology, we’re working on interfacing with the brain in a more natural manner. Stay tuned…

Wouter

Smaller can be better

After the 2011 edition of ELCA Music Festival, I was dragged (by some mysterious power) deep into the idea that came to my mind around three years ago. At that time, I was trying to simultaneously linearize and reduce a transconductance of a Gm cell (VI converter circuit) for very low frequency biomedical filtering. The linearization and transconductance reduction were successful but the success came prices that I needed to pay:

  1. circuit complexity which is really unfriendly to weak inversion CMOS.
  2. more current consumption which was not surprising. It was very well in line with the circuit complexity. 
  3. more noise contribution (this was also a good friend with circuit complexity).

When I looked into the dynamic range of my design, it was not improved that much from that of an ordinary differential pair circuit (even so the paper was published [1] :). Then I got an idea that ‘instead of inventing a sophisticated linearization technique to obtain larger dynamic range, trying to use as less as possible noisy circuit elements and forget about linearization are more reasonable for biomedical signal processing which requires a good deal of power reduction’. The idea was left there since then for two reasons: I had other jobs to do and the idea seemed too sloppy.

Let me tell you more about the mysterious power. Several times we did rehearsals before the ELCA festival. I was in charge of acoustic guitar and harmonica for the song called ‘The end of the world’ http://www.youtube.com/watch?v=KmnKCE99sYE. Playing two instruments at the same time made me tired and it did not make a good harmony as expected. So I stopped playing the guitar and exercised only the harmonica (of course combined with the piano from Wouter, the electric guitar of Mark and Wannaya’s voice (I could not find this song on our Youtube channel — don’t know why). The song turned out better than before and this reminded me of that sloppy idea!!!

I did an investigation and found that there are strong evidences supporting my idea founded in low-pass filter design [2] [3]… It works!!! Large dynamic range was achieved as well as a very good figure of merit. Although the above filters were dedicated to communication systems rather than for low frequency biomedical signals, the underlying concept of the filter should be applicable for biomedical signal as well. Only a bit more effort was needed to work it out.

Good news!!! Recently, with the help from Senad, who has become 22 years old today — the same as me :). Happy Birthday!!!— my sloppy idea was realized. A 6th-order ECG low-pass filter with a large dynamic range of 59dB and extremely low power consumption of 0.45nW has been designed. We plan to submit this work to BioCAS2011. Hopefully, the reviewers will like it, too.

More good news!!! The application is not limited to low-pass filters only. I’m developing this idea further to apply it for a cochlear channel band-pass filter. What I can say now from the circuit simulations is that the filter provides the best figure of merit compared to state of the art designs. The secret is that all terminals of a single MOSFET device are being used, one pole and one zero are achieved by only two transistors sharing the same bias current.

Next time, I will tell you more about this. Stay tuned if you are interested!!!

Healthy Haring is coming. I heard from Marijn that this year, since the weather is warm, the fish is growing bigger. See you in the Pub this coming Thursday for Harings and Beers 😀

June

[1] C. Sawigun, D. Pal and A. Demosthenous, “A wide linear range transconductor subthreshold transconductor for sub-Hz filtering,” Proc. IEEE ISCAS, pp.1567-1570, 2010

[2] D. Python, A. S. Porret and C. Enz, “A 1V 5th-order Bessel filter dedicated to digital standard proceses,” Proc. IEEE CICC, pp. 505-508, 1999

[3] S. D’Amico, M. Conta and A. Baschirotto, “A 4.1mW 10MHz fourth-order source-follower-based continuous-time filter with 79-dB DR,” IEEE J. Solid-State Circuits, pp. 2713-2719, Dec. 2006

Thoughts over an exam…

Besides many research related posts on this weblog, there is another important aspect in universities: education. Currently the spring examinations take place. It is time to see if our efforts in introducing the students into the exciting world of transistors were good enough. Today I was supervising a retake of a first year BSc-course. In order not to get too bored, I printed out a bunch of papers to read through…

Despite the reading material, I was preparing for a long morning. But nothing could be further from the truth! While the students were sweating and battling their way through the exam, I picked up a paper about the history of electrical stimulation [1]. It was discussing about the very first steps of electricity for medical applications. As it turns out, soon after the development of the first electrical devices in the second half of the 18th century (such as static electricity machines, the Leyden jar or later the volta-cell), these devices were put in use for medical research very soon. Just like myself today, people were fascinated by how our body responds to electricity.

It is incredible to read what achievements were made with the extremely limited equipment that was available. Even more incredible were the experiments that were carried out: the effect of electricity on the human body was demonstrated using the decaptivated heads of executed criminals! Furthermore the functionality of pacemakers was demontrated by over-anesthesthetized animals until cardiac arrest occured, to subsequently reanimate them using electrical stimulation. Remarkably the method was also applied to a human subject, but without success…

Besides experiments, the inguinity of researchers to build machines is very remarkable. Without the availability of vacuum tubes (let alone transistors), it is hard to make pulses with accurate duration in the order to hundred milliseconds (which are required for stimulation). Various mechanical systems are described, of which the most remarkable one is a system in which a gun is fired to cut two wires placed at a certain distance from each other. Only during the time the bullet is travelling from the first wire to the second, the system is injecting electrical energy into the tissue. Imagine how being a researcher was like in those days: shooting rifles the whole day! Quite a difference from running circuit simulations like we do today!

For more interesting stories I can highly recommend to read this paper. Or save it for when you have to supervise an exam. For now: time to check the exam!

Marijn

[1] Geddes, L.A., "The first stimulators-reviewing the history of electrical stimulation and the devices crucial to its development", Engineering in Medicine and Biology Magazine, IEEE , vol.13, no.4, pp.532-542, Aug/Sep 1994

Can the upcoming solar storm turn your pacemaker into a killer inside you?

It has been predicted that today (Febr. 17, 2011) one of the largest solar storms in years will reach the earth and may interfere with sensitive electronic equipment, such as GPS receivers in cars and PDAs. Also air traffic and power grids may suffer from this kind of interference.

 Solar Storm 

Solar storms, also called geomagnetic storms, are caused by solar coronal mass ejections and modify the electromagnetic fields in the ionosphere, magnetosphere and heliosphere. They usually last only one or two days and can cause auroras further away from the poles than usually. According to Wikipedia, "On March 13, 1989 a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protection relays tripped in a cascading sequence of events. Six million people were left without power for nine hours, with significant economic loss."

So how dangerous are these solar storms for life-supporting devices like pacemakers and neurostimulators? In order to answer this question, we need to understand the physical and electrical effects of solar storms. Solar storms induce fluctuations in the Earth’s magnetic field. These fluctuations, in turn, can induce currents in large electrically conducting structures, such as power grids and metal pipelines, leading to damaged transformers and corrosion. Solar storms also influence the electrical currents in the magnetosphere and the ionosphere and thereby affect wireless communication that propagates through them.

So my conclusion: as long as you do not use your shortwave radio or CB set to control your implantable device remotely and you do not power it from the mains, you’re safe. Ain’t that a relief?

Wouter