 Hello, welcome everybody. My name is Dr Martin Fry and I'm a lecturer at UCL in medical electronics. Today I'm going to consider how we walk and also look at electrical stimulation to restore lost function. OK, so when we walk, we usually just do it without thinking about it. But if we do think about how we walk, then considering my right leg, I'm about to take a step. So I lift the heel off the ground. I then use the muscle on the front of the leg known as tibialis anterior. That means the muscle in front of the tibialis anterior to lift my toes. I then swing the foot, place the heel on the ground and then I use that muscle again to place my toes. Usually we just do that without thinking about it. So in some conditions such as MS, that's multiple sclerosis and stroke, sometimes the nerves are damaged. And in particular the nerve going to that muscle tibialis anterior may be damaged such that the person isn't able to lift their toe during walking. So if they took a step in the usual manner, they're unable to lift their toes so they're in danger of tripping over their toes. This condition is known as foot drop or drop foot because when you lift the foot off the ground the foot drops. So various ways of alleviating this condition. Someone with foot drop may shuffle their feet so that they avoid tripping. Or they may have anorthosis, a right angled usually plastic bracket that goes down the back of the leg under the shoe to keep the foot at 90 degrees. So someone with anorthosis will probably swing their hips again to avoid tripping under their toes. There is an alternative technique called functional electrical stimulation that's been used for many years now to electrically stimulate tibialis anterior at the right point in the walking cycle, the gait cycle. So I will demonstrate. So I've brought along my director's chair. What I like about this is it has a narrow footprint so I reduce the danger of falling backwards. Tibialis anterior, here's one. I've got another one on the other leg. Something that you could try on yourselves. If you put your fingers over that muscle and lift your toes you will feel that muscle contracting. So clearly a function of that muscle is to lift your toes. Right, so I've brought along a pulse generator that we can use as an electrical stimulator. So I've also brought a piezoelectric transducer to act like a kind of light speaker so that initially we can hear the pulses. I like this device because it has two controls amplitude and rate or frequency. So if I switch on you hear the pulses. These pulses are about 200 microseconds in duration and we can vary the frequency from 1 Hz to about 150 Hz for this device. And we can vary the amplitude from 0 off right up to about 100 volts. So even though this device is powered by a 9 volt battery, on the output stage of the pulse generator there's a little step up transformer to step up 9 volt pulses to about 100 volt pulses. And we need up to 100 volts because in order for the muscle to contract there's a minimum threshold current that we have to pass through the muscle. So it's kind of an application of own-slow voltage with current times resistance. So for a particular resistance that we're passing current through if we need a minimum threshold current there's a minimum voltage that we need to apply. And that may well be up to 100 volts but hopefully I won't have to apply that. So I'm going to take some of these aerogel electrodes, place them at the top of the muscle and at the bottom. And then with this set of leads with two millimetre plugs and sockets I can connect the electrodes to the stimulator. Okay, and I'm just going to sit here really comfortable, relaxed, relaxing on my leg muscles whilst I switch on the stimulator. So watch my foot to see what happens. This is kind of like Luigi Galvani's experiment from way back. And in the 1790s Luigi Galvani found that he had pieces of zinc and copper and he applied them to dead frogs, legs, frogs, legs, twitched. So this is well over 200 years on a version of what Luigi Galvani did but no frogs required. So what's interesting, let's increase the frequency because you might not believe that it's the stimulator stimulating because I could sit here going twitch. That action is under my conscious control. Okay, let's try to demonstrate. Well, obviously I'm giving myself tiny electric shocks, sort of tingling feeling, but actually this particular device was actually first developed as a TENS machine. That's an acronym that stands for Transcutaneous, that just means across the skin, electrical nerve stimulation as a form of pain relief. So it's a curious thing. So if we switch on, this is stimulating at 1 hertz, it doesn't actually hurt. But if we increase, you got it, good, great, as you increase the frequency from 1 hertz. So that's 2, 4, 6, see how the twitching increases. That's 10 hertz. When we get to 15 hertz, the muscle is trembling, but when we get to 20 hertz, we've got a nice smooth foot lift. So if I switch off, my toes go down, and if I switch on, I lift the foot. If you lean on long enough, you'll get tired. Yeah, I will fatigue the muscle. In fact, footclops stimulators actually stimulate the nerve rather than the muscle directly on feet. They contract all the fibres in the muscle, so they have 100% of the treatment of fibres, and that's why the fatigue happens faster than it does in normal contraction, because we don't recruit all of our muscle fibres. So we don't really want to stimulate less than 20 hertz, that's not useful. But if we stimulate around 20 hertz, 25, not much faster, because we'll simply fatigue the muscle more quickly. So if we stimulate at that frequency, then we have a way of lifting our toe. We could do, we could control that stimulation by a push-button switch, so actually I'd like to have this around to different people. Right, so whenever you're ready, but in the meantime, I'm going to look at the photo of Professor of Sydney Russ, sorry, Professor of Sydney Russ, whilst you randomly push the button. And I'm not looking at you so that I don't get any cues or clues. Yes, Professor Sydney Russ, we believe, was the world's first hospital physicist 1913, so over 100 years ago. And all the photos on the wall are, in fact, the family history of the Heads of Department, of this Department of Medical Physics. Obviously, if someone with foot drop was supplied with stimulator electrodes, all these cables and a push-button, and we said, well, every time you want to take a step forward, put a push-button, and that's just too much to think about. So there are various techniques that have been developed to trigger the stimulator, correct? So one idea is to have a heel switch, or, in fact, this shoe insult has three switches, two at the toes inside and outside, and one at the heel. And you can pass this around and have a good look. This kind of switch is simply two perpendicular electrode arrays separated by those green plastic insulating strips. So when the weight of the body is on the sensors, the contacts are shorted out, so it's a simple arm-off switch. You can also use what I know as force sensitive resistors. So in this particular design, we have, and again you can pass this around and have a good look. In this particular design, you have interleaved electrodes sitting on a resistive ink base. And as the force increases on the sensor, so you measure a reduction in the resistance, hence the name, force sensitive resistor. So rather than just giving arm-off information, that can give a pressure profile. So rather than an insult with those switches, we could have force sensitive resistors to act as sensors. And in fact, we could have a whole array of force sensitive resistors if we wanted to map, produce a real-time video map of people, athletes walking, running. And I get other sports shoes manufacturers use those kind of techniques to optimise their shoe design. So, yeah, if we replace the push button switch with the force sensitive resistor, could it make its way back? Yeah, the little one, yeah, great. So if I plug in the force sensitive resistor, and at this time imagine that this is mounted on an insult that's been fitted into my shoe that I'm standing. So the weight of my body is on the sensor. So as soon as I lift my heel off the ground, the sensor detects the change in pressure, turns the stimulator on, stimulates the muscle, lifts the toe so I can swing the foot. And then when I place the heel on the ground, the pressure on the sensor turns the stimulator off. So a simple but quite elegant way of controlling the foot drop stimulator. Over the years there have been various research studies to look at how you may trigger the stimulator in other ways by perhaps detecting EMG, that's electromyo ground signals from other muscles in order to control the stimulation.