Making Physiology Happen

Neuroprosthetics Lab

Neuroprosthetics Lab

Experiment HN-8:
Human To Human
Interface

Introduction to Neuroprosthetics and Human-to-Human Muscle Control

Take control…of your partner that is!

An exciting, new technological development has to deal with the science and research into neuroprosthetics. A neuroprosthetic is a device that replaces the function of a damaged body part and interfaces with the nervous system – think of the body suit that Iron Man wears and the new prosthetic devices that are being 3-D printed for use for kids with malformed limbs. These devices can be controlled by the person using them just by thinking about what they want to do, like writing or holding onto something. These devices are controlled in such a way so there is an interface with the nervous system to make the prosthetic work.

There are many reasons why this research is so exciting. One has to do with how to help people with spinal cord injuries. Currently, if someone damages their spinal cord above a certain point, they are confined to a wheelchair and could be on supportive mechanisms to help them breathe; this is what happened to Christopher Reeves after his accident from falling off a horse. The interesting thing is that even though the spinal cord is damaged, the muscles in the person’s limbs are still “alive” and can function, but they need to receive information from somewhere to be able to move. With a damaged spinal cord, the information being sent from the brain does not reach the limbs. This is where neuroprosthetics comes into play. Imagine if you could send a signal from the brain directly to a prosthesis, and have it work!!
There is currently research out there where this is actually happening. Another method of controlling artificial limbs is by using the electrical activity generated by pectoral or quadriceps muscles to control the sensors and motors right in the robotic arm or leg.
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H-to-H-Interface-TA

HK-TA Human Physiology Teaching Kit

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So, where does this Human-to-human interface come in? In lab, since we do not have the capability to get Iron Man’s suit or 3-D print a prosthetic, we can use one person as the “brain” and one person as the “prosthesis”. This means that one person will have the ability to actually control the movements of the other!This will be done by using the stimulator on the IX-TA unit and having Person A (the “controller”) squeeze a ball that will in turn signal the interface (the IX-TA) to fire a signal off to Person B. Person B’s hand will be holding the hand dynamometer and when “A” squeezes the ball…Person B will squeeze the hand dynamometer…totally without their own control. The stimulator works like a TENS unit (Transcutaneous Electrical Nerve Stimulation) that is used by physical therapists for interrupting nerve and muscle spasms to promote healing. When Person A squeezes the ball, it will signal the stimulator to send a current to Person B, when that current is received by the muscles in the hand, the hand will twitch.This lab opens up many opportunities for hypothesis testing. Can you hold a pencil, balance a ball, or make a Lego car move?Set-up Equipment Required

PC or Mac Computer
IX-TA data acquisition unit
USB cable Power supply for IX-TA
iWire-B3G cable and three EMG lead wires
Disposable snap electrodes (7)
HV stimulator lead wires
FT-220 hand dynamometer

IX-TA Setup

1. Place the IX-TA on the bench, close to the computer.
2. Check Figure T-1-1 in the Tutorial Chapter for the location of the USB port and the power socket on the IX-TA.
3. Check Figure T-1-2 in the Tutorial Chapter for a picture of the IX-TA power supply.
4. Use the USB cable to connect the computer to the USB port on the rear panel of the IX-TA.
5. Plug the power supply for the IX-TA into the electrical outlet. Insert the plug on the end of the power supply cable into the socket on the rear of the IX-TA. Use the power switch to turn on the unit. Confirm that the power light is on.

Start the Software

1. Click on the LabScribe shortcut on the computer’s desktop to open the program. If a shortcut is not available, click on the Windows Start menu, move the cursor to All Programs and then to the listing for iWorx. Select LabScribe from the iWorx submenu. The LabScribe Main window will appear as the program is opens.
2. On the Main window, pull down the Settings menu and select Load Group.
3. Locate the folder that contains the settings group, IPLMv6Complete.iwxgrp. Select this group and click Open.
4. Pull down the Settings menu, again. Select the HumanToHumanInterface settings file.
5. After a short time, LabScribe will appear on the computer screen as configured by the HumanToHumanInterface settings.
6. For your information, the settings used to configure the LabScribe software and the IX-TA unit for this experiment are programmed on the Preferences Dialog window which can be viewed by selecting Preferences from the Edit menu on the LabScribe Main window.
7. Once the settings file has been loaded, click the Experiment button on the toolbar to open any of the following documents:

The Equipment Setup

Note – Connect the iWire-B3G cable to the IX-TA prior to turning it on.

1. Attach the connector on the end of the iWire-B3G cable to the iWire 1 input of the front of the IX-TA (HN-8-S1).
2. Connect the FT-220 to the black tygon extension tubing, connect this to the A2 port on the front of the IX-TA.
3. Connect the stimulator leads to the HVS stimulator on the front of the IX-TA as stated in the directions below.
4. Prepare your subjects.

H-to-H-Interface-TA

Figure HN-8-S1: IX-TA with the FT-220, iWire-B3G and stimulator lead wires for performing the Human to Human Interface lab.

Person A

1. The subject should remove all jewelry from his/her right arm.
2. Clean the areas where the electrodes will be attached with an alcohol swab (Figure HN-8-S1). Abrade the skin in those areas.
HN-8-S2

Figure HN-8-S2: Electrode and lead placement for Person A, who will be generating the signal to be carried to Person B through the stimulator. 

3. Obtain three disposable electrodes.
4. Locate areas on the forearm; place electrodes over these locations and attach the colored recording leads (Figure HN-8-S2).

    • Place the black (-1) electrode just below the crease of the elbow, slightly lateral of midline.
    • Place the red (+1) electrode on the mid-forearm, also slightly lateral.
    • Place the ground (green) electrode between the red and black electrodes as shown.

5. Person A should also hold a tennis ball or other squeezable object.

Person B

1. Obtain two disposable electrodes.
2. Have Person B clean the back and pinkie side of their non-dominant hand with an alcohol swab.
3. Snap the ends of the H.V. Output lead wires onto the stimulating electrodes (FigureN-8-S3), so that:

    • the red (+) lead is snapped on the electrode in the center of the back of the hand,
    • the black (-) lead is snapped on the electrode at the lateral edge of the hand.

4. Have Person B lightly cup the FT-220 hand dynamometer in the palm of their hand, trying not to hold on to it too tightly. It should be just resting in their grip.

HN-8-S3

Figure HN-8-S3: Placement of the stimulating electrodes for Person B.

IX-TA Isolated Stimulator

The IX-TA has a high voltage stimulus isolator designed to deliver constant current to the nerve or muscle being studied. In situations where the resistance (R) along the path of the current increases, the voltage (V) increases to maintain the current (I in V = IR, Ohm’s Law). The ability of the IX-TA to adjust the voltage to deliver the required current is known as voltage compliance. The upper limit of this compliance by the IX-TA is set at 100 Volts.

Constant current devices differ from constant voltage devices when presented with an increase in resistance, like the dehydration of the conductive gel under the electrodes. As pointed out earlier, a constant current stimulator is voltage compliant. In constant voltage stimulators, the current delivered to the tissue decreases as the resistance increases because the power supply of the constant voltage device is not designed to deliver additional current.

Although the IX-TA can generate up to 100 Volts, the current delivered by the unit is limited to a maximum of 20 milliamperes, for a maximum duration of 10 milliseconds per pulse, and a maximum frequency of 50 pulses per second (Hz). At these levels, the maximum amount of power delivered by the IX-TA will not cause injury or tissue damage.

The current is selected using the Stimulator Control Panel. The HV Stimulator can deliver a maximum output of twenty milliamperes.

The duration, frequency, and number of stimulus pulses generated by the stimulator are also controlled by making changes to the values in the Stimulator Control Panel. The initial values of the pulses generated by the IX-TA are programmed by the same settings file that configured the recording software. For example, if a pulse from the IX-TA is programmed for a duration of 1 millisecond and a frequency of 1 Hz, the stimulator will generate a stimulus pulse with the same duration and frequency.

IX-TA Stimulator Setup

1. Place the IX-TA (Figure HN-8-S1) on the bench near the subject.

Warning: Before connecting the IX-TA stimulating electrodes to the subject, check the Stimulator Control Panel to make sure the amplitude value is set to zero (0).

Note: Disconnect the subject from the IX-TA prior to powering off the device

2. Instruct the subject to remove all jewelry before beginning the experiment.

HN-8-S4_250

Figure HN-8-S4: The IX-TA stimulating electrodes.

3. For any of the HVS labs, the stimulator preferences panel will initially come up showing S1, even if S1 is off – use the menu to select the HVS settings.

4. Connect the color-coded stimulator lead wires to the High Voltage Current Stimulator. Make sure you push the safety connector of each lead wire into the appropriate socket as far as possible (Figure HN-8-S4).

5. Connect the 2 stimulating electrodes as stated above.

6. Start with the stimulator programmed in this manner (Table HN-8-S1):

  • On the Stimulator Control Panel that appears 2 lines above the upper recording panel.
  • Amps will be the only variable changed (between 3-10 amps). Begin with 3 amps and increase until a consistent response is achieved (5 amps has yielded consistent results).
  • Make sure to hit APPLY after choosing the settings.

Table HN-8-S1: Settings on the Stimulator Window Used to Configure the Stimulator of the IX-TA for Experiment HN-8.

Stimulator settings

Experiment HN-8: Human to Human Interface

WARNING – The Stimulator should only be used for the method of application for which it is intended as shown in the directions below.

Note: Disconnect the subject from the IX-TA prior to powering off the device.

NOTE: Any changes in amplitude are entered directly into the Stimulator Control Panel. Click “APPLY” to make the change.

Exercise 1: Human to Human Muscle Control

Aim: To determine the effect of a “squeeze” by Person A on Person B’s response.

Procedure

1. Ask Person A to hold a tennis ball, or other squeezable object, in his or her hand. Lay the hand on the bench with the palm up. Make sure Person A is not squeezing the ball and to relax.

    • If preferred, Person A can just curl their hand at the wrist rather than squeezing a ball. This works equally well and generates a good signal.

Note: Person A should make sure to relax his/her forearm and hand completely. Any tensing of the muscles will interfere with the recording and could elicit an unexpected response from Person B.

2. Ask Person B to sit quietly, with their hand lightly cradling the hand dynamometer. Little to no pressure from the fingers should be holding the sensor.

3. Click Record button on the LabScribe Main window.

4. Instruct Person A to squeeze the ball or curl his or her hand towards the wrist. It should be a quick, firm reaction.

5. Click the AutoScale All button on the toolbar to improve the display of the stimulus and the muscle’s response (Figure HN-8-L1).

6. Have Person A squeeze the ball or flex the hand five (5) times.

Note: Person B should have a response each time Person A flexes or squeezes.

7. Select Save As in the File menu, type a name for the file. Choose a destination onthe computer in which to save the file (e.g. the iWorx or class folder). Click the Save button to save the file (as an *.iwxdata file).

HN-8-L1_500

Figure HN-8-L1: A recording showing Person A squeezing or flexing and the subsequent response from Person B. The red vertical cursors are in position to measure the time from the peak of the Integral to the response from Person B.

Data Analysis

1. Use the display time icons to double the display time to get the entire data set on screen (Figure HN-8-L2).

HN-8-L2_500

Figure HN-8-L2: The LabScribe toolbar.

2. Click the Analysis icon in the LabScribe toolbar ( Figure HN- 8 -L 3) to view the recorded responses.

3. Note that T2-T1 is shown in the bar across the tops of all the channels. Measure T2-T1 by placing the two red vertical cursors on the peak of the Integral from Person A and the subsequent response from Person B. Data analysis can also be performed on the main window.

HN-8-L3_500

Figure HN-8-L3: T2-T1 for the time between the stimulus from Person A to the response from Person B. In this example the time is 0.110 seconds between stimulation and response.

4. The functions in the channel pull-down menus of the Analysis window can also be used to enter the names and values of the parameters from the recording to the Journal. To use these functions:

  • Place the cursors at the locations used to measure the time for the muscle response.
  • Transfer the name of the mathematical functions used to determine the muscle response to the Journal using the Add Title to Journal function in the Movement-Person B pulldown menu.
  • Transfer the value for the time for muscle response to the Journal using the Add Ch. Data to Journal function in the Movement-Person B pull-down menu.

Question

1. Is the time of response from Person B the same for each stimulus by Person A? If not, what could be the reason?