Physiodata Systems GP8 Manuale utente

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Hardware Set-up Guide

Physiodata Systems GP8 Amplifier

1 Introduction

This document describes how to set up the GP8 mplifier nd ssoci ted sensors for use with the

Mind-Body Tr ining Tools biofeedb ck pplic tions. It ssumes you h ve lre dy inst lled the

softw re – if you h ven't done th t yet, ple se see the Inst ll tion nd Set-up Guide.

A set of tr ining videos, ccessible from the l uncher pplic tion, offer n ltern tive route to

le rning how to set up the mplifier nd sensors. This guide goes into more depth. Don't let the

technic l det ils put you off s full underst nding isn't necess ry to m ke use of the products.

The GP8 mplifier connects to the computer vi USB port, nd supports ll the biofeedb ck

pplic tions in the suite, me ning th t it c n re d the following physiologic l sign ls:

•EMG (for muscle tension) – used in the EMG nd bre thing pplic tions

•ECG or electro-c rdiogr ph – used in the He rt R te Coherence (HRC) pplic tion to

c lcul te he rt r te.

•Temper ture – monitoring temper ture of inh led nd exh led ir is the b sis of bre th

me surement in both the HRC nd bre thing pplic tions. Addition lly it is used in the skin

temper ture pplic tion.

•Infr -red temper ture – used in the infr -red neurofeedb ck pplic tions.

In both EMG nd ECG we use three sensors to give single me surement. This m y seem

confusing, but it isn't necess ry to underst nd the re sons behind this. All you re lly need to know is

th t EMG is me sure of muscle tension, nd ECG gives you he rt r te.

The unit h s five inputs, three t the front nd two t the side, s shown in figure 1 below. The front

three together re c p ble of recording one ch nnel of EMG, ECG or EEG d t t s mple r te of

up to 1024 per second. EEG is currently not used in ny Mind-Body Tr ining Tools pplic tions.

Input 4 is used for the temper ture nd infr -red temper ture sensors, nd c n re d d t t s mple

r te of up to 512 per second. Other sensors re lso v il ble for the GP8 vi inputs 4 nd 5, such s

PPG (pulse w ve) sensor, but they re not currently used in the Mind-Body Tr ining Tools suite of

pplic tions. Ple se note, the Mind-Body Tr ining Tools pplic tions don't ll use the m ximum

s mple r te v il ble – they typic lly use lower s mple r tes where the loss of precision is not

relev nt, in order to optimise perform nce.

The GP8 requires two AAA b tteries. The m nuf cturer recommends using lk line b tteries

(which give over 100 hours of oper tion). I h ve found th t good qu lity (high power) rech rge ble

Ni MH b tteries work well enough. B tteries re inserted into the underside of the device – see

figure 2. B ttery st tus c n be tested from the softw re – see section 4 below.

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 1

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 2

igure 2 – GP8 amplifier underside with battery cover removed

igure 1 – GP8 amplifier

2 Sensors

The following t ble lists ll the sensors used in the Mind-Body Tr ining Tools pplic tion suite.

Sensor Input igure Description

Set of 3 EMG/ECG

cables (TP60)

White – 1

Green – 2

Black – 3

3 Used for EMG (muscle tension) and ECG (for

heart rate).The white and black leads are

known as the active sensors while the green is

the ground.

Snap electrodes

(SE23) – set of 3

with plastic mounts

4, 5 These snap into the heads of the TP60 cables

above. They are used for EMG and ECG.

The plastic mounts are not strictly needed.

Disposable pre-

gelled electrodes

6 Alternative to SE23 electrodes above. They will

give more accurate readings.

Temperature sensor

(GP-1u)

4 7 Used for breath measurement in the HRC and

breathing applications, and in the skin

temperature application.

Infra-red temperature

sensor (GP-7u)

4 8 Used for infra-red neurofeedback.

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 3

igure 3 – Set of 3 cables (TP40) used for EMG and EKG. The plugs at the left side

are inserted into the GP8 unit. The heads (right side) need to be fitted with snap

electrodes (e.g. see figures 4,5 and 6) before being attached to the skin.

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 4

igure 4 – Set of 3 snap electrodes with plastic mounts, for use with TP60 cables (figure 3)

3 Attaching the Sensors to the Body

This section covers how to tt ch the sensors to the body. There is sub-section for e ch

pplic tion. For both EMG nd ECG, the ccur cy of the me surement depends in p rt on the

qu lity of the connection to the skin. Therefore we begin with gener l discussion of ccur cy in

EMG nd ECG me surement.

3.1 Accuracy in EMG and ECG Measurement

The ccur cy of EMG nd ECG me surement depends on sever l f ctors including h rdw re nd

softw re design. Pr ctic lly spe king, perh ps the most signific nt f ctor is the qu lity of the

electric l cont ct between the sensor nd the skin. This is qu ntified impedance. You don't need to

underst nd ex ctly wh t imped nce is, only th t bro dly spe king the lower the imped nce the

more ccur te your me surement. However in biofeedb ck, since we re usu lly more concerned

with rel tive ch nges th n with bsolute me surements, we c n often s crifice some ccur cy for

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 5

igure 8 – Temperature sensor

igure 7 – Infra-red temperature sensor

the s ke of convenience. As long s the imped nces re st ble over time then we c n still run

effective biofeedb ck sessions with rel tively high imped nces.

For both EMG nd ECG there re three sensors. Think of EMG nd ECG s kind of volt ge. A

volt ge is lw ys difference between two points, so we me sure two volt ges. Two of the sensors

re known s the ctives (white nd bl ck), the third is the ground (green). One volt ge is the

difference between Active 1 nd the ground, nd the other volt ge is between Active 2 nd the

ground.

Likewise we h ve two imped nces.

In the softw re, the two volt ges re converted into single one. It m y seem confusing th t we

h ve three sensors nd two imped nces just to end up with single me surement, but remember

you don't need to underst nd the det ils. Just rec ll th t the lower the two imped nces the better –

nd it lso helps if the two re roughly the s me m gnitude.

In ECG me surement in p rticul r, s long s we c n detect the interv l between he rt be ts, the

imped nce doesn't m tter. Higher imped nce will not re lly ffect the ccur cy of the heart rate

c lcul tion.

Two methods of minimising imped nce re:

•Skin prep r tion (me ning cle ning with lcohol or slightly br sive gel).

•Use of conductive gel (to c rry the electric l current cross the g p between skin nd sensor).

The most convenient w y of doing this is to use dispos ble pre-gelled self- dhesive electrodes

(see figure 6).

Most users c n still chieve good results without either of these. The ltern tive is to hold the

sensors in cont ct with the skin using e.g. wrist b nds. Use the SE23 sn p electrodes in this c se.

You c n use the pl stic mounts, which go between the he d of the c ble nd the sn p electrode, but

they ren't necess ry. However if you don't use them, you must m ke sure th t the sensor he ds

never touch e ch other. The pl stic mounts will prevent this h ppening.

Imped nces c n be me sured using the softw re – see section 4 below for det ils.

3.1.1 Artefact in EMG and ECG

In this context, rtef ct me ns component of your me sured p r meter th t does not origin te

from the source you re interested in. Think of it s cont min tion. For ex mple, in me suring ECG

we re interested in the electric l output of the he rt, but if our me surement picks up ctivity from

muscles then we h ve n rtef ct.

EMG nd ECG re in some w ys the s me me surement – in both we re me suring n oscill ting

volt ge. This volt ge me sured t the skin is complex in the sense th t it does not h ve single

frequency of oscill tion, but r ther is m de up of lots of different frequencies mixed together.

Softw re pplic tions m ke use of process c lled digit l filtering to simplify the sign l. EMG nd

ECG use different choices of frequency r nge for this filtering (ECG uses lower r nge). However

the process is not perfect nd inevit bly me surement of either ECG or EMG picks up ctivity of

both he rt nd muscles. In other words, the one is source of rtef ct for the other.

Extern l sources of electrom gnetic fields c n lso c use rtef ct. In pr ctice this me ns electric l

equipment nd even the m ins electricity supply.

The device driver cont ins mech nism (c lled notch filter) to remove m ins electricity

cont min tion, or interference. It should to be set to frequency of your country's m ins supply,

which in the UK is 50 Hz. See the Inst ll tion nd Set-up Guide for more det ils. In pr ctice this

shouldn't m tter, s unless you re using the EMG pplic tion with the wideb nd filter selected, ll

the pplic tions void using this p rt of the spectrum nyw y.

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 6

A much more likely source of interference is electric l equipment. How do you know if you h ve

this kind of electric l cont min tion?

•In EMG it looks like you h ve stubbornly high muscle tension th t you c n't rel x (bec use it

isn't re lly muscle tension)

•In ECG, when you c nnot see the usu l prominent spikes th t m rk he rt-be ts. Figure 9

below shows wh t rel tively cle n ECG sign l looks like.

3.1.2 How to Minimise E ectrica Interference

If you suspect electric l interference, try to position the mplifier s f r from electric l equipment s

possible – including the computer itself. Simil rly, keep the TP40 c bles s free from possible

interference sources s you c n. This includes the USB c ble th t connects the GP8 unit to the

computer – void h ving it lying longside the TP40 c bles. Also don't let the TP40 c bles lie coiled

or t ngled up with e ch other.

A common source of trouble seems to be the m ins d ptors (tr nsformers) of some l ptop

computers. If you re using l ptop, try unplugging from the m ins so th t the computer runs on its

b ttery power, to see if this m kes difference. If it is n issue the only solution gener lly is to run

your biofeedb ck sessions on b ttery.

3.2 Basic EMG Application

Connect the three TP60 c bles (figure 3) to inputs 1,2 nd 3 (see figure 1). The order is signific nt –

see the t ble in section 2 bove. Att ch sn p electrodes before connecting to the body (they fit like

press studs). You c n either use pre-gelled self- dhesive sn ps (see figure 6) or reus ble gel-free

sn ps (figures 4 nd 5) held to the skin using for ex mple wrist b nds.

Think of EMG s detecting the muscle tension between the two ctive sensors (white nd bl ck).

The third sensor (ground) is less import nt, in terms of where it is pl ced. If you pl ce the ctive

sensors t either end of single muscle, you will detect the tension l rgely (though not exclusively)

from th t one muscle.

In gener l the positions of the two ctive sensors c n be interch nged with no effect.

You c n of course tt ch the sensors wherever you w nt, but two commonly used nd very useful

pl cements re:

•Wrist to wrist (i.e. one ctive t either wrist, nd the ground t either). This detects tension in

the whole rm nd cross the shoulders, nd lso the h nds. To some extent it lso picks up

chest nd neck tension. One re son it's such useful pl cement is th t emotion l tension

commonly m nifests in this group of muscles, especi lly the shoulders. Another re son is th t

it c n distinguish chest-b sed bre thing from bdomin l or di phr gm tic bre thing. If you

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 7

igure 9 – Relatively clean EKG signal

re using non- dhesive electrodes (gel-free) use wrist b nds to hold them g inst the skin.

•Forehe d (or front lis muscle) – the three electrodes should be horizont lly ligned with the

green (ground) in the middle. This pl cement picks up tension from the whole he d,

especi lly the powerful j w muscles. Ag in this is useful reflection of emotion l tension,

though not bre thing. You m y lso find th t intern l self-t lk m nifests s some tension,

picked up with this pl cement. When using non- dhesive (gel-free) electrodes, use he d

b nd to hold them in cont ct with the skin.

3.2.1 Sources of Artefact

See the gener l comments m de e rlier (section 3.1) on rtef ct in EMG nd ECG.

Interference from electric l equipment is common problem. Keep the mplifier nd c bles s f r

from electric l equipment (including the computer) s is pr ctic l. Keep the sensor c bles p rt

from the USB nd other electric l le ds.

As expl ined, the electric field of the he rt is potenti l source of rtef ct in EMG me surement. In

pr ctice it is lmost never problem for pl cements where the two ctives re the s me side of the

he rt nd roughly equidist nt from the he rt – e.g. forehe d pl cement. For the wrist pl cement,

however, it will be there. The he rt be t gener lly shows up s pe k in the sign l every he rt be t.

It is only pp rent when the muscle tension is rel tively low. It c n be smoothed out to l rge

extent by the use of ver ging (see the softw re pplic tion guides). In my experience it does not

signific ntly detr ct from the effective use of EMG biofeedb ck.

3.3 EMG & Breathing Application

Connect the sensors s for the B sic EMG pplic tion – see section 3.2 bove. In f ct ll of section

3.2 pplies here too.

Both the wrist to wrist nd forehe d pl cements re useful for re sons given in section 3.2 bove.

Another pl cement useful for picking up upper chest bre thing is tr pezius to sc lene (cle rly some

n tomic l knowledge is required for this pl cement).

Bre thing is detected using the temper ture sensor (figure 8), pl ced just inside or just below the

nostril. Hold the sensor in pl ce using sm ll piece of surgic l (microporous) t pe. Connect the

c ble to input 4 (see figure 1). Cle rly bre thing through the nose ( t le st to some degree) is

necess ry for this to work. Some people bre the through both nose nd mouth, which gener lly

works fine. There is only problem when the n s l p ss ges re blocked. Before pl cing the sensor,

check which nostril seems to be the cle rest.

The softw re must c libr te to your bre th, s described in the softw re pplic tion user guide.

3.3.1 Sources of Artefact

The sources of EMG rtef ct re the s me s for the b sic EMG pplic tion – see section 3.2 bove.

Bre th detection b sed on temper ture is f irly robust, once c libr ted (see the pplic tion user

guide for discussion of bre th c libr tion). Speech will disrupt the ir flow, nd sniffs, sneezes etc.

re likely to be interpreted s bre ths of short dur tion.

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 8

3.4 H C Application

He rt r te is detected vi ECG. Connect the three TP60 c bles (figure 3) to inputs 1,2 nd 3 (see

figure 1). The order is signific nt – see the t ble in section 2 bove. Att ch sn p electrodes before

connecting to the body. You c n use either self- dhesive pre-gelled sn ps or reus ble gel-free sn ps.

The l tter is in my experience lmost lw ys perfectly dequ te, indeed since we only need to

detect the he rt be t there is no dis dv nt ge t ll.

Any pl cement in which the two ctive sensors re either side of the he rt should work. Pl cing the

sensors on the wrists is usu lly the most convenient.

Unlike with EMG, interch nging the two ctive sensors (white nd bl ck) does m ke difference.

Pl ce the white sensor on the left wrist, nd bl ck on the right. Look t the r w ECG tr ce in the

softw re pplic tion (support window) nd you should see prominent upw rd deflection every

second or so, which crosses the yellow dotted threshold line. Figure 9 bove shows you wh t this

looks like. If the tr ce looks upside-down (i.e. with bigger deflection below the m in body of the

sign l) then sw p the the two ctives over, nd remember this for future occ sions.

Bre thing is detected using the temper ture sensor, pl ced just inside or just below the nostril. Hold

the sensor in pl ce using sm ll piece of surgic l (microporous) t pe. Connect the c ble to input 4

(see figure 1). Cle rly bre thing through the nose ( t le st to some degree) is necess ry for this to

work. Some people bre the through both nose nd mouth, which gener lly works fine. There is only

problem when the n s l p ss ges re blocked. Before pl cing the sensor, check which nostril

seems to be the cle rest.

The softw re must c libr te to your bre th, s described in the softw re pplic tion user guide.

3.4.1 Sources of Artefact

Ag in see the gener l comments m de e rlier (section 3.1) on rtef ct in EMG nd ECG.

Interference from electric l equipment is gener lly less of n issue th n with EMG. However if you

don't get cle r ECG sign l follow the s me dvice: keep the mplifier nd c bles s f r from

electric l equipment (including the computer) s is pr ctic l. Keep the sensor c bles p rt from the

USB nd other electric l le ds. If you re using l ptop, try disconnecting the m ins tr nsformer

nd running on b ttery.

For ECG, muscle ctivity is the potenti l source of rtef ct. If strong enough it c n sw mp the he rt

sign l so th t the he rt be t c nnot be detected. In pr ctice this me ns th t the user needs to sit in

f irly rel xed st te. Gentle movements re mostly toler ted s long s they re not sust ined in time.

More forceful movements do le d to loss of the he rt be t for few seconds but gener lly the

softw re recovers once the user settles g in.

Bre th detection b sed on temper ture is f irly robust, once c libr ted (see the pplic tion user

guide for discussion of bre th c libr tion). Speech will disrupt the ir flow, nd sniffs, sneezes etc.

re likely to be interpreted s bre ths of short dur tion.

3.5 Heart ate Data Collection Application

Use the s me set of c bles nd sensors s for he rt r te, in the HRC pplic tion, nd connect them

to the mplifier in the s me w y. The HR d t collection pplic tion does not monitor bre thing so

you don't need to connect the bre thing (temper ture) sensor.

Sources of ECG rtef ct re the s me s described in section 3.4.1 bove.

3.6 Breathing Application

Bre thing is detected using the temper ture sensor (figure 8), pl ced just inside or just below the

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 9

nostril. Hold the sensor in pl ce using sm ll piece of surgic l (microporous) t pe. Connect the

other end of the c ble to input 4 (see figure 1).(see figure 1). Cle rly bre thing through the nose ( t

le st to some degree) is necess ry for this to work. Some people bre the through both nose nd

mouth, which gener lly works fine. There is only problem when the n s l p ss ges re blocked.

Before pl cing the sensor, check which nostril seems to be the cle rest.

The softw re must c libr te to your bre th, s described in the softw re pplic tion user guide.

3.6.1 Sources of Artefact

Bre th detection b sed on temper ture is f irly robust, once c libr ted (see the pplic tion user

guide for discussion of bre th c libr tion). Speech will disrupt the ir flow, nd sniffs, sneezes etc.

re likely to be interpreted s bre ths of short dur tion.

3.7 Infra-red Neurofeedback Application

The infr -red temper ture sensor (figure 7) is used. Connect the socket to input 4 (figure 1).

Typic lly the sensor is pl ced over the forehe d, firstly bec use h ir will tend to block the infr -red

r di tion, nd secondly bec use of neuro n tomy: the pre-front l cortex behind the forehe d is the

br in's “executive control” region, very useful pl ce to tr in, nd lso responsive to our conscious

efforts. I recommend pl cing the sensor over the centre of the forehe d, lthough it is possible to

pl ce it nywhere else on the forehe d.

There should be n ir g p between the sensor nd the skin, nd ch nnel for the movement of ir.

This is wh t the sensor mount chieves.

At the current time of writing the m nuf cturer h s not finished developing he d mount for the IR

sensor, so I m using home m de version. The IR sensor should be positioned between the two

sponge blocks, where it will be held in pl ce by velcro. H ve the he d b nd f stened loosely, so th t

the tension doesn't signific ntly compress the sponge blocks nd you m int in the ir g p.

3.7.1 Sources of Artefact

Dr ughts of ir over the sensor will c use the sign l to dip. For this re son, it is recommended to

keep the he d rel tively still. Also, he d movements m y c use subtle ch nges in blood flow which

m y register s ch nges in the sign l.

Excessive swe ting m y c use condens tion to form on the sensor, impeding ccur te

me surement.

3.8 I Neurofeedback with Breathing Application

As with the HRC nd EMG & Bre thing pplic tions, the bre thing sensor is the temper ture sensor

(figure 8), pl ced just inside or just below the nostril. Hold the sensor in pl ce using sm ll piece of

surgic l (microporous) t pe. Connect the socket to input 4 (see figure 1). Cle rly bre thing through

the nose ( t le st to some degree) is necess ry for this to work. Some people bre the through both

nose nd mouth, which gener lly works fine. There is only problem when the n s l p ss ges re

blocked. Before pl cing the sensor, check which nostril seems to be the cle rest.

The softw re must c libr te to your bre th, s described in the softw re pplic tion user guide.

The infr -red temper ture sensor (figure 7) is used. This time connect it to input 5 (figure 1). As

with st nd rd IR neurofeedb ck pplic tion, the loc tion for the sensor is the forehe d. See section

3.5 for det ils of tt ching it.

GP8 H rdw re Set-up Guide, copyright Glyn Bl ckett p ge 10

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