Assuming that assembly is complete, batteries
installed [NB - NEVER use this device with any mains 'plug-pack'
or battery charger connected, while patient-leads are in use],serial
cable connected to the sampler and computer (correct COM port selected),
it is first necessary to go through the 'set-up' procedures for the Dataq
sampler (or any alternative digital sampling device you intend to use).
The Dataq starter kit comes with its own operation
software on a CD, together with very full instruction manual, and I will
not go into details about the full procedures here. I suggest setting it
up for a single trace ( you have the choice between 4, 3, 2, or 1 simultaneous
traces, and I do not believe 4 consecutive traces are possible,
but would be nice if they were!). You have a choice of various different
sampling rates, and depending which is chosen the timing is set for scrolling
or triggered 'scope mode. You also have a choice between modes of writing,
and the unit can be configured to give a 'monitoring' trace if desired.
A rate of 100 samples per second would be convenient for saving traces
similar to conventional ECG format, but the nearest to this which is available
is 120. I choose this rate to give one screen output containing about 5
seconds of trace. If it is decided to use the mouse for starting, stopping,
saving etc., it is most convenient to select Toolbox from the View menu;
this allows you to place a set of icons at a convenient position on the
screen; you will only need to use two of these to select the functions
needed for recording and saving the portions of trace which you require.At
this sampling rate, a file size will be large enough to give plenty of
choice in order to obtain a strip for printing. Having set up your requirements,
you then have the option to save these as default settings which will appear
each time you open the program. From this program interface you then have
access to another 'Browser' program, which you will find helpful for editing
your files. (More about this later when describing the use of my display/print-out
software). Use the manufacturer's manual and help-files to find your way
around this device. If you are not used to this type of software, it may
seem confusing at first, but perserverence will soon have you on the right
track!
Connect your lead-selection switch box to the
+ , -, and Earth (Ground) pins on the main PCB via a short length of 3
core shielded cable; the individual leads to the patient electrodes ( I
find stainless steel electrodes lubricated with a little soap (or 'spit')
perfectly adequate); select the lead you want with an appropriate combination
of the 8 switches, (a diagram of these is included at the end of the 'Overlays'
page), switch on the 9 volts power, and you should see the ECG trace appear
on screen. This happens continuously, either triggered automatically, or
scrolling, and you use the mouse of keys to record portions and save to
a file. Use the 1 MV pulse generator to produce a test wave, which should
be 'square' enough to ensure cardiological fidelity.
Standardisation and calibration:
The sensitivity control knob is used to adjust
the height of 1 MV pulse. On my PCB there are positions marked + and -
on that part of the board, where PC pins should be placed for measurement
by a suitable accurate Millivoltmeter, and adjustment of the trimpot with
a screwdriver will set an exact 1 MV when the button is pressed; this setting
will remain reliable so long as the 2 AAA cells are still capable of producing
an output at 2.5 Volts.
In ensuring correct calibration it will be necessary
to observe the timing shown at the bottom of the Dataq screen, and set
your 1 MV to a 'Y' reading suitable to you. My software package assumes
a normal 10 horizontal lines to 1MV, as is usual in conventional direct-writing
machines, but the trace will be slightly elongated along the X (time) axis.
The screen grid pattern assumes an original sampling rate of 120/second,
and will not be accurate for any other. It observes the usual divisions
representing 0.04 and 0.2 second.
Printing and formatting files:
Having recorded your trace, the icons or File menu will give you the option to save to a file format suitable for the Browser program, and from this program you can send a saved trace direct to your installed printer; you are given several options as to exactly what will be printed, including comments, etc. You also have a File option called Save As. This is a little different from the usual, and it gives you a number of file format options; if you choose Option 5, you will be able to save a selected strip of trace in a format suitable for import into my display /print program. Therefore, if you first record and save an entire 12 lead ECG, and convert the 12 files, you will then be able to open my program and display them in a professional manner.
ECGDATAQ.EXE:
This is my application which will open in just
about any PC once loaded. It has a simple menu which appears as the program
is opened, which gives you the option to open 4 different graphics screens,
each showing 3 ECG leads derived from the files you have saved with option
5, above (make sure the files are saved into the root directory of your
C: drive, and that the standard designations I II III aVR aVL aVF
V1 V2 V3 V4 V5 V6 are used). Each screen will ask you to insert
whatever text you wish (e.g. patient details, date, etc.) to a total of
15 characters. While this image is on the screen, you can use your usual
Print Screen routine to send it to your printer (e.g. in Windows, press
Print Screen places the image on the clip board, whence it can be Pasted
into your graphics program, and printed. In DOS, the procedures are slightly
different - ask me, if in doubt). Press ESC to return to the menu and load
your next 3 traces, etc.
Also included on the optionally available floppy
disk, are PROTEL EASYTRAX files for the PCBs, overlays, etc. This
format is used commonly by professional PCB manufacturers, and some individuals
might prefer to have their PCBs so made. All that is needed for their preparation
will be found on the disk.
A NOTE ABOUT TIME-BASES:
If you use the Dataq software for displaying and printing your traces, you will find that the grid displayed is NOT in the format normally applied to professional ECGs. While accurate, the time base will be based on information shown at the bottom of the screen, which will not be the usual 0.04/0.2 seconds divisions. My ECGDATAQ program DOES display the conventional 0.2 seconds divisions, but the small divisions are 0.05 (as opposed to the conventional 0.04 sec.) A warning about this is printed on the bottom of each screen, to avoid confusion. ( It is necessary because of the sampling rate of the Dataq sampler).