An antidromic sensory conduction study (SNCV.edf)

Description

For our purpose, the main difference between sensory and motor conduction studies is that usually sensory potentials use averaging to decrease the noise present in the raw signal. EDF+ codes curves: they can represent a single sweep or an average. The additional information needed to process the signal (e.g., number of sweeps accepted/rejected) can be included in the annotation signal.

The header

This is the content of the global header record

Version	0
Patient	X M 29-JAN-1956 X
Recording	Startdate 01-JAN-2002 emg1 jop N1 SNC_L_Median_Nerve
Startdate	01.01.02
Starttime	10.30.00
Bytes in header	768
Reserved	EDF+D
Data records	2
Duration	0.02
Signals	2

The signal header of each signal is

	First signal	Second signal
Label	NC Second Finger	EDF Annotations
Transducer	Ring elect. 2d finger
Phys. dimension	uV
Phys. minimum	-250	0
Phys. maximum	250	1
Dig. minimum	-9625	-32768
Dig. maximum	9625	32767
Prefiltering	HP:20Hz LP:3kHz
Samples	500	500
Reserved

The traces

The content of the first data record can be seen in figure 4.1

Figure 4.1: Plot of the record 0

The content of the second data record can be seen in figure 4.2

Figure 4.2: Plot of the record 1

The annotations

The annotations of the data records (first and second data record) are

 
+0[20][20]StimA[20]<EDF_XMLnote><!--co...

+60[20][20]StimB[20]<EDF_XMLnote><recor...

The annotation of the first data record includes the following EDF_XMLnote

 
<EDF_XMLnote>
<!--coded as example-->
  <temperature unit="degree C" position="left hand">33.2</temperature>
  <recording>Second finger</recording>
  <distance mode="stimulus to recording" unit="cm">14.0</distance>
  <stimulus label="StimA" mode="constant intensity" 
  duration="0.2 ms" intensity="11.4 mA">wrist</stimulus>
  <average mode="accepted">14</average>
  <measurements>
    <latency unit="ms">2.48</latency>
    <amplitude mode="peak to peak" unit="uV">55.3</amplitude>
  </measurements>
</EDF_XMLnote>

The annotation of the second data record includes the following EDF_XMLnote

<EDF_XMLnote>
  <recording>Second finger</recording>
  <distance mode="stimulus to recording" unit="cm">38.0</distance>
  <stimulus label="StimB" mode="constant intensity" 
  duration="0.2 ms" intensity="12.0 mA">elbow</stimulus>
  <average mode="accepted">13</average>
  <measurements>
    <latency unit="ms">6.32</latency>
    <amplitude mode="peak to peak" unit="uV">22.0</amplitude>
    <velocity mode="segmental" unit="m/s">62.5</velocity>
  </measurements>
</EDF_XMLnote>

Some comments

Notice that the file only includes the averages. Alternatively, the individual sweeps (14 traces for stimulus at wrist and 13 traces for stimulus at elbow) could have been included in different data records, and in this case the use of different processing methods (median averaging, odd-even averaging, different levels of threshold) would be possible. Even inclusion in the same file of the individual sweeps and the final averaging is allowed in EDF+.

The amplitude measurement criteria is different from the one used in the motor conduction in the previous chapter. It is indicated as an attribute. This kind of information can be very important to compare studies carried out by different groups.