In the following section, we describe the dataset that has been used in this paper. Then, we describe the methodology adopted in our work and we highlight the investigated tools in detail.
Furthermore, in this work, we propose an automated approach for the classification of PNP diseases. Therefore, our method involves two major steps including feature extraction and classification. The principle of the proposed approach is presented in Fig. 1 and is mainly divided into two tasks:
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The first task represents the morphologic feature extraction providing the useful information for the second task.
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The second task is the classification process. This system is used to detect and classify PNP; in this task the classification model is simulated using Adaptive Neuro Fuzzy Inference system.
A. Database
EDA recordings of hand and foot skin were taken from 36 normal subjects (17 F,19 M, aged 19–68) recordings of hand and foot skin. Table 1 illustrates the physical characteristics of these groups of subjects. Controls had no clinical peripheral or autonomic nerve involvements and used no drug which could influence sympathetic activity.
105 pathological subjects also studied (aged between 26–86) who were otherwise neurologically (Table 1). Clinical work-up including EMG, motor and sensory nerve conduction measurements were all normal.
Table 1
physical characteristics of these groups of subjects (F: Female, M: Male, SD: Standard Deviation).
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Gender
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Age
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Height(cm)
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Mass (Kg)
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M
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F
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Mean
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SD
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Mean
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SD
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Mean
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SD
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Healthy subjects
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24
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12
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45
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14.3
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174.52
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8.15
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71.4
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7.2
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Pathologic subjects
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56
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50
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66.72
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12.77
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170.58
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10.12
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76.8
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7.56
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The examination room was at a constant temperature between 22 and 24 ° C. The subjects were comfortably seated on the examination table in a semi-sitting position. Except for control subjects, they first benefited from the ENMG conducted in order to characterize PNP. All subjects had at least, in addition to a detection examination, a study of the motor conduction of the deep fibular and posterior tibial nerves and a study of the sensory conduction of the superficial and deep fibular nerves on the side where the symptomatology was maximal. For SSR measurement, after skin cleaning and electrode placement, they were asked to relax and breathe regularly. The stimulations consisted of electrical pulses of 0.2 ms duration, applied to the skin opposite the median nerve on the left wrist The intensity was 20 mA. They were delivered when response monitoring was stable, with a random interval greater than 20 seconds. Their number was the one that allowed to obtain a response with a reliable measurement of latency and amplitude, without exceeding five. The recording was done by 1 cm diameter adhesive electrodes (Nutab Diagnostic Electrodes, Kendall) put at hand and foot contralateral to the stimulation. Cathodes were on the sole of the foot and on the palm of the hand, and anodes on the dorsum of the foot and the hand. Amplification and visualization of the signal were provided by an electromyographic device (Neuro-Mep4, Neurosoft). The input dynamics was 6 mV. The sensitivity was adjusted during the measurement to obtain a clear take off from the response. The bandwidth was between 0.2 and 20 Hz.
In fact, to improve our database for each acquisition, we are remade 5 times. Each measurement began with a rest period of 2 minutes, to ensure that SSR signals were not overlapping. In fact, Fig. 2 illustrates an example of typical examples of SSR data recorded from healthy and pathologic subjects, the upper graph Fig. 2a) shows the SSR data recorded from the hand of subjects haven’t PNP. b) recorded from the foot of subjects haven’t PNP. In the bottom graph Fig. 2c) the EDA data were recorded from the hand subjects have PNP. d) recorded from the foot of subject with PNP.
Measurements of the response parameters were made by the sliders on the device and were the onset of the first negative wave, for its latency, and the peak-to-peak interval between the negative wave and the positive wave for the amplitude. In the absence of a negative wave, the latency was the onset of the positive wave, and the amplitude was the difference between the trough of this wave and the starting point. Of the five trials performed, with horizontal baseline and clear response takeoff, we selected the one with the shortest latency, which most often corresponded to the one with the largest amplitude, and which was usually the first trial. If the responses were not of sufficient quality, the same technique was applied on the other side. In the case where the SSR was not obtained, either in the hand or in the foot, it was tried to record it with stimulations of intensity higher than 30 mA, and after a deep inspiration, to differentiate abolitions by central deficit or deficit of sensory afferences. The length between the foot and the hand corresponded to the distance between the palm and the ground when the subject was standing (see justification in Fig. 2). Hand and foot skin temperature was measured in all subjects at the end of the examination where the cathodes had been placed (Neurosoft thermal probe).
B. features extraction
The SSR is most often utilized in peripheral neuropathies to identify functional impairment of non-myelinated postganglionic sudomotor sympathetic fibers. In the literature, several terms are used depending on the method of measurement such as electrodermal activity (EDA), electrodermal response (EDR), psychogalvanic reflex (PGR), galvanic skin response (GSP), peripheral autonomic surface potential (PASP) and the most frequently used SSR [17–18].
Thus, SSR is characterized by the morphologic features such as the amplitude, latency time, rise time, the typical recovery time of 63% of SSR, and the typical recovery time of 50% of SSR. These features have been previously used in [19–24] and they have showed a very important potential for classification. Figure 3 presents how to extract these features via an SSR signal.
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The latency of SSR (second) is the time interval between the stimulation artifact and the start of the SSR [17].
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the amplitude of SSR (mV) is measured from the peak of the first deflection to the peak of the next one (peak to peak) [17].
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The rise time (seconds) Time interval between the start (the measured latency) of the signal response and the second peak [22].
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Half-recovery time (seconds) the time interval between the second peak and the point at which the signal increases by half the second peak.
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recovery time of 63% (seconds) the time interval between the second peak and the point at which the signal increases by 63% of the second peak.
C. Adaptive Neuro Fuzzy Inference System (ANFIS)
ANFIS belongs to a family of hybrid system, was introduced by Jyh-Shing Roger Jang [24–26] in 1993 which is the combination of both advantages of fuzzy logic principals and artificial neural network. ANFIS is a fuzzy mapping algorithm based on Takagi-Sugeno fuzzy inference system. Its inference system corresponds to a set of fuzzy IF–THEN rules that have learning capability to generate the input/output (I/O) pairs [25], can be written using the following Equations (2) and (3), where the inputs are x and y, the fuzzy sets are Bi and Ai. pi, qi and ri are the parameters of design that are denoted in training and fi are the outputs described by the fuzzy rule.
Rule 1: if x is A1 and y is B1 then \(\mathop f\nolimits_{1} =\mathop p\nolimits_{1} x+{q_1}y+{r_1}\) 1
Rule2: if x is A2 and y is B2 then \(\mathop f\nolimits_{2} =\mathop \text{p}\nolimits_{2} \text{x}+{\text{q}_2}\text{y}+{\text{r}_2}\) 2
ANFIS structure is comprised of five layers (i.e., layer 1 to layer 5) with directional links and nodes. In fact, ANFIS training algorithm is a hybrid Learning Algorithm, which consists of two passes:1) the ordinary least squares algorithm to update coefficients of the output function. 2)the error back propagation algorithm is used to update fundamental factors of the system [27]. Figure 4 shows two input ANFIS architecture. The function of each layer of the ANFIS architecture is described below[24–28].
Layer 1
The first layer is called as the fuzzification layer. The fuzzification layer takes the input value and determines the membership function and belonging to them. Every node i in this layer is a square node with a node function the output of each node is calculated using Equations (3) (4).
\(O_{\text{i}}^{1}={\mu _{{\text{A}_\text{i}}}}(\text{x}), \text{i}=1,2\) 3
\(O_{\text{i}}^{1}={\mu _{{B_{\text{i}-2}}}}(\text{x}), \text{i}=3,4\) 4
where, x is the input to node i, and Ai, is the linguistic label (small, large, etc.) associated with this node function. Parameters in this layer are referred to as premise parameters. Node output is the membership value of the input.
Layer 2
The second layer is called rule layer [28]. It’s responsible for generating the firing strengths for the rules. Every node in this layer is a circle node labeled π, which multiplies the incoming signals and sends the product out as in the Eq. (4).
\(O_{\text{i}}^{2}={\text{w}_i}={\mu _{{\text{A}_\text{i}}}}(\text{x})*{\mu _{{B_\text{i}}}}(x), \text{i}=1,2,...\) 5
Layer 3
this layer is called as Normalization layer. His role is to normalize the computed firing strengths by diving each value with the total firing strength. Every node in this layer is a circle node labeled N.
\(\text{O}_{\text{i}}^{3}={\bar {\text{w}}_\text{i}}=\frac{{{\text{w}_\text{i}}}}{{{\text{w}_1}+{\text{w}_2}}}, \text{i}=1,2,...\) 6
Layer 4
This layer is called as defuzzification layer. Weighted values of rules are calculated in each node of this layer as given in Eq. (6).
\(O_{i}^{4}={\bar {w}_i}{f_i}={\bar {w}_i}({p_i}{x_i}+{q_i}y+{r_i})\) 7
Node outputs are the evaluation of right-hand side polynomials of Eq. 6 where (\(\stackrel{-}{w}\)i) is the output of layer 3.and {pi,qi,ri} is the parameter set. These are called the consequence parameters. The number of consequence parameters of each rule is one more than the number of inputs.
Layer 5
It is called as the summation layer. The actual output of ANFIS is obtained by summing the outputs obtained for each rule in the layer 4.
\(O_{i}^{5}=\sum\limits_{i} {{{\bar {w}}_i}{f_i}=\frac{{\sum\limits_{i} {{w_i}{f_i}} }}{{\sum\limits_{i} {{w_i}} }}}\) 8