Thesis - Instituto de Telecomunicações

48 CHAPTER 3. INFORMATION SOURCESFigure 3.7: The first polygraph that introduced the electrodermal signal. (In Public Domain)In a clinical context, the EDA signal was studied in preoperative stress [227] and postoperativepain [141]. In reference basilar studies, the specificity of the response demonstratedrelevant differences among types of persons [139, 249]; neural justification for the absenceof response in patientes with schizophrenia was studied in [143] and [145].3.3.2 ElectrocardiographyThe electric control of the heart mechanism is externally observed by a clinical techniquedesignated as electrocardiography (ECG or EKG from Elektrokardiogramm given that thefirst electrocardiograms were performed by the Dutch inventor and Noble prize winner,Williem Einthoven [132]). Figure 3.8 depicts an early ECG device developed by WilliemEinthoven.The ECG is a human vital signal, and it is one of the most well known physiologicalsignals. Figure 3.9 shows a schematic view of the ECG waveform with the reference pointsidentified according to the standard notation. The typical structure of an ECG signal trace