1. Field of the Invention
The invention relates to the field of medicine and medical engineering, in particular to methods and devices for diagnostics of the status of an alive organism basing on skin electrical conductivity and can be used in experimental and clinical medicine, as well as in psychophysiology, pedagogics and sports medicine.
2. Background Art
It is known that electrical conductivity of the skin of an alive organism is a sensitive indicator of its physiological and psychological state, parameters of the conductivity response onto an external influence, the so-called galvanic skin reaction (hereinafter referred to as GSR) being capable of estimating the psychophysiological status of an individual. In GSR studies, a tonic and a phasic components of electrodermal activity (hereinafter referred to as EDA) can be distinguished. Changes of tonic activity features in skin conductivity occur rather slowly, with characteristic times of several minutes and more. Phasic activity is implemented in processes occurring much faster on the background of tonic activity, its characteristic times being of the order of few seconds. It is the phasic activity that basically characterizes the response of an organism to an external stimulus, and this is referred to in the technical and patent literature as GSR.
The known methods of GSR monitoring include imposing on an subject's skin of a pair of electrodes connected to a source of a probing current and a monitoring device for the current in the circuit comprising electrodes and the source of current. The response occurs when sweat glands excrete a secret and momentary pulses of electrical current arise in the circuit. Such pulses are generated either spontaneously, or owing to stress or another stimulus (A. A. Aldersons, Mechanisms of Electrodermal Reactions, Riga, "Zinatne", 1985, pp. 59-63).
The known devices for GSR monitoring include a source of electric current connected to electrodes, an electric signal monitoring unit, and a signal processing unit. The signal processing consists in detection of the phasic component of EDA on the background of EDA tonic component. This can be embodied, for example, in the unit using a bridge circuit and a series of direct-current amplifiers with individual zero setting. The value of the tonic component (hereinafter referred to as the trend) is calculated by an analog method, and this is further subtracted from the signal. This value is also used to adjust the base line of graph plotter to zero (U.S. Pat. No. 4,331,160, ZITO, 1982).
In another known device (SU, A1, 1725829, Institute of General Judicial Psychiatry., 1992) the comparative level of the phasic component of the EDA with respect to the trend is determined by a circuit comprising highpass and lowpass filters at the outputs of respective amplifiers, as well as a dividing circuit.
One should mention that in the abovementioned methods and devices for galvanic skin reaction monitoring there are no means provided for the analysis of the EDA phasic component pulses, these pulses being capable of fetching the additional information on a status of the subject.
Closest to the method claimed is the method of monitoring of galvanic skin reaction implemented in the device (SU, A1, 1567427, Moscow Institute of Railway Transport Engineers., 1990). The method requires fastening two electrodes on the body of a subject, application of an electrical voltage to these, monitoring of time variation of the electric current flowing between electrodes and monitoring of the current pulses in the frequency band peculiar to phasic component of EDA.
The prototype of the device for galvanic skin reactions monitoring is the device implementing the above method (SU, A1, 1567427). This device comprises electrodes with a means of their fastening to the skin these electrodes being connected to the input unit, a means for signal discrimination in frequency bands of phasic and tonic components of EDA, a means for detecting EDA phasic component pulses, a means for suppression of pulse interference, and a monitoring unit.
However, the abovementioned method and device are not free from interference brought about by the subject's motions (artifacts) superimposed onto GSR signals temporal sequence and similar to pulses of the EDA phasic component. These artifacts could be, for example, brought about by uncontrollable movements of the subject in the course of registration (so-called artifacts of movement). In a signal there can also exist noises due to variation of contact resistance between electrodes and the person's skin. The abovementioned interference, including artifacts of movement, can feature characteristic frequencies comparable to those of a phasic component of EDA, which makes their revealing and consideration a distinct problem. Heretofore, this problem was being solved by installation onto the body of a subject of special gauges, in addition to electrodermal ones, which complicated experiments (R.NICULA.--"Psychological Correlates of Nonspecific SCR", --Psychophysiology; 1991, vol.28, No 1, p.p. 86-90). Besides, the trend features minimum characteristic time of change of the order of several minutes. These variations should be accounted for especially in cases when amplitude and frequency of the EDA phasic component are rather small, whereas tonic changes are highest. Such kind of a process is also characteristic for hardware drift of the measuring circuit, and it can be wrongly interpreted as an information signal.