Abstract: The invention relates to detection of anomalies related to a measurement of the hypnotic level of a subject. In order to detect when a measure indicative of the hypnotic level of a subject is anomalous either due to a medical reason or due to an interference, the measure is monitored and state information indicative of the activity of the autonomous nervous system of the subject and drug effect information indicative of the hypnotic drug effect in the subject are employed to check whether the measure fulfills a predetermined consistency condition requiring that the measure changes consistently with at least one of the drug effect information and the state information. An anomaly, indicative of an abnormal change in the measure, is detected when the measure fails to fulfill the predetermined consistency condition.

Abstract: The invention relates to a method and apparatus for assessing the reactivity observable in a certain physiological signal, especially the EEG signal, of a comatose subject. In order to obtain an objective and a reliable measure of the reactivity automatically and without the presence of a trained EEG specialist, a time reference corresponding to a stimulus is detected and the physiological signal data obtained from the subject is aligned with the time reference. Two sets of values are determined for a measure indicative of the amount of irregularity in the physiological signal data, both sets including at least one value of the said measure and having defined positions with respect to the time reference in time domain. Based on the two sets, the apparatus determines whether reactivity is present in the physiological signal data.

Abstract: The invention relates to a method and apparatus for assessing the reactivity observable in a certain physiological signal, especially the EEG signal, of a comatose subject. In order to obtain an objective and a reliable measure of the reactivity automatically and without the presence of a trained EEG specialist, a time reference corresponding to a stimulus is detected and the physiological signal data obtained from the subject is aligned with the time reference. Two sets of values are determined for a measure indicative of the amount of irregularity in the physiological signal data, both sets including at least one value of the said measure and having defined positions with respect to the time reference in time domain. Based on the two sets, the apparatus determines whether reactivity is present in the physiological signal data.

Abstract: The invention relates to a method and apparatus for assessing the reactivity observable in a certain physiological signal, especially the EEG signal, of a comatose subject. In order to obtain an objective and a reliable measure of the reactivity automatically and without the presence of a trained EEG specialist, a valid signal model is constructed for an EEG signal obtained from the subject. A time reference corresponding to a stimulus is applied and further signal data is obtained from the time series, the further signal data being subsequent to the time reference. By employing the further signal data, the method tests whether the signal model remains to be a valid signal model for the EEG signal also after the stimulus, and indicates, based on the test, whether reactivity is present in the physiological signal.

Abstract: The invention relates to a method and apparatus for assessing the reactivity observable in a certain physiological signal, especially the EEG signal, of a comatose subject. In order to obtain an objective and a reliable measure of the reactivity automatically and without the presence of a trained EEG specialist, a valid signal model is constructed for an EEG signal obtained from the subject. A time reference corresponding to a stimulus is applied and further signal data is obtained from the time series, the further signal data being subsequent to the time reference. By employing the further signal data, the method tests whether the signal model remains to be a valid signal model for the EEG signal also after the stimulus, and indicates, based on the test, whether reactivity is present in the physiological signal.

Abstract: The invention relates to a method and apparatus for monitoring the cerebral state of a subject. At least one of a first and second parameters is derived from the physiological signal data obtained from the subject, wherein the first parameter is indicative of the sum of spectral values of the physiological signal data in a first frequency band lying above high frequency EEG activity and the second parameter is indicative of the relative magnitudes of a first sum of k-th order spectral values and a second sum of n-th order spectral values. The second sum is calculated over a frequency band lying above high frequency EEG activity (k>2 and n>1). A state index is then formed, which is dependent on the at least one parameter and indicative of the cerebral state of the subject. The first and second parameters may be used in the Bispectral Index (BIS™) algorithm.

Abstract: The invention relates to a method and apparatus for measuring the responsiveness of a subject with lowered level of consciousness. Physiological signal data is obtained from the subject and a first measure indicative of the level of consciousness of the subject is derived from the physiological signal data. In order to obtain an objective measure of the responsiveness of the subject and to improve the specificity of patient monitoring, a sequence of the first measure is recorded without inducing arousals in the subject and a second measure indicative of a responsiveness of the subject is determined based on the recorded sequence. The determination of the second measure may be independent of the unintentional stimuli that cause arousals in the patient or the stimuli causing such arousals in the clinical environment may be detected to find out their effect on the first measure.

Abstract: The invention relates to a method for positioning electrodes in an electrode array comprising a plurality of electrodes for central nervous system (CNS) monitoring from the forehead of a subject. In order to enable efficient detection of eye movement artifacts with a minimum number of electrodes, first and second electrodes are positioned so that eye movement in one of the horizontal or vertical directions causes a negligible overall voltage change between the first and second electrodes and at least a third electrode is positioned so that eye movement in the other of said horizontal and vertical directions causes a high potential difference between the third electrode and an auxiliary electrode, wherein the auxiliary electrode is one of the electrodes in a set comprising one of the first and second electrodes and a fourth electrode.

Abstract: A method and apparatus for ascertaining the cerebral state of a patient using generalized spectral entropy of the EEG signal.

Abstract: A method and apparatus for ascertaining the cerebral state of a patient. The method/apparatus may find use in ascertaining the depth of anesthesia of the patient. In one embodiment, the entropy of the patient's EEG signal data is determined as an indication of the cerebral state. A frequency domain power spectrum quantity is obtained from the patient's EMG signal data. The latter quantity can be updated more frequently than the EEG entropy due to its higher frequency. The EEG entropy indication and the EMG power spectrum indication can be combined into a composite indicator that provides an immediate indication of changes in the cerebral state of the patient. In another embodiment, the frequency range over which the entropy of the biopotential signal from the patient is determined is broadened to encompass both EEG signal data and EMG signal data and the entropy so determined used as an indication of the patient's cerebral state.