EEG changes under hyperbaric conditions: spectral analysis during simulated diving.

Continuing investigations of the influences of the hyperbaric pressure upon EEG record in divers during simulated diving. The hyperbaric ecological system exerts influences on brain bioelectric activity manifesting itself by changes of alpha frequency and appearance of slow waves. The changes in the brain activity are mostly observable at the changes in chamber pressure values. The changes in EEG recordings are smallest at constant pressures. EEG examination can be used as a measure of the safety of newly developed decompression schedules.

EEG changes measured by spectrum analysis under hyperbaric conditions.

The subject of experimental, saturated dividing to 20 m depth was alertness level measured by means of spectral analysis of EEG records. Air was served as breathing mixture compressed to a given depth in closed circulating system. Altogether 49 EEG records made during compression, plateau and decompression, were analysed. Two methods of analysis were applied. "Normality ratio" combined the information from 20 different EEG values and "EEG alertness indicator" showed in three cases pathological slowing and fluctuations of the alertness. According to index of alertness, the most prominent changes were seen during the compression and decompression phase. During the plateau phase sleepiness was recorded. The applied method could provide information when slowing is due to metabolic impairment of brain activity from that of sleepiness.

A method of measuring the conduction velocity of action potentials in a statically loaded muscle.

Basic ideas underlying a method and construction of an instrument for measuring the conduction velocity of action potentials in a statically loaded muscle are described. Periodical fadings in the power spectrum density of the EMG signal and the dependence of the position of these fadings on the conduction velocity of action potentials in a muscle are used. Usefulness of the described method and measuring instrument is discussed with respect to their application for evaluating localized muscle fatigue.

Muscle fatigue simulator.

The above description of the structure and operation of the Muscle Fatigue Simulator was necessarily presented in an abridged fashion (a more complete description to be found in the report (3). The main goal of the construction of the model was creation of a system simulating the changes occurring in the EMG signal under the impact of local muscle fatigue. The performed verification of the model in the aspect of time, frequency and dynamic changes of simulated parameters confirmed simulating faithfulness of the model and thereby the initial assumptions and the general idea of the model may be considered correct. The muscle fatigue simulator has the capability to display some changes occurring in myoelectric signals during fatiguing contractions, and it is believed to have a great merit in demonstration of the signal processes within the muscle. For that reason, the Muscle Fatigue Simulator can be of use in teaching and in demonstration of particulars of the myoelectric signal during isometric contraction. It may also be used in instrument calibrating and in checking the operation of the EMG-signal measuring and analysing equipment applied in ergonomic studies.