No abstract
TELEMETRY (making measurements at a dis¬ tance) is not new. The electrical activity of the heart was telemetered by FM transmission in 1943.'The technical achievements of the past 2 decades, however, have greatly advanced this science.2 Min¬ iaturization of amplifiers and transmitters 3'5 now offers a possible way of monitoring biological phe¬ nomena in free-moving patients in the hospital environment.The following application in clinical neurology is an example. Neurologists frequently have pa¬ tients whose symptoms suggest a seizure disorder, but whose routine electroencephalograms have been repeatedly normal. Activation techniques (hyperventilation, sleep, photic stimulation, pentylenetetrazol, and so forth) also may fail to bring out the abnormalities. Usually, patients cannot be studied electroencephalographically for prolonged periods of up to 24 hours or for days on end. Telemetry, by permitting freedom of movement, facilitates prolonged recording sessions.It also may find clinical application in patients with frequent, very brief, petit mal attacks. In order to evaluate therapy the seizure incidence must be known, but it is difficult, even for nurses and trained attendants in hospitals, to count these seizures. Telemetering the brain waves over pro¬ longed periods of time gives a more reliable index of the seizure incidence, and hence of the efficacy or nonefficacy of therapy in these patients. MethodSolder pellet electrodes are affixed to the scalp with collodion after applying electrode jelly. In these preliminary studies 3 electrodes were used because only one channel was transmitted. Both a differential amplifier for use with low-level signals (within the frequency range of 0.5 cycles per sec¬ ond to 8 kc. ) and an FM transmitter tuned to 90.5 mc. are miniaturized components contained within a plastic case with outside dimension of 5.2 X 3.3 X 9.7 cm. This unit is worn under a shirt, and is taped to the patient's chest. By taping the unit firmly to the chest, the effect of external capaci¬ tance is reduced. No antenna is necessary, as sufficient radiation emanates from the coil to trans¬ mit to a receiver on the hospital ward.The signal is received on an FM tuner placed in the EEG laboratory or in the nearby office of the neurologist. The output from this receiver is fed into a portable 2-channel electroencephalograph which yields an ink-tracing on paper for a perma¬ nent record. CommentThe fidelity of the transmitted electroencephalo¬ gram is good, and alpha rhythm, beta rhythm, spike-wave patterns, and seizure activity are read¬ ily recognized. The major difference between this type of electroencephalography and routine electroencephalography is the increase in the amount of "artifact" in the former type (i.e., changes in potential due to extracerebral causes).Because our patients move about freely, move¬ ment artifacts are to be expected. It is particularly important to recognize rhythmical movement arti¬ facts, such as those produced by swinging the arms when walking. Deep respirations, rotations ...
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