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Biomedical subjects

J J Ackmann

Publications and source records attributed to J J Ackmann.

13 recordsLinked to original sources
PubMed1979

A computer system for neurosurgical patient monitoring.

The variables monitored in intensive care units are generally late indicators of neurologic deterioration. A system based on a LINC-8 computer was therefore developed for on-line monitoring of evoked potentials, electroencephalography (EEG), and transcranial and transthoracic impedances as well as conventional parameters. Somatosensory evoked potentials are recorded at either 30 min or 1 h intervals. One minute epochs of EEG are analyzed every 10 min using a peak-detection algorithm. Impedances and conventional parameters are also monitored at 10 min intervals. In a study of 50 patients, the technical feasibility of this type of monitoring with a small laboratory computer has been demonstrated. In some instances, evoked potentials and EEG show changes prior to detectable neurologic changes. The study suggests that this type of monitoring can provide a valuable adjunct for evaluation of physiologic function in neurosurgical intensive care.

Afferent Pathways↗
PubMed1979

Digital filtering of on-line evoked potentials.

Evoked potentials recorded automatically at frequent intervals are a useful adjunct for monitoring head injury patients; however, unaveraged residual noise due to patient movement and synchronization of th- stimulus to harmonics of the line frequency is sometimes present. A frequency analysis was performed on 23 records with varying degrees of unaveraged noise and the results were used to design a digital filter. The frequency content of the records analyzed was largely contained in a band from D.C. to 200 Hz. A zero phase shift lowpass digital filter with a cutoff frequency of 200 Hz eliminated the majority of noise. Despite the low frequency content, a wide-band amplifier is still required to avoid waveform distortion, particularly latencies. Digital filters can then be applied without causing distortion.

Computers↗
PubMed1978

Early somatosensory evoked potentials.

The early somatosensory evoked potential secondary to median nerve stimulation in the human had an onset latency of 9--12 msec when recorded from scalp electrodes at vertex-to-mastoid, vertex-to-inion or at the base of the skull. Similar latencies were observed from responses recorded over the cervical dorsal columns during neurologic surgery. A latency difference of 1.5 msec was observed between the early response and the responses recorded from the junction of medial lemniscus and nucleus ventralis posterior lateralis of the thalamus during human stereotaxic surgery. Cervical cord transections and transection at the midpontine levels of the monkey showed that the evoked potential was due to generators between these levels. Depth recording of the monkey indicate that the early evoked potential originates in the region of dorsal column nuclei, while the later components are secondary to generators in cerebral cortex.

Animals↗
PubMed1978

Peak-detection algorithm for EEG analysis.

A peak-detection method is described for computer analysis of the the electroencephalogramme (EEG). The technique consists of measuring the amplitude and time interval between successive maxima (peaks) and minima (troughs) in the signal. A critical feature of the peak-detection algorithm is the inclusion of an amplitude threshold criterion which eliminates the registration of low-voltage activity riding on EEG waves. The peak-detection procedure permits the formulation of a variety of intra-band and inter-band EEG statistics which can be useful in on-line computer applications. The peak-detection algorithm has been successfully applied to a number of normal and clinical EEG recordings. Although no computer procedure for EEG analysis has yet been universally adopted, the peak-detection algorithm reported in this paper presents a standardised approach which can be used between EEG clinics.

Diagnosis, Computer-Assisted↗
PubMed1977

Computerized evaluation of electroencephalographic changes accompanying exchange transfusion in Reye's syndrome.

The EEGs of 7 children with Reye's syndrome (fatty liver and encephalopathy) were continuously recorded on magnetic tape for times ranging from 12 to 80 h. During these times the major therapy consisted of exchange blood transfusions. The tapes were automatically processed on a LINC-8 computer using a peak-detection algorithm. The main parameters investigated were the delta and theta indices, the mean EEG frequency, the mean peak-to-peak amplitude, and the frequency versus amplitude characteristics of the delta waves. In 5 patients who responded to therapy, a marked decrease in the delta activity and an increase in mean frequency were noted subsequent to exchange transfusions. In all 5 cases the delta waves exhibited a similar pattern of decreasing amplitude and increasing frequency following therapy. However, in 2 patients with a fatal outcome, no favorable EEG response was observed during treatment, and a simultaneous decline in both delta frequency and delta amplitude was noted as the clinical condition worsened. The results of this study indicate that continuous EEG monitoring in Reye's syndrome may be an important clinical adjunct in evaluating the effectiveness of exchange transfusion therapy and in signaling the need for further treatment.

Adolescent↗
PubMed1977

Mechanical and physiological effects of dentatotomy.

The role of the dentate ligaments in the pathogenesis of myelopathy secondary to disease conditions that alter the normal biomechanics of the spinal canal was studied in 14 dogs. The effects of posterior cord elevation on somatosensory evoked potentials (SSEP's) and tension requirements were compared before and after dentate ligaments section in acute experiments. At levels of posterior elevation usually within the confines of the canine canal, the dentate ligaments were the most significant element increasing tension requirements and SSEP alternations. Human cadaver studies also showed an approximate 50% reduction of force after dentatotomy. These findings suggests that after dentate ligaments section the applied tension is distributed over a longer segments of the cord with a reduction in tension and disruption of axonal conduction at the level at which the force was applied.

Animals↗
PubMed1975

Clinical applications and theoretical analysis of NMR blood flowmeter.

Nuclear magnetic resonance principles have been applied to measure biological blood flow. The method is non-intrusive and can be used to measure peripheral blood flow or blood flow from various organs. The mechanisms of NMR are described and studies of blood flow in limbs and the head are discussed.

Animals↗
PubMedDate not supplied

Determination of tissue viability in experimental electrical injuries.

Electrical burns or ischemia (induced by vascular ligation) were produced in the legs of 15 anesthetized dogs to study evolution of tissue changes compared with impedance alterations. After the application of 1-ampere currents at 60 Hz, animals were monitored from 1 to 4 days. Muscle impendance was measured with frequency sweeping to determine tissue destruction. Nuclear magnetic resonance spectroscopy (phosphorus 31) was used to assess metabolic activity, and results were compared to impedance measurements. In burned limbs, 70% reduction in muscle impedance was seen, which corresponds to decreased metabolic activity (absent organic phosphates) and suggests necrosis. Visually viable tissue had impedance decreases of 25% and levels of organic phosphates slightly lower than normal. Relaxation frequencies in dogs with severe burns exceeded 80 kHz; in viable tissue, 30 to 40 kHz (normal: 30 kHz). In ischemic muscle, organic phosphates decreased rapidly (1 to 2 hours); impedance changes evolved more slowly (1 day), but they ultimately reached the same degree of severity. Measurement of impedance may be a valuable adjunct in the evaluation of electrical burns, since significant changes strongly suggest nonviability.

Animals↗