We describe a temperature-control system for solutions in free flow, suitable for electrophysiological or optical studies of isolated cells, natural epithelia or cell culture monolayers. The system is small enough to be located close to the preparation and was designed specifically to be coupled to the inlets of a modified, continuous-flow Ussing chamber, allowing rapid change of the solutions bathing tissue surfaces. The system consists of a highly compact monoblock heating unit and a control circuit. Solutions from different reservoirs, kept at room temperature or lower (from an ice bath), can be rapidly switched at the inlet of the heating unit by manually or electrically actuated microvalves without affecting the temperature of the fluid leaving the heating unit. The control unit consists of a bead thermistor firmly placed close to the heating unit outlet and an electronic circuit which is basically a proportional controller. This unit continuously regulates the electric current through the Ni-Cr heater, keeping the temperature of the fluid leaving the heating unit constant at a preset value. The system allows control of fluid temperature (normally 37 degrees C) for flow rates in the range of 1.0 ml/min to 12 ml/min. However, the temperature can be set at any value above that of the incoming fluid.
RATIONALE: The development of closed-loop devices suitable for use in the treatment of epileptic patients would very likely rely on the adequate development of paradigms able to forecast the occurrence of seizures. In this paper, we studied the usefulness of approximate enthropy, of a non-linear paradigm, in this patient population. METHODS: We applied approximate entropy (ApEn) analysis to study the variability in the complexity of the peri-ictal electrocorticogram (ECoG) of patients with refractory epileptic seizures of the temporal lobe origin. Three patients were implanted with chronic subdural grids. The ApEn algorithm measured the complexity of interictal, peri-ictal and ictal phases. We selected one representative channel disclosing interictal activity for each patient and two channels per patient with ictal recordings. RESULTS: In all patients, we found one channel where the interictal activity registered in the ECoG was associated with high complexity and where ApEn was higher than 0.59. But in the other two channels, for each patient that presented interictal/ictal transitions, clinical manifestations of epileptic seizures occurred around 3.5 seconds after the entropy drop, when entropy was below 0.5. In contrast, when entropy was higher than 0.5, clinical manifestation occurred 9.5 seconds after the entropy drop. The 3.5 seconds shorter delay possibly indicates focal activity in the channel analyzed. CONCLUSIONS: Our results suggest that ApEn may be a useful instrument for early detection of epileptic activity. Its application may be indicated for prevention and diagnosis of epileptic seizures.
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