Recording evoked potentials during deep brain stimulation: development and validation of instrumentation to suppress the stimulus artefact.

The clinical efficacy of deep brain stimulation (DBS) for the treatment of movement disorders depends on the identification of appropriate stimulation parameters. Since the mechanisms of action of DBS remain unclear, programming sessions can be time consuming, costly and result in sub-optimal outcomes. Measurement of electrically evoked compound action potentials (ECAPs) during DBS, generated by activated neurons in the vicinity of the stimulating electrode, could offer insight into the type and spatial extent of neural element activation and provide a potential feedback signal for the rational selection of stimulation parameters and closed-loop DBS. However, recording ECAPs presents a significant technical challenge due to the large stimulus artefact, which can saturate recording amplifiers and distort short latency ECAP signals. We developed DBS-ECAP recording instrumentation combining commercial amplifiers and circuit elements in a serial configuration to reduce the stimulus artefact and enable high fidelity recording. We used an electrical circuit equivalent model of the instrumentation to understand better the sources of the stimulus artefact and the mechanisms of artefact reduction by the circuit elements. In vitro testing validated the capability of the instrumentation to suppress the stimulus artefact and increase gain by a factor of 1000 to 5000 compared to a conventional biopotential amplifier. The distortion of mock ECAP (mECAP) signals was measured across stimulation parameters, and the instrumentation enabled high fidelity recording of mECAPs with latencies of only 0.5 ms for DBS pulse widths of 50 to 100 µs/phase. Subsequently, the instrumentation was used to record in vivo ECAPs, without contamination by the stimulus artefact, during thalamic DBS in an anesthetized cat. The characteristics of the physiological ECAP were dependent on stimulation parameters. The novel instrumentation enables high fidelity ECAP recording and advances the potential use of the ECAP as a feedback signal for the tuning of DBS parameters.

The efficacy and safety of diclofenac 0.1% versus prednisolone acetate 1% following trabeculectomy with adjunctive mitomycin-C.

BACKGROUND AND OBJECTIVE: To evaluate the efficacy and safety of diclofenac 0.1% versus prednisolone acetate 1% following trabeculectomy with adjunctive mitomycin-C. PATIENTS AND METHODS: The authors prospectively randomized chronic open-angle glaucoma patients who underwent trabeculectomy with adjunctive mitomycin-C to receive postoperatively either diclofenac 0.1% or prednisolone acetate 1% 4 times daily, to be tapered as inflammation resolved. RESULTS: In the diclofenac group (n = 14), the preoperative intraocular pressure of 30.4 +/- 13.1 decreased to 12.4 +/- 6.5 mm Hg at 6 months postoperatively. In the prednisolone acetate group (n = 12), the preoperative intraocular pressure decreased from 29.1 +/- 10.4 to 12.8 +/- 4.2 mm Hg at 6 months postoperatively (P = .85). The average number of medicines used 6 months postoperatively was 0.50 +/- 0.8 in the diclofenac group and 0.24 +/- 0.6 in the prednisolone acetate group (P = .36). Adverse events were similar between groups (P = .51). One patient in the diclofenac group underwent reoperation at 1 month due to uncontrolled intraocular pressure. CONCLUSIONS: This study shows that following trabeculectomy with adjunctive mitomycin-C, a similar intraocular pressure result may be expected when either diclofenac or prednisolone acetate is prescribed postoperatively for intraocular inflammation.