D185

The Digitimer D185 is a sophisticated, multipulse cortical stimulator designed for human neurophysiological research and intraoperative monitoring. This system delivers high-voltage, precisely timed trains of constant current pulses via standard neurostimulating electrodes, making it particularly suited for motor cortex mapping, language mapping, and functional brain localization during neurosurgical procedures.

Used by neurophysiology departments worldwide, the D185 is built to meet the needs of clinicians and researchers seeking reliable cortical stimulation with fine control over pulse parameters, current intensity, and timing. It is typically paired with bipolar ball-tipped probes or strip/grid electrodes.

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Intra-Operative Monitoring with Motor Evoked Potentials (MEPs)

Certain surgical procedures, especially those involving the spinal cord or requiring temporary interruption of spinal blood flow - such as thoraco-abdominal aortic aneurysm repair - pose a significant risk of neurological injury. These risks include sensory deficits and, in severe cases, paraplegia, due to potential trauma, nerve stretching, or vascular occlusion during surgery. To mitigate these risks, real-time monitoring of spinal cord integrity has become a crucial part of intra-operative care.

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Traditional SEP Monitoring

Somatosensory evoked potential (SEP) monitoring is commonly used to assess the ascending sensory pathways. This involves stimulating peripheral nerves (typically at the wrist or ankle) and recording the resulting cortical responses. Changes in the SEP waveform can serve as an early warning of neural compromise, and the technique has played a pivotal role in preventing surgically induced neurological damage.

However, SEP monitoring is not without limitations:

• False reassurance: Unchanged SEP waveforms have, in some cases, failed to reveal motor deficits that only became apparent postoperatively.
• Unnecessary procedure changes: Altered SEPs have led to aborted or curtailed surgeries, even when the patient’s sensory function was ultimately unaffected.
• Low signal amplitude: SEPs are small and can be challenging to detect in patients with existing neuropathologies.
• Limited motor insight: SEP monitoring does not directly assess the descending motor pathways, which may be more vulnerable during surgery.

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The Role of MEP Monitoring and the D185 Stimulator

To address these limitations, the D185 MultiPulse Stimulator from Digitimer was developed in collaboration with leading neurophysiologists. This system enables transcranial electrical stimulation of the motor cortex, eliciting motor evoked potentials (MEPs) recorded from limb muscles. Because MEPs reflect the function of the same neural pathways responsible for voluntary motor control, they provide a direct and reliable assessment of descending motor tract integrity.

MEP monitoring allows surgical teams to detect motor pathway compromise in real time, complementing or even surpassing SEP monitoring in certain contexts. Changes in MEP waveform morphology, latency, or amplitude can offer critical insight, enabling timely intervention and reducing the risk of postoperative motor deficits.

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Evidence-Based Advantages

A large-scale clinical trial involving 1000 patients across two U.S. centers demonstrated that MEP monitoring:

• Provided a more accurate prediction of motor outcomes than SEP monitoring did for sensory outcomes.
• Offered a higher success rate for obtaining meaningful signals during surgery.
• Helped guide surgical decisions, especially in cases where SEP monitoring might have led to unnecessary surgical interruption.

These results led to FDA clearance of the D185, and MEP monitoring is now widely adopted in spinal, cardiovascular, and neurosurgical procedures worldwide.

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Key Features

• Multipulse stimulation: Delivers user-defined trains of pulses at fixed or programmable frequencies.
• Precise constant current output: Up to 60 mA with millisecond-level control of pulse width and frequency.
• Flexible control: Standalone or remote control via TTL inputs for timing synchronization with external systems.
• High compliance voltage: Ensures reliable stimulation across a range of electrode impedances.
• Compact, rack-mountable design: Suitable for OR integration or lab environments.
• Safety-focused: Features include interlocks, stimulation enable key, and isolated outputs to meet clinical safety standards.

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Applications

• Direct Cortical Stimulation (DCS) for intraoperative mapping of motor and language areas
• Intraoperative monitoring in neurosurgery
• Electrocorticography (ECoG) experiments
• Epilepsy surgery planning involving functional area identification
• Neuroscience research involving human cortical excitability

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Accessories & Compatibility

• Compatible with Digitimer D188 Remote Electrode Selector for use with multi-electrode arrays.
• Works with standard clinical cortical stimulation electrodes (e.g., subdural strip or grid electrodes).
• Can be triggered externally via neurophysiology acquisition systems for integrated stimulation-response mapping.