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Peripheral Stimulators DS5 Isolated Bipolar Constant Current Stimulator DS7A & DS7AH HV Constant Current Stimulator NEW DS7R HV Constant Current Research Stimulator NEW DS8R Biphasic Constant Current Stimulator
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The DS8R Biphasic Constant Current Stimulator is a new multi-mode, discrete pulse, constant current stimulator for human research studies involving nerve and muscle stimulation via surface electrodes. It features a high compliance voltage and can be triggered by a TTL compatible input, contact closure foot/hand switch or front panel “single-shot” button. The DS8R can deliver monophasic or biphasic pulses of up to 2ms duration, with an output range of 0-1000mA in 100µA steps (from 400V), however the actual current achieved will be restricted by a pulse energy limit of 300mJ per pulse and the skin/electrode resistance. Most importantly, the new DS8R incorporates features that allow external “on the fly” control of stimulus pulse parameters.
A special edition firmware can also be provided for researchers interested in stimulating at higher frequencies (10kHz) than the standard unit permits. Protocols inspired by “Russian” stimulation” methods are possible with this optional firmware.
The DS8R Biphasic Constant Current Stimulator, has two pulse modes, enabling stimulation using monophasic or biphasic rectangular pulses. Additionally, in biphasic mode the DS8R allows for both symmetric or asymmetric charge-balanced stimuli through implementation of an adjustable stimulus/recovery phase amplitude ratio. Biphasic charge-balanced stimulation offers certain advantages over monophasic stimulation, as it prevents the potentially harmful electrochemical changes which occur under stimulation sites and is reported to be more comfortable for the subject during long periods of stimulation. The recovery phase ratio can be adjusted from 10% to 100% in 1% increments. As illustrated below, at 100% the two phases are identical in terms of duration and amplitude, but as the ratio is reduced from 100% the amplitude of the recovery phase decreases, while its duration is extended to preserve charge balancing.
Researchers often want to adjust stimulus settings (current and duration) during a stimulation protocol and with the arrival of the DS8R, such control becomes a reality. While the DS8R can operate as a standalone isolated stimulator with full control via the front panel, settings can also be modified using Windows PC control software (supplied) via a USB interface. This software provides a Virtual Front Panel for the stimulator, but more importantly incorporates an API allowing the operator to implement control from custom or commercially available software packages.
Pulse current amplitude can be more simply controlled via an analogue voltage input (BNC) on the rear of the DS8R. Using this method of control, the DS8 monitors the voltage applied at this input (0-10V) and adjusts the stimulus current proportionally with this voltage as each trigger input is detected. Note that the control voltage signal does not define the shape of the output pulse, it is merely used as a proportional representation of the output stimulus current.
The DS8R is suitable and safe for human research applications, but because the maximum pulse energy of 300mJ exceeds the 50mJ limit imposed by international standards in relation to clinical evoked-potential stimulation devices , we are not seeking medical device certification for the DS8R.
DS8R Product Literature
DS8R Operator’s Manual V2.0
Publications which cite use of the Digitimer DS8R can be found on Google Scholar.
The 300mJ/pulse limit is present in the EN 60601 international standard and is applicable to medical electrotherapy devices. While the DS8R is intended for research use only, we felt it was prudent to limit the DS8R to a pulse energy that could be applied to a comparable medical device.
No, the DS8R is a triggered pulse stimulator, so the output can only be rectangular in shape. If you need to stimulate with non-rectangular waveforms, please see our DS5 Bipolar Current Stimulator.
Early versions of the DS8R had a minimum pulse amplitude of 2mA, however, from March 2019, all DS8R’s offer a current range of 0-1000mA and can delivery stimuli in the range of sensory thresholds.
Yes, but because of the temporal unreliability of USB communication, we limit the frequency to no more than 10Hz when triggered by the button in the software or via the API.
The standard DS8R can be triggered at a maximum frequency of 1000Hz, however, we have provided a modified firmware to some users which allows the DS8R to be triggered at 10kHz, allowing it to deliver bursts of biphasic pulses with 50us phase durations and <1us phase intervals. Please contact us if you have an interest in this non-standard firmware.
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