Description
DESCRIPTION
The DS8R Biphasic Constant Current Stimulator is a 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 standard 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.
The DS8R is unique amongst our triggered pulse stimulators in that it incorporates features that allow external “on the fly” control of stimulus pulse parameters, either via its USB connection and our software GUI/API or a scaled analogue voltage input that can be used to control the current amplitude.
Optional Firmware for High Frequency (10kHz) Stimulation
A special edition firmware can also be provided (free of charge) for researchers interested in stimulating at higher frequencies (10kHz) than the standard firmware permits. For example transcutaneous spinal cord stimulation (TSCS) protocols being used in a variety of rehabilitation research studies, inspired by “Russian” stimulation” methods, are possible with this optional firmware. This allows researchers involved in spinal cord injury and stroke research to examine the effects of TSCS on recovery of function.
Biphasic Charge-balanced Output
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.
External Control Capabilities – Software (via USB) and Analogue Voltage Input
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, such as CED Signal/Spike2, Python or Matlab.
External Control Capabilities – Analogue Voltage Input
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 DS8R monitors the voltage applied at this input (0-10V) and adjusts the stimulus current proportionally with this voltage as each trigger input via rear panel BNC or other trigger source is detected.
This feature means that the most basic external control just required one digital and one analogue input from a DAQ system.
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.
Designed for Demanding Human Research Applications
The DS8R is suitable and safe for human research applications, but because the maximum pulse energy of 300mJ exceeds the 50mJ limit set by international standards in relation to clinical evoked-potential stimulation devices , we are not seeking medical device certification for the DS8R.
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