Table 1: Therapeutic parameters of neurostimulation
Amplitude	A measure of the intensity or strength of the stimulation. It is experienced by the patient as the strength of the paraesthesia. Amplitude is measured in volts (V). It can be set from 0 to 10.5 V, depending on the patient’s needs
Pulse width	A measure in microseconds (μs) of the duration of a pulse. In general, the wider the pulse width, the larger the tissue area being stimulated, and the stronger the sensation of paraesthesia. For neurostimulation, the pulse width is commonly set at 180 μs
Rate	The number of times per second that a pulse is delivered. It is measured in pulses-per-second (pps) or Hertz (Hz). The rate is typically set between 30 to 80 pps.
Electrode selection	This includes bipolar or unipolar (Itrel system only) stimulation. All four electrodes of each lead can be selected to be active with either negative or positive polarity providing that at least one positive pole and at least one negative pole are selected

 

Figure 1: Stimulation waveform in neurostimulation

Stimulation options
A number of stimulation options can be used to improve comfort, increase battery life and add variety to the stimulation pattern (Table 1). Variety may help to prevent accommodation (an increase in the stimulation threshold of a nerve due to constant direct electrical stimulation). The most commonly used stimulation options are:
● Continuous mode
● Cycling mode
● SingleStim mode
● DualStim mode
Continuous mode
The continuous mode delivers ongoing electrical stimulation to selected nerves over a prolonged period of time, usually 24 hours (Figure 2).
 

Figure 2: Continuous mode

Cycling mode
After the patient has become used to the sensation of stimulation, the cycling mode is usually programmed because it may significantly extend battery life, whilst maintaining good pain coverage. The cycling mode automatically stimulates for specified ON and OFF times e.g., 30 seconds ON and 30 seconds OFF. The cycling mode should be used as soon after implantation as possible; the typical pattern is ON for one minute, OFF for one minute. The ON and OFF time can be increased or reduced depending on patient comfort. Due to a ‘carry-over’ effect, the patient continues to experience pain relief during the OFF part of the cycling mode. All mode selections are programmed based on the physician’s medical judgment, according to the needs of the patient.

  SingleStim mode
Stimulation modes refer to the delivery configuration of the stimulation programs. For example, in SingleStim mode, the two leads are programmed to the same amplitude, pulse width and rate, thereby producing stimulation from one channel. Using SingleStim mode, a neurostimulator can produce one stimulation pattern, or channel, by activating the electrodes on two leads for example, two 4-electrode leads, or one 8-electrode lead. As a result, amplitude, pulse width and rate are identical and in phase. Channel 2 is set to OFF
 

Mattrix®, Itrel® 3 and Synergy™ systems all have SingleStim mode capability.
 

  DualStim mode
DualStim mode increases programming options because two alternating channels are available. This provides different stimulation outputs from channel 1 and channel 2 to two sets of four electrodes for example, two 4-electrode leads, or one 8-electrode lead. The clinician can program each channel with different amplitude and pulse width stimulation parameters, although the rate remains the same for both channels and cannot be programmed differently. For example:
● Channel 1 – Rate = 40 Hz, amplitude = 5.0 V, pulse width = 210 ms
● Channel 2 – Rate = 40 Hz, amplitude = 3.0 V, pulse width = 330 ms
However, the pulses from channel 1 and channel 2 cannot occur simultaneously. Instead, pulses from both channels are interleaved (Figure 3).

Figure 3: SingleStim and DualStim outputs

Guidelines to optimize IPG battery life
Optimization of the neurostimulator battery life allows patients to avoid or delay replacement procedures. To help prolong battery life, the following procedures are often carried out:
● The cycling mode is used whenever possible and at the earliest available opportunity
● Bipolar stimulation is used because it focuses the current flow over a smaller length of the spinal cord. This results in lower resistance or load impedence
● The amplitude, pulse width and rate are set at the lowest levels providing adequate paraesthesia. The pulse width is increased before increasing the amplitude to provide good paraesthesia coverage without significantly draining the battery
● The stimulator is turned off and/or the cycling mode is used for several days to two weeks to reduce the ‘accommodation’ of the patient to stimulation
● The patient is instructed to turn the stimulator OFF when it is not needed to control pain, e.g. at bedtime
 

The Medtronic N’Vision™ programmer N’Vision™ is a small, lightweight, handheld, portable unit especially designed to allow physicians to easily adjust the 3 key parameters for stimulation (amplitude, pulse width and pulse rate) and to program the number of active contacts (anode or cathode combinations). N’Vision™ can also be used to program intrathecal drug delivery pumps. N’Vision™ eliminates the need for multiple programmers for different Medtronic neuromodulation devices. Instead, for greater convenience, N’Vision™ is compatible with both current and future Medtronic neuromodulation. N’Vision™ communicates with the neurostimulators via telemetry. The various settings for all neurostimulation devices can be changed by touching the programmer’s screen with a stylus (Figure 5).
	Figure 4: N’Vision™ programmer	Figure 5: Physician using N’Vision™ to adjust settings on a neurostimulator

N’Vision™ has been designed to simplify patient management by the inclusion of several innovative features:
● Automatic impedence measurement system to facilitate programming in neurostimulation applications
● Offers both a touch-screen and Windows-like software designed to simplify programming
● Stores up to 100 patient session files, as well as basic data on up to 1000 patients
● Provides the flexibility to print to a standard desktop printer with infrared printing support, or to the N’Vision™ portable printer

 

	←Patient ID and session data
	←Settings for stimulation waveform parameters and stimulation options
	←Programmed patient control limits
	←Clears counters for patient compliance
	←Click here to print detailed report
	←Click here to return device to settings at the start of the session
Figure 6: N’Vision™ summary screen for Synergy™

For further information on programming of Synergy™ please refer to the N’Vision™ Quickstart guide