Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-09-09
2001-04-17
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06219578
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the field of vestibular stimulation, and in particular to a galvanic vestibular stimulation system and method.
Galvanic vestibular stimulation has proven to be a valuable technique for studying the role played by vestibular information in the control of stance and balance. With this technique, small-amplitude galvanic current is delivered transcutaneously to the vestibular afferents that lie directly below the mastoid bones. This serves to modulate the continuous firing level of the peripheral vestibular afferents. Specifically, cathodal (negative) currents increase the firing rate of vestibular afferents, whereas anodal (positive) currents decrease the firing rate of vestibular afferents. Thus, constant bipolar galvanic current produces a tonic vestibular asymmetry. This effect causes a standing subject to lean in different directions depending on the polarity of the current and the direction of the subject's head. In general, a subject will tend to lean toward the anodal stimulus (in the direction of the vestibular apparatus with reduced afferent activity levels) and/or away from the cathodal stimulus (away from the vestibular apparatus with increased afferent activity levels).
A considerable number of studies have examined the body-sway response to constant galvanic stimulation of the vestibular system. One study, for instance, used monopolar monaural constant galvanic stimulation and demonstrated that the amplitude of the body-sway response increases linearly with increasing stimulus current (from 0.2 mA to 1.0 mA). Another study used bipolar binaural constant galvanic stimulation and showed that the direction of the evoked sway is approximately in the direction of the intermastoid line. Thus, with bipolar binaural constant galvanic stimulation, lateral sway is produced if a subject's head is facing forward, whereas anteroposterior sway is produced if a subject's head is turned to the left or right (over the left or right shoulder).
A limited number of studies have shown that the application of sinusoidally varying bipolar galvanic currents to the vestibular system can lead to sinusoidally-varying postural sway. With sinusoidal galvanic stimulation, as with constant galvanic stimulation, the body tends to sway towards the positive stimulus and away from the negative stimulus. For low-frequency stimulation, the frequency of the evoked body sway matches the frequency of the stimulus, whereas the amplitude of the evoked body sway varies from subject to subject.
SUMMARY OF THE INVENTION
The invention provides a methodology and system for altering the output of the human vestibular system in a controlled and systematic manner. The invention is based on galvanic vestibular stimulation. With galvanic vestibular stimulation, galvanic current is delivered transcutaneously to the vestibular afferents that lie directly below the mastoid bones. This serves to modulate the continuous firing level of the peripheral vestibular afferents, and causes a standing subject to lean in different directions depending on the polarity of the current and the direction of the subject's head.
The invention utilizes time-varying galvanic vestibular stimulation as the basis for an artificial vestibular control system to reduce or eliminate certain types of pathological postural sway. Such a system can include sensors, e.g., lightweight accelerometers, for monitoring an individual's postural sway, and a galvanic-stimulation control system. In such an arrangement, the sensor output would be used as input to the galvanic-stimulation control system.
A methodology and system of this sort can be used to improve balance control in elderly individuals, who are often predisposed to falls. In addition, patients with vestibular paresis, who have lost some of their hair cells and therefore have a decreased response from the vestibular system during head movement, could also benefit from such a methodology and system. The hair cells, which are responsible for indicating head tilt and acceleration, transmit their information to the vestibular nuclei via the 8
th
nerve. Galvanic vestibular stimulation acts directly on the 8
th
nerve and thus the stimulation technique can be implemented as a vestibular prosthesis to operate in place of the lost hair cells. The invention also utilizes galvanic vestibular stimulation to eliminate or enhance the function of the vestibular system. The former application of the invention can be of use to astronauts, pilots, and sailors. The latter application of the invention can be of use to individuals requiring heightened balance function.
With galvanic vestibular stimulation, small-amplitude galvanic current is delivered transcutaneously to the vestibular afferents that lie directly below the mastoid bones. This serves to modulate the continuous firing level of the peripheral vestibular afferents. Specifically, cathodal (negative) currents increase the firing rate of vestibular afferents, whereas anodal (positive) currents decrease the firing rate of vestibular afferents. Thus, constant bipolar galvanic current produces a tonic vestibular asymmetry. This effect causes a standing subject to lean in different directions depending on the polarity of the current and the direction of the subject's head. In general, a subject will tend to lean toward the anodal stimulus (in the direction of the vestibular apparatus with reduced afferent activity levels), and/or away from the cathodal stimulus (away from the vestibular apparatus with increased afferent activity levels).
With the invention, time-varying binaural galvanic vestibular stimulation is used to produce coherent time-varying postural sway. The galvanic stimulation can be monopolar or bipolar. This application of the invention is based on the aforementioned motor control effects of galvanic vestibular stimulation. With the invention, time-varying galvanic vestibular stimulation is used as the basis for an artificial vestibular control system to reduce or eliminate certain types of pathological postural sway. Such a system would consist of sensors, e.g., lightweight accelerometers, for monitoring an individual's postural sway, and a galvanic-stimulation control system. In such an arrangement, the sensor output would be used as input to the galvanic-stimulation control system.
In addition, with the invention, time-varying monopolar (anodal) binaural galvanic vestibular stimulation is used to eliminate or reduce the function of the vestibular system. This application of the invention is based on the finding that anodal (positive) currents decrease the firing rate of vestibular afferents. Similarly, with the invention, time-varying monopolar (cathodal) binaural galvanic vestibular stimulation is used to heighten or enhance the function of the vestibular system. This application of the invention is based on the finding that cathodal (negative) currents increase the firing rate of vestibular afferents.
For each of these applications, at least two surface electrodes are placed on the mastoid bones of each subject, one behind each ear, in order to apply the galvanic vestibular stimulation. The appropriate stimulation signals are generated on a microprocessor, e.g., a computer chip, and transmitted to the electrodes via a D/A system and isolation unit.
One advantage of the invention is that it utilizes and exploits the features of existing sensory neurons via non-invasive means. In particular, it uses galvanic stimulation signals to alter the firing behavior of peripheral vestibular afferents. In this manner, the invention can modify the dynamics of the human postural control system.
The invention as described includes the utilization of galvanic vestibular stimulation. A possible future modification of this methodology would be to utilize other forms of stimulation, such as mechanical vibration, to alter the output of the human vestibular system.
The invention provides a non-invasive means for altering the output of the human vestibular system in a contro
Collins James J.
Inglis J. Timothy
Getzow Scott M.
Samuels , Gauthier & Stevens, LLP
Trustees of Boston University
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