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SYSTEM AND METHOD FOR GAIT SYNCHRONIZED VIBRATORY STIMULATION OF THE FEET
CROSS REFERENCE TO RELATED
 This application claims the benefit of U.S. Provisional Patent Application No. 60/556,665, filed Mar. 26, 2004, titled "A Device for Gait Synthesized Vibratory Stimulation of the Feet," the entire contents of which are hereby incorporated herein by reference.
STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION  1. Field of the Invention
 This invention is generally related to foot stimulation devices and methods and relates more particularly to a device and method for stimulating foot mechanoreceptors in synchrony with the phase of the gait.
 2. Description of Related Art
 Increased stride-to-stride variability has been associated with neurological gait abnormalities as well as falls. Previous studies suggested that alterations of the proprioceptive feedback using vibratory stimulation might affect the gait.
 Somatosensory feedback plays a critical role in the control of movement, balance and gait. Alterations of the proprioceptive feedback can alter balance, posture and/or gait. For example, vibratory stimulation of muscles facilitates voluntary muscle contractions. Vibratory stimulation of the foot elicits postural responses that control maintenance of the erect posture. Vibration of the feet with noise-like vibration improves motor control in humans by reducing postural sway. Vibrators applied to calf muscles or with galvanic vestibular stimulation enhances recovery of postural functions in post stroke patients In healthy volunteers, plantar stimulation results in a body tilt, affects the postural adjustment to upright posture and may improve balance. Vibratory stimulation of the leg muscles facilitates voluntary muscle contractions. Increase in walking speed is observed during continuous vibration of the neck and hamstring muscles. Moreover, vibration of the biceps femoris tendon affects the interlimb coordination.
 Sensory stimulation has been explored in treatment of several neurological conditions associated with movement abnormalities. For example, vibratory stimulation of muscle tendons can reduce parkinsonian tremor. Vibrators applied on the calf muscles facilitate recovery of postural control in post-stroke patients. Plantar stimulation improves the rightward orientation in patients with spatial neglect after the right hemispheric stroke.
 The shortcoming of commonly used approaches is that they do not take into account the phase of the gait. Foot proprioceptors are activated upon a foot step and deactivated upon elevation of the foot. As such, a device that delivers the
vibration stimulus at a particular phase of the gait could enhance the beneficial effect of vibratory stimulation upon the gait.
 In a particular case, short shuffling steps, reduced walking speed and increased stride variability are the hallmarks of abnormal gait in Parkinson's disease (PD). Abnormal proprioception and impaired kinesthesia may contribute to the parkinsonian gait. PD patients have reduced sensation on the plantar feet, impaired joint position sense, movement perception and movement accuracy. Neurophysiological and functional imaging studies have shown that sensory processing is impaired at a central level.
 In PD, abnormal proprioception may result from an inadequate integration of sensory inputs at the striatum, or from a defective proprioceptive feedback. Clinically, the role of abnormal proprioceptive feedback in generation of PD gait pattern remains unclear. The plantar mechanoreceptors that mediate postural adjustment are activated by the foot pressure during the touch down and stance phases of the step, and can be also activated by the vibration stimulation at 70 Hz.
BRIEF SUMMARY OF THE INVENTION
 In accordance with the present invention, a vibration stimulation of peripheral mechanoreceptors during particular portions of a gait is provided. The stimulation enhances sensory feedback, and facilitates proprioceptive processing in PD, for example. A device according to the present invention delivers vibration stimulation to the soles during an interval that includes a portion of a stance part of a step. The stimulation is may be selectively omitted during a swing phase of each step. Operation of the device may be achieved using a simple closed-loop control. In accordance with the present invention, proprioceptive input during a gait is enhanced using step-synchronized vibration stimulation in healthy and PD subjects.
 In accordance with the present invention, a device and method delivers a vibratory stimulus that is synchronized with the phase of the gait. The device senses the foot pressure at the heel, and upon satisfying predetermined conditions such as, for example, a certain pressure level, delivers vibration stimulus to the forefoot. A vibrator stimulator such as an electric motor with an eccentric load or a piezo-based vibrator can be used.
 In one embodiment, the device consists of a footswitch that turns on the vibration motor upon the foot step. A micro switch and miniature vibrator motor with eccentric load, i.e., a "pager motor," (Namiki, Japan, diameter 4 mm) may be used and are implantable inside the shoes. The device may be embodied into a plastic enclosure of the size 2.5x2.5x0.8 cm. Typically, two or three units are installed into one shoe, one below the heel and one to two unites below the fore heel or fore foot.
 The whole unit is inserted into the modified shoes. It is very simple in use and non-invasive. The effectiveness of vibratory stimulation depends upon the phase of the gait, and the stimulation becomes more effective during a swing phase as compared to a stance phase.
 The advantage of the invented device is that the vibratory stimulation is synchronized with the phase of the
gait. The pulsatile stimulation reduces habituation of the mechanoreceptors and prolongs the battery life.
 According to one embodiment, the device consists of a footswitch and vibrator motor. The device in this embodiment is simple and easy to manufacture in large quantities.
 According to another embodiment, the device accommodates a timer that turns off the vibration after predefined delay to prevent continuous stimulation when the subject stands without movement or sits. According to an advantage of the invention, control is performed by using pressure sensors to obtain an output signal activated by the pressure at the sole. This pressure signal can be processed by a microcontroller/microprocessor, sampled typically using an analog/digital converter. After processing, the microprocessor controls the vibrator motor, typically via a digital/ analog converter or other interface.
 A microcontroller/microprocessor based system enables considerable flexibility in control of the desired vibratory stimulus in terms of gait phase, stimulus duration and intensity as well as interrelation between two stimuli when more than one vibratory device is used. A variety of stimulatory patterns can be employed such as a preemptive stimulation, typically applied a short time before the foot touches the floor, to facilitate response of the locomotory apparatus. Other patterns include stimulation of the fore heel that is phase-shifted from below-heel stimulation and phasecorrelated stimulation of a contralateral foot portion.
 The present invention features synchronization of the vibratory stimulation with the phase of the gait. Accordingly, treatment of variety of gait disorders such as primary gait disorders, gait disorders associated with systemic illness, gait disorders associated with stroke, Parkinson's disease, dementia, multiple sclerosis, aging, etc., may be treated.
 The invention may be battery operated and accommodate recharging/replacement of the batteries. The invention may be waterproof, and suitable for outdoor use. Advanced microprocessors/microcontrollers may be used to obtain greater efficiency and control, permitting activities such as data collection and analysis.
 The device can be made to be extremely cost effective. The estimated wholesale price of one unit is on the order of several dollars. This cost can be substantially reduced if built in large quantities. The potential market is enormous, with the estimated number of subjects that might benefit from the device being on the order of millions in the U.S. alone.
BRIEF DESCRIPTION OF THE SEVERAL
VIEWS OF THE DRAWINGS
 The invention is described in greater detail below with reference to the accompanying drawings, in which:
 FIG. 1 is a block diagram of a device according to the present invention;
 FIGS. 2A-2C are diagrams of a device and placement and operation embodiments;
 FIGS. 3A and 3B are graphs showing stride intervals in a healthy control subject;
 FIG. 4 is a graph showing standard deviation of stride intervals during on and off periods of vibration in a Parkinson's disease patient;
 FIG. 5 is a plan view of an exemplary embodiment of the present invention;
 FIG. 6 is a cross-sectional cutaway view of an exemplary embodiment of the present invention;
 FIG. 7 is a graph showing stride intervals in test subject without foot stimulus; and
 FIG. 8 is a graph showing stride intervals in a test subject with foot stimulus.
DETAILED DESCRIPTION OF THE
 The present invention is the result of a study to assess the effect of vibratory stimulation of the soles of a subject's feet that is synchronized with their step. One variable studied was that of gait variability. Step-synchronized vibratory stimulation (SSV) of the soles was evaluated in 7 healthy subjects (4 females and 3 males, age range 28-53 years) during self-paced normal walk. Stride-to-stride interval was measured using force foot-switches connected to a wearable computer. The device for SSV was mounted into shoe insoles. The vibratory device operates in the closed-loop mode and it is activated upon heel strike and turned off during a push off phase. One observed result is that SSV decreased the standard deviation (p<0.014) and coefficient of variation (p<0.016) of the gait. No statistical difference in other monitored parameters such as walking distance, average speed and step duration, average step length was observed. The observed results indicate that the closed-loop step-synchronized vibratory stimulation of the soles reduced the stride-to-stride variability in healthy subjects. Since the stride-to-stride variability is positively correlated with gait abnormalities, the present invention is apparently useful for treatment of gait disorders.
 To assess the effects of vibratory stimulation on gait, a wearable vibratory device that can be used during normal walking was provided. The mechanoreceptors of the soles that mediate postural adjustment are sensitive to vibratory stimulation and the pressure created during the stance phase of the step activates these receptors. The device delivers a vibratory stimulus to the sole while the foot is in contact with the floor.
 The wearable, battery operated device in an exemplary embodiment of the present invention gives a vibratory stimulus synchronized with stance phase of the gait was designed. FIG. 1 illustrates vibratory device 10, which senses pressure at the sole and turns on vibration upon heel touch and turns off upon push off during swing phase. Device 10 is mounted in the shoe insoles that can be inserted into regular shoes. The stimulus intensity was empirically set to a near-threshold level.
 The subjects felt the stimulation slightly while standing. Upon walking, the subjects sensed vibration typically only when specifically asked to focus on vibratory sensation at their feet.
 Subjects were asked to walk for 6 minutes at their normal speed in a hallway with a length of 73 m and a width of 1.7 m with the device on and 6 minutes with the device