Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-08-29
2002-09-10
Bockelman, Mark (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S030000, C600S030000
Reexamination Certificate
active
06449512
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to implantable medical prostheses, more specifically, implantable pulse generator for treating or controlling urological disorders using pulsed sacral nerve stimulation.
The method and apparatus disclosed herein may also be appropriate for the treatment of other conditions, as disclosed in co-pending application filed on Aug. 29, 2001 entitled APPARATUS AND METHOD FOR TREATMENT OF NEUROLOGICAL AND NEUROPSYCHIATRIC DISORDERS USING PROGRAMMERLESS IMPLANTABLE PULSE GENERATOR SYSTEM.
BACKGROUND OF THE INVENTION
Sacral nerve electrical neuromodulation has shown beneficial medical effects for urinary incontinence and a broad group of urological disorders. This patent is directed to a system of implantable lead and pulse generator which is programmerless, and the pulse generator being controlled by only an external magnet.
Implanted pulse generator (IPG) systems for neuromodulation generally consist of an implantable lead, an implantable pulse generator, and an external programmer for non-invasively programming the parameters of the IPG.
The programmer generally is a microprocessor-based device, which provides a series of encoded signals to the implanted pulse generator by means of a programming head which transmits radio-frequency (RF) encoded signals to pulse generator according to the telemetry system laid out in that system. Such a system requires an antenna which is connected to input/output circuit for purposes of uplink/downlink telemetry through an RF telemetry circuit.
A built-in antenna enables communication between the implanted pulse generator and the external electronics (including both programming and monitoring devices) to permit the device to receive programming signals for parameter changes, and to transmit telemetry information, from and to the programming wand. Once the system is programmed, it operates continuously at the programmed settings until they are reprogrammed (by the attending physician) by means of the external computer and the programming wand.
In such a system any programming methodology may be employed so long as the desired information can be conveyed between the pulse generator and the external programmer.
Generally, neurostimulator systems for urinary incontinence and other urological disorders work quite well, except that their manufacturing costs and corresponding selling price tends to be high and places a burden on the health care system. A significant part of the cost is attributed to the programmability of the implanted device, as well as, the computer-based programmer itself.
Historically, implantable neurostimulator technology evolved based significantly on the existing cardiac pacemaker technology. Both are essentially electrical pulse generators. However, there is one significant difference, which is, for a cardiac pacemaker to function properly it needs to sense the electrical activity of the stimulating tissue. Therefore, in a cardiac pacemaker an external programmer is an integral part of the system to program the sensitivity. A system for neuromodulation is not dependent upon sensing from the stimulating tissue such as the nerve, before providing electrical pulses.
Thus, by incorporating a limited number of predetermined/prepackaged programs into the implantable pulse generator, a significant manufacturing and development cost reduction for the system can be achieved, with very little loss of functionality.
Urinary Urge Incontinance
In considering the background of urinary urge incontinence,
FIG. 1
shows a sagittal section of the human female pelvis showing the bladder
10
and urethra
13
in relation to other anatomic structures. Urinary continence requires a relaxed bladder during the collecting phase and permanent closure of the urethra, whereas at micturition (urination), an intravesical pressure above the opening pressure of the simultaneously relaxing urethra has to be generated. These functions of the bladder and urethra are centrally coordinated and non-separable. At bladder filling, the sensation of urge is mediated by slowly adapting mechanoreceptors in the bladder wall and the same receptors provide the triggering signal for micturition and the main driving force for a sustained micturition contraction. The mechanoreceptors are, technically speaking, tension receptors. It has been found that they respond equally well to tension increases induced passively by bladder filling and those induced actively by a detrusor contraction. These receptors have high dynamic sensitivity and are easily activated by external pressure transients, as may occur during coughing or tapping of the abdominal wall. Their faithful response to active changes in bladder pressure is well illustrated.
When sufficiently activated, the mechanorecptors trigger a coordinated micturition reflex via a center in the upper pons
88
, as depicted schematically in FIG.
2
. The reflex detrusor
92
(muscle in the wall of the urinary bladder) contraction generates an increased bladder pressure and an even stronger activation of the mechanoreceptors. Their activity in turn reinforces the pelvic motor output to the bladder, which leads to a further increase in pressure and more receptor activation and so on. In this way, the detrusor contraction is to a large extent self generating once initiated. Such a control mechanism usually is referred to as a positive feedback, and it may explain the typical all-or-nothing behavior of the parasympathetic motor output to the bladder. Once urine enters the urethra, the contraction is further enhanced by reflex excitation from urethral receptors. Quantitatively, the bladder receptors are most important.
A great advantage of the positive feedback system is that it ascertains a complete emptying of the bladder during micturition. As long as there is any fluid left in the lumen, the intravesical pressure will be maintained above the threshold for the mechanoreceptors and thus provide a continuous driving force for the detrusor. A drawback with this system is that it can easily become unstable. Any stimulus that elicits a small burst of impulses in mechanoreceptor afferents may trigger a full-blown micturition reflex. To prevent this from happening during the filling phase, the neuronal system controlling the bladder is equipped with several safety devices both at the spinal and supraspinal levels.
The best-known spinal mechanism is the reflex control of the striated urethral sphincter
90
, which increases its activity in response to bladder mechanoreceptor activation during filling. An analogous mechanism is Edvardsen's reflex, which involves machanoreceptor activation of inhibitory sympathetic neurons to the bladder. The sympathetic efferents have a dual inhibitory effect, acting both at the postganglionic neurons in the vesical ganglia and directly on the detrusor muscle of the bladder
92
. The sphincter and sympathetic reflexes are automatically turned off at the spinal cord level during a normal micturition. At the supraspinal level, there are inhibitory connections from the cerebral cortex and hypothalamus to the pontine micturition center. The pathways are involved in the voluntary control of continence. Other inhibitory systems seem to originate from the pontine and medullary parts of the brainstem with at least partly descending connections.
Bladder over-activity and urinary urge incontinence may result from an imbalance between the excitatory positive feedback system of the bladder
10
and inhibitory control systems causing a hyperexcitable voiding reflex. Such an imbalance may occur after macroscopic lesions at many sites in the nervous system or after minor functional disturbances of the excitatory or inhibitory circuits. Urge incontinence due to detrusor instability seldom disappears spontaneoulsly. The symptomatic pattern also usually is consistent over long periods.
Based on clinical experience, subtypes of urinary incontinance include, Phasic detrusor instability and uninhibited overactive bladder. Phasic detrusor instability is characterized
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