Abstract:
An improvement for a programmable valve system of the type implanted in a patient and used to divert cerebrospinal fluid (CSF) from an intraventricular space to a terminus such as the peritoneal cavity. Such system includes means for establishing a flow path for the CSF to the terminus, which flow path includes a normally closed valve and means for adjusting the opening pressure of the valve in order to regulate the quantity of CSF diverted. The improvement enables an operator to be apprised of the actual opening pressure setting of the valve. A sensor is implantable at the patient and responds to the actual opening pressure setting, by generating an NIR telemetry signal indicative of the actual setting. This signal is transcutaneously transmitted through the skin of the patient to an external point. The telemetry signal is processed to produce observer intelligible data indicating the opening pressure setting of the valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-In-Part claiming priority benefit from U.S. patent application Ser. No. 11/067,497 entitled “Transcutaneous Telemetry Of Cerebrospinal Fluid Shunt Programmable-Valve Pressure Using Near-Infrared Light” filed on Feb. 25, 2005 now U.S. Pat. No. 7,484,105 which claims priority from U.S. Provisional Applications 60/547,691 filed Feb. 25, 2004; 60/577,807 filed Jun. 8, 2004; and 60/582,337 filed Jun. 23, 2004. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to transcutaneous telemetry with an implantable biomedical device, and more specifically relates to a system which allows transcutaneous telemetry of a programmed valve opening pressure via near-infrared (NIR) light. 
     BACKGROUND OF THE INVENTION 
     Fluidic shunts are commonly employed for the diversion of cerebrospinal fluid from the cranial intraventricular space to a terminus such as the peritoneal cavity in the treatment of hydrocephalus. The quantity of cerebrospinal fluid (CSF) diverted by the shunt may be altered by adjusting the opening pressure of a normally closed integral valve. Several valve designs (e.g. Codman-Hakim® valve, Medtronic Strata® valve) allow transcutaneous adjustment, or programmability, of the opening pressure via a transcutaneously applied magnetic field. 
     The programmed valve pressure is dependent upon the position of the external programmer relative to the implanted valve. Because the valve is implanted beneath the skin, the exact orientation of the valve is not always apparent. Malpositioning of the programmer can introduce errors into the programming process and result in erroneous pressures being programmed. Therefore, it is desirable to be able to confirm the actual programmed pressure after reprogramming or as clinical conditions warrant. By “actual” programmed pressure is meant the de facto pressure which has been set for opening of the valve as opposed to the pressure which may be assumed to have been set as a result of the operator&#39;s manual adjustment. 
     While the Medtronic Strata® valve provides a transcutaneous means of magnetically indicating the valve pressure setting, the Codman-Hakim valve requires the use of an x-ray to determine the valve setting. The use of x-ray to determine valve pressure is undesirable as it is costly, time-consuming, and exposes the patient to ionizing radiation. 
     SUMMARY OF INVENTION 
     The invention disclosed herein provides an improvement pertinent to existing programmable valve systems which allows transcutaneous telemetry of programmed valve opening pressure via near-infrared (NIR) light. NIR light easily penetrates body tissues such as the scalp, and the light beam may be modulated to encode data for transcutaneous transmission. The actual valve pressure setting is determined by an attached cam. An optical disc coaxially mounted with the cam optically encodes the valve position and these data are transmitted extracorporally via NIR light. 
     Light in the near-infrared spectrum is easily transmitted through the skin and is detected by an external sensor head and associated electronics. Indefinite longevity and small size is attained in the implant by not incorporating a power source within the module. Instead, power is derived inductively through rectification of a transcutaneously-applied high-frequency alternating electromagnetic field which is generated by a power source within the external coupling module, in concept much like a conventional electrical transformer. The extracorporeal components of the system calculate the actual valve opening pressure setting. 
     The present invention overcomes the aforementioned disadvantages of existing technologies by providing a means for telemetric conveyance of physiological data via transcutaneous projection of a near infrared light beam. The use of this technique for telemetry of intracranial pressure and other applications is set forth in U.S. Pat. No. 7,435,229 to Wolf filed Feb. 24, 2005. The entire disclosure of that application is hereby incorporated herein by reference. 
     The NIR spectrum is defined as 750-2500 nm. Choice of the preferred NIR wavelength for transcutaneous telemetry pursuant to the present invention is dependent upon the absorption coefficients of the intervening tissues. The absorption by melanosomes dominates over the visible and near-infrared spectra to about 1100 nm, above which free water begins to dominate. Absorption by the dermis decreased monotonically over the 700-1000 nm range. Whole blood has a minimum absorption at about 700 nm but remains low over the 700-1000 nm range. The nadir in the composite absorption spectrum therefore lies in the 800-1000 nm range. 
     The actual wavelength utilized is therefore dictated by-the optimal spectral range (as above) and the availability of suitable semiconductor emitters. Several suitable wavelengths may include, but are not limited to: 760 nm, 765 nm, 780 nm, 785 nm, 790 nm, 800 nm, 805 nm, 808 nm, 810 nm, 820 nm, 830 nm, 840 nm, 850 nm, 870 nm, 880 nm, 900 nm, 904 nm, 905 nm, 915 nm, 920 nm, 940 nm, 950 nm, 970 nm, and 980 nm. Wavelengths outside this range may be used but will be subject to greater attenuation by the intervening tissues. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention is diagrammatically illustrated, by way of Example, in the drawings appended hereto, in which: 
         FIG. 1  is a simplified longitudinal cross sectional diagram illustrating how the sensor may be implanted in a typical use with a patient; 
         FIG. 2  is a schematic diagram, partially in block form, illustrating an overall system in accordance with the invention; 
         FIG. 3  is an electrical schematic diagram of the valve pressure transducer and associated components; and 
         FIG. 4  is a schematic block diagram of the valve position sensor components which are external to the patient. 
         FIG. 5  is a non-schematic diagram of the relationship and positioning of the optical encoder and magnetic flux coupling of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The system of the present invention as shown in the simplified crosssectional view of  FIG. 1  includes an extracorporeal sensor head  70  which provides an interface to a human operator and which telemeters with an implanted component  14 . The latter is integrated into the shunt-valve housing, detects the actual valve setting, and telemeters these data to the extracorporeal sensor head  70 . The implanted component  14  may derive its power via inductive coupling from the extracorporeal sensor head  70 . 
     In a typical in vivo implementation a hollow ventricular catheter  3  is placed surgically into a cerebrospinal fluid (CSF) filled ventricle  2  of the brain  6  of the patient. The CSF is communicated via the ventricular catheter  3  to the implanted component  14  where its flow is controlled by controllable pressure valve  18  ( FIG. 2 ). The normally closed valve opening pressure setting is controlled by an attached cam which is mounted on a rotatable axis. An optical disc on that axis acts with other elements to encode the valve position, data for which is transmitted extracorporally through skin  20  via NIR light to sensor head  70 . Depending on valve position, the CSF may exit the implanted sensor  14  and passes, via distal catheter  4 , ultimately to the peritoneal cavity of the abdomen (not shown) or other appropriate point. The implanted sensor  14  is installed superficial to, or embedded within the skull  5 . 
       FIG. 2  depicts a schematic block diagram of a preferred embodiment of the ICP Valve transducer system.  FIG. 5  shows a non-schematic diagram of the relationship and positioning of the optical encoder disk and magnetic flux coupling. External programmer  16  is an extracorporeal device which is used to set the opening pressure of a programmable pressure valve  18  which is implanted beneath the skin (scalp)  20  of the patient. The opening pressure of normally closed valve  18  dictates the maximum pressure gradient between the cerebrospinal fluid compartment which is connected to inlet  22  to valve  18 , and the outflow for which is via outlet  24 . The valve  18  pressure setting is dependent upon the position of a cam which rotates around the valve&#39;s mechanical axis  26 . 
     The external programmer  16  is able to modify the rotational position of the valve  18  and mechanical axis  26  via magnetic flux coupling  28  between an external magnet  30  and a magnet  32  fixedly attached to the mechanical axis  26  of the valve mechanism. The technology referenced by items  16  through  32  is described in the prior art. 
     In prior art valves exemplified by valve  18 , detents within the valve mechanism define specific rotational angles in which the valve mechanism axis  26  may remain in a static position. In the preferred embodiment of the current invention, an optical encoder disc  34  secured to axis  26  is an optically opaque disc with radially oriented perforations (or optically transparent windows) which encode binary numerals. Each specific static rotational angle which may be assumed by the valve mechanism axis  26  has a corresponding unique encoded binary numeral, n. An NIR light beam  36  transilluminates the optical encoder disc  34  such that the binary encoded numeral, n, may be detected by photodetector array  38 . In the preferred embodiment, these encoded numerals are arranged sequentially around the disc  34  ranging from 1 to ‘N’ where N is the total number of discrete static positions of the valve mechanism axis  26 . A valid encoded numeral, n, is detected by the photodetector array  38  only during transillumination of the encoder disc  34  by NIR light beam  36 . A “data valid” command is generated by logical OR of each of the bits of the binary encoded numeral, n, or by using a single separate photodetector with an additional optical window at each discrete static position of the valve mechanism axis  26 . The “data valid” signal provides a ‘load’ command  40  to a latch  42  which stores the encoded binary numeral, n. 
     The encoded binary numeral, n, is used as the divisor for a divide-by-n counter  44 . A crystal oscillator  46  provides a stable reference frequency  48 , f in , which is divided by the divisor ratio, n. Therefore, the output frequency  50 , f out , is uniquely dependent upon the valve mechanism axis  26  position, and hence the pressure to valve  18 . The near infrared emitter  52  is driven at the output frequency  50 . The infrared beam  54  is passed through a beam-splitter mirror  56  such that a portion of the infrared light beam  36  is used to transilluminate the optical encoder disc  34 . The remainder of beam  54  travels through the skin  20  to become the transcutaneous NIR beam  58 . The transcutaneous beam  58  is detected by a photodetector  82  within sensor head and processing electronics  62  after passing through a narrow bandpass filter  64 . The narrow bandpass filter  64  excludes ambient light at wavelengths other than that expected from the NIR emitter  52 . The frequency of the photodetector  82  output is measured at  63  and is used to index a look-up table  60  which correlates the modulation frequency  50  with the actual valve pressure setting which is then displayed at  68 . 
       FIG. 3  illustrates representative electronic circuitry for the implant. A crystal oscillator composed of crystal X 1 , inverters U 1   a - c , capacitors C 1 , C 2  and feedback resistor R 9 , provides a reference frequency to programmable divider U 2 . The reference frequency is divided by n and the output used to gate the VCSEL, D 3 , via transistor Q 7 . Transistor Q 8  and resistor R 8  act to regulate the maximum current through D 3 . 
     Light from the VCSEL is detected by an array of photodetectors Q 1 -Q 6 . During VCSEL illumination, the disc  34  ( FIG. 2 ) allows selective illumination of phototransistors Q 2 -Q 6 , thus providing a binary representation of the frequency divisor. The light path from the VCSEL to Q 1  is never obstructed, despite the position of disc  34  so that Q 1  conducts each time the VCSEL illuminates. The output of Q 1  is fed to inverter U 1   d  which, in turn, asserts a positive-going ‘load’ signal to U 2  as the VCSEL illuminates. Upon assertion of the ‘load’ signal, the frequency divider divisor data is latched on U 2  inputs D 0 -D 4 . A small capacitance, on the order of several picofarads, may be placed on the base of transistor Q 1  to allow Q 2 -Q 6  to stabilize prior to asserting the ‘load’ signal. A period of 2 N  clock pulses may be necessary for the output frequency to stabilize. 
       FIG. 4  depicts a block diagram of the external circuitry which: 1) provides power to the implant; 2) detects the NIR emission from the implant; and, 3) converts the frequency data from the implant to a graphical representation of valve position. 
     Sensor head  70  is placed over the implant to deliver power and detect the optical output of the implant. A power oscillator  72  delivers a sinusoidal oscillating current with a nominal frequency of 200 kHz to a power amplifier  74  which buffers the current to an isolation transformer  76 . The isolation transformer  76  provides adequate galvanic isolation for a patient-connected device. The output from the isolation transformer is fed to the sensor head coil  78  which acts as the primary winding of a transformer to electromagnetically couple energy to the implant&#39;s secondary coil L 1  ( FIG. 3 ). 
     An optical bandpass filter  64  with center frequency equal to the emission frequency of the VCSEL, excludes ambient light from the photodetector  82 . Light from the implant VCSEL is transmitted through bandpass filter  64  and converted to an electrical current by photodetector  82 . This current is roughly a square wave with the same fundamental frequency as the VCSEL pulses. This signal is amplified by pre-amp  84  and automatic gain amplifier  86 , then converted to a digital signal by Schmitt trigger  88 . A serial data stream  90 , consisting of squarewave pulses, is fed to microprocessor  92  which measures the frequency of the aforementioned pulses. The frequency data is then used to index a look-up table  60  ( FIG. 2 ) through software programming; the result of which is a numerical indication of the valve pressure setting. The result is displayed for the user upon a digital or other graphical display  68 . 
     A bi-colored Light Emitting Diode, or LED, is also included in the sensor head  70  to aid positioning of the sensor head over the implant. In the default state, the red LED  96  is illuminated to indicate that the sensor head is not over the implant. When the sensor head is properly aligned over the implant, the implant begins to receive power through the inductive coupling between coil  78  of the sensor head and L 1  of the implant. Once power is applied to the implant, the VCSEL begins to illuminate in synchrony with the programmable divider (U 2 ) output. When the External device begins to detect the VCSEL, e.g. oscillations present on the ‘serial data’ output of Schmitt Trigger  88 , the microprocessor  92  turns off the red LED  96  and illuminates the green LED  94 . 
     While the present invention has been described in terms of specific embodiments thereof, it will be understood in view of the present disclosure, that numerous variations upon the invention are now enabled to those skilled in the art, which variations yet reside within the scope of the present teaching. Accordingly, the invention is to be broadly construed, and limited only by the scope and spirit of the claims now appended hereto.