Abstract:
A measurement device for measuring activity of the spinal cord of a vertebrate, wherein the device includes at least one main probe ( 1 ) shaped to be fastened to a spinous process ( 2 ) of a vertebra ( 3 ) and to hold in position on opposite sides of the vertebra at least one emitter ( 6 ) for emitting a wave capable of interacting with the spinal cord ( 7 ) and at least one associated receiver ( 8 ) for receiving the wave that has interacted with the spinal cord and for generating a signal representative of the activity of the spinal cord.

Description:
[0001]    The invention relates to a device for measuring activity of the spinal cord of a vertebrate. 
         [0002]    The term “activity” is used herein to mean any variation in an optical, chemical, or physical property of the spinal cord that may characterize in particular a neural reaction to a motor or cognitive action. 
       BACKGROUND OF THE INVENTION 
       [0003]    A motor action results from a set of energetic processes leading a nerve signal via the spinal cord to effector organs. A partial or total lesion of the spinal cord leads to a degeneration of the nerve pathways that can no longer transmit signals to the spinal neurons beyond the lesion, which can lead to paralysis and also to an interruption of the upward pathways towards the brain, thereby leading to an abolition of sensation. 
         [0004]    Understanding the mechanisms for conveying nerve signals along the spinal column is necessary in order to develop the most effective possible therapeutic treatments. 
         [0005]    It is known that variability in the distribution of oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (Hb) can be observed from the blood vessels and capillaries irrigating the neural regions of the cortex and of the spinal column during cognitive or motor activity. 
         [0006]    By relying on an optical imaging device that enables these variations in blood volume and oxygenation to be detected, it has been possible to study the neural tissues of the brain. Nevertheless, the technology used is of too great a size to be placed on some other portion of the body or to be implanted continuously in a vertebrate. Whereas trepanation suffices to gain access to brain tissue, gaining access to medullary tissue is more difficult and requires a laminectomy. Finally, the known optical imaging device mainly comprises optical fibers, and such fibers are difficult to use in the spinal cord since their shape makes it difficult for them to be integrated in simple manner in order to measure the hemodynamic response. 
         [0007]    At present, the main means for studying the spinal cord as a whole thus remains magnetic resonance imaging (MRI) which enables the cord to be viewed and medullary tissues to be analyzed. Nevertheless, such study remains external, and neural activity perceived in the medullary tissues is scrambled and difficult to interpret from one patient to another. 
       OBJECT OF THE INVENTION 
       [0008]    An object of the invention is to provide an implantable device enabling activity of the spinal cord of a vertebrate to be measured, while overcoming the above-mentioned drawbacks. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0009]    In order to achieve this object, the invention proposes a measurement device for measuring activity of the spinal cord of a vertebrate, the device comprising at least one main probe shaped to be fastened to a spinous process of a vertebra and to hold in position on opposite sides of the vertebra at least one emitter for emitting a wave capable of interacting with the spinal cord and at least one associated receiver for receiving the wave that has interacted with the spinal cord and for generating a signal representative of the activity of the spinal cord. 
         [0010]    The main probe is put into place very simply by making an incision in register with the vertebra concerned and by splaying apart the muscles on either side of the vertebra so that the probe can be placed astride it. All that then needs to be done is to fasten the main probe to the spinous process by means of screws or adhesive. The surgery is thus simple and fast. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention can be better understood in the light of the following description with reference to the figures of the accompanying drawings, in which: 
           [0012]      FIG. 1  is a perspective view of a vertebra fitted with a main probe of the invention; 
           [0013]      FIG. 2  is a cross-section view of the vertebra fitted with a main probe as shown in  FIG. 1 ; 
           [0014]      FIG. 3  is a perspective view of the main probe shown in  FIG. 1 ; 
           [0015]      FIG. 4  is a cross-section view of a vertebra fitted with a main probe and with an associated auxiliary probe of the invention; and 
           [0016]      FIG. 5  is a perspective view of the auxiliary probe shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The invention is shown in an application to a cat vertebra. This application is naturally not limiting. 
         [0018]    With reference to  FIGS. 1 to 3 , the measurement device of the invention comprises a main probe  1  shaped to be fastened to a process  2  of a vertebra  3 . The main probe  1 , made of a resin that is transparent to infrared radiation, is in the form of a fork  4  having two tines  4   a,    4   b  and a handle  5  that extends projecting the fork  4 . 
         [0019]    This shape enables surgery to be simplified, the surgeon needing to do no more than splay apart the muscles situated on the sides of the vertebra  3  and place the fork  4  on the process  2  in the direction shown by the arrow in  FIG. 1 . In this position, the fork  4  is astride the portion of the vertebra that forms the medullary canal and the handle  5  extends facing the process  2 . The main probe  1  is then preferably fastened via its handle  5  to the process  2 , e.g. with a biocompatible adhesive, or indeed with a titanium screw. 
         [0020]    The tine  4   a  carries an infrared emitter  6 , and the radiation therefrom passes through the spinal cord  7  of the vertebra and, after interacting with the medullary tissue, it is picked up by an infrared receiver  8  carried by the other tine  4   b.  The infrared radiation passes through the bony wall and interacts with the hemoglobin of the blood contained in the cord  7 , thereby making it possible to track vascular activity of the cord  7  when it is stressed. The receiver  8  transforms the radiation it receives into an electrical signal representative of this vascular activity, itself representative of neural activity. 
         [0021]    The main probe  1  includes electronic means  9  for transforming this electrical signal into digital data. In this example, the digital data is stored in a memory and transmitted subsequently. For this purpose, the main probe  1  includes an infrared emitter  10  and an infrared receiver  11  for communicating in binary frames with an infrared transceiver remote from the main probe  1 . Alternatively, the digital data is transmitted in real time without being stored. 
         [0022]    The digital data as generated in this way is advantageously sent to a remote transceiver D in order to track the vascular activity of the spinal cord in response to a simulation thereof. By way of example, the transceiver may be associated with an external control unit adapted to control actuators acting on the organism of the vertebrate in order to mitigate an insufficiency thereof. For example, the control unit may be used to control a pump or an implant delivering a chemical in response to detecting activity of the cord by means of the main probe. 
         [0023]    In this example, the main probe  1  is powered electrically from a circuit external to the main probe  1  that delivers a varying magnetic field, thereby causing a current to appear in an antenna  12  that, in this example, is arranged on the handle  5 . The electronic means  9  are adapted to condition the potential induced in the antenna  12  so as to produce a potential that is directly usable by the main probe  1 . In this example, in order to enable the probe to operate even while distant from the inductive source, it is preferable to use this potential to charge an on-board battery  13 . 
         [0024]    With reference to  FIGS. 4 and 5 , and according to a particular aspect of the invention, the remote transceiver D may be associated with an auxiliary probe  14  implanted inside the vertebra  3 , so as to come into direct contact with the spinal cord  7 . In a preferred mode of implantation, once the muscles surrounding the vertebra have been splayed apart, the surgeon performs a laminectomy on the vertebra, inserts the auxiliary probe  14  in the medullary canal, and reconstructs the vertebra using a polymer resin. With reference to  FIGS. 3 ,  4 , and  5 , and in a preferred mode of stabilization, the position of the auxiliary probe  14  is stabilized by a magnetic connection with the main probe  1 : each probe has magnets  15 ,  16  with the magnets in a given probe having the same polarity, opposite to that of the magnets of the other probe. The vertebra  3  is sufficiently thin to enable the magnets  15 ,  16  to attract mutually through the bony wall, thereby stabilizing the auxiliary probe  14  relative to the main probe  1 . This fastening is advantageous compared with fastening using surgical sutures in that it simplifies the surgical operation. 
         [0025]    The auxiliary probe  14  may perform several functions:
       measuring neural activity of the spinal cord  7 . For this purpose, the auxiliary probe  14  includes a sensor  17  responsive to the presence of certain biological molecules in the cerebrospinal liquid, and producing an electrical signal. The auxiliary probe  14  includes electronic means  18  for transforming this signal into digital data; and   stimulating neural activity of the spinal cord by chemical and/or electrical means. For this purpose, the auxiliary probe  14  includes a tank  19  having a diaphragm and serving to store chemical compounds; a micromotor  20  co-operates with the diaphragm to move it selectively, thereby causing the chemical compounds to be expelled into the spinal cord  7 . In addition, electrodes  21  may impose a local potential on the axons of the spinal cord  7  that are in contact with the electrodes  21 .       
 
         [0028]    In this example, the transceiver D of the auxiliary probe  14  comprises an infrared emitter  22  and an infrared receiver  23  that communicates by binary frames with the infrared emitter  10  and the infrared receiver  11  of the main probe  1 . Thus, no wired connection is needed between the two probes in order to transmit the data generated by the electronic means  18  or to receive orders from the main probe  1 . Similarly, the auxiliary probe  14  is powered wirelessly: in a preferred device, an antenna  24  is in communication by induction with the antenna  12  of the main probe  1 . The electronic means  18  are adapted to condition the potential induced in the antenna  24  into a potential that is usable directly by the auxiliary probe  14 . In this example it is preferable to use this potential for charging an on-board battery  25 . 
         [0029]    It should be observed that the auxiliary probe needs to be miniaturized because it is implanted very close to the spinal cord, which is an organ that is extremely sensitive. As a result of its size, the length of time the auxiliary probe can run is limited and it needs to be connected to a probe of greater size, here the main probe, in order to be powered regularly. 
         [0030]    The invention is not limited to the above description and covers any variant coming within the ambit defined by the claims. 
         [0031]    In particular, although it is stated that communication between the auxiliary probe  14  and the main probe  1 , and also between the main probe  1  and a transceiver remote from the main probe  1  takes place by infrared radiation, it is possible to use any other mode of communication such as radiofrequency identification (RFID) communication, or indeed for the communication between the main probe  1  and the remote transceiver to be communication by means of wires. Furthermore, although it is stated that the main probe  1  uses a common communications system for communicating with the auxiliary probe  14  and with the transceiver remote from the main probe, it is naturally possible to provide a probe that possesses two distinct communications systems. 
         [0032]    Although the main probe  1  is described as having a system for measuring activity of the spinal cord  7  by emitting electromagnetic waves in the infrared, it is possible to use other known techniques, such as emitting ultrasound waves. 
         [0033]    Although the auxiliary probe is described as being implanted inside a vertebra  3  in order to be in direct contact with the spinal cord  7 , more generally it is possible to implant the auxiliary probe in contact with any functional tissue. 
         [0034]    In a variant, it is possible to envisage coupling the auxiliary probe to an osmotic pump of the Alzet type.