Abstract:
Apparatus for treating obstructive blood flow disorders, is provided, including ( 1 ) an external device, configured for placement outside of a body of a subject and to sense a factor of the subject, and to generate a signal in response to the sensed factor, and ( 2 ) an implant, which comprises a wireless receiver for receiving the signal, and an effector element, the implant configured and positioned to alter a blood flow of the subject in response to the signal.

Description:
FIELD OF THE INVENTION 
       [0001]    Some applications of the present invention generally relate to medical apparatus. Specifically, some applications of the present invention relate to apparatus and methods for treating blood circulation disorders, particularly, congestive heart failure and associated symptoms. 
       BACKGROUND 
       [0002]    Heart failure is a condition in which a problem with the structure or function of the heart impairs its ability to supply sufficient blood flow to meet the body&#39;s needs. The condition impairs quality of life and is a leading cause of hospitalizations and mortality in the western world. Treatment of heart failure is typically aimed at removal of precipitating causes, prevention of deterioration in cardiac function, and control of congestive state. 
       SUMMARY OF THE INVENTION 
       [0003]    In some applications of the invention, an external device is used to detect one or more factors associated with a blood flow disorder of a subject. The external device transmits a signal, which is received by an implant. The implant is configured and positioned to alter a flow of blood of the subject, and alters the flow of blood of the subject at least in part responsively to the received signal. Typically, the apparatus is configured to operate only when the external device is located in proximity to the subject. For example, in some applications of the invention, the external device is located in, near or under a bed of the subject, such that detection of the factors by the external device, and detection of the signal by the implant, occur only when the subject is in the bed. 
         [0004]    In some applications of the invention, the implant alters blood flow by variably occluding a blood vessel of the subject. In some applications of the invention, the implant functions by variably constricting a blood vessel of the subject. In some applications of the invention, the implant functions by providing a variable fistula between two blood vessels. 
         [0005]    In some applications of the invention, the implant receives power wirelessly. In some applications, the implant receives power via electromagnetic induction. In some applications, the implant receives power via electromagnetic radiation. 
         [0006]    There is therefore provided, in accordance with an application of the present invention, apparatus for altering blood flow of a subject, the apparatus including an implant, the implant including: 
         [0007]    a receiver, configured to wirelessly receive a signal generated in response to a detection of a symptom of congestive heart failure (CHF); 
         [0008]    an effector element, being disposable in a vicinity of a portion of a circulatory system of the subject; and 
         [0009]    a driver unit, coupled to the receiver, and configured to drive the effector element to reduce pulmonary blood flow, at least in part responsively to the signal. 
         [0010]    In an application, the implant is configured to receive power from the signal. 
         [0011]    In an application, the implant is configured to receive power via magnetic induction. 
         [0012]    In an application, the effector element includes a tubular element, the tubular element being disposable between two hollow structures of the subject, and configured to provide fluid communication between the two hollow structures of the subject, and the driver unit is configured to reduce the pulmonary blood flow by altering a blood flow through the tubular element. 
         [0013]    In an application, the driver unit is configured to alter the blood flow through the tubular element by altering a cross-sectional area of a lumen defined by the tubular element. 
         [0014]    In an application, the apparatus includes a pump, and the driver unit is configured to alter the blood flow through the tubular element by driving the pump. 
         [0015]    In an application, the driver unit is configured to reduce the pulmonary blood flow by driving the effector element to change a physical configuration thereof. 
         [0016]    In an application, the driver unit is configured to drive the effector element to change the physical configuration thereof in a manner in which a final state of the reduction of the pulmonary blood flow is independent of a speed of the change of the physical configuration. 
         [0017]    In an application, the effector element includes an occlusion structure, and the occlusion structure is disposable within the portion of the circulatory system of the subject. 
         [0018]    In an application, the occlusion structure includes a balloon, and the driver unit is configured to reduce the pulmonary blood flow by changing a level of inflation of the balloon. 
         [0019]    In an application, the effector element includes a cuff, the cuff being disposable around at least a part of a blood vessel of the subject, and the driver unit is configured to reduce the pulmonary blood flow by changing a cross-sectional area of a lumen defined by the cuff. 
         [0020]    In an application, the effector element includes a fistula stent, the fistula stent being disposable in part in a wall of a first blood vessel of the subject and in part in a wall of a second blood vessel of the subject, and being configured to provide fluid communication between the first and second blood vessels, and the driver unit is configured to reduce the pulmonary blood flow by changing a cross-sectional area of a lumen defined by the fistula implant. 
         [0021]    In an application, the effector element includes a tubular element, disposable in a septum between two heart chambers of the subject, and configured to provide fluid communication between the two heart chambers, and the driver unit is configured to reduce the pulmonary blood flow by changing a cross-sectional area of a lumen defined by the tubular element. 
         [0022]    In an application, the effector element includes a cardiac valve-disruptor, the cardiac valve-disruptor being disposable in a cardiac valve of the subject. 
         [0023]    In an application, the driver unit is configured to reduce the pulmonary blood flow by changing a configuration of the cardiac valve-disruptor. 
         [0024]    There is further provided, in accordance with an application of the present invention, apparatus for altering blood flow of a subject, the apparatus including: 
         [0025]    an external device, configured for placement outside of the subject, the external device including:
       a detector, configured to detect a factor associated with a disorder of the subject; and   a control unit, couplable to the detector, configured to automatically generate a signal at least in part responsively to the detected factor; and       
 
         [0028]    an implant, including:
       a receiver, configured to receive the signal;   an effector element, being disposable in a vicinity of a portion of a circulatory system of the subject; and   a driver unit, coupled to the receiver, and configured to drive the effector element to alter a blood flow in the portion of the circulatory system, at least in part responsively to the signal.       
 
         [0032]    In an application, the detector is configured to detect a breathing-related factor of the subject. 
         [0033]    In an application, the external device is configured to detect reclining of the subject, and to generate the signal at least in part responsively to the reclining of the subject. 
         [0034]    In an application, the implant is configured to detect reclining of the subject, and the driver unit is configured to drive the effector element at least in part responsively to the reclining of the subject. 
         [0035]    In an application, the control unit is configured to generate the signal as a radio frequency signal. 
         [0036]    In an application, the control unit is configured to generate the signal as a magnetic signal. 
         [0037]    In an application, the driver unit is configured to drive the effector element to inhibit the blood flow of the subject. 
         [0038]    In an application, the driver unit is configured to drive the effector element to divert the blood flow of the subject. 
         [0039]    In an application, the effector element includes a tubular element, the tubular element being disposable between two hollow structures of the subject, and configured to provide fluid communication between the two hollow structures of the subject, and the driver unit is configured to alter the blood flow by altering a blood flow through the tubular element. 
         [0040]    In an application, the driver unit is configured to alter the blood flow through the tubular element by altering a cross-sectional area of a lumen defined by the tubular element. 
         [0041]    In an application, the apparatus includes a pump, the driver unit is configured to alter the blood flow through the tubular element by driving the pump. 
         [0042]    In an application, the driver unit is configured to alter the blood flow by driving the effector element to change a physical configuration thereof. 
         [0043]    In an application, the driver unit is configured to drive the effector element to change the physical configuration thereof in a manner in which a final state of the alteration of the blood flow is independent of a speed of the change of the physical configuration. 
         [0044]    In an application, the effector element includes an occlusion structure, and the occlusion structure is disposable within the portion of the circulatory system of the subject. 
         [0045]    In an application, the occlusion structure includes a balloon, and the driver unit is configured to alter the blood flow by changing a level of inflation of the balloon. 
         [0046]    In an application, the effector element includes a cuff, the cuff being disposable around at least a part of a blood vessel of the subject, and the driver unit is configured to alter the blood flow by changing a cross-sectional area of a lumen defined by the cuff. 
         [0047]    In an application, the effector element includes a fistula stent, the fistula stent being disposable in part in a wall of a first blood vessel of the subject and in part in a wall of a second blood vessel of the subject, and being configured to provide fluid communication between the first and second blood vessels, and the driver unit is configured to alter the blood flow by changing a cross-sectional area of a lumen defined by the fistula implant. 
         [0048]    In an application, the effector element includes a tubular element, disposable in a septum between two heart chambers of the subject, and being configured to provide fluid communication between the two heart chambers, and the driver unit is configured to alter the blood flow by changing a cross-sectional area of a lumen defined by the tubular element. 
         [0049]    In an application, the effector element includes a cardiac valve-disruptor, the cardiac valve-disruptor being disposable in a cardiac valve of the subject. 
         [0050]    In an application, the driver unit is configured to alter the blood flow by changing a configuration of the cardiac valve-disruptor. 
         [0051]    In an application, the implant is configured to wirelessly receive power. 
         [0052]    In an application, the implant is configured to receive power via magnetic induction. 
         [0053]    In an application, the external device is configured to transmit power via magnetic induction. 
         [0054]    In an application, the implant is configured to receive power via electromagnetic radiation transmitted by the external device, the implant further including a rectifying antenna. 
         [0055]    In an application, the rectifying antenna is configured to receive power from the signal. 
         [0056]    In an application, the rectifying antenna is configured to receive power from a second signal, and the control unit is configured to generate the second signal. 
         [0057]    There is further provided, in accordance with an application of the present invention, a method for altering blood flow of a subject, the method including: 
         [0058]    extracorporeally detecting a factor associated with a disorder of the subject; 
         [0059]    automatically extracorporeally generating a signal, at least in part responsively to the detected factor; 
         [0060]    intracorporeally detecting the signal; and 
         [0061]    automatically altering the blood flow of the subject, at least in part responsively to the signal. 
         [0062]    In an application, the method further includes extracorporeally detecting reclining of the subject, automatically extracorporeally generating the signal includes automatically extracorporeally generating the signal at least in part responsively to the reclining of the subject. 
         [0063]    In an application, the method further includes intracorporeally detecting reclining of the subject, automatically altering the blood flow of the subject includes automatically altering the blood flow of the subject at least in part responsively to the reclining of the subject. 
         [0064]    In an application, extracorporeally detecting the factor includes extracorporeally detecting the factor while the subject is sleeping. 
         [0065]    In an application, extracorporeally detecting the factor includes extracorporeally detecting a breathing-related factor of the subject. 
         [0066]    In an application, altering the blood flow includes occluding a blood vessel of the subject. 
         [0067]    In an application, altering the blood flow includes constricting a blood vessel of the subject. 
         [0068]    In an application, altering the blood flow includes disrupting a function of a heart valve of the subject. 
         [0069]    In an application, altering the blood flow includes inhibiting the blood flow of the subject. 
         [0070]    In an application, intracorporeally detecting the signal includes wirelessly receiving power via the signal, using an implant, and automatically altering the blood flow includes powering the implant using the received power. 
         [0071]    In an application, intracorporeally detecting the signal includes wirelessly receiving data via the signal, using an implant, and automatically altering the blood flow includes operating the implant responsively to the received data. 
         [0072]    In an application, 
         [0073]    intracorporeally detecting the signal includes wirelessly receiving power via the signal, using an implant, and automatically altering the blood flow includes powering the implant using the received power, and 
         [0074]    intracorporeally detecting the signal includes wirelessly receiving data via the signal, using the implant, and automatically altering the blood flow includes operating the implant responsively to the received data. 
         [0075]    In an application, generating the signal includes generating a radio frequency signal, and detecting the signal includes detecting the radio frequency signal. 
         [0076]    In an application, generating the signal includes generating a magnetic signal, and detecting the signal includes detecting the magnetic signal. 
         [0077]    In an application, altering the blood flow of the subject includes diverting the blood flow of the subject. 
         [0078]    In an application, diverting the blood flow includes diverting blood from a first blood vessel of the subject to a second blood vessel of the subject. 
         [0079]    In an application, diverting the blood flow includes diverting blood from a first heart chamber of the subject to a second heart chamber of the subject. 
         [0080]    In an application, diverting the blood flow of the subject includes driving a pump. 
         [0081]    In an application, diverting the blood flow includes adjusting a lumen of a tubular element. 
         [0082]    In an application, diverting the blood flow includes diverting blood from a first heart chamber of the subject to a second heart chamber of the subject. 
         [0083]    In an application, altering the blood flow of the subject includes adjusting a dimension of an effector element. 
         [0084]    In an application, adjusting the dimension of the effector element includes adjusting a dimension of an occlusion structure, disposed within a blood vessel of the subject. 
         [0085]    In an application, adjusting the dimension of the occlusion structure includes adjusting a level of inflation of a balloon. 
         [0086]    In an application, adjusting the dimension of the effector element includes adjusting a cross-sectional area of a lumen of a cuff, disposed around at least a part of a blood vessel of the subject. 
         [0087]    In an application, adjusting the dimension of the effector element includes adjusting a dimension of a heart valve-disruptor, the heart valve-disruptor being disposed in a vicinity of a valve of the heart. 
         [0088]    In an application, adjusting the dimension of the effector element includes adjusting a cross-sectional area of a lumen of a tubular element. 
         [0089]    In an application, adjusting the blood flow of the subject includes adjusting contractility of heart tissue of the subject. 
         [0090]    In an application, adjusting contractility includes providing a non-excitatory signal to the heart tissue of the subject. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0091]      FIG. 1  is a schematic illustration of an implant implanted in a subject, and an external device in a vicinity of the subject, in accordance with some applications of the invention; 
           [0092]      FIGS. 2A-C  are schematic illustrations of the external device, in accordance with some applications of the invention; 
           [0093]      FIGS. 3A-B  are schematic illustrations of the implant, comprising electrodes, in accordance with some applications of the invention; 
           [0094]      FIGS. 4A-B  are schematic illustrations of the implant, embodied as a fistula implant, in accordance with some applications of the invention; 
           [0095]      FIG. 5  is a schematic illustration of the implant, embodied as a fistula implant, in accordance with some applications of the invention; 
           [0096]      FIGS. 6A-B  are schematic illustrations of the implant, embodied as an occlusion implant, in accordance with some applications of the invention; 
           [0097]      FIGS. 7A-B  are schematic illustrations of the implant, embodied as a constriction implant, in accordance with some applications of the invention; 
           [0098]      FIG. 8  is a schematic illustration of the implant, embodied as an aperture implant, in accordance with some applications of the invention; 
           [0099]      FIG. 9  is a schematic illustration of the implant, embodied as a valve-disruptor implant, in accordance with some applications of the invention; and 
           [0100]      FIG. 10  is a schematic illustration of the implant, embodied as a contractility-control implant, in accordance with some applications of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0101]    Reference is made to  FIG. 1 , which is a schematic illustration of a bed  20  and a subject  22  lying in the bed. Typically, the subject is sleeping. Typically, an external device  24  comprises a control unit  26 , a sensor  28 , and one or more antennas  30 . The sensor senses one or more parameters of the subject. The parameters sensed are typically indicative of a pathology of the subject. For example, the sensor may detect breathing-related parameters of the subject that are indicative of an episode of, and/or deterioration in, congestive heart failure (CHF), and/or symptoms of CHF. External device  24  transmits one or more signals  32  to an implant  40 , which is typically implanted in a vicinity of (e.g., in, or adjacent to) a portion of the circulatory system of the subject. Typically, signals  32  are transmitted at least in part in response to the sensed parameters. In some applications of the invention, signals  32  are alternatively or additionally transmitted according to a set program. In some applications of the invention, signals  32  are alternatively or additionally transmitted continuously, such that implant  40  receives the signals when the implant is within a range (e.g., less than 10 m, e.g., less than 5 m, e.g., less than 1 m) of the external device. 
         [0102]    Implant  40  typically alters blood flow in at least the region of implantation and is described in more detail in accordance with  FIGS. 4A-10 . External device  24 , in accordance with some applications of the present invention, is placed in proximity to the subject, under the subject, under or inside the subject&#39;s pillow or mattress, or on another part of the bed (e.g., on a bedpost). Alternatively, the external device can be placed anywhere near the subject, such that implant  40  receives signals  32  from the external device. For some applications of the invention, external device  24  is portable and/or wearable by the subject. External device  24  may be coupled to and/or disposed within an item of clothing (e.g., a hat; a belt) of the subject, or worn on a chest-band. The antennas  30  of external device  24  are typically configured to send signals  32  to the implant, as described hereinbelow. 
         [0103]    External device  24  typically sends signals  32  to implant  40 . At least in part responsively to signals  32 , implant  40  alters the flow of blood in the region of implantation. For some applications, external device  24  sends signals  32  to implant  40  for a pre-determined length of time or in a particular pattern, or both. For some applications, periods of no stimulation by implant  40  are provided. In addition, external device  24  may be configured to detect reclining of the subject, and to only provide signals  32  to implant  40  when subject  22  is reclining (e.g., when the subject is sleeping). For example, in some applications, a sensor (e.g., sensor  28 ) is positioned in, on or under a mattress, and configured to detect the weight of the subject, and control unit  26  is configured to only transmit signals  32  when the weight of the subject is detected. Alternatively or additionally, as described hereinbelow (e.g., with reference to  FIGS. 3A-B ), in some applications, implant  40  may be configured to detect reclining of the subject, and to only respond to signals  32  when the subject is reclining (e.g., when the subject is sleeping). 
         [0104]    Typically, signals  32  comprise data, and implant  40  receives the data and responds to the data. In some applications of the invention, external device  24  wirelessly powers implant  40  via wireless power  132 , as described hereinbelow. When external device  24  wirelessly powers implant  40 , wireless power  132  may comprise signals  32  and, thereby, comprise the data to which implant  40  typically responds. For some applications of the invention, the data may comprise an on/off command. For some applications of the invention, and as described hereinbelow (e.g., with reference to FIGS.  2 A and  3 A-B), implant  40  may be configured to only function when wireless power  132  is being received. In these applications, signals  32  may comprise only wireless power  132 . That is, when signals  32  (i.e., wireless power  132 ) are received by implant  40 , the implant is commanded (i.e., enabled) to function, and when signals  32  (i.e., wireless power  132 ) are not received by the implant, the implant is commanded not to function (i.e., is disabled from operating). 
         [0105]    One or more of the implants are typically implanted into the subject in the vicinity of a blood vessel (e.g., in the blood vessel and/or on the blood vessel) of the subject. These one or more implants  40  may be configured to work in conjunction with other implants or independent of each other and/or external device  24 . It is noted that the number of implants  40  in the illustration is by way of illustration and not limitation. 
         [0106]    Closed-loop control (i.e., feedback control) is typically facilitated by continuous and/or repeated detection, by sensor  28 , of the factors described hereinabove. In some applications of the invention, feedback is alternatively or additionally provided by subject  22  himself, or by other sensors such as additional feedback sensors (not shown). In addition, other sensors known in the art may be used to obtain feedback and to support feedback control of external device  24  and implant  40 . Typically, sensing and responsive adjustment of blood flow is continuous and/or repeated over a duration of time (e.g., more than one hour, e.g., more than 4 hours, e.g., overnight). For severe conditions (e.g., bedridden subjects), sensing and responsive adjustment of blood flow may continue indefinitely. 
         [0107]    Reference is made to  FIGS. 2A-C , which are schematic illustrations of external device  24 , in accordance with some applications of the invention. 
         [0108]    Reference is now made to  FIG. 2A , which is a schematic illustration of external device  24 , in accordance with an application of the invention. External device  24  comprises one or more antennas  30 , a control unit  26 , and one or more sensors  28 . Sensor  28  typically detects one or more parameters of the subject, for example, breathing-related motions, breathing rate, heart rate, electrical activity, blood oxygenation, blood perfusion, sleep pattern and/or other indications of CHF. 
         [0109]    Control unit  26  drives antenna  30  to transmit one or more signals  32 , which is received by implant  40  when within an appropriate range. For example, the apparatus may be configured such that implant  40  is typically able to use signals  32  only when the subject is close to external device (e.g., within 10 m, e.g., within 5 m, e.g., within 1 m, e.g., when the subject is in bed). Typically, control unit  26  drives such signal transmission at least in part responsively to the one or more parameters detected by sensor  28 . Alternatively or additionally, control unit  26  may drive signal transmission for a pre-determined and/or configurable length of time, or in a particular pattern. For some applications of the invention, signals  32  provide power to implant  40 , as described hereinbelow. External device  24  may further comprise one or more additional feedback sensors  44 , which detect one or more feedback parameters that indicate the efficacy and/or efficiency of the treatment applied by the implant  40 . Alternatively or additionally, the feedback parameters may be the same as the parameters detected by sensor  28 , in which case, feedback control is provided without the requirement for feedback sensor  44 . Alternatively or additionally, feedback may be provided by the subject himself. 
         [0110]    In some applications of the invention, external device  24  may further comprise one or more induction coils  42 . Induction coils  42  are configured to supply power, via electromagnetic induction, to implant  40 , in conjunction with one or more corresponding induction coils in the implant (not shown). This power may be consumed immediately by implant  40  and/or may be used to charge a power supply, as described hereinbelow. 
         [0111]    Reference is now made to  FIG. 2B . For some applications of the invention, sensor  28  is external to external device  24 . For example, sensor  28  may be coupled to external device  24  by a wire, or may be wirelessly coupled to the external device. Externally-situated sensor  28  allows the sensor to be placed in a position that is suitable for detecting the parameters described hereinabove, whilst external device  24  is disposed in a position that is suitable for transmitting signals  32  to implant  40  and/or supplying wireless power to the implant. 
         [0112]    Reference is now made to  FIG. 2C . For some applications of the invention, antenna  30  comprises a multidirectional antenna  31  (e.g., a set of mutually-perpendicular antennas), such that signals  32  are receivable by implant  40 , independently of the instantaneous orientation of implant  40  in subject  22  (e.g., due to the position of the subject on bed  20 ). Similarly, implant  40  may comprise a multidirectional antenna for receiving signals  32 , generally independently of the orientation of the subject. 
         [0113]    Reference is made to  FIGS. 3A-B , which are schematic illustrations of implant  40 , in accordance with some applications of the invention. 
         [0114]    Reference is now made to  FIG. 3A , which is a schematic illustration of implant  40 , in accordance with some applications of the invention. Implant  40  typically comprises a driver unit  66 , an antenna  46 , and an effector element  50 . Effector element  50  is typically electronically coupled to driver unit  66 . The effector element may be disposed (i.e., implanted) adjacently to driver unit  66 , or may be disposed at a different site. Implant  40  typically receives signals  32  from external unit  24 , via antenna  46 , and alters blood flow at least in part responsively to the signals, as described hereinbelow. Driver unit  66  typically comprises a power supply  138  (e.g., a battery and/or a capacitor). In some applications of the invention, implant  40  further comprises a power-receiver  130 , which receives power wirelessly. 
         [0115]    As described with reference to  FIGS. 1-2 , in some applications of the invention, implant  40  receives power from external unit  24  via electromagnetic induction. In such applications, power-receiver  130  comprises one or more induction coils  134 , which typically receive power from induction coils  42  in external device  24 . 
         [0116]    In some applications of the invention, implant  40  may receive power via electromagnetic radiation (e.g., radio waves and/or microwaves), such as wireless power  132 . In such applications of the invention, power-receiver  130  comprises a rectifying antenna (rectenna)  136 , which converts wireless power  132  into electrical energy. In some applications of the invention, wireless power  132  may be a dedicated charging signal, transmitted by external device  24 . Alternatively or additionally, wireless power  132  may include signals  32 , which induce blood flow altering by implant  40 . In some applications of the invention, implant  40  either does not comprise antenna  46 , or does not comprise power-receiver  30 . Rather, signals  32  and wireless power  132  are both received via either antenna  46 , or by power-receiver  130 . 
         [0117]    Electrical energy supplied by power-receiver  130  typically charges power supply  138 , such that implant  40  may function in the absence of continuous wireless power. Alternatively or additionally, electrical energy supplied by power-receiver  130  may be consumed by implant  42  as it is supplied. In some applications of the invention, element  50  only operates while wireless power  132  is being received by power-receiver  130 . 
         [0118]    Reference is now made to  FIG. 3B . For some applications of the invention, antenna  46  comprises a multidirectional antenna  47  (e.g., mutually-perpendicular antennas), such that signals  32  from external device  24  are receivable by implant  40 , independently of the orientation of subject  22  (e.g., the position of the subject on bed  20 ). Similarly, external device  24  may comprise a multidirectional antenna for receiving signals  32 , independently of the orientation of the subject. 
         [0119]    Reference is again made to  FIGS. 3A-B . In some applications, implant  40  may be configured to detect reclining of the subject, and/or to only respond to signals  32  when the subject is reclining (e.g., when the subject is sleeping). For example, implant  40  may comprise an orientation sensor, such as a gyroscope (e.g., as is known in the cellular telephone art), and driver unit  66  may be configured to drive effector element  50  only when the subject is reclining (e.g., when the subject is sleeping). 
         [0120]    The applications of the invention described with reference to  FIGS. 1-3  may be combined with those applications described hereinbelow, including those described with reference to  FIGS. 4A-10 . 
         [0121]    Reference is made to  FIGS. 4A-10 , which are schematic illustrations of implant  40 , in accordance with respective applications of the invention. For clarity, only driver unit  66  and effector element  50  of implant  40  are shown in these figures. 
         [0122]    Reference is made to  FIGS. 4A-B , which are schematic illustrations of implant  40 , embodied as an adjustable fistula implant  60   a,  in accordance with some applications of the invention. 
         [0123]    Reference is now made to  FIG. 4A . Effector element  50  of fistula implant  60   a  typically comprises a tubular element  61 , which is shaped to define a lumen and can facilitate communication between two hollow structures, such as a first blood vessel  62  and a second blood vessel  64 . Typically, fistula implant is implanted such that it provides communication between an artery and a vein, whereby arterial blood can pass through fistula implant  60   a  into the venous system. For example, fistula implant  60   a  may be implanted between the iliac artery and iliac vein of the subject, or between another artery and vein of the subject. At least in part responsively to signals  32  from external unit  24 , driver unit  66  drives effector element  50  to alter blood flow through tubular element  61 . For example, driver unit  66  may drive an adjustment of a dimension of tubular element  61 , such as the cross-sectional area of the lumen of the tubular element. 
         [0124]    Reference is now made to  FIG. 4B , which is a schematic illustration of fistula implant  60   a  showing a cross section of tubular element  61 , illustrated in  FIG. 4A . This figure more clearly illustrates the adjustability of a dimension of implant  40 , that is described with reference to  FIG. 4A . Adjustment of the cross-sectional area of the lumen defined by tubular element  61  alters blood flow through the tubular element. For example, in response to detection of a phenomenon related to CHF, driver unit  66  may increase the cross-sectional area of the lumen, to increase blood flow through the tubular element. Mechanisms by which driver unit  66  may drive adjustment of the cross-sectional area of tubular element  61  include, but are not limited to, electromechanical control (e.g., the use of an electroactive polymer) and hydraulic control, and may comprise the use of a servo drive. 
         [0125]    Reference is now made to  FIG. 5 , which is a schematic illustration of fistula implant  60   b,  according to an application of the invention. In this application of the invention, tubular element  61  comprises or is coupled to a conduit  68 . The lengthened implant allows a fistula to be maintained between the two hollow structures (i.e., the blood vessels) when the structures are spaced further apart. The rigidity of conduit  68  may be adapted for use in various situations. Alternatively or additionally to blood flow control via adjustment of the lumen, implant  60   b  may comprise a pump  72 , whereby blood flow is controlled by controlling the rate of pumping. For example, in response to detection of a phenomenon related to CHF, driver unit  66  may drive pump  72  to increase blood flow through implant  60   b.  Although pump  72  is described with reference to  FIG. 5 , it may be combined with other applications of the invention, for example the applications described with reference to  FIGS. 4A-B . 
         [0126]    Reference is again made to  FIGS. 4A-5 . It is to be noted that although fistula implants  60   a  and  60   b  are shown providing fluid communication between two blood vessels of the subject, the scope of the present application includes fistula implants that provide communication between other hollow structures of the subject. 
         [0127]    Reference is made to  FIGS. 6A-B , which are schematic illustrations of implant  40 , embodied as an adjustable occlusion implant  90 , in accordance with an application of the invention. 
         [0128]    Reference is now made to  FIG. 6A . The effector element  50  of occlusion implant  90  comprises an occlusion element that has an adjustable dimension. Typically, the occlusion element comprises a balloon  92 , and the adjustable dimension is a cross-sectional area of the balloon. Typically, the cross-sectional area of the balloon is adjustable via inflation of the balloon. Implant  90  is disposed in the lumen of a blood vessel which, in this application of the invention, is superior vena cava  94 . Additionally or alternatively, implant is disposed in the lumen of another blood vessel such as inferior vena cava  96 . Inflation of balloon  92  increases occlusion of the blood vessel in which the balloon is disposed. Driver unit  66  receives signals  32  from external device  24  and, at least in part responsively to the signals, alters blood flow by adjustment of the level of inflation of balloon  92 . For example, in response to detection of a phenomenon related to CHF, driver unit  66  may increase the inflation of balloon  92 , to reduce blood flow through superior vena cava  94  and into right atrium  98 . Typically, balloon  92  is inflated with saline. In  FIG. 6A , balloon  92  is shown in a deflated state. 
         [0129]    Reference is now made to  FIG. 6B , which is a schematic illustration of occlusion implant  90  with balloon  92  in an inflated state. In this state, balloon  92  at least partly occludes superior vena cava  94 , reducing blood flow into right atrium  98 . Reduction of blood flow into right atrium  98  reduces the congestion of the lungs associated with CHF. Other uses of occlusion implant  90  may be alternatively or additionally employed, in accordance with applications of the invention. 
         [0130]    Reference is now made to  FIGS. 7A-B , which are schematic illustrations of implant  40 , embodied as an adjustable constriction implant  110 , in accordance with an application of the invention. 
         [0131]    Reference is now made to  FIG. 7A . The effector element of constriction implant  110  comprises a constriction element that has an adjustable dimension. Typically, the constriction element comprises an inflatable cuff  112 , and the adjustable dimension is a cross-sectional area of a lumen defined by the cuff. Typically, the cross-sectional area of the lumen is adjustable via inflation of the cuff. Implant  110  is disposed around a blood vessel which, in this application of the invention, is superior vena cava  94 . Additionally or alternatively, implant  110  may be disposed around another blood vessel such as inferior vena cava  96 . Inflation of cuff  112  constricts the blood vessel around which the cuff is disposed. Driver unit  66  receives signals  32  from external device  24  and, at least in part responsively to the signals, alters blood flow by adjustment of the level of inflation of cuff  112 . For example, in response to detection of a phenomenon related to CHF, driver unit  66  may increase the inflation of cuff  112 , to reduce blood flow through superior vena cava  94  and into right atrium  98 . Typically, inflatable cuff  112  is inflated with a fluid (e.g., saline). In this figure, cuff  112  is in a deflated state. 
         [0132]    Reference is now made to  FIG. 7B , which is a schematic illustration of occlusion implant  110  with cuff  112  in an inflated state. In this state, cuff  112  at least partly constricts superior vena cava  94 , reducing blood flow into right atrium  98  of heart  102  of the subject. Other uses of constriction implant  110  may be alternatively or additionally employed, in accordance with applications of the invention. 
         [0133]    Reference is made to  FIG. 8 , which is a schematic illustration of implant  40 , embodied as an adjustable aperture implant  150 , in accordance with an application of the invention. Effector element  50  of aperture implant  150  typically comprises a tubular element  152 , which is shaped to define a lumen. Tubular element  152  is configured to facilitate communication between two hollow structures of the subject. Tubular element  152  is typically implanted in an interatrial septum of the subject, so as to facilitate communication between a right atrium  98  and a left atrium  100  of heart  102  of the subject. That is, tubular element  152  provides a shunt between the two atria. At least in part responsively to signals  32  from external unit  24 , driver unit drives effector element  50  to alter blood flow through tubular element  152 . Typically, driver unit  66  drives tubular element  152  to adjust a dimension thereof. For example, driver unit  66  may cause an increase of the cross-sectional area of the lumen of tubular element  152 , in response to detection of a phenomenon related to CHF, as described with reference to  FIGS. 4A-B , mutatis mutandis. Increasing the cross-sectional area of the lumen of tubular element  152  is hypothesized to increase inter-atrial shunting, thereby reducing the congestion of the lungs associated with CHF. Other uses of adjustable aperture implant  150  may be alternatively or additionally employed, in accordance with applications of the invention. 
         [0134]    Reference is now made to  FIG. 9 , which is a schematic illustration of implant  40 , embodied as an adjustable valve-disruptor implant  160 . Valve-disruptor implant  160  is typically implanted at a native heart valve such as a tricuspid valve  108  of the subject. At least in part responsively to signals  32  from external unit  24 , driver unit drives effector element  50  to adjust a level of interference with leaflets  106  of the native valve. In some applications of the invention, driver unit  66  drives effector element  50  of valve-disruptor implant  160  to adjust a dimension thereof. In some applications of the invention, effector element  50  of valve-disruptor implant  160  comprises one or more wire loops  162  and a sleeve  164 , slidably coupled to the wire loops. Wire loops  162  typically have an expanded configuration in which the wire loops interfere with leaflets  106  to a relatively high degree, and a constricted configuration in which the wire loops interfere with leaflets  106  to a relatively low degree. The degree of expansion of wire loops  162  is controlled by the sliding of sleeve  164  over the wire loops. Driver unit  66  thereby adjusts blood flow through the heart valve by sliding sleeve  164  over wire loops  162 , at least in part responsively to signals  32  from external unit  24 . For example, in response to detection of a phenomenon related to CHF, driver unit  66  may allow wire loops  162  to expand, increasing their interference with leaflets  106 , thereby increasing regurgitation. Increased tricuspid valve regurgitation is hypothesized to reduce the congestion of the lungs associated with CHF. For some applications, valve-disruptor implant  160  is constructed using effector elements  50  other than wire loops and a sheath, in accordance with applications of the invention. 
         [0135]    Reference is now made to  FIG. 10 , which is a schematic illustration of implant  40 , embodied as a contractility-control implant  180 . Effector element  50  of contractility-control implant  180  typically comprises one or more electrodes  182 , electrically coupled to driver unit  66 . Electrodes  102  are typically coupled to respective cardiac sites, facilitating electrical stimulation of heart  102  of the subject, by driver unit  66 . Driver unit  66  is typically configured to provide a non-excitatory signal to the heart, at least in part responsively to signals  32  from external unit  24 . For example, in response to detection of a phenomenon related to CHF, driver unit  66  may provide the non-excitatory signal to the heart. The non-excitatory signal is hypothesized to increase the contractility of cardiac muscle, and thereby increase the power and/or volume of each stroke of the heart. Typically, but not necessarily, the non-excitatory signal is provided during refractory periods in the cardiac cycle. Further typically, the non-excitatory signal comprises a series of closely-paced pulses. The non-excitatory signal supplied by contractility-control implant  180  is hypothesized to increase the contractility of cardiac muscle, thereby increasing the velocity and/or power of beats of the heart. For some applications, apparatus and methods described in U.S. Pat. No. 7,167,748 to Ben-Haim et al., which is incorporated herein by reference, are utilized in combination with the apparatus and methods described herein, in order to produce increased cardiac contractility. 
         [0136]    In some applications of the invention, driver unit  66  is further configured to detect natural cardiac depolarization events, and the non-excitatory signal is provided at least in part responsively to the detected events. 
         [0137]    In some applications of the invention, excitatory signals (e.g., pacing signals) are further provided to the heart of the subject. For example, contractility-control implant  180  may be used in combination with a cardiac pacemaker, or a single implant may provide both contractility-control and pacing, via non-excitatory and excitatory signals, respectively, at least in part responsively to signals  32  from external unit  24 . Other uses of contractility-control implant  180  may be alternatively or additionally employed, in accordance with applications of the invention. 
         [0138]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.