Abstract:
Constituents of a network of medical devices communicate according to a synchronous communication protocol. A constituent of the network is established as a conductor. Time slots are assigned to each constituent of the network other than the conductor. Information is communicated between the constituents of the network in the assigned time slots.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     Reference is made to the following applications:  
         [0002]     U.S. application Ser. No. 11/224,591 filed Sep. 12, 2005 for “SYSTEM AND METHOD FOR UNSCHEDULED WIRELESS COMMUNICATION WITH A MEDICAL DEVICE” by Quentin S. Denzene and George C. Rosar;  
         [0003]     U.S. application Ser. No. 11/224,593 filed Sep. 12, 2005 for “SYSTEM AND METHOD FOR UNSCHEDULED WIRELESS COMMUNICATION WITH A MEDICAL DEVICE” by Gregory J. Haubrich, Len D. Twetan, David Peichel, Charles S. Dudding, George C. Rosar and Quentin S. Denzene;  
         [0004]     U.S. application Ser. No. 11/224,594 filed Sep. 12, 2005 for “IMPLANTABLE MEDICAL DEVICE COMMUNICATION SYSTEM WITH MACRO AND MICRO SAMPLING INTERVALS” by Glenn Spital; and  
         [0005]     U.S. applicaton No. 11/224,595 filed Sep. 12, 2005 for “COMMUNICATION SYSTEM AND METHOD WITH PREAMBLE ENCODING FOR AN IMPLANTABLE MEDICAL DEVICE” by Gregory j. Haubrich, Javaid Masoud, George C. Rosar, Glenn Spital and Quentin S. Denzene. 
     
    
     BACKGROUND OF THE INVENTION  
       [0006]     The present invention relates to wireless communication with medical devices such as implantable medical devices.  
         [0007]     Medical devices, including implantable medical devices (IMDs) are now used to provide countless therapies and to monitor a wide variety of physiological events. With the increased uses of IMDs has also come the need for improved methods of communicating with and between IMDs.  
         [0008]     Conventionally, communication with IMDs has been performed with magnetic field communication technology. Systems that employ this communication technology, however, are generally only capable of communicating over very short distances, on the order of a few inches. As a result, a magnetic head of a programmer (or other external device) must be located on or near the IMD for communication to occur. More recently, radio frequency (RF) communication systems have been developed for use with IMDs. RF communication provides a number of benefits over magnetic field communication systems, including much greater communication distances.  
         [0009]     Because an IMD is surgically implanted within the body of a patient, battery life is one of the factors to be considered in the design of IMD communication systems. There is also an ongoing desire to enable more and more advanced communications between IMDs and other devices. Accordingly, there is a need for systems and methods to provide advanced communication capabilities while limiting the amount of time that the transceiver of an IMD stays active to conserve battery life.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     Medical devices in a network communicate with one another according to a synchronous communication protocol. A constituent of the network is established as a conductor. Time slots are assigned by the conductor for communication to occur. Information is communicated between the constituents of the network in the assigned time slots. The medical devices preserve battery life by limiting how often their transceivers need to operate or remain active.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic diagram illustrating a communication system for communicating medical data and other information between one or more medical devices and an external unit.  
         [0012]      FIG. 2A  is a flow diagram illustrating a first example of the operation of receivers to detect a wake-up signal.  
         [0013]      FIG. 2B  is a flow diagram illustrating a second example of the operation of receivers to detect a wake-up signal.  
         [0014]      FIG. 2C  is a flow diagram illustrating a third example of the operation of receivers to detect a wake-up signal.  
         [0015]      FIG. 2D  is a flow diagram illustrating a fourth example of the operation of receivers to detect a wake-up signal.  
         [0016]      FIG. 3  is a diagram illustrating the timing of synchronous communication in a communication system.  
         [0017]      FIG. 4  is a flow diagram illustrating a protocol for communication that involves sensors without receiver capability.  
         [0018]      FIG. 5  is a flow diagram illustrating a protocol for communication that involves sensors having limited receiver capability. 
     
    
     DETAILED DESCRIPTION  
       [0019]      FIG. 1  is a schematic diagram illustrating communication system  10  for communication involving IMD  12 , which includes lead  14  and antenna  16 . IMD  12  has the capability to communicate with external unit  18  via antenna  20 , and also with device  22  via communication link  24 . In one embodiment, IMD  12  is an implantable cardioverter defibrillator (ICD), but the present invention is equally applicable to many types of medical devices, including both implantable medical devices and external medical devices. IMD  12  is capable of providing therapies and/or sensing physiological events of the heart of patient P via one or more leads  14 . Antenna  16  is used to communicate with external unit  18  and with device  22 , and may be any apparatus capable of sending or receiving electromagnetic waves, including for example a surface mounted antenna, an inductor, or a half-wave strip. Alternatively, antenna  16  may be configured only for communication with external unit  18 , and a separate, independent antenna may be employed for communication with device  22 .  
         [0020]     External unit  18  is a device, such as a programmer, capable of bi-directional communication with IMD  12  via antenna  20 . Antenna  20  may be any type of RF antenna capable of communicating in the desired RF frequencies with IMD  12 , and may be located inside or outside of a housing of external unit  18 .  
         [0021]     Device  22 , similar to IMD  12 , is capable of providing therapies and/or sensing physiological events in the body of patient P. Device  22  may be any of a number of different devices, such as an insulin pump, a drug pump, a cardiac sensor, a neurological sensor, a glucose sensor, or another device (the location of device  22  shown in  FIG. 1  is, of course, not representative of a typical implantation location of all of these types of devices). Additional devices (not shown) may be implanted in or otherwise associated with patient P as well, communicating with other devices in a manner similar to device  22 .  
         [0022]     Communication between IMD  12  and external unit  18 , between IMD  12  and IMD  22 , and between external unit  18  and IMD  22 , can be performed over any communication band. In one embodiment, the communication occurs over a public radio frequency band. In another embodiment, the communication occurs over the Medical Implant Communication (MICs) band between 402 MHz and 405 MHz. Other frequency bands may also be used. Although the present invention is described with reference to radio frequency bands, it is recognized that the present invention is also useful with other types of electromagnetic communication.  
         [0023]     Because IMD  12  and device  22  have finite battery capacity, an important consideration in the design of RF communication system  10  is the energy efficiency of IMD  12  and device  22 . A substantial factor in the energy efficiency of IMD  12  and device  22  is the time that their transceivers spend either transmitting or receiving. Energy efficiency is less of an issue in the design of external unit  18 , because external unit  18  is generally connected to an external power source such as a 120V AC. Therefore, methods of operating the transceivers of IMD  12  and device  22  that reduce the energy consumption of those components, even in exchange for additional energy consumption by the transceiver of external unit  18 , are beneficial.  
         [0024]     While transmitters only need to be turned on when there is something to transmit, receivers must be turned on much more frequently. No communication can take place unless the receiver is on, at least momentarily, to detect an attempted transmission. To provide a fast response time, a receiver may sample a communication channel as often as twice every second or more. But, a receiver that turns on just twice every second will turn on 172,800 times in one day. A transmitter, on the other hand, may turn on only a handful of times in that same period. Therefore, an improvement in the efficiency of use of a receiver can provide an increase in the effective life of the device.  
         [0025]     External unit  18  assists in reducing the energy consumed by medical device receivers by transmitting a preamble signal (sometimes referred to as a “wake-up” signal) prior to the transmission of data. This use of a preamble signal allows the device receivers to sample the communication channel(s) periodically, rather than having to remain on at all times, while still ensuring that the transmission of any data will not be missed. The preamble signal contains a modulation pattern known by the device receivers. If the receivers detect energy on a communication band, but find that it does not contain the known modulation pattern, the receivers can shut down knowing that the detected energy is not a communication initiated by external unit  18  for its benefit. Furthermore, the preamble signal may contain embedded data which further improves the energy efficiency of the device receivers. This data informs the receivers of information pertinent to the communication link (such as channel information and communication mode) for the subsequent transmission of data. The receivers may continue operating in a low power mode while receiving the embedded data, and then adjust their configuration settings as specified by the embedded data to initiate the higher power receiver mode for receipt of the transmitted data. Further discussion of the embedding of data in the preamble signal may be found in the aforementioned U.S. application Ser. No. 11/224,595.  
         [0026]      FIG. 2A  is a flow diagram illustrating a first example of the operation of receivers to detect a wake-up signal. A device receiver periodically operated to listen for a transmission in order to detect the existence of a transmission, as indicated by box  50 A. This initial listening operation is performed by a wideband receiver. The wideband receiver is operated to detect whether transmission energy above a threshold on any channel of a selected group of channels is occurring, as indicated by decision box  52 A. If energy above the threshold is not detected, the receiver can turn off until the next listening period, as indicated by box  53 A. If energy above the threshold is detected, the receiver remains on to attempt to identify a transmission pattern associated with the detected energy that matches the pattern of a wake-up signal, as indicated by decision box  54 A. If the transmission pattern corresponds to a wake-up signal, the receiver will then switch to a narrowband receiving mode. If channel information is encoded in the wake-up signal (decision box  56 A), then the receiver will switch to the appropriate channel based on that information, as indicated by box  58 A. If channel information is not encoded in the wake-up signal, the receiver performs a scan of the available channels, as indicated by box  60 A, and determines which channel contains the wake-up signal transmission. Once the correct channel is determined, the receiver switches to the appropriate channel, as indicated by box  58 A. After the receiver has switched to the appropriate channel, data can be received on the channel in the customary manner. Further discussion of a wake-up procedure of this kind can be found in the aforementioned U.S. application Ser. No. 11/224,593.  
         [0027]      FIG. 2B  is a flow diagram illustrating a second example of the operation of receivers to detect a wake-up signal. A device receiver is periodically operated to listen for a transmission in order to detect the existence of a transmission, as indicated by box  50 B. This initial listening operation is performed by a narrowband receiver (unlike the wideband listening example described above with respect to  FIG. 2A ) operating on a channel designated as “channel X.” In a synchronous communication system, each channel (such as channel X) has an assigned time slot, and the narrowband receiver listens for a transmission in the time slot that is assigned to channel X. The narrowband receiver is operated to detect whether transmission energy above a threshold on channel X is occurring, as indicated by decision box  52 B. If energy above the threshold is not detected, the receiver can turn off until the next listening period, as indicated by box  53 B. If energy above the threshold is detected, the receiver remains on to attempt to identify a transmission pattern associated with the detected energy that matches the pattern of a wake-up signal, as indicated by decision box  54 B. If the transmission pattern corresponds to a wake-up signal, the receiver listens for data on channel X in the customary manner, as indicated by box  58 B.