Abstract:
An ambulatory repeater for use in automated patient care is presented. A local memory store includes a cryptographic key, sensitive information, and physiological measures. The cryptographic key is uniquely assigned to the implantable medical device prior to implant of the implantable medical device into a patient. The sensitive information is preencrypted under the cryptographic key and physiological measures are measured by the implantable medical device. An authentication module is in receipt of the cryptographic key. A permissions module confirms authorization of an external data processing device against the cryptographic key. A decryption module decrypts the sensitive information with the cryptographic key into decrypted information. A processor is operatively coupled to the local memory store. A communications module exchanges the decrypted information and the physiological measures with the external data processing device over a wireless interface contingent upon the authorization confirmation. An internal power supply supplies power to the foregoing components.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is a divisional of U.S. patent application Ser. No. 11/113,206, filed Apr. 22, 2005, now U.S. Pat. No. 7,270,633, issued Sep. 18, 2007, the priority of filing date of which is claimed, and the disclosure of which is incorporated by reference. 
    
    
     FIELD 
     The present invention relates in general to automated patient care and, specifically, to an ambulatory repeater for use in automated patient care. 
     BACKGROUND 
     In general, implantable medical devices (IMDs) provide in situ therapy delivery, such as pacing, cardiac resynchronization, defibrillation, neural stimulation and drug delivery, and physiological monitoring and data collection. Once implanted, IMDs function autonomously by relying on preprogrammed operation and control over therapeutic and monitoring functions. IMDs can be interfaced to external devices, such as programmers, repeaters and similar devices, which can program, troubleshoot, and download telemetered data, typically through induction or similar forms of near-field telemetry. 
     Telemetered data download typically occurs during follow-up, which requires an in-clinic visit by the patient once every three to twelve months, or as necessary. Following interrogation of the IMD, the telemetered data can be analyzed to evaluate patient health status. Although clinical follow-up is mandatory, the frequency and type of follow-up are dependent upon several factors, including projected battery life, type, mode and programming of IMD, stability of pacing and sensing, the need for programming changes, underlying rhythm or cardiac condition, travel logistics, and the availability of alternative follow-up methods, such as transtelephonic monitoring, for example, the CareLink Monitor, offered by Medtronic, Inc., Minneapolis, Minn.; Housecall Plus Remote Patient Monitoring System, offered by St. Jude Medical, Inc., St. Paul, Minn.; and BIOTRONIK Home Monitoring Service, offered by BIOTRONIK GmbH &amp; Co. KG, Berlin, Germany. 
     Telemetered data generally includes information on all programmed device parameters, as well as real time or measured and recorded data on the operation of the IMD available at the time of interrogation. In addition, telemetered data can include parametric and physiological information on the output circuit, battery parameters, sensor activities for rate adaptive IMDs, event markers, cumulative totals of sensed and paced events, and transmission of electrograms. Derived measures include battery depletion, which can be gauged by the downloaded battery voltage and impedance levels, and lead integrity, which is reflected by pacing impedance. Event markers depict pacing and sensing simultaneously recorded with electrograms to indicate how the IMD interprets specifically paced or sensed events with timing intervals. Other types of telemetered data are possible. 
     Clinical follow-up is conventionally performed using a programmer under the direction of trained healthcare professionals. The programmer is typically interfaced to an IMD through inductive near field telemetry. Fundamentally, IMDs are passive devices that report on operational and behavioral patient status, including the occurrence of significant events, only when interrogated by an external device. As a result, the programmer-based follow-up sessions generally provide the sole opportunity for the IMD to report any significant event occurrences observed since the last follow-up session. Moreover, the latency in reporting significant event occurrences becomes dependent upon the timing of the clinical follow-up sessions for non-closely followed patients. Thus, in some circumstances, delays in downloading telemetered data can result in lost data or chronic cardiac conditions recognized too late. 
     Recently, far field telemetry using radio frequency (RF) carrier signals has provided an alternative means for interfacing programmers and similar external devices to IMDs, such as described in commonly-assigned U.S. Pat. No. 6,456,256, issued Sep. 24, 2002, to Amudson et al.; U.S. Pat. No. 6,574,510, to Von Arx et al., issued Jun. 3, 2003; and U.S. Pat. No. 6,614,406, issued Sep. 2, 2003, to Amudson et al., disclosures of which are incorporated by reference. Far field telemetry has a higher data rate, which results in shorter downloading times, and the patient experiences greater freedom of movement while the IMD is being accessed. Nevertheless, despite the higher data rate, the IMD remains a passive device that only reports significant event occurrences when interrogated using an RF-capable programmer. 
     Similarly, dedicated monitoring devices, known as repeaters, have become available to patients to provide monitoring and IMD follow-up in an at-home setting similar to transtelephonic monitoring. Each repeater is specifically matched to an IMD. Once a day or as required, the patient uses the repeater to actively poll the IMD through induction or far field telemetry. Alternatively, some repeaters can be passively polled. During each session, any significant events occurrences are reported, although programming of the IMD is generally not allowed for safety reasons. As well, repeaters download recorded telemetered data. Despite the improved frequency and speed of telemetered data downloads, the latency to report significant event occurrences can be as long as a full day. The patient must also be physically proximal to the repeater during interrogation in the same fashion as a programmer. In addition, repeaters, by virtue of being stationary devices, are unable to capture patient physiological and behavioral data while the patient is engaged in normal everyday activities or at any other time upon the initiation of the patient or by a remote patient management system. 
     Furthermore, the use of RF telemetry in IMDs potentially raises serious privacy and safety concerns. Sensitive information, such as patient-identifiable health information (PHI), exchanged between an IMD and the programmer or repeater should be safeguarded to protect against compromise. Recently enacted medical information privacy laws, including the Health Insurance Portability and Accountability Act (HIPAA) and the European Privacy Directive underscore the importance of safeguarding a patient&#39;s privacy and safety and require the protection of all patient-identifiable health information (PHI). Under HIPAA, PHI is defined as individually identifiable health information, including identifiable demographic and other information relating to the past, present or future physical or mental health or condition of an individual, or the provision or payment of health care to an individual that is created or received by a health care provider, health plan, employer or health care clearinghouse. Other types of sensitive information in addition to or in lieu of PHI could also be protectable. 
     The sweeping scope of medical information privacy laws, such as HIPAA, may affect patient privacy on IMDs with longer transmission ranges, such as provided through RF telemetry, and other unsecured data interfaces providing sensitive information exchange under conditions that could allow eavesdropping, interception or interference. Sensitive information should be encrypted prior to long range transmission. Currently available data authentication techniques for IMDs can satisfactorily safeguard sensitive information. These techniques generally require cryptographic keys, which are needed by both a sender and recipient to respectively encrypt and decrypt sensitive information transmitted during a data exchange session. Cryptographic keys can be used to authenticate commands, check data integrity and, optionally, encrypt sensitive information, including any PHI, during a data exchange session. Preferably, the cryptographic key is unique to each IMD. However, authentication can only provide adequate patient data security if the identification of the cryptographic key from the IMD to the programmer or repeater is also properly safeguarded. 
     Therefore, there is a need for an approach to providing an ambulatory solution to retrieving physiological and parametric telemetered data from IMDs. Preferably, such an approach would provide authenticated and secure communication with IMDs and include configurable activation settings. 
     SUMMARY 
     A system and method provide an ambulatory repeater for securely exchanging information, including sensitive patient data, between an implantable medical device and one or more external data processing devices, such as a base repeater, server, or programmer. The ambulatory repeater is interfaced to one or more external sensors to provide the capability to directly monitor patient health information at any time. The ambulatory repeater includes a power supply for operating separately and independently from an external power source and can be held or worn by a patient. The ambulatory repeater interrogates the IMD over a secure data connection on a regular basis or on demand and interfaces periodically to the external data processing device to exchange the information retrieved from the implantable medical device. 
     One embodiment provides a secure wireless ambulatory repeater. A cryptographic key is uniquely assigned to an implantable medical device. Sensitive information is preencrypted under the cryptographic key. Physiological measures are measured by the implantable medical device. A decryption module decrypts the sensitive information with the cryptographic key into decrypted information. A communications module exchanges the decrypted information and the physiological measures with the external data processing device over a wireless interface contingent upon authorization of the external data processing device. 
     A further embodiment provides an ambulatory repeater for use in automated patient care. A local memory store includes a cryptographic key, sensitive information, and physiological measures. The cryptographic key is uniquely assigned to the implantable medical device prior to implant of the implantable medical device into a patient. The sensitive information is preencrypted under the cryptographic key and physiological measures are measured by the implantable medical device. An authentication module is in receipt of the cryptographic key. A permissions module confirms authorization of an external data processing device against the cryptographic key. A decryption module decrypts the sensitive information with the cryptographic key into decrypted information. A processor is operatively coupled to the local memory store. A communications module exchanges the decrypted information and the physiological measures with the external data processing device over a wireless interface contingent upon the authorization confirmation. An internal power supply supplies power to the foregoing components. 
     A further embodiment provides a system for applying an ambulatory repeater to secure information exchange in automated patient care. An implantable medical device is implanted into a patient. A cryptographic key is uniquely assigned prior to implant. Sensitive information is preencrypted under a cryptographic key. Physiological measures are measured on an ad hoc basis by a sensor. An ambulatory repeater includes a storage, which stores the cryptographic key. A permissions module confirms authorization of an external data processing device against the cryptographic key. A decryption module decrypts the sensitive information with the cryptographic key into decrypted information. An external data processing device includes an interrogator receiving the decrypted information and the physiological measures from the ambulatory repeater over a wireless interface contingent upon the authorization confirmation. 
     Still other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein are described embodiments of the invention by way of illustrating the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and the scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing, by way of example, an implantable medical device. 
         FIG. 2  is a process flow diagram showing interfacing with the implantable medical device of  FIG. 2  using an ambulatory repeater. 
         FIG. 3  is a functional block diagram showing, by way of example, an ambulatory repeater in handheld form factor, in accordance with one embodiment. 
         FIG. 4  is a functional block diagram showing, by way of example, an ambulatory repeater in wearable form factor, in accordance with a further embodiment. 
         FIG. 5  is a functional block diagram showing, by way of example, systems for securely communicating using an ambulatory repeater, in accordance with one embodiment. 
         FIG. 6  is a functional block diagram showing, by way of example, the internal components of the ambulatory repeater in the wearable form factor of  FIG. 4 . 
         FIG. 7  is a flow diagram showing a method for providing automated patient care using an ambulatory repeater, in accordance with one embodiment. 
         FIG. 8  is a flow diagram showing a routine for obtaining a cryptographic key for use in the method of  FIG. 7 . 
         FIG. 9  is a flow diagram showing a routine for activating an ambulatory repeater for use in the method of  FIG. 7 . 
         FIG. 10  is a flow diagram showing a routine for performing a secure data exchange for use in the method of  FIG. 7 . 
         FIG. 11  is a flow diagram showing a routine for interrogating an IMD for use in the method of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Implantable Medical Device 
       FIG. 1  is a block diagram showing, by way of example, an implantable medical device (IMD)  103 . The IMD  103 , such as a pacemaker, implantable cardiac defibrillator (ICD) or similar device, is surgically implanted in the chest or abdomen of a patient to provide in situ therapy, such as pacing, cardiac resynchronization, defibrillation, neural stimulation and drug delivery, and physiological data monitoring. Examples of cardiac pacemakers suitable for use in the described embodiment include the Pulsar Max II, Discovery, and Discovery II pacing systems and the Contak Renewal cardiac resynchronization therapy defibrillator, sold by Guidant Corporation, St. Paul, Minn. 
     The IMD  103  includes a case  104  and terminal block  105  coupled to a set of leads  106   a - b . The leads  106   a - b  are implanted transvenously for endocardial placement. The IMD  103  is in direct electrical communication with the heart  102  through electrodes  111   a - b  positioned on the distal tips of each lead  106   a - b . By way of example, the set of leads  106   a - b  can include a right ventricular electrode  111   a , preferably placed in the right ventricular apex  112  of the heart  102 , and a right atrial electrode  111   b , preferably placed in the right atrial chamber  113  of the heart  102 . The set of leads  106   a - b  can also include a right ventricular electrode  114   a  and a right atrial electrode  114   b  to enable the IMD  103  to directly collect physiological measures, preferably through millivolt measurements. 
     The IMD  103  includes a case  104  and terminal block  105  coupled to a set of leads  106   a - b . The IMD case  104  houses hermitically-sealed components, including a battery  107 , control circuitry  108 , memory  109 , and telemetry circuitry  110 . The battery  107  provides a finite, power source. The control circuitry  108  controls therapy delivery and monitoring, including the delivery of electrical impulses to the heart  102  and sensing of spontaneous electrical activity. The memory  109  includes a memory store in which the physiological signals sensed by the control circuitry  108  can be temporarily stored, pending telemetered data download. 
     The telemetry circuitry  110  provides an interface between the IMD  103  and an external device, such as a programmer conventional or ambulatory repeater, or similar device. For near field data exchange, the IMD  103  communicates with a programmer or conventional or ambulatory repeater (not shown) through inductive telemetry signals exchanged through a wand placed over the location of the IMD  103 . Programming or interrogating instructions are sent to the IMD  103  and the stored physiological signals are downloaded into the programmer or repeater. For far field data exchange, the IMD  103  communicates with an external device capable of far field telemetry, such as a radio frequency (RF) programmer, conventional or ambulatory repeater, or other wireless computing device, as further described below with reference to  FIG. 2 . Other types of data interfaces are possible, as would be appreciated by one skilled in the art. 
     Other configurations and arrangements of leads and electrodes can also be used. Furthermore, although described with reference to IMDs for providing cardiac monitoring and therapy delivery, suitable IMDs also include other types of implantable therapeutic and monitoring devices in addition to or in lieu of cardiac monitoring and therapy delivery IMDs, including IMDs for providing neural stimulation, drug delivery, and physiological monitoring and collection. 
     Process Flow 
       FIG. 2  is a process flow diagram  120  showing interfacing with the IMD  103  of  FIG. 2  using an ambulatory repeater  123 . The ambulatory repeater  123  provides a portable means for securely transacting a data exchange session with the IMD  103  and, in turn, at least one of a conventional or “base” repeater  124 , server  125 , or programmer  126 , as further described below with reference to  FIG. 5 . Unlike a base repeater  124 , the ambulatory repeater  123  can collect patient health information as frequently or infrequently as needed and, due to being immediately proximate to the patient, can measure the activity level of the patient during normal everyday activities, rather than only at home or in a clinical setting. 
     Interfacing  120  with the IMD  103  includes key generation  121 , authentication  129 , activation  130 , protected data storage and retrieval  131 , unprotected data storage and retrieval  136 , and optional data exchanges  132 ,  133 ,  134  with the base repeater  124 , server  125 , and programmer  126 . Key generation  121  creates a cryptographic key  122 , which is used to encrypt and decrypt any sensitive information exchanged with the IMD  103 , such as during protected data storage and retrieval  131  using long range telemetry or over any other unsecured interface. The cryptographic key  122  can be statically generated and persistently stored, dynamically generated and persistently stored, dynamically generated and non-persistently stored as a session cryptographic key  122 , or a combination of the foregoing. Persistently-stored cryptographic keys  122  are maintained in a fixed secure key repository, such as a programmer, patient designator, secure database, token, base repeater  124 , ambulatory repeater  123 , and on the IMD  103  itself. Statically generated and persistently-stored cryptographic keys are stored in the IMD  103  prior to implantation, such as during the manufacturing process. Dynamically generated and persistently-stored cryptographic keys are generated dynamically, such as by the ambulatory repeater  123  for subsequent download to the IMD  103  using short range telemetry following implantation. Dynamically generated and non-persistently-stored session cryptographic keys are also generated dynamically and shared with the IMD  103 , but are not persistently stored and are used for a single patient data exchange. Each cryptographic key  122  is uniquely assigned to the IMD  103 . In one embodiment, the cryptographic key  103  has a length of 128 bits, is symmetric or is both 128-bits long and symmetric. Other cryptographic key lengths and symmetries are possible. 
     Authentication  129  provides an opportunity to securely obtain the cryptographic key  122  uniquely assigned to the IMD  103 . In one embodiment, the IMD  103  interfaces with an external source, such as the ambulatory repeater  123  or other wireless computing device, to either receive or share the cryptographic key  122  assigned to the IMD  103 , such as described in commonly-assigned U.S. Pat. No. 7,838,828, issued Nov. 9, 2010, the disclosure of which is incorporated by reference. In a further embodiment, the ambulatory repeater  123  retrieves the cryptographic key  122  from the IMD  103  using secure, short range telemetry, such as inductive telemetry, as further described below with reference to  FIG. 5 . 
     In a further embodiment, the cryptographic key  122  is entrusted to a third party, such as hospital or emergency services, as a form of key escrow. Under normal circumstances, the cryptographic key  122  will not be released unless the requester performs proper authentication  129 . However, the cryptographic key  122  could be released under specifically-defined circumstances, such as a bona fide medical emergency, to a third party to facilitate access to patient health information in the IMD  103 , ambulatory repeater  123 , base repeater  124 , server  125 , programmer  126 , or other such authenticated device. 
     Following authentication  126 , the ambulatory repeater  123  can be used to securely transact data exchange sessions with the IMD  103 . Each data exchange session is secure in that the patient health information being exchanged is safely protected from compromise and interception by encryption prior to being transmitted. Thus, the communication channel can be unsecured, as the data itself remains protected. As the ambulatory repeater  123  remains physically proximal to the patient, secure data exchange sessions are performed either as on demand or per a schedule, as further described below with reference to  FIGS. 6 and 9 . Briefly, activation  130  can occur due to a patient-initiated interrogation, on demand or at scheduled times. A patient-initiated interrogation is triggered by a manual override of the ambulatory repeater  123  by the patient when the patient, for instance, feels ill, or otherwise inclined to take a reading of data values. On demand interrogation occurs due to a remote or local event, such as remote activation request from the server  125 . Scheduled interrogation is specified by a healthcare provider and remains in effect until a new schedule is downloaded. 
     Upon activation  130 , protected data storage and retrieval  131  and unprotected data storage and retrieval  136  are performed. During protected data storage and retrieval  131 , sensitive information  127  (SI), particularly PHI, is provided to and retrieved from the IMD  103 , as further described below. During unprotected data storage and retrieval  136 , non-sensitive information (non-SI)  135  is retrieved from and sent to the IMD  103  directly via the ambulatory repeater  123 . Protected data storage and retrieval  131  and unprotected data storage and retrieval  136  can occur simultaneously during the same data exchange session. In a further embodiment, the SI  127  provided to the IMD  103  can include programming instructions for the IMD  103 . 
     In one embodiment, the bulk of the patient health information retrieved from the IMD  103  is non-SI  135 . SI  127  is generally limited to only patient-identifiable health information, which typically does not change on a regular basis. The non-SI  135  loosely falls into two categories of data. First, physiological data relates directly to the biological and biochemical processes of the body, such as salinity, pulse, blood pressure, glucose level, sweat, and so forth. Second, behavioral data relates to physical activities performed by the patient either during the course of a normal day or in response to a specific request or exercise regimen, such as sitting, standing, lying supine, and so forth. Other types of patient health measures are possible. 
     During protected data storage and retrieval  131 , SI  127 , particularly PHI, can be received into the ambulatory repeater  123  from one or more sensors  128  and from a patient or clinician, respectively via the base repeater  124  and server  125  or programmer  126 . Part or all of the sensitive information  127  is preferably preencrypted using the cryptographic key  122 , including any PHI, which can be stored on the IMD  103  as static data for retrieval by health care providers and for use by the IMD  103 , such as described in commonly-assigned U.S. Pat. No. 7,475,245, issued Jan. 6, 2009, the disclosure of which is incorporated by reference. If the sensitive information needs to be retrieved, the ambulatory repeater  123  obtains the cryptographic key  122 , if necessary, through authentication  126  and retrieves the encrypted information  128  from the IMD  103  for subsequent decryption using the cryptographic key  122 . In one embodiment, the sensitive information  127 , including any PHI, is encrypted using a standard encryption protocol, such as the Advanced Encryption Standard protocol (AES). Other authentication and encryption techniques and protocols, as well as other functions relating to the use of the cryptographic key  122  are possible, including the authentication and encryption techniques and protocols described in commonly-assigned U.S. Pat. No. 7,155,290, issued Dec. 26, 2006, the disclosure of which is incorporated by reference. 
     Ambulatory repeater-to-sensor data exchanges  139  enable the ambulatory repeater  123  to receive patient health information from the sensors  138 , including external sensors, such as a weight scale, blood pressure monitor, electrocardiograph, Holter monitor, or similar device. In a further embodiment, one or more of the sensors  138  can be integrated directly into the ambulatory repeater  123 , as further described below with reference to  FIG. 6 . 
     The non-SI  135  and SI  127  is exchanged with at least one of three external data processing devices, which include the base repeater  124 , server  125 , and programmer  126 . In addition, the ambulatory repeater  123  is communicatively interfaced to at least one external sensor to directly measure patient health information, as further described below beginning with reference to  FIG. 5 . Ambulatory repeater-to-base repeater data exchanges  132  enable the ambulatory repeater  123  to function as a highly portable extension of the base repeater  124 . Unlike the base repeater  124 , the ambulatory repeater  123  includes a power supply that enables secure interfacing with the IMD  103  while the patient is mobile and away from the base repeater  124  and can interrogate the IMD  103  at any time regardless of the patient&#39;s activity level. 
     Ambulatory repeater-to-server data exchanges  133  enable the server  125  to directly access the IMD  103  via the ambulatory repeater  123  through remote activation, such as in emergency and non-emergency situations and in those situation, in which the base repeater  125  is otherwise unavailable. 
     Ambulatory repeater-to-programmer data exchanges  134  supplement the information ordinarily obtained during a clinical follow-up session using the programmer  126 . The ambulatory repeater  123  interfaces to and supplements the retrieved telemetered data with stored data values that were obtained by the ambulatory repeater  123  on a substantially continuous basis. 
     In addition, patient health information can be shared directly  137  between the base repeater  124 , server  125 , and programmer  126 . Other types of external data processing devices are possible, including personal computers and other ambulatory repeaters. 
     Ambulatory Repeater in Handheld Form Factor 
       FIG. 3  is a functional block diagram  150  showing, by way of example, an ambulatory repeater  123  in handheld form factor  151 , in accordance with one embodiment. The handheld form factor  151  enables the ambulatory repeater  123  to be carried by the patient and can be implemented as either a stand-alone device or integrated into a microprocessor-equipped device, such as a personal data assistant, cellular telephone or pager. Other types of handheld form factors are possible. 
     The handheld form factor  151  includes a display  152  for graphically displaying indications and information  157 , a plurality of patient-operable controls  153 , a speaker  154 , and a microphone  155  for providing an interactive user interface. The handheld form factor  151  is preferably interfaced to the IMD  103  through RF telemetry and to the base repeater  124 , server  125 , and programmer  126  through either RF telemetry, cellular telephone connectivity or other forms of wireless communications, as facilitated by antenna  156 . The display  152  and speaker  154  provide visual and audio indicators while the controls  153  and microphone  155  enable patient feedback. In addition, one or more external sensors (not shown) are interfaced or, in a further embodiment, intergraded into the handheld form factor  151  for directly monitoring patient health information whenever required. 
     The types of indications and information  157  that can be provided to the patient non-exclusively include: 
     (1) Health measurements 
     (2) Active or passive pulse generator or health information monitoring 
     (3) Data transmission in-process indication 
     (4) Alert condition detection 
     (5) Impending therapy 
     (6) Ambulatory repeater memory usage 
     (7) Ambulatory repeater battery charge 
     In addition to securely exchanging data with the IMD  103 , the ambulatory repeater  123  can perform a level of analysis of the downloaded telemetered data and, in a further embodiment, provide a further visual indication  158  to the patient for informational purposes. 
     The handheld form factor  151  can also include a physical interface  159  that allows the device to be physically connected or “docked” to an external data processing device, such as the base repeater  124 , for high speed non-wireless data exchange and to recharge the power supply integral to the handheld form factor  151 . The ambulatory repeater  123  can continue to securely communicate with the IMD  103 , even when “docked”, to continue remote communication and collection of telemetered data. 
     Ambulatory Repeater in Wearable Form Factor 
       FIG. 4  is a functional block diagram  170  showing, by way of example, an ambulatory repeater  123  in wearable form factor  171 , in accordance with a further embodiment. The wearable form factor  171  enables the ambulatory repeater  123  to be worn by the patient and can be implemented as either a stand-alone device or integrated into a microprocessor-equipped device, such as a watch or belt. Other types of wearable form factors are possible. 
     Similar to the handheld form factor  151 , the wearable form factor  171  includes a display  172  for graphically displaying indications and information  177 , a plurality of patient-operable controls  173 , a speaker  174 , and a microphone  175  for providing an interactive user interface. The wearable form factor  171  is preferably interfaced to the IMD  103  through RF telemetry and to the base repeater  124 , server  125 , and programmer  126  through either RF telemetry, cellular telephone connectivity or other forms of wireless communications, as facilitated by antenna  176 . The display  172  and speaker  174  provide visual and audio indicators while the controls  173  and microphone  175  enable patient feedback. In addition, one or more external sensors (not shown) are interfaced or, in a further embodiment, intergraded into the wearable form factor  171  for directly monitoring patient health information whenever required. The wearable form factor  171  also includes a physical interface  179  that allows the device to be physically connected or “docked” to an external data processing device. 
     Ambulatory Repeater System Overview 
       FIG. 5  is a functional block diagram  190  showing, by way of example, systems for securely communicating using an ambulatory repeater  123 , in accordance with one embodiment. By way of example, an ambulatory repeater  123  in a wearable form factor  171  is shown, although the ambulatory repeater  123  could also be provided in the handheld form factor  151 . The ambulatory repeater  123  securely interfaces to the IMD  103  over a secure data communication interface  191 , such as described above with reference to  FIG. 2 . The ambulatory repeater interrogates the IMD  103  due to a patient-initiated interrogation, on demand, or at scheduled times. Patient-initiated interrogations are triggered by the patient through a manual override of the ambulatory repeater  123 . In one embodiment, the patient is limited in the number of times that a patient-initiated interrogation can be performed during a given time period. However, in a further embodiment, a healthcare provider can override the limit on patient-initiated interrogations as required. On demand interrogations occur in response to a remote or local event, such as a health-based event sensed by the ambulatory repeater  123 . Scheduled interrogations occur on a substantially regular basis, such as hourly or at any other healthcare provider-defined interval. The schedule is uploaded to the ambulatory repeater  123  and remains in effect until specifically replaced by a new schedule. The ambulatory repeater  123  can also be activated by indirect patient action, such as removing the device from a “docking” station. 
     Once activated, parametric and behavioral data collected and recorded by the IMD  103  from the external sensors are monitored by the ambulatory repeater  123  in a fashion similar to the base repeater  124 . However, the power supply enables the ambulatory repeater  123  to operate separately and independently from external power sources, thereby allowing the patient to remain mobile. The ambulatory repeater  123  also provides the collateral benefits of functioning as an automatic data back-up repository for the base repeater  124  and alleviates patient fears of a lack of monitoring when away from the base repeater  124 . In a further embodiment, the parametric and behavioral data is gathered and analyzed by either the ambulatory repeater  123  or an external data processing device, such as repeater  124 , server  125  or programmer  126 , and provided for review by a healthcare provider. Alternatively, the analysis can be performed through automated means. A set of new IMD parameters can be generated and provided to the ambulatory repeater  123  for subsequent reprogramming of the IMD  103 . 
     Periodically or as required, the ambulatory repeater  123  interfaces to one or more of the base repeater  124 , server  125 , and programmer  126  to exchange data retrieved from the IMD  103 . In one embodiment, the ambulatory repeater  123  interfaces via a cellular network  191  or other form of wireless communications. The base repeater  124  is a dedicated monitoring device specifically matched to the IMD  103 . The base repeater  124  relies on external power source and can interface to the IMD  103  either through inductive or RF telemetry. The base repeater  124  further interfaces to the ambulatory repeater  123  either through a physical or wireless connection, as further described above. 
     The server  125  maintains a database  192  for storing patient records. The patient records can include physiological quantitative and quality of life qualitative measures for an individual patient collected and processed in conjunction with, by way of example, an implantable medical device, such a pacemaker, implantable cardiac defibrillator (ICD) or similar device; a sensor  138 , such as a weight scale, blood pressure monitor, electrocardiograph, Holter monitor or similar device; or through conventional medical testing and evaluation. In addition, the stored physiological and quality of life measures can be evaluated and matched by the server  123  against one or more medical conditions, such as described in related, commonly-owned U.S. Pat. No. 6,336,903, to Bardy, issued Jan. 8, 2002; U.S. Pat. No. 6,368,284, to Bardy, issued Apr. 9, 2002; U.S. Pat. No. 6,398,728, to Bardy, issued Jun. 2, 2002; U.S. Pat. No. 6,411,840, to Bardy, issued Jun. 25, 2002; and U.S. Pat. No. 6,440,066, to Bardy, issued Aug. 27, 2002, the disclosures of which are incorporated by reference. 
     The programmer  126  provides conventional clinical follow-up of the IMD  103  under the direction of trained healthcare professionals. In one embodiment, the ambulatory repeater  123  interfaces via a cellular network  191  or other form of wireless communications. Other types of external data processing devices and interfacing means are possible. 
     In a further embodiment, the ambulatory repeater  123  interfaces to emergency services  193 , which posses a copy of the cryptographic key  122  (shown in  FIG. 2 ) held in a key escrow. Under ordinary circumstances, patient health information is exchanged exclusively between the ambulatory repeater  123  and authenticated external data processing devices, such as the base repeater  124 , server  125 , and programmer  126 . However, in a bona fide emergency situation, the emergency services  193  can use the cryptographic key  122  to access the patient health information in the ambulatory repeater  123  and IMD  103 , as well as the repeater  124 , server  125 , and programmer  126 . Other forms of key escrow are possible. 
     Ambulatory Repeater Internal Components 
       FIG. 6  is a functional block diagram  190  showing, by way of example, the internal components of the ambulatory repeater  123  in the wearable form factor  171  of  FIG. 4 . By way of example, the ambulatory repeater  123  includes a processor  202 , memory  203 , authentication module  212 , communications module  205 , physical interface  213 , optional integrated sensor  214 , and alarm  215 . Each of the components is powered by a power supply  204 , such as a rechargeable or replaceable battery. The internal components are provided in a housing  201  with provision for the antenna  176  and physical interface  179 . 
     The processor  202  enables the ambulatory repeater  123  to control the authentication and secure transfer of both non-sensitive and sensitive information between the IMD  103 , one or more external sensors (not shown), and one or more of the base repeater  124 , server  125 , and programmer  126 . The processor  202  also operates the ambulatory repeater  123  based on functionality embodied in an analysis module  207 , schedule module  208  and override module  209 . The analysis module  207  controls the translation, interpretation and display of patient health information. The schedule module  208  controls the periodic interfacing of the ambulatory repeater  123  to the IMD  103  and external data processing device. The override module  209  controls the patient-initiated interrogation. Other control modules are possible. 
     The communications module  205  includes an IMD telemetry module  210  and external data processing device (EDPD) telemetry module  211  for respectively interfacing to the IMD  103  and external data processing device, such as the base repeater  124 , server  125 , and programmer  126 . Preferably, the ambulatory repeater  123  interfaces to the IMD  103  and external sensors through inductive RF telemetry, Bluetooth, or other form of secure wireless interface, while the ambulatory repeater  123  interfaces to external data processing device preferably through RF telemetry or via cellular network or other form of wireless interface. The authentication module  206  is used to securely authenticate and encrypt and decrypt sensitive information using a retrieved cryptographic key  212 . The memory  203  includes a memory store, in which the physiological and parametric data retrieved from the IMD  103  are transiently stored pending for transfer to the external data processing device and, in a further embodiment, download to the IMD  103 . The physical interface  213  controls the direct physical connecting of the ambulatory repeater  123  to an external data processing device or supplemental accessory, such as a recharging “dock” or other similar device. The optional integrated sensor  214  directly monitors patient health information, such as patient activity level. Lastly, the alarm  215  provides a physical feedback alert to the patient, such as through a visual, tactual or audible warning, for example, flashing light, vibration, or alarm tone, respectively. Other internal components are possible, including a physical non-wireless interface and removable memory components. 
     Ambulatory Repeater Method Overview 
       FIG. 7  is a flow diagram showing a method  220  for providing automated patient care using an ambulatory repeater  123 , in accordance with one embodiment. The purpose of this method is to periodically activate and securely exchange information with the IMD  103 , one or more sensors  138 , and an external data processing device that includes one or more of a base repeater  124 , server  125 , and programmer  126 . The method  220  is described as a sequence of process operations or steps, which can be executed, for instance, by an ambulatory repeater  123 . 
     The method begins by obtaining the cryptographic key  122  (block  221 ), as further described below with reference to  FIG. 8 . The method then iteratively processes data exchange sessions (blocks  222 - 226 ) as follows. First, the ambulatory repeater  123  is activated (block  223 ), which includes securely interrogating the IMD  103 , as further described below with reference to  FIG. 9 . Next, the ambulatory repeater  123  performs a data exchange session with one or more of the external data processing devices, including the base repeater  124 , server  125 , and programmer  126 , as further described below with reference to  FIG. 10 . Following completion of the data exchange session, the ambulatory repeater  123  returns to a stand-by mode (block  225 ). Processing continues (block  226 ) while the ambulatory repeater  123  remains in a powered-on state. 
     Obtaining a Cryptographic Key 
       FIG. 8  is a flow diagram showing a routine  240  for obtaining a cryptographic key  122  for use in the method  220  of  FIG. 7 . The purpose of this routine is to securely receive the cryptographic key uniquely assigned to the IMD  103  into the ambulatory repeater  123 . 
     Initially, the cryptographic key  122  is optionally generated (block  241 ). Depending upon the system, the cryptographic key  122  could be generated dynamically by the base repeater  124  or programmer  126  for subsequent download to the IMD  103  using short range telemetry following implantation. Similarly, the cryptographic key  122  could be generated during the manufacturing process and persistently stored in the IMD  103  prior to implantation. Alternatively, the cryptographic key  122  could be dynamically generated by the IMD  103 . 
     Next, a secure connection is established with the source of the cryptographic key  122  (block  242 ). The form of the secure connection is dependent upon the type of key source. For instance, if the key source is the IMD  103 , the secure connection could be established through inductive or secure RF telemetric link via the base repeater  124  or programmer  126 . If the key source is the base repeater  124 , a secure connection could be established through the dedicated hardwired connection. 
     Finally, the cryptographic key  122  is authenticated and obtained (block  243 ) by storing the cryptographic key  122  into the authentication module  206 . 
     Ambulatory Repeater Activation 
       FIG. 9  is a flow diagram showing a routine  260  for activating an ambulatory repeater  123  for use in the method  220  of  FIG. 7 . The purpose of the routine is to activate the ambulatory repeater  123  prior to interrogating the sensors  138  and IMD  103 . 
     The ambulatory repeater  123  can be activated as scheduled (block  261 ) or through manual action directly or indirectly by the patient (block  262 ) or remotely, such as by the server  125  (block  265 ). 
     Manual activation typically involves either a direct patient-initiated interrogation (block  263 ), such as operating a manual override control, or indirect action, such as removing the ambulatory repeater  123  from a “docking” cradle (block  264 ). Similarly, remote activation involves either health-based data transfer triggers (block  266 ) or system-based data transfer triggers (block  267 ). A health-based data transfer is triggered when a prescribed or defined health status or alert condition is detected. A system-based data transfer trigger occurs typically due to a device-specific circumstance, such as data storage nearing maximum capacity. Other forms of manual and remote ambulatory repeater activations are possible. Upon activation, the sensors  138  and IMD  103  are interrogated (blocks  268  and  269 ), as further described below with reference to  FIG. 11 . 
     Secure Data Exchange 
       FIG. 10  is a flow diagram showing a routine  280  for performing a secure data exchange for use in the method  220  of  FIG. 7 . The purpose of this routine is to exchange data between the ambulatory repeater  123  and one or more external data processing device, such as the base repeater  124 , server  125 , and programmer  126 . 
     Initially, any sensitive information  127  is encrypted (block  281 ) using, for instance, the cryptographic key  122  that is uniquely assigned to the IMD  103 , or other cryptographic key (not shown) upon which the ambulatory repeater  123  and external data processing device have previously agreed. A secure connection is opened with the external data processing device (block  282 ) and the sensitive information is exchanged (block  283 ). The connection is “secure” in that the sensitive information is only exchanged in an encrypted or similar form protecting the sensitive information from compromise and interception by unauthorized parties. In the described embodiment, the secure connection is served through a Web-based data communications infrastructure, such as Web-Sphere software, licensed by IBM Corporation, Armonk, N.Y. Other types of data communications infrastructures can be used. Upon the competition of the exchange of sensitive information, the secure connection with external data processing device is closed (block  284 ) and a non-secure connection is open (block  285 ). Similarly, non-sensitive information is exchanged (block  286 ) and the non-secure connection is closed (block  287 ). The non-sensitive information can be sent in parallel to the sensitive information and can also be sent over the secure connection. However, the sensitive information cannot be sent over the non-secure connection. 
     IMD Interrogation 
       FIG. 11  is a flow diagram showing a routine  300  for interrogating an IMD  103  for use in the method  220  of  FIG. 7 . The purpose of this routine is to retrieve encrypted sensitive information  128 , including any PHI, from the IMD  103  and to decrypt the encrypted sensitive information  128  using the cryptographic key  122  uniquely assigned to the IMD  103 . 
     Initially, the ambulatory repeater  123  authenticates with the IMD  103  (block  301 ). A connection is established between the IMD  103  and the ambulatory repeater  123  (block  302 ) via an RF connection. Encrypted sensitive information  127 , including any PHI, is retrieved from the IMD  103  (block  303 ) and the connection between the IMD  103  and the ambulatory repeater  123  is closed (block  304 ). The encrypted sensitive information  128  is then decrypted using the cryptographic key  122  (block  305 ). 
     While the invention has been particularly shown and described as referenced to the embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.