U.S. patent application number 10/778886 was filed with the patent office on 2004-12-23 for control of data transmission between a remote monitoring unit and a central unit.
This patent application is currently assigned to CardioNet, Inc., a California corporation.. Invention is credited to Eggers, Philip N., Severe, Lon M..
Application Number | 20040260189 10/778886 |
Document ID | / |
Family ID | 25284157 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040260189 |
Kind Code |
A1 |
Eggers, Philip N. ; et
al. |
December 23, 2004 |
Control of data transmission between a remote monitoring unit and a
central unit
Abstract
A patient is monitored using a monitoring apparatus including a
remote monitoring unit associated with the patient and having a
sensor that measures a physiological characteristic of the patient,
a central unit, and a communications device which selectively
establishes a communications link between the remote monitoring
unit and the central unit. The remote monitoring unit obtains a
monitored data set for the patient, analyzes the monitored data set
to obtain a derived data set from the monitored data set, and
determines from the derived data set that communication with the
central unit is required. A communications link is established with
the central unit, and the remote monitoring unit transmits to the
central unit an initially transmitted data set related to the
monitored data set. The central unit analyzes the initially
transmitted data set and instructs the remote monitoring unit as to
any additional transmitted data set related to the monitored data
set that is to be transmitted from the remote monitoring unit to
the central unit and a time at which the additional transmitted
data set is to be transmitted.
Inventors: |
Eggers, Philip N.; (Poway,
CA) ; Severe, Lon M.; (San Diego, CA) |
Correspondence
Address: |
FISH & RICHARDSON, PC
12390 EL CAMINO REAL
SAN DIEGO
CA
92130-2081
US
|
Assignee: |
CardioNet, Inc., a California
corporation.
|
Family ID: |
25284157 |
Appl. No.: |
10/778886 |
Filed: |
February 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10778886 |
Feb 13, 2004 |
|
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09841152 |
Apr 23, 2001 |
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6694177 |
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Current U.S.
Class: |
600/509 |
Current CPC
Class: |
A61B 2560/0271 20130101;
A61B 5/0002 20130101; A61B 2560/0209 20130101 |
Class at
Publication: |
600/509 |
International
Class: |
A61B 005/04 |
Claims
1. (Canceled)
2. A system comprising: a remote monitoring unit including: a
sensor to measure a physiological characteristic of a heart of a
patient, a first data processing unit to analyze the sensor
measurements of the physiological characteristic to determine if
communication with a central unit is desired, and a first
communications device to communicate with the central unit in
response to prompting by the first data processing unit, the first
communications device to transmit data corresponding to the sensor
measurements; and a central unit including: a second data
processing unit to receive the data communicated from the remote
monitoring unit and to identify additional data to be transmitted
by the remote monitoring unit, and a second communications device
to communicate the identity of the additional data to the remote
monitoring unit.
3. The system of claim 2, wherein: the second data processing unit
is configured to identify a time when the additional data is to be
transmitted by the remote monitoring unit; and the second
communications device is configured to communicate the time to the
remote monitoring unit.
4. The system of claim 2, wherein the remote monitoring unit
further includes a data storage device configured to store data
including additional data marked for later transmission to a
central unit, and immediate data for current transmission to the
central unit.
5. The system of claim 2, wherein the first communications device
is configured to transmit a code for a cardiac abnormality to the
central unit.
6. The system of claim 2, wherein the remote monitoring unit is
configured to identify the immediate measurement information using
a patient-specific warning limit.
7. The system of claim 2, wherein the first communications device
comprises: a wireless communications device configured to transmit
data over a wireless connection to the central unit; and a wired
communications device configured to transmit data over a wired
connection to the central unit.
8. The system of claim 2, wherein the sensor is configured to
measure a cardiogram of the patient.
9. The system of claim 2, wherein the remote monitoring unit
further comprises at least one other sensor configured to measure
another physiological characteristic of the patient.
10. The system of claim 2, wherein the central unit further
comprises a patient history storage to store a personal history of
the patient.
11. The system of claim 2, wherein the central unit further
comprises a communications link to a human for review of the data
communicated from the remote monitoring unit.
12. A remote monitoring device comprising: a sensor configured to
measure a physiological characteristic of a heart of a patient; a
data processing unit configured to analyze the sensor measurements
of the physiological characteristic; and a data storage device
including: prior measurement information marked for later
transmission to a central unit, immediate measurement information
for current transmission to the central unit, and a warning limit
used by the data processing unit to identify the immediate
measurement information.
13. The remote monitoring device of claim 12, wherein the prior
measurement information comprises sensor measurements marked for
later transmission.
14. The remote monitoring device of claim 12, wherein the immediate
measurement information comprises data derived from current sensor
measurements.
15. The remote monitoring device of claim 14, wherein the data
derived from current sensor measurements comprises a heart rate
derived from current sensor measurements.
16. The remote monitoring device of claim 12, wherein the immediate
measurement information comprises a code for a cardiac
abnormality.
17. The remote monitoring device of claim 12, wherein the warning
limit comprises a patient-specific warning limit previously
determined for the patient.
18. The remote monitoring device of claim 12, further comprising a
communications device configured to communicate measurement
information to the central unit.
19. The remote monitoring device of claim 12, wherein the data
storage device further includes adjacent measurement information
that relates to sensor measurements adjacent in time to the
immediate measurement information.
20. The remote monitoring device of claim 12, wherein the data
storage device further includes time information identifying a time
for transmission of the prior measurement information to the
central unit.
21. The remote monitoring device of claim 12, wherein the sensor is
configured to measure a cardiogram of the patient.
22. The remote monitoring device of claim 12, further comprising at
least one other sensor configured to measure another physiological
characteristic of the patient.
23. A remote monitoring device, the device including instructions
operable to cause the device to perform operations comprising:
receiving sensor measurements relating to a physiological
characteristic of a heart of a patient; transmitting information
related to the received sensor measurements to a central unit;
receiving a request for additional information from the central
unit; and transmitting the requested additional information to the
central unit.
24. The device of claim 23 further including instructions operable
to cause the device to perform operations comprising receiving a
request for additional information related to the sensor
measurements from the central unit.
25. The device of claim 23 further including instructions operable
to cause the device to perform operations comprising analyzing the
sensor measurements to determine if the transmission of the
information to the central unit is warranted.
26. The device of claim 25 further including instructions operable
to cause the device to perform operations comprising determining if
the transmission of the information to the central unit is
warranted using a patient-specific warning limit to analyze the
sensor measurements.
27. The device of claim 23 further including instructions operable
to cause the device to perform operations comprising deriving a
data set from the received sensor measurements.
28. The device of claim 27 further including instructions operable
to cause the device to perform operations comprising transmitting
the derived data set to the central unit.
29. The device of claim 23 further including instructions operable
to cause the device to perform operations comprising: receiving,
from the central unit, a time for the transmission of the
additional information to the central unit; and delaying the
transmission of the additional information until the received
transmission time.
30. The device of claim 23 further including instructions operable
to cause the device to perform operations comprising receiving a
cardiogram of the patient.
31. A method comprising: receiving, from a remote unit, information
related to an electrocardiograph measurement on a patient;
determining that additional information absent from the received
information warrants communication from the remote unit; conveying
the determination to the remote unit; and receiving the additional
information from the remote unit.
32. The method of claim 31, wherein conveying the determination to
the remote unit comprises identifying the additional information to
the remote unit.
33. The method of claim 31, wherein conveying the determination to
the remote unit comprises identifying a time for transmission of
the additional information to the remote unit.
34. The method of claim 31, wherein determining that the additional
information warrants communication comprises deciding that
additional information related to the electrocardiograph
measurement warrants communication.
35. The method of claim 31, wherein deciding that the additional
information warrants communication comprises receiving human input
regarding the decision.
36. The method of claim 31, further comprising analyzing the
received information to determine whether an emergency situation
exists.
37. The method of claim 36, wherein analyzing the received
information comprises consulting a medical history of the
patient.
38. The method of claim 36, wherein analyzing the received
information comprises analyzing the received information in light
of other information related to electrocardiograph measurements on
the patient.
39. The method of claim 31, wherein receiving the additional
information comprises receiving the additional information from the
remote unit at a later time.
40. The method of claim 31, wherein: receiving information related
to the electrocardiograph measurement comprises receiving the
information over a first communication link; and receiving the
additional information comprises receiving the additional
information over a second communication link.
41. The method of claim 31, wherein receiving information related
to the electrocardiograph measurement comprises receiving
information derived from the electrocardiograph measurement.
Description
[0001] This invention relates to the transmission of data between a
remote monitoring unit and a central unit, and more particularly to
the optimization of such data transfer.
BACKGROUND OF THE INVENTION
[0002] Advances in sensor technology, electronics, and
communications have made it possible for physiological
characteristics of patients to be monitored even when the patients
are ambulatory and not in continuous, direct contact with a
hospital monitoring system. For example, U.S. Pat. No. 5,959,529
describes a monitoring system in which the patient carries a remote
monitoring unit with associated physiological sensors. The remote
monitoring unit conducts a continuous monitoring of one or more
physiological characteristics of the patient according to the
medical problem of the patient, an example being the heartbeat and
its waveform.
[0003] Under prescribed conditions, the remote monitoring unit
contacts a central unit to communicate information on the condition
of the patient. For example, if the remote monitoring unit
determines that the monitored physiological data suggests that the
patient may be in distress or in an emergency, it may immediately
and automatically transfer the monitored data to the central unit
over a cellular telephone or comparable communications device. The
central unit automatically, or in conjunction with medical
personnel who are stationed at or are in contact with the central
unit, analyzes the data and coordinates the provision of assistance
to the patient when necessary. Where the analysis of the
transmitted data indicates that there is no patient situation
requiring immediate attention, the data is stored and may also be
forwarded to the patient's physician so that treatments may be
altered.
[0004] While operable, this approach may in some cases be wasteful
of the battery power of the remote monitoring unit and require the
expenditure of too much data transfer time over the cellular
telephone system with its associated charges. The time of the
medical personnel may also be used inefficiently.
[0005] There is a need for an improved approach for the control of
data transfers between the remote monitoring unit and the central
unit. The present invention fulfills this need, and further
provides related advantages.
SUMMARY OF THE INVENTION
[0006] The present invention provides an approach for monitoring a
patient and providing support to the patient. The present approach
adopts a new data transfer architecture with improved selectivity
of data transmission but retention of the data accumulation
capability to build the patient history and also the emergency
capability to assist the patient on an urgent basis when needed.
The battery power of the remote monitoring unit is thereby used
more judiciously, the cellular telephone connect time is reduced,
and medical personnel time is better managed.
[0007] In accordance with the invention, a method of monitoring a
patient comprises providing a monitoring apparatus including a
remote monitoring unit associated with the patient. The remote
monitoring unit includes a sensor that measures a physiological
characteristic of the patient such as a cardiogram, a central unit,
and a communications device which selectively establishes a
communications link between the remote monitoring unit and the
central unit. The remote monitoring unit obtains a monitored data
set for the patient, analyzes the monitored data set to obtain a
derived data set from the monitored data set, and determines from
the derived data set that communication with the central unit is
required. A communications link is established with the central
unit, and the remote monitoring unit transmits to the central unit
an initially transmitted data set related to the monitored data
set. The central unit analyzes the initially transmitted data set
and instructs the remote monitoring unit as to any additional
transmitted data set, which may be related to the monitored data
set, that is to be transmitted from the remote monitoring unit to
the central unit and a time at which the additional transmitted
data set is to be transmitted.
[0008] The present invention is therefore based in an architecture
where the main body of data is not automatically transmitted from
the remote monitoring unit to the central unit. That approach is
likely to produce unnecessarily large and unnecessarily frequent
data transfers which result in depletion of the batteries of the
remote monitoring unit and large transmission-time costs. Instead,
the central unit analyzes the initially transmitted data set, which
is usually a reduced data set that is derived from or determined by
the monitored data set, to determine whether a more complete data
transfer in the form of the additional transmitted data set is
required. If so, that transmission is made at a time specified by
the central unit. The time of transmission may be immediate, as
when an emergency condition is sensed, or deferred, as when the
additional transmitted data set is needed for the patient history.
The efficiency of communication is thereby optimized while at the
same time meeting the medical requirements for the patient.
[0009] The step of the remote monitoring unit analyzing the
monitored data set may be accomplished by comparing at least one
element of the derived data set to a warning limit. The analysis of
the initially transmitted data set may include obtaining a patient
history from a memory, and analyzing the initially transmitted data
set in relation to the patient history. The central unit may
instruct the remote monitoring unit to transmit the additional
transmitted data set substantially immediately or at a delayed
time. The additional transmitted data set and the monitored data
set may be the same or may not be the same data sets.
[0010] In one embodiment, the communications device comprises a
radio frequency telephone terminal (such as a cellular or satellite
telephone terminal) and a land-line telephone terminal. The radio
frequency telephone connection may be made at any time, but the
land-line telephone terminal is available only when the remote
monitoring unit is physically connected to a land line. The
transmission of the initially transmitted data set, which usually
is a much smaller amount of data than the monitored data set, may
be made over the radio frequency telephone connection. Upon
analysis at the central unit, if there appears to be the
possibility of an emergency wherein more data is needed
immediately, the larger additional transmitted data set may be
immediately transmitted over the radio frequency telephone
connection. On the other hand, where the central unit determines
that there is not an emergency but that it would be useful to have
the additional transmitted data set for future reference as a part
of the patient history, the central monitoring unit may instruct
the remote monitoring unit to store and then transmit the
additional transmitted data set at a later time over the land-line
telephone terminal when such a connection is available or the radio
frequency telephone connection when transmission costs are lower
(i.e., off-peak hours).
[0011] This selective transmission approach, wherein data
transmission from the remote monitoring unit is not automatic but
instead is under control of the central unit, reduces the amount of
data that must be transmitted over a cellular telephone connection
or similar expensive communication device. This selectivity reduces
cellular telephone connect time and charges to the user, and also
may significantly increase the lifetime of the remote monitoring
unit between battery charging, because establishing and maintaining
the cell phone connection constitutes a significant portion of the
battery usage of the remote monitoring unit. The human resources of
the medical personnel at or in communication with the central unit
are also better utilized. Only those situations that are more
likely to be actual emergencies are brought to the attention of
those medical personnel, so that they have more time for such
potential actual emergencies.
[0012] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention. The scope of the invention is not, however, limited
to this preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a block flow diagram of a method for practicing
the present invention; and
[0014] FIG. 2 is a simplified schematic block diagram of a
preferred apparatus with which the present invention may be
used.
DETAILED DESCRIPTION OF THE INVENTION
[0015] FIG. 1 depicts an approach for practicing the present
invention. A monitoring apparatus is provided, numeral 20. The
monitoring apparatus may be of any operable form, and one preferred
form of the monitoring apparatus 50 is illustrated in FIG. 2. The
monitoring apparatus 50 is shown in a simplified form illustrating
only those portions that are required to discuss the present
invention. More detail of a monitoring apparatus may be found in
U.S. Pat. No. 5,959,529, whose disclosure is incorporated by
reference.
[0016] The monitoring apparatus 50 includes a remote monitoring
unit (RMU) 52 carried by an ambulatory patient, and a central unit
(CU) 54. The central unit 54 may be a single computer, but it is
more typically a file server or a network. Other remote monitoring
units, that are not "portable" in the sense that they are not
carried on the person of the patient but may be at a fixed location
in a patient's home or hospital facility, may be used as well. A
sensor 56 measures a physiological characteristic of a patient, and
is typically in contact with the patient. ("Patient" is used in a
broad sense, and refers to a person being monitored.) There may be
one sensor or more than one sensor 56, depending upon the
parameters of the patient that are of interest. Examples of
operable sensors 56 include a heart monitor sensor, a blood
pressure monitor sensor, a temperature monitor sensor, a
respiration sensor, a brain wave sensor, a blood chemistry sensor
such as a blood glucose sensor or a blood oxygen sensor, a patient
position sensor, and a patient activity sensor. Sensors of various
types are known in the art, and details of their construction and
operation do not form a part of the present invention.
[0017] In either event, the sensor 56 is in communication with a
central processing unit (CPU) 58 of the remote monitoring unit 52,
with intermediate signal conditioning equipment as necessary (not
shown here). The central processing unit 58 performs analyses of
the signals of the sensor 56, as will be discussed subsequently.
Similarly, the central unit 54 includes a central processing unit
(CPU) 60 to perform calculations and analyses, as will be discussed
subsequently. (As noted, the central unit 54 and its CPU 60 may be
of any operable type, such as a dedicated system, a network, or a
file server. Each CPU 58 and 60 typically includes a
microprocessor.)
[0018] The remote monitoring unit 52 and the central unit 54 may be
placed in two-way communication with each other through a
transceiver 62 located in the remote monitoring unit 52 and a
communicating transceiver 64 located in the central unit 54. (The
description that the transceiver is "in" the described device
includes the case where the transceiver is not physically within
the same structure as the CPU, but is instead in another location
but in communication with the CPU. Thus, for example, the central
unit 54 may include a file server in which the CPU 60 is located
and a physically separate cellular transceiver 64 with a
communication link to the file server and the CPU 60.) The
transceivers 62, 64 may include any operable type of communications
devices. For example, they may include a modem to establish
communications over a conventional land line for routine
communications. They may also include a cellular telephone
transceiver to establish communications on an urgent or routine
basis. The transceivers 62, 64 may also be equipped for two-way
voice communication between the patient and a person at the central
unit 54. The transceivers 62, 64 may interconnect over the
internet, with or without land line or cellular links at each end,
as well, with the internet having its own communications
capabilities. The present invention is concerned in part with
determining how much data should be transmitted as urgent
communications and how much data should be transmitted as routine
communications. The central unit 54 is provided with an interface
to allow human review 66 of recommended actions of the central
processing unit 60, as by the patient's physician.
[0019] Returning to the discussion of FIG. 1, the remote monitoring
unit 52 obtains a monitored data set for the patient using the
sensor(s) 56, numeral 22. The monitored data set is often fairly
voluminous, such as a continuous loop of 24 hours of a cardiograph
of the patient in the form of (voltage, time) data pairs.
[0020] The remote monitoring unit 52 analyzes the monitored data
set to obtain a derived data set from the monitored data set,
numeral 24. The derived data set is typically much smaller in size
than the monitored data set, and includes types of data that have
been previously found to be significant. The derived data set may
include, for example, an indication of a specified type of an
abnormal heart beat (i.e., a code for the sensed abnormality), a
heart rate (number of beats per minute), maximum voltage value,
basic wave-shape assessment, and whether patient-specific criteria
were violated by the heartbeat waveform. The derived data set is
obtained from the monitored data set by conventional waveform
processing procedures.
[0021] The central processing unit 58 of the remote monitoring unit
52 analyzes the derived data set, typically by comparing the values
of the parameters with warning limits previously determined for the
patient and provided to the remote monitoring unit 52 or by other
suitable approaches. For example, if the heart rate exceeds a heart
rate warning limit, the maximum voltage value is greater than a
voltage warning limit, and/or the wave shape is not within a
waveshape warning limit, the remote monitoring unit 52 may
determine that there is a potential emergency with the patient or
that data should be transmitted immediately for diagnostic
purposes. In that event, the remote monitoring unit 52 determines
that communication with the central unit 54 is required
immediately, numeral 26. The remote monitoring unit 52 may instead
determine that the data is of interest for inclusion in the
patient's centrally stored history, but that there is no emergency
at hand. In that case, the data of interest is marked for
transmission at a later time, as in a daily routine transmission.
The remote monitoring unit 52 may instead determine that the data
is of no particular interest. In the majority of situations there
is no potential emergency and communications are not required, and
the monitoring apparatus then cycles from step 24 back to step 22
and repeats steps 22 and 24.
[0022] Where it has been determined that communication is required
immediately, a communications link is immediately established
through the transceivers 62, 64 between the remote monitoring unit
52 and the central unit 54, numeral 28. If it is not possible to
establish communications through a land line, then there is an
attempt to establish the more expensive and less dependable radio
frequency cellular link.
[0023] The remote monitoring unit 52 transmits to the central unit
54 an initially transmitted data set, numeral 30. The initially
transmitted data set may be related to the monitored data set or
unrelated to the monitored data set (as for example information
suggesting a sensor failure), the former being the most common. The
initially transmitted data set may be the same as the derived data
set, or it may include different data. For example, the initially
transmitted data set may also include information from other
sensors, such as a respiration rate or blood pressure of the
patient. The initially transmitted data set is structured to
contain the most significant information for decision making and to
permit transmission to the central unit 54 in a relatively short
time. The central unit 54 therefore has the most significant
information needed for further decision making concisely.
[0024] The central processing unit 60 of the central unit 54
analyzes the initially transmitted data set, numeral 32. In
performing this analysis, the central unit 54 often relies on
patient history (numeral 34) that is stored in the central unit 54
or is obtainable by a further link to the doctor or hospital that
is responsible for the patient. The central unit 54 may be aided in
its decision making by human review and consideration of the
situation, numeral 66 of FIG. 2. The human review 66 may be
conducted by a medical technician or by the patient's physician.
However, at this stage it is preferred that the analysis step 32 be
as fully automated as possible so that a decision may be made
quickly regarding the need for further information. The analysis
and human review at this point are not performed for the purposes
of diagnosis, but instead to determine whether more information is
required immediately from the remote monitoring unit 52.
[0025] From the information provided to it by the initially
transmitted data set and from other sources such as the patient
history, the central unit 54 determines the subsequent flow of
information from the remote monitoring unit 52 and instructs the
remote monitoring unit 52 as appropriate, numeral 36. The central
unit 54 may, for example, determine that no further information
need be transmitted, may determine that more information in the
form of an additional transmitted data set is required on an urgent
basis, or may determine that more information in the form of the
additional transmitted data set is required at a later time. The
volume and type of data to be transmitted is also determined. In
the case where no further information is required, the
communication between the remote monitoring unit 52 and the central
unit 54 may be immediately terminated, and the remote monitoring
unit 52 cycles back to step 22. In the case where further
information is required on an urgent basis, the communication link
remains open and the additional transmitted data set is transmitted
from the remote monitoring unit 52 to the central unit 54
immediately, numeral 38. In the case where further information is
required at a later time such as at the time of routine data
transmissions, the communication link is terminated as far as the
urgent communication is concerned but the data of interest is
marked for later transmission. At a later delayed time, such as at
the time of routine data transmissions for the day, the additional
transmitted data is transmitted from the remote monitoring unit 52
to the central unit, numeral 40. In a typical case, the additional
transmitted information is transmitted with routine transmissions
using a telephone land line, which is substantially less expensive
than using a cellular telephone link and also is accomplished when
the remote monitoring unit is receiving line power so that there is
no battery drain. The additional transmitted data set selected by
the central unit 54 may include the monitored data set, less than
the full monitored data set, or more than the monitored data set
because, for example, additional information from other sensors is
required.
[0026] An example is helpful in illuminating the role of the
central unit. If the doctor in charge of the patient has instructed
that fewer than three premature ventricular contraction (PVC)
events per hour is not of concern, but that three or more events
per hour is of sufficient concern to require more information on an
urgent basis, the remote monitoring unit 52 contacts the central
unit upon the occurrence of each such event. The central unit 54
consults the patient history, which contains a running listing of
the occurrence of such events. If the present event is found to be
the third event in the last hour, then the central unit 54
instructs the remote monitoring unit 52 to transmit the additional
transmitted data set on an urgent basis. If the present event does
not result in a condition of three or more events in the last hour,
it still may be desirable to transmit the waveform for the event
and the adjacent time periods for the patient history but only at
the next routine transmission. (Alternatively, the PVC count may be
maintained by the remote monitoring unit 52, and contact
established with the central unit 54 only when three PVC events are
counted in any one-hour period.)
[0027] The advantages of the present approach are illustrated in
another example. By making decisions based on the initially
transmitted data set, it may be necessary to maintain a cellular
connection for at most a minute. On the other hand, if the entire
monitored data set were automatically transmitted from the remote
monitoring unit 52 to the central unit 54, the time required might
be on the order of several minutes of cellular connection time to
transmit each 5 minutes of the cardiogram. This connection results
in a significant drain on the battery of the remote monitoring unit
and extra cellular connection time and cost, which are to be
avoided if possible. Where it is judged that there is an urgent
need for the additional transmitted data set because the patient
may be in danger or the data is of immediate diagnostic value, the
cellular link is maintained and the full additional transmitted
data set is communicated as necessary so that the patient may be
aided.
[0028] Although a particular embodiment of the invention has been
described in detail for purposes of illustration, various
modifications and enhancements may be made without departing from
the spirit and scope of the invention. Accordingly, the invention
is not to be limited except as by the appended claims.
* * * * *