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PRESSURE ULCER CONDITION SENSING
BACKGROUND OF THE INVENTION
This invention relates generally to sensing and monitoring 5 one or more conditions related to the health of the human body, such as the development, prevention and treatment of pressure ulcers. The present invention more particularly relates to a medical sensor and a system and method of monitoring one or more pressure sensitive areas of a human 1° body. Although aspects of the present invention have application with regard to other human body conditions, the invention will be specifically described in the context of pressure that contributes to the development of external skin ulcers (e.g., decubitus ulcers). In this context, the invention :5 also relates to a computer-implemented pressure ulcer management method.
Pressure ulcers can develop in a person who is bedridden or confined to a wheelchair, for example. Intrinsic and extrinsic factors may be involved in the development of such 20 pressure sores. Intrinsic factors include impaired mobility, incontinence, skin condition, nutrition, and mental status.
Exposure to pressure is one extrinsic factor. When a bony, protuberant body portion, for example, is pressed against a support such as a bed or a chair under the person's weight or part of that weight, pressure is applied to that portion; if this position is maintained, such as due to the person's immobility, this pressure can be at least one contributing factor in causing a break in the person's skin, reduced blood ^ flow to that tissue and the loss of surface tissue and the disintegration and necrosis of epithelial tissue (i.e., an ulcer).
The scope and cost of such pressure ulcers in the United States are significant. No dollar amount is placed on the cost of human suffering from this debilitating condition. 35
Implementation of guidelines set forth by the Agency for Health Care Policy and Research (AHCPR) has resulted in measurable improvements in carefully monitored institutions. These studies demonstrated that with diligent nursing care, many pressure ulcers are preventable. However, with 40 staff/patient ratios typically found in nursing homes, it may be impractical to expect all aspects of the AHCPR guidelines to be followed for all but high-risk patients. Factors found to influence pressure ulcer development in one study included: inadequate numbers of nursing staff, the use of agency 45 personnel instead of regular staff, supply shortages, and the effects of micromanagement. The extent of this problem may grow as medical advances prolong the life expectancy of seriously ill patients and as the population over the age of 65 expands. In view of the foregoing, and as an increased 50 number of patients are given home care, there is the need for effective and simple techniques and equipment for pressure ulcer prevention.
Various equipment has been proposed or used in trying to prevent or treat pressure sores. This equipment includes 55 overlays, replacement mattresses, and specialty beds that attempt to reduce the amount of pressure to which tissues are exposed. These may vary in effectiveness, practicality of use, and maintenance requirements. Although pertinent to the prevention and treatment of pressure sores, this particu- 60 lar equipment is distinct from the sensing and monitoring equipment and methods to which the present invention is directed.
Pressure sensing and monitoring systems have been proposed in, for example, U.S. Pat. No. 4,554,930 to Kress and 65 U.S. Pat. No. 5,253,656 to Rincoe et al. Another device, a Tekscan body pressure measurement system, monitors pres
sure; however, the sensor construction may lend itself to limited life because creases that may be formed in it due to a peak pressure may damage the small resistive ink sensors. Furthermore, this is a relatively complex and expensive system. Less expensive pressure analyzers have been available from Talley and Cleveland Medical Devices; however, these use air bladder sensors that have a relatively high profile not recommended for continuous pressure monitoring between a patient and an adjacent support.
Accordingly, there is still the need for novel and improved equipment and methods for sensing and monitoring one or more conditions related to the health of the human body and especially related to the development, prevention and treatment of pressure ulcers. There is the particular need for a novel and improved medical sensor and system and method of monitoring one or more pressure sensitive areas of a human body. There is also the need for a computerimplemented pressure ulcer management method. These preferably should facilitate the acquisition of pressure and time information that can be used in the prevention or treatment of pressure ulcers.
SUMMARY OF THE INVENTION
The present invention meets the aforementioned needs by providing novel and improved equipment and methods for sensing and monitoring one or more conditions related to the health of the human body and especially related to the development, prevention and treatment of pressure ulcers. The present invention particularly provides a novel and improved medical sensor and system and method of monitoring one or more pressure sensitive areas of a human body. The present invention also provides a computerimplemented pressure ulcer management method. These facilitate the acquisition of pressure and time information that can be used in the prevention or treatment of pressure ulcers.
The preferred embodiment of the present invention provides real-time monitoring of pressure status over time, whereby at-risk patients requiring immediate intervention can be quickly identified. The preferred embodiment also offers the advantage of relatively inexpensive disposable sensors that safely monitor exposure time to pressure. Although disposable, the sensors are repeatedly operable during their time of use. Such sensors provide for wireless communication so that there are no wires extending from the patients to whom the sensors are attached. The sensors are thin and flexible whereby they do not add significant profile to dressings with which they are preferably used, and they do not require additional manipulation by a care provider.
Monitoring the wireless communications from the sensors permits tracking when a patient is in a position in which pressure is applied to a pressure sensitive area. Tracking can occur from different directions since a patient might move in a variety of orientations relative to the monitoring equipment. Local warnings can be given in response to defined conditions, and data can be transferred to a central location managing a network of monitored sites. Monitoring at any one site can use a plurality of sensors, and the monitoring can be on an intelligent polling basis in which no polling occurs for sensors that are not present in a particular application.
The network can be used to provide warnings to a centralized location when defined conditions are sensed and reported, to manage overall monitored information for all patients in the network, and to monitor and record patient handling schedules, for example. This can include maintain3
ing information about specific patient ulcer history/current status, prevention or treatment protocols used, and costs related to prevention or treatment. This can also include information about how long a patient remained in a particular condition, compliance by personnel with patient schedules, and data derived from the monitored conditions.
A medical sensor of the present invention responds to a predetermined condition, and the sensor provides wireless communication of the sensing of the condition. In one embodiment, the medical sensor comprises a substrate applicable to a human body and an electric circuit connected to the substrate. The electric circuit includes: a switch operable in a circuit operative state in response to the predetermined condition; and resonant circuit elements connected to the switch as a resonant circuit to provide a signal at a resonant frequency in response to electromagnetic induction when the switch is in the circuit operative state. Such a medical sensor can be used in implementing a method of monitoring a condition of a human body. Such method comprises: changing a characteristic of a resonant circuit, applied to the human body, in response to a sensed change in the monitored condition; energizing, by electromagnetic induction, the resonant circuit such that the resonant circuit generates a resonant signal dependent on the changed characteristic; and detecting the resonant signal.
In one implementation of the aforementioned medical sensor, the switch is in a different operative state when not responding to the predetermined condition such that the resonant circuit provides a signal at another resonant frequency in response to electromagnetic induction when the switch is in the different operative state.
Although the present invention is more broadly applicable to monitoring a condition of a patent, a particular monitoring system of the present invention monitors a pressure sensitive area of a patient positioned on a support. An electromagnetic wave transmitter of the system is disposed adjacent the support. A resonant signal detector is disposed adjacent the support in operative association with the electromagnetic wave transmitter. The system also comprises a medical sensor adapted to be attached to the patient such that the medical sensor is responsive to pressure applied to the pressure sensitive area of the patient. The medical sensor includes a resonant circuit operative in at least two states in response to pressure applied to the pressure sensitive area of the patient; in at least one of the states the resonant circuit causes a resonant signal to be propagated in cooperative operation with the electromagnetic wave transmitter. The medical sensor is not tangibly attached to the electromagnetic wave transmitter or the resonant signal detector when the medical sensor is attached to the patient.
The monitoring system can also comprise a controller that is connected to the resonant signal detector such that the controller receives a respective signal from the resonant signal detector in response to the resonant signal detector detecting a respective propagated resonant signal. In one implementation, the controller computes an exposure time value in response to a predetermined exposure time monitoring period and the cumulative time within the exposure time monitoring period during which the controller receives signals from the resonant signal detector indicating pressure applied to the pressure sensitive area greater than a predetermined magnitude. In addition or alternatively, the controller can compute a shift frequency value in response to a predetermined shift frequency monitoring period and the number of transitions relative to receiving signals from the resonant signal detector during the monitoring period.
In accordance with another definition of the present invention, a method of monitoring one or more pressure
sensitive areas of a patient on a support comprises: providing an electromagnetic field across a region of the patient on the support; and propagating, in operative association with the electromagnetic field, resonant signals in response to
5 pressure above a predetermined magnitude at one or more external areas of the patient susceptible to ulceration and wirelessly communicating the resonant signals to a resonant signal detector disposed adjacent the support. In a particular embodiment, providing an electromagnetic field includes transmitting radio frequency signals having different respective frequencies within a predetermined frequency range; and propagating resonant signals includes emitting from each respective external area resonant signals having a respective resonant frequency responsive to a respective s frequency of the radio frequency signals.
Another definition of the present invention includes a method of monitoring at least one pressure sensitive area of a patient on a support, comprising providing an electromagnetic field across a region of the patient on the support, and
2Q propagating, in operative association with the electromagnetic field, respective resonant signals in response to respective pressure magnitudes at the at least one pressure sensitive area of the patient and wirelessly communicating the resonant signals to a resonant signal detector disposed
25 adjacent the support.
The present invention also provides a method of monitoring for a sensor adapted to be attached to a patient. This method comprises transmitting, across a region in which a patient is disposed, a driving signal having at least one
30 frequency to which a sensor adapted to be attached to the patient is responsive if the sensor is attached to the patient. This method further comprises detecting whether a first response signal is emitted from the sensor in the region in response to the driving signal, the first response signal
35 indicating the presence of the sensor in the region. This method also comprises detecting whether a second response signal is emitted from the sensor in the region in response to the driving signal, the second response signal indicating a condition related to the patient. This method can still further
40 comprise: repeating the transmitting and detecting steps for respective selected frequencies of the driving signal and respective responsive frequencies for the first and second response signals for a plurality of sensors adapted to be attached to the patient.
45 The present invention still further provides a computerimplemented pressure ulcer management method. This method comprises: maintaining in a computer a database containing a respective ulceration history for each of a plurality of patients, each ulceration history including data
50 identifying information relevant to the respective patient's susceptibility to ulcer formation; monitoring the patients, including for each patient sensing pressure application to at least one location on the respective patient at risk to ulcer formation and communicating additional data to the com
55 puter in response to sensed pressure application; storing in the computer the additional data with the data in the database; and managing the care of each patient in response to that patient's respective ulceration history and the respective stored additional data.
60 In one aspect of the pressure ulcer management method, each ulceration history further includes respective patient historical data identifying any unhealed ulcers, previous ulcers, when each previous ulcer was detected, when each previous ulcer was healed, the number of pressure applica
65 tions sensed during the period between when a respective previous ulcer was detected and when the respective previous ulcer was healed, and the cumulative exposure time to
pressure during the period between when a respective previous ulcer was detected and when the respective previous ulcer was healed. Furthermore, the additional data can include the number of pressure applications and a cumulative exposure time to pressure for each unhealed ulcer. In 5 this context, managing the care of each patient includes computing an estimated remaining treatment period for a respective unhealed ulcer in response to the historical data for at least one previous ulcer of the patient and the additional data for the respective unhealed ulcer. 10
In another aspect of the pressure ulcer management method, each ulceration history further includes historical data identifying previous ulcers, the number of previous ulcers occurring at the same location of the respective patient, when each previous ulcer was detected at the ^ respective location, and when each previous ulcer was healed. In this context, managing the care of each patient includes determining in the computer a respective frequency of ulcer formation in response to the historical data for each location; and managing the care of each patient further 2o includes determining in the computer a respective time since the last previous ulcer was healed at each respective location for the respective patient and comparing the determined time with the respective determined frequency of ulcer formation for the respective location. 25
Another definition of the computer-implemented pressure ulcer management method comprises: maintaining in a computer a database containing a respective predetermined ulceration event for each of a plurality of patients; monitoring the patients, including for each patient sensing pressure 30 application to at least one location of the respective patient susceptible to ulceration and communicating data to the computer defining shifts of the respective patient between pressure-on and pressure-off events relative to the at least one location in response to sensed pressure application; and 35 correlating in the computer the communicated data with the respective predetermined ulceration event for each of the patients. In one aspect, the predetermined ulceration event includes a time the respective patient is to be turned relative to the respective at least one location susceptible to ulcer- 40 ation; and correlating the communicated data with the respective predetermined ulceration event includes determining whether a transition from a pressure-on event to a pressure-off event occurred at the respective time. In another aspect, the predetermined ulceration event includes a 45 pressure-on threshold relative to the respective at least one location susceptible to ulceration; and correlating the communicated data with the respective predetermined ulceration event includes determining the length of time from a sensed pressure exceeding the predetermined pressure-on threshold 50 to the next sensed pressure-off event.
Therefore, from the foregoing, it is a general object of the present invention to provide novel and improved equipment and methods for sensing and monitoring one or more conditions related to the health of the human body and 55 especially related to the development, prevention and treatment of pressure ulcers. Another object of the present invention is to provide a novel and improved medical sensor and a novel and improved system and method of monitoring one or more pressure sensitive areas of a human body. A 60 further object of the present invention is to provide a novel and improved computer-implemented pressure ulcer management method. Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art when the following description of 65 the preferred embodiments is read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates part of a human body, showing some locations susceptible to pressure ulcers and showing a sensor of the present invention applied to the body at one of the locations.
FIG. 2 illustrates one type of support, namely a bed, having part of one embodiment of the monitoring system of the present invention associated with it.
FIG. 3 illustrates the bed but having part of another embodiment of the monitoring system of the present invention associated with it.
FIG. 4 is a block diagram illustrating a third association with a support for the patient as well as also illustrating an overall monitoring system.
FIG. 5 is a block diagram of the monitoring system for a plurality of patients.
FIG. 6 is a schematic circuit diagram of one embodiment of a medical sensor of the present invention.
FIG. 7 is a schematic circuit diagram of another embodiment of a medical sensor of the present invention.
FIGS. 8A-8C illustrate a particular implementation of the medical sensor.
FIG. 9 is a schematic circuit diagram for one resistive type of medical sensor.
FIG. 10 is a graph illustrating a sequence of pressure-on conditions in which a pressure above a predetermined threshold is exerted for respective lengths of time against one embodiment of the medical sensor of the present invention.
FIG. 11 illustrates one embodiment for a message string communicated in an embodiment of the present invention.
DETAILED DESCRIPTION OF THE
The present invention can be used to respond to various conditions associated with the human body. Non-limiting examples include temperature, heart rate, and blood pressure. Localized pressure application is another example and one of particular medical significance as described above; therefore, the preferred embodiments of the present invention will be described with reference to a human body pressure condition, specifically pressure created by part or all of the weight of the human body applied at one or more predetermined locations of the human body against a support surface (e.g., a bed, a wheelchair). Particular reference is made to responding to pressure above or below a predetermined pressure magnitude applied to a pressure sensitive area susceptible to ulceration; however, reference is also made to sensing and responding to pressure throughout a range of magnitudes. In a particular implementation, a predetermined pressure magnitude is selected within the range of 4.07 kilopascals to 4.7 kilopascals and more specifically it is selected at a pressure magnitude equal to an accepted average capillary closing pressure above which blood flow is reduced.
In FIG. 1, for a person 2, circled areas 4 exemplify locations of the body susceptible to the formation of decubitus ulcers when the person is in a supine position. For the person 2, such as illustrated in FIG. 1, lying on a bed 6, such as illustrated in FIGS. 2 and 3, ulcers can occur at one or more of the pressure sensitive areas due to prolonged weight of the human body against the support surface of the bed. The body typically moves such that pressure at any one location changes repeatedly between less than a predeter