US20050148882A1 - Vital signs monitor used for conditioning a patient's response - Google Patents

Abstract

The invention provides a method for monitoring a patient, comprising the following steps: 1) outfitting the patient with a ambulatory blood pressure monitor that features an optical system for measuring blood pressure without using a cuff, and a wireless system configured to send and receive information sent from an Internet-based system through a wireless network; 2) sending from the Internet-based system to the ambulatory blood pressure monitor a signal that indicates a blood pressure level; 3) comparing a blood pressure value measured with the ambulatory blood pressure monitor to the blood pressure level; and 4) generating a signal in response to the comparing step.

Description

• This application is a continuation-in-part application of U.S. patent application Ser. No. 10/752,198, filed on Jan. 6, 2004.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
• Not Applicable
BACKGROUND OF THE INVENTION
• The present invention relates to medical devices for monitoring vital signs such as heart rate, pulse oximetry, and blood pressure, and using this information to condition a patient's response.
DESCRIPTION OF THE RELATED ART
• Pulse oximeters are medical devices featuring an optical module, typically worn on a patient's finger or ear lobe, and a processing module that analyzes data generated by the optical module. The optical module typically includes first and second light sources (e.g., light-emitting diodes, or LEDs) that transmit optical radiation at, respectively, red (λ˜630-670 nm) and infrared (λ˜800-1200 nm) wavelengths. The optical module also features a photodetector that detects radiation transmitted or reflected by an underlying artery. Typically the red and infrared LEDs sequentially emit radiation that is partially absorbed by blood flowing in the artery. The photodetector is synchronized with the LEDs to detect transmitted or reflected radiation. In response, the photodetector generates a separate radiation-induced signal for each wavelength. The signal, called a plethysmograph, varies in a time-dependent manner as each heartbeat varies the volume of arterial blood and hence the amount of transmitted or reflected radiation. A microprocessor in the pulse oximeter processes the relative absorption of red and infrared radiation to determine the oxygen saturation in the patient's blood. A number between 94%-100% is considered normal, while a value below 85% typically indicates the patient requires hospitalization. In addition, the microprocessor analyzes time-dependent features in the plethysmograph to determine the patient's heart rate.
• Pulse oximeters work best when the appendage they attach to (e.g., a finger) is at rest. If the finger is moving, for example, the light source and photodetector within the optical module typically move relative to the hand. This generates ‘noise’ in the plethysmograph, which in turn can lead to motion-related artifacts in data describing pulse oximetry and heart rate. Ultimately this reduces the accuracy of the measurement. Various methods have been disclosed for using pulse oximeters to obtain arterial blood pressure values for a patient. One such method is disclosed in U.S. Pat. No. 5,140,990 to Jones et al., for a ‘Method Of Measuring Blood Pressure With a Photoplethysmograph’. The '990 patent discloses using a pulse oximeter with a calibrated auxiliary blood pressure monitor to generate a constant that is specific to a patient's blood pressure. Another method for using a pulse oximeter to measure blood pressure is disclosed in U.S. Pat. No. 6,616,613 to Goodman for a ‘Physiological Signal Monitoring System’. The '613 patent discloses processing a pulse oximetry signal in combination with information from a calibrating device to determine a patient's blood pressure.
BRIEF SUMMARY OF THE INVENTION
• The present invention provides a cuffless blood-pressure monitor that features a behavior modification system. The blood pressure monitor is typically worn on a patient's head and makes a transdermal, optical measurement of blood pressure, which it then sends to a processing component (e.g., a PDA). The processing component preferably features an embedded, short-range wireless transceiver and a software platform that displays, analyzes, and then transmits the information through a wireless network to an Internet-based system. This system generates an audio or visual alarm when the patient's blood pressure trends high, and thus the patient may modify their behavior through conditioned response. In addition, a medical professional can continuously monitor a patient's blood pressure during their day-to-day activities. Monitoring patients in this manner minimizes erroneous measurements due to ‘white coat syndrome’, increases the accuracy of a blood-pressure measurement and additionally allows patients to modify behavior to lower blood pressure while wearing the device.
• The invention has many advantages. In particular, one aspect of the invention provides a system that continuously monitors a patient's blood pressure using a cuffless blood pressure monitor and an off-the-shelf mobile communication device. Information describing the blood pressure can be viewed using an Internet-based website, using a personal computer, or simply by viewing a display on the mobile device. Blood-pressure information measured continuously throughout the day provides a relatively comprehensive data set compared to that measured during isolated medical appointments. This approach identifies trends in a patient's blood pressure, such as a gradual increase or decrease, which allows for the patient to view and conditionally respond to high blood pressure through behavior modification such as breathing exercises. The monitor can also characterize the patient's heart rate and blood oxygen saturation using the same optical system for the blood-pressure measurement. This information can be wirelessly transmitted along with blood-pressure information and used to further diagnose the patient's cardiac condition. The monitor is small, easily worn by the patient during periods of exercise or day-to-day activities, and makes a non-invasive blood-pressure measurement in a matter of seconds. The resulting information has many uses for patients, medical professionals, hospitals, insurance companies, pharmaceutical agencies conducting clinical trials, and organizations for home-health monitoring.
• In one aspect, the invention provides a system for measuring blood pressure from a patient that features: 1) an optical module configured to be worn on (or in) the patient's head that includes at least one optical source and a photodetector; 2) a calibration source configured to make a blood pressure measurement; and, 3) a processing module configured to: i) receive a first signal from the optical module; ii) receive a second signal from the calibration source; iii) process the first and second signals to generate a calibration table; and iv) receive a third signal from the optical module and compare it to the calibration table to determine the patient's blood pressure.
• The preferred invention includes a response alert system designed to alert the patient when escalated vital signs reach dangerously harmful levels. The alert system alerts the patient when blood pressure levels reach dangerous levels caused by stress and anxiety. Each patient's blood pressure level parameters are set during the time of calibration by a physician.
• In embodiments, the blood pressure monitor features a head-worn clip that includes the optical module (e.g., a photodetector and first and second LEDs that emit, respectively, red radiation and infrared radiation). The optical calibration source is typically a cuff-based blood pressure module that includes a cuff and a pump worn around the patient's arm. In other embodiments, the optical module includes a short-range wireless transmitter configured to send signals to the processing module, which in turn may include a matched short-range wireless receiver.
• The short-range wireless transceiver preferably operates on a wireless protocol such as Bluetooth™, 802.15.4 or 802.11. The long-range wireless transmitter preferably transmits information over a terrestrial, satellite, or 802.11-based wireless network. Suitable networks include those operating at least one of the following protocols: CDMA, GSM, GPRS, Mobitex, DataTac, iDEN, and analogs and derivatives thereof.
• In addition, the cuffless blood pressure-measuring device of the invention combines all the benefits of conventional cuff-based blood-pressure measuring devices without any of the obvious drawbacks (e.g., restrictive, uncomfortable cuffs). Its measurement is basically unobtrusive to the patient, and thus alleviates conditions, such as a poorly fitting cuff, that can erroneously affect a blood-pressure measurement. The device is small and makes a non-invasive blood-pressure measurement in a matter of seconds. An on-board or remote processor can analyze the time-dependent measurements to generate statistics on a patient's blood pressure (e.g., average pressures, standard deviation, beat-to-beat pressure variations) that are not available with conventional devices that only measure systolic and diastolic blood pressure.
• These and other advantages of the invention will be apparent from the following detailed description and from the claims.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
• FIG. 1 is a semi-schematic diagram of a method for developing a conditioned response that utilizes the cuffless ambulatory blood-pressure monitor of the invention;
• FIGS. 2A and 2B are semi-schematic views of the cuffless ambulatory blood-pressure monitor ofFIG. 1 featuring a head-band with an optical system and a wireless hub connected, respectively, by a cable and short-range wireless connection;
• FIG. 3 is a semi-schematic view of a calibration process used with the ambulatory blood-pressure monitor ofFIGS. 2A and 2B;
• FIG. 4 is a schematic view of an Internet-based system that operates with the ambulatory blood-pressure monitor ofFIGS. 2A and 2B;
• FIG. 5A is a schematic top view of an adhesive patch sensor that measures blood pressure according to the invention;
• FIG. 5B is a schematic, cross-sectional view of the patch sensor ofFIG. 1A; and
• FIG. 6 is a graph of time-dependent optical and electrical waveforms generated by the patch sensor ofFIG. 5A.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 shows a semi-schematic diagram illustrating a conditionedresponse alert system8 that features an ambulatory blood pressure monitor (ABPM) according to the invention. In preferred embodiments, a physician prescribes to a patient an ABPM that identifies harmfully high blood pressure levels using the conditionedresponse alert system8. While outfitting the patient, the physician sets vital signs parameter limits, e.g. blood pressure limits, into the ABPM that indicate when an audio alarm will sound (step 1). Patients typically wear the ABPM for an extended period of time, during which they are typically exposed to stressful situations that may cause their blood pressure to rise (step 2). As blood pressure levels elevate into dangerously high levels, the ABPM emits an audio response and/or a visual alert that indicates high blood pressure levels (step 3). The patient responds to the alert (step 4) by, e.g., using breathing and other relaxation techniques to lower their blood pressure (step 5), or by activating a ‘snooze’ feature on the monitor to delay the alert (step 6). Over time the patient develops a conditioned response to the alert and becomes aware that their blood-pressure levels are dangerously high. Ultimately this lowers the patient's blood pressure, thereby reducing the chance that a serious medical condition, e.g. heart attack or stroke, occurs.
• As shown inFIGS. 2A and 2B, theABPM20 typically features an optical head-mountedcomponent105 that attaches to a patient'shead70, and aprocessing component19 that preferably attaches to the patient's belt. In a preferred embodiment, acable118 provides anelectrical connection81 between the head-mountedcomponent105 and theprocessing component19. During operation, the head-mountedcomponent105 measures optical and electrical ‘waveforms’, described in more detail below, that theprocessing component19 processes to determine real-time beat-to-beat diastolic and systolic blood pressure, heart rate, and pulse oximetry. The processing component also includes an internal wireless system that relays this information to an Internet-based system through anantenna86.
• Methods for processing the optical and electrical waveform to determine blood pressure are described in the following co-pending patent applications, the entire contents of which are incorporated by reference: 1) CUFFLESS BLOOD-PRESSURE MONITOR AND ACCOMPANYING WIRELESS, INTERNET-BASED SYSTEM (U.S. Ser. No. 10/709,015; filed Apr. 7, 2004); 2) CUFFLESS SYSTEM FOR MEASURING BLOOD PRESSURE (U.S. Ser. No. 10/709,014; filed Apr. 7, 2004); 3) CUFFLESS BLOOD PRESSURE MONITOR AND ACCOMPANYING WEB SERVICES INTERFACE (U.S. Ser. No. 10/810,237; filed Mar. 26, 2004); 4) VITAL-SIGN MONITOR FOR ATHLETIC APPLICATIONS (U.S. Ser. No.; filed Sep. 13, 2004); 5) CUFFLESS BLOOD PRESSURE MONITOR AND ACCOMPANYING WIRELESS MOBILE DEVICE (U.S. Ser. No. 10/967,511; filed Oct. 18, 2004); 6) BLOOD PRESSURE MONITORING DEVICE FEATURING A CALIBRATION-BASED ANALYSIS (U.S. Ser. No. 10/967,610; filed Oct. 18, 2004); 7) PERSONAL COMPUTER-BASED VITAL SIGN MONITOR (U.S. Ser. No. 10/906,342; filed Feb. 15, 2005); and 8) PATCH SENSOR FOR MEASURING BLOOD PRESSURE WITHOUT A CUFF (U.S. Ser. No. 10/906,315; filed Feb. 14, 2005).
• FIG. 2B shows an alternate embodiment of the invention wherein anoptical patch sensor106 sends vital-sign information to aprocessing component18 using a short-range wireless link24. In this embodiment theoptical patch sensor106 includes a short-range wireless transmitter84, and theprocessing component18 features an embedded, matched short-range wireless transceiver89. Theoptical patch sensor106 attaches free from wires to the patient'sforehead70 to increase mobility and flexibility. The short-range wireless transceiver89 is preferably a transmitter operating on a wireless protocol, e.g. Bluetooth™, 802.15.4 or 802.11. Apreferred processing component18 is a personal digital assistant (PDA) or cellular phone that operates with the above-described ABPM with little or no modifications. For example, theprocessing component18 can be a PDA that includes a wireless CDMA chipset, such as the MSM family of mobile processors manufactured by Qualcomm, each of which includes an internal Bluetooth™ radio. Suitable chipset within this family include the MSM6025, MSM6050, and the MSM6500, and are described and compared in detail in http://www.qualcomm.com. In addition to circuit-switched voice calls, the wireless transmitters used in these chipsets transmit data in the form of packets at speeds up to 307 kbps in mobile environments.
• Theprocessing component18 preferably supports a custom firmware application that displays and analyzes information for theABPM20. The firmware application is typically written to operate on a variety of mobile device operating systems including BREW, Palm OS, Java, Pocket PC, Windows CE, and Symbian. A more detailed explanation of the custom firmware application is disclosed in co-pending U.S. patent application Ser. No. 10/967511, filed on Oct. 18, 2004, for a CUFFLESS BLOOD-PRESSURE MONITOR AND ACCOMPANYING WIRELESS MOBILE DEVICE, the contents of which have been previously incorporated by reference.
• FIG. 3 shows asystem120 wherein a physician calibrates the above-describedABPM20 for aparticular patient70 and additionally enters blood pressure limits used in the conditioned response alert system. In a preferred embodiment, the physician initiates the calibration process using apersonal computer15 that sends a signal through awired connection34 to aprocessing component19 within theABPM20. In response, theprocessing component19 measures and processes optical and electrical waveforms collected by theoptical patch sensor105 to determine the patient's calibration parameters. These calibration parameters are described in more detail in BLOOD PRESSURE MONITORING DEVICE FEATURING A CALIBRATION-BASED ANALYSIS (U.S. Ser. No. 10/967,610; filed Oct. 18, 2004) and PATCH SENSOR FOR MEASURING BLOOD PRESSURE WITHOUT A CUFF (U.S. Ser. No. 10/906,315; filed Feb. 14, 2005), the contents of which have been previously incorporated herein by reference. Thesystem120 correlates the calibration parameters to blood pressure by subsequently measuring the patient's blood pressure using acalibration device100, typically a conventional blood-pressure cuff, which temporarily attaches to anupper portion112 of the patient's arm. Immediately after measuring the calibration parameters, thepersonal computer15 sends a second signal through a secondwired connection95 to a controller110 embedded within thecalibration device100. The signal directs the controller110 to initiate the cuff-based blood pressure measurement using a motor-controlledpump102. Once the signal is received, thecalibration device100 collects blood pressure values (e.g. systolic and diastolic pressures), and sends these back through thewired connection95 to thepersonal computer15. Thesystem120 repeats this process at a later time (e.g., 15 minutes later) to collect a second set of calibration parameters. The physician then removes thecalibration device100. Thepersonal computer15 then calculates a calibration table associating the calibration parameters and blood pressure values that passes through thewired connection34 to theprocessing component19 within the ABPM, where it is stored in memory. The ABPM uses the calibration table for all future cuffless measurements of blood pressure.
• Once theABPM20 is calibrated, the physician enters blood pressure limits into thepersonal computer15. The blood pressure limits pass through thewired connection34 to theprocessing component19, where they are stored in memory. During an actual measurement, theprocessing module19 compares the patient's blood pressure measured with theABPM20 to the blood pressure limits stored in memory to determine if the patient's blood pressure is trending high or low. If this is the case, thecontroller19 initiates an audio and/or visual alert as described above.
• FIG. 4 shows a preferred embodiment of an Internet-based system53 that operates in concert with theABPM20 to send information from a patient through awireless network54 to aweb site66 hosted on an Internet-basedhost computer system57. Asecondary computer system69 accesses thewebsite66 through theInternet67. The system53 functions in a bi-directional manner, i.e. theABPM20 can both send and receive data. Most data flows from theABPM20; using the same network, however, themonitor20 can also receive data (e.g., calibration parameters, pre-determined blood pressure levels, software upgrades, and text messages indicating ‘alerts’ or trending blood pressure) through thewireless network54. Awireless gateway55 connects to thewireless network54 and receives data from one or more ABPMs. Thewireless gateway55 additionally connects to ahost computer system57 that includes adatabase63 and a data-processingcomponent68 for, respectively, storing and analyzing the data. Thehost computer system57, for example, may include multiple computers, software pieces, and other signal-processing and switching equipment, such as routers and digital signal processors. Thewireless gateway55 preferably connects to thewireless network54 using a TCP/IP-based connection, or with a dedicated, digital leased line (e.g., a frame-relay circuit or a digital line running an X.25 or other protocols). Thehost computer system57 also hosts theweb site66 using conventional computer hardware (e.g. computer servers for both a database and the web site) and software (e.g., web server and database software).
• During typical operation, the patient continuously wears theABPM20 for a period of time, ranging from a 1-2 days to weeks. For longer-term monitoring (e.g. several months), the patient may wear theABPM20 for shorter periods of time during the day. To view information sent from theABPM20, the patient or medical professional accesses a user interface hosted on theweb site66 through theInternet67 from thesecondary computer system69. The system53 may also include a call center, typically staffed with medical professionals such as doctors, nurses, or nurse practioners, whom access a care-provider interface hosted on thesame website66.
• In an alternate embodiment, thehost computer system57 includes aweb services interface70 that sends information using an XML-based web services link to a secondary, web-basedcomputer application71. Thisapplication71, for example, could be a data-management system operating at a hospital.
• FIGS. 5A and 5B show anadhesive patch sensor205 according to the invention that features a pair ofLEDs210,212 andphotodetector214 that, when attached to a patient, generate an optical waveform (231 inFIG. 6). A horseshoe-shapedmetal electrode217 surrounds these optical components and generates an electrical waveform (232 inFIG. 6). The electrical and optical waveforms, once generated, pass through acable218 to a processing module, which analyzes them as described in detail below to measure a patient's systolic and diastolic blood pressure, heart rate, and pulse oximetry. Thepatch sensor205 features anadhesive component219 that adheres to the patient's skin and secures theLEDs210,212,photodetector214, andelectrode217 in place to minimize the effects of motion.
• During operation, thecable218 snaps into aplastic header216 disposed on a top portion of thepatch sensor205. Both thecable218 andheader216 include matched electrical leads that supply power and ground to theLEDs210,212,photodetector214, andelectrode219. Thecable218 andheader216 additionally supply a high-frequency electrical signal to the electrode that helps generate the electrical waveform. When thepatch sensor205 is not measuring optical and electrical waveforms (e.g., when the patient is sleeping), thecable218 unsnaps from theheader216, while thesensor205 remains adhered to the patient's skin. In this way a single sensor can be used for several days. After use, the patient removes and then discards thesensor205.
• To measure blood pressure, heart rate, and pulse oximetry, theLEDs210,212 generate, respectively, red and infrared radiation that irradiates an underlying artery. Blood volume increases and then decreases as the heart pumps blood through the patient's artery. Blood cells within the blood absorb and transmit varying amounts of the red and infrared radiation depending the on the blood volume and how much oxygen binds to the cells' hemoglobin. Thephotodetector214 detects a portion of the radiation that reflects off an underlying artery, and in response sends a radiation-induced photocurrent to an analog-to-digital converter embedded within the processing component. The analog-to-digital converter digitizes the photocurrent to generate a time-dependent optical waveform for each wavelength. In addition, the microprocessor analyzes waveforms generated at both red and infrared wavelengths, and compares a ratio of the relative absorption to a calibration table coded in its firmware to determine pulse oximetry. The microprocessor additionally analyzes the time-dependent properties of one of the optical waveforms to determine the patient's heart rate.
• Concurrent with measurement of the optical waveform, theelectrode219 detects an electrical impulse from the patient's skin that the processing component processes to generate an electrical waveform. The electrical impulse is generated each time the patient's heart beats.
• Thepatch sensor205 preferably has a diameter, ‘D’, ranging from 0.5 centimeter (‘cm’) to 10 cm, more preferably from 1.5 cm to 3.0 cm, and most preferably 2.5 cm. Thepatch sensor205 preferably has a thickness, ‘T’, ranging from 1.0 millimeter (“mm”) to 3 mm, more preferably from 1.0 mm to 1.5 mm, and most preferably 1.25 mm. Thepatch sensor205 preferably includes a body composed of a polymeric material such as a neoprene rubber. The body is preferably colored to match a patient's skin color, and is preferably opaque to reduce the affects of ambient light. The body is preferably circular in shape, but can also be non-circular, e.g. an oval, square, rectangular, triangular or other shape.
• FIG. 6 shows both optical231 and electrical232 waveforms generated by the patch sensor ofFIGS. 5A and 5B and used in the calibration procedure described above. Following a heartbeat, the electrical impulse travels essentially instantaneously from the patient's heart to the patch sensor, where the electrode detects it to generate theelectrical waveform232. At a later time, a pressure wave induced by the same heartbeat propagates through the patient's arteries and arrives at the sensor, where the LEDs and photodetector detect it as described above to generate theoptical waveform231. The propagation time of the electrical impulse is independent of blood pressure, whereas the propagation time of the pressure wave depends strongly on pressure, as well as mechanical properties of the patient's arteries (e.g., arterial size, stiffness). The microprocessor runs an algorithm that analyzes the time difference ΔT between the arrivals of these signals, i.e. the relative occurrence of the optical231 and electrical232 waveforms as measured by the patch sensor.
• In still other embodiments, the above-described system can receive inputs from other measurement devices, such as weight scales, glucometers, EKG/ECG monitors, cuff-based blood pressure monitors, dietary monitors, pedometers and other exercise monitors, and GPS systems.
• Still other embodiments are within the scope of the following claims.

Claims (15)

1. A system for monitoring blood pressure, the system comprising:

a monitoring device comprising a patch sensor component that generates an optical signal;

and a processing component configured to process the optical signal with calibration information to obtain blood pressure information, and then compare the blood pressure information to a pre-programmed value to generate a signal.

2. The system ofclaim 1, further comprising an audio component.

3. The system ofclaim 2, wherein the audio component is further configured to receive the signal and in response generate an audio alert.

4. The system ofclaim 1, further comprising a display component.

5. The system ofclaim 4, wherein the display component is further configured to receive the signal and in response display an alert message.

6. The system ofclaim 1, further comprising a drug-delivery system.

7. The system ofclaim 1, further comprising a wireless transceiver.

8. The system ofclaim 7, wherein the wireless transceiver is further configured to send and receive information through a wireless network.

9. The system ofclaim 8, further comprising an Internet-based system configured to send information through the wireless network to the wireless transceiver, and receive information through the wireless network from the wireless transceiver.

10. The system ofclaim 8, wherein the Internet-based system is further configured to send information describing a blood pressure level to the processing component.

11. A method for monitoring a patient, comprising the following steps: outfitting the patient with a ambulatory blood pressure monitor comprising an optical system that measures blood pressure without using a cuff, and a wireless system configured to send and receive information sent from an Internet-based system through a wireless network; sending from the Internet-based system to the ambulatory blood pressure monitor a signal that indicates a blood pressure level; comparing a blood pressure value measured with the ambulatory blood pressure monitor to the blood pressure level; and generating a signal in response to the comparing step.

12. The method ofclaim 11, further comprising a step for generating an audio alert in response to the signal.

13. The method ofclaim 12, wherein the audio alert indicates to the patient that their blood pressure value is above or below the blood pressure level.

14. The method ofclaim 12, further comprising a step for generating a visual alert in response to the signal.

15. The method ofclaim 14, wherein the visual alert indicates to the patient that their blood pressure value is above or below the blood pressure level.

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