Abstract:
The invention features a medical device that measures vital signs (e.g., blood pressure, pulse oximetry, and heart rate) from a patient using at least two optical modules. Each optical module typically features two light sources (red, infrared) and a photodetector. Both optical modules are configured to measure time-dependent signals describing the patient&#39;s flowing blood. A processor analyzes the time-dependent signals to determine the patient&#39;s vital signs. Once the vital signs are measured, a wireless transmitter in the body-worn device transmits them to an external device. Processing signals from least two optical modules compensates for motion-related artifacts and noise normally present in signals used to determine vital signs from a device featuring just a single optical module.

Description:
CROSS REFERENCES TO RELATED APPLICATION  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to medical devices for monitoring pulse oximetry and blood pressure.  
         [0005]     2. Description of the Related Art  
         [0006]     Pulse oximeters are medical devices featuring an optical module, typically worn on a patient&#39;s finger or ear lobe, and a processing module that analyzes data generated by the optical module. The optical module typically features first and second light sources (e.g., light-emitting diodes, or LEDs) that transmit optical radiation at, respectively, red (λ˜630 nm) and infrared (λ˜900 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 flowing blood in the artery. The photodetector detects transmitted or reflected radiation and in response 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&#39;s blood. A number between 94%-100% is considered normal. In addition, the microprocessor analyzes time-dependent features in the plethysmograph to determine the patient&#39;s heart rate.  
         [0007]     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. 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 &#39;990 patent discloses using a pulse oximeter with a calibrated auxiliary blood pressure to generate a constant that is specific to a patient&#39;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 &#39;613 Patent discloses processing a pulse oximetry signal in combination with information from a calibrating device to determine a patient&#39;s blood pressure.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The present invention measures vital signs (e.g., blood pressure, pulse oximetry, and heart rate) from a patient using a body-worn device that features at least two optical modules. Each optical module typically features two light sources (red, infrared) and a photodetector. Both optical modules are configured to measure time-dependent signals describing the patient&#39;s flowing blood. A processor analyzes the time-dependent signals to determine the patient&#39;s vital signs. Once the vital signs are measured, a wireless transmitter in the body-worn device transmits them to an external device. Processing signals from least two optical modules compensates for motion-related artifacts and noise normally present in signals used to determine vital signs from a device featuring just a single optical module.  
         [0009]     In one aspect, the invention features a medical device for measuring vital signs from a patient that includes: 1) a first optical module that includes a first light source and a first photodetector, the first light source and first photodetector oriented to optically measure blood flowing in an underlying artery; 2) a second optical module that includes a second light source and a second photodetector, the second light source and second photodetector oriented to optically measure blood flowing in an underlying artery; and 3) a processor, in electrical communication with the first and second photodetector, configured to run a firmware algorithm that processes signals from the first and second photodetectors to determine at least one vital sign from the patient.  
         [0010]     In one embodiment, the first and second optical modules are included in a finger-worn component, e.g. a ring, or a component that attaches to the patient&#39;s ear or forehead. Alternatively, the first and second optical modules operate in a ‘reflection mode’ geometry and can be attached to any part of the patient&#39;s body that includes an underlying artery. In another embodiment, the firmware algorithm running on the processor calculates the patient&#39;s pulse oximetry, heart rate, and blood pressure by first averaging signals from the first and second optical modules. Alternatively, the firmware algorithm selects a preferred signal from at least one of the modules, e.g. a signal that has an optimal signal-to-noise ratio.  
         [0011]     In another embodiment, the medical device additionally includes a short-range wireless component that sends information describing the patient&#39;s vital signs to an external device, e.g. a cellular telephone or a personal digital assistant.  
         [0012]     Another aspect of the present invention is a pulse oximetry device including an annular body containing at least four light sources, at least four photodetectors, and a pulse oximetry circuit. The annular body has a diameter preferably ranging from 0.5 inch to 3.0 inches. The annular body has an aperture with a diameter preferably ranging 0.40 inch to 2.0 inches. The annular body has a length preferably ranging from 0.10 inch to 2.0 inches. Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0013]      FIG. 1  is a front view of an optical ring module featuring multiple optical modules for measuring vital signs according to the present invention;  
         [0014]      FIG. 2  is a cross-sectional view of the optical ring module and multiple optical modules of  FIG. 1 ;  
         [0015]      FIG. 3A  is a cross-sectional view of the optical ring module of  FIG. 2  surrounding a patient&#39;s finger;  
         [0016]      FIG. 3B  is a cross-sectional view of the optical ring module of  FIG. 3A  rotated by a few degrees relative to the patient&#39;s finger;  
         [0017]      FIG. 4  is a schematic view of a microprocessor in electrical communication with the optical modules of  FIG. 1 ;  
         [0018]      FIG. 5  is a schematic view of an algorithm for processing the plethysmographs of  FIG. 5  to generate a compiled and averaged plethysmograph; and  
         [0019]      FIG. 6  shows a semi-schematic view of a system for measuring blood pressure based on the optical ring module of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]      FIGS. 1 and 2  show a medical device  19  according to the invention that features an annular optical ring module  20  that includes multiple optical modules  4 - 11 , each of which measures a plethysmograph from a patient. The optical modules  4 - 11  are evenly disposed around a perimeter of the ring module  20  and each feature a photodetector  4 B- 11 B that detects radiation, and a pair of LEDs  4 A- 11 A that generate red and infrared radiation. An electrical cable  21  connects the optical modules  4 - 11  to a processing module  22 . When a patient wears the ring module  20  on a finger, each optical module  4 - 11  simultaneously measures a signal describing the flow of blood in an underlying artery. The signal from each optical module  4 - 11  passes through the cable  21  to the processing module  22 , which includes a microprocessor  32  that processes the signals to determine an individual plethysmograph for each optical module  4 - 11 . An algorithm running on the microprocessor  32  then analyzes the plethysmographs as described below to determine the patient&#39;s vital signs (e.g., heart rate, pulse oximetry, and blood pressure).  
         [0021]     Multiple optical modules  4 - 11  within the ring module  20  correct for motion-related artifacts normally present during conventional pulse-oximetry measurements. In one embodiment, for example, the LEDs  4 A- 11 A within each optical module simultaneously emit red, and then infrared, radiation. Radiation from the LEDs  4 A- 11 A forms a symmetrical ‘optical field’ that surrounds the finger and is partially absorbed by pulsing blood in the underlying arteries. Each photodetector  4 B- 11 B detects a portion of the optical field and sends it to the processing module  22  for analysis by a firmware program. In this way, the photodetectors  4 B- 11 B generate an average signal that is relatively independent on the finger&#39;s position. Compared to signals from conventional pulse oximeters, the average signal is relatively immune from motion-related artifacts. In another embodiment, LEDs  4 A- 11 A within each optical module sequentially emit radiation in a strobe-like manner. In this case, each photodiode  4 B- 11 B sequentially detects a signal that the processing module  22  analyzes as described above. The processing module  22  runs a firmware program that selects the plethysmograph that is least affected by motion-related artifacts and consequently has the best signal-to-noise ratio. In general, a variety of methodologies for powering the optical modules, coupled with different signal-processing techniques, can be used to analyze plethysmographs generated with the multiple optical modules  4 - 11  within the ring module  20 .  
         [0022]      FIGS. 3A and 3B  show in more detail how the ring module  20  featuring multiple optical modules  4 - 11  effectively compensates for motion-related artifacts. Referring first to  FIG. 3A , the ring module  20  surrounds a patient&#39;s finger  35  that includes several arteries  32  and a bone  31 . A first axis  16 ′ describes the relative position of the finger  35  to the ring module  20 . During a measurement, the LEDs  4 A- 11 A can either emit radiation simultaneously or sequentially as described above. The radiation scatters off the bone  31  and tissue in the finger  35  to form a constant, symmetric optical field that surrounds the underlying arteries  32 . The photodetectors  4 B- 11 B collect both reflected and transmitted portions of the optical field to generate a collection of radiation-induced signals that a microprocessor then analyzes to determine an average plethysmograph. Because of the configuration of the optical modules  4 - 11 , the optical field is constant regardless of how the finger  35  and arteries  32  are oriented. For example, in  FIG. 3B  a second axis  16 ″ shows how movement in the patient&#39;s hand rotates the finger  35 , bone  31 , and the underlying arteries  32  a few degrees relative to the multiple optical modules  4 - 11 . Since the optical modules  4 - 11  surround the finger  35 , however, the LEDs  4 A- 11 A still radiate the arteries  32  with an optical field that is the same as that for  FIG. 3A . This means the resultant plethysmograph is basically independent of the relative position between the ring module  20  and the patient&#39;s finger  35  and is consequently immune to motion.  
         [0023]      FIG. 4  shows in detail how the microprocessor  32  within the processing module  22  of  FIG. 1  collects and processes signals from each optical module  4 - 11  in the ring module  20 . The microprocessor  32  features an analog-to-digital converter  34  that includes multiple channels that each connect through a first electrical lead  28   a - h  to the individual optical modules  4 - 11 . Each channel converts an analog signal from an optical module into a digital signal that can be processed as described below to determine the patient&#39;s vital signs. The microprocessor also includes a second electrical lead  26   a - h  that supplies power to the LEDs  4 A- 11 A and photodetectors  4 B- 11 B in each optical module. A third electrical lead  30  connects to the microprocessor  32  and each optical module  4 - 11  to provide a ground for powering the LEDs  4 A- 11 A and photodetectors  4 B- 11 B, as well as a ground for the signal transported by the first electrical lead  28   a - h . During operation, the microprocessor  32  supplies power and ground to each optical module  4 - 11  through, respectively, the second  26   a - h  and third electrical lead  30 . In response to reflected and/or transmitted optical radiation, each optical module  4 - 11  generates photocurrent that passes as an analog signal through the second electrical lead  28   a - h  to the analog-to-digital converter  34 . The analog-to-digital converter  34  converts the analog signal to a digital signal, which the microprocessor  32  then processes to determine a plethysmograph. The microprocessor  32  additionally runs a firmware program that controls the LEDs  4 A- 11 A and photodetectors  4 B- 11 B in each optical module  4 - 11 . The firmware program, for example, may power each optical module  4 - 11  simultaneously or sequentially as described above with reference to  FIGS. 1-3 .  
         [0024]      FIG. 5  shows a process  50  for measuring and processing multiple plethysmographs  46   a - 46   h  from the optical modules  4 - 11  with an algorithm  48  to generate an ‘optimal’ plethysmograph  49 . During the process  50  the optical modules  4 - 11  are powered either simultaneously or sequentially as described above to generate analog signals that the analog-to-digital converter converts to digital plethysmographs  46   a - h . The algorithm  48  receives the digital plethysmographs  46   a - h  and processes them to determine the optimal plethysmograph  49 . In one example, the algorithm  48  averages all the plethysmographs  46   a - h  to determine the optimal plethysmograph  49 . Or it may select the plethysmograph with the best signal-to-noise ratio, or that which can be best represented by a mathematical model. In still other embodiments, the microprocessor takes a Fourier transform of each plethysmograph  46   a - h , and then processes the transforms to generate the optimal plethysmograph  49 .  
         [0025]     The optimal plethysmograph  49 , once generated, can be processed to determine vital signs such as heart rate, pulse oximetry, and blood pressure. Methods for determining heart rate and pulse oximetry from the plethysmograph are well known and are briefly described above. Methods for determining systolic and diastolic blood pressure from the plethysmograph typically involve calibrating a device with a conventional blood pressure monitor to correlate features of the plethysmograph to blood pressure. Specific methods for processing the plethysmograph to determine blood pressure are described in the following co-pending patent applications, the entire contents of which are incorporated by reference: 1) U.S. patent Application Ser. No. 10/967,610, filed Oct. 18, 2004, for a BLOOD PRESSURE MONITORING DEVICE FEATURING A CALIBRATION-BASED ANALYSIS; 2) U.S. patent application Ser. No. 10/810,237, filed Mar. 26, 2004, for a CUFFLESS BLOOD PRESSURE MONITOR AND ACCOMPANYING WEB SERVICES INTERFACE; 3) U.S. patent application Ser. No. 10/709,015, filed Apr. 7, 2004, for a CUFFLESS BLOOD-PRESSURE MONITOR AND ACCOMPANYING WIRELESS, INTERNET-BASED SYSTEM; and 4) U.S. patent application Ser. No. 10/752,198, filed Jan. 6, 2004, for a WIRELESS, INTERNET-BASED MEDICAL DIAGNOSTIC SYSTEM.  
         [0026]      FIG. 6  shows a monitoring system  100  that measures a patient&#39;s vital signs using the above-described ring module  20  and processing module  22 . The system  100  features a wrist-worn monitoring device  68  that measures vital signs as described above and wirelessly transmits them through a short-range wireless link  86  to an external laptop computer  88  or hand-held device  89 . The monitoring device  68  preferably includes a wrist-mounted module  61  that attaches to an area of the user&#39;s wrist  65  where a watch is typically worn. The ring module  20  typically attaches to the patient&#39;s index finger  64 . An electrical cable  21  provides an electrical connection between the ring module  20  and wrist-mounted module  61 . Preferably the wrist-mounted module  61  includes a microprocessor  32  and a short-range wireless transceiver  67 . The components are typically embedded within a comfortable, non-conductive material, such as neoprene rubber, that wraps around the patient&#39;s wrist.  
         [0027]     The short-range wireless transceiver  67  is preferably a transmitter operating on a wireless protocol, e.g. Bluetooth™, 802.15.4 or 802.11. During operation, the short-range wireless transceiver  67  receives information from the microprocessor  32  and transmits this in the form of a packet to the external laptop computer  88  or hand-held device  89 . In certain embodiments, the hand-held device  89  is a cellular telephone with a Bluetooth™ circuit and antenna integrated directly into a chipset used therein. In this case, the cellular telephone may include a software application that receives, processes, and displays the information. Both the hand-held device  89  and laptop computer  88  may also include a long-range wireless transmitter that transmits information over a network  94 , e.g. 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 this case, the network  94  connects to an Internet-based host computer system  96  that can display the patient&#39;s vital signs on a website. A user then accesses this information using a secondary computer system  97 . A detailed description of this component of the invention can be found in the above-mentioned patent applications, previously incorporated by reference, and in U.S. patent application Ser. No. 10/709,015, filed Apr. 7, 2004, for a CUFFLESS BLOOD-PRESSURE MONITOR AND ACCOMPANYING WIRELESS MOBILE DEVICE, the contents of which are also incorporated herein by reference.  
         [0028]     In other embodiments, the above-described device for measuring vital signs can include between about one and twenty optical modules. These optical modules are typically included in a finger or wrist-worn device, but alternatively can be included in a device that attaches to a patient&#39;s ear or forehead. Typically the optical modules are disposed in a symmetric configuration. Alternatively, the modules can be disposed in a non-symmetric configuration, i.e. they can be grouped in a particular area on the device. In this case the processing module may be worn on the patient&#39;s body, e.g., on the patient&#39;s waist. Or the optical modules can operate in a ‘reflection mode’ geometry and attach to any part of the patient&#39;s body that includes an accessible artery.  
         [0029]     The microprocessor can implement a wide variety of algorithms to compensate for motion and calculate vital signs from the patient. For example, the microprocessor may use a Fourier Transform algorithm to determine an optimal time to collect plethysmographs from the multiple optical modules.  
         [0030]     Still other embodiments are within the scope of the following claims.