Abstract:
A system for measuring a blood pressure value from a patient features a sensor configured to be worn on the patient&#39;s thumb. The sensor includes one or two light sources that emit optical radiation, and a photodetector that detects the optical radiation after it passes through a portion of a vessel (e.g. an artery or capillary) in the patient&#39;s thumb to generate a first time-dependent signal (e.g. a PPG waveform). In embodiments the sensor is made from a flexible material that wraps around a portion of the patient&#39;s thumb (e.g. the base) while leaving the thumb&#39;s tip uncovered. This configuration is less awkward than most finger-worn sensors, and allows the patient to comfortably go about their day-to-day activities (e.g. reading, eating) with little obstruction. The system also includes at least two electrodes that are configured to be worn on the patient&#39;s body and detect electrical signals that are processed by an electrical circuit to generate a second time-dependent signal (e.g. an ECG waveform).

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 61/073,681, filed Jun. 18, 2008, all of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]    The present invention relates to medical devices for monitoring vital signs, e.g., blood pressure. 
       BACKGROUND OF THE INVENTION 
       [0003]    Pulse transit time (PTT), defined as the transit time for a pressure pulse launched by a heartbeat in a patient&#39;s arterial system, has been shown in a number of studies to correlate to both systolic and diastolic blood pressures. In these studies, PTT is typically measured with a conventional vital signs monitor that includes separate modules to determine both an electrocardiogram (ECG) and pulse oximetry. During a PTT measurement, multiple electrodes typically attach to a patient&#39;s chest to determine a time-dependent ECG component characterized by a sharp spike called the ‘QRS complex’. 
         [0004]    The QRS complex indicates an initial depolarization of ventricles within the heart and, informally, marks the beginning of the heartbeat and a pressure pulse that follows. Pulse oximetry is typically measured with a bandage or clothespin-shaped sensor that attaches to a patient&#39;s finger, and includes optical systems operating in both the red and infrared spectral regions. A photodetector measures radiation emitted from the optical systems that transmits through the patient&#39;s finger. Other body sites, e.g., the ear, forehead, and nose, can be used in place of the finger. During a measurement, a microprocessor analyses both red and infrared radiation measured by the photodetector to determine the patient&#39;s blood oxygen saturation level and a time-dependent waveform called a photoplethysmograph (&#39;PPG&#39;). Time-dependent features of this waveform indicate both pulse rate and a volumetric absorbance change in an underlying artery caused by the propagating pressure pulse. 
         [0005]    Typical PTT measurements determine the time separating a maximum point on the QRS complex, indicating the peak of ventricular depolarization, and a foot of the PPG waveform, indicating the time when a pressure pulse launched by the heartbeat reaches vasculature underneath the optical sensor. PTT depends primarily on arterial compliance, the propagation distance of the pressure pulse (which is closely approximated by the patient&#39;s arm length), and blood pressure. To account for patient-dependent properties, such as arterial compliance, PTT-based measurements of blood pressure are typically ‘calibrated’ using a conventional blood pressure cuff and oscillometry. Typically during the calibration process the blood pressure cuff is applied to the patient, used to make one or more blood pressure measurements, and then removed. Going forward, the calibration blood pressure measurements are used, along with a change in PTT, to determine the patient&#39;s blood pressure and blood pressure variability. PTT typically relates inversely to blood pressure, i.e., a decrease in PTT indicates an increase in blood pressure. 
         [0006]    A number of issued U.S. Patents describe the relationship between PTT and blood pressure. For example, U.S. Pat. Nos. 5,316,008; 5,857,975; 5,865,755; and 5,649,543 each describe an apparatus that includes conventional sensors that measure ECG and PPG waveforms, which are then processed to determine PTT. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, a system for measuring a blood pressure value from a patient features a sensor configured to be worn on the patient&#39;s thumb. The sensor includes one or two light sources that emit optical radiation, and a photodetector that detects the optical radiation after it passes through a portion of a vessel (e.g. an artery or capillary) in the patient&#39;s thumb to generate a first time-dependent signal (e.g. a PPG waveform). In embodiments the sensor is made from a flexible material that wraps around a portion of the patient&#39;s thumb (e.g. the base) while leaving the thumb&#39;s tip uncovered. This configuration is less awkward than most finger-worn sensors, and allows the patient to comfortably go about their day-to-day activities (e.g. reading, eating) with little obstruction. The system also includes at least two electrodes that are configured to be worn on the patient&#39;s body and detect electrical signals that are processed by an electrical circuit to generate a second time-dependent signal (e.g. an ECG waveform). 
         [0008]    A processing system worn on a portion of the patient&#39;s arm collectively process both the first and second time-dependent signals to determine the blood pressure value. It features a mechanical housing with a first input port that receives the first time-dependent signal, or a signal used to generate the first time-dependent signal, and a second input port that receives the second time-dependent signal, or a signal used to generate the second time-dependent signal. The first input port is located on one side portion of the housing, and the second input port is located on a second side portion that is opposite to the first side portion. This configuration minimizes cable clutter around the processing system: a first cable can run down the patient&#39;s wrist to the thumb-worn sensor, and a second cable can run up the patient&#39;s arm to chest-worn electrodes. 
         [0009]    In embodiments, the processing system includes at least two separate portions, or compartments, both configured to be worn on separate portions of the patient&#39;s arm. A flexible housing can include both portions and securely wrap around the patient&#39;s arm. In embodiments, the first portion can include a processor (e.g. a microprocessor or microcontroller) programmed to process the first and second time-dependent signals to determine the blood pressure value. And the second portion can include a pneumatic system that features a pump, valve, and manifold, and generates a third time-dependent signal (e.g. a pressure waveform) representing pressure applied to the patient&#39;s arm. Typically the first and second portions connect to each other through a flexible cable. An armband that can be inflated by the pneumatic system attaches one or both portions to the patient&#39;s arm. 
         [0010]    The processor can be programmed to process a time difference separating a first feature of the first time-dependent signal, and a second feature of the second time-dependent signal. This time difference can be processed by the composite technique to determine the blood pressure value. According to this technique, for example, the pneumatic system can supply a pressure to the patient&#39;s arm, and the processor is then programmed to process the first time-dependent signal in the presence of the supplied pressure (represented, e.g., by the third time-dependent signal) to determine a blood pressure calibration relating PTT to blood pressure. In one case, the processor processes the time difference in the presence of the supplied pressure to determine the blood pressure calibration according to the composite technique. In another case the processor processes a decrease in the amplitude of the first time-dependent signal to determine the blood pressure calibration. 
         [0011]    In other embodiments the processing system includes a wireless transmitter that can transmit information to an external display. 
         [0012]    The composite technique includes both pressure-dependent and pressure-free measurements. It is based on the discovery that PTT and the PPG waveform used to determine it are strongly modulated by an applied pressure. Two events occur as the pressure gradually increases to the patient&#39;s systolic pressure: 1) PTT increases in a non-linear manner once the applied pressure exceeds diastolic pressure; and 2) the magnitude of the PPG waveform&#39;s amplitude systematically decreases, typically in a linear manner, as the applied pressure approaches systolic pressure. The applied pressure gradually decreases blood flow and consequent blood pressure in the patient&#39;s arm, and therefore induces the pressure-dependent increase in PTT. Each of the resulting pairs of PTT/blood pressure readings measured during the period of applied pressure can be used as a calibration point. Moreover, when the applied pressure equals systolic blood pressure, the amplitude of the PPG waveform is completely eliminated, and PTT is no longer measurable. In total, analyzing both PTT and the PPG waveform&#39;s amplitude over a suitable range yields the patient&#39;s systolic and diastolic blood pressures. The composite technique measures systolic blood pressure directly; in contrast, conventional cuff-based systems based on the oscillometric technique measure this property indirectly, which is typically less accurate. 
         [0013]    In addition, the composite technique can include an ‘intermediate’ pressure-dependent measurement wherein the armband is only partially inflated. This applies pressure to the patient&#39;s arm and partially decreases the amplitude of the PPG waveform in a time-dependent manner. The amplitude&#39;s pressure-dependent decrease can then be ‘fit’ with a numerical function to estimate the pressure at which the amplitude completely disappears, indicating systolic pressure. 
         [0014]    For the pressure-dependent measurement, a small mechanical pump in the body sensor inflates the bladder to apply pressure to an underlying artery according to the pressure waveform. The armband is typically located on the patient&#39;s upper arm, proximal to the brachial artery, and time-dependent pressure is measured by an internal pressure sensor in the body sensor. The pressure sensor is typically an in-line Wheatstone bridge or strain gauge. The pressure waveform gradually ramps up in a mostly linear manner during inflation, and then rapidly deflates through a ‘bleeder valve’ during deflation. During inflation, mechanical pulsations corresponding to the patient&#39;s heartbeats couple into the bladder as the applied pressure approaches diastolic pressure. 
         [0015]    The mechanical pulsations modulate the pressure waveform so that it includes a series of time-dependent oscillations. The oscillations are similar to those measured with an automated blood pressure cuff using oscillometry, only they are measured during inflation rather than deflation. They are processed as described below to determine mean arterial pressure, which is then used going forward in the pressure-free measurement. Specifically, the maximum amplitude of the pulsations corresponds to mean arterial pressure; measuring this property from the pressure waveform represents a direct measurement. Once determined, direct measurements of systolic and mean arterial pressure made during the pressure-dependent measurement are used to determine diastolic pressure using a numerical calculation, described in more detail below. 
         [0016]    Pressure-free measurements immediately follow the pressure-dependent measurements, and are typically made by determining PTT with the same optical and electrical sensors used in the pressure-dependent measurements. Specifically, the body sensor processes PTT and other properties of the PPG waveform, along with the measurements of systolic, diastolic, and mean arterial pressure made during the pressure-dependent measurement, to determine blood pressure. 
         [0017]    Advantages of the flexible body sensor include: i) a light-weight flexible form factor that easily conforms to a patient&#39;s arm; ii) a durable, sterile housing that protects internal electrical components from heat, moisture, and direct submersion in water; and, iii) simple, clutter-free wiring to the optical sensor and electrodes. 
         [0018]    In addition to blood pressure, the body sensor measures heart rate and respiratory rate from components of the ECG waveform. These measurements are made using conventional algorithms. An optional pulse oximeter measures SpO2. The body sensor can also measure temperature (with a thermocouple); motion, posture, and activity level (with one or more accelerometers); and respiratory rate (with a chest-worn acoustic sensor or accelerometer integrated with one of the electrodes). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  shows a schematic drawing of a patient wearing a body sensor, in communication with an external monitor, and connected to an optical sensor and electrical sensors to measure blood pressure. 
           [0020]      FIGS. 2A and 2B  show schematic drawings of the optical sensor of  FIG. 1  that is to be worn on a patient&#39;s thumb. 
           [0021]      FIG. 3  shows a cross-sectional view the optical sensor of  FIGS. 2A and 2B . 
           [0022]      FIG. 4  shows a schematic view of the optical sensor of  FIG. 3  worn on a patient&#39;s thumb. 
           [0023]      FIGS. 5A and 5B  show graphs of time-dependent PPG waveforms measured, respectively, from a patient&#39;s forearm and thumb measured with the optical sensor of  FIGS. 2A and 2B . 
           [0024]      FIGS. 6A and 6B  show, respectively, schematic top-side and bottom-side views of the electrical components in the body sensor of  FIG. 1 . 
           [0025]      FIG. 7  shows a schematic top view of the electrical components of  FIGS. 6A and 6B . 
           [0026]      FIG. 8  shows a schematic top view of a flexible housing used to enclose the electrical components of  FIG. 7 . 
           [0027]      FIG. 9  is a cross-sectional view of the flexible housing of  FIG. 8  with its armband wrapped around a patient&#39;s arm. 
           [0028]      FIG. 10  shows a three-dimensional plan view of the monitor of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  shows a patient  30  wearing a system for measuring blood pressure  20  featuring a body sensor  46  connected to an optical sensor  1  worn on the patient&#39;s thumb and electrical sensors  32   a - c  (e.g. ECG electrodes) worn on the patient&#39;s chest. The body sensor  46  communicates wirelessly (as shown by the arrow  32 ) with a remote monitor  25 . It attaches to the patient&#39;s arm  31  with an armband  35  similar to a blood pressure cuff. The ECG electrodes  32   a - c  adhere to the patient&#39;s chest in a standard Einthoven&#39;s triangle configuration, and connect to the body sensor  46  though a first cable  219 . These electrodes  32   a - c , in combination with a differential amplifying ECG circuit within the body sensor  46 , measure an ECG waveform. 
         [0030]    The optical sensor  1  wraps around the base of the patient&#39;s thumb with an adhesive band, and in combination with the body sensor  46  measures a PPG waveform similar to that indicated in graph  75  in  FIG. 5B . During a pressure-dependent measurement, pneumatic components (i.e. a pump, valves, and pressure manifold) within a compartment in the body sensor  46  inflate a bladder within the armband  35 , causing it to apply pressure to the patient&#39;s arm  31 . The applied pressure has essentially no affect on the ECG waveform, but decreases the amplitude and delays the onset of pulses in the PPG waveform. A microprocessor in the body sensor  46  processes waveforms measured during the pressure-dependent measurement to ‘calibrate’ the measure for the particular patient  30  according to the composite technique. Subsequent pressure-free measurements use the calibration, along with a PTT determined from the PPG and ECG waveforms, to continuously determine the patient&#39;s blood pressure. 
         [0031]      FIGS. 2A ,  2 B, and  3  show top, bottom, and cross-sectional views of the above-described optical sensor  1 ,  1 ′. It adheres to the patient&#39;s thumb with an adhesive wrap and connects to the body sensor  46  through a cable  10 ,  10 ′. The optical sensor  1 ,  1 ′ measures a PPG waveform from the patient during both pressure-dependent and pressure-free measurements. In the embodiment shown in  FIGS. 2A and 2B , the optical sensor includes a single photodetector  5  between a pair of LEDs  4 ,  6 . The LEDs typically operate in either the visible (e.g. 400-700 nm) or near-infrared (700-1000 nm) spectral regions. A flexible sensor housing  2 ,  2 ′ supports these optical components to make a measurement using either a reflection-mode or transmission-mode geometry. The optical components can be disposed in other configurations, e.g. the optical sensor  1 ,  1 ′ can include even more LEDs and photodetectors, or one or more separate optical modules, each including a single LED, photodetector, and analog amplifier. To make an optical measurement, the patient applies the flexible right flap  8 ,  8 ′ and left flap  9 ,  9 ′ of the flexible sensor housing  2 ,  2 ′, typically made up of black latex rubber or a comparable composite material, to the interior base of the thumb. The above-described system measures PPG waveforms for both the pressure-dependent and pressure-free measurements. 
         [0032]    The following co-pending patent applications, the contents of which are fully incorporated herein by reference, describe the above-mentioned sensors and their use with the composite technique in more detail: 1) VITAL SIGN MONITOR FOR CUFFLESSLY MEASURING BLOOD PRESSURE USING A PULSE TRANSIT TIME CORRECTED FOR VASCULAR INDEX (U.S. Ser. No. 12/138,199, filed Jun. 12, 2008); and 2) VITAL SIGN MONITOR FOR MEASURING BLOOD PRESSURE USING OPTICAL, ELECTRICAL, AND PRESSURE WAVEFORMS (U.S. Ser. No. 12/138,194, filed Jun. 12, 2008). 
         [0033]    To hold the optical sensor  1 ,  1 ′ in place, an extension or mushroom cap  12  provides a pressure point where an adhesive strip wraps around the patient&#39;s thumb, immobilizing the sensor to help reduce any motion-related artifacts and ambient noise generated from movement of the sensor. A thin flexible cable  10 ,  10 ′, roughly 42 cm to 54 cm in length, provides an electrical connection to the body sensor  46 . 
         [0034]      FIG. 3  shows a cross-sectional diagram and dimensions of the optical sensor  1  and optical radiation reflecting off the princeps pollics artery  21  in a patient&#39;s thumb  15 . Both the flexible black latex rubber housing  2  and an internal circuit board  7  that supports the optical components  4 ,  5 ,  6  conform to the patient&#39;s thumb  15 , allowing radiation to pass through the patient&#39;s skin and reflect around the bone  43 , capillaries  44 ,  45 , and artery  21  in the thumb  15 . The flexible black latex rubber flaps  8 ,  9  are each approximately 12 mm in length each (represented by ˜T). The flexible circuit board  7  that supports the LEDS  4 ,  6 , and photodetector  5  is embedded within the rubber housing  2 , and is approximately 12 mm across (represented by ˜D). The combined height of the flexible housing  2  and body  7  is approximately 3 mm (represented by ˜R). Each flap  8 ,  9  has a thickness of approximately 1.5 mm (represented by ˜L). 
         [0035]    Referring to  FIG. 4 , with each heartbeat blood pumps through the patient&#39;s hand  40 , starting from the ulnar  29  and radial  41  arteries, to deliver blood to patient&#39;s palmer arches  27 ,  28  and further distribute oxygenated blood to the digital arteries  22 ,  23 ,  24 ,  25 , and  26  in each finger and thumb. Blood pressure, however, is typically strongest in the princeps pollics artery  21  of the thumb, which represents a direct extension of the radial artery  41 . Placement of the sensor  1  on the lower inner portion of the thumb is therefore ideal to generate a PPG waveform that is: i) relatively free of motion-related artifacts; and, ii) of high signal strength due to the relatively strong blood pressure and good circulation within the princeps pollics artery. 
         [0036]    Referring to  FIG. 5B , the PPG waveform measured from the thumb in graph  75  shows a strong peak  65   a , well-defined base  65   c , and identifiable dichrotic notch  65   b ; each of these features is useful for generating accurate PTT-based blood pressure readings according to the composite technique. In contrast, the PPG waveform generated by measuring the patient&#39;s forearm  70  shows less-defined pulses, as shown in  FIG. 5A . Signal quality from the pulse amplitudes measured in the forearm region tend to decrease gradually over time and have more rounded peaks  60   a , less-defined bases  60   c , and an almost non-existent dichotic notch  60   b . These waveforms, in contrast to the PPG waveforms shown in  FIG. 5B , tend to yield PTT-based blood pressure readings with relatively low accuracy. 
         [0037]      FIGS. 6A ,  6 B, and  7  show top-side, bottom-side, and top views of the body sensor  46  used to conduct the above-described measurements. The body sensor  46  features a single motherboard  150  connected to a battery component  160  and pneumatic component  165  through a series of flexible electrical wire harness cables  155   a - d . In this way, the body sensor  46  is divided into three different compartmentalized components that, collectively, can easily wrap around the patient&#39;s arm. The motherboard  150  includes connectors  166   a - c  that connect through separate cables to the ECG electrodes worn on the patient&#39;s chest, and a DB-9 connector  157  that connects through the cable  10  to the optical sensor worn on the patient&#39;s thumb. The connectors  166   a - c  also make electrical connections to a defibrillation-protection circuit  167  that protects the internal electrical components from voltage spikes that occur during defibrillation. During both pressure-dependent and pressure-free measurements, these optical and electrical sensors measure signals that pass through the connectors  166   a - c ,  157  to discrete circuit components on the top-side and bottom-side of the motherboard  150 . 
         [0038]    The discrete components on the motherboard  150  include: i) analog circuitry for amplifying and filtering the time-dependent PPG and ECG waveforms; ii) an analog-to-digital converter for converting the time-dependent analog signals into digital waveforms; and iii) a microprocessor configured/programmed for processing the digital waveforms to determine blood pressure according to the composite technique, along with other vital signs, as described above. 
         [0039]    To measure the pressure waveform during a pressure-dependent measurement, the pneumatic system  165  additionally includes a small mechanical pump  154  for inflating the bladder within the armband (shown in  FIG. 1  as  35 ), and solenoid valves  151  for controlling the bladder&#39;s inflation and deflation rates. The pump  154  and solenoid valves  151  connect through a manifold  152  to a connector  156  that attaches through a tube (not shown in the figure) to the bladder within the armband, and additionally to a pressure sensor  153  that senses the pressure in the bladder. The solenoid valve  151  couples through the manifold  152  to a small, adjustable ‘bleeder’ valve  166  featuring a small hole that quickly releases pressure once a measurement is complete. Typically the solenoid valve  151  is closed as the pump  154  inflates the bladder. For measurements conducted during inflation, pulsations caused by the patient&#39;s heartbeats couple into the bladder as it inflates, and are mapped onto the pressure waveform. The pressure sensor  153  generates an analog pressure waveform, which is then digitized with the analog-to-digital converter described above, and finally filtered and processed to measure blood pressure during inflation. These blood pressure values are used to calibrate the PTT-based pressure-free measurements. 
         [0040]    Alternatively, for measurements done on deflation, the pump  154  inflates the bladder to a pre-programmed pressure above the patient&#39;s systolic pressure. Once this pressure is reached, the microprocessor opens the solenoid valve  151 , which couples to the ‘bleeder’ valve  166  adjusted to a setting that slowly releases pressure in the armband. During this deflation period, pulsations caused by the patient&#39;s heartbeat are coupled into the bladder and are mapped onto the pressure waveform, which is then measured by the digital pressure sensor, as described above. Once the microprocessor determines systolic, mean arterial and diastolic blood pressure, it opens the solenoid valve  151  to rapidly evacuate the pressure. 
         [0041]    A rechargeable lithium ion battery  160  connects to a battery-protection circuit  159 , which further connects through a harness  155 d directly to the motherboard board  150  to power all the above-mentioned circuit components. The battery  160  also includes an O-ring  161  to ensure proper placement and stabilization. The motherboard  150  additionally includes a vertical circuit board  163  supporting a USB port for programming a microprocessor, and an SD card for portable memory. The min-USB port also accepts a mini-USB adapter cable that supplies power from a wall-mounted AC adaptor. The AC adaptor is used, for example, when measurements are made over an extended period of time that exceeds the battery&#39;s life, or to recharge the battery  160 . A Bluetooth transmitter  168  is mounted directly on the circuit board  150  and, following a measurement, wirelessly transmits information to an external monitor. 
         [0042]    A flexible rubber housing  82 , shown in  FIG. 8 , covers all the electronic components shown in  FIG. 7 . The housing  82  is divided into three separate compartments  85 ,  86 ,  87  covering, respectively, the battery  160 , motherboard  150 , and pneumatic components  165 . On either side of the housing  82  a D-ring opening  88   a ,  88   b  receives a Velcro strap that connects to the armband  35 , as described in  FIG. 1 . The housing  82  is typically formed from a polymeric flexible rubber which is relatively unaffected by heat, moisture, and sunlight. Alternatively, the housing  82  can be made of hard plastic with compartments that are joined by a hinged crease with electrical connections embedded into the hard plastic. 
         [0043]      FIG. 9  shows a cross-sectional view of the body sensor  46  wrapping around the curvature of the patient&#39;s arm  31  and connected to the armband  35  that includes an inflatable bladder. The body sensor  46  and armband  35  are joined together by two D-ring connectors and Velcro straps (not shown in figure). Collectively the divided compartment  85 ,  86 ,  87  form a flexible housing that easily bends around the patient&#39;s arm  31 . In this configuration the body sensor  46 , which is centrally located on the arm  31 , connects to the optical sensor on the thumb and to the ECG electrodes worn on the chest with minimal cable clutter, as described above. 
         [0044]      FIG. 10  shows a three-dimensional plan view of the monitor  250  that receives the Bluetooth-transmitted information from the body sensor. A front face of the monitor  250  includes a touchpanel display  255  that renders an icon-driven graphical user interface, and a circular on/off button  259 . During an actual measurement, the touchpanel display  255  renders vital sign information from the body sensor. Such a monitor has been described previously in the following co-pending patent application, the contents of which are fully incorporated herein by reference: BLOOD PRESSURE MONITOR (U.S. Ser. No. 11/530,076; filed Sep. 8, 2006) and MONITOR FOR MEASURING VITAL SIGNS AND RENDERING VIDEO IMAGES (U.S. Ser. No. 11/682,177; filed Mar. 5, 2007). 
         [0045]    The monitor  250  includes an internal Bluetooth transmitter (not shown in the figure) that includes an antenna  260  to increase the strength of the received signal. To pair with a body sensor, such as that shown in  FIG. 9 , the monitor  250  includes a barcode scanner  257  on its top surface. During operation, a user holds the monitor  250  in one hand, and points the barcode scanner  257  at a printed barcode adhered to the plastic cover surrounding the body sensor. The user then taps an icon on the touchpanel display  255 , causing the barcode scanner  257  to scan the barcode. 
         [0046]    The printed barcode includes information on the body sensor&#39;s Bluetooth transceiver that allows it to pair with the monitor&#39;s Bluetooth transceiver. The scanning process decodes the barcode and translates its information to a microprocessor within the monitor  250 . Once the information is received, software running on the microprocessor analyzes it to complete the pairing. This methodology forces the user to bring the monitor into close proximity to the body sensor, thereby reducing the chance that vital sign information from another body sensor is erroneously received and displayed. The above-described system can be used in a number of different settings, including both the home and hospital. 
         [0047]    In addition to those methods described above, a number of additional methods can be used to calculate blood pressure from the PPG and ECG waveforms. These are described in the following co-pending patent applications, the contents of which are incorporated herein 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); 8) PATCH SENSOR FOR MEASURING BLOOD PRESSURE WITHOUT A CUFF (U.S. Ser. No. 10/906,315; filed Feb. 14, 2005); 9) PATCH SENSOR FOR MEASURING VITAL SIGNS (U.S. Ser. No. 11/160,957; filed Jul. 18, 2005); 10) WIRELESS, INTERNET-BASED SYSTEM FOR MEASURING VITAL SIGNS FROM A PLURALITY OF PATIENTS IN A HOSPITAL OR MEDICAL CLINIC (U.S. Ser. No. 11/162,719; filed Sep. 9, 2005); 11) HAND-HELD MONITOR FOR MEASURING VITAL SIGNS (U.S. Ser. No. 11/162,742; filed Sep. 21, 2005); 12) CHEST STRAP FOR MEASURING VITAL SIGNS (U.S. Ser. No. 11/306,243; filed Dec. 20, 2005); 13) SYSTEM FOR MEASURING VITAL SIGNS USING AN OPTICAL MODULE FEATURING A GREEN LIGHT SOURCE (U.S. Ser. No. 11/307,375; filed Feb. 3, 2006); 14) BILATERAL DEVICE, SYSTEM AND METHOD FOR MONITORING VITAL SIGNS (U.S. Ser. No. 11/420,281; filed May 25, 2006); 15) SYSTEM FOR MEASURING VITAL SIGNS USING BILATERAL PULSE TRANSIT TIME (U.S. Ser. No. 11/420,652; filed May 26, 2006); 16) BLOOD PRESSURE MONITOR (U.S. Ser. No. 11/530,076; filed Sep. 8, 2006); 17) TWO-PART PATCH SENSOR FOR MONITORING VITAL SIGNS (U.S. Ser. No. 11/558,538; filed Nov. 10, 2006); and, 18) MONITOR FOR MEASURING VITAL SIGNS AND RENDERING VIDEO IMAGES (U.S. Ser. No. 11/682,177; filed Mar. 5, 2007). 
         [0048]    Other embodiments are also within the scope of the claims. For example, other techniques, such as conventional oscillometry, can be used to determine systolic blood pressure for the above-described algorithms. 
         [0049]    In other embodiments, a variety of software configurations can be run on the monitor to give it a PDA-like functionality. These include, for example, Micro C OS®, Linux®, Microsoft Windows®, embOS, VxWorks, SymbianOS, QNX, OSE, BSD and its variants, FreeDOS, FreeRTOX, LynxOS, or eCOS and other embedded operating systems. The monitor can also run a software configuration that allows it to receive and send voice calls, text messages, or video streams received through the Internet or from the nation-wide wireless network it connects to. The barcode scanner described with reference to  FIG. 10  can also be used to capture patient or medical professional identification information, or other such labeling. This information, for example, can be used to communicate with a patient in a hospital or at home. In other embodiments, the device can connect to an Internet-accessible website to download content, e.g., calibrations, software updates, text messages, and information describing medications, from an associated website. As described above, the device can connect to the website using both wired (e.g., USB port) or wireless (e.g., short or long-range wireless transceivers) means. In still other embodiments, ‘alert’ values corresponding to vital signs and the pager or cell phone number of a caregiver can be programmed into the device using its graphical user interface. If a patient&#39;s vital signs meet an alert criteria, software on the device can send a wireless ‘page’ to the caregiver, thereby alerting them to the patient&#39;s condition. For additional patient safety, a confirmation scheme can be implemented that alerts other individuals or systems until acknowledgment of the alert is received. 
         [0050]    Still other embodiments are within the scope of the following claims.