Abstract:
A storage device for storing a plurality of portable medical devices includes a plurality of bays for receiving and storing the plurality of portable medical devices. Each portable medical device includes an electrical connector. Each bay includes a first electrical connector. The first electrical connector of each bay is configured to interface with the electrical connector of one of the portable medical devices. A second electrical connector is configured to be coupled to a computer. A battery charger is coupled to at least one of the first electrical connectors of a bay for charging a battery of one of the portable medical devices. A switch is coupled to the first electrical connector of each bay and coupled to the second electrical connector for selectively coupling each bay to the computer for data transfer between the bay and the computer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     None. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a system and method for storage of, and interfacing with, portable medical devices. In particular, the invention relates to a docking system and method for storing, charging, and transmitting data to and from portable medical devices, including non-invasive blood pressure measurement devices. 
     There has been a continuing need for devices which will measure blood pressure non-invasively, with accuracy comparable to invasive methods. Medwave, Inc. the assignee of the present invention, has developed non-invasive blood pressure measurement methods and devices which are described in the following United States patents, hereby incorporated by reference: U.S. Pat. No. 5,649,542 entitled CONTINUOUS NON-INVASIVE BLOOD PRESSURE MONITORING SYSTEM; U.S. Pat. No. 5,450,852 entitled CONTINUOUS NON-INVASIVE PRESSURE MONITORING SYSTEM; U.S. Pat. No. 5,640,964 entitled WRIST MOUNTED BLOOD PRESSURE SENSOR; U.S. Pat. No. 5,720,292 entitled BEAT ONSET DETECTOR; U.S. Pat. No. 5,738,103 entitled SEGMENTED ESTIMATION METHOD; U.S. Pat. No. 5,722,414 entitled CONTINUOUS NON-INVASIVE BLOOD PRESSURE MONITORING SYSTEM; U.S. Pat. No. 5,642,733 entitled BLOOD PRESSURE SENSOR LOCATOR; U.S. Pat. No. 5,797,850 entitled METHOD AND APPARATUS FOR CALCULATING BLOOD PRESSURE OF AN ARTERY; and U.S. Pat. No. 5,941,828 entitled HAND-HELD NON-INVASIVE BLOOD PRESSURE MEASUREMENT DEVICE. 
     As described in these patents, blood pressure is determined by sensing pressure waveform data derived from an artery. A pressure sensing device includes a sensing chamber with a diaphragm which is positioned over the artery. A transducer coupled to the sensing chamber senses pressure within the chamber. A flexible body conformable wall is located adjacent to (and preferably surrounding) the sensing chamber. The wall is isolated from the sensing chamber and applies force to the artery while preventing pressure in a direction generally parallel to the artery from being applied to the sensing chamber. As varying pressure is applied to the artery by the sensing chamber, pressure waveforms are sensed by the transducer to produce sensed pressure waveform data. The varying pressure may be applied automatically in a predetermined pattern, or may be applied manually. 
     The sensed pressure waveform data is analyzed to determine waveform parameters which relate to the shape of the sensed pressure waveforms. One or more blood pressure values are derived based upon the waveform parameters. The Medwave blood pressure measurement devices include both automated devices for continually monitoring blood pressure (such as in a hospital setting) and hand-held devices which can be used by a physician or nurse, or by a patient when desired. 
     When multiple hand-held or portable medical devices, such as the Medwave blood pressure measurement devices, are used in a common environment, such as a hospital, it would be convenient to provide a central storage medium for holding the devices, charging the batteries of the devices, as well as communicating with the devices to obtain stored information. 
     The information obtained from the devices through the docking station may be used in multiple ways. The information can be used by doctors and nurses for remote patient monitoring. The information can be used for billing purposes. Charts and graphs can be generated from the information, such as blood pressure or pulse rate historical data for a patient. The information can be used for sensor management (e.g., displaying sensor usage information, sensor test information and warnings, sensor expiration information and warnings, etc.). 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a storage device and method for storing a plurality of portable medical devices and gathering and centrally storing a set of patient data gathered from the portable medical devices. In a preferred embodiment, the storage device includes a plurality of bays for receiving and storing the plurality of portable medical devices. Each portable medical device includes an electrical connector. Each bay includes a first electrical connector. The first electrical connector of each bay is configured to interface with the electrical connector of one of the portable medical devices. A second electrical connector is configured to be coupled to a computer. A battery charger is coupled to at least one of the first electrical connectors of a bay for charging a battery of one of the portable medical devices. A switch is coupled to the first electrical connector of each bay and coupled to the second electrical connector for selectively coupling each bay to the computer for data transfer between the bay and the computer. 
     A preferred method according to the present invention for gathering and centrally storing a set of patient data for each one of a plurality of patients includes applying a plurality of portable medical devices to a plurality of patients to obtain the patient data. The patient data is stored in the plurality of portable medical devices. The plurality of portable medical devices are placed in a docking station coupled to a computer. The stored patient data is transmitted from each portable medical device through the docking station to the computer and stored therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a non-invasive blood pressure measurement device suitable for use with the present invention. 
     FIG. 2A is a side view of the blood pressure measurement device of FIG.  1 . 
     FIG. 2B is a bottom view of the blood pressure measurement device of FIG.  1 . 
     FIG. 3 is an electrical block diagram of the blood pressure measurement device. 
     FIG. 4 is a perspective view of a docking station according to the present invention. 
     FIG. 5 is a schematic diagram of multiple docking stations coupled together. 
     FIG. 6 is a high level flow diagram illustrating the flow of information in the present invention. 
     FIGS. 7A and 7B are electrical schematic diagrams of the docking station. 
    
    
     DETAILED DESCRIPTION 
     Prior to describing the docking system and method of the present invention, a description is provided of a blood pressure measurement device, which is suitable for use in conjunction with the docking system. 
     FIG. 1 illustrates a blood pressure measurement device being used to measure and display blood pressure within an underlying artery within wrist  12  of a patient. Blood pressure measurement device  10  includes placement guide  13 , main housing  14 , display panel  16 , patient identification toggle  18 , power switch  20 , and sensor interface assembly  22  (best shown in FIGS.  2 A and  2 B). 
     Using placement guide  13  of measurement device  10 , measurement device  10  is placed at the projection of the styloid process bone perpendicular to wrist  12 . With device  10 , a small amount of force is manually applied to the radial artery, which runs along the styloid process bone. As the force is manually applied, blood pressure waveforms are recorded and the corresponding hold down pressure which is being manually applied is also recorded. Using the shape of the blood pressure waveforms, waveform parameters are generated. These parameters, along with universal coefficients, are used to calculate pressure values which then can be displayed. 
     Placement guide  13  is connected to housing  14  at the base of housing  14 . Placement guide  13  straddles the styloid process bone, automatically placing sensor interface assembly  22  over the underlying artery. Housing  14  contains all of the electrical components of measurement device  10 . The shape and configuration of housing  14  allows it to hang on the patient&#39;s wrist, using placement guide  13  as a type of hook. Housing  14  includes pressure platform  15 , which is a flattened depression directly above sensor interface assembly  22 . In operation, the user (medical personnel) applies pressure on pressure platform  15  with a thumb or finger. The hold-down force from the user&#39;s thumb applies a force in an axial direction (i.e., an axial direction with respect to a central cylindrical axis of sensor interface assembly  22 ) to wrist  12  of the patient. The axial force is transmitted from pressure platform  15  of housing  14  to sensor interface assembly  22 . 
     In a preferred embodiment, display panel  16  simultaneously displays the following values based upon blood pressure measurements: systolic pressure, diastolic pressure, pulse rate, and mean blood pressure. Display panel  16  also preferably provides visual prompting for manually applying a varying hold down pressure. 
     Power switch  20  is actuated to turn on power to the circuitry within housing  14 . Timing circuitry within housing  14  automatically turns power of f after a predetermined period of inactivity. Actuation of switch  20 , after the unit is turned on, causes display panel  16  to indicate previous readings of blood pressure and pulse rate. 
     Patient identification toggle  18  is used to organize the recorded blood pressure information with respect to a particular patient. After actuating power switch  20 , the user selects the specific patient for which blood pressure will be measured by pressing patient identification toggle  18 . In one embodiment, display panel  16  displays a patient identification number for the currently selected patient. The patient identification number changes as patient identification toggle  18  is pressed. In one embodiment the user can scroll through a list of  16  patient identification memory locations. 
     FIG. 2A is a side view of blood pressure measurement device  10 , and FIG. 2B is a bottom view of blood pressure measurement device  10 . As can be seen from FIGS. 2A and 2B, placement guide  13  is generally U-shaped. Placement guide  13  includes hook  23 , pad  25 , and opening  27 . Opening  27  is a generally circular aperture that has a notch  29  near hook  23 . Guide ribs  17  and  19  encircle opening  27  and notch  29 , and meet at the base of hook  23 . 
     When device  10  is placed on the patient, pad  25  contacts the palm side of the wrist of the patient, while hook  23  wraps around the backside of the wrist. Placement guide  13  is made of a flexible plastic so as to fit all patients, with the styloid process bone fitting into notch  29  of opening  27 . Opening  27  also allows sensor interface assembly  22  to come in contact with the patient&#39;s wrist. Pad  25  becomes a pivot point about which force is applied. 
     Relying on a cantilever type action, device  10  allows the user to apply a force at pressure platform  15  of housing  14 . Housing  14  pivots about pad  25 , and sensor interface assembly  22  applies an axial force to the underlying artery. Sensor interface assembly  22  is pivotally mounted to housing  14 . As pressure is manually applied by moving housing  14  toward the artery, that force is transferred from housing  14  to sensor interface assembly  22 . 
     Device  10 , with placement guide  13  and the cantilever type action, allows sensor interface assembly  22  to be consistently placed in the proper position, and the hold-down force to be consistently applied in the axial direction with respect to wrist  12 . This improvement greatly simplifies the procedure of applying pressure by the user, because the user no longer controls the direction and angle at which pressure is applied with respect to the patient&#39;s wrist. 
     Instead of having to palpate wrist  12  to identify the location of the radial artery, a user simply places device  10  adjacent wrist  12  so that placement guide  13  hooks onto the patient&#39;s wrist with guide ribs  17  and  19  straddling the projection of the styloid process bone. The measurement process is significantly simplified with the present invention. 
     The force applied to the artery is swept in an increasing fashion so the pressure waveform data from a series of pulses are obtained with different amounts of force being applied. To achieve the desired pattern of variable force, user feedback is preferably provided with device  10 . 
     In a preferred embodiment, feedback is in the form of a visual counter on display panel  16 . As the user begins to apply pressure, a number is displayed corresponding to the amount of pressure applied by the user. As the user increases the applied pressure, the displayed number proportionally increases. The user (medical personnel) is previously instructed to increase pressure smoothly so that the displayed counter increases one integer at a time, approximately one per second. If the user increases the hold-down pressure too quickly, the displayed counter will also jump quickly through the corresponding numbers to indicate the choppy applied pressure. The user applies greater pressure until device  10  shows the resulting blood pressure measurements on display panel  16 . Preferably, the user applies enough pressure to get the counter up to the number 15, but it could be as low as 4 or 5, or as high as 27 or 28, depending on the patient. If a patient has higher blood pressure, greater applied force will be necessary, and the corresponding ending counter number will be a higher integer. 
     After the measurement, the user can then view the blood pressure reading. In a preferred embodiment, display panel  16  provides a digital readout of systolic, diastolic, and mean blood pressure, as well as pulse rate. An indication of memory location (by number) corresponding to the patient is also displayed. 
     As soon as the reading is complete, device  10  is ready to take another reading. There is no need to clear display  16 . Device  10  stores a predetermined number of previous readings (such as the last 10 readings). To review prior readings, patient identification toggle  18  or power switch  20  is pressed. This causes a different reading from memory to be displayed on display  16 . 
     Alternatively, the feedback to the user can be audible tones and/or visual movable bars. The process of applying force in response to audible tones and/or visual movable bars on display  16  is fully described in U.S. Pat. No. 5,941,828, entitled “Non-Invasive Blood Pressure Sensor With Motion Artifact Reduction”, which is incorporated herein. 
     As can be seen in FIG. 2B, device  10  includes external connector  30 . External connector  30  is a five pin connector that is used to transmit and receive data, recharge battery  36  (see FIG. 3) contained within housing  14  and provide an alternative power source to device  10 . External connector  30  allows device  10  to be connected to a docking station  100  (shown in FIG. 4) so that its internal battery can be recharged, and the collected blood pressure information can be downloaded to a central system. Device  10  can be used by a nurse or other employee in a hospital setting to collect blood pressure and heart rate information from a series of patients. Docking station  100  is described below with reference to FIGS. 4-7. 
     FIG. 3 is an electrical block diagram of device  10 . Device  10  includes patient marker switch  18 , power supply circuit  42 , sensor interface assembly  22 , connectors  58  and  60 , amplifiers  62 A and  62 B, analog-to-digital (A/D) converter  64 , microprocessor  68 , display driver and memory circuit  82 , display panel  16 , non-volatile memory  78  and real-time clock  80 . Power supply circuit  42  includes external connector  30 , amplifiers  32  and  34 , rechargeable battery  36 , supply switch  38 , reverse battery protection  40 , switch  20 , integrated power switch  44 , OR circuit  46 , voltage divider  48 , analog regulator  50  and supervisor circuit  52 . 
     Device  10  can be powered through an external power source, such as docking station  100 . An external power source couples to device  10  through external connector  30 . Power from external connector  30  on the VSUPPLY line causes supply switch  38  to disconnect rechargeable battery  36  from supplying power to supply circuit  42 . Instead, rechargeable battery  36  is recharged using the CHRGR line while the external power source supplies power to supply circuit  42  on the VSUPPLY line. External connector  30  also allows device  10  to receive and transmit data, such as blood pressure information and device serial number, to docking station  100  (see FIG. 4) over the RX (receive) line and TX (transmit) line. The RX and TX lines are coupled to amplifiers  32  and  34 , respectively, which amplify the signals transmitted and received by microprocessor  68 . Amplifiers  32  and  34  are enabled when power is received through the VSUPPLY line, and are disabled when no power is received through the VSUPPLY line. External connector  30  also includes a GND line, which is connected to ground. 
     Switch  20  is partially a monitoring pushbutton switch. Pressing switch  20  causes OR circuit  46  to turn on integrated power switch  44 . Integrated power switch  44  supplies power to all digital circuits, including microprocessor  68 , display panel  16  and associated display driver and memory circuit  82 . Integrated power switch  44  supplies power to microprocessor  68 , which in turn latches on OR circuit  46 . The turn of f of the circuit is controlled by microprocessor  68  discontinuing a signal to OR circuit  46 . This occurs through a fixed time of no activity. 
     Analog regulator  50  outputs electrical power which is used to energize analog circuitry, including amplifiers  62 A and  62 B, and analog-to-digital (A/D) converter  64 . 
     Pressure transducers  56 A and  56 B and nonvolatile memory  54  within sensor interface assembly  22  are connected through connector  58  and connector  60  to circuitry within housing  14 . Transducers  56 A and  56 B sense pressure communicated within sensor interface assembly  22  and supply electrical signals to connector  58 . In a preferred embodiment, transducers  56 A and  56 B are piezoresistive pressure transducers. Nonvolatile memory  54  stores offsets of transducers  56 A and  56 B and other information such as a sensor serial number. Nonvolatile memory  54  is, in a preferred embodiment, an EEPROM. 
     The outputs of transducers  56 A and  56 B are analog electrical signals representative of sensed pressure. These signals are amplified by amplifiers  62 A and  62 B and applied to inputs of A/D converter  64 . The analog signals to A/D converter  64  are converted to digital data and supplied to the digital signal processing circuitry  66  of microprocessor  68 . 
     Microprocessor  68  includes digital signal processing circuitry  66 , read only memory (ROM) and electrically erasable programmable read only memory (EEPROM)  70 , random access memory (RAM)  72 , timer circuitry  74 , and input/output ports  76 . A/D converter  64  may be integrated with microprocessor  68 , while some of the memory may be external to microprocessor  68 . 
     Based upon the pressure data received, microprocessor  68  performs calculations to determine blood pressure values. As each pulse produces a cardiac waveform, microprocessor  68  determines a peak amplitude of the waveform. Microprocessor  68  controls display driver  82  to create the visual counter on display  16  that counts in correlation to the hold down pressure applied by the user. The visual counter guides the user in applying a variable force to the artery. 
     When a measurement cycle has been completed, microprocessor  68  reorders the cardiac waveforms in increasing order of their corresponding hold down pressure and performs calculations to determine systolic pressure, diastolic pressure, mean blood pressure, and pulse rate. The process of calculating pressure using shape, amplitude, and hold down is described in the previously mentioned Medwave patents, which are incorporated by reference. If patient identification toggle  18  is pressed, a signal is supplied to microprocessor  68 , causing it to toggle to a new pressure reading with a new memory location. In one embodiment, the memory location of that pressure reading is also displayed. 
     The blood pressure calculations, organized by patient, are preferably time-stamped at the time of calculation using real-time clock  80 , and stored in non-volatile memory  78 , so that the calculations are not lost when power to device  10  is turned off. Non-volatile memory is preferably an EEPROM. 
     A preferred docking station according to the present invention is illustrated in FIG.  4 . Docking station  100  includes four bays  102 A- 102 D (collectively referred to as bays  102 ) for receiving and holding blood pressure devices  10 . Bays  102 A- 102 D include five-pin connectors  104 A- 104 D, respectively, for interfacing with external connector  30  of a device  10 . Only connector  104 B is visible in FIG. 4, but connectors  104 A,  104 C and  104 D are the same as connector  104 B. Docking station  100  further includes AC adapter  106 , LED indicators  108 A- 108 D (collectively referred to as LED indicators  108 ) and DB-9 connector  112 . LED indicator  108 B is not visible in FIG. 4, but is positioned adjacent bay  102 B similar to the positioning of LED indicator  108 A adjacent bay  102 A. LED indicators  108  are preferably dual color (red-green) LEDs. AC adapter  106  plugs into a wall receptacle for AC power, and outputs a DC voltage through DC connector  110 . DC connector  110  plugs into docking station  100  and provides DC power for the circuitry therein. Alternatively, power for docking station  100  and for recharging devices  10  may be obtained from another source, such as from personal computer (PC)  120  (shown in FIG.  6 ). 
     Docking station  100  preferably has a modular design, allowing multiple docking stations  100  to be connected together. FIG. 5 shows a diagram of four docking stations  100 A- 100 D (collectively referred to as docking stations  100 ) connected together. When multiple docking stations  100  are coupled together, one docking station  10 A acts as a master, while the remaining docking stations  100 B- 100 D act as slaves. Docking stations  100  are electrically coupled together via bus input connectors  166 A- 166 D (collectively referred to as bus input connectors  166 ), first bus output connectors  156 A- 156 D (collectively referred to as first bus output connectors  156 ) and second bus output connectors  158 A- 158 D (collectively referred to as second bus output connectors  158 ). Bus connectors  156 ,  158  and  166  are preferably positioned on the back and both sides of a docking station  100 , allowing the docking stations to be connected side-to-side or back-to-back. 
     In a preferred embodiment, docking station  100  is connected to a personal computer (PC)  120  as shown in FIG.  6 . After blood pressure and heart rate data are obtained by a blood pressure measurement device  10 , the nurse places device  10  into a docking station  100 , and PC  120  transmits commands through docking station  100  to device  10  via external connector  30 . In response, device  10  outputs stored data through docking station  100  to PC  120 . Concurrently, the rechargeable battery  36  within device  10  is recharged, and power is supplied to device  10  from docking station  100  via external connector  30 , while device  10  is in docking station  100 . 
     Device  10  outputs pulse rate data and blood pressure data to PC  120 , including systolic blood pressure and diastolic blood pressure. Each set of pulse rate and blood pressure data includes a patient ID number, and a time stamp and a date stamp of the reading. As described above, the patient ID number is a number from 1-16 that is set using patient identification toggle  18 , and allows blood pressure and pulse rate data to be organized within device  10  with respect to particular patients. In a preferred embodiment, a sensor serial number is also output from device  10  to PC  120 , so that blood pressure and pulse rate information can be organized with respect to particular measurement devices  10 . Device  10  may also transmit to PC  120  any other information stored in the device  10 , including mean blood pressure information, usage history information and sensor test information. 
     PC  120  preferably includes database  122  for all of the patients in the hospital. PC  120  runs a custom software application that associates actual patients with patient ID numbers and serial numbers for devices  10 . Each time PC  120  obtains information from a device  10  stored in docking station  100 , PC  120  stores the information in database  122 . The information obtained from devices  10  may also be stored on an Internet server  124 . The information obtained from devices  10  and stored in database  122  or Internet server  124  may be accessed by other computers, such as computers  126  used by clinical personnel, computers  128  used by administrative personnel and computers  130  used by payers. 
     The information obtained from devices  10  through docking station  100  may be used in multiple ways. The information can be used by doctors and nurses for remote patient monitoring. The information can be used for billing purposes. Charts and graphs can be generated from the information, such as blood pressure or pulse rate historical data for a patient. The information can be used for sensor management (e.g., displaying sensor usage information, sensor test information and warnings, sensor expiration information and warnings, etc.). 
     FIGS. 7A and 7B show an electrical schematic diagram of docking station  100 . Docking station  100  includes five-pin connectors  104 A- 104 D (collectively referred to as connectors  104 ), LED indicators  108 A- 108 D (collectively referred to as LED indicators  108 ), battery chargers  140 A- 140 D (collectively referred to as battery chargers  140 ), switches  142 A- 142 D (collectively referred to as switches  142 ), input switch  144 , output switch  146 , serial interface  148 , DB-9 connector  112 , counter  154 , first bus output  156 , second bus output  158 , bay address decoder  160 , board address switch  162 , board address decoder  164 , bus input  166  and DC power supplies +V 1  and +V 2 . Power supplies +V 1  and +V 2  are provided power from DC connector  110  (shown in FIG.  4 ). 
     Each connector  104  of docking station  100  may be connected to external connector  30  of a blood pressure measurement device  10 . Five lines are connected to each connector  104 —DATAIN, DATAOUT, CHRGR, GND and VSUPPLY. Each DATAIN line connects with the TX line of a device  10  (see FIG.  3 ), and is used for transmitting data from device  10  to docking station  100 . The DATAIN line from each connector  104  is connected to input switch  144 . Each DATAOUT line connects with the RX line of a device  10 , and is used for transmitting data from docking station  100  to a device  10 . The DATAOUT line from each connector  104  is connected to output switch  146 . Each GND line within docking station  100  is connected to the GND line of a device  10 , and is coupled to ground. 
     Each CHRGR line of docking station  100  connects with the CHRGR line of a device  10 . Each CHRGR line of docking station  100  is also coupled to one of the battery chargers  140 . Battery chargers  140  provide a current source for recharging battery  36  within a device  10 . Battery chargers  140 A- 140 D are coupled to LED indicators  108 A- 108 D, respectively. When a device  10  is first plugged into a bay  102  of docking station  100 , for example bay  102 A, battery charger  140 A detects the presence of device  10 , begins charging device  10 , starts a timer, and uses the RED 1  output line to cause LED indicator  108 A to display a red light. The display of the red light indicates that device  10  is charging. In a preferred embodiment, battery charger  140 A monitors the timer and uses the GREEN 1  and FLASH 1  output lines to cause LED indicator  108 A to display a flashing green light after 15 hours of charging. If device  10  is removed from bay  102 A, and then replaced back in bay  102 A, battery charger  140 A resets the timer. Other battery chargers with different charging times may be used. Battery chargers  140 B- 140 D operate in the same manner as battery charger  140 A. 
     Each VSUPPLY line of docking station  100  is connected to the VSUPPLY line of a device  10 , and is used to provide power to device  10 . Each VSUPPLY line of docking station  100  is connected to one of the switches  142 . Each switch  142  is controlled by one of the battery chargers  140 . When a device  10  is first plugged into a bay  102  of docking station  100 , for example bay  102 A, battery charger  140 A detects the presence of the device  10 , and closes switch  142 A. Power is then supplied to the device  10  from power supply +V 2 . Supplying power to device  10  from power supply +V 2  guarantees not only that the digital voltage levels are the same in device  10  and docking station  100  (optimizing noise margin and reducing likelihood of latch-up and/or damage), but that the saved pressure readings, pulse rates and other data in device  10  may be obtained even with a fully discharged battery  36 . 
     When multiple docking stations  100  are coupled together as shown in FIG. 5, one docking station  100 A is a master unit, and the remaining docking stations  100 B- 100 D are slave units. The slave units  100 B- 100 D are similar to the master unit  100 A, with the deletion of counter  154 , serial interface  148  and DB-9 connector  112 . When multiple docking stations  100  are connected together, only the master docking station  100 A connects directly to PC  120 , while the remaining docking stations  100  share a common bus  155  for communicating with PC  120 . 
     Each docking station  100  includes a first bus output  156 , a second bus output  158  and a bus input  166 , which are each implemented with a 10-pin connector. Each bus line coupled to first bus output  156  is also coupled to a corresponding pin of second bus output  158  and bus input  166 . The bus lines are numbered from 1 to 10. Bus lines  1 - 4  are connected to lines ADDR 0 , ADDR 1 , ADDR 2  and ADDR 3 , respectively. Bus line  5  is connected to input switch  144 . Bus line  6  is connected to output switch  146 . Bus lines  7  and  8  are connected to +V 1 , which is a DC power supply. Bus lines  9  and  10  are connected to ground. 
     In a preferred embodiment, bus input connector  166  is positioned on the left side of docking station  100 , first bus output connector  156  is positioned on the back side of docking station  100 , and second bus output connector  158  is positioned on the right side of docking station  100 . Other configurations are possible. 
     Each docking station  100  includes a circuit board for holding and connecting the electronics in FIGS. 7A and 7B. When multiple docking stations  100  are coupled together, each circuit board (and correspondingly each docking station  100 ) is assigned a board address. The board address for each docking station  100  is set with board address switch  162 . Similarly, each bay  102  within a docking station  100  is assigned a bay address. Each circuit board and each bay  102  is assigned one address in the set { 00 ,  01 ,  10 ,  11 }. The lines ADDR 0  and ADDR 1  are used to cycle through the four bay addresses. The lines ADDR 2  and ADDR 3  are used to cycle through the four board addresses. 
     DB-9 connector  112  of docking station  100  is preferably connected to a serial port of PC  120 , although DB-9 connector  112  may alternatively be connected to any other device that is able to manipulate TX, RX, DTR (Data Terminal Ready), and RTS (Request to Send) lines. In order to access bays  102 , and therefore the blood pressure measurement devices  10 , PC  120  toggles the RTS line, which then toggles the CLK line of counter  154 . Counter  154  generates binary addresses in a sequence of 0 (i.e., 0000) to 15 (i.e., 1111). The first two digits of the four digit binary address represent a board address and are sent out on lines ADDR 2  and ADDR 3 . The last two digits of the four digit binary address represent a bay address and are sent out on lines ADDR 0  and ADDR 1 . The DTR line may toggled by PC  120  in order to reset counter  154  to 0. In this way, the data may be re-synchronized at any time to start from board  00 , bay  00 . 
     When counter  154  toggles to a new address, the new address goes out to bay address decoder  160  and board address decoder  164 . Board address decoder  164  includes four output lines, each output line corresponding to one of the four possible board addresses. Board address decoder  164  decodes the two digit board address portion of the four digit address and, based on the decoded address, sets one of its four output lines high. If the line set high by board address decoder  164  corresponds to the board address set at board address switch  162 , board address switch  162  sends an enable signal to bay address decoder  160 , allowing bay address decoder  160  to decode the bay address. If the line set high by board address decoder  164  does not correspond to the board address set at board address switch  162 , board address switch  162  maintains its output line low, thereby maintaining bay address decoder  160  in a disabled state. 
     Bay address decoder  160  includes four output lines, each output line corresponding to one of the four possible bay addresses. When bay address decoder  160  is enabled by board address switch  162  and receives a bay address, bay address decoder  160  decodes the bay address and, based on the decoded address, sets one of its four output lines high. The output lines of bay address decoder  160  are coupled to input switch  144  and output switch  146 . Based on the output of bay address decoder  160 , input switch  144  and output switch  146  couple the DATAIN and DATAOUT lines for the currently selected bay  102  to serial interface  148  and to bus lines  5  and  6 . Serial interface  148  includes amplifiers  150 A- 150 D, which amplify signals on the DATAIN, DATAOUT, DTR/CLR and RTS/CLK lines. 
     After toggling to a new address, PC  120  sends characters on the DATAOUT line and then waits for a response. If PC  120  does not receive a response within an allotted time, PC  120  assumes that no blood pressure measurement device  10  is present at the current board and bay address, moves on to the next board and bay address, and repeats the process. If a blood pressure measurement device  10  is present at the current board and bay address, the device  10  responds by sending characters to PC  120  on the DATAIN line. In this fashion, PC  120  is constantly scanning bays  102 , looking for blood pressure measurement devices  10  that may be present. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.