PATENT ABSTRACT
A Universal/Upgrading Pulse Oximeter (UPO) comprises a portable unit and a docking station together providing three-instruments-in-one functionality for measuring oxygen saturation and related physiological parameters. The portable unit functions as a handheld pulse oximeter. The combination of the docked portable and the docking station functions as a standalone, high-performance pulse oximeter. The portable-docking station combination is also connectable to, and universally compatible with, pulse oximeters from various manufacturers through use of a waveform generator. The UPO provides a universal sensor to pulse oximeter interface and a pulse oximetry measurement capability that upgrades the performance of conventional instruments by increasing low perfusion performance and motion artifact immunity, for example. Universal compatibility combined with portability allows the UPO to be transported along with patients transferred between an ambulance and a hospital ER, or between various hospital sites, providing continuous patient monitoring in addition to plug-compatibility and functional upgrading for multiparameter patient monitoring systems. 
     The image on the portable display is rotatable, either manually when undocked or as a function of orientation. In one embodiment, the docking station has a web server and network interface that allows UPO data to be downloaded and viewed as web pages over a local area network or the Internet.

PATENT DESCRIPTION
This application is a continuation of prior application Ser. No. 09/491,175 filed Jan. 25, 2000, and claims the benefit of priority under 35 U.S.C. §119(e) from U.S. Provisional Application No. 60/117,097, filed Jan. 25, 1999 and Provisional Application No. 60/161,565 filed Oct. 26, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     Oximetry is the measurement of the oxygen level status of blood. Early detection of low blood oxygen level is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter -of minutes. Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of oxygen supply. A pulse oximetry system consists of a sensor applied to a patient, a pulse oximeter, and a patient cable connecting the sensor and the pulse oximeter. 
     The pulse oximeter may be a standalone device or may be incorporated as a module or built-in portion of a multiparameter patient monitoring system, which also provides measurements such as blood pressure, respiratory rate and EKG. A pulse oximeter typically provides a numerical readout of the patient&#39;s oxygen saturation, a numerical readout of pulse rate, and an audible indicator or “beep” that occurs in response to each pulse. In addition, the pulse oximeter may display the patient&#39;s plethysmograph, which provides a visual display of the patient&#39;s pulse contour and pulse rate. 
     SUMMARY OF THE INVENTION 
     FIG. 1 illustrates a prior art pulse oximeter  100  and associated sensor  110 . Conventionally, a pulse oximetry sensor  110  has LED emitters  112 , typically one at a red wavelength and one at an infrared wavelength, and a photodiode detector  114 . The sensor  110  is typically attached to an adult patient&#39;s finger or an infant patient&#39;s foot. For a finger, the sensor  110  is configured so that the emitters  112  project light through the fingernail and through the blood vessels and capillaries underneath. The LED emitters  112  are activated by drive signals  122  from the pulse oximeter  100 . The detector  114  is positioned at the fingertip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues. The photodiode generated signal  124  is relayed by a cable to the pulse oximeter  100 . 
     The pulse oximeter  100  determines oxygen saturation (SpO 2 ) by computing the differential absorption by arterial blood of the two wavelengths emitted by the sensor  110 . The pulse oximeter  100  contains a sensor interface  120 , an SpO 2  processor  130 , an instrument manager  140 , a display  150 , an audible indicator (tone generator)  160  and a keypad  170 . The sensor interface  120  provides LED drive current  122  which alternately activates the sensor red and IR LED emitters  112 . The sensor interface  120  also has input circuitry for amplification and filtering of the signal  124  generated by the photodiode detector  114 , which corresponds to the red and infrared light energy attenuated from transmission through the patient tissue site. The SpO 2  processor  130  calculates a ratio of detected red and infrared intensities, and an arterial oxygen saturation value is empirically determined based on that ratio. The instrument manager  140  provides hardware and software interfaces for managing the display  150 , audible indicator  160  and keypad  170 . The display  150  shows the computed oxygen status, as described above. The audible indicator  160  provides the pulse beep as well as alarms indicating desaturation events. The keypad  170  provides a user interface for such things as alarm thresholds, alarm enablement, and display options. 
     Computation of SpO 2  relies on the differential light absorption of oxygenated hemoglobin, HbO 2 , and deoxygenated hemoglobin, Hb, to determine their respective concentrations in the arterial blood. Specifically, pulse oximetry measurements are made at red and IR wavelengths chosen such that deoxygenated hemoglobin absorbs more red light than oxygenated hemoglobin, and, conversely, oxygenated hemoglobin absorbs more infrared light than deoxygenated hemoglobin, for example 660 nm (red) and 905 nm (IR). 
     To distinguish between tissue absorption at the two wavelengths, the red and IR emitters  112  are provided drive current  122  so that only one is emitting light at a given time. For example, the emitters  112  may be cycled on and off alternately, in sequence, with each only active for a quarter cycle and with a quarter cycle separating the active times. This allows for separation of red and infrared signals and removal of ambient light levels by downstream signal processing. Because only a single detector  114  is used, it responds to both the red and infrared emitted light and generates a time-division-multiplexed (“modulated”) output signal  124 . This modulated signal  124  is coupled to the input of the sensor interface  120 . 
     In addition to the differential absorption of hemoglobin derivatives, pulse oximetry relies on the pulsatile nature of arterial blood to differentiate hemoglobin absorption from absorption of other constituents in the surrounding tissues. Light absorption between systole and diastole varies due to the blood volume change from the inflow and outflow of arterial blood at a peripheral tissue site. This tissue site might also comprise skin, muscle, bone, venous blood, fat, pigment, etc., each of which absorbs light. It is assumed that the background absorption due to these surrounding tissues is invariant and can be ignored. Thus, blood oxygen saturation measurements are based upon a ratio of the time-varying or AC portion of the detected red and infrared signals with respect to the time-invariant or DC portion: 
     
       
           RD/IR =(Red Ac /Red DC )/( IR   AC   /IR   DC ) 
       
     
     The desired SpO 2  measurement is then computed from this ratio. The relationship between RD/IR and SpO 2  is most accurately determined by statistical regression of experimental measurements obtained from human volunteers and calibrated measurements of oxygen saturation. In a pulse oximeter device, this empirical relationship can be stored as a “calibration curve” in a read-only memory (ROM) look-up table so that SpO 2  can be directly read-out of the memory in response to input RD/IR measurements. 
     Pulse oximetry is the standard-of-care in various hospital and emergency treatment environments. Demand has lead to pulse oximeters and sensors produced by a variety of manufacturers. Unfortunately, there is no standard for either performance by, or compatibility between, pulse oximeters or sensors. As a result, sensors made by one manufacturer are unlikely to work with pulse oximeters made by another manufacturer. Further, while conventional pulse oximeters and sensors are incapable of taking measurements on patients with poor peripheral circulation and are partially or fully disabled by motion artifact, advanced pulse oximeters and sensors manufactured by the assignee of the present invention are functional under these conditions. This presents a dilemma to hospitals and other caregivers wishing to upgrade their patient oxygenation monitoring capabilities. They are faced with either replacing all of their conventional pulse oximeters, including multiparameter patient monitoring systems, or working with potentially incompatible sensors and inferior pulse oximeters manufactured by various vendors for the pulse oximetry equipment in use oat the installation. 
     Hospitals and other caregivers are also plagued by the difficulty of monitoring patients as they are transported from one setting to another. For example, a patient transported by ambulance to a hospital emergency room will likely be unmonitored during the transition from ambulance to the ER and require the removal and replacement of incompatible sensors in the ER. A similar problem is faced within a hospital as a patient is moved between surgery, ICU and recovery settings. Incompatibility and transport problems are exacerbated by the prevalence of expensive and non-portable multiparameter patient monitoring systems having pulse oximetry modules as one measurement parameter. 
     The Universal/Upgrading Pulse Oximeter (UPO) according to the present invention is focused on solving these performance, incompatibility and transport problems. The UPO provides a transportable pulse oximeter that can stay with and continuously monitor the patient as they are transported from setting to setting. Further, the UPO provides a synthesized output that drives the sensor input of other pulse oximeters. This allows the UPO to function as a universal interface that matches incompatible sensors with other pulse oximeter instruments. Further, the UPO acts as an upgrade to existing pulse oximeters that are adversely affected by low tissue perfusion and motion artifact. Likewise, the UPO can drive a SpO 2  sensor input of multiparameter patient monitoring systems, allowing the UPO to integrate into the associated multiparameter displays, patient record keeping systems and alarm management functions. 
     One aspect of the present invention is a measurement apparatus comprising a sensor, a first pulse oximeter and a waveform generator. The sensor has at least one emitter and an associated detector configured to attach to a tissue site. The detector provides an intensity signal responsive to the oxygen content of arterial blood at the tissue site. The first pulse oximeter is in communication with the detector and computes an oxygen saturation measurement based on the intensity signal. The waveform generator is in communication with the first pulse oximeter and provides a waveform based on the oxygen saturation measurement. A second pulse oximeter is in communication with the waveform generator and displays an oxygen saturation value based on the waveform. The waveform is synthesized so that the oxygen saturation value is generally equivalent to the oxygen saturation measurement. 
     In another aspect of the present invention, a measurement apparatus comprises a first sensor port connectable to a sensor, an upgrade port, a signal processor and a waveform generator. The upgrade port is connectable to a second sensor port of a physiological monitoring apparatus. The signal processor is configured to compute a physiological measurement based on a signal input to the first sensor port. The waveform generator produces a waveform based on the physiological measurement, and the waveform is available at the upgrade port. The waveform is adjustable so that the physiological monitoring apparatus displays a value generally equivalent to the physiological measurement when the upgrade port is attached to the second sensor port. 
     Yet another aspect of the present invention is a measurement method comprising the steps of sensing an intensity signal responsive to the oxygen content of arterial blood at a tissue site and computing an oxygen saturation measurement based on the intensity signal. Other steps are generating a waveform based on the oxygen saturation measurement and providing the waveform to the sensor inputs of a pulse oximeter so that the pulse oximeter displays an oxygen saturation value generally equivalent to the oxygen saturation measurement. 
     An additional aspect of the present invention is a measurement method comprising the steps of sensing a physiological signal, computing a physiological measurement based upon the signal, and synthesizing a waveform as a function of the physiological measurement. A further step is outputting the waveform to a sensor input of a physiological monitoring apparatus. The synthesizing step is performed so that the measurement apparatus displays a value corresponding to the physiological measurement. 
     A further aspect of the present invention is a measurement apparatus comprising a first pulse oximeter for making an oxygen saturation measurement and a pulse rate measurement based upon an intensity signal derived from a tissue site. Also included is a waveform generation means for creating a signal based upon the oxygen saturation measurement and the pulse rate measurement. In addition, there is a communication means for transmitting the signal to a second pulse oximeter. 
     Another aspect of the present invention is a measurement apparatus comprising a portable portion having a sensor port, a processor, a display, and a docking connector. The sensor port is configured to receive an intensity signal responsive to the oxygen content of arterial blood at a tissue site. The processor is programmed to compute an oxygen saturation value based upon the intensity signal and to output the value to the display. A docking station has a portable connector and is configured to accommodate the portable so that the docking connector mates with the portable connector. This provides electrical connectivity between the docking station and the portable. The portable has an undocked position separate from the docking station in which the portable functions as a handheld pulse oximeter. The portable also has a docked position at least partially retained within the docking station in which the combination of the portable and the docking station has at least one additional function compared with the portable in the undocked position. 
     A further aspect of the present invention is a measurement apparatus configured to function in both a first spatial orientation and a second spatial orientation. The apparatus comprises a sensor port configured to receive a signal responsive to a physiological state. The apparatus also has a tilt sensor providing an output responsive to gravity. In addition, there is a processor in communication with the sensor port and the tilt sensor output. The processor is programmed to compute a physiological measurement value based upon the signal and to determine whether the measurement apparatus is in the first orientation or the second orientation based upon the tilt sensor output. A display has a first mode and a second mode and is driven by the processor. The display shows the measurement value in the first mode when the apparatus is in the first orientation and shows the measurement value in the second mode when the apparatus is in the second orientation. 
     Another aspect of the present invention is a measurement method comprising the steps of sensing a signal responsive to a physiological state and computing physiological measurement based on the signal. Additional steps are determining the spatial orientation of a tilt sensor and displaying the physiological measurement in a mode that is based upon the determining step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a prior art pulse oximeter, 
     FIG. 2 is a diagram illustrating a patient monitoring system incorporating a universal/upgrading pulse oximeter (UPO) according to the present invention; 
     FIG. 3 is top level block diagram of a UPO embodiment; 
     FIG. 4 is a detailed block diagram of the waveform generator portion of the UPO embodiment shown in FIG. 3; 
     FIG. 5 is an illustration of a handheld embodiment of the UPO; 
     FIG. 6 is a top level block diagram of another UPO embodiment incorporating a portable pulse oximeter and a docking station; 
     FIG. 7 is a detailed block diagram of the portable pulse oximeter portion of FIG. 6; 
     FIG. 8A is an illustration of the portable pulse oximeter user interface, including a keyboard and display; 
     FIGS. 8B-C are illustrations of the portable pulse oximeter display showing portrait and landscape modes, respectively; 
     FIG. 9 is a detailed block diagram of the docking station portion of FIG. 6; 
     FIG. 10 is a schematic of the interface cable portion of FIG. 6; 
     FIG. 11A is a front view of an embodiment of a portable pulse oximeter, 
     FIG. 11B is a back view of a portable pulse oximeter; 
     FIG. 12A is a front view of an embodiment of a docking station; 
     FIG. 12B is a back view of a docking station; 
     FIG. 13 is a front view of a portable docked to a docking station; and 
     FIG. 14 is a block-diagram of one embodiment of a local area network interface for a docking station. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 depicts the use of a Universal/Upgrading Pulse Oximeter (“UPO”)  210  to perform patient monitoring. A pulse oximetry sensor  110  is attached to a patient (not illustrated) and provides the UPO  210  with a modulated red and IR photo-plethysmograph signal through a patient cable  220 . The UPO  210  computes the patient&#39;s oxygen saturation and pulse rate from the sensor signal and, optionally, displays the patient&#39;s oxygen status. The UPO  210  may incorporate an internal power source  212 , such as common alkaline batteries or a rechargeable power source. The UPO  210  may also utilize an external power source  214 , such as standard 110V AC coupled with an external step-down transformer and an internal or external AC-to-DC converter. 
     In addition to providing pulse oximetry measurements, the UPO  210  also separately generates a signal, which is received by a pulse oximeter  268  external to the UPO  210 . This signal is synthesized from the saturation calculated by the UPO  210  such that the external pulse oximeter  268  calculates the equivalent saturation and pulse rate as computed by the UPO  210 . The external pulse oximeter  268  receiving the UPO signal may be a multiparameter patient monitoring system (MPMS)  260  incorporating a pulse oximeter module  268 , a standalone pulse oximeter instrument, or any other host instrument capable of measuring SpO 2 . The MPMS  260  depicted in FIG. 2 has a rack  262  containing a number of modules for monitoring such patient parameters as blood pressure, EKG, respiratory gas, and SpO 2 . The measurements made by these various modules are shown on a multiparameter display  264 , which is typically a video (CRT) device. The UPO  210  is connected to an existing MPMS  260  with a cable  230 , advantageously integrating the UPO oxygen status measurements with other MPMS measurements. This allows the UPO calculations to be shown on a unified display of important patient parameters, networked with other patient data, archived within electronic patient records and incorporated into alarm management, which are all MPMS functions convenient to the caregiver. 
     FIG. 3 depicts the major functions of the UPO  210 , including an internal pulse oximeter  310 , a waveform generator  320 , a power supply  330  and an optional display  340 . Attached to the UPO  210  is a sensor  110  and an external pulse oximeter  260 . The internal pulse oximeter  310  provides the sensor  110  with a drive signal  312  that alternately activates the sensor&#39;s red and IR LEDs, as is well-known in the art. A corresponding detector signal  314  is received by the internal pulse oximeter  310 . The internal pulse oximeter  310  computes oxygen saturation, pulse rate, and, in some embodiments, other physiological parameters such as pulse occurrence, plethysmograph features and measurement confidence. These parameters  318  are output to the waveform generator  320 . A portion of these parameters may also be used to generate display drive signals  316  so that patient status may be read from, for example, an LED or LCD display module  340  on the UPO. 
     The internal pulse oximeter  310  may be a conventional pulse oximeter or, for upgrading an external pulse oximeter  260 , it may be an advanced pulse oximeter capable of low perfusion and motion artifact performance not found in conventional pulse oximeters. An advanced pulse oximeter for use as an internal pulse oximeter  310  is described in U.S. Pat. No. 5,632,272 assigned to the assignee of the present invention and incorporated herein by reference. An advanced pulse oximetry sensor for use as the sensor  110  attached to the internal pulse oximeter  310  is described in U.S. Pat. No. 5,638,818 assigned to the assignee of the present invention and incorporated herein by reference. Further, a line of advanced Masimo SET® pulse oximeter OEM boards and sensors are available from the assignee-of the present invention. 
     The waveform generator  320  synthesizes a waveform, such as a triangular waveform having a sawtooth or symmetric triangle shape, that is output as a modulated signal  324  in response to an input drive signal  322 . The drive input  322  and modulation output  324  of the waveform generator  320  are connected to the sensor port  262  of the external pulse oximeter  260 . The synthesized waveform is generated in a manner such that the external pulse oximeter  260  computes and displays a saturation and a pulse rate value that is equivalent to that measured by the internal pulse oximeter  310  and sensor  110 . In the present embodiment, the waveforms for pulse oximetry are chosen to indicate to the external pulse oximeter  260  a perfusion level of 5%. The external pulse oximeter  260 , therefore, always receives a strong signal. In an alternative embodiment, the perfusion level of the waveforms synthesized for the external pulse oximeter can be set to indicate a perfusion level at or close to the perfusion level of the patient being monitored by the internal pulse oximeter  310 . As an alternative to the generated wavefor, a digital data output  326 , is connected to the data port  264  of the external pulse oximeter  260 . In this manner, saturation and pulse rate measurements and also samples of the unmodulated, synthesized waveform can be communicated directly to the external pulse oximeter  260  for display, bypassing the external pulse oximeter&#39;s signal processing functions. The measured plethysmograph waveform samples output from the internal pulse oximeter  310  also may be communicated through the digital data output  326  to the external pulse oximeter  260 . 
     It will be understood from the above discussion that the synthesized waveform is not physiological data from the patient being monitored by the internal pulse oximeter  310 , but is a waveform synthesized from predetermined stored waveform data to cause the external pulse oximeter  260  to calculate oxygen saturation and pulse rate equivalent to or generally equivalent (within clinical significance) to that calculated by the internal pulse oximeter  310 . The actual physiological waveform from the patient received by the detector is not provided to the external pulse oximeter  260  in the present embodiment. Indeed, the waveform provided to the external pulse oximeter will usually not resemble the plethysmographic waveform of physiological data from the patient being monitored by the internal pulse oximeter  260 . 
     The cable  230  (FIG. 2) attached between the waveform generator  320  and external pulse oximeter  260  provides a monitor ID  328  to the UPO, allowing identification of predetermined external pulse oximeter calibration curves. For example, this cable may incorporate an encoding device, such as a resistor, or a memory device, such as a PROM  1010  (FIG. 10) that is read by the waveform generator  320 . The encoding device provides a value that uniquely identifies a particular type of external pulse oximeter  260  having known calibration curve, LED drive and modulation signal characteristics. Although the calibration curves of the external pulse oximeter  260  are taken into account, the wavelengths of the actual sensor  110 , advantageously, are not required to correspond to the particular calibration curve indicated by the monitor ID  328  or otherwise assumed for the external pulse oximeter  260 . That is, the wavelength of the sensor  110  attached to the internal pulse oximeter  310  is not relevant or known to the external pulse oximeter  260 . 
     FIG. 4 illustrates one embodiment of the waveform generator portion  320  of the UPO  210  (FIG.  3 ). Although this embodiment is illustrated and described as hardware, one of ordinary skill will recognize that the functions of the waveform generator may be implemented in software or firmware or a combination of hardware, software and firmware. The waveform generator  320  performs waveform synthesis with a waveform look-up table (“LUT”)  410 , a waveform shaper  420  and a waveform splitter  430 . The waveform LUT  410  is advantageously a memory device, such as a ROM (read only memory) that contains samples of one or more waveform portions or segments containing a single waveform. These stored waveform segments may be as simple as a single period of a triangular waveform, having a sawtooth or symmetric triangle shape, or more complicated, such as a simulated plethysmographic pulse having various physiological features, for example rise time, fall time and dicrotic notch. 
     The waveform shaper  420  creates a continuous pulsed waveform from the waveform segments provided by the waveform LUT  410 . The waveform shaper  420  has a shape parameter input  422  and an event indicator input  424  that are buffered  470  from the parameters  318  output from the internal pulse oximeter  310  (FIG.  3 ). The shape parameter input  422  determines a particular waveform segment in the waveform LUT  410 . The chosen waveform segment is specified by the first address transmitted to the waveform LUT  410  on the address lines  426 . The selected waveform segment is sent to the waveform shaper  420  as a series of samples on the waveform data lines  412 . 
     The event indicator input  424  specifies the occurrence of pulses in the plethysmograph waveform processed by the internal pulse oximeter  310  (FIG.  3 ). For example, the event indicator may be a delta time from the occurrence of a previously detected falling pulse edge or this indicator could be a real time or near real time indicator of the pulse occurrence. The waveform shaper  420  accesses the waveform LUT  410  in a manner to create a corresponding delta time between pulses in the synthesized waveform output  428 . In one embodiment, the waveform shaper is clocked at a predetermined sample rate. From a known number of samples per stored waveform segment and the input delta time from the event indicator, the waveform shaper  420  determines the number of sequential addresses to skip between samples and accesses the waveform LUT  410  accordingly. This effectively “stretches” or “shrinks” the retrieved waveform segment so as to fit in the time between two consecutive pulses detected by the UPO. 
     The waveform splitter  430  creates a first waveform  432  corresponding to a first waveform (such a red wavelength) expected by the external pulse oximeter  260  (FIG. 3) and a second waveform (such as infrared)  434  expected by the external pulse oximeter  260 . The relative amplitudes of the first waveform  432  and second waveform  434  are adjusted to correspond to the ratio output  444  from a calibration curve LUT  440 . Thus, for every value of measured oxygen saturation at the sat input  442 , the calibration curve LUT  440  provides a corresponding ratio output  444  that results in the first waveform  432  and the second waveform  434  having an amplitude ratio that will be computed by the external pulse oximeter  260  (FIG. 3) as equivalent to the oxygen saturation measured by the internal pulse oximeter  310  (FIG.  3 ). 
     As described above, one particularly advantageous aspect of the UPO is that the operating wavelengths of the sensor  110  (FIG. 3) are not relevant to the operating wavelengths required by the external pulse oximeter  260  (FIG.  3 ), i.e. the operating wavelengths that correspond to the calibration curve or curves utilized by the external pulse oximeter. The calibration curve LUT  440  simply permits generation of a synthesized waveform as expected by the external oximeter  260  (FIG. 3) based on the calibration curve used by the external pulse oximeter  260  (FIG.  3 ). The calibration curve LUT  440  contains data about the known calibration curve of the external pulse oximeter  260  (FIG.  3 ), as specified by the monitor ID input  328 . In other words, the waveform actually synthesized is not a patient plethysmographic waveform. It is merely a stored waveform that will cause the external pulse oximeter to calculate the proper oxygen saturation valve and pulse rate values. Although this does not provide a patient plethysmograph on the external pulse oximeter for the clinician, the calculated values, which is what is actually sought, will be accurate. 
     A modulator  450  responds to an LED drive input  322  to generate a modulated waveform output  324  derived from the first waveform  432  and second waveform  434 . Also, a data communication interface  460  transmits as a digital data output  326  the data obtained from the sat  442 , pulse rate  462  and synthesized waveform  428  inputs. 
     FIG. 5 depicts a handheld UPO  500  embodiment. The handheld UPO  500  has keypad inputs  510 , an LCD display  520 , an external power supply input  530 , an output port  540  for connection to an external pulse oximeter and a sensor input  550  at the top edge (not visible). The display  520  shows the measured oxygen saturation  522 , the measured pulse rate  524 , a pulsating bar  526  synchronized with pulse rate or pulse events, and a confidence bar  528  indicating confidence in the measured values of saturation and pulse rate. Also shown are low battery  572  and alarm enabled  574  status indicators. 
     The handheld embodiment described in connection with FIG. 5 may also advantageously function in conjunction with a docking station that mechanically accepts, and electrically connects to, the handheld unit. The docking station may be co-located with a patient monitoring system and connected to a corresponding SpO 2  module sensor port, external power supply, printer and telemetry device, to name a few options. In this configuration, the handheld UPO may be removed from a first docking station at one location to accompany and continuously monitor a patient during transport to a second location. The handheld UPO can then be conveniently placed into a second docking station upon arrival at the second location, where the UPO measurements are displayed on the patient monitoring system at that location. 
     FIG. 6 shows a block diagram of a UPO embodiment, where the functions of the UPO  210  are split between a portable pulse oximeter  610  and a docking station  660 . The portable pulse oximeter  610  (“portable”) is a battery operated, fully functional, stand-alone pulse oximeter instrument. The portable  610  connects to a sensor  110  (FIG. 2) through a UPO patient cable  220  (FIG. 2) attached to a patient cable connector  618 . The portable  610  provides the sensor  110  with a drive signal  612  that alternately activates the sensor&#39;s red and IR LEDs, as is well-known in the art. The portable also receives a corresponding detector signal  614  from the sensor. The portable can also input a sensor ID on the drive signal line  612 , as described in U.S. Pat. No. 5,758,644 entitled Manual and Automatic Probe Calibration, assigned to the assignee of the present invention and incorporated herein by reference. 
     The portable  610  can be installed into the docking station  660  to expand its functionality. When installed, the portable  610  can receive power  662  from the docking station  660  if the docking station  660  is connected to external power  668 . Alternately, with no external power  668  to the docking, station  660 , the portable  610  can supply power  662  to the docking station  660 . The portable  610  communicates to the docking station with a bi-directional serial data line  664 . In particular, the portable  610  provides the docking station with SpO 2 , pulse rate and related parameters computed from the sensor detector signal  614 . When the portable  610  is installed, the docking station  660  may drive a host instrument  260  (FIG. 2) external to the portable  610 . Alternatively, the portable  610  and docking station  660  combination may function as a standalone pulse oximeter instrument, as described below with respect to FIG.  13 . 
     In one embodiment, the docking station  660  does not perform any action when the portable  610  is not docked. The user interface for the docking station  660 , i.e. keypad and display, is on the portable  610 . An indicator LED on the docking station  660  is lit when the portable is docked. The docking station  660  generates a detector signal output  674  to the host instrument  260  (FIG. 2) in response to LED drive signals  672  from the host instrument and SpO 2  values and related parameters received from the portable  610 . The docking station  660  also provides a serial data output  682 , a nurse call  684  and an analog output  688 . 
     An interface cable  690  connects the docking station  660  to the host instrument patient cable  230  (FIG.  2 ). The LED drive signals  672  and detector signal output  674  are communicated between the docking station  660  and the host instrument  260  (FIG. 2) via the interface cable  690 . The interface cable  690  provides a sync data output  692  to the docking station  660 , communicating sensor, host instrument (e.g. monitor ID  328 , FIG. 3) and calibration curve data. Advantageously, this data allows the docking station  660  to appear to a particular host instrument as a particular sensor providing patient measurements. 
     FIG. 7 provides further detail of the portable  610 . The portable components include a pulse oximeter processor  710 , a management processor  720 , a power supply  730 , a display  740  and a keypad  750 . The pulse oximeter processor  710  functions as an internal pulse oximeter, interfacing the portable to a sensor  110  (FIG. 2) and deriving SpO 2 , pulse rate, a plethysmograph and a pulse indicator. An advanced pulse oximeter for use as the pulse oximeter processor  710  is described in U.S. Pat. No. 5,632,272, referenced above. An advanced pulse oximetry sensor for use as the sensor  110  (FIG. 2) attached to the pulse oximeter processor  710  is described in U.S. Pat. No. 5,638,818, also referenced above. Further, a line of advanced Masimo SET® pulse oximeter OEM boards and sensors are available from the assignee of the present invention. In one embodiment, the pulse oximeter processor  710  is the Masimo SEr® MS-3L board or a low power MS-5 board. 
     The management processor  720  controls the various functions of the portable  610 , including asynchronous serial data communications  724  with the pulse oximeter processor  710  and synchronous serial communications  762  with the docking station  660  (FIG.  6 ). The physical and electrical connection to the docking station  660  (FIG. 6) is via a docking station connector  763  and the docking station interface  760 , respectively. The processor  720  utilizes a real-time clock  702  to keep the current date and time, which includes time and date information that is stored along with SpO 2  parameters to create trend data. The processor of the portable  610  and the docking station  660  (FIG. 6) can be from the same family to share common routines and minimize code development time. 
     The processor  720  also controls the user interface  800  (FIG. 8A) by transferring data  742  to the display  740 , including display updates and visual alarms, and by interpreting keystroke data  752  from the keypad  750 . The processor  720  generates various alarm signals, when required, via an enable signal  728 , which controls a speaker driver  770 . The speaker driver  770  actuates a speaker  772 , which provides audible indications such as, for example, alarms and pulse beeps. The processor  720  also monitors system status, which includes battery status  736 , indicating battery levels, and docked status  764 , indicating whether the portable  610  is connected to the docking station  660  (FIG.  6 ). When the portable  610  is docked and is on, the processor  720  also decides when to turn on or off docking station power  732 . 
     Advantageously, the caregiver can set (i.e. configure or program) the behavior of the portable display  740  and alarms when the docked portable  610  senses that an interface cable  690  has connected the docking station  660  to an external pulse oximeter, such as a multiparameter patient monitoring system. In one user setting, for example, the portable display  740  stops showing the SpO 2    811  (FIG. 8) and pulse rate  813  (FIG. 8) values when connected to an external pulse oximeter to avoid confusing the caregiver, who can read equivalent values on the patient monitoring system. The display  740 , however, continues to show the plethysmograph  815  (FIG. 8) and visual pulse indicator  817  (FIG. 8) waveforms. For one such user setting, the portable alarms remain active. 
     Another task of the processor  720  includes maintenance of a watchdog function. The watchdog  780  monitors processor status on the watchdog data input  782  and asserts the UP reset output  784  if a fault is detected. This resets the management processor  720 , and the fault is indicated with audible and visual alarms. 
     The portable  610  gets its power from batteries in the power supply  730  or from power  766  supplied from the docking station  660  (FIG. 6) via the docking station interface  760 . A power manager  790  monitors the on/off switch on the keypad  750  and turns-on the portable power accordingly. The power manager  790  turns off the portable on command by the processor  720 . DC/DC converters within the power supply  730  generate the required voltages  738  for operation of the portable  610  and docking station power  732 . The portable batteries can be either alkaline rechargeable batteries or another renewable power source. The batteries of the power supply  730  supply docking station power  732  when the docking station  660  (FIG. 6) is without external power. A battery charger within the docking station power supply provides charging current  768  to rechargeable batteries within the power supply  730 . The docking station power supply  990  (FIG. 9) monitors temperature  734  from a thermistor in the rechargeable battery pack, providing an indication of battery charge status. 
     A non-volatile memory  706  is connected to the management processor  720  via a high-speed bus  722 . In the present embodiment, the memory  706  is an erasable and field re-programmable device used to store boot data, manufacturing serial numbers, diagnostic failure history, adult SpO 2  and pulse rate alarm limits, neonate SpO 2  and pulse rate alarm limits, SpO 2  and pulse rate trend data, and program data. Other types of non-volatile memory are well known. The SpO 2  and pulse rate alarm limits, as well as SpO 2  related algorithm parameters, may be automatically selected based on the type of sensor  110  (FIG.  2 ), adult or neonate, connected to the portable  610 . 
     The LCD display  740  employs LEDs for a backlight to increase its contrast ratio and viewing distance when in a dark environment. The intensity of the backlight is determined by the power source for the portable  610 . When the portable  610  is powered by either a battery pack within its power supply  730  or a battery pack in the docking station power supply  990  (FIG.  9 ), the backlight intensity is at a minimum level. When the portable  610  is powered by external power  668  (FIG.  6 ), the backlight is at a higher intensity to increase viewing distance and angle. In one embodiment, button on the portable permits overriding these intensity settings, and provides. adjustment of the intensity. The backlight is controlled in two ways. Whenever any key is pressed, the backlight is illuminated for a fixed number of seconds and then turns off, except when the portable is docked and derives power from an external source. In that case, the backlight is normally on unless deactivated with a key on the portable  610 . 
     FIG. 8A illustrates the portable user interface  800 , which includes a display  740  and a keypad  750 . In one embodiment, the display  740  is a dot matrix LCD device having 160 pixels by 480 pixels. The display  740  can be shown in portrait mode, illustrated in FIG. 8B, or in landscape mode, illustrated in FIG. 8C. A tilt sensor  950  (FIG. 9) in the docking station  660  (FIG. 6) or a display mode key on the portable  610  (FIG. 6) determines portrait or landscape mode. The tilt sensor  950  (FIG. 9) can be a gravity-activated switch or other device responsive to orientation and can be alternatively located in the portable  610  (FIG.  6 ). In a particular embodiment, the tilt sensor  950  (FIG. 9) is a non-mercury tilt switch, part number CW 1300-1, available from Comus International, Nutley, N.J. (www.comus-intl.com). The tilt sensor  950  (FIG. 9) could also be a mercury tilt switch. 
     Examples of how the display area can be used to display SpO 2    811 , pulse rate  813 , a plethysmographic waveform  815 , a visual pulse indicator  817  and soft key icons  820  in portrait and landscape mode are shown in FIGS. 8B and 8C, respectively. The software program of the management processor  720  (FIG. 7) can be easily changed to modify the category, layout and size of the display information shown in FIGS. 8B-C. Other advantageous information for display is SpO 2  limits, alarm, alarm disabled, exception messages and battery status. 
     The keypad  750  includes soft keys  870  and fixed keys  880 . The fixed keys  880  each have a fixed function. The&#39;soft keys  870  each have a function that is programmable and indicated by one of the soft key icons  820  located next to the soft keys  870 . That is, a particular one of the soft key icons  820  is in proximity to a particular one of the soft keys  870  and has a text or a shape that suggests the function of that particular one of the soft keys  870 . In one embodiment, the button portion of each key of the keypad  750  is constructed of florescent material so that the keys  870 ,  880  are readily visible in the dark. 
     In one embodiment, the keypad  750  has one row of four soft keys  870  and one row of three fixed keys  880 . Other configurations are, of course, available, and specific arrangement is not significant. The functions of the three fixed keys  880  are power, alarm silence and light/contrast. The power function is an on/off toggle button. The alarm silence function and the light/contrast function have dual purposes depending on the duration of the key press. A momentary press of the key corresponding to the alarm silence function will disable the audible alarm for a fixed period of time. To disable the audible alarm indefinitely, the key corresponding to the alarm silence function is held down for a specified length of time. If the key corresponding to the alarm silence function is pressed while the audible alarm has been silenced, the audible alarm is reactivated. If the key corresponding to the light/contrast function is pressed momentarily, it is an on/off toggle button for the backlight. If the key corresponding to the light/contrast function is held down, the display contrast cycles through its possible values. 
     In this embodiment, the default functions of the four soft keys  870  are pulse beep up volume, pulse beep down volume, menu select, and display mode. These functions are indicated on the display by the up arrow, down arrow, “menu” and curved arrow soft key icons  820 , respectively. The up volume and down volume functions increase or decrease the audible sound or “beep” associated with each detected pulse. The display mode function rotates the display  740  through all four orthogonal orientations, including portrait mode (FIG. 8B) and landscape mode (FIG.  8 C), with each press of the corresponding key. The menu select function allows the functionality of the soft keys  870  to change from the default functions described above. Examples of additional soft key functions that can be selected using this menu feature are set SpO 2  high/low limit, set pulse rate high/low limit, set alarm volume levels, set display to show trend data, print trend data, erase trend data, set averaging time, set sensitivity mode, perform synchronization, perform rechargeable battery maintenance (deep discharge/recharge to remove battery memory), and display product version number. 
     FIG. 9 provides further details of the docking station  660 , which includes a docking station processor  910 , a non-volatile memory  920 , a waveform generator  930 , a PROM interface  940 , a tilt sensor  950 , a portable interface  970  and associated connector  972 , status indicators  982 , a serial data port  682 , a nurse call output  684 , an analog output  688  and a power supply  990 . In one embodiment, the docking station  660  is intended to be associated with a fixed (non-transportable) host instrument, such as a multiparameter patient monitoring instrument in a hospital emergency room. In a transportable embodiment, the docking station  660  is movable, and includes a battery pack within the power supply  990 . 
     The docking station processor  910  orchestrates the activity on the docking station  660 . The processor  910  provides the waveform generator  930  with parameters  932  as discussed above for FIGS. 3 and 4. The processor  910  also provides asynchronous serial data  912  for communications with external devices and synchronous serial data  971  for communications with the portable  610  (FIG. 6) in addition, the processor  910  determines system status including sync status  942 , tilt status  952  and power status  992 . The portable management processor  720  (FIG. 7) performs the watchdog function for the docking station processor  910 . The docking station processor  910  sends watchdog messages to the portable processor  720  (FIG. 7) as part of the synchronous serial data  972  to ensure the correct operation of the docking station processor  910 . 
     The docking station processor  910  accesses non-volatile memory  920  over a high-speed bus  922 . The non-volatile memory  920  is re-programmable and contains program data for the processor  910  including instrument communication protocols, synchronization information, a boot image, manufacturing history and diagnostic failure history. 
     The waveform generator  930  generates a synthesized waveform that a conventional pulse oximeter can process to calculate SpO 2  and pulse rate values or exception messages, as described above with respect to FIG.  4 . However, in the present embodiment, as explained above, the waveform generator output does not reflect a physiological waveform. It is merely a waveform constructed to cause the external pulse oximeter to calculate the correct saturation and pulse rate. In an alternative embodiment, physiological data could be provided to the external pulse oximeter, but the external pulse oximeter would generally not be able to calculate the proper saturation values, and the upgrading feature would be lost. The waveform generator  930  is enabled if an interface cable  690  (FIG.  6 ), described below with respect to FIG. 10, with valid synchronization information is connected. Otherwise, the power to the waveform generator  930  is disabled. 
     The status indicators  982  are a set of LEDs on the front of the docking station  660  used to indicate various conditions including external power (AC), portable docked, portable battery charging, docking station battery charging and alarm. The serial data port  682  is used to interface with either a computer, a serial port of conventional pulse oximeters or serial printers via a standard RS-232 DB-9 connector  962 . This port  682  can output trend memory, SpO 2  and pulse rate and support the system protocols of various manufacturers. The analog output  688  is used to interface with analog input chart recorders via a connector  964  and can output “real-time” or trend SpO 2  and pulse rate data. The nurse call output  684  from a connector  964  is activated when alarm limits are exceeded for a predetermined number of consecutive seconds. In another embodiment, data, including alarms, could be routed to any number of communications ports, and even over the Internet, to permit remote use of the upgrading pulse oximeter. 
     The PROM interface  940  accesses synchronization data  692  from the PROM  1010  (FIG. 10) in the interface cable  690  (FIGS. 6,  10 ) and provides synchronization status  942  to the docking station processor  910 . The portable interface  970  provides the interconnection to the portable  610  (FIG. 6) through the docking station interface  760  (FIG.  7 ). 
     As shown in FIG. 9, external power  668  is provided to the docking station  660  through a standard AC connector  968  and on/off switch  969 . When the docking station  660  has external power  668 , the power supply  990  charges the battery in the portable power supply  730  (FIG. 7) and the battery, if any, in the docking station power supply  990 . When the portable  610  (FIG. 6) is either removed or turned off, the docking station power  973  is removed and the docking station  660  is turned off, except for the battery charger portion of the power supply  990 . The docking station power  973  and, hence, the docking station  660  turn on whenever a docked portable  610  (FIG. 6) is turned on. The portable  610  (FIG. 6) supplies power for an embodiment of the docking station  660  without a battery when external power  668  is removed or fails. 
     FIG. 10 provides further detail regarding the interface cable  690  used to connect between the docking station  660  (FIG. 6) and the patient cable  230  (FIG. 2) of a host instrument  260  (FIG.  2 ). The interface cable  690  is configured to interface to a specific host instrument and to appear to the host instrument as a specific sensor. A PROM  1010  built into the interface cable  690  contains information identifying a sensor type, a specific host instrument, and the calibration curve of the specific host instrument. The PROM information can be read by the docking station  660  (FIG. 6) as synchronization data  692 . Advantageously, the synchronization data  692  allows the docking station  660  (FIG. 6) to generate a waveform to the host instrument that causes the host instrument-to display SpO 2  values equivalent to those calculated by the portable  610  (FIG.  6 ). The interface cable  690  includes an LED drive path  672 . In the embodiment shown in FIG. 10, the LED drive path  672  is configured for common anode LEDs and includes IR cathode, red cathode and common anode signals. The interface cable  690  also includes a detector drive path  674 , including detector anode and detector cathode signals. 
     A menu option on the portable  610  (FIG. 6) also allows synchronization information to be calculated in the field. With manual synchronization, the docking station  660  (FIG. 6) generates a waveform to the host instrument  260  (FIG. 2) and displays an expected SpO 2  value. The user enters the SpO 2  value displayed on the host instrument using the portable keypad  750  (FIG.  7 ). These steps are repeated until a predetermined number of data points are entered and the SpO 2  values displayed by the portable and the host instrument are consistent. 
     FIGS. 11A-B depict an embodiment of the portable  610 , as described above with respect to FIG.  6 . FIGS. 12A-B depict an embodiment of the docking station  660 , as described above with respect to FIG.  6 . FIG. 13 depicts an embodiment of the UPO  210  where the portable  610  is docked with the docking station  660 , also as described above with respect to FIG.  6 . 
     FIG. 11A depicts the portable front panel  1110 . The portable  610  has a patient cable connector  618 , as described above with respect to FIG.  6 . Advantageously, the connector  618  is rotatably mounted so as to minimize stress on an attached patient cable (not shown). In one embodiment, the connector  618  can freely swivel between a plane parallel to the front panel  1110  and a plane parallel to the side panel  1130 . In another embodiment, the connector  618  can swivel between, and be releasably retained in, three locked positions. A first locked position is as shown, where the connector is in a plane parallel to the front panel  1110 . A second locked position is where the connector  618  is in a plane parallel to the side panel  1130 . The connector  618  also has an intermediate locked position 45° between the first and the second locked positions. The connector  618  is placed in the first-locked position for attachment to the docking station  660 . 
     Shown in FIG. 11A, the portable front panel  1110  also has a speaker  772 , as described with respect to FIG.  7 . Further, the front panel  1110  has a row of soft keys  870  and fixed keys  880 , as described above with respect to FIG.  8 . In addition, the front panel  1110  has a finger actuated latch  1120  that locks onto a corresponding catch  1244  (FIG. 12A) in the docking station  660 , allowing the portable  610  to be releasably retained by the docking station  660 . An OEM label can be affixed to a recessed area  1112  on the front panel  1110 . 
     FIG. 11B depicts the portable back panel  1140 . The back panel  1140  has a socket  763 , a pole clamp mating surface  1160 , and a battery pack compartment  1170 . The socket  763  is configured to mate with a corresponding docking station plug  972  (FIG.  12 A). The socket  763  and plug  972  (FIG. 12A) provide the electrical connection interface between the portable  610  and the docking station  660  (FIG.  12 A). The socket  763  houses multiple spring contacts that compress against plated edge-connector portions of the docking station plug  972  (FIG.  12 A). A conventional pole clamp (not shown) may be removably attached to the mating surface  1160 . This conveniently allows the portable  610  to be held to various patient-side or bedside mounts for hands-free pulse oximetry monitoring. The portable power supply  730  (FIG. 7) is contained within the battery pack compartment  1170 . The compartment  1170  has a removable cover  1172  for protection, insertion and removal of the portable battery pack. Product labels, such as a serial number identifying a particular portable, can be affixed with the back panel indent  1142 . 
     FIG. 12A depicts the front side  1210  of the docking station  660 . The front side  1210  has a docking compartment  1220 , a pole clamp recess  1230 , pivots  1242 , a catch  1244 , a plug connector  972  and LED status indicators  982 . The docking compartment  1220  accepts and retains the portable  610  (FIGS.  11 A-B), as shown in FIG.  13 . When the portable  610  (FIGS. 11A-B) is docked in the compartment  1220 , the pole clamp recess  1230  accommodates a pole clamp (not shown) attached to the portable&#39;s pole clamp mating surface  1160  (FIG.  11 B), assuming the pole clamp is in its closed position. The portable  610  (FIGS. 11A-B) is retained in the compartment  1220  by pivots  1242  that fit into corresponding holes in the portable&#39;s side face  1130  and a catch  1244  that engages the portable&#39;s latch  1120  (FIG.  11 A). Thus, the portable  610  (FIGS. 11A-B) is docked by first attaching it at one end to the pivots  1242 , then rotating it about the pivots  1242  into the compartment  1220 , where it is latched in place on the catch  1244 . The portable  610  (FIGS. 11A-B) is undocked in reverse order, by first pressing the latch  1120  (FIG.  11 A), which releases the portable from the catch  1244 , rotating the portable  610  (FIGS. 11A-B) about the pivots  1242  out of the compartment  1220  and then removing it from the pivots  1242 . As the portable is rotated into the compartment, the docking station plug  972  inserts into the portable socket  763  (FIG.  11 B), providing the electrical interface between the portable  610  and the docking station  660 . The status indicators  982  are as described above with respect to FIG.  9 . 
     FIG. 12B depicts the back side  1260  of the docking station  660 . The back side  1260  has a serial (RS-232 or USB) connector  962 , an analog output and nurse call connector  964 , an upgrade port connector  966 , an AC power plug  968 , an on/off switch  969  and a ground lug  1162 . A handle  1180  is provided atone end and fan vents  1170  are provided at the opposite end. A pair of feet  1190  are visible near the back side  1260 . A corresponding pair of feet (not visible) are located near the front side  1210  (FIG.  12 A). The feet near the front side  1210  extend so as to tilt the front side  1210  (FIG. 12A) upward, making the display  740  (FIG. 13) of a docked portable  610  (FIG. 13) easier to read. 
     FIG. 13 illustrates both the portable  610  and the docking station  660 . The portable  610  and docking station  660  constitute three distinct pulse oximetry instruments. First, the portable  610  by itself, as depicted in FIGS. 11A-B, is a handheld pulse oximeter applicable to various patient monitoring tasks requiring battery power or significant mobility, such as ambulance and ER situations. Second, the portable  610  docked in the docking station  660 , as depicted in FIG. 13, is a standalone pulse oximeter applicable to a wide-range of typical patient monitoring situations from hospital room to the operating room. Third, the portable  610  docked and the upgrade port  966  (FIG. 12B) connected with an interface cable to the sensor port of a conventional pulse oximeter module  268  (FIG. 2) within a multiparameter patient monitoring instrument  260  (FIG. 2) or other conventional pulse oximeter, is a universal/upgrading pulse oximeter (UPO) instrument  210 , as described herein. Thus, the portable  610  and docking station  660  configuration of the UPO  210  advantageously provides a three-in-one pulse oximetry instrument functionality. 
     Another embodiment of the docking station  660  incorporates an input port that connects to a blood pressure sensor and an output port that connects to the blood pressure sensor port of a multiparameter patient monitoring system (MPMS). The docking station  660  incorporates a signal processor that computes a blood pressure measurement based upon an input from the blood pressure sensor. The docking station  660  also incorporates a waveform generator connected to the output port that produces a synthesized waveform based upon the computed measurement. The waveform generator output is adjustable so that the blood pressure value displayed on the MPMS is equivalent to the computed blood pressure measurement. Further, when the portable  610  is docked in the docking station  660  and the blood pressure sensor is connected to the input port, the portable displays a blood pressure value according to the computed blood pressure measurement. Thus, in this embodiment, the docking station  660  provides universal/upgrading capability for both blood pressure and SpO 2 . 
     Likewise, the docking station  660  can function as an universal/upgrading instrument for other vital sign measurements, such as respiratory rate, EKG or EEG. For this embodiment, the docking station  660  incorporates related sensor connectors and associated sensor signal processors and upgrade connectors to an MPMS or standalone instrument. In this manner, a variety of vital sign measurements can be incorporated into the docking station  660 , either individually or in combination, with or without SpO 2  as a measurement parameter, and with or without the portable  610 . In yet another embodiment, the docking station  660  can be configured as a simple SpO 2  upgrade box, incorporating a SpO 2  processor and patient cable connector for a SpO 2  sensor that functions with or without the portable  610 . 
     Unlike a conventional standalone pulse oximeter, the standalone configuration shown in FIG. 13 has a rotatable display  740  that allows the instrument to be operated in either a vertical or horizontal orientation. A tilt sensor  950  (FIG. 9) indicates when the bottom face  1310  is placed along a horizontal surface or is otherwise horizontally-oriented. In this horizontal orientation, the display  740  appears in landscape mode (FIG.  8 C). The tilt sensor  950  (FIG. 9) also indicates when the side face  1320  is placed along a horizontal surface or is otherwise horizontally oriented. In this vertical orientation, the display  740  appears in portrait mode (FIG.  8 B). A soft key  870  on the portable  610  can override the tilt sensor, allowing the display to be presented at any 90° orientation, i.e. portrait, landscape, “upside-down” portrait or “upside-down” landscape orientations. The handheld configuration (FIG.  11 A), can also present the display  740  at any 90° orientation using a soft key  870 . In the particular embodiment described above, however, the portable  610  does not have a tilt sensor and, hence, relies on a soft key  870  to change the orientation of the display when not docked. 
     FIG. 14 illustrates the docking station  660  incorporated within a local area network (LAN). The LAN shown is Ethernet-based  1460 , using a central LAN server  1420 .to interconnect various LAN clients  1430  and other system resources such as printers and storage (not shown). An Ethernet controller module  1410  is incorporated with the docking station  660 . The controller module  1410  can be incorporated within the docking station  660  housing or constructed as an external unit. In this manner, the UPO, according to the present invention, can communicate with other devices on the LAN or over the Internet  1490 . 
     The Ethernet controller module  1410  can be embedded with web server firmware, such as the Hewlett-Packard (HP) BFOOT-10501. The module  1410  has both a 10 Base-T Ethernet interface for connection to the Ethernet  1460  and a serial interface, such as RS-232 or USB, for connection to the docking station  660 . The module firmware incorporates HTTP and TCP/IP protocols for standard communications over the World Wide Web. The firmware also incorporates a micro web server that allows custom web pages to be served to remote clients over the Internet, for example. Custom C++ programming allows expanded capabilities such as data reduction, event detection and dynamic web page configuration. 
     As shown in FIG. 14, there are many applications for the docking station  660  to Ethernet interface. Multiple UPOs can be connected to a hospital&#39;s LAN, and a computer on the LAN could be utilized to upload pulse rate and saturation data from the various UPOs, displaying the results. Thus, this Ethernet interface could be used to implement a central pulse oximetry monitoring station within a hospital. Further, multiple UPOs from anywhere in the world can be monitored from a central location via the Internet. Each UPO is addressable as an individual web site and downloads web pages viewable on a standard browser, the web pages displaying oxygen saturation, pulse rate and related physiological measurements from the UPO. This feature allows a caregiver to monitor a patient regardless of where the patient or caregiver is located. For example a caregiver located at home in one city or at a particular hospital could download measurements from a patient located at home in a different city or at the same or a different hospital. Other applications include troubleshooting newly installed UPOs or uploading software patches or upgrades to UPOs via the Internet. In addition alarms could be forwarded to the URL of the clinician monitoring the patient. 
     The UPO may have other configurations besides the handheld unit described in connection with FIG. 5 or the portable  610  and docking station  660  combination described in connection with FIGS. 11-13. The UPO may be a module, with or without a display, that can be removably fastened to a patient via an arm strap, necklace or similar means. In a smaller embodiment, this UPO module may be integrated into a cable or connector used for attaching a sensor to a pulse oximeter. The UPO may also be a circuit card or module that can externally or internally plug into or mate with a standalone pulse oximeter or multiparameter patient monitoring system. Alternatively, the UPO may be configured as a simple standalone upgrade instrument. 
     Further, although a universal/upgrading apparatus and method have been mainly described in terms of a pulse oximetry measurement embodiment, the present invention is equally applicable to other physiological measurement parameters such as blood pressure, respiration rate, EEG and ECG, to name a few. In addition, a universal/upgrading instrument having a single physiological measurement parameter or a multiple measurement parameter capability and configured as a handheld, standalone, portable, docking station, module, plug-in, circuit card, to name a few, is also within the scope of the present invention. 
     The UPO has been disclosed in detail in connection with various embodiments of the present invention. These embodiments are disclosed by way of examples only and are not to limit the scope of the present invention, which is defined by the claims that follow. One of ordinary skill in the art will appreciate many variations and modifications within the scope of this invention.