Abstract:
A noninvasive physiological sensor includes electrical isolation to isolate the patient and the sensor electronics from potentially harmful electrical surges.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application claims priority benefit under 35 U.S.C. §120 to and is a continuation of U.S. patent application Ser. No. 11/235,617, filed Sep. 26, 2005, entitled “Isolation and Communication Element for Resposable Pulse Oximetty Sensor,” which is a continuation of U.S. patent application Ser. No. 10/351,643 (now U.S. Pat. No. 6,950,687), filed Jan. 24, 2003, entitled “Isolation and Communication Element for Resposable Pulse Oximetry Sensor,” which is a continuation-in-part of U.S. patent application Ser. No. 10/128,721, filed Apr. 23, 2002 (now U.S. Pat. No. 6,725,075), entitled “Resposable Pulse Oximetry Sensor,” which is a continuation of U.S. patent application Ser. No. 09/456,666 filed Dec. 9, 1999 (now U.S. Pat. No. 6,377,829), entitled “Resposable Pulse Oximetry Sensor” Moreover, the Ser. No. 10/351,643 application claims priority benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 60/351,784, filed Jan. 25, 2002, entitled “Isolation and Communication Element for a Resposable Pulse Oximetry Sensor.” The present application incorporates the foregoing disclosures herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Early detection of low blood oxygen is critical in a wide variety of medical applications. For example, when a patient receives an insufficient supply of oxygen in critical care and surgical applications, brain damage and death can result in just a matter of minutes. Because of this danger, the medical industry developed oximetry, a study and measurement of the oxygen status of blood. One particular type of oximetry, pulse oximetry, is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of the oxygen status of the blood. A pulse oximeter relies on a sensor attached to a patient in order to measure the blood oxygen saturation.  
         [0003]     Conventionally, a pulse oximeter sensor has a red emitter, an infrared emitter, and a photodiode detector. The sensor is typically attached to a patient&#39;s finger, earlobe, or foot. For a finger, the sensor is configured so that the emitters project light through the outer tissue of the finger and into the blood vessels and capillaries contained inside. The photodiode is positioned at the opposite side of the finger to detect the emitted light as it emerges from the outer tissues of the finger. The photodiode generates a signal based on the emitted light and relays that signal to a pulse oximeter. The pulse oximeter determines blood oxygen saturation by computing the differential absorption by the arterial blood of the two wavelengths (red and infrared) emitted by the sensor.  
         [0004]     Conventional sensors are either disposable or reusable. A disposable sensor is typically attached to the patient with an adhesive wrap, providing a secure contact between the patient&#39;s skin and the sensor components. A reusable sensor is typically a clip that is easily attached and removed, or reusable circuitry that employs a disposable attachment mechanism, such as an adhesive tape or bandage.  
         [0005]     The disposable sensor has the advantage of superior performance due to conformance of the sensor to the skin and the rejection of ambient light. However, repeated removal and reattachment of the adhesive tape results in deterioration of the adhesive properties and tearing of the tape. Further, the tape eventually becomes soiled and is a potential source of cross-patient contamination. The disposable sensor must then be thrown away, wasting the long-lived emitters, photodiode and related circuitry.  
         [0006]     On the other hand, the clip-type reusable sensor has the advantage of superior cost savings in that the reusable pulse sensor does not waste the long-lived and expensive sensor circuitry. However, as mentioned above, the clip-type reusable sensor does not conform as easily to differing patient skin shape, resulting in diminished sensitivity and increased ambient light.  
         [0007]     Similar to the clip-type reusable sensor, the circuit-type reusable sensor advantageously does not waste the sensor circuitry. On the other hand, the circuit-type reusable sensor fails to provide quality control over the attachment mechanism. Much like the disposable sensors, the attachment mechanism for the circuit-type reusable sensor may become soiled or damaged, thereby leading to cross-patient contamination or improper attachment. Moreover, because the reusable circuit is severable from the attachment mechanism, operators are free to use attachment mechanisms that are either unsafe or improper with regard to a particular type of reusable circuitry.  
         [0008]     Based on the foregoing, significant and costly drawbacks exist in conventional disposable and reusable oximetry sensors. Thus, a need exists for a pulse oximetry sensor that incorporates the advantages found in the disposable and reusable sensors, without the respective disadvantages.  
       SUMMARY OF THE INVENTION  
       [0009]     A reusable sensor with the performance features of a disposable may incorporate a disposable adhesive tape component that can be removed from other reusable sensor components. The disposable tape may include a mechanism for the electrical connection of an information element to the emitters, where the information element provides an indication to an attached pulse oximeter of various aspects of the sensor and also insures the sensor is from an authorized supplier. The information element electrical connection mechanism may be a breakable conductor located within the disposable component such that excessive wear of the disposable component prevents connection of the information element to an attached pulse oximeter, thereby indicating that the disposable component should be replaced. There are some drawbacks to this approach, however, including patient-instrument electrical isolation and electromagnetic interference (EMI).  
         [0010]     Electrical isolation between an electrical source and a patient needs to be 4,000V. A pulse oximeter instrument typically provides 2,500V of isolation and a pulse oximeter sensor another 1,500V. The 1,500V sensor isolation is difficult to achieve with a breakable conductor located within the tape used for patient sensor attachment. Further, a breakable conductor formed as a loop around the periphery of the disposable attachment tape, although advantageous for wear detection, creates an antenna that receives EMI, which can be conducted directly into the sensor circuitry.  
         [0011]     A sensor incorporating an isolation and communications element (ICE) that reduces or eliminates the aforementioned drawbacks has a connector adapted to electrically communicate with a physiological measurement instrument, such as a pulse oximeter. A breakable conductor incorporated by the sensor transitions from a continuity state to a discontinuity state as the result of sensor wear. An isolation and communications element (ICE) has an instrument port and an electrically isolated loop port. The instrument port is in communications with the connector and the loop port is in communications with the breakable conductor. The ICE generates a control output responsive to the discontinuity state to render the sensor inoperable. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates a circuit diagram of a conventional disposable sensor having an information element.  
         [0013]      FIGS. 2A and 2B  illustrate perspective views of the conventional disposable sensor.  
         [0014]      FIG. 3  illustrates an exploded view of a resposable sensor having two disposable tape layers, according to one embodiment of the invention.  
         [0015]      FIG. 4  illustrates a top view of one of the disposable tape layers of  FIG. 3  incorporating an information element.  
         [0016]      FIG. 5  illustrates a top view of one of the disposable tape layers of  FIG. 3  incorporating a breakable conductor.  
         [0017]      FIGS. 6A and 6B  illustrate cross-sectional views of a portion of the disposable tape layer of  FIG. 5 .  
         [0018]      FIG. 7  illustrates a top view of one of the disposable tape layers of  FIG. 3  incorporating the information element with a breakable conductor.  
         [0019]      FIG. 8A and 8B  illustrate a top view and a side view, respectively, of one of the disposable layers of  FIG. 3  configured as a fold-over tape.  
         [0020]      FIG. 9A  illustrates a perspective view of a resposable sensor having a disposable portion configured as a tape sleeve and a reusable portion directly attached to a patient cable, according to another embodiment of the invention.  
         [0021]      FIG. 9B  illustrates a perspective view of a resposable sensor having a reusable portion removably attached to a patient cable, according to another embodiment of the invention.  
         [0022]      FIG. 10  is a schematic of a sensor circuit incorporating a breakable conductor.  
         [0023]      FIG. 11  is a schematic of a sensor circuit incorporating an embodiment of an isolation and communications element (ICE).  
         [0024]      FIG. 12  is a block diagram of an ICE embodiment.  
         [0025]      FIG. 13  is a schematic of a sensor circuit incorporating an alternative embodiment of an isolation and communications element (ICE).  
         [0026]      FIG. 14  is a block diagram of an alternative ICE embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0000]     Resposable Pulse Oximeter Sensor  
         [0027]     The configuration of an information element for an oximeter sensor and method of reading an information element with an attached oximeter is described in U.S. Pat. No. 5,758,644 entitled “Manual And Automatic Probe Calibration,” assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein. Accordingly, the configuration and the implementation of an information element will be greatly summarized as follows.  
         [0028]      FIG. 1  illustrates a conventional oximeter sensor circuit  100 . The oximeter sensor circuit  100  includes an emitter  105  comprising a first LED  107  and a second LED  110 . The oximeter sensor circuit further includes an information element comprising a resistor  115 . The first LED  107 , the second LED  110  and the resistor  115  are connected in parallel. The parallel connection has a common input electrical connection  120  and a common return  125 . The oximeter sensor circuit  100  also includes a photodetector  130  having an input electrical connection  135  connected to one end and having the common return  125  connected to the other end.  
         [0029]     As mentioned, the resistor  115  is provided as an information element that can be read by an attached oximeter. In order to read the resistor  115 , the oximeter drives the oximeter sensor circuit  100  at a level where the emitter  105  draws effectively insignificant current. As is well understood in the art, the emitter  105  becomes active only if driven at a voltage above a threshold level. Thus, at this low level, significantly all of the current through the input electrical connection  120  flows through the resistor  115 . By reducing the drive voltage across the input electrical connection  120  and common return  125  to a low enough level to not activate the emitter  105 , the emitter  105  is effectively removed from the oximeter sensor circuit  100 . Thus, the oximeter can determine the value of the resistor  115 .  
         [0030]     The value of the resistor  115  can be preselected to indicate, for example, the type of sensor (e.g., adult, pediatric, or neonatal), the operating wavelength, or other parameters about the sensor. The resistor  115  may also be utilized for security and quality control purposes. For example, the resistor  115  may be used to ensure that the oximeter sensor circuit  100  is configured properly for a given oximeter. For instance, the resistor  115  may be utilized to indicate that the oximeter sensor circuit  100  is from an authorized supplier.  
         [0031]     An information element other than the resistor  115  may also be utilized. The information element need not be a passive device. Coding information may also be provided through an active circuit, such as a transistor network, memory chip, or other identification device.  
         [0032]     Furthermore, it will be understood by a skilled artisan that a number of different circuit configurations can be implemented that allow the oximeter sensor circuit  100  to include an information element. For example, the emitter  105  and the information element may each have individual electrical connections.  
         [0033]     As mentioned above, the resistor  115  is preselected such that at low drive voltages, it is the only circuit element sensed by the oximeter. On the other hand, the resistor  115  can also be preselected be of a sufficiently high value that when the drive voltage rises to a level sufficient to drive the emitter  105 , the resistor  115  is effectively removed from the oximeter sensor circuit  100 . Thus, the resistor  115  does not affect normal operations of the emitter  105 . In summary, an information element may form an integral part of the oximeter sensor circuit  100  by providing valuable information to the attached oximeter.  
         [0034]      FIGS. 2A and 2B  illustrate a conventional disposable sensor  200 . The disposable sensor  200  includes an adhesive substrate  205  having an elongated center portion  210  with front and rear flaps,  215  and  220 , extending outward from the elongated center portion  210 . The adhesive substrate  205  may also have an image  225  superimposed on the adhesive substrate  205  so as to indicate proper use.  
         [0035]     The elongated center portion  210  includes the oximeter sensor circuit  100  of  FIG. 1 . For example, the emitter  105  is housed on an underside of the elongated center portion  210  approximately beneath the superimposed image  225 . Thus, as shown in  FIG. 2A , the emitter  105  may be housed approximately beneath the asterisk superimposed on the image of a fingernail. On the other hand, the photodetector  130  is housed on the topside of the elongated center portion  210  in proximity with the rear flaps  220 .  
         [0036]     The elongated center portion  210  further includes an electrical connector  230  to drive the emitter  105  and to receive an output from the photodetector  130 . The electrical connector  230  is preferably configured to attach to a connector cable  235  via a sensor connector  240 . Also, the connector cable  235  attaches to or connects with an oximeter via an oximeter connector  245 .  
         [0037]      FIG. 2B  illustrates an example of how the disposable sensor  200  wraps the front and rear flaps  215  and  220  around a finger such that the adhesive substrate  205  provides a secure contact between the patient&#39;s skin, the emitter  105  and the photodetector  130 .  FIG. 2B  also illustrates an example of the sensor connector  240  (shown in broken lines) encompassing the electrical connector  230 .  
         [0038]     As shown in  FIGS. 1-2B , the conventional disposable sensor  200  integrates the components of the conventional oximeter sensor circuit  100  such that disposal of the disposable sensor  200  includes disposal of the longer lasting, expensive circuitry found therein.  
         [0039]      FIG. 3  illustrates an exploded view of one embodiment of a resposable (reusable/disposable) sensor  300 . In this embodiment, the resposable sensor  300  includes a reusable portion  305  having an emitter  306 , a photodetector  307  and an electrical connector  308 . The resposable sensor also includes a disposable portion  310  having a face tape layer  315  and a clear base tape layer  320 . As shown in  FIG. 3 , the disposable portion  310  attaches to the reusable portion  305  by sandwiching the reusable portion  305  between a face tape layer  315  and a clear base tape layer  320 .  
         [0040]     According to this embodiment, conventional adhesives or other attaching methodology may be used to removably attach the face tape layer  315  to the clear base tape layer  320 . Furthermore, the adhesive properties associated with the base of the conventional disposable sensor  200  may be the same as the adhesive properties on the base of the clear base tape layer  320 , as both portions are provided to attach to the patient&#39;s skin.  
         [0041]     As mentioned, the disposable portion  310  removably attaches to the reusable portion  305  in, for example, a sandwich or layered style. After removably attaching the disposable portion  310  to the reusable portion  305 , the resposable sensor  300  functions similar to the disposable sensor  200 , i.e., the resposable sensor  300  wraps flaps around a patient&#39;s tissue such that the emitter  306  and the photodetector  307  align on opposite sides of the tissue. However, in contrast to the disposable sensor  200 , the resposable sensor  300  provides for reuse of the reusable portion  305 . For example, when the disposable portion  310  becomes contaminated, worn, or defective, rather than discarding the entire resposable sensor  300 , the disposable portion  310  is removed such that the reusable portion  305  may be re-removably attached to a new disposable portion  310 . The discarding of the disposable portion  310  completely avoids cross-contamination through the reuse of adhesive tapes between patients without wasting the more costly and longer lasting sensor circuitry of the resposable portion  305 . Note that optional sterilization procedures may be advantageously performed on the reusable portion  305  before reattachment to either the new disposable portion  310  or to the patient, in order to further ensure patient safety.  
         [0042]      FIG. 4  illustrates a top view of an embodiment of the face tape layer  315  of the disposable portion  310  of the resposable sensor  300 . According to this embodiment, the face tape layer  315  further includes an information element  405  as an integral part of the face tape layer  315 . In this embodiment, the information element  405  is a resistive element made by depositing a conductive ink trace having a predetermined length and width. As is known in the art, the length, width and conductivity of the conductive ink trace determines the resistance of the resistive element. The information element  405  is deposited between contacts  410  that are also implemented with conductive ink. It will be understood by a skilled artisan that a variety of methods can be used for mating the contacts  410  with the electrical circuitry of the reusable portion  305 . For example, the contacts  410  may advantageously physically touch the leads or the electrical connector  308  such that the reusable portion  305  is electrically configured to include the information element  405 . Such a configuration employs the oximeter sensor circuit  100  of  FIG. 1 , having elements thereof distributed in both the reusable portion  305  and the disposable portion  310  of the resposable sensor  300 .  
         [0043]     In the foregoing embodiment, the disposable portion  310  comprises the information element  405  along with the face tape layer  315  and the clear base layer  320 . As mentioned, the disposable portion  310  is removably attached to the reusable portion  305  and is employed in a similar manner as the disposable sensor  200 . In contrast to the disposable sensor  200 , when the disposable portion  310  of the resposable sensor  300  becomes worn, the disposable portion  310  and the information element  405  are discarded and the reusable portion  305  is saved. By discarding the information element, the attached oximeter can perform quality control. For example, if the reusable portion  305  is reattached to a patient using either a simple adhesive or any other non-authorized disposable mechanism, the resposable sensor  300  will not include the information element  405 . As mentioned above, an attached oximeter can recognize the absence of the information element  405  and create an appropriate response indicating inappropriate use of the reusable portion  305  of the resposable sensor  300 .  
         [0044]      FIG. 5  illustrates a top view of yet another embodiment of the face tape layer  315  of the disposable portion  310  of the resposable sensor  300 . In this embodiment, the face tape layer  315  includes a breakable conductor  505  comprising a conductive ink trace located approximately along the periphery of the face tape layer  315 . This location ensures that a tear along the periphery of the face tape layer  315  results in a tear, or electrical discontinuity, in the breakable conductor  505 . For example,  FIGS. 6A and 6B  illustrate the face tape layer  315  in which the breakable conductor  505  is layered between a tape stock  605  and a tape base  610 . The reusable portion  305  of the resposable sensor  300  then attaches to the tape base  610  through a pressure sensitive adhesive (PSA)  615 . The PSA  615 , the conductor  505  and the tape base  610  include a score  620  such that multiple attachment and removal of the resposable sensor  300  will result in a peripheral tear, or electrical discontinuity, in the breakable conductor  505 , as illustrated in  FIG. 6B .  
         [0045]     Thus, like the information element  405 , the breakable conductor  505  also provides security and quality control functions. In particular, repeated use of the disposable portion  305  of the resposable sensor  300  advantageously severs at least one part of the breakable conductor  505 . An attached oximeter can detect such severance and initiate an appropriate notification to, for example, monitoring medical personnel. Providing security and quality control through a breakable conductor advantageously assists in controlling problems with patient contamination or improper attachment due to weakened adhesives.  
         [0046]      FIG. 7  illustrates yet another embodiment of the face tape layer  315 . In this embodiment, the face tape layer  315  combines the breakable conductor  505  and the information element  405 . In this embodiment, the breakable conductor  505  is printed in a serpentine pattern to further increase the probability of a discontinuity upon the tearing of any portion of the face tape layer  315 . This combination of the information element  405  and the breakable conductor  505  advantageously adds significant safety features. For example, in this embodiment, the information element  405  is connected serially with the breakable conductor  505  and in parallel with the emitter  306  of the reusable portion  305 . Therefore, any discontinuity or tear in the breakable conductor  505  separates the information element  405  from the circuitry of the reusable portion  305 .  
         [0047]     According to the foregoing embodiment, the attached oximeter receives an indication of both overuse and misuse of the resposable sensor  300 . For example, overuse is detected through the tearing and breaking of the breakable conductor  505 , thereby removing the information element  405  from the resposable sensor  300  circuitry. In addition, misuse through employment of disposable portions  310  from unauthorized vendors is detected through the absence of the information element  405 . Moreover, misuse from purposeful shorting of the contacts  410  is detected by effectively removing the emitter  306  from the circuit, thereby rendering the resposable sensor  300  inoperative. Therefore, the resposable sensor  300  of this embodiment advantageously provides a multitude of problem indicators to the attached oximeter. By doing so, the resposable sensor  300  advantageously prevents the likelihood of contamination, adhesive failure, and misuse. The resposable sensor  300  also advantageously maintains the likelihood of quality control.  
         [0048]     A skilled artisan will recognize that the concepts of  FIGS. 3-7  may be combined in total or in part in a wide variety of devices. For example, either or both of the breakable conductor  505  and the information element  405  may advantageously be traced into the clear base tape layer  320  rather than into the face tape layer  315 .  
         [0049]      FIGS. 8A and 8B  illustrate yet another embodiment of the disposable portion  310  of the resposable sensor  300 . As shown in this embodiment, the disposable portion  310  includes a face tape layer  805  and a clear base tape layer  810 . According to this embodiment, the clear base tape layer  810  includes a preattached section  815  and a fold over section  820 . The preattached section  815  attaches approximately one third of the face tape layer  805  to the clear base tape layer  810 . On the other hand, the fold over section  820  forms a flap configured to create a cavity between the face tape layer  805  and the clear base tape layer  810 . The cavity is configured to receive the reusable portion  305  of the resposable sensor  300 . According to one embodiment, a release liner  825  fills the cavity and separates the face tape layer  805  from the clear base tape layer  810 . When the release liner  825  is removed, newly exposed adhesive on the fold over section  820  and the face tape layer  805  removably attaches the reusable portion  305  between the face tape layer  805  and fold over section  820  of the clear base tape layer  810 .  
         [0050]     According to another embodiment, the cavity is so formed that adhesive is not needed. For example, the fold over section  820  may comprise resilient material that can form a friction fit relationship so as to fix the reusable portion  305  in an appropriate position relative to the disposable portion  310 . On the other hand, the fold over section  820  may also comprise material having other than resilient or adhesive properties, but still allow for proper placement of the reusable portion  305  and disposable portion  310  on the patient. For example, hook-and-loop type materials like VELCRO® may be used.  
         [0051]     It will be understood that a skilled artisan would recognize that the fold over embodiment of the responsible sensor  300  may employ the properties discussed in relation to  FIGS. 3-7 , such as the information element  405  and the breakable wire  505 .  
         [0052]      FIG. 9A  illustrates an embodiment of a resposable sensor  900  integrated with an attached patient cable  905 , according to another embodiment of the invention. In this embodiment, a disposable portion  910  is attached to a reusable portion  915  by removably inserting the reusable portion  915  into a tape envelope  920  formed in the disposable portion  910 .  
         [0053]     A skilled artisan will recognize that the disposable portion  910  may include the information element  405 , the breakable wire  505 , or both. Inclusion of one or both of these electronic components in the resposable sensor  900  advantageously provides the security, quality control, and safety features described in the foregoing embodiments.  
         [0054]      FIG. 9B  illustrates an embodiment of a resposable sensor  300  of  FIG. 3 , according to another embodiment of the invention. According to this embodiment, the resposable sensor  300  removably attaches to the patient cable  905  via a sensor connector  925 . The patient cable  905  then attaches to an oximeter via an oximeter connector  930 . Use of the sensor connector  925  enables the replacement of both the reusable portion  305  of the resposable sensor  300  without replacement of the sensor connector  925  or patient cable  905 . In such an embodiment, the disposable portion  310  would follow a different, more frequent, replacement schedule than that of the reusable portion  305 .  
         [0055]     A skilled artisan will recognize that the variety of configurations described above that include the information element  405 , the breakable wire  505 , or both, may be incorporated into the embodiment of  FIG. 9B .  
         [0056]     Although the foregoing invention has been described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art. For example, select aspects of  FIGS. 3-9B  may be combined. For example, the envelope configured disposable portion  910  of  FIG. 9A  may be combined with the reusable portion  305  of  FIG. 3 . A responsable sensor is described in U.S. patent application Ser. No. 09/456,666 filed Dec. 9, 1999 entitled “Responsable Pulse Oximetry Sensor,” assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.  
         [0000]     Isolation And Communications Element  
         [0057]      FIG. 10  illustrates a sensor circuit  1000  incorporating a breakable conductor, as described above. The sensor circuit  1000  has emitters  107 ,  110 , a corresponding detector  130 , and an information element  115 , as described with respect to  FIG. 1 . The sensor circuitry  1000  also has a breakable conductor  505 , as described with respect to  FIG. 5 . Further, the sensor circuit  1000  has an emitter input  1010  and a detector output port  1020 , which are both accessible via a connector  308  ( FIG. 3 ). A pulse oximeter (not shown) attached to the connector  308  ( FIG. 3 ) outputs emitter drive current to the emitter input  1010  and inputs a resulting detector current from the output port  1020 , as described with respect to  FIG. 1 . The pulse oximeter also reads the information element  115  via the emitter input  1010 , as described with respect to  FIG. 1 . Excessive wear results in a discontinuity in the breakable conductor  505 , as described above. There are drawbacks, however, to this circuit configuration. If routed within the sensor face tape layer  315  ( FIG. 5 ), as described with respect to  FIGS. 5-7 , the breakable conductor  505  reduces patient electrical isolation from the pulse oximeter. Further, the breakable conductor may act as an antenna for EMI and conduct the resulting electrical noise into the sensor circuitry.  
         [0058]      FIG. 11  illustrates a sensor circuit  1100  incorporating one embodiment of an isolation and communications element (ICE)  1200 . In addition to the ICE  1200 , the sensor circuit  1100  has a breakable conductor  505 , an emitter input  1010 , a detector output  1020 , one or more switches  1110 , emitters  107 ,  110 , a detector  130  and an information element  115 . The emitters  107 ,  110 , detector  130  and information element  115  are described above. The ICE senses a discontinuity in the breakable conductor  505  and renders the sensor inoperable accordingly. The ICE is configured to optically isolate the breakable conductor  505  from the remainder of the sensor circuitry  1100  so as to improve electrical isolation of the patient from the pulse oximeter electrical supply and prevent electromagnetic interference (EMI) inductively coupled into the breakable conductor  505  from being conducted into the sensor circuitry  1100 . Further, the ICE provides a communication feature, described below, that allows bidirectional data transfers between a pulse oximeter and the sensor, advantageously utilizing the emitter input  1010 .  
         [0059]     As shown in  FIG. 11 , this embodiment of the ICE  1200  is connected in parallel with the input  1010 , and the switches  1110  are external to the ICE  1200 . The ICE  1200  has a instrument port  1201 , a loop port  1203  and a control port  1205 . The instrument port  1201  connects in parallel to the emitter input  1010 . The loop port  1203  provides a current loop that connects to the breakable conductor  505 . The control port  1205  actuates the switches  1110 , which connect the emitters  107 ,  110  to the emitter input  1010 . The switches  1110  may be normally open or normally closed and actuated accordingly. Further, the switches may be electromechanical or purely electrical devices.  
         [0060]     Also shown in  FIG. 11 , the instrument port  1201  taps current from the modulated signal which drives the emitters  107 ,  110 , in order to supply power to the ICE  1200 . The instrument port  1201  also provides bi-directional communications between the ICE  1200  and a pulse oximeter attached to the sensor connector  308  ( FIG. 3 ). Advantageously, this bi-directional communications is conducted via the emitter input  1010 , eliminating the need for additional connector pinouts. The loop port  1203  provides a current loop so as to detect discontinuities in the attached breakable conductor  505 . In response to a breakable conductor discontinuity, the control port  1205  actuates one or more of the switches  1110  to an open position so as to disconnect the information element  115  or emitters  107 ,  110  from the emitter input  1010 . In this manner, an attached pulse oximeter is unable to read the information element  115  and/or the sensor is otherwise rendered inoperable when the breakable conductor is broken.  
         [0061]      FIG. 12  illustrates one embodiment of an isolation and communications element  1200 . The ICE  1200  has a processor  1210 , a memory  1220 , an opto-isolator driver/receiver  1230 , a serial transceiver  1240 , and a power converter  1250 . The opto-isolator  1230  detects an open circuit at the loop port  1203  and asserts a logic output OC  1232  in response, indicating a discontinuity in the breakable conductor. The opto-isolator  1230  electrically isolates the loop port  1203  utilizing LED and photodiode pairs (not shown), as is well-known in the art. One pair drives the current loop created by the breakable conductor  505  ( FIG. 11 ). Another pair detects an open-circuit, for example by measuring the voltage across a sampling resistor in series with the breakable conductor  505  ( FIG. 11 ) and generating the OC logic output  1232  accordingly. The processor  1210  reads the OC output  1232  and, in response, generates a control output  1212  to the control port  1205 , which actuates the switches  1110  ( FIG. 11 ).  
         [0062]     The power converter  1250  is an AC-to-DC converter that taps a portion of the modulated emitter drive current at the emitter input  1201  and provides one or more DC voltage outputs  1252  to power the remainder of the ICE  1200 . The memory  1220  is connected to the processor  1210  with a bi-directional bus  1222  for transferring instructions and data. The memory  1220  may be volatile RAM or nonvolatile programmable ROM or a combination of RAM and PROM. The memory  1220  stores a variety of sensor information downloaded at the time of manufacture or during communications with a pulse oximeter, as described below.  
         [0063]     As shown in  FIG. 11 , a modulated waveform applied to the emitter input  1201  for driving the emitters  107 ,  110  is described in U.S. Pat. No. 6,229,856 entitled “Method and Apparatus for Demodulating Signals in a Pulse Oximetry System” assigned to the assignee of the present application and incorporated by reference herein. In particular, a current is first applied in a forward direction with respect to one LED  107  during a first time interval. Thereafter, no current is applied to either LED  107 ,  110  during a second time interval. Then, current is applied in a forward direction with respect to the other LED  110  during a third time interval. Then, no current is applied to either LED  107 ,  110  during a fourth time interval. Thereafter, the current is again applied in the forward direction for one LED  107  during a fifth time interval that corresponds to the first time interval. Typically, each emitter  107 ,  110  is active for a duty cycle of 25%, and an inactive period having a 25% duty cycle separates each active period.  
         [0064]     As shown in  FIG. 12 , the serial transceiver  1240  is connected to the emitter input  1201  and provides a bidirectional data bus  1242  to the processor  1210 . During a start-up, calibration, initialization or re-initialization period, an attached instrument, such as a pulse oximeter or testing device, may alter the modulated waveform described above for the purpose of transmitting information to the sensor processor  1210 . That is, the emitter drive current applied to the emitter input  1201  may be modulated in a manner other than a constant 25% on and 25% off cycle so as to convey information. For example, the current waveform may be pulse position modulated (PPM) or pulse width modulated (PWM) with a bit pattern, as is well known in the art. Transmitted bit patterns may contain information such as calibration data, emitter specifications, and/or manufacturing data to name a few. The serial transceiver  1240  demodulates this data, which is then transferred over the data bus  1242  to the processor  1210 , either as serial or parallel data. The processor  1210  may in turn store this information in memory  1220 .  
         [0065]     Further, the serial transceiver  1240  may also transfer data from the processor  1210  to an attached instrument. A data upload may occur during emitter “off” periods, described above, which may be the 25% duty off-cycles or specifically designated off periods timed so that the power converter  1250  is still operational. The upload may be at a voltage that is less than the turn-on voltage of either emitter  107 ,  110  so as to limit the required output power from the ICE  1200 . Alternatively, the emitters may be disconnected during data uploads by the switches  1110  ( FIG. 11 ). The data upload may be accomplished by any of a number of conventional serial data transfer waveforms, such as PPM or PWM to name a few.  
         [0066]      FIG. 13  illustrates a sensor circuit  1300  incorporating an alternative embodiment of an isolation and communications element  1400 . The sensor circuit  1300  has a breakable conductor  505 , an emitter input  1010 , a detector output port  1020 , emitters  107 ,  110  and a detector  130  as described with respect to  FIG. 11 , above. In this embodiment, the ICE  1400  is connected in series between the emitter input  1010  and the emitters  107 ,  110  and utilizes internal switches  1420  ( FIG. 14 ). The ICE  1400  has a instrument port  1401  and a loop port  1403 , also as described with respect to  FIG. 11 , above. Further, the ICE  1400  has a component port  1405  that connects to the emitters  107 ,  110 . The ICE  1400  decouples the breakable conductor  505  from the emitter input  1010  and other portions of the sensor circuit  1300 , such as the detector  130 , as described with respect to  FIG. 11 , above. The instrument port  1401  taps power from the modulated drive signal on the emitter input  1010  and provides bidirectional communications between the ICE  1400  and an attached pulse oximeter, also as described with respect to  FIG. 11 , above.  
         [0067]      FIG. 14  illustrates a block diagram of an alternative embodiment of an isolation and communications element  1400 . The ICE  1400  has a processor  1210 , a memory  1220 , an opto-isolator driver/receiver  1230 , a serial transceiver  1240 , and a power converter  1250 , as described with respect to  FIG. 12 , above. The ICE also has an internal information element  1410  and one or more internal switches  1420 . In response to a breakable conductor discontinuity as signaled by the OC logic output  1232  of the opto-isolator  1230 , the processor  1210  generates a control output  1430  that activates the switches  1420 . When activated, the switches  1420  disconnect the component port  1405  from the emitter input  1010 . In this manner, the information element  1410  cannot be read by an attached pulse oximeter and/or the sensor is rendered otherwise inoperable when the breakable conductor is broken  
         [0068]     Other combinations, omissions, substitutions and modifications of the ICE embodiments and the ICE-sensor circuit configurations will be apparent to the skilled artisan in view of the disclosure herein. For example, the sensor circuit was described as having back-to-back emitters and a parallel connected information element all sharing a pair of connector pinouts. The ICE, however, can also be configured with a sensor circuit having emitters and an information element with only partially shared pinouts, such as common cathode or common anode configurations, or with unshared pinouts. As another example, the sensor circuit was described with switches actuated to disconnect sensor components from the sensor connector. Other devices that can be actuated to decouple one or more sensor components from the sensor connector may be used, such as high impedance capable series devices or low impedance capable parallel devices. Further, the isolation and communications element (ICE) is described in the conjunctive, it is understood that a sensor may be configured with either an isolation function or a communications element or both.