Active Optical Oximeter Probe Adapter

This invention relates in general to optical oximeters and relates more particularly to an adapter that enables an optical oximeter probe, that is designed/configured to be utilized on an associated oximeter monitor, to be used on a different oximeter monitor that utilizes a different probe configuration.

Because of the importance of oxygen for healthy human metabolism, it is important to be able to measure the oxygen content of a patient's blood. The monitoring of a patient's arterial hemoglobin oxygen saturation during and after surgery is particularly critical.

Non-invasive oximeters have been developed that direct light through a patient's skin into a region, such as a finger, containing arterial blood. This light typically contains two or more primary wavelengths of light. Examples of such oximeters are disclosed in U.S. Pat. No. 5,209,230 entitled "Adhesive Pulse Oximeter Sensor With Reusable Portion" issued to Swedlow, et al. and in U.S. Pat. No. 4,700,708 entitled "Calibrated Optical Oximeter Probe" issued to New, Jr. et al., both assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference. The oximeter in the patent by New, Jr. et al. includes a probe that contains a resistor having a resistance that can be measured by a monitor to which the probe is attached. The measured value of this resistance is indicative of the wavelengths of the light directed from the light emitting diodes (LEDs) through the patient's epidermis. The monitor uses this information and the measured intensities of light detected at those wavelengths to calculate the blood arterial oxygen content of the patient. The LEDs are activated in non-overlapping temporal intervals, so that the amount of absorption of light at each of these two wavelengths is measured separately.

Optical probes can be electrically configured in a plurality of ways. U.S. Pat. No. 5,249,576 entitled "Universal Pulse Oximeter Probe" issued to Goldberger, et al., illustrates two configurations of a red light emitting diode (LED) and an infrared LED that emit light into a patient's finger. These two prior art configurations are illustrated in FIGS. 1 and 2. FIG. 1 shows a probe configuration 10 in which a pair of LEDs 11 and 12 are connected in a "3-lead configuration" 13 in which the two LED anodes are connected to a terminal 14 and in which the two LED cathodes are each connected to uniquely associated leads 15 and 16. This probe also includes: a photodetector 17 that detects light emitted from LEDs 11 and 12; and a resistor 18 having a resistance which is indicative of the wavelength of light produced by at least one of LEDs 11 and 12 (alternately, the resistance can indicate other or additional parameters). A probe having a 3-lead configuration of LEDs will be referred to herein as a "3-lead probe" 10. The leads to the LEDs 14, 16, and 15 are indicated as ground, VO1, and VO2, respectively. The VO1 and VO2 designations indicate these are the first and second LED drive voltage leads for oximeters made by other than Nellcor, the assignee of this application. The "O" in the VO1 and VO2 terms is intended to refer to "other." Thus, this probe is sometimes referred to as an "other probe."

In a second embodiment, shown in FIG. 2, two LEDs 21 and 22 are connected in a "2-lead configuration" 23 in which the anode of first LED 21 and the cathode of a second LED 22 are connected to a first lead 24, and the cathode of the first LED 21 and the anode of the second LED 22 are connected to a second lead 25. This probe also includes a photodetector 26 and a resistor 27 (or other type of mechanism which is indicative of the wavelength produced by one or both LEDs, and/or other parameters). A probe having a 2-lead configuration of LEDs will be referred to herein as a "2-lead probe 20". The leads to the LEDs are indicated as VN1, and VN2, corresponding to the Nellcor probe first and second voltage signals. This type of probe is also sometimes referred to as a "Nellcor probe."

An oximeter monitor that is designed to utilize a probe having the 2-lead configuration of LEDs will be referred to herein as an "2-lead monitor" or "Nellcor oximeter monitor." Similarly, an oximeter monitor that is designed to utilize a probe having the 3-lead configuration of LEDs will be referred to herein as a "3-lead monitor" or "other oximeter monitor."

Some oximeter probes may use one or more additional LEDs. For instance, a second red LED is sometimes used in combination with the first red LED to achieve more balanced light levels.

For either of the above two configurations of FIGS. 1 and 2, power is applied to the two LEDs in a manner such that only one of them is activated at any given time, so that, at any given time, the output signal from the detector is produced in response to light from at most one of these two LEDs. This simplifies calculations needed to convert detected light intensities into an indication of the oxygen concentration in a patient's blood.

The incompatibility between different types of probes and different types of oximeters significantly increases the cost of supplying probes for both types of oximeters. In particular, for the manufacturer of such probes, not only is there the cost of designing multiple different types of probes, there is also the cost of building multiple different manufacturing lines, purchasing components for multiple different manufacturing lines, sorting components for multiple different manufacturing lines and selling multiple different types of probes. In addition, the manufacturing and distribution costs of each different type of probe do not benefit as much from the economies of scale associated with the increased product volume that would occur if there were only one type of probe. The total cost of these probes also includes the indirect costs incurred by hospitals that use both types of probes so that such hospitals also bear the increased costs associated with the smaller volume orders of each type of probe, the cost of stocking multiple different types of probes and the costs of interacting with multiple vendors. All of these factors significantly increase the cost of monitoring patient oxygen saturation.

The Goldberger patent discussed above addresses this problem by presenting a probe that can be configured to work with any oximeter. The photodetector and light sources within this probe are mounted without any interconnections, and a cable interconnects these elements into various configurations by means of appropriately inserted jumper leads. Unfortunately, although this structure enables this probe to be adapted for a wide variety of oximeters, it does not allow any way for a probe which already has its electrical elements interconnected to be used with any arbitrarily selected oximeter.

It is an object of the invention to provide an adapter that can be connected between a probe that has its electrical elements interconnected in a first configuration and a monitor designed for use with a probe having a second electrical interconnect configuration such that this probe and this monitor will function properly with one another.

The present invention provides an adapter which actively connects a 2-lead oximeter probe or monitor to a 3-lead monitor or probe. This is done actively, with the alternating drive signals from the oximeter monitor providing a control signal for switching the adapter connections. The adapter connections are preferably made with diodes, transistors, or other active devices.

In one embodiment, the invention provides a conversion circuit in the adapter for connecting between M inputs for connecting to the oximeter monitor, and N outputs for connecting to the probe. The conversion circuit includes a number of opto-isolators, such that the probe is entirely optically isolated from the monitor. Signals from the monitor intended to drive the probe are detected through the opto-isolators, and the N outputs are appropriately driven. In one embodiment, a resistor in series with a common node input of the M inputs is used to generate a voltage for detecting the amplitude of a signal being driven, so than an appropriate amplitude of current can be provided to the outputs to drive the LEDs in the probe to the appropriate intensity. Preferably, a current source circuit is used for this drive, with a current limit to avoid providing too much current and burning the patient to whom the probe is connected.

The adapters in accordance with the invention are preferably either mounted on the monitor or in a cable used to connect a probe to a monitor, so that each adapter can become an extension of the oximeter itself and can be used by many different patients and can be used by each patient many times.

Several preferred adapter embodiments are specifically described for use with the two particular types of monitors and probes described below. However, the invention is applicable to any adapter which is to interconnect probes and monitors having differing numbers or configurations of light source signal connections.

The present invention also provides a dual-use probe which contains LEDs for both 3-lead and 2-lead type monitors. The LEDs are not interconnected inside the probe itself, allowing it to be dual-use since the interconnections can be done externally to provide the particular configuration required for the monitor being used. However, rather than duplicating all LEDs, only the IR LED is reproduced, with a common connector for all the LEDs allowing the red LED to be used for both types of monitors, with only one or the other of the IR LEDs being connected or used. Unlike the Goldberger patent, only three LED leads are required to allow the probe to be connected to either a 2-lead or 3-lead oximeter.

FIG. 1 illustrates a probe with a 3-lead configuration of a pair of LEDs.

FIG. 2 illustrates a probe with a 2-lead configuration of a pair of LEDs.

FIG. 3 illustrates the use of a double-pole, double-throw switch as a 2-to-3 Type Adapter for connecting a 2-lead monitor to a 3-lead probe.

FIG. 4 illustrates the use of a double-pole, double-throw switch as a 3-to-2 Type Adapter for connecting a 3-lead monitor to a 2-lead probe.

FIG. 5 illustrates a first preferred embodiment of a 2-to-3 Type Adapter.

FIG. 6 illustrates a first preferred embodiment of a 3-to-2 Type Adapter.

FIG. 7 illustrates a second preferred embodiment of a 2-to-3 Type Adapter.

FIG. 8 illustrates a second preferred embodiment of a 3-to-2 Type Adapter for use with a high impedance output oximeter monitor.

FIG. 9 illustrates a combined adapter cable.

FIG. 10 illustrates the multiple adapter connections in the cable of FIG. 9 for a combined adapter.

FIG. 11 illustrates a preferred embodiment of a dual use probe and corresponding adapter.

FIG. 12 is a perspective view illustrating an embodiment of a housing for an adapter according to the invention.

FIG. 13 is an exploded view of the housing of FIG. 12.

FIG. 14 is a block diagram of the adapter according to one embodiment of the invention using opto-isolation.

FIG. 15 is a block diagram illustrating some of the elements of the embodiment of FIG. 14.

FIGS. 16-18 are circuit diagrams illustrating one embodiment of the circuit of FIG. 14.

3-Lead Other Monitor: This monitor is designed to drive a pair of LEDs that are connected in the 3-lead configuration, discussed above, in which:

the two LED anodes are connected to a common lead; and

the two LED cathodes are each connected to its own, uniquely associated lead.

This type of monitor therefore has the following three terminals for coupling to this type of probe: a first terminal for coupling to the cathode of the first of these two LEDs; a second terminal for coupling to the cathode of the second of these two LEDs; and a third terminal for coupling to both anodes. As will be seen below, only two of these three terminals conduct electricity at any instant to the probe, a constraint that should be maintained when an adapter is used to interconnect a 2-lead probe to this type of monitor.

2-Lead Nellcor Monitor: In the second of these two types of oximeter monitors, the monitor is designed and adapted to drive a pair of LEDs connected in the 2-lead configuration in which:

the anode of a first LED and the cathode of a second LED are connected to a first lead; and

the cathode of the first LED and the anode of the second LED are connected to a second lead.

This type of monitor therefore has the following two terminals for coupling to this type of probe: a first terminal for coupling to the first lead; and a second terminal for coupling to the second lead.

Alternatively, other types of probes may be used. In a variation of the 3 lead probe, the 2 LEDs may have the anode of one LED connected to the cathode of the other LED for the common (ground) terminal. In yet another alternative, the two cathodes could be connected to the common terminal, rather than the two anodes.

A first type of adapter is presented that enables a 3-lead oximeter monitor to drive an oximeter probe having a 2-lead configuration of two LEDs. This type of adapter will be referred to herein as a "3-to-2-Type Adapter".

A second type of adapter is also presented that enables a 2-lead oximeter monitor to drive an oximeter probe having a 3-lead configuration of two LEDs. This type of adapter will be referred to herein as a "2-to-3-Type Adapters". Thus, these two adapters enable each of these two types of oximeter monitors to be utilized with both of these two types of oximeter probes.

For each of these two types of adapters, the adapter can be mounted at a number of different points in the electrical path from the monitor to the probe. In particular, it can be mounted: within the monitor, externally on a front panel of the monitor, within the cable connecting the probe to the monitor, in the connector at the monitor end of the cable, or at the connector to the probe.

These 2 types of adapters must each function to: (1) convert LED drive signals, from one type of monitor, to the type of LED drive signals expected by a probe designed to operate with the other type of monitor; and (2) transmit data from this probe back to the monitor in a format expected by the monitor.

In order to convert LED drive signals of the form produced by one of these types of monitors into LED drive signals of the form produced by the other of these types of monitors, it is necessary to selectively redirect portions of the input signals received from the monitor. This is achieved by using the LED drive signals produced by the monitor in a dual role of providing power to the LEDs in the probe and also providing timing data for controlling the adapter to produce the desired output signals. The preferred embodiments of the adapters presented herein use active switching to adapt the LED drive signals into signals applied to the LEDs.

In a preferred embodiment, the adapter has the form of a double-pole, double-throw (DPDT) switch, that is actively switched in response to at least one of the LED drive signals from the monitor. However, a 3-to-2-type adapter can be implemented by any structure that converts a pair of LED drive signals VO1 and VO2 into a pair of LED drive signals VN1 and VN2. Likewise, a 2-to-3-type adapter can be implemented by any structure that converts a pair of LED drive signals VN1 and VN2 into a pair of LED drive signals VO1 and VO2.

A 3-to-2-type adapter must convert LED drive signals from a 3-lead monitor into LED drive signals required by a 2-lead probe and a 2-to-3-type adapter must convert LED drive signals from a 2-lead monitor into LED drive signals required by a 3-lead probe. The following two sections describe particular examples of these two sets of probes, monitors, and signals.

A 3-lead monitor 51 provides, at a first terminal, a signal VO1 (illustrated in FIGS. 1 and 4) that can be no signal, with the terminal switched into an open state (i.e., high impedance state) or can be driven to a negative voltage. A second terminal provides a signal VO2 (also illustrated in FIGS. 1 and 4) that can be no signal with the terminal switched into an open state (i.e., high impedance state) or can be driven to a negative voltage. A return common ground GND at a third terminal is also provided. This monitor is intended to be utilized with a 3-lead probe, with the return common ground connected to the anodes of the LEDs 11, 12 illustrated in FIG. 1. Alternately, the common terminal could be connected to a positive voltage, with the other terminals alternately grounded.

LED 12 emits light when VO1 is negative and LED 11 emits light when VO2 is negative. VO1 and VO2 are intentionally never negative at the same time, so that only one or none of LEDs 11 and 12 is activated at any given time. This ensures that a patient is exposed to only one wavelength of light at a time, so that the photodetector receives optical signals for at most a single wavelength of light at any given time. This simplifies analyzing the spectral data contained in the light received by photodetector 17. Optionally, a dark signal is also measured when both LEDs are off.

In a 2-lead monitor 41, a first terminal provides a signal VN1 (illustrated in FIGS. 2 and 3) and a second terminal provides a signal VN2 (also illustrated in FIGS. 2 and 3). This monitor is intended to be utilized with a 2-lead probe.

LED 21 emits light when VN1 is high and VN2 is low. LED 22 emits light when VN2 is high and VN1 is low. Neither LED is on if either of the lines for these two signals is open (in a high impedance state). Because VN1 and VN2 are applied to opposite ends of both LEDs, if VN1 and VN2 are both equally high or are both equally low at the same time, a net zero voltage drop is produced across both LEDs and therefore both LEDs are also off in such intervals. The current through the LEDs is typically limited by limiting circuits in the LED drivers in the monitor.

A 3-to-2-type adapter can take any structural form that enables the signals VN1 and VN2 (illustrated in FIG. 2) to be generated in response to input signals VO1 and VO2 (illustrated in FIG. 1).

According to a preferred embodiment the adapters can each be implemented in the form of a double-pole, double-throw switch (hereinafter referred to as a "DPDT switch"), that is switched in response to one or both of the signals provided by the monitor. Thus, such signals from the oximeter monitor are utilized in a dual manner: to provide power to an associated LED; and to control switching of the adapter. The LED drive current can be varied by the oximeter to achieve the desired light levels at the detector. The switches must be chosen so that they will operate over the entire range of possible current levels.

FIG. 3 illustrates the use of a double-pole, double-throw (DPDT) switch 90 as a 2-to-3 Type Adapter for connecting a 2-lead monitor 41 to a 3-lead probe 10. Input signal VN1 is applied to a first input lead 42 of DPDT switch 90 and input signal VN2 is applied to a second input lead 43 of DPDT switch 90. The operation of this DPDT switch is most easily understood by viewing this switch as a pair of single-pole, double throw (SPDT) switches 44 and 45 having input leads 42, 43 and output leads 46-49. Output leads 46 and 49 are shorted together and are to be connected to the common anode terminal 410 of diodes 11 and 12. Output lead 47 is connected to the cathode 411 of LED 12 and output lead 48 is connected to the cathode 412 of LED 11.

A control signal C controls the states of the SPDT switches such that the switches are either in: a first state in which only LED 11 is activated or in a second state in which only LED 12 is activated. This first state is illustrated by the solid line positions of SPDT switches 44 and 45 and the second state is illustrated by the dashed line positions of SPDT switches 44 and 45. In an alternate embodiment, the control signal C could be from lead 43.

In this first state, input lead 42 which is positive, is connected through output lead 46 to the common anode 410, and input lead 43 which is now negative is connected through output lead 48 to the cathode 412 of LED 11, thereby turning on only LED 11. In this second state, input lead 42 which is now negative is connected through output lead 47 to the cathode 411 of LED 12, and input lead 43 which is now positive is connected through output lead 49 to common anode 410 thereby turning on only LED 12. The resulting signal pattern produced across LED 11 is therefore substantially identical to VO1 and the resulting signal pattern produced across LED 12 is therefore substantially identical to VO2.

FIG. 4 illustrates an embodiment of a 3-to-2-type adapter that utilizes a double-pole, double-throw (DPDT) switch to enable input signals VO1 and VO2 to drive a 2-lead probe 20.

In FIG. 4, a double-pole, double-throw switch 92 functions as a 3-to-2-type adapter to connect a 3-lead monitor 51 to a 2-lead probe 20. Input signal VO1 is applied to a first input lead 52 of DPDT switch 92, input signal VO2 is applied to a second input lead 53 of DPDT switch 92 and a ground GND of the monitor is connected to a third (common) input lead 54 of DPDT switch 92.

A control signal D (which in this embodiment is derived from VO1) controls the state of the DPDT switch. The operation of this DPDT switch can be understood in terms of its equivalence to a pair of single-pole, double-throw switches 55 and 56. In a first state (illustrated by the solid line positions of SPDT switches 55 and 56), which occurs when VO1 is negative and VO2 is off, VO1 is applied to a first output lead 57 that is connected to a first input lead 58 of probe 20 and ground GND is connected to a second output lead 59 that is connected to a second input lead 510 of probe 20, thereby turning on only LED 22.

In a second state (illustrated by the dashed line positions of SPDT switches 55 and 56), which occurs when VO1 is off and VO2 is negative, VO2 is applied to output lead 59 and ground GND is connected to output lead 57, thereby turning on only LED 21. The resulting signal pattern produced across LED 21 is therefore substantially identical to VN1 and the resulting signal pattern produced across LED 22 is therefore substantially identical to VN2.

Adapters 40, 50 can be packaged into an oximeter system in a number of different ways. Either of these adapters can be: included within the monitor; mounted on a front panel of the monitor such that it can be connected to the appropriate leads from the monitor; included in the cable that connects the probe to the monitor (in a housing spliced within the length of the cable); mounted at an input end of the probe such that it can be connected to appropriate leads from the probe; mounted in the cable connector to the monitor or to the probe; or included within the probe. It is preferred to have the adapter detachably connected to the cable and/or the monitor so that a user can utilize such adapter with existing types of cables and monitors to enable each of the above-discussed types of probes to be utilized with the other type of monitor.

Preferred Embodiments

FIG. 5 illustrates one preferred embodiment of a 2-to-3 Type Adapter 40, corresponding to the adapter presented in FIG. 3. This adapter enables a 2-lead monitor 41 to drive a 3-lead probe 10. This adapter contains a DPDT switch 90 consisting of LEDs 60-63 with corresponding phototransistors 60'-63'. The optical coupling does not require external power separate from the current provided by the monitor for the LEDs for this DPDT switch to operate. It is important to keep the current to the optical switches low by using resistors R because the adapter drains some of the current provided by the input signals VN1 and VN2, thereby reducing the amount of current applied to the probe LEDs 11 and 12.

When VN1 is high and VN2 is low (the first state of DPDT switch 90), LEDs 62 and 63 emit light to photo-transistors 62' and 63', respectively, thereby connecting signal VN2 through photo-transistor 63', LED 12 and photo-transistor 62' to VN1. This turns LED 12 on. However, because LEDs 60 and 61 are reverse biased, the associated photo-transistors 60' and 61' are in an off state so that LED 11 is off.

When VN1 is low and VN2 is high (the second state of DPDT switch 40), LEDs 60 and 61 emit light to photo-transistors 60' and 61', respectively, thereby connecting signal VN1 through photo-transistor 61', LED 11 and photo-transistor 60' to VN2. This turns LED 11 on. However, because LEDs 62 and 63 are reverse biased, the associated photo-transistors 62' and 63' are in an off state so that LED 12 is off.

FIG. 6 illustrates a first preferred embodiment of a 3-to-2 Type Adapter that utilizes a set of four optically isolated switches with switching transistors 81-84 and control LEDs 81'-84'. The resistive current limiting on the switch inputs (LEDs 81'-84') again minimizes power consumption for active switching. These optically-coupled embodiments typically pass 80-90% of the power in the input signals to the output signals from the adapter. VO1 functions as an input signal that is selectively gated to the probe and also functions as a first control signal E. VO2 likewise functions as an input signal that is selectively gated to the probe and also functions as a second control signal E'. Switches 81 and 84 are conductive only when VO2 is negative and switches 82 and 83 are conductive only when VO1 is negative. When VO1 and VO2 are both at zero volts, all the switches 81-84 are nonconductive and neither of LEDs 21 and 22 is turned on. When VO1 is negative and VO2 is at zero volts, only switches 82 and 83 are turned on. This applies VO1, through switch 82 to lead 24 (making it negative), thereby turning LED 22 on through 83 to ground GND and turning LED 21 off. When VO1 is at zero volts and VO2 is negative, only switches 81 and 84 are turned on. This applies VO2 through switch 84 to lead 25 (making it negative), thereby turning LED 21 on through 81 to ground GND and turning LED 22 off. VO1 and VO2 are never both low simultaneously, so there are only three distinct states: only LED 21 on; only LED 22 on; or both LED 21 and LED 22 off.

The embodiment of FIG. 6 could be modified to eliminate transistors 82 and 84 (and the corresponding LEDs, 81'-84'), providing direct connections instead. Transistors 82 and 84 serve to isolate VO1 or VO2 when it is not being used, and this is not necessary if the lines for VO1 and VO2 are at a high-impedance state when not being activated. An embodiment which would work with an output that is high impedance is shown in FIG. 8, described below.

FIG. 6 also shows an external coding element 86 which can be added in parallel (or alternately in series) with coding resistor 27 to modify its value to a value expected by a different type of monitor (element 86 can be a resistor or some other active or passive element). This is useful because different monitors use different resistor values for the same wavelength. This could be added to any of the probes or adapters shown, not just the embodiment of FIG. 6.

FIG. 7 illustrates a second preferred embodiment of a 2-to-3 Type Adapter 40. This adapter uses two Schottky diodes 94 and 96. When VN1 is high, current will flow through Schottky diode 94 to the common node and through LED 12 back to the VN2 lead, which is low at this time. LED 11 will be reverse biased, and will not conduct, and neither will the Schottky diode 96. When VN2 is high, current will flow through Schottky diode 96 and LED 11, returning to VN1, which is low at this time. Here, LED 12 and Schottky diode 94 are reverse biased, with neither of them conducting. Schottky diodes are preferred over normal diodes since they have lower forward voltage drops.

FIG. 8 illustrates a second preferred embodiment of a 3-to-2 Type Adapter 50. This adapter includes two transistors 98 and 100. The VO1 terminal is connected through a resistor 102 to the base of transistor 100. The VO2 signal is connected through a resistor 104 to the base of transistor 98. Both the transistors are PNP type transistors and thus will turn on when the base is low compared to their emitter. The emitters are connected to the ground terminal.

In use, VO1 or VO2 becomes negative with respect to ground. When VO1 becomes negative, that turns on transistor 100, forming a path between ground and terminal 25 of the probe 20. Thus, current will flow from ground through transistor 100 through LED 22, which is turned on, and return to VO1. With VO2 in a high impedance state, the base of transistor 98 will be negative by only the amount of the collector to emitter voltage drop of transistor 100, which will be insufficient to turn on transistor 98.

Alternately, when VO2 goes negative with respect to ground, transistor 100 will turn off (because VO1 is in a high impedance) and transistor 98 will turn on. Thus, current will flow from ground, through transistor 98, through LED 21 and return to VO2. The resistors are used to limit the amount of current drawn to activate transistors 98 and 100. This embodiment assumes VO1 and VO2 are in a high impedance state when inactive, and thus another set of switches for isolation is not needed.

As can be seen from the above descriptions, the present invention "steals" power (current) from the monitor's LED drive current in order to perform a function not performed within the pulse oximeter monitor. In particular, the function performed in a preferred embodiment is controlling the switching of connections. This is particularly true in the embodiments of FIGS. 5, 6 and 8, in which power is used to control the switches. The power not "stolen" is used to drive the probe LEDs. As shown in particular in FIGS. 6 and 8, resistors can be used to limit the amount of current diverted.

FIG. 9 illustrates an embodiment of the present invention which may be incorporated into a cable for interconnecting a probe to an oximeter monitor. FIG. 9 shows a cable 106 with a monitor connector 108 for connecting to a 3-lead monitor, and a probe connector 110 for connecting to a 3-lead probe. Similarly, a connector 112 for connecting to a 2-lead monitor is provided, along with a connector 114 for connecting to a 2-lead probe. The use of such a universal cable would allow any type of monitor to be connected to any type of probe, eliminating the need to stock multiple types of adapters.

FIG. 10 shows the interconnections of the connector of FIG. 9, with an adapter 50 interconnecting the 3-lead oximeter connector 108 to the 2-lead probe connector 114. Similarly, adapter 40 interconnects the 2-lead oximeter monitor connector 112 to the 3-lead probe connector 110. This cable can be operated so that the connections not used are simply left open, providing an open circuit (high impedance) that would not affect the operation of the other adapter. Alternately, a mode switch 116 could be added to actively disconnect the adapter which is not being used to prevent any possible power drain through its components while the other adapter is being used. The adapters 50, 40 and mode switch 116 would be preferably formed as a part of cable 106 or connected thereto.

FIG. 11 is a diagram showing a dual use probe 120 and a corresponding adapter 122. Alternately, these could be combined in a single unit. In yet another alternative, the adapter could be eliminated and the probe 120 could be directly connected to either a two LED drive monitor or a 3 LED drive monitor. The dual use probe contains an 2-lead arrangement of LEDs 124 and 126. In this instance, LED 124 is preferably in the red wavelength band, and LED 126 is in the IR wavelength band. An additional LED 128 is added, corresponding to the second LED of the 3-lead arrangement. Three output terminals are provided, an output terminal 130 which is common to all the LEDs, a terminal 132 from the cathode of LED 128, and a terminal 134 from the cathode of LED 124, also connected to the anode of LED 126. In this configuration, the LEDs necessary for either type of probe, 10 or 20, are provided.

Adapter 122 shows two different connectors, a connector 136 for a 3-lead monitor, and a connector 138 for a 2-lead monitor. For the 2-lead connector 138, only leads 130 and 134 of dual use probe 120 are used. On the other hand, for 3-lead connector 136, all three leads 130, 132, and 134 are utilized.

Lines 138' show how the 2 LED drive connector 138 is connected to alternately drive LEDs 124, 126, and lines 136' show how the 3 LED drive connector 136 is connected to alternately drive LEDs 126, 128. The drive interconnections can thus be made externally to the probe, thus making the probe equally applicable to either type of monitor.

As can be seen, when connector 138 is connected to a 2-lead monitor, only leads 130, 134 are utilized, with 132 being open. Since lead 132 is open, LED 128 is effectively taken out of the circuit, and the probe and monitor can operate in the normal manner using LEDs 124 and 126.

When connector 136 for a 3-lead type monitor is used, all three leads are used. However, LED 126 is effectively taken out of the circuit since current never flows in a direction which would activate it. In a first mode, lead 130, which is connected to ground, provides current to a negatively-biased lead 132 through IR LED 128. At this point, lead 134 is high impedance, and no current flows in this direction. In the second mode, lead 130 is again ground, with lead 132 being at a high impedance and lead 134 being pulled negative. This causes current to flow through red LED 124, but not through LED 126, which is reverse biased.

Two different IR LEDs are used rather than two different red LEDs, since oximeter probes currently on the market will typically have red LEDs of approximately the same wavelength, while their IR LEDs differ.

In addition, dual use probe 120 contains two coding elements (active or passive), 140 and 142. Coding element 140 is used to indicate the wavelength of red LED 124 (and/or other significant parameters) to a 3-lead type oximeter monitor connected to connector 136. A separate coding element 142 is used to indicate the wavelength of the red LED 124 (and/or other significant parameters) for a 2-lead monitor. Although the red LED will have the same wavelength, alternate coding schemes are used for monitors currently in the market for the same wavelengths. Accordingly, the leads of element 140 are only connected to connector 136, and the leads of element 142 are only connected to connector 138. The detector 144 is connected to both connectors.

FIG. 12 is a perspective view of one embodiment of an adapter or translator 200 according to the invention. The translator electronics are contained in a housing 205, which is connected by a cable 210 to a connector 212 for attaching to a sensor or probe. Another cable 214 attaches to a connector 216 for attaching to an oximeter monitor. A separate power cable 218 provides power to the electronics of adapter 200.

FIG. 13 is an exploded view of the housing of FIG. 12. Shown are an upper housing shell 220 with an associated label 224, and a lower housing shell 222. The cables connect to an internal motherboard 226 which holds electronic components of the adapter. A daughterboard 228 holds circuitry for converting the detector signal to take into account a different LED wavelength from what the oximeter anticipates, as discussed in more detail below. This is sometimes referred to as a ratio of ratios conversion, or RAT/RAT conversion.

FIG. 14 is a block diagram of a monitor, a probe, and electronic circuits contained in adapter 200. An oximeter monitor 230 is shown, with the lines making up electrical connector 214. Also shown is the sensor or probe 232, along with the lines making up cable 210.

Three LED drive lines, marked COMMON, VO1 and VO2, are shown coming out of oximeter monitor 230. These connect to first and second LEDs 234 and 236. These are connected in the manner expected to be seen in an actual probe by monitor 230. Instead, however, the LEDs are each part of an optical isolator element, elements 238 and 240. The optically sensed signal through LEDs 234 and 236 are thus provided to an LED drive circuit 242. Circuit 242 provides the necessary conversion and drives a pair of LEDs 244 and 246 in probe 232, which are connected in a two-lead, anti-parallel arrangement. Thus, LED drive circuit 242 converts the signals from the three-lead configuration of LEDs 234 and 236 to the two-lead, anti-parallel configuration of LEDs 244 and 246.

In addition, a transformation is provided for the signals from the photodetector 248 in probe 232. The signals are provided to an amplifier 250, and then to a RAT/RAT conversion circuit 252. The output of the conversion circuit is provided through another LED 254 in an opto-isolator 256, which is then provided to monitor 230. As can be seen, the circuitry of the adapter is electrically isolated from oximeter monitor 230, and is separately powered by a power supply 258. The electrical isolation provides patient isolation to ground.

RAT/RAT conversion circuit 252 is used because the actual LEDs 244 and 246 of probe 232 may have a different wavelength than expected by monitor 230. This will result in incorrect calculation of oxygen saturation by oximeter monitor 230. To compensate for this, the actual value of the detected signal is modified accordingly, thus compensating for the fact that different coefficients are used than should be for the actual LEDs. This is done by conversion circuit 252, in a manner described in more detail in copending application Ser. No. 08/575,256, assigned to the same assignee as the present application, the disclosure of which is hereby incorporated by reference.

FIG. 15 is another block diagram illustrating other aspects of the embodiment of FIG. 14. The multiple optical isolators are shown generally as isolation interface 260. Additionally, a calibration resistor 262 is shown in probe 232. A decoder circuit 264 is provided to select the appropriate gains in the RAT/RAT circuit.

FIGS. 16-18 are circuit diagrams illustrating the embodiment of FIG. 14 in more detail. FIGS. 16 and 17 illustrate the components which would be on motherboard 226 of FIG. 13, while FIG. 18 illustrates the components on daughterboard 228. FIG. 16 shows the components of RAT/RAT conversion circuit 252, which continues in the circuitry on the daughterboard, as shown in FIG. 18. FIG. 16 also illustrates the circuitry for power supply 258. FIG. 16 also shows the detector 248 in probe 232, along with the amplifier circuit 250 in adapter 200.

FIG. 17 illustrates the circuit details of LED drive circuit 242, and also shows opto-isolators 238, 240 for the LED drives, and opto-isolator 256 for the detector.

Additional opto-isolators 266 and 268 are provided to disable the circuitry in response to a disconnect signal provided through circuit 270 to a transistor 272, which would activate the opto-isolators. Opto-isolator 266 is in series with the opto-isolators 240 and 238 for the drive LEDs, while opto-isolator 268 is in series with the detector output opto-isolator 256.

LED drive circuit 242 receives an input from a small resistor 274 in series with the common node 276. The amplitude of an applied signal is detected through amplifier 278. It is important to detect the amplitude in order to determine the current levels to drive the LEDs with, since the monitor will use a feedback loop to set the intensity to an appropriate level. The amplified signal is provided through an additional optical isolator 282 to LED drive circuit 242. From there, the signal is applied to another amplifier 284, which provides through a voltage divider 286 a voltage level to a current drive circuit 288.

The current from drive circuit 288 is provided either to an IR LED drive line 290, or a RED LED drive line 292. Which one of these is activated is controlled by the signals from opto-isolators 238 and 240 on IR sync line 294 and RED sync line 296, respectively. When opto-isolator 238 pulls line 294 active low, it turns on transistor 302 and turns off transistor 298 (which turns on transistor 300). Since line 296 is inactive high, it turns off transistor 308 and turns on transistor 304 (which turns off transistor 306). Current flows out of line 290 through the IR LED and into line 292. When opto-isolator 240 pulls line 296 active low, it turns on transistor 308 and turns off transistor 304 (which turns on transistor 306). Since line 294 is inactive high, it turns off transistor 302 and turns on transistor 298 (which turns off transistor 300). Current flows out of line 292 through the red LED and into line 290. The current is limited, preferably to a maximum of 50 mA, to limit the temperature at the patient/probe interface, and avoid potential patient burns. This limiting is done by scaling the gain in the current source.

Though the invention has been described with reference to certain preferred embodiments thereof, it is not to be limited thereby. For example, in addition to the opto-isolators, additional series or parallel components may be used to match the forward voltage characteristics of the expected LED more closely. Numerous electronic elements other than the phototransistors and transistors described herein could be utilized to effectuate the electronic switching. For example, a light emitter other than an LED could be used, with its terminals broadly referred to as an emitter drive terminal and an emitter output terminal, rather than an anode and cathode. Alternatively, the adapter could be designed to allow the 2-lead portion of the adapter to connect to either a 2-lead oximeter or a 2-lead probe, rather than being specialized to just one of these orientations. Similarly, the 3-lead portion of the adapter could connect to either a 3-lead monitor or a 3-lead probe. All such equivalents are encompassed by the invention, the invention only being limited by the appended claims.