Note: Descriptions are shown in the official language in which they were submitted.
CA 02239080 2004-06-02
OPTICAL OXIMETER PROBE ADAPTER
Technical Field
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.
l0 Convention Regarding Reference Numerals
In the figures, each element indicated by a reference numeral will be
indicated by the same reference numeral in every figure in which that element
appears.
BACKGROUND OF THE INVENTION
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.
Noninvasive oxirneters have been developed that direct light through a
2 o 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. patent 5,209,230 entitled "Adhesive Pulse Oximeter Sensor
With Reusable
Portion" issued to Swedlow, et al. and in U.S. patent 4,700,708 entitled
"Calibrated Optical
Oximeter Probe" issued to New, Jr, et al., both assigned to the assignee of
the present
2 5 invention. 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
3 0 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.
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Optical probes can be electrically configured in a plurality of ways. U.S.
patent 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 Figures
1 and 2. Figure 1 shows a probe configuration I O in which a pair of LEDs 1 I
and I2 are
connected in a "3-lead conf guration" i 3 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 Ieast one of LEDs I 1 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, VOi, and V02, respectively. The VOI and V02 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 V02 terms is intended to
refer to
"other." Thus, this probe is sometimes referred to as an "other probe."
In a second embodiment, shown in Figure 2, two LEDs 2I and 22 are
connected in a "2-Iead 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
2 o 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
2 5 - 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-
3 0- lead configuration of LEDs will be referred to herein as a "3-lead
monitor" or "other
oximeter monitor."
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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
achie~~e more
balanced light levels.
For either of the above two configurations of Figures l 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
2 0 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
2 5 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.
3 o 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.
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4
SUMMARY OF THE INVENTION
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.
The adapter of the present invention thus first connects the 2 leads of the 2-
lead device between the f rst and second terminals of the 3-lead device while
a first light
1 o emitter is activated, and then connects the 2 leads between the second and
third terminals of
the 3-lead device. The 3-lead device can be either the oximeter monitor or the
oximeter
probe.
In one type of three-terminal monitor, only one of the two drive terminals
(VO1, VO~) is active at a time, with the other drive terminal being in a high
impedance
state, and the third terminal connected to ground. In such a configuration,
the adapter does
not need to disconnect the other drive terminal. In another type of three-
terminal monitor,
the second drive terminal is not in a high impedance state. Thus, one adapter
according to
the present invention provides an extra switch to isolate this second drive
terminal which is
not being used. In one embodiment, this provides a four-transistor switch
embodiment,
2 0 rather than a two-transistor switch or two-diode embodiment.
In accordance with the illustrated preferred embodiments, two types of
adapters are presented that are specially adapted to enable an oximeter probe
to be utilized
with an oximeter monitor with which it would otherwise be unable to be
utilized. These
two types of adapters are particularly useful because they enable two widely
utilized types
2 5 of oximeter probes to be utilized on both of their associated types of
oximeter monitors.
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.
3 0 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.
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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.
l0
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a probe with a 3-lead configuration of a pair of LEDs.
Figure 2 illustrates a probe with a 2-lead configuration of a pair of LEDs.
Figure 3 illustrates the use of a double-pole, double-throw switch as a 2-to-3
Z5 Type Adapter for connecting a 2-lead monitor to a 3-lead probe.
Figure 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.
Figure 5 illustrates a first preferred embodiment of a 2-to-3 Type Adapter.
Figure 6 illustrates a first preferred embodiment of a 3-to-2 Type Adapter.
2 o Figure 7 illustrates a second preferred embodiment of a 2-to-3 Type
Adapter.
Figure 8 illustrates a second preferred embodiment of a 3-to-2 Type Adapter
for use with a high impedance output oximeter monitor.
Figure 9 illustrates a combined adapter cable.
Figure 10 illustrates the multiple adapter connections in the cable of Figure
9
2 5 for a combined adapter.
Figure I 1 illustrates a preferred embodiment of a dual use probe and
corresponding adapter.
DESCRIPTION OF THE PREFERRED EMBODIMENT
3 0 Types of Monitors
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
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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
2 0 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.
Types of Adapters
2 5 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
3 0 of adapter will be referred to herein as a "2-to-3-Type Adapter". 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.
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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.
1 p 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
2 0 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 V02 into a
pair of LED
drive signals VN 1 and VN2. Likewise, a 2-to-3-type adapter can be implemented
by any
structure that converts a pair of LED drive signals VN 1 and VN2 into a pair
of LED drive
signals VOl and V02.
A 3-to-2-type adapter must convert LED drive signals from a 3-Iead 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.
Operation Of A 3-Lead Monitor With A 3-Lead Probe
A 3-lead monitor 51 provides, at a first terminal, a signal VOI (illustrated
in
Figures I and 4) that can be no signal, with the terminal switched into an
open state (i.e.,
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high impedance state) or can be driven to a negative' voltage. A second
terminal provides a
signal V02 (also illustrated in Figures 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 Figure I. 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 1 I emits Iight when
V02 is negative. VO1 and V02 are intentionally never negative at the same
time, so that
only one or none of LEDs 1 l 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:
Operation Of A 2-Lead Monitor
With A 2-Lead Probe
In a 2-lead monitor 41, a first terminal provides a signal VNI (illustrated in
Figures 2 and 3) and a second terminal provides a signal VN2 (also illustrated
in Figures 2
2 0 and 3). This monitor is intended to be utilized with a 2-lead probe.
LED 21 emits light when VNI 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 VNl and VN2 are applied
to opposite
ends of both LEDs, if VN I and VN2 are both equally high or are both equally
Iow 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.
General Structure of the Adapters
3 o A 3-to-2-type adapter can take any structural form that enables the
signals
VNI and VN2 (illustrated in Figure 2) to be generated in response to input
signals VO1 and
V02 (illustrated in Figure 1).
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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.
1 p 2-to-3-Type Adapter
Figure 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 VN 1 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
I 1 and I2. 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.
2 0 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
2 5 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
3 0 to the cathode 411 of LED 12, and input lead 43 which is now positive is
connected through
output lead 49 to common anode 4I0 thereby turning on only LED 12. The
resulting signal
pattern produced across LED 11 is therefore substantially identical to VOl and
the resulting
signal pattern produced across LED 12 is therefore substantially identical to
V02.
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3-to-2-Type Adapter
Figure 4 illustrates an embodiment of a 3-to-2-type adapter that utilizes a
double-pole, double-throw (DPDT) switch to enable input signals VOl and V02 to
drive a
5 2-lead probe 20.
In Figure 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 V02 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)
10 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 V02 is off, VOl 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 VOl is off and V02 is negative, V02 is applied
to output
Iead 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.
Packaging
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
Ieads from the
3 0 monitor; included in the cable that connects the probe to the monitor (in
a housing spliced
withing the length of the cable); mounted at an input end of the probe such
that it can be
connected to appropriate Ieads 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
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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
Figure 5 illustrates one preferred embodiment of a 2-to-3 Type Adapter 40,
corresponding to the adapter presented in Figure 3. This adapter enables a 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
l0 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 VN 1 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 Iight to photodiodes 62' and 63', respectively, thereby
connecting signal
VN2 through photodiode 63', LED 12 and photodiode 62' to VN 1. This turns LED
i 2 on.
However, because LEDs 60 and 61 are reverse biased, the associated photodiodes
60' and
61' are in an off state so that LED 11 is off.
2 o When VN 1 is low and VN2 is high (the second state of DPDT switch 40),
LEDs 60 and 61 emit light to photodiodes 60' and 61', respectively, thereby
connecting
signal VNl through photodiode 61', LED 11 and photodiode 60' to VN2. This
turns LED 11
on. However, because LEDs 62 and 63 are reverse biased, the associated
photodiodes 62'
and 63' are in an off state so that LED 12 is off.
Figure 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
3 0 from the adapter. VOI functions as an input signal that is selectively
gated to the probe and
also functions as a first control signal E_ V02 likewise functions as an input
signal that is
selectively gated to the probe and also functions as a second control signal
E'. Switches 8I
and 84 are conductive only when V02 is negative and switches 82 and 83 are
conductive
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only when VO1 is negative. When VO1 and V02 are both at zero volts, all the
switches 81-
84 are nonconductive and neither of LEDs 21 and 22 is turned on. When VOl is
negative
and V02 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 V02 is negative,
only
switches 81 and 84 are turned on. This applies V02 through switch 84 to lead
25 (making it
negative), thereby turning LED 21 on through 81 to ground GND and turning LED
22 off.
VOl and V02 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 Figure 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 V02 when it is not being used,
and this is not
necessary if the lines for VO1 and V02 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 Figure 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
2 o the same wavelength. This could be added to any of the probes or adapters
shown, not just
the embodiment of Fig. 6.
Figure 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 I2 back
to the
2 5 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 VNl, 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.
3 o Figure 8 illustrates a second preferred embodiment of a 3-to-2 Type
Adapter 50. This adapter includes two transistors 98 and 100. The VOl terminal
is
connected through a resistor 102 to the base of transistor 100. The V02 signal
is connected
through a resistor 104 to the base of transistor 98. Both the transistors are
PNP type
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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 V02 becomes negative with respect to ground. When VOl
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 V02 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 V02 goes negative with respect to ground, transistor 100
will turn ofF (because VOl 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 V02.
The resistors are used to limit the amount of current drawn to activate
transistors 98 and
100. This embodiment assumes VO1 and V02 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 Figures 5, 6 and 8, in which power is used to control
the switches.
2 0 The power not "stolen" is used to drive the probe LEDs. As shown in
particular in Figures
6 and 8, resistors can be used to limit the amount of current diverted.
Figure 9 illustrates an embodiment of the present invention which may be
incorporated into a cable for interconnecting a probe to an oximeter monitor.
Figure 9
shows a cable 106 with a monitor connector 108 for connecting to a 3-lead
monitor, and a
2 5 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.
Figure 10 shows the interconnections of the connector of Figure 9, with an
3 0 adapter 50 interconnecting the 3-lead oximeter connector 1 OS 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
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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.
Figure 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
lot-lead arrangement of LEDs I24 and I26. In this instance, LED 124 is
preferably in the red
wavelength band, and LED I26 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 I 32 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
I38, only leads
130 and 134 of dual use probe I20 are used. On the other hand, for 3-lead
connector 136,
2 o all three leads 130, I 32, and 134 are utilized.
Lines I38' 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, I34 are utilized, with I32 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
3 0 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 I32 through IR LED 128. At this
point,
lead 134 is high impedance, and no current flows in this direction. In the
second mode,
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lead 130 is again ground, with lead 132 being at a high impedance and Iead 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
1 o 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.
Though the invention has been described with reference to certain preferred
embodiments thereof, it is not to be limited thereby. Any one of a variety of
active switches
are well known in the art and could readily be substituted for the double pole
double throw
switches described herein. In addition, numerous electronic elements other
than the
2 0 phototransistors and transistors described herein could be utilized to
effectuate the electronic
switching. For example, a light emitter other than a 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.
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