Pulse oximetry sensor adapter

Details Pulse oximetry sensor adapter Pulse oximetry sensor adapter

1999-09-23

2002-02-19

Winakur, Eric F. (Department: 3736)

Surgery

Diagnostic testing

Measuring or detecting nonradioactive constituent of body...

C439S909000

Reexamination Certificate

active

06349228

ABSTRACT:

BACKGROUND OF THE INVENTION
Oximetry is the measurement of the oxygen status of blood. Early detection of low blood oxygen is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of oxygen supply. A pulse oximetry system consists of a sensor attached to a patient, a monitor, and a cable connecting the sensor and monitor.
Conventionally, a pulse oximetry sensor has both red and infrared LED emitters and a photodiode detector. The sensor is typically attached to an adult patient's finger or an infant patient's foot. For a finger, the sensor is configured so that the emitters project light through the fingernail and into the blood vessels and capillaries underneath. The photodiode is positioned at the finger tip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues.
The pulse oximetry monitor determines oxygen saturation by computing the differential absorption by arterial blood of the two wavelengths emitted by the sensor. The monitor alternately activates the sensor LED emitters and reads the resulting current generated by the photodiode detector. This current is proportional to the intensity of the detected light. A ratio of detected red and infrared intensities is calculated by the monitor, and an arterial oxygen saturation value is empirically determined based on the ratio obtained. The monitor contains circuitry for controlling the sensor, processing sensor signals and displaying a patient's oxygen saturation, heart rate and plethysmographic waveform. A pulse oximetry monitor is described in U.S. Pat. No. 5,632,272 assigned to the assignee of the present invention.
The patient cable provides conductors between a first connector at one end, which mates to the sensor, and a second connector at the other end which mates to the monitor. The conductors relay the drive currents from the monitor to the sensor emitters and the photodiode detector signals from the sensor to the monitor.
SUMMARY OF THE INVENTION
A drawback to conventional pulse oximetry systems is the lack of standardization of the sensor and the monitor. Unless the sensor and the monitor are manufactured by the same company, it is unlikely that these two components can be connected as a functioning pulse oximetry system. This incompatibility is mainly due to physical configuration and signal parameter differences among both the sensors and the monitors. Sensors differ primarily with respect to the configuration, drive requirements and wavelength of the LEDs. Sensors also differ in the configuration and value of coding and calibration resistors used to identify, for example, sensor type or LED wavelength. Monitors differ primarily with respect to the configuration and current limit of the LED driver; the amount of preamplifier gain applied to the photodiode detector signal; and the method of reading and interpreting sensor coding and calibration resistors. Further, the physical interface between sensors and monitors, such as connector types and pinouts, is also variable. Sensor and monitor variations among various pulse oximetry systems are discussed in detail below with respect to
FIGS. 1 through 3
.
FIG. 1
depicts one type of sensor
100
and a corresponding monitor
150
for one type of pulse oximetry system. For this particular sensor
100
, the red LED
110
and infrared LED
120
are connected back-to-back and in parallel. That is, the anode
112
of the red LED
110
is connected to the cathode
124
of the infrared LED
120
and the anode
122
of the infrared LED
120
is connected to the cathode
114
of the red LED
110
. Also for this sensor
100
, the photodiode detector
130
is configured so that the photodiode leads
102
,
104
are not in common with either of the LED leads
106
,
108
.
As shown in
FIG. 1
, the sensor
100
is also configured with a coding resistor
140
in parallel with the LEDs
110
,
120
. The coding resistor
140
is provided as an indicator that can be read by the monitor
150
, as described in pending U.S. patent application Ser. No. 08/478,493, filed Jun. 7, 1995 and assigned to the assignee of the present application. The resistor
140
is used, for example, to indicate the type of sensor
100
. In other words, the value of the coding resistor
140
can be selected to indicate that the sensor
100
is an adult probe, a pediatric probe, a neonatal probe, a disposable probe or a reusable probe. The coding resistor
140
is also utilized for security purposes. In other words, the value of the coding resistor
140
is used to indicate that the sensor
100
is from an authorized sensor supplier. This permits control over safety and performance concerns which arise with unauthorized sensors. In addition, the coding resistor
140
is used to indicate physical characteristics of the sensor
100
, such as the wavelengths of the LEDs
110
,
120
.
Also shown in
FIG. 1
is a portion of a monitor
150
that is compatible with the sensor described above. The monitor
150
has drive circuitry that includes a pair of current drivers
162
,
164
and a switching circuit
170
. The monitor
150
also has a signal conditioner, which includes an input buffer
195
that conditions the output of the sensor photodiode
130
. In addition, the monitor has a low-voltage source
164
and corresponding reference resistor
194
that read the sensor coding resistor
140
.
Each current driver
162
,
164
provides one of the LEDs
110
,
120
with a predetermined activation current as controlled by the switching circuit
170
. The switching circuit
170
, functionally, is a double-pole, triple throw (2P3T) switch. A first switch
172
connects to a first LED lead
106
and a second switch
174
connects to a second LED lead
108
. The first switch
172
has a first position
181
connected to the red LED driver
162
; a second position
182
connected to a reference resistor
194
and a buffer
195
; and a third position
183
connected to ground
168
. The second switch
174
has a first position
181
connected to ground
168
; a second position
182
connected to a low-voltage source
192
; and a third position
183
connected to the infrared LED driver
164
.
During a particular time interval, the switching circuit
170
causes the first switch
172
to connect the red LED driver
162
to the red LED anode
112
and simultaneously causes the second switch
174
to connect the ground
168
to the red LED cathode
114
. As a result, a forward current is established in the red LED
110
, which is activated to emit light. During another particular time interval, the switching circuit
170
causes the first switch
172
to connect the ground
168
to the infrared LED cathode
124
and simultaneously causes the second switch
174
to connect the infrared LED driver
164
to the infrared LED anode
122
. As a result, a forward current is established in the infrared LED, which is activated to emit light. This cycle is repeated to cause the sensor to alternately emit red and infrared light. These alternating light pulses result in currents in the photodiode detector
130
, which are input to a monitor buffer
166
and multiplexed
197
into an analog-to-digital converter (ADC)
199
. The digitized outputs from the ADC
199
, representing detected intensities, are then processed by the monitor
150
and displayed as oxygen status.
During a monitor initialization interval, the switching circuit
170
causes the first and second switches
172
,
174
to be in a second position
182
. This isolates the LED leads
106
,
108
from the drivers
162
,
164
and ground
168
. Further, the low-voltage source
192
is connected to one LED lead
108
and the reference resistor
194
is connected to the other LED lead
106
. As a result, a voltage is established across the parallel combinatio

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