Blood constituent measuring device and method

A non-invasive blood constituent measuring device and method are disclosed for measuring changes in blood thickness of predetermined blood constituents relative to total change in blood thickness at a test area to thereby determine the concentration of such constituents in the blood in a living body, which measured constituents may be, for example, hemoglobin and oxyhemoglobin to enable determination of oxygen saturation of blood. The device includes a plurality of light emitting diodes operationally controlled by timing circuitry for sequentially emitting light at different predetermined wavelengths toward a blood containing tissue sample, such as an ear lobe. A linear sensor receives emitted light passing through the sample and a train of AC modulated pulses indicative thereof is formed and then the signal representative of the light received from each emitter is scaled so that the DC components of each are normalized to a predetermined reference level with the pulse train being divided into channels at a decoder where remaining DC offset is removed and the DC component in each channel is then removed at a low pass filter, after which the AC signals in each channel are multiplexed and converted to a digital signal indicative of changes in the thickness of blood constituents for processing in a digital processor to determine therefrom the saturation of the measured blood constituents. A test unit is also included for testing operation of the device by introducing known AC modulated test signals into the circuitry.

FIELD OF THE INVENTION 
This invention relates to a blood constituent measuring device and method, 
and, more particularly, relates to a non-invasive device and method for 
determining concentration of constituents in the blood through measurement 
of changes in the thickness of such constituents relative to total 
thickness change of blood at a test area. 
BACKGROUND OF THE INVENTION 
As is known, one blood constituent measuring device is an oximeter which is 
a photoelectric photometer utilized for measurement of the fraction of 
hemoglobin in blood which is in the form of oxygenated Hb, which fraction 
is normally expressed in percentage with the percentage value being 
referred to as the oxygen saturation of blood. Oximetry is discussed, for 
example, in an article entitled "Oximetry" by Earl H. Wood, William F. 
Sutterer and Lucille Cronin, appearing at pages 416-445, of Medical 
Physics, Vol. 3, O. Glasser, Ed., Year Book Medical, Chicago, Ill. (1960). 
Various oximetry devices and methods have been heretofore suggested and/or 
utilized, and have included devices that are non-invasive in nature as 
well as devices wherein the emitted light was either passed through the 
sample or reflected therefrom to light sensors. In addition, oximetry 
devices and/or methods have heretofore been suggested and/or utilized that 
include a plurality of light emitters operating in the red and infrared 
regions. Such devices and/or methods are shown, for example, in U.S. Pat. 
Nos. 4,167,331, 4,086,915, 3,998,550, 3,804,539, 3,704,706 (single beam), 
3,647,299, and 3,638,640. 
With respect to oximetry devices and methods now known, accuracy and/or 
dependability have often presented a problem, as has a requirement for 
quite complicated circuitry. 
With respect to such devices and methods, it has heretofore been found 
necessary, for example, to use logarithmic functions in order to determine 
the oxygen saturation of blood (see, for example, U.S. Pat. Nos. 
4,167,331, 3,998,550, 3,804,539, and 3,638,640), take derivatives of the 
intensity of transmitted light (see, for example, U.S. Pat. No. 
4,086,915), or have used three frequencies in conjunction with three 
synchronous detectors, peak detectors and a ratio circuit (see, for 
example, U.S. Pat. No. 3,647,299) in order to determine the oxygen 
saturation of blood. In addition, while a digital processor has heretofore 
been suggested as a part of oximeter apparatus to determine oxygen 
saturation of blood, the oximeter apparatus also included a logarithmic 
amplifier (see, for example, U.S. Pat. No. 4,167,339). 
While oximetry devices and/or methods have heretofore been suggested and/or 
utilized, none of these devices and/or methods have proved to be 
completely satisfactory, and improvements have therefore still been needed 
with respect to such devices and/or methods. In addition, a need exists 
for measuring devices and methods for measuring other constituents of 
blood such as, for example, carboxyhemoglobin, carbon dioxide in blood 
and/or glucose in blood. 
SUMMARY OF THE INVENTION 
This invention provides a blood constituent measuring device and method 
that is capable of measuring changes in blood thickness of predetermined 
constituents related to total change in blood thickness. An AC modulated 
pulse train is developed indicative of light received from a tissue sample 
at a plurality of wavelengths with the received pulses being normalized by 
scaling the signals developed by light from each emitter to make the 
average component from each light source equal, with the pulses then being 
separated into continuous channels and the DC component removed, and then 
the AC components are multiplexed and converted to digital form for 
processing in a digital processor. 
It is therefore an object of this invention to provide a blood constituent 
measuring device and method. 
It is another object of this invention to provide a blood constituent 
measuring device and method capable of determining concentrations of 
various constituents of blood through measurement of relative changes of 
the thickness of such constituents relative to total change in thickness 
of the blood. 
It is still another object of this invention to provide a blood constituent 
measuring device and method that normalizes signals so that the average 
(DC) component from each light source is equal. 
It is yet another object of this invention to provide an improved oximetry 
device and method that includes digital processing of received signals to 
determine oxygen saturation of blood. 
It is still another object of this invention to provide a blood constituent 
measuring device and method that includes providing an AC modulated test 
signal for testing of the device. 
With these and other objects in view, which will become apparent to one 
skilled in the art as the description proceeds, this invention resides in 
the novel construction, combination, arrangement of parts and method 
substantially as hereinafter described and more particularly defined by 
the appended claims, it being understood that such changes in the precise 
embodiment of the herein disclosed invention are meant to be included as 
come within the scope of the claims.

DESCRIPTION OF THE INVENTION 
Referring now to the drawings, the device 20 of this invention is shown in 
block and schematic form as an oximeter, by way of example, to determine 
oxygen saturation of blood. The device includes a signal generating and 
timing section 22, a light emitting section 23, a light sensing section 
24, a signal converting section 25, a device testing section 26, a 
normalizing section 27, a demultiplexing section 28, a multiplexing and 
signal conversion section 29, a digital processing section 30 and a 
display section 31. 
Signal generating and timing section 22 provides timing signals for the 
device and includes an oscillator 33 connected with a timing circuit 34 
which supplies a plurality of outputs at different related frequencies, as 
is conventional. 
As indicated in FIG. 1, timing unit 34 provides output signals to LED 
drivers 36 and 37, which drivers are connected with light emitting diodes 
(LEDs) 39 and 40, respectively, to cause selective and sequential 
energization of each LED. As shown in the timing diagrams of FIGS. 2A and 
2B, each LED is preferably energized for 25% of each energization cycle of 
LED's 39 and 40 (i.e., LED 39 is energized during the time period from T1 
to T2 with the time period T0 to T1 providing a zero reference for channel 
A, and LED 40 is energized during the time period T3 to T4 with the time 
period T2 to T3 providing a zero reference for channel B). 
LED's 39 and 40 emit light at different frequencies with LED 39 preferably 
emitting light in the red region and LED 40 preferably emitting light in 
the infrared region. LEDs 39 and 40 could, however, emit light in 
different regions as desired so long as the absorption characteristics 
differ when passing through the blood-containing tissue, this being 
essential to determining the value of oxygen saturation in the blood as is 
well known. In addition, while the light emitters are indicated herein to 
be light emitting diodes, it is to be realized that other sources of 
electromagnetic energy might be utilized, and it is likewise to be 
realized that the electromagnetic source could include a plurality of 
wavelengths and the sensors could be responsive to selected wavelengths. 
As indicated in FIG. 1, device 20 of this invention is a non-invasive 
device, with the light emitted from LEDs 39 and 40 being preferably 
directed through a light diffusing disc 42 to the blood containing sample 
45 to be tested, which sample may be, for example, tissue such as an ear 
lobe or the like. At the opposite side of sample 45, light passing through 
the tissue is sensed at light sensing section 24, which includes a linear 
sensing device, which may be a photodiode 48 (or an array of such diodes). 
An electronic shield 50 in preferably positioned in the light path over the 
front of the photodiode and such a shield may be as described and claimed 
in a U.S. patent application entitled "Improved Photodetector" by Scott A. 
Wilber. 
The current developed at light sensing element 48 is coupled to current to 
voltage convertor 25, where a train of pulses (as shown in FIG. 2C) is 
developed (due to the duty cycle of emitted light from the LEDs) with the 
height of the pulses being dependent upon the amount of light passing 
through the tissue and the amount of DC offset introduced due to factors 
such as ambient light. In addition, the pulses are AC modulated (not shown 
in FIG. 2C) due to blood pulsations in the tissue sample then at the test 
area. 
The pulse train output from converter 25 is coupled through test unit 26 to 
normalization unit 52 of normalizing section 27 where the signal 
representative of the light received from each emitter is scaled so that 
the DC components of each are normalized to a predetermined reference 
level and the DC voltage offset due to ambient light and the like is also 
removed from the pulses (through charging of capacitors in the 
normalization unit to a voltage equal to the offset as brought out more 
fully hereinafter) to produce an output pulse train signal as shown in 
FIG. 3C. The normalization circuit functions to scale both the AC and DC 
components of each signal so that the DC (average) component is made equal 
to a known, preset level. The mathematical transformation is: 
##EQU1## 
where K=1.5 (specific to embodiment shown). It is to be understood that 
the normalization is performed on the peak to peak amplitude of the 
pulses. 
The pulse train output signal from normalization unit 52 is coupled to 
demultiplexing section 28, and, more particularly, is coupled to decoders 
54 and 55 therein. Decoders 54 and 55 (which function as sample and hold 
circuits) also receive timing signals from timing unit 34 (as shown in 
FIGS. 3A and B and 3D and E) to provide a 25% dead time at the beginning 
of each pulse received from normalization unit 52 to allow the photodiode 
and other circuitry to settle within their limited rise and fall times. 
Typical outputs from decoders 54 and 55 are shown in FIGS. 4A and 4B as an 
AC component riding on a DC component (the relative size of the AC 
component is highly exagerated). This output is coupled to low pass 
filters 57 and 58 which filters also receive an input from voltage 
reference generator 60. As shown in FIG. 5, the low pass filters also 
operate to subtract the DC voltage supplied by generator 60 from the input 
signal to produce an output signal that is essentially an AC component on 
a zero reference level. 
The outputs of channels A and B (i.e., the outputs from filters 57 and 58) 
are coupled to integrators A and B (designated in FIG. 1 as integrators 62 
and 63), respectively. The outputs from integrators 62 and 63 are coupled 
to multiplexer 65 with the output from multiplexer 65 being coupled to 
normalization unit 52 to supply the signals needed to adjust the 
amplitudes of signals A and B so that their DC components are precisely 
equal. 
The outputs from channels A and B are also coupled through amplifiers 67 
and 68 to multiplexer 70 of multiplexing and signal converting section 29. 
Multiplexer 70 samples both inputs simultaneously at a rate of 30 times 
per second and holds the two levels until analog to digital (A/D) 
convertor 72 has converted each incoming analog signal to a digital signal 
and has transferred the data to digital processor 30 (which data 
conversion and transfer occurs before the next sample needs to be taken, 
i.e., within 1/30th of a second). While multiplexing and demultiplexing of 
signals are indicated herein, it is to be realized that other techniques 
as would be obvious to one skilled in the art could also be utilized. In 
addition, the analog signals could be digitized at any point after being 
developed in current to voltage converter 25 and then processed by a 
digital processor appropriately programmed. 
Digital processor 30 is preferably comprised of a 6502 Digital 
Micro-Processor and associated RAM and ROM, and is connected with A/D 
converter 72 through tristate buffers and a data bus, as is conventional. 
As shown in FIG. 6, processor 30 also preferably receives timing and sync 
inputs from timing units 34. The output of digital processor 30 is 
preferably displayed at display 31 in conventional manner. Display 31 can 
be a visual display and/or can include a hard copy readout such as, for 
example, a strip chart recorder. 
Referring to FIGS. 6 through 12, a more detailed schematic and block 
diagram with respect to this invention is shown with the signal generating 
and timing section being shown in FIG. 6, light emitting section 23 being 
shown in FIG. 7, light sensing section 24 and signal converting section 25 
being shown in FIG. 8, device testing section 26 being shown in FIG. 9, 
normalizing section 27 and related integrators 62 and 63, and multiplexer 
section 65 being shown in FIG. 10, demultiplexing section 28 being shown 
in FIG. 11, multiplexing and signal conversion section 29 being shown in 
FIG. 12, and a flow diagram and operating algorithm for processor 30 being 
shown in FIGS. 13 and 14. 
As shown in FIG. 6, oscillator 33 includes a 1.832 MHz crystal 76 having a 
resistor 77 connected in parallel therewith. NOR gate 79 has one input 
connected to one side of crystal 76 and the output connected as one input 
to NOR gate 80. The output of NOR gate 80 is connected as one input to NOR 
gates 81 and 82 with the output of NOR gate 81 being connected to the 
other side of crystal 76 and the output of NOR gate 82 providing the 
oscillator output to timing circuitry 34. The remaining input of gates 79, 
80, 81 and 82 are connected with ground. 
The output of oscillator 33 is coupled to a countdown chain consisting of 
series connected integrated circuits 84, 85, 86 and 87, with integrating 
circuit 84 providing a timing signal output to processor 30. As shown in 
FIG. 6 (and throughout FIGS. 6 through 12), various connections between 
components, to positive and negative voltage sources, and to ground, are 
shown either as direct connections or through components such as 
resistors, capacators and/or diodes which have been numbered and 
illustrative values for the same can be found in the table of components 
hereinafter set forth. 
As shown in FIG. 6, pin 5 of integrated circuit 87 is connected with one 
input of NOR gate 94 through resistor 95, while the other input is 
connected with pin 3 of integrated circuit 87, and the output of NOR gate 
94 is connected to pin 1 of integrated circuit 97. In addition, a 960 Hz 
input and a 480 Hz input is provided to integrated circuit 97 from 
integrated circuit 87, with the 480 Hz output from integrated circuit 87 
also being coupled to test unit 26 (FIG. 9) and to normalization circuit 
52 (FIG. 10) and with the 960 Hz signal also being coupled to test unit 26 
(FIG. 9). 
Timing signal outputs (at 240 Hz) are coupled from integrated circuit 97 on 
pins 9 and 11 to LED drivers 36 and 37 for channels A and B, respectively. 
In addition, timing outputs designated as .0.1, .0.2, .0.3 and .0.4 are 
provided on pins 4, 5, 6 and 7, respectively, to provide switching at 
normalization unit 52 (FIG. 10). 
The 30.72 KHz output from integrated circuit 87 is coupled to pin 4 of 
integrated circuit 99, while the 60 Hz output from integrated circuit 87 
is coupled to pin 11 of integrated circuit 99 and to pin 3 of integrated 
circuit 100 with a 60 Hz output also being coupled to test unit 26 (FIG. 
9). 
The output of pin 1 of integrated circuit 99 is coupled through diode 102 
(having resistor 103 to ground connected thereto) to provide a CNVT output 
to A/D convertor 72 (FIG. 12), while pins 3 and 12 are connected through 
resistor 104 as one input to NOR gate 105 (the other input of gate 105 is 
connected to pins 2 and 5 of integrated circuit 100), which gate provides 
the S/H output to multiplexer unit 70 (FIG. 12). 
The output on pin 1 of integrated circuit 100 is coupled through NOR gate 
107 and resistor 108 to provide a R/B output to processor 30 (as a sync 
input signal to the processor), while pins 2 and 5 are connected to the 
multiplexer unit 70 (FIG. 12). 
Referring now to FIG. 7, the channel A input from integrated circuit 97 is 
coupled through resistor 110 to the positive input of amplifier 111 of LED 
driver 36, while the channel B input from integrated circuit 97 is coupled 
through resistor 114 to the positive input of amplifier 115 of LED driver 
37. 
The output of amplifier 111 is connected to the base of transistor 118 the 
emitter of which is connected to the negative input of amplifier 111. In 
like manner, the output of amplifier 115 is connected to the base of 
transistor 119 the emitter of which is connected to the negative input of 
amplifier 115. The collector of transistor 118 is connected with one side 
of LED 39, while the collector of transistor 119 is connected with one 
side of LED 40, with the other side of the LEDs being connected to the 
positive voltage power source through resistor 123. 
Referring now to FIG. 8, one side of photodiode 48 is shown connected to 
the negative input of amplifier 127, while the other side of the 
photodiode is connected with the power source through resistor 128 (and 
with ground through capacitor 129). The output from amplifier 127 is 
coupled to test unit 26 (FIG. 9). 
Referring now to FIG. 9, the output from amplifier 127 of current to 
voltage convertor 25 is coupled through resistor 134 of test unit 26 to 
the output of the unit (so that the signals are coupled through the unit 
when the test unit is off) and to pin 3 of analog switches 136 and 137. 
Timing signals for switches 136 and 137 are provided by integrated circuit 
138 which receives a 60 Hz clock input from timing unit 34 and, more 
particularly, from integrated circuit 87 pin 14 (FIG. 6). 
Test unit 26 is utilized only for test purposes and is not in circuit 
during operation of the device to determine the oxygen saturation of a 
tissue sample, the unit being switched off and on by off/on switch 139. 
Oximeter device 20 is tested by use of test unit 26. During test, there is 
no incoming signal, i.e., there is no tissue sample then being tested. 
Instead, test unit 26 supplies a test signal to both channels A and B 
through use of analog switches 136, 137 and 140 and resistors 141 through 
147 to switch the modulation envelope and supply modulation of a known 
percentage of amplitude to channels A and B. In addition, a high-low 
switch 159 is provided to pin 9 of analog switch 140. 
Referring now to FIG. 10, the output from test circuit 26 (or the signal 
coupled through resistor 134 from current to voltage convertor 25) is 
coupled to the positive input of amplifier 161 of normalization unit 52. 
Amplifier 161 has a gain of two and has a high impedance input. The output 
from amplifier 161 is connected with one side of parallel connected 
capacitors 166 and 167, the other sides of which are connected with ground 
through switches 168 and 169, respectively, and are connected through 
switches 170 and 171, respectively, to a low pass filter. 
Switches 168 and 169, and 170 and 171, are controlled by timing outputs 
from pins 4, 6, 5 and 7, respectively, of integrated circuit 97 (FIG. 6). 
The low pass filter connected to switches 170 and 171 includes resistor 
173 connected to one side of capacitors 174 and 175, the other side of 
which are connected with ground through switch 176. Switch 176 (along with 
switch 177 which is also connected with capacitors 166 and 167) is 
controlled by the 480 Hz output from integrated circuit 87 (FIG. 6). The 
junction of resistor 173 and capacitors 174 and 175 is also connected with 
the positive input of amplifier 178 which functions as an impedance 
converter with a low impedance output. 
Amplifier 181, connected with switch 177, also functions as a voltage to 
current converter and provides a low impedence output through resistor 182 
to the negative input of amplifier 183 and to the positive input of 
amplifier 184. Amplifiers 183 and 184 provide outputs to the bases of 
transistors 189 and 190 to form, in association therewith, voltage to 
current converters with the outputs from the collectors of transistors 189 
and 190 being coupled to the positive and negative inputs, respectively, 
of operational transconductance amplifier 194. Amplifier 194 includes 
linearizing diodes 196 and 197 and the output is a current source output 
that is coupled through buffer amplifier 199 to provide an output to 
decoders 54 and 55 (FIG. 11). 
Normalization circuit 52 also receives an input at operational 
tranconductance amplifier 194 from multiplexer 65 of the normalizing 
section which, in turn, receives inputs from integrators 62 and 63 
connected with channels A and B, respectively. The input from channel A is 
coupled through resistor 203 to amplifier 204 of integrator 62, while the 
input of channel B is coupled through resistor 206 to amplifier 207 of 
integrator 63. 
The outputs from the integrators are coupled to switch 210, which switch is 
controlled by the 450 Hz timing signal from integrated circuit 87 (FIG. 6) 
for control of this switch in the same manner as switches 176 and 177 are 
controlled. The movable contact of switch 210 is connected through 
resistor 212 and a voltage to current converter consisting of amplifier 
214, transistor 215 and diode 216, which converter provides a low 
impedence output to the output side of operational transconductance 
amplifier 194. 
Referring now to FIG. 11, the output from normalization circuit 52 is 
coupled from amplifier 199 to decoders 54 and 55 (defining channels A and 
B, respectively). The input to decoder 54 is coupled through capacitor 219 
(for offset removal) to resistor 220, the junction of which has a switch 
221 to ground, and then through switch 222 to capacitor 223 (to ground) 
and to the positive input of amplifier 224 (to form a sample and hold 
circuit). Switches 221 and 222 are controlled by the .0.1 and .0.2 inputs 
from integrated circuit 97 (FIG. 6), and amplifier 224 functions as an 
impedence converter with a low impedence output. 
In like manner, the input to decoder 55 is coupled through capacitor 226 
(for offset removal) to resistor 227, the junction of which has a switch 
228 to ground, and then through switch 229 to capacitor 230 (to ground) 
and to the positive input of amplifier 231 (to form a sample and hold 
circuit). Switches 228 and 229 are controlled by the .0.3 and .0.4 inputs 
from integrated circuit 97 (FIG. 6), and amplifier 231 functions as an 
impedence converter with a low impedence output. 
The output from decoder 54 is coupled through resistors 233 and 234 to the 
positive input of amplifier 235 of low pass filter 57. The positive input 
of amplifier 235 has a capacitor 236 to ground connected thereto, and the 
output is connected with the junction of resistors 233 and 234 through 
capacitor 237. Filter 57 is an active filter with a gain of 2, and 
receives an input from voltage reference generator 60, and, more 
particularly, from the output of amplifier 239 of generator 60, at the 
negative input of amplifier 235 through resistor 240. 
In like manner, the output from decoder 55 is coupled through resistors 245 
and 246 to the positive input of amplifier 247 of low pass filter 58. The 
positive input of amplifier 247 has a capacitor 248 to ground connected 
thereto, and the output is connected with the junction of resistors 245 
and 246 through capacitor 249. Filter 58 is an active filter with a gain 
of 2, and receives an input from voltage reference generator 60, and, more 
particularly, from the output of amplifier 239 of generator 60, at the 
negative input of amplifier 247 through resistor 250. 
Voltage reference generator 60 is used to provide a voltage to the low pass 
filters to subtract the DC component from the incoming signal in each 
channel. 
The output from low pass filter 57 is coupled from the output of amplifier 
235 to amplifier 204 of integrator 62 (FIG. 10) and through resistor 253 
to the negative input of amplifier 67, the output of which is coupled to 
multiplexer 70 (FIG. 12). In like manner, the output from low pass filter 
58 is coupled from the output of amplifier 247 to amplifier 207 of 
integrator 63 (FIG. 10) and through resistor 256 and variable resistance 
257 (to vary gain for calibration purposes) to the negative input of 
amplifier 68, the output of which is coupled to multiplexer 70 (FIG. 12). 
The output from voltage reference generator 60 is also coupled through 
resistor 260 and amplifier 261 to A/D converter 72 (FIG. 12). 
Referring now to FIG. 12, the output from amplifier 67 (FIG. 11) is coupled 
through resistor 266 and sample-and-hold 267 (which also receives an input 
from gate 105 (FIG. 6)) to multiplexer 70. In like manner, the output from 
amplifier 68 (FIG. 11) is coupled through resistor 271 and sample-and-hold 
272 (which also receives an input from gate 205 (FIG. 6)) to multiplexer 
70. Although only two channels have been illustrated herein, it is to be 
realized that additional channels could be utilized as needed. 
The output from multiplexer 70 is coupled from pin 3 through resistor 277 
to pin 14 of A/D converter 72. A/D converter 72 provides a plurality of 
outputs to conventional digital processor 30. 
A list of components which have been utilized in a working embodiment of 
this invention is set forth hereinafter. It is to be realized, however, 
that the invention is not meant to be limited to the components as listed. 
The component list is as follows: 
Resistors: 77-1M; 89-3K; 92-10K; 95-10K; 103-20K; 104-10K; 108-10K; 
110-82K; 112-9.1K; 114-82K; 116-9.1K; 121-100; 122-27; 123-200; 128-1K; 
130-510K; 141-5.6K; 142-6.8K; 143-8.2K; 144-12K; 145-18K; 146-36K; 
147-100K; 150-100K; 151-100K; 152-20K; 153-20K; 163-10K; 164-10K; 164-10K; 
173-160K; 179-5.49K; 180-16.4K; 182-5.49K; 186-5.49K; 187-5.49K; 
200-13.3K; 203-2.4M; 206-2.4M; 212-20K; 220-130 K; 227-130K; 233-33K; 
234-33K; 240-133K; 241-97.6K; 242-147K; 244-133K; 245-33K; 246-33K; 
250-133K; 251-133K; 253-1K; 254-20K; 256-820; 257-0 to 500; 258-20K; 
260-97.6K; 262-47K; 263-97.6K; 266-10K; 271-10K; 277-590K; 278-590K; 
280-100; 282-147K; and 284-39K. 
Capacitors: 124-22 .mu.F; 129-4.7.mu.; 131-10PF; 166 & 167-4.7 .mu.F; 174 & 
175-0.47 .mu.F; 201-270PF; 205-0.47 .mu.F; 208-0.47 .mu.F; 219 & 226-4.7 
.mu.F. 223 and 230-0.01 .mu.F; 236 & 237-0.47 .mu.F; 243-4.7 .mu.F; 248 & 
249-0.47 .mu.F; 268-0.1 .mu.F; 269-0.047 .mu.F; 273-0.1 .mu.F; 274-0.047 
.mu.F; 279-68pF; 281-270pF; 283-0.1 .mu.F; and 285-0.1 .mu.F. 
Transistors: 118 & 119-2N2219; 189 & 190-2N3904; and 215-2N3906. 
Diodes: 1N914 
NOR Gates: 4001B 
Crystal: 76-1.832 MHz 
Multiplexer: 70-4051 
A/D Converter: 72-8702 
Digital Processor: 6502 
Analog Switches: 4051B 
Integrated Circuits: 84-74LS90; 85-74LS107; 86-4007; 87-40408; 97-4555B; 
99-4073; 100-4073; 136, 137 & 140-4051B; and 138-4024. 
Amplifiers: 67 & 68-LM324; 111 & 115-LM324; 127-LF356; 161,178,181,183 & 
184-TL084C; 199, 204 & 207-TL084C; 214-LM324; 224 & 231-TL084C; 235, 239 & 
247-LM324; and 261-LM324. 
Sample-and-hold: 267 and 272-LF398. 
Switches: 168, 168, 170 & 171-4016; 176, 177 & 210-4053; and 221, 222, 228 
& 229-4016. 
Operational Transconductance Amplifier: LM13600. 
The flow diagram for processor 72 is shown in FIG. 13, with definitions for 
the flow diagram being as follows: 
A: Sampled Analog Channel A (R where channel A is in Red Region) 
B: Sampled Analog Channel B (IR where channel B is in Infrared Region) 
.DELTA.A: A.sub.new -A.sub.old 
.DELTA.B: B.sub.new -B.sub.old 
P: P=.vertline..DELTA.A+4.times.66 B.vertline. (proportional to blood 
thickness change) 
OS: Oxygen saturation computed point by point a,b,c&d: Constants used in OS 
calculation 
W: W=1+.vertline.OS-OT.vertline. 
F: F=P/W 
WS: WS=F.times.OS 
SF: Sum of loop max F's 
SW: Sum of loop max W's 
LW: Running sum of 9 SW's 
LF: Running sum of 9 SF's 
OT: Final oxygen saturation calculation 
LOOPMAX: A constant equal to 10 or 20 depending on status of front panel 
switches 
LOOPCOUNT: A counter 
THRESHOLD: A constant used to compare with LF to determine if perfusion is 
too low 
OFF EAR FLAG: Flag which is high if an off ear condition is sensed 
The fundamental equation is: 
##EQU2## 
where .DELTA.L=The change in blood thickness 
K(.lambda.)=The attenuation coefficient of the blood at wavelength.lambda. 
.DELTA.I(.lambda.)=The change in electromagnetic intensity at the 
measurement site at wavelength.lambda. 
I(.lambda.)=The average electromagnetic intensity at the measurement site 
at wavelength.lambda.. 
It follows immediately from equation (1) that if K(.lambda.) is known, 
.DELTA.L may be calculated by measuring .DELTA.I(.lambda.) and 
I(.lambda.). 
For blood in living tissue, the attenuation coefficient, K(.lambda.), is 
generally the result of a linear combination of the attenuation 
coefficients of two or more attenuating substances, such as hemoglobin 
(Hb), oxyhemoglobin (HbO.sub.2) and carboxyhemoglobin (HbCO): 
##EQU3## 
where the superscripts A.sub.1 through A.sub.m indicate that the 
associated quantities relate to the different attenuating substances which 
are designated A.sub.1 through A.sub.m. 
It is to be understood that the total volume change is, 
EQU .DELTA.L=.DELTA.L.sup.A.sbsp.1 +.DELTA.L.sup.A.sbsp.2 . . . 
+.DELTA.L.sup.A.sbsp.m (3) 
Combining equations (1) and (2) results in a general expression: 
##EQU4## 
By making measurements of 
##EQU5## 
at "m" different wavelengths (.lambda..sub.1, .lambda..sub.2, . . . 
.lambda..sub.m), a set of linear equations results which may be solved 
simultaneously for .DELTA.L.sup.A.sbsp.1 through .DELTA.L.sup.A.sbsp.m. 
The general form of this solution is: 
EQU .DELTA.L.sup.A.sbsp.n =N.sub.1 R(.lambda..sub.1)+N.sub.2 R(.lambda..sub.2) 
. . . +N.sub.m R(.lambda..sub.m) (5) 
where A.sub.n designates the nth attenuator of "m" attenuators 
##EQU6## 
N.sub.1 through N.sub.m are constants related to the nth attenuator and 
the specific wavelengths .lambda..sub.1 through .lambda..sub.m. 
The fractional or percentage concentration of any of the attenuators is, 
from equation (5): 
##EQU7## 
where .DELTA.L is defined by equation (3). 
An example of this is the determination of Oxygen Saturation (O.S.) which 
is the percentage of oxyhemoglobin relative to total hemoglobin: 
##EQU8## 
Equation (7) may be simplified and rewritten: 
##EQU9## 
where the constants X.sub.1 through X.sub.4 may be derived if the 
appropriate physical constants are known, or they may be calculated by 
curve fitting techniques using empirical measurements of the ratio 
##EQU10## 
versus simultaneous standard blood gas determinations. 
Thus the simplified, general equation is of the form: 
##EQU11## 
In the present invention, the quantities .DELTA.I(.lambda.) and 
I(.lambda.) are converted by a detector to electronic signals, 
AC(.lambda.) and DC(.lambda.), respectively, which are representative of 
the magnitudes of the electromagnetic quantities. Therefore, in equation 
(10), the terms R(.lambda.) may be represented by: 
##EQU12## 
wherein the AC(.lambda.) term may be a representation of the peak-to-peak 
amplitude or any portion thereof, the peak-to-peak amplitude (or any 
portion thereof) of the first or higher derivatives, or the differential 
of the AC(.lambda.) term or any of its first or higher derivatives. The 
AC(.lambda.) term may also be a representation as described above of any 
of the spectral components or any transformation thereof as produced by 
analog or digital processing. 
In equation (11), R(.lambda.) may be a representation of a typical average 
or "best estimate" value of the ratio as produced by the invention herein 
described. 
The general algorithm for processor 30 is set forth in FIG. 14, the use of 
which causes operation of the processor to determine oxygen saturation of 
blood through measurement of blood thickness changes with respect to the 
specific device set forth hereinabove. The device could, however, be 
adapted for use in measuring many other constituents of blood utilizing 
the general algorithm as set forth in FIG. 14. To utilize the algorithm 
for determining other constituents of blood, it is necessary that the 
number of wavelengths be equal to or greater than the number of unknown 
constituents. For example, the device and method can be used to determine 
constituents such as carboxyhemoglobin, carbon dioxide in blood and/or 
blood glucose. The essential is that the constituent be determinable 
through measurement of changes in blood thickness relative to total 
thickness, and therefore the device and method can also be utilized to 
measure hematocrit (i.e., percent of packed blood cells relative to total 
blood volume) and/or total blood volume change in a tissue segment 
(plethysmography) and/or total blood flow through a tissue segment per 
unit time. 
From the foregoing it should be realized that this invention provides a 
blood constituent measuring device and method one use of which is to 
provide an improved oximetry device and method.