U.S. patent number 4,201,222 [Application Number 05/829,420] was granted by the patent office on 1980-05-06 for method and apparatus for in vivo measurement of blood gas partial pressures, blood pressure and blood pulse.
Invention is credited to Thomas Haase.
United States Patent |
4,201,222 |
Haase |
May 6, 1980 |
**Please see images for:
( Certificate of Correction ) ** |
Method and apparatus for in vivo measurement of blood gas partial
pressures, blood pressure and blood pulse
Abstract
An optical catheter including an absorption chamber and
distensible semipermeable diaphragm are disclosed for the
simultaneous measurement of blood gases, blood pressure and pulse
rate.
Inventors: |
Haase; Thomas (Laguna Beach,
CA) |
Family
ID: |
25254495 |
Appl.
No.: |
05/829,420 |
Filed: |
August 31, 1977 |
Current U.S.
Class: |
600/311; 600/480;
600/486; 600/502; D24/169 |
Current CPC
Class: |
A61B
5/02154 (20130101); A61B 5/024 (20130101); A61B
5/1459 (20130101); A61B 5/1495 (20130101); G01N
21/8507 (20130101) |
Current International
Class: |
A61B
5/00 (20060101); A61B 5/024 (20060101); A61B
5/0215 (20060101); G01N 21/85 (20060101); A61B
005/02 (); A61B 005/00 () |
Field of
Search: |
;128/2L,2.5D,2E,2.07,2.5P ;73/19,23,23.1 ;356/39,40,41,42
;23/254R,254E |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Webster's Seventh New Collegiate Dictionary, p. 528,
(1961)..
|
Primary Examiner: Michell; Robert W.
Assistant Examiner: Tayon; Jeffrey W.
Attorney, Agent or Firm: Peterson; Gordon L.
Claims
What is claimed is:
1. A catheter for use in making at least one blood-related
measurement including the partial pressure of at least one blood
gas comprising:
wall means defining chamber means for light absorption spectral
analysis of said one blood gas, said chamber means being of a size
small enough to allow the chamber to be placed within a blood
carrying member of a human body, said chamber means having first
and second spaced apart regions defining a void space
therebetween;
said wall means including a semi-permeable membrane at said first
region of the chamber means, said wall means having an interior
surface facing toward said chamber means, said semi-permeable
membrane being permeable to at least said one blood gas and
substantially not permeable to blood whereby when the
semi-permeable membrane is placed in contact with blood it allows
said one blood gas to pass through the semi-permeable membrane into
the chamber means to fill the void space and substantially prevents
the blood from passing through the semi-permeable membrane into the
chamber means so that the blood gas in the chamber means is
separated from the blood;
first elongated light-conducting means for conducting light to said
second region of said chamber means so that the light can pass
along a light path through said void space and through the blood
gas in said chamber means and be at least partially absorbed by
said one blood gas;
second elongated light-conducting means for conducting light away
from the chamber;
means for attaching the first and second light-conducting means to
said chamber means;
a reflector within said chamber means including a reflective
coating on said interior surface of said membrane for receiving
light at said first region of the chamber means after the light has
passed through at least some of the void space and the blood gas in
the chamber means, the light path from the first elongated
light-conducting means to the reflector being unobstructed except
for the blood gas in the chamber means, said reflector reflecting
at least some of the light it receives toward the second elongated
light-conducting means for transmission away from the chamber means
whereby an indication of the partial pressure of said one blood gas
can be obtained; and
said semi-permeable membrane being resiliently deformable into the
void space by the blood with which it is placed in contact whereby
blood pressure and heart rate information can be obtained.
2. A catheter as defined in claim 1 wherein said chamber is
generally cylindrical and has a length greater than its diameter,
said semi-permeable membrane being at one end of the cylindrical
chamber and both of said elongated light-conducting means
terminating at the other end of said cylindrical chamber.
3. A method of making at least one blood-related measurement
including the partial pressure of at least one blood gas
comprising:
providing a sensor which includes wall means defining a chamber
with the wall means including a semi-permeable membrane which is
permeable to at least said one blood gas and substantially not
permeable to blood;
performing in vivo spectral analysis by light absorption through
said at least one blood gas utilizing said sensor; and
said step of performing including positioning the sensor with the
semi-permeable membrane contacting blood and allowing at least said
one blood gas to flow through the permeable wall into the chamber,
directing light into the sensor and through the blood gas therein
with the light having a wave length which is highly absorbed by
said one blood gas, reflecting the light which has passed through
at least some of the blood gas in the chamber out of the chamber,
and comparing a characteristic of the light directed into the
chamber with a characteristic of the light reflected out of the
chamber to obtain an indication of the partial pressure of said one
blood gas.
4. A method as defined in claim 3 wherein said step of providing
includes providing the membrane as a resiliently deformable
membrane and providing a reflective coating on the interior surface
of the membrane, carrying out said step of reflecting utilizing
said reflective coating, allowing the blood to resiliently deform
the membrane to alter the reflectance from the reflective coating,
and using the altered reflectance to obtain an indication of a
blood pressure related measurement.
5. An apparatus for in vivo measurement of two blood gas partial
pressures comprising:
wall means defining a chamber adapted to be inserted into the blood
stream to be analyzed, said chamber having first and second spaced
apart regions defining a void space therebetween, said wall means
including a semi-permeable membrane at said first region which is
permeable to at least said two blood gases and is substantially not
permeable to blood whereby when the membrane is placed in contact
with blood, it allows said two blood gases to pass through the
membrane into the chamber and substantially prevents the blood from
passing through the semi-permeable membrane into the chamber so
that the two blood gases in the chamber are separated from the
blood;
first and second light sources, said first source producing light
of a wavelength suitable for absorption analysis of one of said two
blood gases, said second source producing light of a wavelength
suitable for the absorption analysis of a second of said blood
gases;
first light-conducting means for conducting the light from said
sources to said second region of the chamber so that the light can
pass through the void space and the blood gases in said chamber and
be at least partially absorbed thereby;
first means for alternately pulsing the light from said first and
second sources through said first light-conducting means to said
chamber;
second light-conducting means for conducting light away from the
chamber;
means for attaching the first light-conducting means to said
chamber;
a reflector in said chamber for receiving light from said first
light-conducting means after the light has passed through at least
some of the blood gases in the chamber, said reflector reflecting
at least some of the light it receives toward the second
light-conducting means;
means for attaching the second light conducting means to said
chamber at a position to receive light reflected by said
reflector;
first and second light detectors;
means for alternately pulsing the light from said second
light-conducting means to said first and second detectors whereby
said first and second detectors receive at least some of the light
from said first and second light sources, respectively, each of
said detectors including means for providing an output signal
responsive to a characteristic of the light received by such
detector;
means responsive to the output signals from said first and second
detectors to provide indications of the partial pressures of said
first and second blood gases, respectively;
said semi-permeable membrane having an interior surface facing
toward said chamber and said reflector includes a reflective
coating on said interior surface; and
said semi-permeable membrane being resiliently deformable into the
void space by the blood with which it is placed in contact whereby
blood pressure and heart rate information can be obtained.
6. An apparatus as defined in claim 5 wherein said apparatus
includes means responsive to at least one of said output signals
for providing an indication of at least one blood pressure related
parameter.
7. An apparatus as defined in claim 5 wherein said first pulsing
means includes a rotatably mounted wheel and at least two prisms
mounted on said wheel for the reflection of light from said first
source, said prisms being spaced apart to define spaces
therebetween for the direct transmission of light from said second
source to said first light-conducting means.
Description
BACKGROUND OF THE INVENTION
This invention relates to cardiovascular monitoring and, more
particularly, to an absorption spectroscopic catheter for the in
vivo measurement of blood gas partial pressures as well as blood
pressure and pulse rate.
Pressure transducer catheters are well-known (References 1, 2), as
are electrolytic type catheters for determining blood gases (3).
Various optical catheters have been conceived for the measurement
of gas content in blood (4-9) and for providing both blood gases
and pressure-pulse rate data (8). Some of such systems utilize
fiber optic technology to introduce light in the red-visible region
of the spectrum into the bloodstream which is reflected by blood
molecules. The reflected light is then colorimetrically analyzed to
determline blood color from which information pertaining to oxygen
saturation can be derived. This information, however, is actually a
ratio of the number of oxygenated hemoglobin molecules to
non-oxygenated hemoglobin molecules, and does not provide data in
terms of the partial pressure of oxygen which is a vital parameter
vis-a-vis the life of the catheterized patient. Another
disadvantage of colorimetric systems is that carbon dioxide content
in the blood is not directly obtainable.
Other catheter systems utilizing the arts of gas chromotography
(10) or mass spectrometry (11) have been devised to measure
cardio-vascular functions. Such systems, however, generally require
the removal of a blood sample from the body before analysis can
take place. The analytical components are very large and are
usually located in laboratories which are often far removed from
the operating room. Once the blood reaches the laboratory the
analysis response time of such systems is typically slow. Delay is
a primary disadvantage of mass spectrometric and gas
chromotographic systems. Expense is a further disadvantage.
The principles of absorption spectrometry are well-known and find
application in a number of analytical systems, procedures and
devices. These principles, however, have not been applied to the
rapid and accurate in vivo analysis of dissolved gases in blood.
Briefly, and in a very much simplified manner, the principle of
operation of the present absorption spectrometry catheter system is
described as follows.
Each atom or molecule absorbs and radiates electromagnetic
radiation in discrete quantitative increments at a number of
discrete levels of energy. In the present instance, the
electro-magnetic energy is in the energy range referred to as
"light," including both the visible and the invisible infrared and
ultra-violet regions of the light spectrum. When a light beam of a
specific energy level, i.e. wavelength, preferably of only one
wavelength, i.e. monochromatic light, is passed through a chamber
containing a specific substance which absorbs at that wavelength,
the amount of absorbed light, and hence the reduction in the
intensity of the light beam, is proportional to the number of atoms
or molecules of the substance in the chamber which interact with
the incident radiation. The ratio of intensity incident light,
I.sub.o, to the intensity of the exit light, I.sub.f, is a measure
of the absorbed light and, therefore, a measure of the amount of
the substance in the absorption chamber.
Actually, any given substance will absorb light of many differnt
energy levels (wavelengths), some wavelengths being strongly
absorbed and others much less strongly absorbed. This variation in
amount of absorption with wavelength is referred to as the
absorption spectrum of the particular material.
When the substance to be measured is a gas, such as oxygen or
carbon dioxide, it is convenient to measure the amount of the gas
present in a chamber of defined dimensions. According to the gas
law, the pressure of the gas in such a chamber is directly
proportional to the amount, or number of molecules, of gas in the
chamber. Thus, it is possible to measure directly the pressure of a
given gas in the chamber simply by measuring the total amount of
the gas in the chamber. Where more than one gas is present the
pressure contribution of each constituent gas is referred to as the
"partial pressure" of that gas.
In any system which includes gases, whether it be a gaseous system,
such as a chamber of defined proportions, or a liquid system, such
as flowing blood, each gaseous component exerts a pressure
proportional to the total amount of the gas in the system. Thus,
each gas dissolved in the blood exerts a "partial pressure" in the
blood stream. If such a system having a partial pressure of a given
gas, for example blood with an oxygen or carbon dioxide partial
pressure, is placed in contact with a barrier which is permeable to
the gas but not to the blood, the gas will permeate and diffuse
through the barrier, i.e. dissolve in one side and out the other,
until the partial pressure of that gas on the other side of the
barrier equals the partial pressure of the gas in the blood stream.
Actually, the pressures on each side of the barrier need not be
exactly equal since there are permeation factors, and other
factors, which effect the flow through the barrier; however, the
gas will flow through the barrier until an equilibrium value is
reached at which time the rate of diffusion through the barrier is
equal in both directions.
This principle is applied in the present invention by placing a
catheter which includes a chamber of defined dimensions in the
blood stream. All or part of the wall of the chamber is made of a
barrier membrane which is permeable to oxygen and carbon dioxide
and/or selected other gases, referred to as a semipermeable
membrane. The partial pressure of a given gas in the chamber, at
equilibrium, is directly proportional to the partial pressure of
gas in the blood. Accordingly, by measuring the partial pressure of
the gas in the chamber, by measuring the total amount present as
discussed before, the partial pressure of dissolved gas in the
blood can be determined. The unique application of these principles
in the apparatus and systems and methods of this invention are an
important feature of this invention.
Absorption spectroscopy is particularly useful where emission
spectra are difficult to obtain due to the high energy levels
required to achieve electronic configurations excitations. This is
especially true of polyatomic and diotonic gases. For example,
absorption spectroscopy has been successfully employed to measure
the ozone level of the atmosphere. Since low energy radiation is
sufficient for obtaining absorption spectra, measuring systems
based on this concept are very advantageous and well suited for use
in the in vivo measurement of cardiovascular functions. The
development of high infrared transmissive optical fibers has made
possible the efficient utilization of the absorption concept in
blood catheters. The use of absorption chambers in conjunction with
such catheters provides for flexible and accurate monitoring of one
or a combination of several blood gases.
The preferred embodiment of the present invention allows for the
simultaneous measurement of oxygen and carbon dioxide partial
pressures, vital indicators with respect to cardiovascular
performance. Furthermore, the same monitor is easily adapted to
also measure the equally vital overall blood pressure and pulse
rate, thereby embodying a complete, yet convenient and accurate,
monitoring device. Convenience in use and mobility of the monitor,
because of its small dimensions and reduced space requirements of
the optical and electronic components, are important features of
the present invention. Use of monochromatic light of strongly
absorbed wavelength provides both accuracy and sensitivity for both
gases, with minimum effect from the presence of other gases.
Response time of the absorption catheter is very short, only about
three seconds.
SUMMARY OF THE INVENTION
The present invention provides an optical catheter system, based on
the art of absorption spectroscopy, for the accurate and efficient
cardiovascular monitorization of blood gas content, as well as
overall blood pressure and pulse rate.
In general, the catheter of this invention comprises a pair of
elongate fiber optic bundles, which may be randomly mixed with each
other, in an elongate sheath of any of several biologically
compatible materials. The fiber optic bundles are adapted at the
proximal end to receive incident monochromatic radiation, I.sub.o,
of known intensity and predetermined wavelength and to transmit the
incident radiation the lengths of the catheter to an absorption
chamber at the distal end of the catheter. The absorption chamber
may be of any configuration but is conveniently of generally
cylindrical shape with the fiber optic bundles at one end directing
the incident radiation the length of the chamber to a reflective
surfaced semipermeable membrane forming the other end of the
chamber. In this configuration the radiation is absorbed by gases
present in the chamber during two passes through the chamber, to
the mirror and from the mirror back to the fiber optic bundle. The
remaining, or exit radiation, is transmitted by the fiber optics
back along the length of the catheter to radiation detectors which
measure the intensity of the final radiation, I.sub.f. It is the
ratio I.sub.o /I.sub.f which is proportional to the partial
pressure of the dissolved gas in the blood stream. In the preferred
form, the distal wall of the chamber serves both as a semipermeable
membrance and as a mirror, being coated with gold or some other
reflective coating to about a 50% reflectivity; however, separate
semipermeable membranes, e.g. in the cylinder walls, could be
provided to result in the same basic chamber. Similarly, the
chamber may be spherical or of some other configuration. It is
intended that the specific embodiments referred to here and
hereinafter are not limiting but are merely exemplary.
In accordance with the preferred embodiment of this invention, the
blood partial pressures of two gases, oxygen and carbon dioxide,
are concurrently measured and displayed. Where two gases are
present in the chamber, each will absorb light passed through it,
to one degree or another, depending upon the wavelength of the
incident light rays. Thus, the absorption by both gases will
contribute to the decrease in intensity of the incident light, that
is, I.sub.o less I.sub.f, thereby making inaccurate the measurement
of either one of the two gases. It is therefore necessary for the
measurement of a first gas, to supply light to the chamber of a
wavelength at which absorption by that particular gas is very high,
and at which absorption by the other gas present is very low.
Similarly, absorption analysis of the second gas should utilize
light of a wavelength at which absorption by that gas is high and
at which absorption by the first gas is very low, or
negligible.
The present invention accomplishes this objective by utilizing
light with a predeterined wavelength of approximately 7596
angstroms for the absorption analysis of oxygen, and of
approximately 2 microns for the measurement of carbon dioxide. At
these wavelengths, the respective absorption by carbon dioxide and
oxygen, as well as other gases present, water vapor and nitrogen
will be negligible. The optical fibers employed by the present
invention are unique in that they exhibit high transmissive
qualities, that is, above 30%, of light in the infrared region.
Two distinct light sources, one visible and one infrared, are
provided for the production of light beams of these wavelengths.
The visible source in the preferred embodiment is a laser,
well-known for the coherent and monochromatic nature of its light
rays (22-24). Dual detectors, responsive to light in the visible
and infrared regions of the spectrum, respectively, are also
provided.
Light from the two sources is alternately pulsed by the use of an
optical multiplexer, referred to as a "chopper," towards the
incidence channel of the fiberoptical system for transmission to
the chamber. Pulsing is necessary not only because there are two
light sources and only a single incidence channel, but also because
a continous beam of light falling on the detectors substantially
dampens its sensitivity and reduces the signal to noise ratio. The
chopper herein employed, however, is novel in that it not only
produces the necessary pulsation of light, but also simultaneously
synchronizes the alternate pulsation of light from two light
sources, and the alternate detection of reflected light rays by two
detectors.
A further advantage of the present invention is that it provides
for the measurement of gases present in the blood stream, other
than oxygen and carbon dioxide. The structure and concept of this
invention allows the absorption analysis of one or a combination of
several gases.
Finally, besides the measurement of blood gas partial pressures,
the present invention is capable of simultaneous monitoring of
overall blood pressure and pulse rate. The semipermeable window
contained in the absorption chamber is made of a flexible substance
which allows it to deflect in response to blood pressure and pulse
rate. These responsive deflections are transmitted to the light by
the window at the point of reflection, and are exhibited by the
reflected light in the form of amplitude modulations. These
modulations are sensed by the detectors which generate electronic
signals in response thereto. These signals can then be properly
converted and visually displayed to provide the instantaneous and
complete monitorization of cardiovascular functions, including
blood gas partial pressures, overall blood pressure and pulse
rate.
These and other advantages of the present invention are readily
apparent by reference to the drawings in which:
FIG. 1 is a perspective drawing of the Cardiovascular Monitor
including digital display of oxygen and carbon dioxide partial
pressures, blood pressure and cardiacrate, detectable optical
catheter chambered sensor end tip;
FIG. 2 is a perspective and schematic diagram optical multiplexing
system and fiber optics of the preferred embodiment of the present
invention;
FIG. 3 is a section view, taken along lines 3--3, of the sensor end
tip showing absorption chamber and peripheral sensor
construction;
FIG. 4 is a block diagram illustrating the electronic analog to
digital conversion of the output signals; and
FIGS. 5 and 6 are signal output waveforms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Shown in FIG. 1 is an exemplary cardiovascular moniter with
catheter attachment, indicated generally at 10 and 12,
respectively, which embody the present invention. Other forms of
equipment of like function, e.g. using a strip chart display are
obviously within the scope of this invention. Moniter 10 provided
for the visual digital display of blood pressure 14, both systolic
and diastolic, cardiac rate 16, pulse rate indicator light 18, and
partial blood pressures of oxygen and carbon dioxide, 20 and 22,
respectively. On/off switch 24 and power light indicator 26 are
also shown.
Housed within monitor 10 is the optical multiplexing system of the
present invention, including light sources, detectors and rotary
multiplexor, as well as the electronic analog-to-digital conversion
system, necessary for the processing and display of the
cardiovascular data. This mode of housing and display is, however,
merely a preferred example. In many cases it may be desirable to
record, by means of a strip chart for example, the signals
corresponding to the above data.
The monitor face is provided with input/output connection 28, which
receives dual jacks 30 of the bifurcated optical catheter 12.
Incidence channel 32 and reflection channel 34 combine to form
catheter body 36, the former for transmitting light to sensor end
tip 38 and the latter for return transmission of reflected light.
The construction of the bifurcated fiber optical system will be
dealt with in more detail below.
FIG. 2 illustrates the primary components of the preferred
embodiment, the optical multiplexing system 40, fiber optical
catheter 12, and the sensor end tip 38 and the manner in which
these systems interface. Sensor 38 is generally defined as a
cylindrical housing 46, fitted at one end with a semipermeable
window 48. The sensor housing can be constructed of stainless
steel, or of less rigid materials such as nylon, ABS or of any of
the well-known biologically acceptable materials. Its diameter is
approximately 2 mm and measures about 4 mm in overall length.
The window material must be flexible, so as to be sensitive to
blood pressure and cardiac rate, and also permeable, in the
preferred embodiment, to oxygen and carbon dioxide. Sylastic brand
(General Electric) silicon rubber of thickness about 10 microns is
generally accepted as a biologically compatible semipermeable
membrane material and is quite satisfactory.
A circular light aperture 50 generally defines the proximal end of
housing 46 and receives the non-bifurcated end of fiber optic
bundle 53, thereby allowing the entrance and exit of light into and
out of sensor end tip 38.
The detailed construction of the sensor end tip 38 is shown in FIG.
3. Sensor housing 46 narrows at its proximal end to facilitate
attachment to the optical catheter body 36. Window 48 is affixed to
the housing using an autoclavable epoxy glue. The deflection of the
window 48, shown in phantom line 56, is due to the pressure of the
blood on its exterior surface, indicated by the arrows 58, the
frequency of such deflections being dependent upon the rate of
heartbeat. In addition to flexing in response to blood pressure and
pulse rate, the window is permeable to oxygen and carbon dioxide
molecules dissolved in the blood.
Gas molecules 60 diffuse through the window membrane into the
absorption chamber 54 until equilibrium is reached. At this point,
the partial pressures of O.sub.2 +CO.sub.2 inside chamber 54 will
equal, or at least be directly proportional, to the surrounding
partial pressure of these gases in the bloodstream. A reflective
coating 62 is applied to the interior surface of the window using
conventional vacuum deposit or evaporational techniques. The
coating material can be gold or aluminum and is applied so as to
exhibit an optical density of about 46%, not opaque enough to
reduce to any substantial degree the permeability of the window and
yet sufficient to allow for reflection of incident light rays, as
shown by arrows 64 and 66.
Body 36 of optical catheter 12 is comprised of a sheathing material
such as flexible polyvinyl chloride, nylon, Tygon, chlorinated
rubber, or other biocompatible material. The body is, conveniently,
shrink molded for attachment to housing 46 of sensor end tip
38.
Referring again to FIG. 2 the bifurcated construction of the fiber
optical catheter 12 is shown. Ten fibers, in a typical structure,
each constitute the incidence and reflection channels 32, 34 of the
catheter, to form the 20-fiber, randomly mixed bifurcated bundle,
shown in section at 68. Corning fiber optics No. 44-49016-1499 is a
presently preferred fiber optic material.
The optical multiplexing system, indicated generally at 40,
consists essentially of red visible and infrared light sources 70
and 72, visible and IR detectors 74 and 76, and an optical
multiplexer 78, referred to as a "chopper." The rotary chopper 78
is powered by motor 80. Visible source 70 is a laser which produces
light with an approximate wavelength of 7596 angstroms and
intensity of 5-10 mw, e.g. Spectraphysics Model 142 or Model 335
used for the absorption analysis of oxygen. A laser source is
preferred because of the characteristically coherent and
monochromatic narrow beam produced thereby. A further advantage is
the reduced size of the source optics required, providing for a
monitor of reduced dimensions.
The infrared source 72 is a standard incandescent reflective source
for the absorption measurement of carbon dioxide. For the reasons
discussed above, a carbon dioxide laser is a desirable source but
cost considerations presently suggest the use of conventional IR
source. The wavelength of light produced by the IR source is
approximately 2 microns and has an intensity of 250-300 watts.
The visible detector 74 consists of a silicon phototransistor,
peaked for detection via narrow band filters of light wavelengths
of around 7596 angstroms. Texas Instruments Co. Model TIL 78 is an
example of such a detector. While a silicon phototransistor could
be utilized as the IR detector 76, a triglycine sulfate crystal
detector is preferred because of its proper gain special frequency
and time response. The IR detector is selected and adjusted to
sense light wave lengths of around 2 microns. Narrow band filters
of, respectively, 7596 angstroms and 2 microns with a band width of
1/2A are part of the detector and not depicted separately.
It is well-known that a continuous beam of light falling upon an
optical detector will substantially dampen its response, and that
pulsation of the incident light is therefore necessary. Optical
chopper 78 accomplishes this result, as well as the multiplexing of
two discrete light rays down a single fiber optical channel. As
shown in FIG. 2, each 90.degree. rotation of the chopper wheel 78
allows light procuded by the visible source 70 to be reflected by
one of its four prisms 82 towards the incidence channel 32 of fiber
optic catheter 12. Instantaneously, the incident light ray will be
reflected by window 48 for return transmission via reflection
channel 34, whereupon it impinges upon another prism located on the
chopper 180.degree. from the first. Turning of the visible beam at
the locations shown in FIG. 2 is provided for by totally reflective
optical flats 84.
With each 45.degree. rotation of the chopper, the infra-red light
produced by IR source 72 is allowed to pass through and enter the
incidence channel 32 for transmission to the absorption chamber 54.
Reflected IR light will similarly pass through the chopper for
direct sensing by IR detector 76.
The electrical output signals produced by the sensors, indicated
generally at 100, in response to reflected light rays are processed
in accordance with the analog/digital conversion electronics system
shown in FIG. 4. The analog signal first undergoes pre-calibration
in a conventional scaler amplifier 102 where it is scaled to
correspond to the voltage input limits of the microprocessor.
A calibration source 104, which may be any of a large number of
stable signal generators of conventional design, is selectively fed
to the scaler amplifier 102 to ensure electronic stability. The
sensor output also triggers the syncronization detector 106 which,
along with syncronization driver 108, generates a sync pulse to
ensure proper syncronization in the input multiplexer 110 and the
output multiplexer 112. The processed signal from the multiplexer
110 is processed by a peak detector 114 which senses the maximum
amplitude of each peak of the alternating signal resulting from the
optical multiplexer. An automatic gain control amplifier 116
receives an output signal from the peak detector and feeds the
scaler amplifier 102 to ensure proper voltage input to the
multiplexer 110. The peak detector output is an analog signal which
is converted to a digital signal for further processing by a
conventional analog to digital converter 118 which feeds the
digital signal to the output multiplexer 112 where the signal is
processed for individual display and may then be displayed as a
digital signal by means of counters 120, catch decoder drivers 122
over predetermined time intervals controlled by the update clock
124 and then visually presented by displays 126 which may be
conventional neon glow tube devices of any design, or any other
digital signal responsive display device. A plotter or printer
could, for example, be used in lieu of the neon glow tubes of the
exemplary embodiment depicted in FIG. 1. In addition, or
alternatively, the processed signal may be converted by a
conventional digital to analog converter 128 to be displayed by an
analog display device 130, such as a conventional strip chart
recorder.
No novelty or unique features reside in the electronic circuits;
indeed, all electronic circuits and signal handling devices and
displays are well-known and generally used thoughout the
electronics and instrument industries and are described in numerous
standard texts and other publications. See, for example, Brophy, J.
J., 1972, Basic Electronics for Scientists, 2nd Ed., McGraw-Hill,
New York; Offner, F. F., 1967, Electronics for Biologists,
McGraw-Hill, New York; Vassos, B. H. and Ewing, G. W., Analog and
Digital Electronics for Scientists, 1972, Wiley-Interscience, New
York. Off-the-shelf electronic signal processing instruments which
are adaptable for producing suitable readout of the signals are
available from a number of instrument manufacturers.
In use, the optical catheter 12 is inserted into the bloodstream
such that sensor end tip 38 is in the desired location. Carbon
dioxide and oxygen molecules dissolved in the blood diffuse across
the permeable window 48 and occupy absorption chamber 54. The
systolic and diastolic pressures of the blood produce corresponding
deflections in window 48 which occur at the frequency of the pulse
rate. The rotary action of the chopper 78 multiplexes alternate
light rays of known intensities down incidence channel 32 of the
optical catheter 12 to chamber 54. As shown in FIG. 3, incident
light rays 64 pass through the chamber, and are reflected by the
reflective coating 62 of window 48 back through the chamber,
whereupon the reflected rays 66 enter one of the fibers
constituting reflection channel 34 for transmission to the
detectors. The reflected light pulse is amplitude modulated at the
point of reflection by the deflections of window 48, resulting from
pulsing of the blood and the average blood pressure. Calibration of
each catheter, or selection of like-sensitivity catheters, is
required for quantitization of the signal output; however, it will
be apparent from the geometry of the sensor chamber that an
increase in blood pressure, either long term or transitional, will
cause distension of the membrane and will result in greater
scattering of the light thus reducing the proportion of the light
reflected to the reflecting channel optical fiber bundle. This
phenomenon, in itself, is known (8) and therefore, no detailed
discussion is required.
The light of each frequency, in addition, undergoes two absorptions
by the respective gas to which each corresponds. For example, light
from the visible source 70, having a predetermined wavelength of
about 7596 A, precedes the pulse of light from the IR source 72
down the incidence channel to the chamber. As this pulse of light
twice traverses the chamber, its energy is absorbed by the oxygen
molecules present. CO.sub.2 and other gases, on the other hand,
will absorb only a negligible amount of energy. Therefore, the
intensity of the reflected visible beam, as determined by the
visible detector 74, when compared to the known intensity of the
incident beam, will correspond accurately to the partial pressure
of oxygen in the absorption chamber and bloodstream. Partial
pressure of gases is displayed or recorded in units of mmHg.
The output signals of the detectors will contain information
relating not only to the intensities of reflected light, but also
to blood pressure and pulse rate. These data then enter the
electronic processing system, illustrated in FIG. 4, previously
described.
FIG. 5 depicts, in a very general fashion, the gross signal that
may be obtained from an oxygen sensor of the type described, the
ordinate indicating increasing dissolved oxygen, partial pressure,
in the blood, increasing upwardly, the abscissa indicating time,
from an arbitrary zero starting point, in seconds, increasing to
the right. As the partial pressure of oxygen in the blood increases
(in the course of graph of FIG. 5 the increase being very rapid
simply to illustrate the type of signal output) the absorption by
the oxygen in the sensor chamber increases, thus decreasing the
intensity of the output signal. This gross decrease in signal is
depicted by the sharp downward turn of the output signal curve,
followed by a levelling as the oxygen partial pressure stabilizes
and then by a sharp decrease accompanied by a rapid, shallow pulse
at the right of the figure. The pulse rate and pressure is carried
on the signal in the form of a more rapid amplitude modulation
component which is effectively averaged electronically when
considering the oxygen partial pressure signal. The relative
magnitude of the pulse and partial pressure signals depends upon
the geometry of the sensor and may be predetermined at any desired
ratio by making the chamber longer and the membrane smaller to
increase the partial pressure to pulse signal ratio or by making
the membrane larger and the chamber smaller to increase the pulse
to partial pressure signal ratio.
FIG. 6 is short time period depiction of a signal of the type
depicted in FIG. 5 except that the pulse to partial pressure ratio
is very much higher than that ratio in FIG. 5, simply to illustrate
the manner in which the pulse rate-blood pressure data are carried
by the signal. In FIG. 6, the partial pressure component is ignored
because of the short time duration, the entire figure representing
only about two seconds, and to focus upon the pulse rate-blood
pressure data. The signal is in the form of a modulated AC, the AC
component resulting from the optical multiplexer, the amplitude
modulation resulting from the distension of the membrane by the
pulsation pressure in the blood vessel in which the catheter dwells
during use. In practice, the pulse rate is read directly, e.g. 83
pulses per minute, and the pressure is converted electronically to
correspond to the blood pressure as determined by the conventional
sphygmometer, e.g. 130/95, the conversion factor being determined
empirically.
As pointed out before, the invention resides in the application of
absorption spectrometry to the in vivo determination of oxygen and
carbon dioxide, or other gases, in blood and, more particularly in
the design and operation of the catheter and optical system and not
in the manner or means for electronically processing and displaying
the output signal. Considerable variation in the precise manner and
apparatus in which the invention is embodied is contemplated
without departing from the concept of the invention of the scope of
the invention as defined in the claims, it being immaterial to the
invention that any particular method or means of electronic signal
processing and display is used. It is, accordingly, the intent that
the claims which follow be read in light of and consistently with
the scope and nature of the inventive concept and the manner in
which that concept is utilized and not upon the merely exemplary
embodiment by which the invention is depicted and described
hereinbefore.
REFERENCES CITED IN THE SPECIFICATION
The following references, and those specifically referred to in the
specification, are incorporated herein as if fully set forth.
1. U.S. Pat. No. 3,249,105, Polanyi, May 3, 1966.
2. U.S. Pat. No. 3,273,447, Frank, Sept. 20, 1966.
3. U.S. Pat. No. 3,791,376, Rybak, Feb. 12, 1974.
4. U.S. Pat. No. 3,123,066, Brumley, Mar. 3, 1964.
5. U.S. Pat. No. 3,136,310, Meltzer, June 9, 1964.
6. U.S. Pat. No. 3,498,286, Polanyi et al, Mar. 3, 1970.
7. U.S. Pat. No. 3,814,081, Mori, June 4, 1974.
8. U.S. Pat. No. 3,822,695, Takayama, July 9, 1974.
9. U.S. Pat. No. 3,847,483, Shaw et al, Nov. 12, 1974.
10. U.S. Pat. No. 3,983,864, Sielaff et al, Oct. 5, 1976.
11. U.S. Pat. No. 3,952,730, Key, Apr. 27, 1976.
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