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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to the art of measuring blood parameters and more
particularly pH and oxygen present in blood.
In a critical care setting, there is a need for measurement of various
blood parameters. Included among these parameters are pH and oxygen. The
values of these parameters are used in patient management. For example,
both the pH content and the oxygen content are important parameters in the
study of blood oxygen content. pH is an important parameter in studying
some diseases such sickle cell anemia. Oxygen content is also an important
parameter in the study of sickle cell anemia.
Both pH and oxygen blood parameters have been studied in the past by
external means, wherein blood samples are withdrawn from a patient and
studied externally of the body. However, there is concern in critically
ill patients that blood withdrawal, even in small amounts, could present
problems to a patient. Moreover, it is frequently desirable in studying
such diseases as sickle cell anemia that an analysis be made in place
during exercise.
It has been known to provide devices for use during in-dwelling measurement
of various blood parameters. For example, U.S. Pat. No. 3,787,119 to Tybak
discloses a catheter having a microlamp and a photosensitive element and
other elements including a cup-like element for use in receiving blood and
providing electrical output signals by means of wires extending through
the catheter. Such construction could well present size limitations as
well as stiffness limitations of the sensor carrier or catheter employed
for incorporating suitable sensor wires.
The U.S. Pat. No. 3,814,081 to Morie discloses an optical measuring
catheter employing fiber optic means for use in measuring oxygen
saturation in blood, as well as blood pressure.
Whereas Rybak and Morie employ teachings of in-dwelling catheters which may
be employed for measuring a plurality of blood parameters, there is no
teaching of a device which can be employed for measuring both partial
pressure of oxygen (PO.sub.2) as well as pH content of blood.
The U.S. Pat. No. 4,200,110 to Peterson et al. discloses a fiber optic pH
probe wherein the probe includes an ion permeable membrane which encloses
a guide containing solid material comprised of a hydrophilic copolymer
having a pH sensitive dye attached thereto. The probe operates on the
concept of optically detecting a change in color of the pH sensitive dye
when excited by light. A phenol red dye is employed so that it absorbs
light at a particular wavelength, on the order of 550 nm, with the amount
of light being absorbed varying in dependence upon the pH level. There is
no teaching, then, as to how the probe may also be employed for measuring
oxygen partial pressure (pO.sub.2).
The U.S. patent to Peterson et al. U.S. Pat. No. 4,476,870 discloses a
fiberoptic oxygen partial pressure (pO.sub.2) probe. This probe includes a
hydrophobic gas permeable envelope which contains an adsorptive support
which contains a fluorescent dye. Use of the probe for measuring partial
pressure of gaseous oxygen in the bloodstream is based on the principle of
dye fluorescent oxygen quenching. Thus, with the probe in place within a
bloodstream, fluorescent dye is excited by light of a blue wavelength
causing the dye to fluoresce at a green wavelength with the intensity of
emitted light decreasing (quenching) with increasing levels of the partial
pressure of gaseous oxygen in the bloodstream. There is no teaching in
Peterson U.S. Pat. No. 4,476,870 of employing the same probe to also
measure the pH content of the blood.
There is no teaching in the two Peterson patents, supra, by which features
of the two probes could be combined together to provide a single probe for
measuring pH and oxygen partial pressure with a single probe either
simultaneously or in sequence. For example, if one employs the hydrophilic
material containing the pH sensitive dye of Peterson U.S. Pat. No.
(4,200,110) within the hydrophobic envelope in Peterson U.S. Pat. No.
(4,476,870), the resultant probe would not be effective to sense pH
content.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a fiberoptic sensitive
probe which may be employed for sensing both pH and oxygen partial
pressure either simultaneously or in sequence without having to remove the
probe from its in-dwelling location within a blood vessel.
It is a still further object of the present invention to provide such an
improved fiberoptic probe employing an improved composite membrane
constructed of hydrophilic material containing hydrophobic microspheres
therein with the former containing pH sensitive dye and the latter
containing oxygen quenching dye.
In accordance with the present invention, there is provided an improved
optical probe for use in measuring both pH and oxygen in a blood vessel
within a living body. The probe includes an elongated flexible optical
fiber having a proximal end and a distal end and adapted to be inserted
into a blood vessel. The optical fiber serves to permit transmission of
light between the proximal and distal ends thereof. A composite membrane
is secured to the distal end of the optical fiber for use in receiving
light therefrom and returning light thereto. The membrane is constructed
of hydrophilic porous material with pH sensitive dye carried thereby. A
plurality of microspheres constructed of hydrophobic material are embedded
within and carried by the membrane. The microspheres carry a fluorescent
dye quenchable in the presence of oxygen. Consequently, when exciting
light is supplied to the proximal end and conveyed to the membrane, the pH
sensitive dye will fluoresce and emit light at an intensity level
depending upon the pH level in the blood, whereas the oxygen quenching dye
will fluoresce and emit light, the intensity level varying inversely with
that of the partial pressure of oxygen.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and advantages of the present invention
will become more readily apparent from a consideration of the following
description as taken in conjunction with the accompanying drawings,
wherein:
FIG. 1 is a schematic illustration of the optical probe in conjunction with
one application of this invention;
FIG. 2 is an enlarged view of the distal end of the optical probe;
FIG. 3 is an enlarged longitudinal section of the distal end of the optical
probe taken along line 3--3, looking in the direction of the arrows of
FIG. 2, but with the end placed mirror removed; and
FIG. 4 is another illustration similar to that of FIG. 1 showing a still
further application of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is now made to the drawings wherein the showings are for purposes
of illustrating a preferred embodiment only, and not for limiting same.
FIG. 1 illustrates an application of the invention as applied to the
measurement of oxygen partial pressure and pH content of blood within a
patient's blood vessel and includes an optical fiber 10 which extends
through an elongated single lumen catheter 12, the distal end of which may
be inserted into a patient's blood vessel 14 and advanced to a site at
which measurements are to be made. The optical fiber 10 may be carried by
the catheter during the insertion into the blood vessel or, alternatively,
once the distal end of the catheter is in place, the optical fiber 10 may
be inserted and advanced through the lumen of the catheter. The distal end
of the optical fiber may be advanced beyond the distal end of the
catheter, as is shown in FIG. 1, while measurements are being made. A
composite membrane 16, to be discussed in greater detail hereinafter, is
secured to the distal end of the optical fiber and is employed in the
measurement of oxygen partial pressure and pH content.
The optical fiber 10 is bifurcated at its proximal end defining two legs 18
and 20. Leg 18 is positioned to receive light from a light source 22 by
way of a suitable filter 24 for transmission to the composite membrane 16.
As will be described in greater detail hereinafter, the membrane 16
responds to changes in fluoresce and/or absorption of light in the
presence of blood and this information is returned in the light signal
returning to the proximal end of the optical fiber and is conveyed by leg
20 to a detector 26 by way of a suitable filter 28.
As shown in FIG. 1, the optical fiber 10 is looped at least once prior to
insertion into the proximal end of catheter 12. This is done to enhance
light distribution throughout the fiber. The catheter 12 may suitably take
the form of a single lumen, thin walled catheter, such as that provided by
Cordis Corporation, and known as Cordis FR5 thin walled catheter. This
catheter may have a diameter on the order of 0.066 inches and is
constructed of plastic material, such as polyurethane.
The optical fiber 10 may take various forms well known in the art and, for
example, may take the form of a silica core having a core diameter on the
order of 368 micrometers. The core is covered with a cladding, which may
also be of silica, and with a clad diameter on the order of 400
micrometers, nominally. Other optical fibers may be used, such as one
having a polymethymethacrylate core and a fluorcarbon cladding. Also, the
optical fiber used may not be confined to one with a core cladding
construction, but may be a step index fiber or a graded index fiber.
Attention is now more particularly directed to FIGS. 2 and 3, which
illustrate the optical probe in greater detail. As shown there, the
composite membrane 16 is mounted to the distal end of the cladded optical
fiber 10. Membrane 16 is preferably constructed of hydrophilic material in
which microspheres 40 of hydrophobic material are carried. Hydrophilic
materials which may be employed for the membrane 16 include hydroxyethyl
methacrylate (HEMA) and polyacrylamide. The hydrophilic membrane
preferably contains a pH sensitive dye of the type which will fluoresce
when excited by light. A suitable fluorescent dye for pH is fluorescein.
The pH content may be measured by either fluorescence or absorbance of
light. Whereas this embodiment prefers measurement by fluorescence, it is
contemplated that the pH measurement may be obtained by absorbance. In
which case, it may be necessary to employ a mirror 42 at the distal end,
as is illustrated in FIG. 2 (but not in FIG. 3). Examples of absorbance
dyes for measuring pH include phenol red and brilliant yellow.
The hydrophobic microspheres 40 dispersed throughout the hydrophilic
membrane 16 may be constructed of such hydrophobic materials as silastic,
poly (acrylates), polystrene, or rubber (natural or synthetic). These
hydrophobic microspheres contain oxygen quenchable fluorescent dyes. Such
dyes include 9, 10 diphenyl anthracene, or rubrene, perylene, and
decacyclene. In constructing the optical probe as illustrated in FIGS. 2
and 3, the membrane may be attached to the distal end of the optical fiber
10 by applying the membrane to the fiber tip in the following manner. The
membrane may initially take the form of a liquid monomer into which
microspheres 40 are dispersed. The microspheres are filled with the oxygen
quenchable fluorescent dye, as with the use of a swelling agent. With the
distal end of the optical fiber in contact with the monomer, the monomer
is then exposed to light causing it to polymerize. The hydrophilic
membrane preferably contains a pH sensitive dye of the type that will
fluoresce and such a fluorescent dye, as discussed above, may be
fluorescein.
With the optical probe in place for sensing pH and oxygen within a blood
vessel, such as vessel 14, the operator will energize a suitable
polychromatic light source 122. A filter 24 may be employed so that the
excitation light is at a wavelength on the order of 480 nm. It has been
determined that light at this wavelength will excite the pH sensitive dye,
causing it to fluoresce at a wavelength on the order of 520 nm. The
intensity of this light will decrease with the level of pH content in the
blood being examined. The emitted light will then be passed by the optical
fiber 12 from the distal end to the proximal end thereof and will be
directed by leg 20 to the filter 28, which, in this example, serves to
pass light at a wavelength on the order of 520 nm. The detector 26, which
may take any suitable form, responds to the intensity of the received
light for providing a readout indicative of the pH content of the blood.
The operator may then test the blood for the oxygen concentration, and
this may be done by employing a substitute filter for filter 24 which will
pass light having a wavelength on the order of 375 nm. It has been
determined that light at this wavelength will excite the fluorescent dye
in the hydrophobic microspheres so that it fluoresces and emits light at a
wavelength on the order of 430 nm. However, the intensity of this emitted
light is quenched or diminished by oxygen. The emitted light is
transmitted from the distal end to the proximal end of the optical fiber
and is directed by leg 20 to a filter 28. At this time, the filter 28 is
chosen so as to pass light at a wavelength on the order of 430 nm. This is
detected by detector 26 which provides an output indication representative
of the partial pressure of oxygen.
In the embodiment described thus far, the pH content is measured by
fluorescence. As previously discussed, it may also be measured by
absorbance. In which case, an absorbance dye for pH will be employed.
Also, to assist in detecting the amount of light that has been absorbed, a
mirror 42 is used on the distal end of the optical probe. The mirror may
take the form of a flat hemispheric of parabolic surface. The surface of
the mirror adjacent to the membrane is preferably aluminized or of
sputtered aluminum. This will help reflect light back into the optical
fiber for transmission to the proximal end. Again, the excitation light is
on the order of 480 nm so that a filter 24 for passing light at this
wavelength is employed.
Reference is now made to the embodiment illustrated in FIG. 4 which serves
to excite the pH sensitive dye as well as the oxygen quenchable dye with
light at the same wavelength. Thus, in this embodiment, the operator may
turn on the polycromatic light source 22 which supplies light into leg 18
at the proximal end of the optical fiber 10 by way of a filter 50. In this
embodiment, the filter 50 serves to pass light having a wavelength on the
order of 480 nm. It has been determined that light at this wavelength will
excite the fluorescent dye used for pH so that the dye will fluoresce and
emit light at a wavelength on the order of 525 nm. Additionally, it has
been determined that light at this wavelength will excite the oxygen
quenchable fluorescent dye in the microspheres so as to fluoresce and emit
light at a wavelength on the order of 600 nm. A mirror is not required in
this embodiment, since absorbance is not being employed for measuring pH
content.
With the optical fiber in place within the blood vessel, the operator may
turn on the light source 22 so that light is passed by way of the optical
fiber to the optical probe. The pH sensitive dye and the oxygen quenchable
fluorescent dye will be excited and emit light in their respective
wavelengths. Light emitted from these dyes is returned to the proximal end
of the optical fiber, which has been modified so as to include an
additional bifurcated leg 21 so that leg 20 is employed for directing
light to a filter 52 whereas leg 21 is employed for directing light to a
filter 54. Filter 52 is chosen so as to pass light emitted from the pH
sensitive dye with this light being on the order of 525 nm, whereas filter
54 is chosen so as to pass light emitted from the oxygen quenchable
fluorescent dye and this is on the order of 600 nm. A suitable detector 56
receives the light passed by filter 52 and provides an output indication
representative of the pH content of the blood. Similarly, a detector 58
receives light passed by filter 54 and provides a suitable output
indicative of the partial pressure of oxygen in the blood.
Although the invention has been described in conjunction with preferred
embodiments, it is to be appreciated that various modifications may be
made without departing from the spirit and scope of the invention as
defined by the appended claims.
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