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BACKGROUND OF THE INVENTION
This invention relates to a catheter system for measuring blood pressure
while simultaneously measuring the degree of oxygen saturation in blood.
The invention is described in conjunction with measuring oxygen saturation
as well as blood pressure within the cardiovascular system, although these
two parameters may be measured in other systems of the body.
It is known in the prior art to provide an optically based catheter system
for measuring the degree of oxygen saturation in blood of a living body
while simultaneously measuring blood pressure at a site of interest. Such
systems are known, for example, in the U.S. Pat. Nos. to Takayama,
3,822,695 and Mori, 3,814,081. In such systems, the two parameters, oxygen
and blood pressure, are measured simultaneously employing an elongated
catheter containing a bundle of optical fibers. These catheters are
provided with an end hole at the distal end with the end hole being
covered with a diaphragm. The diaphragm is transparent to light passing
through the optical fibers in the red and infrared regions, but reflects
light at shorter wavelengths. The oxygen content of blood is determined in
such systems by comparing the absorption of light in the infrared region
to absorption of light in the red region. Thus, carbohemoglobin and
oxyhemoglobin in the blood are different in the light absorption spectrum.
Both have like absorption rates for light in the infrared region, but
carbohemoglobin has a much larger absorption rate for light in the red
region. The percentage content of oxygen contained in the blood, that is,
the ratio of oxyhemoglobin to carbohemoglobin is obtained in such systems
by transmitting light in both the red and infrared regions into blood and
then detecting light reflected from the blood and determining therefrom
the ratio of the amount of reflected light in the two regions.
The systems described in the aforesaid patents measure the blood pressure
at the site of interest with the diaphragm covered end hole. The diaphragm
reflects the shorter wavelength light back into the optical fibers for
transmission to an externally located meter. Since the catheter is
inserted into the bloodstream of a patient, the blood pressure deflects
the diaphragm, causing modulation of the light intensity so that the meter
provides an indication of blood pressure.
Such catheters employing diaphragm covered end holes actually measure total
pressure rather than the desired measurand; mainly, static pressure. By
aligning the end hole of a catheter with the direction of blood flow,
kinetic energy terms are introduced. If the catheter end hole is directed
upstream, a kinetic term will be added to the pressure. If the end hole is
facing downstream, the kinetic term will be subtracted from the pressure.
The magnitude of the error will vary with the velocity and density of the
fluid. This error will vary during the course of a cardiac cycle and will
distort the shape and magnitude of a pressure wave. In the pulmonary
artery, the kinetic pressure may be on the order of 10% of total pressure
at rest and 50% of total pressure at a cardiac output equal to three times
that at rest. The importance of the kinetic pressure error is particularly
great in stenotic areas where velocities are high.
The catheters discussed above are also limited in their application to
measuring pressure at a single site at a time. If pressure readings are
required at different sites, then the readings must be taken at different
times and the catheter must be moved so the transducer at the distal end
is moved from site to site.
It is known in the prior art to provide a catheter capable of performing
intravascular pressure measurements in more than one site with the
readings being taken simultaneously. One such device known in the prior
art is disclosed in the U.S. Pat. No. 4,543,961, to D. C. Brown, assigned
to the same assignee as the present invention. In Brown, there is provided
an elongated catheter having a plurality of optical fibers aligned
end-to-end in the lumen of the catheter. A plurality of pressure
transducers are provided along the length of the catheter with each being
associated with the spacing between two aligned optical fibers. The
pressure transducer includes a filter-mirror which is movable between the
adjacent ends of two spaced apart fibers, the movement being in response
to pressure acting against the catheter. Light is directed into the
proximal end of the catheter and is transmitted by the optical fibers. At
each pressure transducer, light at one wavelength only will be modulated
in accordance with pressure. All other light will remain nearly unchanged.
Consequently, at the proximal end, the reflected light of three different
colors may be individually examined to determine the pressure exerted at
each of the three sites under examination.
The multiple site pressure transducer structure in Brown serves to provide
measurements of but a single blood parameter; namely, blood pressure.
There is no teaching of measuring other blood parameters, such as the
oxygen saturation in blood. Moreover, Brown's construction employs a
plurality of optical fibers aligned end-to-end within the lumen of an
elongated catheter. This results in difficulty of construction, since a
typical catheter may have a diameter on the order of 0.06 inches and the
optical fiber carried therein may be on the order of 400 micra. Placing a
plurality of such fibers in end-to-end alignment along with associated
filter-mirrors within such a catheter presents substantial difficulty in
manufacture.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide an improved
catheter for use in measuring a plurality of blood parameters, including
pressure and oxygen.
It is a still further object of the present invention to provide such a
catheter having an improved optical fiber pressure transducer employing
side port measuring of static pressure as opposed to end hole monitoring
of total pressure.
It is a still further object of the present invention to provide such an
improved catheter which permits measurement of oxygen saturation in blood
while simultaneously obtaining measurement of static blood pressure at one
or more sites of interest.
In accordance with the present invention, the foregoing and other
objectives are achieved in a fiber optic based catheter system for
measuring blood pressure at one or more locations while simultaneously
measuring oxygen saturation in blood. The apparatus includes an elongated
tubular catheter having a proximal end and a distal end with the latter
adapted to be inserted into a passageway within a body cavity containing
blood. A single elongated optical fiber is carried within the catheter and
extends throughout the length thereof for receiving light at the proximal
end of the catheter and transmitting it to the distal end thereof. The
distal end of the catheter is provided with an end hole which is covered
by a filter which passes light in the red and infrared region, but
reflects light of shorter wavelengths. The filter is positioned forwardly
of the distal end of the optical fiber to receive light therefrom. The
filter reflects light of shorter wavelength back into the distal end of
the optical fiber so that the reflected light is transmitted back to the
proximal end of the catheter. The longer wavelength light, i.e., that in
the red and infrared region, is passed by the filter and reflected
differently by the blood in dependence upon oxygen saturation. The
differently reflected light is passed back through the filter to the
optical fiber for passage to the proximal end of the catheter. A detector
may be located near the proximal end of the catheter and respond to the
returned light in the red and infrared region to provide an indication as
to the oxygen saturation in the blood. The catheter carries one or more
pressure transducers which operate on the optical fiber for measuring
pressure acting transversely thereof. The optical fiber is coaxially
surrounded by cladding means essentially throughout its length and is
uncladded for at least one portion of its length proximate to the distal
end thereof. The pressure transducer is located adjacent the uncladded
portion and includes a flexible transducer member having an irregular
surface facing the uncladded core portion for making surface area contact
therewith such that the contacting surface area varies with pressure
applied to the transducer member acting transversely of the uncladded core
portion. The transducer member is constructed of material exhibiting a
greater index of refraction than the cladding so that the intensity of
light passing through the core proximate to the transducer member is
modulated in its intensity as a function of the transversely acting
pressure.
In accordance with another aspect of the present invention, the catheter
carries a plurality of pressure transducers, each is operating on an
uncladded portion of the length of the core.
In accordance with a still further aspect of the present invention, the
plurality of pressure transducers each include light wavelength dependent
means for modulating light at a particular wavelength different from that
at the other of the transducers.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and advantages of the present invention
will become more apparent from a consideration of the following
description as taken in conjunction with the accompanying drawings,
wherein:
FIG. 1 is a schematic illustration of a multi-site pressure measuring
catheter in conjunction with one application of this invention;
FIG. 2 is an enlarged sectional view of the distal end of the catheter in
accordance with one embodiment of the invention;
FIG. 3 is an enlarged sectional view taken along line 3--3 looking in the
direction of the arrows of FIG. 2;
FIG. 4 is an enlarged view showing a portion of a transducer member in
surface engagement with an uncladded core and used for purposes of
explanation herein;
FIGS. 5A, 5B and 5C are graphical waveforms illustrating reflectivity
versus wavelength useful in the description of the embodiment shown in
FIGS. 2 and 3;
FIGS. 6A-6C are graphical waveforms illustrating light transmission as a
function of wavelength and which is useful in the description of the
embodiment of FIGS. 2 and 3;
FIG. 7 is a schematic-block diagram illustration of the optical system as
well as the electronic detecting circuitry employed in the embodiment of
FIGS. 2 and 3;
FIG. 8 is an enlarged sectional view of the distal end of the catheter
showing a second embodiment of the invention;
FIG. 9 is an enlarged cross sectional view taken along line 9--9 looking in
the direction of the arrows in FIG. 8;
FIGS. 10A-10C are graphical waveforms illustrating excitation amplitude
with respect to wavelength and is useful in describing the embodiment of
FIGS. 8 and 9;
FIGS. 11A-11C are waveforms of emission amplitude versus wavelength and
which is useful in describing the embodiments of FIGS. 8 and 9;
FIG. 12 is a schematic-block diagram illustration of the detector circuitry
employed in conjunction with the embodiment of FIGS. 8 and 9;
FIG. 13 is an enlarged sectional view of the distal end of the catheter
showing a third embodiment of the invention;
FIG. 14 is a cross sectional view taken along line 14--14 looking in the
direction of the arrows in FIG. 13;
FIGS. 15A-15C are waveforms showing light absorption with respect to
wavelength which is useful in describing the embodiment of FIGS. 13 and
14; and
FIG. 16 is a schematic-block diagram illustration of the detector circuitry
employed in conjunction with the embodiment of FIGS. 13 and 14.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is now made to the drawings wherein the showings are for purposes
of illustrating preferred embodiments only, and not for limiting same.
FIG. 1 illustrates an application of the invention as applied to
simultaneous measurement of blood pressure as well as the degree of oxygen
saturation of blood within a patient's cardiovascular system. This
includes an elongated single lumen catheter 10 containing an optical fiber
12 which extends throughout the length of the catheter. At its distal end,
the catheter carries a filter F employed for use in measuring the degree
of oxygen saturation in the blood. In addition, the catheter carries three
blood pressure transducers T.sub.A, T.sub.B, and T.sub.C for
simultaneously measuring the blood pressure within the cardiovascular
system at three different sites, such as sites A, B and C. The spacing
between the pressure transducers may be varried as desired and, for
example, the transducer T.sub.A may be located adjacent the distal end of
the catheter with transducers T.sub.B and T.sub.C spaced therefrom toward
the proximal end. It is contemplated, for example, that these transducers
may be used for simultaneously recording of pulmonary wedge pressure,
right ventricular pressure, and atrial pressure. In such case, the
transducers will be spaced approximately 10 centimeters apart.
As will be described in greater detail with respect to the three specific
embodiments disclosed herein, filter F at the distal end of the catheter
is chosen to transmit light in the red and infrared regions and to reflect
light of shorter wavelengths. In this context, it has been determined that
there is a large difference in light reflectance between oxygenated and
unoxygenated blood with light having a wavelength on the order of 805
nanometers. However, the reflectance is equal for both oxygenated and
unoxygenated blood for light having a wavelength on the order of 930
nanometers Consequently, the ratio of light reflected from blood at
wavelengths of 805 nanometers and 930 nanometers provides an indication of
the degree of oxygen saturation of blood. For this reason, then, the
filter F is chosen to transmit light above approximately 750 nanometers,
while reflecting light below that level. The light source is chosen to
emit a broad band of light, including light in the range from
approximately 750 nanometers through 950 nanometers for oximetry and light
in another waveband (e.g., 350-700 nm) for pressure sensing. This light
passes through the optical fiber 12 and then to the distal end thereof, at
which the longer wavelength light, i.e., above 750 nanometers is
transmitted through the filter F into the bloodstream. There, light is
reflected differently at 805 nanometers and at 930 nanometers, as
discussed above. This light reflected from the blood is redirected back
into the optical fiber to the proximal end thereof. The detector circuit
24 in addition to detecting blood pressure, also includes detector
circuitry for determining the ratio of light reflected at 805 nanometers
to that reflected at 930 nanometers. This provides an indication of the
oxygen saturation of blood and this information may then be displayed as
with the use of a conventional chart recorder 26, or displayed as with an
oscilloscope 28.
The catheter 10 preferably takes the form of a torque controlled catheter,
such as that constructed in accordance with the U.S. Pat. No. 3,585,707,
R. C. Stevens, assigned to the same assignee as the present invention and
disclosure of which patent is herein incorporated by reference. Briefly,
as described in that patent, the catheter is an intravascular catheter
having an elongated body portion 15 and a tip portion 17 at the distal end
of the catheter. The body portion 15 is reinforced so that it may be
twisted at its proximal end to impart a twisting motion throughout its
length. This body portion is constructed to have high longitudinal
flexibility and high torsional control without being elastic. Moreover,
the body portion includes tubing made up of an inner plastic tubular core
covered by a braided wire intermediate sheath and an outer plastic
covering which penetrates through the interstices in the braiding of the
sheath and closely overlies the tubular core.
The tip portion 17 is designed to direct the catheter during insertion into
a selected body vessel and is preferably formed with a tapered end as a
pair of curves including a relatively sharp curve on the order of
45.degree. just before the distal end thereof and a less sharp curve a
short distance proximally thereof. The tip portion 17 does not employ a
braided sheath and it is preferably more flexible than the body portion.
As will be described in greater detail hereinafter with respect to each
embodiment of the invention, each of the transducers serves to measure
pressure acting in a direction transversely of the long axis of the
optical fiber. For this purpose, each transducer is provided with an array
of side ports spaced equidistant apart circumferentially about the
catheter with each side port being covered with an elastic membrane which
may, for example, take the form of silastic. Each membrane covers a
transducer member constructed of flexible material having an index of
refraction greater than that of the cladding and serves to make surface
area contact with an uncladded core portion of the optical fiber. The
contacting surface area will vary with pressure applied to the transducer
acting transversely of the optical axis of the optical fiber. As the
pressure increases, more light will be refracted and absorbed by the
transducer member. Consequently, any light entering the proximal end of
the optical fiber 12 will be modulated in each of the pressure transducers
in dependence upon the magnitude of the pressures applied at the
transducer sites. A mirror surface is provided at the distal tip of the
optical fiber so that the light reflected therefrom is again modulated at
the transducers as the light returns to the proximal end of the optical
fiber. To assist in measuring pressure relative to atmospheric pressure,
the catheter is vented, as with an aperture 14 in the wall of the catheter
at a location near the proximal end where it is exterior to the patient.
In general, it is contemplated that for each embodiment herein, there will
be provided a suitable light source 20 which transmits light into the
proximal end of the optical fiber 12 so that the light may be modulated in
dependence upon the pressure applied to each of the transducers T.sub.A,
T.sub.B and T.sub.C. The input light may first pass through a beam
splitter 22 which passes a portion of the light into the proximal end of
the optical fiber 12 and directs the remaining light in an upward
direction. Light that has been modulated and reflected from the distal end
of the catheter is returned to the proximal end of the optical fiber 12
and is passed to the beam splitter 22 and a portion of this modulated
light is then directed downwardly to an optical detector circuit 24. As
will be described with respect to each embodiment, the detector circuitry
operates to determine from the modulated light the values of the pressures
P.sub.A, P.sub.B and P.sub.C acting at the monitored sites A, B and C.
This information may then be displayed as with the use of a conventional
chart recorder 26 and/or displayed as with an oscilloscope 28. Having now
provided a general description of one application of the invention,
attention is directed to the specific description of each of the
embodiments herein as presented below.
Reference is now made to FIG. 2 which presents an enlarged sectional view
of the distal end of catheter 10 and showing pressure transducers T.sub.A,
T.sub.B and T.sub.C. As seen, the catheter 10 is a single lumen, thin wall
catheter, such as that provided by Cordis Corporation, and known as Cordis
FR5 Thin Wall 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 12 carried within the single lumen of the catheter
preferably takes the form of a cladded multimode optical fiber. This fiber
has a core 30 of a fluoropolymer of a diameter on the order of 400 micra.
The core 30 is covered throughout essentially all of its length with
cladding 32 constructed of an acrylic material having a thickness on the
order of 16 micra. Surrounding the cladding 32 are Kevlar reinforcing
strands 34 for purposes of strengthening the optical fiber 30. The Kevlar
strands 34 are, in turn, covered with a layer of black Hytrel 36. Optical
fibers, such as fiber 30, are commercially available. Light passing
through the optical fiber 30 of wavelength greater than 750 nanometers is
passed by filter F suitably mounted, as by bonding, to an end hole 38 at
the distal end of the catheter. Light of shorter wavelength is reflected
by the filter.
At the locations for each of the pressure transducers T.sub.A, T.sub.B and
T.sub.C, the cladding is removed. At each location there are provided four
side ports 40, 42, 44, and 46 spaced in an annular array equidistant from
each other, as is best shown in FIG. 3, which is a cross sectional view
taken along line 3--3 looking in the direction of the arrows in FIG. 2. On
each of the side ports, the cladding 32 and strands 34 and coating 36 are
removed and replaced with a sponge-like transducer insert 48. The outer
surface of each insert may, in turn, be coated with a protective membrane
50 which may be of a latex material and may be formed by applying viscous
liquid of latex over the insert filled side port in adjacent exterior
surface areas of the catheter and then air drying it. The membrane, while
covering the insert, will adhere and form a seal with the outer surface of
the catheter, but will not adhere to the sponge-like material forming the
transducer inserts.
In the embodiment shown in FIGS. 2 and 3, the inner surface of each
transducer insert faces a portion of the uncladded surface of the optical
core 30. Intermediate the insert and the uncladded core 30, there is
provided an optical coating defining a filter. These filters are
illustrated and identified as filters 52A, 52B and 52C.
The filters 52A, 52B and 52C are standard coatings with each filter having
a different functional relationship between index of refraction and
wavelength. Thus, these filters are so chosen that each will partially
refract a different waveband and reflect all other wavebands. This will be
discussed in greater detail hereinafter.
In the construction of the embodiment as shown in FIG. 2, the cladding is
removed at the locations for transducers T.sub.A, T.sub.B and T.sub.C.
This may be accomplished in a controlled manner, as with the use of a
solvent, such as tetrahydrofuran, so that the removal takes place only at
desired locations. The transducer inserts 48 are constructed of a
sponge-like material, such as polyurethane foam. This may take the form of
hypol foamable hydrophilic polyurethane polymer which may be obtained from
the Organic Chemicals Division of the W. R. Grace & Company. This is a
porous material and includes interconnecting pores. The insert may be held
in place by an interference fit.
Reference is now made to FIG. 4 which is an enlarged sectional view showing
a portion of the length of the uncladded optical fiber core 30 in
engagement with a transducer insert 48. The transducer insert is made of a
sponge-like material and has interconnecting pores 60. The interior
surface 62 of the transducer insert is irregular in shape and makes
intermittent surface contact with the surface 64 of the uncladded core 30,
such as at locations 66 and 68 separated by an air pocket 70. The air
pockets 70 are vented to the atmosphere by way of pores 60 and the annular
space surrounding the cladded core within the lumen of the catheter 10 and
which leads to the aperture 14 located near the proximal end of the
catheter. This, then, provides the basis for a pressure differential with
exterior applied pressure. As the pressure P increases, the interior
surface 62 of the insert will move toward the uncladded surface 64, as
indicated by the dotted lines 62', so as to increase the surface area
contact with the uncladded surface 64. Likewise, as the pressure is
removed, the sponge-like material, being resilient, will return to that as
indicated by the solid line 62 and make less surface area contact with the
uncladded surface 64. Pressure less than atmospheric will cause the
surface 62 to move radially away from the core, thus reducing contact
area. These variations in surface area contact between the transducer
insert 48 and the uncladded surface of the optical fiber core with
variations in pressure modulate the intensity of light traveling through
the optical fiber. At this point, it is to be noted that the index of
refraction n is different for the various materials employed. Thus, the
index of refraction n for the fiber core 30 is on the order of 1.5 and for
the surrounding air within the air pockets 60 and in the lumen, as vented
to the atmosphere, is on the order of 1.0. The cladding 32 exhibits an
index of refraction slightly less than that of core 30. However, light to
be transmitted through filters 52 and be absorbed or refracted by the
sponge inserts 48, the filters 52 must have an index of refraction greater
than that of cladding 32 and, in turn, the inserts 48 must have an index
of refraction greater than that of the filters so as to refract light that
is passed by the filters.
Each of the filters 52A, 52B and 52C pass light within a particular
waveband and reflect the remaining light. Thus, for example, filter 52A
reflects light within a waveband containing wavelengths W.sub.1 and
W.sub.2 while passing light within a waveband containing light of
wavelength W.sub.3. This is illustrated in FIGS. 5A and 6A. Similarly,
filter 52B passes light only within a waveband containing light in
wavelength W.sub.2, but reflects all remaining light, and this is
illustrated in FIGS. 5B and 6B. Also, filter 52C passes light in a
waveband containing wavelength W.sub.1 while reflecting all remaining
light, and this is illustrated in FIGS. 5C and 6C.
In this embodiment, the light source emits a broad band of light. A
filament lamp or an arc lamp or other wide band light source may be
employed as the light source 20. This light is passed by a beam splitter
22 and focused, as with a lens 74, into the proximal end of the optical
fiber 12. The light that travels through the core 30 and which strikes the
core-air interface (see FIG. 4) will be totally internally reflected.
However, the light that strikes the core-sponge interface will be
partially refracted and partially reflected. The amount of light that is
refracted and thereby absorbed will be a function of the surface contact
area. Thus, light that is traveling from the proximal end to the distal
end of the catheter will pass through the transducer area and a portion of
the light will be refracted in dependence upon the pressure P. The light
that is internally reflected will be reflected back by the filter F at the
distal end of the optical fiber. This reflected back light will also be
attenuated as it passes the transducer area as it travels back toward the
proximal end of the catheter. The intensity of light returning at the
proximal end of the catheter will vary inversely with the pressure applied
to the transducers.
At transducer T.sub.A, only light that has been passed by filter 52A will
be refracted and, hence, attenuated by the transducer insert 48. This
light will be at wavelength W.sub.3 and the remaining light is reflected
by the filter 52A. Consequently, it is the light which exits from the
proximal end of the optical fiber 12 at wavelength W.sub.3 that includes
the intelligence representing the pressure applied at transducer T.sub.A.
In similar fashion, it is only the light exiting from the proximal end of
the optical fiber at wavelength W.sub.2 that includes the intelligence
relative to the pressure applied at the transducer T.sub.B. Also, it is
only the light exiting from the proximal end of the optical fiber at
wavelength W.sub.1 that includes the intelligence as to the pressure at
the transducer T.sub.C.
Referring now to FIG. 7, it is seen that as the light exits from the
proximal end of the optical fiber 12, it is applied by way of lens 74 to
the beam splitter 22 and a portion is then directed in a downward
direction. A first beam splitter 76 intercepts this light and directs a
portion of it through a filter 78 that passes only light at wavelength
W.sub.1. This is detected by optical-electrical detector 80, which
converts intelligence into an electric signal to drive a suitable meter 82
to provide an output indicative of the pressure at the transducer T.sub.C.
As the pressure at transducer T.sub.C increases, there will be a reduction
in the amount of light returned to the proximal end at wavelength W.sub.1.
This is detected by detector 80 and displayed as with meter 82.
In a similar fashion, the light that is passed by the beam splitter 76
strikes a second beam splitter 84 and light reflected therefrom is passed
through a filter 86 which passes light only at wavelength W.sub.2.
Detector 88 converts this information into an electrical signal which is
supplied to a suitable meter 90. This circuitry provides an output
indication representative of the pressure at transducer T.sub.B. Also,
light passing through the beam splitter 84 will strike an additional beam
splitter 92 causing light reflected therefrom to be applied to a filter 94
which passes only light at wavelength W.sub.3. This is detected by a
suitable detector 96 which supplies an electrical signal to meter 98 for
displaying an output signal representative of the pressure applied at
transducer T.sub.A.
The light from the light source 20 in FIG. 7 includes light in the red and
infrared light regions, i.e., from at least 800 nanometers through 950
nanometers. This longer wavelength light through the filter F at the
distal end of the catheter and is reflected by blood back into the
catheter. As previously discussed, two peak wavelengths are of importance,
namely, 805 nanometers and 930 namometers. The first may be considered as
wavelength W.sub.4 and the second as wavelength W.sub.5.
Referring now to FIG. 7, light exiting from the proximal end of the optical
fiber 12 is reflected by splitter 22 and a portion of the light passes
through beam splitters 76, 84 and 92. Light passing through beam splitter
92 strikes another beam splitter 79 and a portion of the light is directed
to a filter 81. This filter is selected to pass only light at wavelength
W.sub.4 and this is passed to a detector 83 which converts the optical
intelligence into an electrical signal having a magnitude representative
of the magnitude of light at wavelength W.sub.4. This electrical signal is
applied as one input to a ratio circuit 91.
In a similar fashion, light passing through splitter 79 strikes a mirror 85
and the reflected light is directed to a filter 87. This filter passes
only light at wavelength W.sub.5 and this is passed to a detector 89 that
converts the optical intelligence into an electrical signal having a
magnitude representative of the amount of light at this wavelength. This
electrical signal is supplied as a second input to the ratio circuit 91.
This ratio circuit provides an output signal corresponding to the ratio of
light intensity at wavelength W.sub.4 to that at W.sub.5 and this is
supplied to a meter 93 for providing a suitable output indication and
which, in turn, provides an indication of the percentage of oxygen
saturation of the blood.
Reference is now made to a second embodiment of the invention which is
illustrated in FIGS. 8, 9, 10, 11 and 12. This embodiment is quite similar
to that described thus far and, consequently, like components are
identified with like character references and only the differences over
the previous embodiment will be described in detail herein.
In this embodiment, no filters are employed. Instead, each of the
transducer inserts 48A', 48B' and 48C' is doped with a different
fluorescent dye. Each insert is covered on its exterior surface with a
membrane, such as membranes 50 constructed in the same manner as that
discussed herebefore with respect to membranes 50 in FIGS. 2 and 3. The
fluorescent dye doped transducer inserts have been doped such that each
fluoresces in a different waveband.
Reference is also made to FIGS. 10, 11 and 12. In this embodiment, light
transmitted into the optical fiber 12 includes light at wavelengths
capable of exciting the fluorescent doped inserts 48A', 48B' and 48C', but
none of this excitation light is at any of the wavelengths at which these
inserts fluoresce. For this reason, a filter 100 is employed for blocking
light in the emission waveband of from approximately 350 to 700
nanometers. This filtered light is then passed by the beam splitter 22 and
focused by lens 74 into the proximal end of the optical fiber 12. Within
the catheter, the excitation light will be transmitted by core 30. This
excitation light is at the excitation wavelengths from 300-350 nanometers
and does not include light at a wavelength corresponding to that at which
the fluorescent doped transducers fluoresce. In the example given, the
excitation wavelengths may be considered a waveband which includes
wavelengths from 300-350 nanometers, as is illustrated in FIGS. 10A, 10B
and 10C. The transducer inserts will fluoresce at higher wavelengths with
that of transducer insert 48C' having an emission wavelength of W.sub.1 '
on the order of 400 nanometers. The insert 48B' will have an emission
wavelength W.sub.2 ' which will be on the order of 500 nanometers, and
transducer 48A' will have an emission wavelength W.sub.3 ' on the order of
600 nanometers.
Thus, light passing through the optical fiber 10 within the core 30 will be
refracted by the transducers 48A', 48B' and 48C' in accordance with the
pressure exerted at each transducer. The greater the applied pressure, the
greater will be the refraction of light. Consequently, the greater the
pressure, then, the greater will be the amplitude or amount of energy
emission at wavelengths W.sub.1 ', W.sub.2 ' and W.sub.3 '. Light exiting
from the proximal end of the optical fiber 12 will contain light at each
of these wavelengths W.sub.1 ', W.sub.2 ' and W.sub.3 '. This light is
reflected in part by the beam splitter 22 (FIG. 12) and directed
downwardly to the beam splitter 76. A portion of the light striking beam
splitter 76 is reflected through a filter 78' which passes only light
centered at the wavelength W.sub.1 ' indicative of the amount of pressure
in transducer T.sub.C '. This is detected by detector 80 and an electrical
signal representative of the pressure level in tranducer T.sub.C ' is then
displayed as with meter 82. Similarly, a portion of tne light passed
through the beam splitter 76 to a beam splitter 84 which reflects a
portion of the light to a filter 86' which passes only light centered
about the wavelength W.sub.2 '. This is indicative of the amount of
pressure at transducer T.sub.B ' and this is converted into an electrical
signal by detector 88 with the pressure reading then being displayed as
with meter 90.
Also, a portion of the light is passed through a beam splitter 84 and is
reflected by beam splitter 92 to a filter 94' which passes only light
centered about wavelength W.sub.3 '. This is indicative of the amount of
pressure at transducer T.sub.A ' and this is converted into an electrical
signal by detector 96 and the electrical output is supplied to meter 98
for providing a visual readout. This excitation light is diminished
somewhat in intensity at each transducer in accordance with pressure.
Thus, a more accurate reading could be obtained by scaling up each
successive reading by an amount related to the other rea | | |
