Interference No. 103,197
3. In Vivo Spectrophotometry
Whereas reflection and transmission
spectrophotometry of specimens in vitro are well
established [end note omitted], these techniques are not
practical when a specimen is in a remote location and in
a dynamic state. Under such conditions, if the specimen
is located in a normal channel in the body, a flexible
fiber bundle can be used to transmit light from an
external source to the specimen and another bundle used
to return the signal from the specimen to an appropriate
detector. When the specimen is located subcutaneously,
then it is possible to use a fiber optics hypodermic
probe in which a rigid fiber bundle is used to illuminate
the specimen as well as to return the signal to the
detector for processing. The mode of illumination would
be dependent on whether the reflectance, transmittance,
or fluorescence property of the specimen is to be
measured. The distal end configuration is governed by
the optical conditions to which a tissue is most
sensitive. [Our emphasis.]
. . . .
An example of a remote spectrophotometer that has
received considerable attention is that used in the field
of cardiac and vascular oximetry [end notes omitted].
One of the principal measurements required by
cardiologists is the oxy-hemoglobin concentration of the
blood in vitro. A method commonly used for this purpose
is one in which a flexible hollow catheter is inserted
into the cardiac chamber and a sample of blood is removed
for chemical analysis by the Van Slyke method or the
spectrophotometric method. Obviously, this procedure
results in considerable delay and is not amenable to
measurements of the spatial or temporal variations of
oxyhemoglobin concentration in various regions and in a
dynamic state.
Figure 7.18 shows a diagram of the in vivo
spectrophotometer system for cardiac oximetry and three
different optical configurations for the distal end. In
this device, the light is condensed onto a fiber bundle
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