Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2000-11-27
2003-04-08
Doerrler, William C. (Department: 3744)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S344000
Reexamination Certificate
active
06546267
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a biological sensor for non-invasively measuring a concentration of a material in a living body by the utilization of a plurality of lights having different wavelengths the light absorbing characteristics of which in the living body are different from one another. More particularly, the invention relates to a biological sensor which may easily be attached to the living body with high accuracy in measurement.
2. Related Art
The technique on the pulse oximeter is known for the technique for non-invasively and continuously measuring a concentration of a material in a living body by the utilization of different light absorbing characteristics of a plurality of wavelengths of lights. The measuring technique calculates an oxidation difference of hemoglobin in a blood of a living body by using a ratio of intensities of two wavelengths of lights whose light absorbing characteristics are different. It is known that the technique using a plurality of wavelengths of lights may also be available for calculating another material in the living body. An example of this is a technique to calculate a concentration of indo-cyanine green (ICG) in a blood by using three wavelengths of lights. A pulse oximeter using two wavelengths will be discussed, for explanation, in the description to follow. Also in the measurement using three or more wavelengths, however, the same thing is correspondingly applied to the basic technique, mainly the detection technique on the probe, a kind of biological sensors.
The pulse oximeter has rapidly been prevailed in the medical field in the world since the principle of the pulse oximeter disclosed in JP-B-53-26437. Presently, the pulse oximeter is one of the parameters indispensable for monitoring a condition of a patient, and it is a fairly general measuring item. The advantageous feature of the pulse oximeter resides in that it is able to measure an oxygen saturation in an arterial blood by a non-invasive measuring method.
The principle of the pulse oximeter is based on the fact that hemoglobin contained in the red blood cell in the blood changes its color when it is combined with oxygen, and hence, the arterial oxygen saturation can be obtained by measuring the light absorbing characteristic of the hemoglobin. Actually, one and the same sample being in the same state is measured by using two wavelengths of lights which are different in light absorbency, in the same condition. In this case, a ratio of the measurement results corresponds to the oxygen saturation in one-to-one correspondence. Lights having two wavelengths of about 660 nm and about 900 nm are used for the pulse oximeter measurement. A change of the light absorbancy of the light of 660 nm, caused by the oxygen saturation of the hemoglobin, is much larger than that of the light of 900 nm.
Specifically, as shown in
FIG. 7
, when a thickness D of a sample is changed by &Dgr;D by a pulsation, and transmitted light I is attenuated by &Dgr;I, a change &Dgr;A of the light absorbancy is given by
&Dgr;
A
≡log[
I
/(
I−&Dgr;I
)]=
EC&Dgr;D
(1)
Changes &Dgr;A
1
and &Dgr;A
2
of the light absorbancy (where
1
and
2
affixed to letters A indicate 660 nm and 900 nm) are measured and a ratio &PHgr; of them is calculated, then we have
&PHgr;≡&Dgr;A
1
/&Dgr;
A
2
=
E
1
/
E
2
(2)
Thus, we have the light absorbancy ratio.
FIG. 8
shows in block and schematic form a basic construction of a pulse oximeter. A light source consists of two light emitting diodes (LEDs), and those LEDs alternately and rapidly flicker when receiving a signal from an oscillator (OSC). Light passes through a living tissue and reaches a photo diode (PD) which in turn converts an intensity of transmitted light into a corresponding current. The current is converted into a voltage, amplified, and split according to two wavelengths by a multiplexer (MPX). As a result, electric pulse signals of each wavelengths are obtained. Those pulse signals are logarithmically converted and the pulsating components of the signals are extracted through a band-pass filter (BPF). Each extracted one is a pulsating component &Dgr;A of an attenuation of an object to be measured.
The pulsating component &Dgr;A is defined by
&Dgr;
A
≡log(
I
out/
I
)≈
AC/DC
(3)
&PHgr;≡&Dgr;
A
1
/&Dgr;
A
2
≈(
AC
1
/
DC
1
)/(
AC
2
/
DC
2
) (4)
In the above expressions, AC and DC are, respectively, an amplitude of the pulsating component and a stationary component of the transmitted light. Thus, &PHgr; as a ratio of the pulsating components of the lights of the two wavelengths can be obtained by using the division in place of the logarithmic process.
Finally, the oxygen saturation can be obtained by mathematically processing &PHgr; or by using a conversion table for the &PHgr;.
To cause the computer to compute an exact oxygen saturation, the conditions required at the measuring location of the measured object through which the lights are transmitted may be concluded from the principle of the pulse oximeter such that “the lights having the wavelengths to be detected must be transmitted through the same location and travel an equal distance, and further must be influenced by the same living tissue and blood”.
Let us consider the current measurement on the basis of the conditions required for the pulse oximeter “the lights having the wavelengths to be detected must be transmitted through the same location and travel an equal distance, and further must be influenced by the same living tissue and blood”.
In an early stage of a probe for the pulse oximeter, an incandescent light bulb was used as a light source, and optical filters corresponding to the wavelengths were provided at two light receiving portions, whereby information on the two wavelengths was obtained.
FIG. 9
shows an example of the early probe where an earlobe is used for an object to be measured.
In
FIG. 9
, an ear piece
2
forming an ear oximeter
1
is constructed with a light emitting portion
3
and a light receiving portion
4
, which are optically coupled to each other, and a holder
6
including an appropriate slide which supports those elements and is able to adjust a distance between them and a fixing mechanism
5
. A light emitting portion
3
contains a light source
7
therein, and a couple of photo transistors
8
and
9
are attached to the inside of the light receiving portion
4
. The photo transistors
8
and
9
receives lights of wavelengths 660 nm and 900 nm, respectively. The ear piece
2
interposes an earlobe
12
with cushions
10
and
11
attached to the opposed surfaces of the light emitting portion
3
and the light receiving portion
4
.
Thereafter, the LEDs are introduced into the probe, so that the probe size becomes small. This kind of probes as shown in
FIGS. 10 and 11
have been used. The probe is attached to a finger, and the light emitting portion and the light receiving portion are provided in the upper and lower attaching portions of the probe. Those light emitting and receiving portions are oppositely disposed, and a tissue is interposed between them. Light transmitted through the tissue is detected. This type of the probe will be referred to as a “transmit type” of probe.
Another probe is shown in FIG.
12
. As shown, a light emitting portion and a light receiving portion are secured onto a surface of a flexible member while being spaced a fixed distance (e.g., 10 mm). Lights scattered and reflected in the inner side of the fingertip or the like are measured. This type of the probe is referred to as a “reflection type” of probe.
The transmit type of the probe generally consists of a clip type of probe as shown in
FIGS. 10
an
11
, and a winding type of probe, which utilizes adhesion, as shown in
FIGS. 13 and 14
.
FIG. 14
is a cross sectional view showing a structure of the
FIG. 13
probe. In
FIGS. 13 and 14
, reference numeral
14
is a flexible tape member for holding the light emitting portion
Maeda Toru
Nakae Yoshinobu
Ozawa Hideo
Sugiura Keiichi
Todokoro Noriaki
Doerrler William C.
Nihon Kohden Corporation
Sughrue & Mion, PLLC
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