Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2000-11-20
2003-12-16
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S310000
Reexamination Certificate
active
06665551
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a current driving system of a light emitting diode (LED) applied to a measurement apparatus for measuring the concentration of light absorbing material in a living tissue, the measurement apparatus having a main body for calculating the concentration of light absorbing material in a living tissue.
2. Related art
As a common example of the measurement apparatus for measuring the concentration of light absorbing material in a living tissue, there is conventionally provided a pulse oximeter by which the oxygen saturation in arterial blood is measured. This pulse oximeter is known as a measurement apparatus by which the oxygen saturation in arterial blood (SpO
2
) can be continuously measured non-invasively into an artery by utilizing a variation of blood volume in the artery caused by pulsation.
In this case, the oxygen saturation (SpO
2
) represents a ratio (%) of hemoglobin contained in blood which is combined with oxygen. Hemoglobin combined with oxygen is referred to as oxyhemoglobin (HbO
2
), and hemoglobin not combined with oxygen is referred to as deoxyhemoglobin (Hb).
However, red of blood is the color of hemoglobin. Therefore, oxyhemoglobin absorbs less red light, and deoxyhemoglobin absorbs much red light. Accordingly, arterial blood containing much oxygen absorbs less red light because a ratio of oxyhemoglobin is high. Therefore, arterial blood containing much oxygen appears brightly red. On the other hand, venous blood in which oxygen has already been consumed appears dark because it contains much deoxyhemoglobin. As described above, the color of blood reflects the degree of combination of hemoglobin with oxygen, that is, the color of blood reflects the oxygen saturation.
When the pulse oximeter is used, it is possible to obtain only information of arterial blood by using light electric pulses. According to the pulse oximeter, measurement is made in such a manner that a relatively thin portion of a human body such as a finger is irradiated with light and an intensity of transmitted light is measured, that is, light electric pulses are recorded. In this case, the light absorbing characteristic of blood is changed by the oxygen saturation. Even in the case of the pulsation of the same variation of blood volume, the obtained pulse wave amplitude is different according to the oxygen saturation of the blood.
As shown in
FIG. 16
, in general, the pulse oximeter includes: a probe
10
attached to a patient; and a measurement apparatus body
20
. The probe
10
is composed of a light emitting section
12
and a light receiving section
14
. A portion of a human body to be measured such as a finger, that is, a living tissue is interposed between the light emitting section
12
and the light receiving section
14
. In the light emitting section
12
, there are provided two light emitting diodes (LED
1
and LED
2
). One is a light emitting diode LED
1
, the wave length of the emitted light of which is 660 nm (red light), and the other is a light emitting diode LED
2
, the wave length of the emitted light of which is 940 nm (infrared light). On the other hand, a photo-diode is used for the light receiving section
14
.
The above two light emitting diodes LED
1
and LED
2
alternately emit light when they are alternately energized by the timing generation circuit
22
, which is provided in the measurement apparatus body
20
via the light emitting diode driving circuit
23
at a predetermined timed relation.
As described above, rays of light are outputted from the respective light emitting diodes LED
1
and LED
2
in the light emitting section
12
and transmitted through a living tissue such as a finger
16
. Then the rays of light arrive at the light receiving section
14
. Intensities of these rays of light, the wave lengths of which are 660 nm and 940 nm, are converted into currents by the photo-diodes. The thus obtained currents are converted into voltages by the current/voltage converter
24
arranged in the measurement apparatus body
20
. At the same time, these signals are separated into transmitted light signals of the respective wave lengths by the demodulator
25
.
Then, the pulse wave components (&Dgr;A660, &Dgr;A940) of each absorbance are taken out from the two transmitted light signals, which have been obtained by the demodulator
25
, by the pulse wave component detectors
26
a
,
26
b
of each wave length. Ratio &PHgr; of absorbance (=&Dgr;A660/&Dgr;A940) is calculated by the absorbance ratio calculator
27
. Further, the oxygen saturation S [=f(&PHgr;)] is converted by the oxygen saturation converter
28
.
However, the pulse oximeter has come into wide use as a vital sign signal monitor, because it is possible for the pulse oximeter to make a continuous non-invasive measurement and further it is unnecessary to make a calibration by principle when the pulse oximeter is used, that is, the pulse oximeter meets the essential requirements necessary for the monitor to be used for monitoring a condition of a patient. Accordingly, various pulse oximeters, in which the apparatus arrangement shown in
FIG. 14
is used, are manufactured and sold by a large number of manufacturers nowadays.
For example, as a lead connection system for connecting the probe
10
with the measurement apparatus body
20
in the conventional pulse oximeter in which two light emitting diodes are used, there are provided two lead connection systems. One is a three line system shown in
FIG. 17
, and the other is a two line system shown in FIG.
18
.
As shown in
FIG. 17
, in the three line connection system, two light emitting diodes LED
1
and LED
2
are connected in parallel to each other by the common line LED-COMMON and two driving lines LED-DRV
1
, LED-DRV
2
. As shown in
FIG. 18
, in the two line connection system, two light emitting diodes LED
1
and LED
2
are connected in reverse-parallel to each other by two driving lines LED-DRV
1
, LED-DRV
2
.
As a variation of the lead connection system, there is provided a lead connection system in which four light emitting diodes LED
1
to LED
4
are connected by the three line system as shown in FIG.
19
. Also, there is provided a lead connection system in which three light emitting diodes LED
1
to LED
3
are connected by the three line system as shown in FIG.
20
. In the lead connection system shown in
FIG. 20
, one of the light emitting diodes incorporated into the lead connection system shown in
FIG. 19
is omitted.
In this case, for example, in the pulse oximeter in which the three line type lead connection system is used, it is preferable that the three line type probe and the two line type probe can be connected with one measurement apparatus body being compatible with each other and the light emitting diode of each probe can be appropriately driven. However, although the light emitting diode in the three line type probe and the light emitting diode in the two line type probe respectively have two driving lines LED-DRV
1
and LED-DRV
2
, their electrical connection system are different from each other. Therefore, the three line type probe and the two line type probe are not compatible with each other, that is, it is impossible to appropriately drive the light emitting diode of each lead connection system with compatibility.
SUMMARY OF INVENTION
It is an object of the present invention to provide a current driving system of a light emitting diode provided in that: only when a simple additional circuit is arranged in a light emitting diode driving circuit, various probes can be used being made compatible with each other when they are connected with the measurement apparatus body without changing the basic structure of the circuit of the measurement apparatus body and without providing a redundant connection means and without being restricted by the lead connection system of the light emitting diode on the probe side.
In order to accomplish the above objects, the present invention provides a current driving system of a l
Kremer Matthew
Nihon Kohden Corporation
Sughrue & Mion, PLLC
Winakur Eric F.
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