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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for detecting pulse waves and,
more particularly, to a pulse wave detection device which detects pulse
waves by transmitting ultrasound to an artery and by receiving reflected
ultrasound from the artery.
2. Description of the Related Art
Detection of pulse waves of blood flowing in arteries is being widely
performed in medical and health care environments. For such pulse wave
detection, the method of automatically and electronically determining the
pulse rate by using a pulse wave detection device is being widely
practiced, as is the method of detecting pulse waves by palpation for a
predetermined time period to determine the pulse rate.
Known devices capable of determining the pulse rate by electronically
detecting pulse waves are, for example, a device having a piezoelectric
element used as a sensor to determine the pulse rate in such a manner that
the piezoelectric element is positioned on an artery to detect changes in
the pressure of the outermost skin layer (displacements of the skin layer
due to the pressure) resulting from changes in the pressure in the artery,
and a device utilizing ultrasound to determine the pulse rate.
Pulse wave detection devices utilizing ultrasound include those utilizing
the Doppler effect of a flow of blood, e.g., one disclosed in Japanese
Patent Application Laid-Open No. Hei 1-214335 and one disclosed in U.S.
Pat. No. 4,086,916.
FIGS. 9(a) and 9(b) are diagrams showing changes in the frequency of
ultrasound according to the Doppler effect. When ultrasound, such as shown
in FIG. 9(a), having a frequency f0, is emitted from a body surface to an
artery, the emitted ultrasound is reflected by blood flowing in the
artery. The reflected sound is received by a receiving element to detect
changes in the frequency of the reflected sound. That is, during a heart
contraction period, the speed at which blood flows in the artery becomes
high and the frequency of the received sound, indicated by f1, becomes
higher (in region A) by the Doppler effect, as shown in FIG. 9(b).
Conversely, during a heart relaxation period, the blood flowing speed is
low and the frequency of the received sound is low (in region B) relative
to that in the region A.
As described above, a bloodstream in an artery, the speed of which changes
according to pulsation of the heart, is irradiated with ultrasound, and
pulse waves are detected by detecting changes in the frequency of
reflected ultrasound, thus enabling determination of the pulse rate, the
speed at which blood flows, etc.
To detect pulse waves from an artery at a wrist by the above-described
conventional method, a sensor is ordinarily positioned on the radial
artery because the existence of the radial artery is generally easily
recognizable; the position of the radial artery can be easily determined;
and the level of a pulse wave signal detected therefrom is comparatively
high.
However, the radial artery on which the sensor is placed is located close
to a wrist cord. Therefore, there is a possibility of the sensor being
lifted or shifted from the suitable position by a movement of the hand to
cause noise, which considerably affects the detection of pulse waves. For
this reason, a pulse wave detection error or failure can occur
comparatively and easily.
Also, while the facility with which the sensor is positioned is influenced
by the shape and the size of the sensor, it is difficult to position the
sensor on the some people's wrists. Accordingly, the pulse wave detection
performance depends on individual differences of wrists.
SUMMARY OF THE INVENTION
In view of the above-described problems of the conventional art, an object
of the present invention is to provide a pulse wave detection device
capable of accurately detecting pulse waves without being influenced by
noise caused by a movement of the hand or the like.
Another object of the present invention is to provide a pulse wave
detection device capable of performing pulse wave detection with
reliability regardless individual differences in wrists.
To achieve the above-described objects, according to one aspect of the
present invention, there is provided a device for detecting pulse waves,
comprising a first sensor having first emitting means for emitting
ultrasound toward the radial artery and first receiving means for
receiving ultrasound emitted from the first emitting means and reflected
by blood flowing in the radial artery, a second sensor having second
emitting means for emitting ultrasound toward the ulnar artery and second
receiving means for receiving ultrasound emitted from the second emitting
means and reflected by blood flowing in the ulnar artery, pulse wave
information acquisition means for acquiring pulse wave information on
pulse waves from the ultrasound received by one of the first receiving
means and the second receiving means, and output means for outputting the
pulse wave information acquired by the pulse wave information acquisition
means.
Thus, two sensors: the first sensor and the second sensor are provided.
Therefore, even if the operation of one of the first and second sensors
results in a detection error or detection failure, detection can be
performed by using the other of the first and second sensors. For example,
if the first sensor is unable to perform detection, the second sensor can
be operated to perform detection, thus reducing occurrence of a detection
error or failure.
Storage means for storing obtained pulse wave information may be provided.
Pulse wave information stored in the storage means can be output
afterwards. If pulse wave information obtained as a result of detection
during a predetermined period of time is stored, the information can be
output to, for example, an external apparatus for a medical diagnosis or
the like to be utilized for a medical diagnosis of a user's daily
condition.
In the pulse wave detection device according to the present invention,
effectiveness determination means may be provided to determine whether the
ultrasound received by one of the first receiving means and the second
receiving means is effective in detecting pulse wave information. The
pulse wave information acquisition means acquires pulse wave information
on pulse waves from the ultrasound recognized as effective by the
effectiveness determination means. The effectiveness determination means
determines the effectiveness of the pulse wave information signals to
enable control for selectively acquiring pulse wave information from one
of the first and second sensors, thereby reducing occurrence of a
detection error or failure.
In the pulse wave detection device according to the present invention,
switching means for selectively driving the first sensor or the second
sensor may be provided. The switching means selects driving of one of the
first and second sensors if it is determined that the ultrasound received
by one of the first receiving means and the second receiving means during
driving is ineffective. Also, in the pulse wave detection device according
to the present invention, the switching means may select driving of the
first sensor after a lapse of a predetermined period of time from the time
when the switching means selected driving of the second sensor. If this
selective drive enabled by the switching means is performed, there is no
need to emit ultrasound so that both the first and second sensors always
receive ultrasound. Ultrasound may be emitted to be received by only one
of the two sensors selectively used, and the consumption of electricity
can be reduced.
In the pulse wave detection device according to the present invention,
indication means may also be provided. If the effectiveness determination
means determines that both the ultrasounds received by the first receiving
means and the second receiving means are ineffective, the indication means
indicates this condition. This indication means enables the user using the
pulse wave detection device to know whether pulse waves are being
accurately detected. If the pulse wave detection device is unable to
detect pulse waves due to, for example, a failure to maintain the device
in the correct position, the user may press a reset button or turn off the
power and then turn on the power again, thereby accurately redoing pulse
wave detection.
The pulse wave detection device according to the present invention
comprises a first sensor having a first transmitter to transmit ultrasound
toward the radial artery, and a first receiver to receive ultrasound
transmitted from said first transmitter and reflected by blood flowing in
the radial artery, a second sensor having a second transmitter to transmit
ultrasound toward the ulnar artery, and a second receiver to receive
ultrasound transmitted from said second transmitter and reflected by blood
flowing in the ulnar artery, a pulse wave information acquisition circuit
to acquire pulse wave information on pulse waves from the ultrasound
received by one of said first receiver and said second receiver, and an
output circuit to output the pulse wave information acquired by said pulse
wave information acquisition circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIGS. 1(a)-1(b) are a diagram showing the configuration of a pulse wave
detection device which represents a first embodiment of the present
invention;
FIGS. 2(a) through 2(d) are diagrams showing waveforms output from the
essential components of the pulse wave detection device shown in FIG. 1;
FIGS. 3(a) through 3(c) are diagrams showing a state where pulse waves are
detected by a pulse wave detection device incorporated in a watch
according to the first embodiment;
FIGS. 4(a) and 4(b) are diagrams showing an external appearance of the
pulse wave detection device (watch) shown in FIGS. 3(a) through 3(c);
FIG. 5 is a diagram for explaining the principle of changing arteries from
which pulse waves are detected;
FIG. 6 is a flowchart showing the process performed by a signal intensity
comparison section;
FIG. 7 is a diagram showing the configuration of a pulse wave detection
device which represents a second embodiment of the present invention;
FIGS. 8(a) and 8(b) are diagrams showing examples of modification of
sensors; and
FIGS. 9(a) and 9(b) are diagrams showing changes in the frequency of
ultrasound by the Doppler effect.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described in detail
with reference to FIGS. 1 through 8.
(1) Outline of Embodiments
A pulse wave detection device according to embodiments of the present
invention has two sensors 19 and 19' for emitting ultrasound f0 toward
arteries and for, determining pulse rates as pulse wave information from
reflected sound f1. The two sensors 19 and 19' are positioned inside a
belt of a watch such that they can be positioned on a radial artery 2 and
an ulnar artery 3, respectively.
The sensor 19 on the radial artery 2 is used as a main sensor while the
sensor 19' on the ulnar artery 3 is used as an auxiliary sensor.
Ordinarily, the sensor 19 is used to detect the pulse rate. The sensor 19
has a receiving element 21 which receives reflected sound f1. If the
amplitude of reflected wave f1A' obtained as a result of predetermined
processing of the received sound signal is not between two threshold
values ATh1 and ATh2, it is determined that detection of the pulse rate
from the radial artery 2 is too difficult to perform, and the pulse rate
is detected from the ulnar artery 3 by using the auxiliary sensor 19'.
The main sensor 19 and the auxiliary sensor 19' are switched by switch
circuits 10 and 20 according to selection signals supplied from a control
unit 70.
The period of time for detection by the auxiliary sensor 19' is limited to
a predetermined fixed time period (e.g., one minute). After a lapse of
this time period, the sensor 19 is selected in place of the sensor 19'. If
detection with the sensor 19 is possible, detection with the main sensor
19 is continued. If detection with the sensor 19 is difficult even after
the lapse of the predetermined time period, the sensor 19' is again
switched on in place of the sensor 19. If detection with the sensor 19' is
also difficult, a user is informed of this state by a buzzer.
If it is difficult to determine the pulse rate (pulsation information) from
the radial artery 2, the pulse rate (pulse information) is determined from
the ulnar artery 3. In this manner, occurrence of a pulse wave detection
error or failure is reduced and detection is performed with improved
accuracy.
(2) Details of Embodiments
FIGS. 1(a)-1(b) are a diagram showing the configuration of a pulse wave
detection device which represents a first embodiment of the present
invention.
As shown in FIGS. 1(a)-1(b), the pulse wave detection device has a sensor
19 (first sensor) for detecting pulse waves from the radial artery 2 and a
sensor 19, (second sensor) for detecting pulse waves from the ulnar artery
3. The sensor 19 has an emitting element 11 (first emitting means) for
emitting ultrasound f0A toward the radial artery 2, and a receiving
element 21 (first receiving means) for receiving reflected sound f1A from
the radial artery 2. The sensor 19' has an emitting element 11' (second
emitting means) for emitting ultrasound f0B toward the ulnar artery 3, and
a receiving element 21' (second receiving means) for receiving reflected
sound f1B from the ulnar artery 3.
The pulse wave detection device has an emitting system constituted by a
switch circuit 10 for selecting one of the emitting elements 11 and 11' to
emit ultrasound f0 (generically referred to in place of f0A or f0B,
hereinafter) according to a selection signal A or B supplied from a
control unit 70, a high-frequency oscillator circuit 13 for generating a
high-frequency signal having a frequency of 10 MHz, and a drive circuit 12
for amplifying the high-frequency signal supplied from the high-frequency
oscillator circuit 13 so that the signal has a power at an output level,
and for emitting ultrasound f0 from the emitting element 11 or 11'
selected by the switch circuit 10.
The pulse wave detection device also has a receiving system constituted by
a switch circuit 20 for selecting one of the receiving elements 21 and 21'
to receive reflected sound f1 according to the selection signal A or B, a
high-frequency amplifier circuit 31, a frequency to voltage (F/V)
converter circuit 32, a detector circuit 33, a sample and hold circuit 34,
an amplifier circuit 35, a filter circuit 36, and analog to digital (A/D)
converter circuit 37, and a low-frequency oscillator circuit 51 for
generating a signal oscillating at a frequency of 32 kHz. The pulse wave
detection device also has the control unit 70.
To the control unit 70, a display panel 42 which functions as an output
means to display the pulse rate thereon, and a buzzer 43 are connected. A
personal computer and an external apparatus 44 of any kind, such as a
diagnosis apparatus for a medical treatment, can also be connected to the
control unit 70.
Ultrasound f0A emitted from the emitting element 11 is reflected by blood
flowing in the radial artery 2. Simultaneously, ultrasound f0A is
frequency-modulated by the flow of blood. Reflected sound f1A obtained is
received by the receiving element 21, and a signal representing the
received reflected sound f1A is supplied to the switch circuit 20.
Similarly, ultrasound f0B emitted from the emitting element 11' is
reflected and frequency-modulated by blood flowing in the ulnar artery 3.
Reflected sound f1B thus obtained is received by the receiving element
21', and a signal representing the received reflected sound f1B is
supplied to the switch circuit 20.
The switch circuit 20 supplies one of the two supplied signals for
reflected sounds f1A and f1B to the high-frequency amplifier circuit 31
according to selection control SA or SB.
The high-frequency amplifier circuit 31 is a circuit for amplifying the
supplied signal for reflected sound f1 (generically referred to in place
of f1A or f1B, hereinafter) and for supplying the amplified signal to the
F/V converter circuit 32.
The F/V converter circuit 32 outputs a voltage in accordance with the
frequency value by utilizing the change in the voltage gain according to
the frequency value, and supplies the voltage to the detector circuit 33.
The detector circuit 34 outputs a voltage corresponding to the envelope of
the supplied signal by amplitude detection, and supplies the voltage to
the sample and hold circuit 34.
The sample and hold circuit 34 is a circuit for sampling the signal from
the detector circuit 33 and for holding sampled signal values.
The filter circuit 36 is a circuit for removing noise from the signal after
amplification.
The A/D conversion circuit 37 is a circuit for converting the noise-removed
signal into a digital signal, and for supplying the digital signal to the
control unit 70 as a processed reflected wave f1' (fundamental signal)
used as a basis for detection of pulse wave information.
The control unit 70 is constituted of a microcomputer system whose main
components are a central processing unit (CPU), a read only memory (ROM),
and a random access memory (RAM), and also has a display element drive
section 71, a time measurement section 72, a storage section 73, a pulse
rate computation section 74, and a signal intensity comparison section 75.
The signal intensity comparison section 75 functions as an effectiveness
determination means, and has threshold values Th1 and Th2 on the amplitude
(generically referred to in place of threshold values ATh1 and ATh2 for
comparison with the processed reflected wave f1A' and threshold values
BTh1 and BTh2 for comparison with the processed reflected wave f1B').
The signal intensity comparison section 75 compares the amplitude of
processed reflected wave f1' with the two threshold values Th1 and Th2 to
determine the effectiveness of the processed reflected wave f1' supplied
from the A/D conversion circuit 37. That is, if the amplitude of the
processed reflected wave f1' is not between the threshold values Th1 and
Th2, the signal intensity comparison section 75 determines that detection
of pulse wave information (pulse rate) from the supplied processed
reflected wave f1A' or f1B' is difficult (the signal is ineffective).
In the case where the signal intensity comparison section 75 determines
that the processed reflected wave f1A' is ineffective, the control unit 70
supplies the selection signal B to the switch circuits 10 and 20.
Conversely, in the case where the signal intensity comparison section 75
determines that the processed reflected wave f1B' is ineffective, the
control unit 70 supplies the selection signal A to the switch circuits 10
and 20.
The signal intensity comparison section 75 supplies the display element
drive section 71 with a power signal according to the amplitude of the
processed reflected wave f1' supplied from the A/D converter circuit 37.
The pulse rate computation section 74 functions as a pulse wave information
acquisition means to determine, by a method described below, the pulse
rate as pulse wave information from the processed reflected wave f1'
having adequate effectiveness determined by the signal intensity
comparison section 75.
The display element drive section 71 controls the contents of a display on
the display panel 42. It controls a time display made by the time
measurement section 72, and displays the pulse rate obtained as pulse wave
information in this embodiment. The display element drive section 71 makes
a pulse wave power display on the display panel 42 according to the
selection signal A or B supplied from the control unit 70 to the switch
circuits 10 and 20 and the power signal supplied from the signal intensity
comparison section 75.
The time measurement section 72 controls the clock functions of the pulse
wave detection device, i.e., a time display function, a time measurement
function, etc.
The storage section 73 may use any of various recording mediums, such as a
dynamic random access memory (DRAM), a static random access memory (SRAM),
an electrically erasable programmable ROM (EEPROM), and a hard disk, for
storing data magnetically, electrically or optically. The storage section
73 may have any capacity according to one's need. However, it should have
a capacity for storing pulse wave information at least for one hour to
twenty-four hours, preferably for one week, more preferably for one month.
If pulse wave information obtained over such a predetermined period can be
stored in the storage section 73, the pulse wave information stored in the
storage section 73 can be outputted and used for a medical diagnosis some
days later by being read to the external apparatus 44 connected to the
pulse wave detection device.
The storage section 73 may store, for example, pulse wave information
obtained from the reflected sounds f1 respectively received by the
receiving elements 21 and 21' to enable a diagnosis apparatus for a
medical treatment (external apparatus) to obtain pulse wave information
over a long period of time and to thereby enable a more accurate diagnosis
of the user's condition in daily life from a medial viewpoint.
Information on times at which pulse wave information is stored is supplied
from the time measurement section 72 and stored in the storage section 73
together with the pulse wave information, thereby enabling a diagnostician
to know the condition of pulsation at each time.
The operation of the above-described embodiment will now be described.
The principle of detection of pulse waves from ultrasound emitted to the
radial artery 2 and the ulnar artery 3 and frequency-modulated by the
Doppler effect according to the speed at which blood flows will first be
described.
The speed at which blood flows in the artery changes with alternation of
the heart contraction period (pulse) and the heart relaxation period.
Therefore, the frequency of ultrasound emitted to the flow of blood is
changed by the Doppler effect when the ultrasound is reflected by the flow
of blood.
If the frequency of the ultrasound is f0; the speed at which blood flows is
v; the sound velocity in the body is c; and the angle of incidence of the
ultrasound on the blood flowing speed is .theta., then the frequency f1 of
the reflected sound is obtained by the following equation 1:
f1=f0(1+2v.times.cos .theta./c) (1)
The frequency of the ultrasound ranges from f0 to f1 by reflection, and the
deviation df of the frequency is expressed by the following equation 2:
df=f1-f0=f0.times.2v.times.cos .theta./c (2)
As a result, if, for example, c=155 m/s; v=0.3 m/s; and f0=9.5, the
frequency deviation df is 3.8 KHz.
According to the equation 2, since the blood flowing speed v is changed by
pulsation, the frequency deviation df changes through the range of about 2
to 4 kHz.
In this embodiment, changes in this frequency deviation df are detected by
a frequency-modulated sound demodulation system, thereby detecting pulse
waves.
FIGS. 2(a) through 2(d) are diagrams showing waveforms output from the
essential components of the pulse wave detection device.
The high-frequency oscillator circuit 13 generates, from its internal
portion, ultrasound f0 which is a high-frequency signal having a frequency
of 10 MHz, as shown in FIG. 2(a).
Ultrasound f0 is emitted to blood flowing in the artery, and sound f1
reflected by the blood is frequency-modulated by the Doppler effect when
it is reflected. Reflected and frequency-modulated sound f1 is received by
the receiving element 21 or 21', as shown in FIG. 2(b).
A signal representing this reflected sound f1 is amplified by the
high-frequency amplifier 31 and is thereafter supplied to the F/V
converter circuit 32. The F/V converter circuit 32 converts a change in
the frequency of the reflected sound f1 signal into a change in voltage,
i.e., a change in the amplitude as shown in FIG. 2(c), and supplies the
converted signal to the detector circuit 33.
The detector circuit 33 obtains a continuous signal such as shown in FIG.
2(d) from the signal supplied from the F/V converter circuit 32, and
supplies the obtained signal to the amplifier circuit 35. The signal
output from the detector circuit 33 is amplified by the amplifier circuit
35, is processed by the filter circuit 36 to remove noise components, and
is converted into a digital signal by the A/D converter circuit 37. This
digital signal is supplied as processed reflected wave f1' to the control
unit 70.
The control unit 70 determines the effectiveness of the processed reflected
wave f1' supplied to it, and determines, by processing in the pulse rate
computation section 74, the pulse rate as pulse wave information from the
processed reflected wave f1A' or f1B' having adequate effectiveness.
The principle of determination of the pulse rate from the reflected wave
f1' obtained by processing the received ultrasound will now be described.
In the pulse rate computation section 74, a pulse is generated by, for
example, a comparison circuit when the level of the processed reflected
wave f1' becomes higher than a reference value, and time intervals at
which pulses are generated in this manner are measured a predetermined
number of times (e.g., three times, five times, seven times, or ten
times). An average time T is obtained by averaging the time periods
measured in this manner. The number N of pulse waves during one minute is
obtained by the following equation 3:
N=60/T (3)
This method of obtaining the pulse rate from the average time T of the time
intervals of pulse waves is not exclusively used. For example, a method
may alternatively be used in which the number w of pulses generated during
a predetermined time period t (e.g., ten seconds) is detected and the
number N of pulse waves during one minute is obtained by the following
equation 4:
N=w.times.(60/t) (4)
The pulse rate computation section 74 supplies the display element drive
section 71 with the obtained number N of pulse waves and pulse signals
generated in correspondence with the pulse waves.
FIGS. 3(a), 3(b), and 3(c) are diagrams showing a state where pulse waves
are detected by a pulse wave detection device incorporated in a watch 60
according to this embodiment. FIGS. 4(a) and 4(b) are diagrams showing an
external appearance of the pulse wave detection device (watch) 60.
As shown in FIGS. 3(a) to 3(c) and FIGS. 4(a) and 4(b), the pulse wave
detection device (watch) 60 has a watch body 61 and a belt 62, and sensors
19 and 19' are attached to inner portions of the belt 62.
As shown in FIG. 3(a), the watch 60 is fitted around a left (or right)
wrist 2a like an ordinary watch, with the watch body 61 placed on the side
corresponding to the back of the hand. The sensors 19 and 19' can be
positioned by being moved in the longitudinal direction of the belt 62 so
that the sensor 19 is positioned on the radial artery 2 while the sensor
19' is positioned on the ulnar artery 3 when the watch is worn, as shown
in FIG. 3(b).
As shown in FIG. 3(c) and FIG. 4(a), the emitting element 11 and the
receiving element 21 of the sensor 19 are disposed side by side along the
radial artery 2 and in a direction perpendicular to the longitudinal
direction of the belt 62, and the emitting element 11' and the receiving
element 21' of the sensor 19' are disposed in the same manner along the
ulnar artery 3. The emitting elements 11 and 11' are located on the
forearm distal sides of the sensors while the receiving elements 21 and
21' are located on the forearm proximal side. The order of the emitting
elements 11 and 11' and the receiving elements 21 and 21' in the direction
along the arteries may be reversed.
As shown in FIGS. 3(c) and 4(a), the face of each of the emitting elements
11 and 11' and the receiving elements 21 and 21' to be brought into
contact with the wrist body surface is formed into a rectangular shape and
is positioned along the longitudinal direction of the belt 62 so that its
longitudinal axis perpendicularly intersects the radial artery 2 or ulnar
artery 3.
Drive components, i.e., a watch movement, etc., are provided in the watch
body 61. In the watch body 61 are also provided a drive circuit 12, a
high-frequency oscillator circuit 13, switch circuits 10 and 20, a
high-frequency amplifier circuit 31, an F/V converter circuit 32, a
detector circuit 33, a sample and hold circuit 34, an amplifier circuit
35, a filter circuit 36, an A/D converter circuit 37, a control unit 70, a
display panel 42, and a low-frequency oscillator circuit 51. A reset
button 68 and a switching button 69 are provided in side portions of the
watch body 61 (see FIGS. 4(a) and 4(b)). The low-frequency oscillator
circuit 51 has the same oscillation frequency as a drive circuit used for
clock functions. Therefore, a common oscillator circuit may be formed for
both the pulse wave detection function and the clock functions.
The sensors 19 and 19' provided on the belt 62 and the switch circuits 10
and 20 provided in the watch body 61 are connected by wiring 80 laid in
the belt 62 as shown in FIGS. 4(a) and 4(b).
In a display surface (face) of the watch body 61, a watch display 63 on
which time and other information (a day, a day of the week, etc.) are
displayed, and the display panel 42 are provided. The display panel 42 has
a pulse rate display portion 64 on which the number N of pulse waves is
displayed, a pulsation on-and-off signaling portion 67 with a lighting
means which is turned on and off according to pulsation, and pulsation
display portions 65 and 66 for displaying the intensity of the pulsation
signal.
On the pulsation display portion 65 (ch1), the intensity of the pulsation
signal obtained as a result of pulse wave detection from the radial artery
2 is displayed. On the pulsation display portion 66 (ch2), the intensity
of the pulsation signal obtained as a result of pulse wave detection from
the ulnar artery 3 is displayed. The pulsation display portions 65 and 66
are alternatively activated for display. When selection signal A is
supplied from the control unit 70 to the switch circuits 10 and 20, the
pulsation display portion 65 is activated for display. When selection
signal B is supplied, the pulsation display portion 66 is activated for
display.
In a scale of 0 to 100 from the left end to the right end on each of the
pulsation display portions 65 and 66, the signal intensity is indicated at
a larger scale value if the signal intensity is higher. The indicated
scale value is determined by the display element drive section 71
according to the power signal supplied from the signal intensity
comparison section 75.
A user can know the state of detection of pulsation through the receiving
elements 21 and 21' from a display in the scale on the pulsation display
portion 65 or 66. The user can also know, from the scale value on the
pulsation display portion 65 or 66, whether the number N of pulse waves
displayed on the pulse rate display portion 64 is a value obtained by
detection from the radial artery 2 or a value obtained by detection from
the ulnar artery 3.
The color of on-and-off lighting each of the pulsation display portions 65
and 66 may be changed according to the number of pulse waves. For example,
on-and-off lighting in yellow is performed when the number of pulse waves
is 69 or smaller; on-and-off lighting in blue when the number of pulse
waves is 70 to 90; on-and-off lighting in green when the number of pulse
waves is 91 to 110; on-and-off lighting in orange when the number of pulse
waves is 111 to 130; and on-and-off lighting in red when the number of
pulse waves is 131 or greater. The condition of pulsation can be easily
recognized discriminatingly from such display colors set with respect to
the number of pulse waves.
The switching button 69 attached to the watch body 61 is used to change
displays made on the watch display 63 and the display panel 42 for
displaying the number N in such a manner that, for example, time and pulse
rate information are simultaneously displayed in the display surface of
the watch 60 or displayed separately from each other. The reset button 68
attached to the watch body 61 is pressed to reset the detection device in
a case where the detection device is unable to perform pulse wave
detection from the radial artery 2 or ulnar artery 3, thereby retrying
accurate detection of pulse waves from the radial artery 2 or ulnar artery
3.
FIG. 5 is a diagram for explaining the principle of determination in the
signal intensity comparison section 75 as to whether the processed
reflected wave f1' is effective in detecting pulse waves. Although the
processed reflected wave f1' is converted into a digital signal, it is
shown as an analog signal in FIG. 5 for ease of understanding.
A case in which pulse wave information (the number of pulses) is detected
from the radial artery 2 will be described by way of example with
reference to FIG. 5.
In this embodiment, adequate effectiveness is recognized if the amplitude.
of the processed reflected wave f1A' supplied from the A/D converter
circuit 37 is between the two threshold values ATh1 and ATh2 previously
set for measurement on the radial artery 2.
The amplitude of the processed reflected wave f1A' obtained by detection
from the radial artery 2 is sometimes so small that it does not reach the
first threshold value ATh1 designating the necessary amplitude for
detection of pulse. waves, as indicated by (c) in FIG. 5. Such a condition
results from a shift of the pulse wave detection device from the correct
position, weak pulsation in the radial artery 2, etc. Also, the amplitude
of the processed reflected wave f1A' obtained by detection from the radial
artery 2 can exceed the second threshold value ATh2, as indicated by (b)
in FIG. 5, when influenced by large noise caused by movements of fingers
or the like, a shift of the sensor 19 from the correct position,
separation from the body surface, etc, resulting in failure to accurately
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