U.S. patent application number 12/728326 was filed with the patent office on 2010-09-30 for method and system of monitoring respiratory signal by radio.
This patent application is currently assigned to Chungbuk National University Industry Academic Cooperation Foundation. Invention is credited to Eun Jong Cha, Kyung Ah Kim, In Kwang Lee.
Application Number | 20100249632 12/728326 |
Document ID | / |
Family ID | 40089053 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100249632 |
Kind Code |
A1 |
Lee; In Kwang ; et
al. |
September 30, 2010 |
METHOD AND SYSTEM OF MONITORING RESPIRATORY SIGNAL BY RADIO
Abstract
A method and system is provided for monitoring a respiratory
signal by radio. The method includes the steps of converting a
change in electric resistance, which is caused by a change in
abdominal circumference measured through a rubber waistband that is
made of conductive rubber and is mounted on a lower garment of a
testee during respiration, into a voltage signal, performing A/D
conversion on the voltage signal, and transmitting the converted
digital signal a short distance by radio using a wireless
communication protocol for ZigBee, and receiving the respiratory
signal transmitted by radio, transmitting it to a computer unit by
wire through an RS-232 port that is a serial communication port,
and enabling a tester to monitor the respiratory signal through a
screen.
Inventors: |
Lee; In Kwang;
(Cheongju-City, KR) ; Kim; Kyung Ah;
(Cheongju-City, KR) ; Cha; Eun Jong;
(Cheongju-City, KR) |
Correspondence
Address: |
GREER, BURNS & CRAIN
300 S WACKER DR, 25TH FLOOR
CHICAGO
IL
60606
US
|
Assignee: |
Chungbuk National University
Industry Academic Cooperation Foundation
Cheongju-si
KR
|
Family ID: |
40089053 |
Appl. No.: |
12/728326 |
Filed: |
March 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11879999 |
Jul 19, 2007 |
|
|
|
12728326 |
|
|
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|
Current U.S.
Class: |
600/534 |
Current CPC
Class: |
A61B 5/002 20130101;
A61B 5/1135 20130101; A61B 5/6804 20130101 |
Class at
Publication: |
600/534 |
International
Class: |
A61B 5/08 20060101
A61B005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2007 |
KR |
10-007-0054379 |
Claims
1. A system of monitoring a respiratory signal by radio, the system
comprising: a connector that is connected to opposite ends of a
rubber waistband, the rubber waistband being mounted on a lower
garment of a testee and being made of rubber including conductive
particles; a radio transmitter that is electrically connected with
the connector, converts a change in electric resistance, which is
caused by a change in abdominal circumference measured through the
rubber waistband during respiration, into a voltage signal,
performs analog/digital (A/D) conversion on the voltage signal, and
transmits the converted digital signal to a short distance by radio
using a wireless communication protocol for ZigBee; and a radio
receiver that receives the respiratory signal, transmitted by radio
using the ZigBee wireless communication protocol, through a
reception antenna, converts the respiratory signal into serial
information, and outputs the converted serial information through a
RS-232 port, wherein the respiratory signal is monitored by
calculating the input respiratory signal and checkup parameters at
the radio receiver, and outputting the calculated result to a
monitor screen.
2. The system as claimed in claim 1, wherein the radio transmitter
comprises: a Wheatstone bridge circuit, one resistor of which
operates the rubber waistband to convert a change in electric
resistance of the rubber waistband into a voltage signal; a
differential amplifier circuit that amplifies and outputs a
difference between the voltage signals output from the Weston
bridge circuit to one voltage signal; a low-pass filter circuit
that extracts a voltage signal corresponding to the respiratory
signal, from which high-band noise is minimized by allowing only a
low-band signal to pass therethrough, from the voltage signal
amplified through the differential amplifier; an analog/digital
(A/D) converter circuit that converts the respiratory signal output
from the low-pass filter circuit into a digital signal; and a
ZigBee transmission circuit that transmits the digital signal
output from the A/D converter circuit through a reception antenna
by radio to a short distance using a ZigBee wireless communication
protocol.
3. The system as claimed in claim 1, wherein the radio transmitter
is carried in a pocket of a lower or upper garment of the
testee.
4. The system as claimed in claim 1, wherein the A/D converter
circuit and ZigBee transmission circuit of the radio transmitter
make use of a semiconductor ship.
Description
PRIORITY CLAIM
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/879,999, filed on Jul. 19, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a method and
system of monitoring a biological signal by radio. More
particularly, the present invention relates to a method and system
of monitoring a respiratory signal by radio, in which a respiratory
frequency and a lung volume are precisely measured using an elastic
device fastened around the abdomen without the trouble of measuring
the biological signal, the respiratory signal, which is most
frequently measured for inpatients, through an oral cavity.
[0004] 2. Description of the Prior Art
[0005] In general, respiration is a physiological function that
supplies fresh air (oxygen) into the body and then releases a
byproduct, carbon dioxide, of the metabolism out of the body, and
thus is essential for life. The respiration, blood pressure, pulse,
and body temperature are important biological signals showing a
vital sign, and thus are the highest measurement frequency of
biological signals that must be measured three or four times for
all the inpatients of the hospital from day to day. For this
reason, whether or not the respiration occurs or measuring and
monitoring an amount of respiration is very important
medically.
[0006] Up to now, respiratory airflow transducer, respiratory
inductive plethysmography, contactless respiration measurement, and
breathing air temperature measurement have been used or studied for
sensing, measuring, and monitoring of a breathing signal.
[0007] As illustrated in FIG. 1a, the respiratory airflow
transducer converts an amount of air, which is inhaled when a
testee closes the nose to breathe through the mouth with a
breathing pipe 11 held in the mouth, into an electrical variable
through a flow sensor 12 connected with the breathing pipe 11, and
measures an amount of respiration using the electrical variable
converted by the flow sensor 12. However, the respiratory airflow
transducer is troublesome because the testee must breathe with the
breathing pipe 11 held in the mouth. As such, the respiratory
airflow transducer is used for a clinical spirometry test that must
continuously measure respiratory airflow with precision.
[0008] As illustrated in FIG. 1b, the respiratory inductive
plethysmography is a technique of measuring a change of the skin
without the trouble of holding the breathing pipe in the mouth of a
testee, thereby estimating a lung volume. In other words, the lung
volume is estimated by contraction and expansion of the lung. More
specifically, the lung volume is estimated by measuring and summing
up changes of the peripheries of the thorax and abdomen caused by
the respiration on the basis of a principle that the respiration
causes the volumes of the thorax and abdomen to be changed.
[0009] Elastic bands, in which thorax and abdomen coils 21 and 22
of conductive metal are disposed in a zigzag shape, are fastened to
the thorax and abdomen of the testee, respectively. As the
peripheries of the thorax and abdomen of the testee, to whom the
thorax coil 21 and the abdomen coil 22 are attached breathes, are
varied while the testee breathes, a distance between the adjacent
crests (or roots) of each zigzag coil is varied or displaced.
Thereby, the inductances 23 of the thorax and abdomen coils that
are attached to the thorax and the abdomen are changed and measured
electrically. At this time, although the lung volumes are equal to
each other, the contributions of the thorax and the abdomen to the
lung volumes are dependent on the testee. Thus, the relative
contributions k.sub.1 and k.sub.2 of each testee are calculated and
applied in advance.
[0010] However, the respiratory inductive plethysmography is
difficult to handle, and furthermore is impossible to wash with
water, because the separate elastic bands must be fastened on the
clothes and because the metal coils are attached in the elastic
bands. Further, because the AC signal is required to measure the
change of the inductance, a signal extracting circuit, which
includes circuits of generating and measuring the AC signal having
constant frequency and amplitude, becomes complicated.
[0011] As illustrated in FIG. 1c, the contactless respiration
measurement is a technique for detecting respiration with no
contact between a device and the body, and makes use of the fact
that during respiration, the skin of the thorax moves backwards and
forwards to undergo displacement. More specifically, a wave
generator 31 generates waves such as ultrasonic waves or
electromagnetic waves, and then sends the waves to the front of the
body. Thus, the waves are reflected from the body. At this time, a
wave detector 32 detects properties of the reflected waves, and
compares the reflected waves with the incident waves. Thereby, the
displacement caused by the periodic motion of the physical skin is
measured. However, the wave signals are greatly attenuated in the
air, and thus become weak. As a result, a quality of measurement
becomes very bad. Furthermore, if the waves are not accurately
emitted to the front of the body in the direction perpendicular to
the front of the body, such measurement is impossible. The wave
generator and detector are difficult to produce in the technical
aspect, and thus have high production cost. Due to this problem,
the contactless respiration measurement is under the development,
and thus has a small possibility of practical use.
[0012] As illustrated in FIG. 1d, the breathing air temperature
measurement is a technique based on the facts that, because a room
temperature and a body temperature are is about 25.degree. C. and
about 37.degree. C. respectively, a difference between the room
temperature and the body temperature is about 10.degree. C., and
that, because a temperature of expiratory air when a testee exhales
is equal to the body temperature, it is higher than that of
inspiratory air when the testee inhales.
[0013] When a sensor (e.g. thermocouple or thermistor) 41 for
sensing a temperature is located near the nostrils of the testee, a
period of temperature change is equal to a respiratory period, so
that it can be calculated to measure a respiratory frequency.
However, this technique can measure only the respiratory frequency,
but not a variable related to ventilation (i.e. the volume of air
breathed in and out of the lungs) such as a lung volume. According
to the normal physiological function of the body, the lung volume
is increased first when the metabolism of the body increases to
require increasing the ventilation, and then the respiratory
frequency is increased only for still greater ventilation. Taking
this fact into consideration, the measurement of the respiratory
frequency makes it possible to determine whether or not the
respiration occurs, but it makes it impossible to measure the
ventilation that is more important than the respiratory frequency
from the physiological viewpoint.
SUMMARY OF THE INVENTION
[0014] Accordingly, the present invention has been made keeping in
mind the above problems occurring in the prior art, and a first
object of the present invention is to provide a method of
monitoring a respiratory signal by radio, in which the respiratory
signal is monitored using an elastic waistband made of conductive
rubber is fastened around the abdomen of a testee without the
trouble of holding the breathing pipe in the mouth of the testee,
thereby providing a personal customized respiratory measurement
technique that accurately measures a respiratory frequency and
measures a lung volume within an allowable error range, and
transmitting and monitoring the measured respiratory signal by
radio.
[0015] A second object of the present invention is to provide a
system for accomplishing the first object.
[0016] To accomplish these objects, according to one aspect of the
present invention, there is provided a method of monitoring a
respiratory signal by radio. The method comprises: a respiratory
signal measuring and transmitting step of converting a change in
electric resistance, which is caused by a change in abdominal
circumference measured through a rubber waistband that is made of
conductive rubber and is mounted on a lower garment of a testee
during respiration, into a voltage signal, performing
analog/digital (A/D) conversion on the voltage signal, and
transmitting the converted digital signal to a short distance by
radio using a wireless communication protocol for ZigBee; and a
respiratory signal receiving and monitoring step of receiving the
respiratory signal transmitted by radio, transmitting it to a
computer unit by wire through an RS-232 port that is a serial
communication port, and enabling a tester to monitor the
respiratory signal through a screen.
[0017] According to another aspect of the present invention, there
is provided a system of monitoring a respiratory signal by radio.
The system comprises: a connector that is connected to opposite
ends of a rubber waistband, the rubber waistband being mounted on a
lower garment of a testee and being made of rubber including
conductive particles; a radio transmitter that is electrically
connected with the connector, converts a change in electric
resistance, which is caused by a change in abdominal circumference
measured through the rubber waistband during respiration, into a
voltage signal, performs analog/digital (A/D) conversion on the
voltage signal, and transmits the converted digital signal to a
short distance by radio using a wireless communication protocol for
ZigBee; and a radio receiver that receives the respiratory signal,
transmitted by radio using the ZigBee wireless communication
protocol, through a reception antenna, converts the respiratory
signal into serial information, and outputs the converted serial
information through a RS-232 port. The respiratory signal is
monitored by calculating the input respiratory signal and checkup
parameters at the radio receiver, and outputting the calculated
result to a monitor screen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description when taken in conjunction with the
accompanying drawings, in which:
[0019] FIG. 1a is a conceptual view for explaining a respiratory
airflow transducer used for detecting, measuring, and monitoring a
respiratory signal;
[0020] FIG. 1b is a conceptual view for explaining a respiratory
inductive plethysmogrpahy used for detecting, measuring, and
monitoring a respiratory signal;
[0021] FIG. 1c is a conceptual view for explaining contactless
respiration measurement used for detecting, measuring, and
monitoring a respiratory signal;
[0022] FIG. 1d is a conceptual view for explaining breathing air
temperature measurement used for detecting, measuring, and
monitoring a respiratory signal;
[0023] FIG. 2 is a conceptual view for explaining configuration and
operation of a system of monitoring a respiratory signal by radio
according to the present invention;
[0024] FIG. 3 is a view illustrating an embodiment in which a
rubber waistband for the system of FIG. 2 is mounted on a lower
garment worn by a testee
[0025] FIG. 4 is a graph illustrating a change in electric
resistance measured while elongating the rubber waistband of FIGS.
2 and 3 by 0.5 cm;
[0026] FIG. 5 is a block diagram for explaining the configuration
and operation of a radio transmitter in a system of monitoring a
respiratory signal by radio according to the present invention;
[0027] FIG. 6 is a block diagram for explaining the configuration
and operation of a radio receiver in a system of monitoring a
respiratory signal by radio according to the present invention.
[0028] FIG. 7 is a graph showing the result of a respiratory
monitoring (change in output voltage based on respiration) test
using a system of monitoring a respiratory signal by radio
according to the present invention; and
[0029] FIG. 8 is a graph showing correlation between abdominal
respiratory signal and tidal volume of a particular testee in a
CO.sub.2 inhalation test performed for respiratory monitoring in a
patient personal customized type using a system of monitoring a
respiratory signal by radio according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Hereinafter, exemplary embodiments of the present invention
will be described in detail.
[0031] FIG. 2 is a conceptual view for explaining configuration and
operation of a system of monitoring a respiratory signal by radio
according to the present invention. FIG. 3 is a view illustrating
an embodiment in which a rubber waistband for the system of FIG. 2
is mounted on a lower garment worn by a testee.
[0032] As illustrated in FIG. 2, the system of monitoring a
respiratory signal by radio according to the present invention
includes a rubber waistband 110, which is mounted in a lower
garment worn by a testee 102. The rubber waistband 110 mounted on
the trousers is made of conductive rubber having electrical
conductivity, rather than ordinary rubber having electrical
non-conductivity. Owing to the elasticity, the rubber waistband 110
also functions as a belt for the waist.
[0033] While the testee respires, the abdomen of the testee is
changed in circumference, and simultaneously the rubber waistband
110 is elongated or contracted. Thereby, the rubber waistband 110
is changed in cross section and length, and thus is changed in
electric resistance. A radio transmitter 120 connected to the
rubber waistband 110 converts the electric resistance change, which
is input through the rubber waistband 110, into an analog voltage
signal, performs A/D conversion on the voltage signal, and
transmits the respiratory signal based on digital information to a
short distance using a wireless communication protocol for
ZigBee.
[0034] The radio transmitter 120 is put into a pocket of the lower
or upper garment of the testee in electrical connection with the
rubber waistband 110. The ZigBee wireless communication protocol
applied to the radio transmitter 120 conforms to the IEEE 802.15.4
wireless standard for data networks, operates in frequency bands
2.4 GHz, 868 MHz, and 915 MHz, uses direct-sequence spread spectrum
(DSSS) coding, has a data transfer rate from 20 kbps to 250
kbps.
[0035] The radio signal transmitted from the radio transmitter 120
is received by a radio receiver 130. The radio receiver 130
receives the respiratory signal transmitted using the ZigBee
wireless communication protocol, and transmits it to a computer
unit 140 such as a personal computer (PC) by wire through an RS-232
port that is a serial communication port, so that it enables a
tester to monitor the respiratory signal through a screen.
[0036] The respiratory signal transmitted to the computer unit 140
by wire is continuously displayed on the screen, and exhibits
clinically important checkup parameters, such as a tidal volume, a
respiration frequency, and a minute ventilation, at fixed
periods.
[0037] The testee is guaranteed mobility within a predetermined
distance in which transmission and reception are performed by
radio, and the respiratory signal of the testee is transmitted and
monitored by radio without a stop motion. Accordingly, the trouble
of the testee is reduced during the respiration checkup.
[0038] As illustrated in FIG. 3, among the components of the
present invention, the rubber waistband used to sense the abdominal
circumference change is made of conductive rubber, is mounted on
the lower garment, which is typically worn by an inpatient, and
also serves as the belt for the waist. In the present invention,
the opposite ends of the rubber waistband 110 are connected to a
connector 112 that can be connected using an electric wire. The
connector 112 is electrically connected with the radio transmitter
120, which is adapted to be carried in the pocket 121 of the lower
or upper garment of the testee. Thus, the rubber waistband of the
lower garment of the testee functions as a respiratory sensor by
itself without mounting a separate sensor unit for measuring the
respiratory signal.
[0039] The conductive rubber used for the rubber waistband 110 of
the present invention is produced by mixing a small quantity of
conductive particles (e.g. of carbon, platinum, etc.) when a rubber
as a nonconductor is formed in a desired shape. In this case in
which the conductive rubber is produced so as to have the range
from tens of .OMEGA. to several .OMEGA. according to a mixing
ratio, the electric resistance change caused by the change in
length can be easily measured.
[0040] FIG. 4 is a graph illustrating a change in electric
resistance measured whenever the rubber waistband of FIGS. 2 and 3
is elongated by 0.5 cm. FIG. 5 is a block diagram for explaining
the configuration and operation of a radio transmitter in a system
of monitoring a respiratory signal by radio according to the
present invention. Further, FIG. 6 is a block diagram for
explaining the configuration and operation of a radio receiver in a
system of monitoring a respiratory signal by radio according to the
present invention.
[0041] As illustrated in FIG. 4, the rubber waistband 110 of the
present invention is cut to a proper length so as to be mounted on
the lower garment, and then the change of electric resistance is
measured whenever the cut rubber waistband 110 is gradually
elongated by 0.5 cm. As a result, as the length of the rubber
waistband 110 increases, a value of the electric resistance is
increased exponentially.
[0042] In this manner, when the length is changed within a range of
1 cm or less (range from 56 cm to 57 cm in FIG. 4), the electric
resistance shows linear correlation in which it is almost
proportional to the length. When the respiratory signal is measured
within this range, an optimal sensitivity of measurement can be
obtained. In other words, while the abdominal circumference of the
testee is periodically changed by the respiration of the testee,
the electric resistance of the rubber waistband 110 mounted on the
lower garment of the testee is alternately increased and
decreased.
[0043] The electric resistance change measured through the rubber
waistband 110 is input into the radio transmitter 120. As
illustrated in FIG. 5, the radio transmitter 120 establishes a
circuit such that the electric resistance of the rubber waistband
110 operates to have the resistance in one arm (of four arms) of
the Wheatstone bridge circuit 122. It is assumed that the electric
resistance of the expanded rubber waistband 110 when the testee
exhales is R. The rubber waistband 110 is connected with three
resistors having the same resistance as the electric resistance
thereof, and thereby the bridge circuit is constructed. At this
time, voltages V.sub.+ and V.sub.- on the bridge circuit are
expressed by the following Equation 1.
V + = V - = V E 2 ( 1 ) ##EQU00001##
[0044] In Equation 1, V.sub.E is the DC voltage that drives the
bridge circuit.
[0045] When the testee begins to inhale, the electric resistance
increases to R+.DELTA.R, and thus the voltage V+ of Equation 1 is
transformed into the following Equation 2.
V + = R + .DELTA. R R + ( R + .DELTA. R ) V E = 1 + .DELTA. R R 1 +
1 + .DELTA. R R V E ( 2 ) ##EQU00002##
[0046] In Equation 2, if the change .DELTA.R of the electric
resistance that is increased by inhalation is sufficiently less
than R (i.e. R>>.DELTA.R), .DELTA.R/R of the denominator is
approximated to 0, and thus Equation 2 is transformed into the
following Equation 3.
V + .apprxeq. 1 + .DELTA. R R 2 V E = V E 2 + .DELTA. R 2 R V E ( 3
) ##EQU00003##
[0047] In Equation 3, because the voltage V.sub.- maintains the
value, V.sub.E/2, of Equation 1 irrespective of the elongation of
the conductive rubber waistband (FIG. 5), a difference between
V.sub.+ and V.sub.- is calculated, and thereby is expressed by the
following Equation 4.
V + - V - = .DELTA. R 2 R V E ( 4 ) ##EQU00004##
[0048] Accordingly, the voltage difference between V.sub.+ and
V.sub.- is proportional to the electric resistance change .DELTA.R
of the conductive rubber waistband. In other words, when the DC
Wheatstone bridge circuit 122 of FIG. 5 is used, the electric
resistance change is converted into a voltage signal. The voltage
signal output from the Wheatstone bridge circuit 122 is applied to
a differential amplifier circuit 124, and then the differential
amplifier circuit 124 amplifies and outputs a difference between
the input V.sub.+ and V_voltage signals to one voltage signal.
[0049] The voltage signal amplified by the differential amplifier
circuit 124 is applied to a low-pass filter circuit 125, and then
the low-pass filter circuit 125 extracts a voltage signal
corresponding to the respiratory signal, from which high-band noise
is minimized by allowing only a low-band signal to pass
therethrough.
[0050] The respiratory signal output from the low-pass filter
circuit 125 is input into an A/D converter circuit 126, and thereby
is converted into a digital signal. In other words, because the
respiratory signal output from the low-pass filter circuit 125 is
an analog voltage signal, it is converted into a digital signal
(information) by the A/D converter circuit 126.
[0051] The digital signal output from the A/D converter circuit 126
is input into a ZigBee transmission circuit 127, and then is
transmitted to a short distance through a transmission antenna 128
by radio. The A/D converter circuit and the ZigBee transmission
circuit can be easily realized using a commercialized semiconductor
chip. Since the entire radio transmitter 120 can be configured of a
low electric power circuit, it can be operated with a dry battery,
and be reduced in size when produced. As a result, the radio
transmitter is designed to be carried in a pocket of a lower or
upper garment of the testee. In this manner, because the radio
transmitter 120 is carried in the pocket, the respiratory signal of
the testee can be freely monitored during moving within a range in
which it can be received by radio.
[0052] As illustrated in FIG. 6, the respiratory signal, which is
transmitted from the ZigBee transmission circuit 127 of the radio
transmitter by radio, is input into a ZigBee reception circuit 132
of the radio receiver 130 through a reception antenna 131, is
converted into serial information, and is input into the computer
unit 133 through the RS-232 port. The computer unit 133 functions
to display the respiratory signal and the whole checkup parameters
on the monitor screen 134, and to perform respiratory monitoring
for which a user makes a request.
[0053] FIG. 7 is a graph showing the result of a respiratory
monitoring test (change of output voltage based on respiration)
using a system of monitoring a respiratory signal by radio
according to the present invention. FIG. 8 is a graph showing
correlation between abdominal respiratory signal and tidal volume
of a particular testee in a CO.sub.2 inhalation test performed for
respiratory monitoring in a patient personal customized type using
a system of monitoring a respiratory signal by radio according to
the present invention.
[0054] FIG. 7 shows the test result using the system of monitoring
a respiratory signal by radio according to the present invention.
The testee sequentially performed comfortable respiration, maximum
inhalation, comfortable respiration, unnatural cough, and maximum
inhalation in the state where he/she sited on a chair in the lower
garment on which the conductive rubber waistband was mounted. At
that time, the respiratory signals were monitored by radio.
[0055] In FIG. 7, the vertical axis represents the time, and the
horizontal axis represents the voltage. It can be found that
accurate respiratory frequencies were obtained because respective
respiratory modes (patterns) were easily discriminated by obtained
respiratory signals, and because periodical respiration was
accurately recognized. Because the possibilities of measuring the
accurate respiratory frequencies and simultaneously discriminating
the respiratory modes were proved as shown in FIG. 7, a measurement
test of the lung volume, as shown in FIG. 8, was performed in a
manner such that, in order to increase a tidal volume without being
unconscious of his/her respiration in a normal state, the testee
breathed a mixed gas consisting of carbon dioxide from 0% to 5% and
air through the mouth for three minutes, and the respiratory
signals were monitored for one minute when reaching a steady
state
[0056] The testee held a respiratory airflow transducer in his/her
mouth, and then accurate respiratory airflow and a tidal volume
were measured together with an abdominal respiratory signal. It can
be seen from the correlation between the abdominal respiratory
signal and the tidal volume as shown in FIG. 8 that the abdominal
respiratory signal increased when the tidal volume increased by
CO.sub.2 inhalation, and was statistically significant (P<0.005)
because a coefficient of correlation was over 0.96.
[0057] Therefore, the fact that the system of monitoring a
respiratory signal by radio according to the present invention
could estimate the tidal volume in a relatively accurate manner by
monitoring the respiratory signal from the conductive rubber
waistband 110 by radio was experimentally proved.
[0058] As described above, when the abdominal respiratory signals
are monitored using the conductive rubber waistband (or belt), the
respiratory frequencies can be accurately measured without an error
as in the graph of FIG. 7, and the tidal volume has linear
correlation with respect to an actual true value within a relative
error from 10% to 20%.
[0059] This relative error is attributed to a relative ratio at
which the respiration varies the volumes of the thorax and abdomen
and is distributed to the thorax and the abdomen. As such, the
contribution of the thorax is regarded as nothing in the present
invention because only the tidal volume of the abdomen is measured.
Although the contributions of the thorax and abdomen are different
from each other depending on the testees, they are invariably
maintained to each particular testee. Thus, the tidal volume can be
reliably measured even when it is measured respect to only the
abdomen. In other words, after each testee is subjected to
customized calibration in terms of an individual difference, the
respiratory signals are measured. Thereby, accurate measurement
results can be obtained.
[0060] The system of monitoring a respiratory signal by radio
according to the present invention is designed so that the elastic
conductive rubber waistband (or belt) serving as the respiratory
sensor is mounted on the lower garment of the patient. The lower
garments are not exchanged between the patients, so that the
personal customized calibration is effective. As shown in FIG. 8,
in order to carry out the personal customized calibration, a
calibration procedure of performing the CO.sub.2 inhalation test on
each testee once, obtaining the correlation between the abdominal
respiratory signal and the tidal volume of the particular testee,
calculating a regression line, which obtains the lung volume from
the abdominal respiratory signal, from the correlation, and then
substituting the abdominal respiratory signal into the regression
line to measure the lung volume has only to be performed in
advance.
[0061] As can be seen from the foregoing, the present invention
improves convenience of use because it does not provide the trouble
of mounting a separate unit in the mouth or nose when the
respiratory signals is measured and checked up, can be cleaned due
to the conductive rubber material unlike a complete conductor, and
can be the garment wearable type serving as the belt for the waist.
Further, because the DC is used instead of the AC when the signal
is extracted, the circuit is simplified. Due to the radio
transmission mode, the measurement is performed in a free state
without restricting activity of the patient. Furthermore, the
respiratory monitoring is possible during moving. In addition, the
accurate lung volume can be estimated only by the abdomen
respiratory measurement through the personal customized
calibration.
[0062] Although a preferred embodiment of the present invention has
been described for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *