U.S. patent application number 09/732873 was filed with the patent office on 2001-04-19 for process for determining respiratory phases of the sleep of a user.
Invention is credited to Jonquet, Benoit, Ruton, Stephane.
Application Number | 20010000346 09/732873 |
Document ID | / |
Family ID | 9527546 |
Filed Date | 2001-04-19 |
United States Patent
Application |
20010000346 |
Kind Code |
A1 |
Ruton, Stephane ; et
al. |
April 19, 2001 |
Process for determining respiratory phases of the sleep of a
user
Abstract
A process for determining respiratory phases of the sleep of a
user (3), comprising measuring at least two physical variables of
which at least a first physical variable is representative of the
nasal flow of the user (3) and of which at least a second physical
variable is representative of the user's buccal flow. The process
furthermore comprises processing and converting each physical
variable with a view to establishing its degree of membership in at
least one state of a fuzzy variable, and applying pre-established
rules between at least one state of a first fuzzy variable and a
state of a second fuzzy variable so as to evaluate the degree of
membership in a respiratory phase state of the sleep of the user
(3) according to fuzzy logic.
Inventors: |
Ruton, Stephane; (Viroflay,
FR) ; Jonquet, Benoit; (Palaiseau, FR) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Family ID: |
9527546 |
Appl. No.: |
09/732873 |
Filed: |
December 11, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09732873 |
Dec 11, 2000 |
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09335724 |
Jun 18, 1999 |
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6190328 |
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Current U.S.
Class: |
600/538 ;
600/529 |
Current CPC
Class: |
A61B 5/09 20130101; A61M
16/024 20170801; A61B 5/7264 20130101; A61M 2016/0021 20130101;
A61M 2016/0027 20130101; A61M 16/0069 20140204; G16H 50/20
20180101; A61B 5/087 20130101; A61M 16/00 20130101 |
Class at
Publication: |
600/538 ;
600/529 |
International
Class: |
A61B 005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 18, 1998 |
FR |
98 07695 |
Claims
What is claimed is:
1. A process for determining respiratory phases of the sleep of a
user, comprising: measuring at least two physical variables of
which at least a first physical variable is representative of the
nasal flow of the user, and of which at least a second physical
variable is representative of the user's buccal flow; processing
and converting each physical variable with a view to establishing
its degree of membership in at least one state of a fuzzy variable;
and applying pre-established rules between at least one state of a
first fuzzy variable and a state of a second fuzzy variable so as
to evaluate the degree of membership in a respiratory phase state
of the sleep of the user according to fuzzy logic.
2. The process according to claim 1, wherein the respiratory state
comprises at least one of a state of normal respiration, a state of
apnea and a state of hypopnea.
3. The process according to claim 1, wherein each fuzzy variable
possesses at least two states.
4. The process according to claim 1, wherein the degrees of
membership of the states associated with a fuzzy variable are
established on the basis of continuous curves defined over the
entire universe of discourse of a measured physical variable.
5. The processing according to claim 1, wherein one of the measured
physical variables is a pressure signal measured by a pressure
sensor linked to a nose piece worn by the user.
6. The process according to claim 5, further comprising, during the
step of processing and converting, extracting from the measured
pressure signal snoring phases associated with
breathing-obstruction phenomena.
7. The process according to claim 6, further comprising high-pass
filtering of the pressure signal during extraction to obtain a
filtered signal; amplifying the filtered signal to obtain an
amplified filtered signal; interpolating the amplified filtered
signal so as to obtain an envelope curve; and comparing the
envelope curve with the reference curve so as to determine the
presence of snoring phases.
8. The process according to claim 1, further comprising measuring
the current consumed by a low-inertia turbine linked to a nose
piece intended to be worn by the user to obtain an image of the
nasal flow of the user.
9. The process according to claim 8, further comprising determining
the phases of nasal inhalation and exhalation of the user during
extraction; calculating the time derivative of the amplitude of the
nasal flow during an inhalation phase; and utilizing the derivative
so as to determine whether the user is or is not suffering from a
partial obstructive phenomenon.
10. The process according to claim 9, wherein the step of utilizing
the derivative of the amplitude of the nasal flow comprises
comparing the absolute value of the derivative with at least one
reference value, and measuring the duration for which the absolute
value of the derivative is less than said at least one reference
value.
11. The process according to claim 10, wherein the step of
utilizing the derivative comprises charting the number of charges
of sign of the derivative when the latter is less than the
reference value.
12. The process according to claim 1, further comprising measuring
the resistance of a thermistor placed in proximity to the mouth of
the user to obtain an image of the buccal flow of the user.
13. Method for diagnosing the respiratory phases of the sleep of a
patient suffering from respiratory sleep disorders, wherein said
respiratory phases are determined according to the process
according to claim 1.
14. Method for diagnosing according to claim 13, wherein the
respiratory sleep disorder is sleep apnea or hypopnea.
Description
1. The invention relates to a device and to a process for
determining respiratory phases of the sleep of a user.
2. Respiratory disorders of sleep, such as the Sleep Apnoea
Syndrome (SAS) are characterized, in general, by a disfunctioning
of the respiratory function during sleep.
3. Considerable fragmentation of sleep is observed in subjects
affected by such a syndrome, with short phases of sleep and the
resumption of normal respiration usually accompanied by a brief
period of wakefulness, lasting a few seconds.
4. The normal course of sleep, from the stage of light sleep to the
stage of deep sleep, via a stage of paradoxical sleep, is greatly
disturbed, this having consequences on the daytime routine of these
subjects. Thus, they tend to be drowsy, or even to fall asleep when
fully active, and a decrease in intellectual and sexual functions
is also observed in them, together with the risks of hypertension
and cardiac insufficiency.
5. Respiratory disorders may be of the obstructive or central
type.
6. In the first case, a total obstruction (obstructive apnoea) or
partial obstruction (obstructive hypopnoea) of the upper airways is
observed while muscular effort is maintained. Disorders of this
type are often associated with considerable snoring.
7. In the second case, muscle control is absent (central apnoea) or
diminished (central hypopnoea), the upper airways being open.
8. Obstructive disorders represent the great majority of nocturnal
respiratory disorders.
9. Customarily, diagnosis of respiratory sleep disorders is
performed in a sleep laboratory by recording and studying numerous
parameters related:
10. either to sleep: electroencephalogram, electroocculogram,
electromyogram,
11. or to cardio-respiratory function: electrocardiogram,
respiratory frequency, nasal and/or buccal flow, thoracic and
abdominal movements, arterial oxygen saturation, snoring.
12. Diagnosis of these sleep pathologies is recent and its
implementation is unwieldy and requires that the subject be
hospitalized for one or two nights.
13. The treatment of respiratory sleep disorders customarily
employs an appliance for keeping the upper airways open.
14. This appliance usually comprises a mask-based positive pressure
apparatus (CPAP), in which a means of compressing the ambient air,
operated by a control device, delivers air pressure to a pipe and
then to a mask placed on the patient's nose in a leaktight
manner.
15. The control device compares the value of the pressure in the
mask with a set pressure target value and, depending on the
deviation measured, adjusts a control signal which it delivers to
the means for compressing the ambient air.
16. At present, the pressure target value to be applied in the mask
of the patient is determined empirically in the sleep laboratory by
progressively increasing an initial target value and observing the
consequences for the respiratory disorders, the value chosen being
the first value for which normal unfragmented sleep is
observed.
17. There are apparatuses for diagnosing or/and treating these
nocturnal respiratory disorders, which detect apnoeas or
hypopnoeas, but do not differentiate between central and
obstructive events.
18. Others, after having detected an apnoea, send a pressure pulse
to the patient's mask and study any echo: if there is no echo, the
event is central, and if an echo returns, the event is
obstructive.
19. Such apparatuses are described in particular in the documents
FR-A-2663547 and FR-A-2674133.
20. However, in order to be able to establish a correct diagnosis
of respiratory disorders (apnoeas, hypopnoeas, pathology of
increased resistance, etc.) and/or to determine and/or initiate
adequate and effective treatment, it may be necessary or even vital
for the practitioner, that is to say the doctor or the like, to
have a reliable image representative of the succession of the
various inhalatory and exhalatory phases of his patient, that is to
say the image of the subject's respiratory flow or rate of
flow.
21. However, existing processes and apparatuses do not allow this
kind of reliable and accurate determination of the image of the
said respiratory rate of flow.
22. Henceforth, it is readily understood that diagnosis and/or
subsequent treatment may be incorrect or incomplete.
23. The aims of the present invention are therefore to propose a
process and an apparatus for diagnosing and/or treating respiratory
sleep disorders:
24. which are able to allow the reliable and accurate
determination, from various respiration parameters for a patient,
of the latter's various respiratory phases,
25. which are able to determine accurately the phases of snoring
and/or phenomena with a partial obstruction of the patient's
respiratory passages,
26. which can be used both in a sleep laboratory, that is to say in
a hospital environment, and also at the patient's home, and
27. which have a reasonable cost.
28. To this end, the subject of the invention is a device for
determining respiratory phases of the sleep of a user, comprising
means for measuring at least two physical variables of which at
least a first physical variable is representative of the nasal flow
of the user and of which at least a second physical variable is
representative of the user's buccal flow, characterized in that it
furthermore comprises means for processing and converting each
physical variable with a view to establishing its degree of
membership in at least one state of a fuzzy variable, and means for
applying pre-established rules between at least one state of a
first fuzzy variable and a state of a second fuzzy variable so as
to evaluate the degree of membership in a respiratory phase state
of the sleep of the user according to fuzzy logic.
29. The device according to the invention can additionally comprise
one or more of the following characteristics:
30. each fuzzy variable possesses at least two states,
31. the said states of respiratory phases of sleep comprise at
least one state of normal respiration, a state of apnoea and a
state of hypopnoea,
32. the degrees of membership of the states associated with a fuzzy
variable are established on the basis of continuous curves defined
over the entire universe of discourse of a measured physical
variable,
33. the measurement means comprise a pressure sensor linked to a
nose piece intended to be worn by the user and one of the measured
physical variables is the pressure signal measured by the said
pressure sensor,
34. the said processing and conversion means comprise means for
extracting from the measured pressure signal snoring phases
associated with breathing-obstruction phenomena,
35. the said means for extracting snoring phases comprise means of
high-pass filtering of the pressure signal, means for amplifying
the filtered signal, means for interpolating the said amplified
filtered signal so as to obtain an envelope curve, means for
storing a reference curve and means for comparing the said envelope
curve with the said reference curve so as to determine the presence
of snoring phases,
36. the measurement means comprise a current sensor measuring the
current consumed by a low-inertia turbine which is linked to the
said nose piece and one of the measured physical variables is the
current consumed by the said turbine,
37. the processing and conversion means comprise means for
extracting from the signal of current consumed an image of the
nasal flow of the user, means for determining the phases of nasal
inhalation and exhalation of the said user, means for calculating
the time derivative of the amplitude of the nasal flow during an
inhalation phase and means for utilizing the derivative so as to
determine whether the user is or is not suffering from a partial
obstructive phenomenon,
38. the said means for utilizing the derivative of the amplitude of
the nasal flow comprise means for comparing the absolute value of
the derivative with at least one reference value and means for
measuring the duration for which the absolute value of the
derivative is less than the said at least one reference value,
39. the said means for utilizing the derivative furthermore
comprise means for charting the number of changes of sign of the
derivative when the latter is less than the reference value,
40. the measurement means comprise a member for measuring the
resistance of a thermistor intended to be placed in proximity to
the mouth of the said user, and one of the measured physical
variables is the resistance measured by the said member for
measuring the resistance of the thermistor.
41. The subject of the invention is also a process for determining
respiratory phases of the sleep of a user, characterized in that it
comprises the following steps:
42. at least two physical variables are measured, of which at least
a first physical variable is representative of the nasal flow of
the user and of which at least a second physical variable is
representative of the user's buccal flow,
43. each physical variable is processed and converted with a view
to establishing its degree of membership in at least one state of a
fuzzy variable, and
44. pre-established rules between at least one state of a first
fuzzy variable and a state of a second fuzzy variable are applied
so as to evaluate the degree of membership in a respiratory phase
state of the sleep of the user according to fuzzy logic.
45. This process can moreover comprise one or more of the following
characteristics:
46. each fuzzy variable possesses at least two states,
47. the said states of respiratory phases of sleep comprise at
least one state of normal respiration, a state of apnoea and a
state of hypopnoea,
48. the degrees of membership of the states associated with a fuzzy
variable are established on the basis of continuous curves defined
over the entire universe of discourse of a measured physical
variable,
49. one of the measured physical variables is the pressure in a
nose piece worn by the user,
50. during the processing and conversion, snoring phases associated
with breathing-obstruction phenomena are extracted from the
measured pressure signal,
51. during extraction, high-pass filtering of the pressure signal
is carried out, the filtered signal is amplified, the said
amplified filtered signal is interpolated so as to obtain an
envelope curve, and the said envelope curve is compared with a
reference curve so as to determine the presence of snoring
phases,
52. to obtain an image of the nasal flow, the current consumed by a
low-inertia turbine which is linked to the said nose piece worn by
the user is for example measured,
53. during extraction of the said image of the nasal flow, the
phases of inhalation and exhalation of the said user are determined
and the time derivative of the amplitude of the nasal flow during
an inhalation phase is calculated and this derivative thus
calculated is utilized to determine whether or not the user is
suffering from a partial obstructive phenomenon,
54. during utilization of the derivative of the amplitude of the
nasal flow, the absolute value of this derivative is compared with
at least one reference value, and the duration for which the
absolute value of the derivative is less than the said at least one
reference value is measured,
55. during utilization of the derivative of the amplitude of the
nasal flow, the number of changes of sign of the derivative when
the absolute value of the latter is less than the said at least one
reference value is moreover charted,
56. to obtain an image of the buccal flow, the resistance of a
thermistor placed in proximity to the said user's mouth is for
example measured.
57. The subject of the invention is also a method for diagnosing
the respiratory phases of the sleep of a patient suffering from
respiratory sleep disorders, in particular sleep apnoea,
characterized in that it comprises the following steps:
58. at least two physical variables are measured, of which at least
a first physical variable is representative of the nasal flow of
the user and of which at least a second physical variable is
representative of the user's buccal flow,
59. each physical variable is processed and converted with a view
to establishing its degree of membership in at least one state of a
fuzzy variable, and
60. pre-established rules between at least one state of a first
fuzzy variable and a state of a second fuzzy variable are applied
so as to evaluate the degree of membership in a respiratory phase
state of the sleep of the user according to fuzzy logic.
61. This process can additionally comprise one or more of the
following characteristics:
62. each fuzzy variable possesses at least two states,
63. the said states of respiratory phases of sleep comprise at
least one state of normal respiration, a state of apnoea and a
state of hypopnoea,
64. the degrees of membership of the states associated with a fuzzy
variable are established on the basis of continuous curves defined
over the entire universe of discourse of a measured physical
variable,
65. one of the measured physical variables is the pressure in a
nose piece worn by the user,
66. during the processing and conversion, snoring phases associated
with breathing-obstruction phenomena are extracted from the
measured pressure signal,
67. during extraction, high-pass filtering of the pressure signal
is carried out, the filtered signal is amplified, the said
amplified filtered signal is interpolated so as to obtain an
envelope curve, and the said envelope curve is compared with a
reference curve so as to determine the presence of snoring
phases,
68. to obtain an image of the nasal flow, the current consumed by a
low-inertia turbine which is linked to the said nose piece worn by
the patient is for example measured,
69. during extraction of the said image of the nasal flow, the
phases of inhalation and exhalation of the said patient are
determined and the time derivative of the amplitude of the nasal
flow during an inhalation phase is calculated and this derivative
thus calculated is utilized to determine whether or not the patient
is suffering from a partial obstructive phenomenon,
70. during utilization of the derivative of the amplitude of the
nasal flow, the absolute value of this derivative is compared with
at least one reference value, and the duration for which the
absolute value of the derivative is less than the said at least one
reference value is measured,
71. during utilization of the derivative of the amplitude of the
nasal flow, the number of changes of sign of the derivative when
the absolute value of the latter is less than the said at least one
reference value is moreover charted,
72. to obtain an image of the buccal flow, the resistance of a
thermistor placed in proximity to the said patient's mouth is for
example measured.
73. Other characteristics and advantages of the invention will
emerge from the following description given by way of example,
without limiting character, with regard to the appended drawings in
which:
74. FIG. 1 is a schematic diagram of a device according to the
invention,
75. FIG. 2 is a flowchart showing certain steps in the processing
of a physical variable representative of the nasal flow of a
user,
76. FIG. 3 shows two graphs to illustrate in particular the steps
described with reference to FIG. 2,
77. FIG. 4 represents a graph showing a nasal flow as a function of
time in the case where the user's respiratory passages are impaired
by partial obstruction,
78. FIG. 5 represents a graph showing the time derivative of the
nasal flow of FIG. 4,
79. FIG. 6 shows two graphs to illustrate the determination of a
snoring phenomenon from a pressure signal measured at the nose
piece and/or mouthpiece applied to the user, and
80. FIG. 7 shows a graph to illustrate the conversion of a measured
physical variable with a view to establishing its degrees of
membership in one or more states of a fuzzy variable.
81. 1. Structure of the device according to the invention
82. Represented in FIG. 1 is a device 1 according to the invention
making it possible to determine respiratory phases of the sleep of
a user 3.
83. This device 1 comprises means 5 for measuring at least two
physical variables, of which at least a first physical variable is
representative of the nasal flow of the user and of which at least
a second physical variable is representative of the user's buccal
flow.
84. To this end, the user 3 wears a mouth- and/or nose-piece 7,
such as a mask and/or breathing kit which are known per se and will
not be described in detail here.
85. To this nose/mouth piece 7 is connected a low-inertia turbine 9
by means of a breathing pipe 11 making it possible to convey the
pressurized breathing gas to the respiratory passages of the user
3.
86. As the case may be, the breathing gas is dispensed at a
positive pressure which is constant over time, that is to say at a
single pressure level (CPAP type apparatus), or at a pressure which
varies between at least one low pressure level and at least one
higher pressure level, that is to say at several pressure levels
(BPAP type apparatus) The manner of operation of such apparatuses
having already been described many times in the prior art, it will
not be detailed hereinbelow. However, for further details,
reference may be made in particular to the following documents:
U.S. Pat. No. 5,492,113, U.S. Pat. No. 5,239,995, EP-A-0 656 216 or
EP-A-0 505 232.
87. A pressure sensor 13 whose pressure tap point is arranged on
the nose/mouth piece 7, that is to say in immediate proximity to
the respiratory passages of the user 3, makes it possible to detect
the pressure variations due to the breathing of the user. This
sensor 13 is linked to means 15 controlling the turbine 9 so as to
supply these means 15 with a pressure signal. On the basis of the
pressure signal received and of a specified overpressure target
value, these means 15 supply a control signal to the turbine 9 in
such a way as to modulate the overpressure supplied by the turbine
9 to the user 3 (see also EP-A-505232 or U.S. Pat. No.
5,443,061).
88. Given that the pressure of the breathing gas supplied to the
user must be almost constant, it is understood that the motor speed
of the said turbine 9 and therefore the amount of current consumed
by the latter is dependent on the control signal of the means 15
and therefore corresponds to the nasal flow of the user 3.
89. This is why, to obtain an image of the nasal flow, a current
sensor 17 measures the current consumed by the turbine 9.
90. Moreover, in order to supplement the image of the nasal flow
with an image of the buccal flow, a sensor such as for example a
thermistor (not visible in the figure) is placed in the mouth/nose
piece in immediate proximity to the mouth of the user 3,
91. This sensor, for example the abovementioned thermistor, is
linked to a measurement member 19 measuring, in the case of a
thermistor, the resistance of the latter.
92. In effect, the measurement value such as, for example, the
resistance of the thermistor is modified by temperature variations
caused by any buccal flow issuing from the mouth of the user 3,
thereby making it possible to obtain an image of the buccal flow
which is reliable and accurate.
93. To determine the respiratory phases of the sleep of the user 3
from the values of the physical variables measured by way of the
sensors 13, 19 and 17, that is to say the images of the pressure,
of the nasal flow and of the buccal flow, the device 1 furthermore
comprises means 21 for processing and converting each physical
variable charted with a view to establishing its degree of
membership in at least one state of a fuzzy variable. The degrees
of membership of the respective states of the fuzzy variables are
input into means 23 for applying rules stored in a memory 25
forming a knowledge base.
94. The processing and conversion means 21 comprise means 27 for
extracting from the signal of current consumed, measured by the
current sensor 17, an image of the nasal flow of the user 3, that
is to say the variation of the nasal flow over time. This image of
the nasal flow of the user 3 is input into means 29 for determining
the phases of nasal inhalation and exhalation of the user, into
means 30 for determining the amplitude of the nasal flow and into
means 31 for calculating the time derivative of the amplitude of
the nasal flow.
95. The means 30 furthermore receive a control signal for the means
29 indicating which phase of respiration the user is in.
96. The means 31 only calculate the derivative of the nasal flow
during an inhalation phase. This is why the means 29 also send a
control signal to the means 31 for calculating the derivative when
they have determined that the user is in a nasal inhalation
phase.
97. The derivative calculated by the means 31 is input into
utilizing means 33. These utilizing means 33 comprise means 35 for
comparing the absolute value of the derivative with at least one
reference value recorded in a memory 37. Depending on the result of
the comparison, the means 35 activate means 39 for measuring the
duration for which the absolute value of the derivative is less
than the said at least one reference value.
98. Moreover, the means 33 comprise, linked to the means 31 for
calculating the derivative as well as to the comparison means 35,
means 41 for charting the number of changes of sign of the
derivative when the absolute value of the latter is less than the
reference value.
99. The means 33 for utilizing the derivative of the amplitude of
the nasal flow are employed to determine whether or not the user is
suffering from a partial obstruction of the respiratory passages,
as will be explained in detail hereinbelow.
100. The processing and conversion means 21 furthermore comprise
means 42 for processing the signal delivered by the member 19 for
measuring for example the resistance of the thermistor.
101. Additionally, the processing and conversion means 21 comprise
means 43 for extracting from the pressure signal, measured by the
pressure sensor 13, snoring phases associated with
breathing-obstruction phenomena.
102. These extraction means 43 comprise means 45 of high-pass
filtering of the pressure signal, means 47 for amplifying the
filtered signal, means 49 for interpolating the said amplified
filtered signal so as to obtain an envelope curve, means 51 for
storing a reference curve and means 53 for comparing the said
envelope curve with the said reference curve so as to determine the
presence of snoring phases.
103. The various physical variables thus processed are input into
means 55 for converting each of these variables with view to
establishing its degree of membership in at least one state of an
associated fuzzy variable. This conversion, which will be explained
in greater detail below, is carried out on the basis of continuous
curves defined over the entire universe of discourse of the
physical variables stored in a database 57 linked to the conversion
means 55.
104. II. Manner of operation of the device according to the
invention
105. The manner of operation of the device 1 according to the
invention will be explained hereinbelow while setting forth in
detail on the one hand the various processing and conversion steps
implemented in the processing and conversion means 21, and on the
other hand the implementing of the application of the rules to the
fuzzy variables by the means 23 according to fuzzy logic.
106. II.1 Determination of the phases of nasal inhalation and
exhalation of the user as well as of the amplitude of the nasal
flow
107. Represented in FIG. 2 are the main operating steps implemented
by the means 27 and 29.
108. During a first step 60, the signal of current consumed by the
turbine 9, delivered by the current sensor 17, is input into the
extraction means 27 and is then digitized there and sampled at a
rate of .DELTA.t.sub.s=25 ms during a second step 62.
109. Next, during a step 64, the average M.sub.1 of eighty sampled
values is calculated, this corresponding to an average of the
measurement values over a duration of 20 seconds. This duration of
20s corresponds to two or three breathing cycles of the user.
110. In parallel with this, during a step 66, the average M.sub.2
of five sampled values is calculated, this corresponding to an
average of the measurement values over a duration of 125
milliseconds and being in fact the almost raw signal, slightly
smoothed.
111. During a next step 68, the nasal flow F.sub.nasal is
calculated as the difference between M.sub.2 and M.sub.1.
112. Then, during steps 70 and 72, F.sub.nasal is compared with
respective thresholds S.sub.inhal and S.sub.exhal. The thresholds
S.sub.inhal and S.sub.exhal correspond to values representative of
the rate of flow of the nasal flow respectively above or below
which it is almost certain that the user is in a phase of
inhalation or exhalation. Of course S.sub.inhal is greater than
S.sub.exhal. The thresholds S.sub.inhal and S.sub.exhal can be
determined empirically by clinical trials on users.
113. If, during step 70, F.sub.nasal is greater than the threshold
S.sub.inhal, the value one is allocated during a step 74 to a
variable named cycle, cycle=1 therefore signifying that the user 3
is in a nasal inhalation phase, and then we return to step 62. If
F.sub.nasal is less than the threshold value S.sub.inhal, we return
directly to step 62.
114. If, during the comparison step 72, F.sub.nasal is less than
S.sub.exhal, then the value zero is allocated during step 76 to the
variable cycle, cycle=0 signifying that the user 3 is in a nasal
exhalation phase, and then we return to step 62. If F.sub.nasal is
greater than the threshold value S.sub.exhal, we return directly to
step 62.
115. These steps making it possible to determine the phases of
nasal inhalation and exhalation of the user are illustrated in FIG.
3. This FIG. 3 shows two graphs of which one, the upper graph,
shows a curve 78 of the nasal flow F.sub.nasal as a function of
time and the other, the lower graph, shows a curve 80 of the values
of the variable cycle which are allocated to this variable as a
function of the value of the nasal flow F.sub.nasal.
116. In this figure, it is clearly seen that as soon as F.sub.nasal
exceeds the threshold S.sub.inhal, cycle takes the value 1, and if
F.sub.nasal is less than S.sub.exhal, cycle takes the value 0. Up
to the instant referenced to it is possible to regard the user
having a normal breathing cycle.
117. Beyond t.sub.0, F.sub.nasal no longer manages, after entering
an exhalation phase, to exceed S.sub.inhal and cycle remains at the
value 0. This may be due to buccal respiration of the user, but
also to sleep hypopnoea or apnoea.
118. Furthermore, by measuring the time between the start of two
inhalation phases (cycle=1), the duration of the user's breathing
cycles is determined. By measuring the duration of the exhalation
phases, the potential ranges of sleep hypopnoea and apnoea are
determined since these phenomena are regarded as occurring only for
prolonged nasal exhalation phases, typically for exhalation phases
having a duration of greater than 3 seconds. For example, in FIG. 3
the user is, onwards of the instant t.sub.0, in a nasal exhalation
phase. Onwards of the instant t.sub.1, 3s later than t.sub.0, the
user is again in the nasal exhalation phase and therefore in a
potential time range of sleep hypopnoea or apnoea.
119. Additionally, to calculate the amplitude of the nasal flow
A.sub.nasal the means 30 determine, during an inhalation phase, the
maximum of the nasal flow F.sub.nasal (bearing the reference number
82) and during an exhalation phase the minimum of the nasal flow
F.sub.nasal (bearing the reference number 84), and calculate the
difference between this maximum and this minimum.
120. During a prolonged exhalation phase, that is to say one having
for example a duration of greater than 3 seconds, the means 30
receive from the means 29 a control signal so as to calculate the
amplitude of the nasal flow at each second, that is to say to
calculate the difference between the nasal flow determined at a
given instant and that at an instant preceding it by, for example,
one second. In FIG. 3, this determination at closely-spaced
intervals of time of the amplitude of the nasal flow is implemented
by the means 30 onwards of the instant t.sub.1.
121. II.2 Determination of an obstructive respiratory event termed
"limiting rate of flow"
122. A normal breathing cycle possesses a sinusoidal shape as
represented in FIG. 3 up to the instant t.sub.0. In the case of a
partial obstruction of the user's respiratory passages, the
inhalatory flow which increases at the start of an inhalation
phase, is rapidly limited so that the curved F.sub.nasal possesses
a clipped form. Such a curve 82 of F.sub.nasal as a function of
time in the case of a limiting rate of flow is represented by way
of example in the graph of FIG. 4.
123. In order to be able to detect such phenomenon accurately, the
means 31 calculate, during an inhalation phase, the time derivative
of the amplitude of the nasal flow F.sub.nasal, represented by the
curve 84 of FIG. 5.
124. The absolute value of the time derivative thus calculated is
compared at each instant by the means 35 with a reference value
V.sub.R recorded in the memory 37. Of course, it is also possible
to make provision for several reference values if this proves
necessary.
125. Furthermore, controlled by the comparison means 35, the means
39 measure the duration .DELTA.t.sub.DL for which the absolute
value of the derivative is less than the reference value
V.sub.R.
126. Additionally, during .DELTA.t.sub.DL the means 41 chart the
number of changes of sign of the derivative.
127. From the moment that .DELTA.t.sub.DL is greater than a
threshold duration lying for example between one and two seconds,
it is possible to conclude that the user is suffering from a
partial obstructive phenomenon. This diagnosis is reinforced when
the sign of the derivative changes many times during
.DELTA.t.sub.DL.
128. II.3 Determination of the amplitude of the buccal flow of the
user
129. The determination of the amplitude A.sub.buccal of the buccal
flow F.sub.buccal by the means 42 for processing the signal
delivered by the member 19 for qualitative measurement of the rate
of flow, for example by measurement of the resistance of a
thermistor, is similar to that of the amplitude A.sub.nasal for the
nasal flow F.sub.nasal. In effect, after some smoothing of the raw
signal and the subtracting of an offset, the difference between the
maximum and the minimum of the buccal flow F.sub.buccal is
calculated.
130. Preferably, so as to reduce the calculation and processing
steps, the amplitude A.sub.buccal is determined only during a phase
of prolonged nasal exhalation, that is to say one having a duration
of greater than 3 seconds. In this case, that is to say onwards of
the instant t.sub.1 represented in FIG. 3, the means 42 received
from the means 29 a control signal so as to calculate the amplitude
of the buccal flow at each second, that is to say to calculate the
difference between the buccal flow determined at a given instant
and that at an instant preceding it by, for example, one
second.
131. II.4 Determination of a phase of snoring of the user
132. Snoring is characteristic of an obstructive phenomenon in the
respiratory passages of a user. At the level of the pressure signal
measured by the sensor 13, it is manifested by oscillations which
are superimposed on the normal pressure signal as is represented in
the upper graph of FIG. 6 showing by way of example a curve 90
representative of snoring.
133. To determine whether the user 3 is suffering from snoring, a
high-pass filtering of the pressure signal is firstly carried out
in the means 45 and the filtered signal is amplified in the means
47. The filtered and amplified signal is represented as a function
of time by the curve 92 in the lower graph of FIG. 6.
134. Next, the amplified filtered signal is interpolated by way of
the means 49 so as to obtain an envelope curve 94. This envelope
curve 94 passes through all the maxima of the filtered and
amplified signal and, in the case of snoring, exhibits a
characteristic shape, This is why this envelope curve 94 is then
compared in the means 53 with the reference curve recorded in the
storage means 51 so as to determine the presence of snoring
phases.
135. II.5 Conversion of the processed physical variables into
states of fuzzy variables with degrees of membership
136. By way of example, explained in detail below is the conversion
of a processed physical variable, the amplitude of the nasal flow
A.sub.nasal when the duration of the nasal exhalation phase is
greater than three seconds, so as to establish its degree of
membership in one or more states of an associated fuzzy variable,
called A.sup.f.sub.nasal this conversion procedure is applied in a
similar manner to all the other physical variables to be taken into
account for applying rules according to fuzzy logic.
137. Represented in FIG. 7 is a graph showing, along the abscissa,
the universe of discourse of the nasal flow A.sub.nasal and, along
the ordinate, the membership values of states of the associated
fuzzy variable A.sup.f.sub.nasal.
138. As may be seen in the figure, the fuzzy variable
A.sup.f.sub.nasal can take four states, namely the states called
"low", "medium-low", "medium-high" and "high".
139. With each state of A.sup.f.sub.nasal there is associated a
continuous curve 100, 102, 104 and 106 making it possible to
establish the degree of membership of a value of A.sub.nasal in one
or more states of the fuzzy variable A.sup.f.sub.nasal.
140. Thus for example, curve 100 is associated with the "low" state
and exhibits the shape of a plateau following by a negative slope.
Curve 102 is associated with the "medium-low" state and exhibits a
trapezium shape. Curve 104 is associated with the "medium-high"
state and exhibits a triangular shape, and curve 106 is associated
with the "high" state and exhibits a positive slope followed by a
plateau.
141. The shape of the curves 100, 102, 104 and 106 is defined
empirically from clinical trials on users. It is noted that the
plateaus at the ends of the universe of discourse of the physical
variables are generally retained.
142. Furthermore, the ordinate values of the curves 100, 102, 104
and 106 lie between zero (0) and one (1).
143. Moreover, it is important to note that the various curves 100,
102, 104 and 106 overlap in such a way that a value of A.sub.nasal
can belong to two states of A.sup.f.sub.nasal.
144. Thus for example the value A.sub.nasal=0.1 belongs to
145. a "low" state of the fuzzy variable A.sup.f.sub.nasal with a
degree of membership of 0.1, and
146. a "medium-low" state of the fuzzy variable A.sup.f.sub.nasal
with a degree of membership of 0.9.
147. This is also represented in FIG. 7.
148. These other physical variables are converted by the conversion
means 55 according to the same principle.
149. II.6 Application of rules to the states of fuzzy variables
with degrees of membership
150. The states together with their respective degrees of
membership of the fuzzy variables are input into means 23 for
applying rules stored in the memory 25 forming a knowledge base.
These rules are defined empirically from clinical trials on
users.
151. Each rule involves at least two different fuzzy variables to
obtain for example a degree of membership in a state of a phase of
sleep respiration of the user 3.
152. By way of example, indicated below is a suite of eleven rules
for two fuzzy variables, the abovementioned fuzzy variable
A.sup.f.sub.nasal as well as the fuzzy variable A.sup.f.sub.buccal.
This fuzzy variable A.sup.f.sub.buccal can also take four states,
namely the states referred to as "low", "medium-low", "medium-high"
and "high", and the degrees of membership in these states are
established from the amplitude of the buccal flow A.sub.buccal when
the duration of the exhalation phase is greater than three
seconds.
1 Phase of No. A.sup.f.sub.buccal A.sup.f.sub.nasal .fwdarw.
respiration 1 medium-high medium-high normal 2 low medium-high
hypopnoea 3 medium-low medium-high hypopnoea 4 medium-high low
hypopnoea 5 low low apnoea 6 medium-low low hypopnoea 7 medium-high
medium-low hypopnoea 8 low medium-low hypopnoea 9 medium-low
medium-low hypopnoea 10 high normal 11 high normal
153. Let us assume that A.sub.nasal belongs to
154. a "low" state of the fuzzy variable A.sup.f.sub.nasal with a
degree of membership of 0.1, and
155. a "medium-low" state of the fuzzy variable A.sup.f.sub.nasal
with a degree of membership 0.9,
156. and that A.sub.buccal belongs to
157. a "low" state of the fuzzy variable A.sup.f.sub.buccal with a
degree of membership of 0.7, and
158. a "medium-low" state of the fuzzy variable A.sup.f.sub.buccal
with a degree of membership 0.2.
159. The means 23 apply rules 1 to 11 in the following manner so as
to determine the phases of respiration according to fuzzy
logic.
160. Initially, the means 23 consider only the relevant rules, that
is to say those rules for which a degree of membership is assigned
to a state of the first fuzzy variable and a degree of membership
is assigned to a state of the second fuzzy variable. In the present
example, these are rules No. 5, 6, 8 and 9.
161. Next, a "MIN-MAX" selection order is applied. This order
consists in assigning, initially, to a respiratory phase,
associated with a specified rule, a degree of membership equal to
the minimum of the degrees of membership of the states of the said
fuzzy variables which are to be considered in respect of this
specified rule.
162. In the present example, by applying for example rule No. 5, we
find that the sleep of the user 3 is in an "apnoea" respiratory
phase with a degree of membership equal to MIN (0.7; 0.1)=0.1.
163. Similarly, by applying rule No. 6 we find that the sleep of
the user 3 is in a "hypopnoea" respiratory phase with a degree of
membership equal to MIN (0.2; 0.1)=0.1, by applying rule No. 8, in
a "hypopnoea" respiratory phase with a degree of membership equal
to MIN (0.7; 0.9)=0.7, and by applying rule No. 9, in a "hypopnoea"
respiratory phase with a degree of membership equal to MIN (0.2;
0.9)=0.2.
164. As final result of the degrees of membership of the respective
states of the respiratory phases of the sleep of the user according
to fuzzy logic, consideration is subsequently given to the maximum
membership value obtained for each state, namely in the present
example 0 for the state of normal respiration, 0.1 for the state of
apnoea respiration and 0.7 for the state of hypopnoea
respiration.
165. Thus, it is understood that the use of fuzzy logic makes it
possible to refine the diagnosis of the respiratory phases of a
user.
166. Advantageously, the processing and conversion means 21 as well
as the means 23 for applying rules and the memory 25 are embodied
mainly through a computer comprising interfaces adapted for
capturing the signals from the sensors 13, 17 and 19 and loaded
with programs adapted for processing and utilizing these
signals.
* * * * *