Note: Descriptions are shown in the official language in which they were submitted.
CA 02361631 2006-12-18
GAS SUPPLY FOR SLEEP APNEA
BACKGROUND OF THE INVENTION
The invention concerns a method of controlling an apparatus for supplying air
pressure to a patient suffering from sleep problems.
The invention also concerns an apparatus for supplying air pressure to a
patient
suffering from sleep problems.
These sleep problems are respiratory and tend to waken the patient
inopportunely.
They are for example apnoeas, hypopnoeas, acoustic vibrations or snores, or
limitation of the respiratory flow, due to a narrowing of the upper airways of
the
patient.
The document U.S. Pat. No. 5,458,137 describes a method and a device for
controlling respiration in the case of sleep problems, which use multiple and
variable
pressure levels.
A pressure source supplies a breathable gas compressed at a relatively low
pressure to
the airways of the user.
Pressure sensors monitor the pressures and convert them into electrical
signals.
The electrical signals are filtered and processed in order to extract specific
characteristics such as the duration and energy levels.
If these characteristics exceed chosen duration and energy level thresholds
beyond a
minimum time period, the microprocessor indicates the presence of a sleep
respiratory
problem.
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If a chosen number of these events appears during a chosen time period, the
microprocessor adjusts the pressure supplied by the source.
The document U.S. Pat. No. 5,490,502 describes a method and an apparatus for
optimizing the controlled positive pressure in order to minimize the air flow
coming
from a generator while ensuring that flow limitation in the airways of the
patient does
not take place.
Provision is made therei;n to detect flow limitation by analysing a
respiratory flow
wave.
As soon as the presence of a flow limitation has been analysed, the system
determines
an action to be performed for adjusting the controlled positive pressure.
The pressure is increased, reduced or maintained depending on whether flow
limitation has been detected and according to the previous actions implemented
by the
system.
The documents U.S. Pat. No. 5,335,654, EP-A-661 071 and EP-A-651 971 should
also be cited.
SUMMARY OF THE INVENTION
The invention aims to improve the methods and devices of the state of the art,
to
automatically and continuously adapt the delivered pressure to the state of
the patient
and to anticipate and prevent the appearance of problems.
A first object of the invention is a method of controlling an apparatus for
supplying air
pressure to a patient suffering from sleep problems such as apnoeas.
A second object of the invention is an apparatus for supplying air pressure to
a patient
suffering from sleep problems such as apnoea, implementing the supply method.
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As embodied and broadly described herein, the invention provides an apparatus
for
supplying air under pressure to a patient. The apparatus comprises: means for
providing a flow of air at a pressure to a patient during a respiratory cycle
of the
patient; means for determining the pressure of the flow of air during the
respiratory
cycle; means for determining the flow of air during the respiratory cycle;
means for
determining an amplitude of the flow of air during the respiratory cycle;
means for
determining a mean amplitude of the flow of air to the patient during a
predetermined
number of respiratory cycles; means for incrementing a hypopnoea time counter
when
the amplitude of the flow of air during a current respiratory cycle is less
than the mean
amplitude of the flow of air multiplied by a hypopnoea factor; means for
increasing
the pressure of the flow of air to the patient by a first pressure increase
value when the
hypopnoea time counter is greater than or equal to a first hypopnoea time
threshold;
means for reducing the pressure of the flow of air by a first pressure
reduction value
after increasing the pressure of the flow of air and when the pressure of the
flow of air
is less than a comparative pressure value; and means for reducing the pressure
of the
flow of air by a second pressure reduction value after increasing the pressure
of the
flow of air and when the pressure of the flow of air is greater than or equal
to the
comparative pressure value.
The patient wears a mask by means of which air under pressure is supplied to
his
upper airways by the apparatus.
According to the invention, a control algorithm is provided using an output
flow
signal from the apparatus for detecting apnoea, hypopnoea, flow limitation
events and
leakages, and using the analysis of an item of pressure information for
determining
the presence of snoring, also referred to as acoustic vibrations.
The pressure supplied to the upper airways of the patient by the apparatus can
be
maintained constant, be increased or reduced according to the determination of
the
event which has been performed by the control algorithm.
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Thus, if no respiration is detected by the control algorithm within a
predetermined
minimum time depending on a calculated mean respiration time, the presence of
an
apnoea is determined.
This predetermined minimum apnoea detection time is for example equal to a
time
constant, for example 10 seconds, added to a proportionality factor multiplied
by the
calculated mean respiration time, this factor being for example equal to 5/8.
For each apnoea, the output flow signal is amplified and filtered in order to
determine
the presence or absence of cardiac oscillations.
If cardiac oscillations were detected during the last elapsed time interval,
for example
equal to 5 seconds, then the apnoea is classified as being central and no
control takes
place in the algorithm.
If no cardiac oscillation was detected in this time interval, the apnoea is
classified as
being obstructive, and the pressure is increased by a predetermined value a
first time
and, during the same apnoea, twice more regularly, for example every 15
seconds.
The control algorithm compares peak-to-peak flow variations during the latest
respiration of the patient with respect to a predetermined number of previous
respirations, for example equal to 8.
After each respiration, a classification is performed into: normal
respiration, if the last
peak-to-peak flow value is within a given range with respect to the mean value
over
the previous 8 respirations, for example from 40% to 150% or 140% thereof;
hypopnoeic respiration, if the last flow value is below this range;
hyperpnoeic
respiration, if the last flow value is above this range.
A hypopnoea determination is made if hypopnoeic respiration detection takes
place
during at least a given time, for example 10 seconds, and terminates after a
given
number of normal or hyperpnoeic respirations, for example equal to 2.
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A hypopnoea determination causes a given increase in pressure, for example 1
cm
H20 first, and then, during the same hypopnoea, an increase in pressure by
another
given value, regularly, foi- example 0.5 cm H20 every two hypopnoeic
respirations.
The control algorithm analyses and compares, respiration by respiration, the
waveform of the respiratory flow with a sinusoidal waveform of the same period
and
same gradient.
After the comparison based on two flow form criteria, each respiration is
first
classified as normal, intermediate or limited flow.
A final classification, based on the combination of the flow classification
and the
occurrence of snores, changes the classification of respirations from normal
into
intermediate, respectively from intermediate into limited flow respiration.
Processing is decided upon when a certain number, for example 2, of successive
limited flow respirations or a certain number, for example 5, of successive
intermediate respirations itake place after for example two normal
respirations.
This processing causes a given increase in pressure, repeated regularly a
certain
number of times, for example 0.3 cm H20 three times every two respirations.
For each respiration, the pressure signal is amplified and filtered in order
to detect the
presence or absence of acoustic vibrations or snoring.
A determination of a valid snore is made by the control algorithm if the
detected
acoustic vibration occurred at least for a certain time, for example 7% of the
mean
duration of the last three respirations, and with a period less than a factor
proportional
to this mean time, for example 120% thereof.
In the case of a valid snore, the algorithm increases the pressure by a given
value, for
example 1 cm H20, if the last control due to a snore took place more than a
given
time previously, for example 1 minute.
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A mean leakage is deterrriined as being equal to the mean flow during
respiration.
The control algorithm continuously compares the current leakage with a leakage
limit,
it being possible to regulate said limit from the pressure.
If the current leakage exceeds the limit, all pressure increase controls
generated
following event detections are disabled.
After detection of an apnoea or a snoring event or a hypopnoea control or a
processing
decision, the algorithm will reduce the pressure by a given value, for example
0.5 cm
H20, in a first step after a given time, for example 5 minutes, and regularly
for the
following reductions, for example every minute.
A given maintenance pressure, for example 8 cm H20, is supplied by the
apparatus if
no respiration has been detected during a given time, for example two minutes,
or if
the pressure supplied has been greater than or equal to a given value for a
given time,
for example 17 cm H20 for 10 or 30 minutes.
One advantage of the method is an automatic adaptation of the detection
criteria to the
respiratory characteristics of the patient.
Thus, any modification of the respiratory rhythm is taken into account by the
algorithm for performing the detection.
The fact of involving a mean value of respiratory cycle time over a certain
number of
previous respiratory cycles has the effect of variations in the cycle and
respiratory
amplitude being tracked regularly and better detection.
The invention will be better understood from a reading of the following
description,
given with reference to the figures.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the apparatus for supplying air pressure to the
patient.
FIG. 2 depicts an algorithm for taking a decision with a view to a first
pressure
increase control.
FIG. 3 depicts an algorithm for indicating the appearance of problems.
FIG. 4 depicts a respiration designation algorithm.
FIG. 5 depicts an algorithm for detecting central and obstructive apnoea and
for
pressure control according to the result of these detections, as well as an
algorithm for
reducing pressure according to the previous appearance or not of events
representing
sleep problems.
FIG. 6 depicts an algorithm for designating cycles as normal ventilation,
hyperventilation or hypoventilation.
FIG. 7 depicts a hypopnoeic respiration detection algorithm.
FIG. 8 depicts a hyperpnoeic respiration detection algorithm.
FIG. 9 depicts a normal respiration detection algorithm.
FIG. 10 depicts a high pressure detection algorithm.
FIG. 11 depicts a mask leakage detection algorithm.
FIG. 12 depicts an acoustic vibration detection algorithm.
FIG. 13 depicts an algorithm for reducing pressure in the event of acoustic
vibration
detection.
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DETAILED DESCRIPTION OF EMBODIMENTS
In FIG. 1, the apparatus for supplying air pressure to a patient has a central
processing
and pressure control unit U, a controlled pressure supply module MPD, a mask
MVA
for the upper airways of the patient, and a tube CF for supplying air pressure
from the
module MPD to the mask MVA.
The air flow supplied to the patient and the air pressure prevailing in the
mask MVA
are measured by means of a supplied air flow sensor CDAF, connected to the
central
unit U, and by means of' a sensor CPM of pressure in the mask MVA, connected
to the
central unit U.
It is determined from the measured variables whether or not events
representing sleep
problems appear.
The algorithms of the method according to the invention are implemented by
software
integrated in the central unit U.
In FIG. 2, it is determined from the measured variables whether the current
respiratory
cycle of the patient corresponds to a predetermined valid respiratory cycle.
A problem appearance indicator BLN is set to a first problem appearance state
ON, if
the appearance of one or more of the events representing sleep problems is
determined.
The indicator BLN is set to a second problem absence state OFF, if the
appearance of
events representing sleep problems is not determined.
A count is made of a first number CCAR of valid respiratory cycles determined
since
the last pressure control.
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A count is made of a second number CCON of valid respiratory cycles determined
since the last change of the indicator BLN to the first state ON.
A count is made of a third number RC of successive changes of the indicator
BLN
from the second state OFF to the first state ON.
When the indicator BLN is in the first state ON, a first given increase of
supplied air
pressure is controlled, by means of the control C1, when all the following are
true:
- the current respiratory cycle has been determined as being valid;
- the first number CCAR is greater than a first predetermined integer number
RP;
- the second number CCON corresponds to one or more other second
predetermined integer numbers N;
- the third number RC is greater than or equal to a third predetermined
integer
number X.
When the indicator BLN changes from the second state OFF to the first state
ON, the
first given increase of supplied air pressure is controlled, by means of the
control C 1,
when, solely all the following are true:
- the current respiratory cycle has been determined as being valid;
- the first number CCAR is greater than a first predetermined integer number
RP;
- the third number RC is greater than or equal to a third predetermined
integer
number X.
In one embodiment, the second integer numlbers N are between 1 and 300.
In another embodiment, the second integer niumbers N are the first three
multiples of a
given integer No.
In another embodiment, the second integer numbers N are respectively 2, 4 and
6, No
being equal to 2.
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In another embodiment, the first predetermined integer number RP is between 1
and
255.
In another embodiment, the first predetermi ned integer number RP is equal to
10.
In another embodiment, the third predetermined integer number X is between 1
and
100.
In another embodiment, the third predetermined integer number X is equal to 1.
In another embodiment, the first given pressure increase control Cl is less
than +10
mbar.
In another embodiment, the first given pressure increase control Cl is
substantially
equal to +0.3 mbar.
The first and third numbers CCAR; RC of counted valid respiratory cycles and
counted changes are reset to 0, after the second counted number CCON of valid
cycles has reached the largest of the second predetermined integer numbers N.
The second counted number CCON is reset to 0 when the indicator BLN changes
from the second state OF]F to the first state ON.
The predetermined valid :respiratory cycle corresponds to a maximum
respiratory flow
greater than a predeterniined flow value such as 50 ml/s, an inspiratory
volume
greater than a predetermined volume value such as 0.05 liters and an absence
of
saturation at flow detection time.
In FIG. 3, in order to give the state ON or OFF to the problem appearance
indicator
BLN,
CA 02361631 2006-12-18
- when the apparatus is started up, a state variable ER is initialized to a
third
processing absence state NIR and the indicator BLN is initialized to the
second state OFF.
Then, sequentially,
- from the measured variables, the respiratory cycles are designated as
belonging to different categories such as limited flow cycle, intermediate
cycle, normal cycle and invalid cycle, each corresponding respectively to
weightings RSVO, REVO; RSV1, REV1; RSV2, REV2; 0,0;
- the weightings of the category of the currently designated cycle are
assigned to
first and second weighting accumulators SV; EV;
- if the designated cycle belongs to the invalid cycle category, the state
variable
ER is reset to the third state NIR and the indicator BLN is reset to the
second
state OFF and a first counter FLC is initialized to a predetermined value.
If the state of the state variable ER corresponds to the third state NIR:
- if the value of a first accumulator SV is less than a first comparative
value, the
counter FLC is reinitialized to its predetermined value;
- if the value of the first accumulator SV is substantially equal to its first
comparative value, no action is taken and the next test is passed to;
- if the value of the first accumulator SV is greater than its first
comparative
value, the state variable ER is changed to a fourth processing possibility
state
PR and the indicator BLN is set to the second state OFF.
If the state of the state variable ER corresponds to the fourth state PR and
- if the value of the first accumulator SV is less than its first comparative
value,
the first counter FLC is reinitialized to its predetermined value, and the
state
variable ER and the indicator BLN are reset respectively to the third and
second states NIR; OFF;
- if the value of the first accumulator SV is substantially equal to its first
comparative value, no action is taken and the next test is passed to;
- if the value of the first accumulator SV is greater than its first
comparative
value, the first counter FLC is made to take its previous value with the value
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of the first accumulator SV added to it, and if then the value of the first
counter FLC is greater than or equal to a predetermined high stop RMS:
- a second counter NC is reinitialized to a predetermined value;
- the state variable ER is changed to a fifth processing state IR; and
- the indicator BLN is changed to the first state ON.
If the state of the state variable ER corresponds to the fifth processing
state IR:
- if the value of the second accumulator EV is greater than a second
comparative value, the second counter NC is made to take its previous value
with the value of the second accumulator EV added to it, and
- if then the value of the second counter NC is greater than or equal to a
low stop RME, the state variable ER and the indicator BLN are reset
respectively to the third and second states NIR; OFF and the first and
second counters FLC; NC are reinitialized to their predetermined
respective values;
- or otherwise, the indicator BLN is changed to its first state ON;
- if the value of the second accumulator EV is less than its second
comparative
value, the second counter NC is reinitialized to its predetermined respective
value and the indicator BLN is changed to the first state ON;
- if the value of the second accumulator EV is substantially equal to its
second
comparative value, no action is taken.
In one embodiment, the weightings RSV2, REV2; RSV1, REV1; RSVO, REVO; 0,0
corresponding to the norrnal cycle, intermediate cycle, limited flow cycle and
invalid
cycle categories, are respectively substantially equal to -1; 1; 5 and 0 for
the first
accumulator SV and are respectively substantially equal to 1; -1; -1 and 0 for
the
second accumulator EV.
The first and second comparative values and the predetermined initialization
values of
the first and second counters FLC; NC are each substantially equal to 0.
The high and low stops RMS; RME are respectively substantially equal to 10 and
2.
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In FIG. 4, the measured respiratory cycles are designated.
The predetermined valid respiratory cycle corresponds to a maximum inspiratory
flow
greater than a predetermined flow value such as 50 ml/s, an inspiratory volume
greater than a predetermined volume value such as 0.05 liters, an absence of
saturation at flow detection time, a measured inspiratory time within a
predetermined
interval such as 0.5 seconds to 6 seconds and a measured respiratory cycle
duration
within another predetermined interval such as 1.5 seconds to 20 seconds.
If the measured respiratory cycle is determined as being valid, then
- a calculation is made of an equivalent sinusoidal curve meeting
predetermined
characteristics with respect to the inspiratory curve of the measured
inspiratory
cycle;
- a calculation is made of a surface criterion CS proportional to the ratio of
the
area delimited by the inspiratory curve to the area delimited by the
equivalent
sinusoidal curve, each being taken over the same time interval, within the
inspiratory phase of the measured respiratory cycle;
- a calculation is made of a criterion of correlation CC between the
inspiratory
curve of the measured inspiratory cycle and the equivalent sinusoidal curve;
- if the calculated correlation criterion CC is greater than or equal to a
first predetermined normal limit LN, and if the calculated surface
criterion C'S is greater than a second predetermined surface limit LS,
the measured respiratory cycle is designated as normal and otherwise,
it is designated as a limited flow cycle.
If the measured respiratory cycle was designated as a limited flow cycle,
- if the calculated surface criterion CS is greater than a third predetermined
expert limit LE, the measured respiratory cycle is redesignated as normal,
- or otherwise,
- if the calculated surface criterion CS is greater than a fourth
predetermined flow limit LD, the measured respiratory cycle is
redesignated as intermediate,
- and in the contrary case, it is designated as a limited flow cycle.
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The second surface limit LS, the fourth flow limit LD and the third expert
limit LE are
predetermined in an ascending order.
The predetermined characteristics of the equivalent sinusoidal curve comprise
a half
period substantially equal to the measured inspiratory time and a gradient at
the origin
substantially equal to that of the inspiratory curve when it reaches
substantially one
third of its maximum amplitude.
In one embodiment, the calculated surface criterion CS is substantially equal
to one
hundred times the ratio of the areas each taken from substantially one quarter
to three
quarters of the duration of the inspiratory phase of the measured respiratory
cycle.
The calculated correlation criterion CC is substantially equal to the maximum
of one
hundred times the coefficients of correlation between the inspiratory curve
and the
equivalent sinusoidal curve taken respectively over the second half of the
inspiratory
phase and over the whole thereof.
The first, second, fourth and third limits LN; LS; LD; LE are respectively
between 45
and 100; 0 and 100; 0 and 100; 0 and 100 and are for example substantially
equal to
87; 40; 60 and 90 respectively.
In FIG. 5, obstructive apnoeas and central apnoeas are detected.
The algorithm depicted in FIG. 5 is performed during each of a number (NINT)
of
predetermined consecutive time intervals TAC(j).
The predetermined consecutive time intervals TACO) are those within a
predetermined apnoea detection period PDAC.
In this algorithm, there are detected, for example by hardware means such as
analogue
or digital filters, the oscillations of the measured flow curve, which are of
frequencies
within a frequency range P2.
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Then it is detected whether the amplitude of the detected oscillations of the
measured
flow curve goes successively above and then below a first predetermined
central
apnoea threshold SAC or whether this amplitude remains less than the first
central
apnoea threshold SAC, as depicted is schematically at the right of FIG. 5 by:
- the behaviour of an obstructive apnoea flow curve (curve constantly below
the
first threshold SAC);
- the behaviour of a central apnoea flow curve (curve going a number of times
successively above and then below the first threshold SAC).
In the presence of at least one detection of a passage above and then below
the first
threshold SAC, a central apnoea detection CAC(D) is counted.
Then, at each apnoea detection period PDAC,
- the sum SIG is performed of the numbers CAC(i) of central apnoea detections
counted, successi'vely over the last (D+1) apnoea detection periods;
- a second predetermined increase of delivered air pressure is controlled C2
if
the sum SIG of the numbers CAC(i) of counted detections is less than or equal
to a second predetermined central apnoea designation threshold SQAC;
- a maintenance of delivered air pressure is controlled, if the sum SIG of the
numbers CAC(i) of counted detections is greater than the second threshold
SQAC.
In one embodiment, the second central apnoea designation threshold SQAC is
between 0 and 50, and is for example substantially equal to 10.
The predetermined consecutive time intervals TAC(j) correspond to ten (NINT)
consecutive time intervals each of substantially 100 ms, the apnoea detection
period
PDAC corresponding substantially to 1 second.
The second pressure increase control C2 is between 1 and 10 mbar and is for
example
substantially equal to +1 mbar.
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The number (D+1) of apnoea detection periods PDAC, over which the sum of the
counted central apnoea detection numbers CAC(i) is performed, is substantially
equal
to 5.
The second oscillation frequency range P2 is between substantially 2.5 and 47
Hz.
The counted central apnoea detection numbers CAC(i) are reset to 0 when the
apparatus is started up.
FIG. 5 also depicts an algorithm for pressure reduction according to the
previous
appearance or not of events representing sleep problems.
According to this algorithm, depicted at the bottom of FIG. 5, the measured
pressure P
is compared with a predetermined pressure value MPL.
After determination of the appearance of one or more events,
- if the measured pressure P is less than the predetermined value MPL, a third
predetermined pressure reduction control 0 is performed;
- if the measured pressure P is greater than or equal to the predetermined
value
MPL, a fourth predetermined pressure reduction control C4 is performed;
- then, if no event appearance has been detected after one or more of the
pressure reduction controls C3; C4, the fourth predetermined pressure
reduction control C4 is performed.
The fourth pressure reduction control C4 is such that it causes a greater
pressure
reduction per unit of time than that caused by the third control C3.
In one embodiment, the fourth pressure reduction control C4 is substantially -
0.5
mbar/1 minute and the third pressure reduction control C3 is substantially -
0.5 mbar/5
minutes, the comparative pressure value MPL is between 4 and 19 mbar and is
for
example substantially equal to 17 mbar.
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This algorithm for pressure reduction according to the appearance or not of
events is
implemented after the one for central and obstructive apnoea detection as
depicted in
FIG. 5 but is also implemented, in non-depicted embodiments, after the other
algorithms such as:
- the one for processing decision taking, when the indicator BLN has changed
from the first state ON to the second state OFF;
- the one for hypopnoeic respiration detection described below;
- the one for acoustic vibration detection described below.
In FIGS. 6 to 9, the respiratory cycles are designated as hyperventilated,
hypoventilated or normal ventilation cycles and pressure controls are
generated
according to the designations made.
At each measured respiratory cycle end, the mean amplitude AM over a fourth
predetermined number Y4 of previous respiratory cycles is calculated.
As depicted in FIG. 7, if the measured amplitude of the last respiratory cycle
is less
than the calculated mean amplitude AM multiplied by a first predetermined
hypopnoea factor FHO, then the duration TC of the last measured respiratory
cycle is
added to a hypopnoea tinle counter CTHO,
- if the current value of the hypopnoea time counter CTHO is greater than or
equal to a minimum hypopnoea time TMHO, a fifth predetermined pressure
increase is controlled by means of a control C5;
- after the end of a fifth predetermined number Y5 of respiratory cycles
following the fifth pressure increase control C5, a sixth predetermined
pressure increase is controlled C6;
- after the end of a sixth predetermined number Y6 of respiratory cycles,
greater
than the fifth number Y5, following the fifth pressure increase control C5, a
seventh pressure increase is controlled by means of a control C7.
The hypopnoea time counter CTHO is initialized to 0 when the apparatus is
started
up.
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In one embodiment, the fourth given number Y4 of respiratory cycles for mean
amplitude calculation is substantially equal to 8.
The first predetermined hypopnoea factor FHO is between 1 and 100% and is for
example substantially equal to 40%.
The minimum hypopnoea time TMHO is between 1 second and 25 seconds and is for
example substantially equal to 10 seconds.
The fifth and sixth predetermined numbers Y5; Y6 of respiratory cycles are
substantially equal to respectively 2 and 4.
The fifth predetermined pressure increase C5 is between 0.1 mbar and 10 mbar
and is
for example substantially equal to +1 mbar.
The sixth and seventh predetermined pressure increases C6; C7 are each less
than the
fifth control C5 and are for example each substantially equal to half the
fifth pressure
increase C5.
As depicted in FIGS. 8 and 9, if the measured amplitude of the last
respiratory cycle is
greater than or equal to the calculated mean amplitude AM multiplied by the
first
hypopnoea factor FHO, then the mean respiratory cycle time TCM over a seventh
predetermined number Y7 of previous cycles is calculated.
If the measured duration TC of the last cycle is greater than an eighth
predetermined
number Y8 multiplied by the calculated mean respiratory cycle time TCM, the
measured duration TC of the last cycle, multiplied by a second hypopnoea
factor F2,
is added to the hypopnoea time counter CTHO.
If the measured amplitude of the last measured respiratory cycle is greater
than a third
hyperventilation factor F3, greater than the first hypopnoea factor FHO,
multiplied by
the calculated mean amplitude AM, the last cycle is designated as
hyperventilated, a
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hyperventilated cycle counter CCH is incremented by one unit, a normal
ventilation
cycle counter CCN is reset to 0 and
- if the value of the hyperventilated cycle counter CCH is greater than or
equal
to a ninth predetermined number Y9,
- if the duration of the last cycle TC is greater than or equal to the eighth
number Y8 multiplied by the calculated mean cycle time TCM, the
second factor F2 multiplied by the duration of the last respiratory cycle
TC is added to the hypopnoea time counter CTHO;
- and otherwise, the hypopnoea time counter CTHO is reset to 0;
then a hypoventilated cycle counter CCHO is reset to 0 and the mean
respiratory cycle
amplitude AM over the predetermined number Y4 of previous respiratory cycles
is
calculated.
If the measured amplitud.e of the last measured respiratory cycle is less than
or equal
to the third factor F3 multiplied by the calculated mean amplitude AM, the
last cycle
is designated as a normal ventilation cycle, the hyperventilated cycle counter
CCH is
reset to 0 and the normal ventilation cycle counter CCN is incremented by one
unit,
and
- if the value of the normal ventilation cycle counter CCN is greater than or
equal to a tenth predetermined number Y 10,
- if the duration of the last cycle TC is greater than or equal to the eighth
number Y8 multiplied by the calculated mean cycle time TCM, the
second factor F2 multiplied by the duration of the last cycle TC is
assigned to the hypopnoea time counter CTHO and the normal
ventilation cycle counter CCN is reset to 0,
- and otherwise, the hypopnoea time counter CTHO is reset to 0;
then the hypoventilated cycle counter CCHO is reset to 0 and the mean
amplitude of
the respiratory cycle over the predetermined number Y4 of respiratory cycles
is
calculated.
In one embodiment, the second factor F2 is substantially equal to 5/8.
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The third hyperventilation factor F3 is between 100% and 200% and is for
example
substantially equal to 140%.
The seventh, eighth, ninth and tenth predetermined numbers Y7; YB; Y9; Y10 are
respectively substantially equal to 3; 2; 2; and 2.
In FIG. 10, it is detectect whether the pressure is too high.
If the measured pressure P is less than a predetermined high pressure value
PH, a high
pressure time counter TPH is reset to 0.
If the value of the high pressure time counter TPH is greater than a maximum
high
pressure time TMPH and
- if the maximum regulated pressure value Pmaxi is less than a predetermined
safety pressure value PSEC, the pressure P is controlled to this maximum
regulated pressure value Pmaxi;
- if the minimum regulated pressure value Pmini is greater than a
predetermined
safety pressure value PSEC, the pressure P is controlled to this minimum
regulated pressure value Pmini;
- if the previous two conditions are not fulfilled, the pressure P is
controlled to
the safety pressure value PSEC.
then
- the high pressure time counter TPH is reset to 0.
In one embodiment, the high pressure value PH is between 10 mbar and 25 mbar
and
is for example substantially equal to 17 mbar.
The maximum high pressure time TMPH is between 1 and 100 minutes and is for
example substantially equal to 10 minutes or 30 minutes.
The safety pressure value PSEC is substantially equal to 8 mbar.
CA 02361631 2006-12-18
In FIG. 11, an air leakage is measured, substantially equal to the mean flow
during
respiration of the patient.
If the measured air leakage is greater than a predetermined leakage level NFM,
the
pressure increase controls are invalidated.
In one embodiment, NFM = A x Pfiltered + B.
According to this formula, the predetermined leakage level NFM is
substantially
equal to a leakage coefficient A multiplied by a filtered air pressure in the
mask,
added to an additive leakage coefficient B, the leakage coefficient A being
between 0
and 10 liters/minute.mbar and being for example substantially equal to 2.5
liters/minute.mbar.
The additive leakage coefficient B is between 0 and 100 liters/min and is for
example
substantially equal to 50 liters/min.
In FIG. 12, it is detected whether the measured pressure curve has
oscillations, such as
acoustic vibrations, within a frequency range P 1.
This detection is performed for example by hardware means such as analogue or
digital filters.
A measurement is made of the detected oscillation presence time RF 1 between
two
successive absences of detected oscillations and the detected oscillation
absence time
RFO between two successive presences of detected oscillations.
If the sum of the measured detected oscillation absence and presence times
RFO; RF 1
is within a prescribed time range SIP; BSP.
If the measured oscillation presence time RF 1 is greater than or equal to a
minimum
oscillation time TMRH and if the value of a counter CTAR of elapsed time since
the
last but one time that the previous time conditions were fulfilled is greater
than a
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CA 02361631 2006-12-18
prescribed waiting time TAR, an eighth predetermined pressure increase is
controlled
C8 and the elapsed time counter CTAR is reset to 0.
The algorithms for acoustic vibration detection and control in the case of
acoustic
vibrations are implemented at prescribed time intervals, notably regularly and
for
example every 100 ms.
At the start of the acoustic vibration detection algorithm depicted in FIG.
12, if the
value of the elapsed time counter CTAR is less than the prescribed waiting
time TAR,
this counter is incremented (INC CTAR) by the prescribed time interval
mentioned
above.
If the sum of the measured detected oscillation presence and absence times
RFO; RF1
is below the prescribed time range BIP; BSP or if the measured detected
oscillation
presence time RF1 is less than the minimum oscillation time TMRH,
- the measured detected oscillation absence time RFO is replaced by the sum of
the measured detected oscillation absence and presence times RFO; RF 1, and
then
- the measured detected oscillation presence time RF 1 is reset to 0.
If the sum of the measured detected oscillation absence and presence times
RFO; RF1
is above the predetermined time range BIP; BSP or a predetermined maximum time
TCMax, each of the measured detected oscillation absence and presence times
RFO;
RF I is reset to 0.
If the two conditions rnentioned above concerning the sum of the presence and
absence times RF 1, RFO and the presence time RF 1 are not fulfilled, each of
the
measured detected oscillation absence and presence times RFO; RF 1 is reset to
0.
In one embodiment, the predetermined maximum time TCMax is substantially equal
to twice the mean respiratory cycle time TCM over the last three measured
cycles.
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The prescribed time range BIP; BSP is substantially between 10% and 120% of
the
calculated mean cycle time TCM.
The minimum oscillation time TMRH is substantially equal to 7% of the
calculated
mean cycle time TCM.
The prescribed waiting time TAR is between 1 and 30 minutes and is for example
substantially equal to 1 minute.
The eighth pressure increase control C8 is between 0.1 mbar and 10 mbar and is
for
example substantially equal to I mbar.
The oscillation detection frequency range P1 is between substantially 30 and
300 Hz.
The chronology of the detected events is stored and the stored chronology is
read, for
example after one night.
To that end, the central unit U of the apparatus has a memory, not depicted,
capable of
being written and read with the chronology of the detected events.
This chronology can be displayed, for example on a monitor, by reading the
content
of the memory, by means of a computer, not depicted.
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