CA2138132C

CA2138132C - Breathing aid apparatus particularly for treating sleep apnoea

Info

Publication number: CA2138132C
Application number: CA002138132A
Authority: CA
Inventors: Guy Bourdon
Original assignee: Mallinckrodt Developpement France SAS
Current assignee: Covidien AG
Priority date: 1992-06-15
Filing date: 1993-06-09
Publication date: 2006-06-06
Anticipated expiration: 2013-06-09
Also published as: US20010004894A1; FR2692152B1; US6283119B1; JP2001000547A; ATE165982T1; JP3477200B2; JP3474522B2; EP0680350A1; EP0680350B1; DE69318576T2; AU4331293A; AU679917B2; WO1993025260A1; CA2138132A1; DE69318576D1; JPH07507466A; FR2692152A1; US6571795B2

Abstract

A compressor (1) driven by motor (3) sends to a nasal mask (4) a breathable gas at a low positive relative pressure. The motor (3) is controlled in order to maintain the pressure in the delivery pipe (2) of the compressor (1) substantially equal to a set point (P c), independently of the inspiration and expiration of the patient. A computer (16) receives on an input (14) a motor speed signal (3) as a parameter representative of the respiratory activity of the patient. When the analysis of the motor speed variations reveals a hypopnoea, the computer increases the pressure set point (P c). When the analysis of the motor speed variations reveals an absence of hypopnoea during a predetermined period of time, the computer reduces the pressure set point (P c) by a predetermined amount.
Utilization in order to optimize the pressure applied to the patient while taking into account the different phases of sleep, the evolution of the disease, etc.

Description

.
-~- 2 "Breathing aid apparatus in particular for treating sleep apnoea"

The present invention relates to a breathing aid apparatus, in particular for treating people which are prone to the disease called "sleep apnoea".

Sleep apnoea syndrome (SAS) is the accumulation of signs as well as their consequences due to the periodic interruption of respiration during sleep. The re-establishment of respiration generally only occurs when the person concerned wakes up. This phenomenon can occur several hundred times per night, with interruptions of 10 seconds or more each time.
Three types of apnoea syndrome exist, each corresponding to a particular pathology.
The first type, which is the most common, is obstructive apnoea. It results from an obstruction of the upper respiratory tracts caused by a collapse of the tongue and the palate. The respiratory movements continue, but because of this obstruction, air can neither enter nor leave the lungs.
The second type, which is rarer, is called "central apnoea". It is produced when the respiratory centre of the brain no longer controls respiration. In the absence of a signal originating from the brain, the respiratory muscles do not function and air can neither enter nor leave the lungs.
The third type is mixed apnoea which is a combination of the two previous types, the start of the apnoea being of central type.
In the case of obstructive apnoea and mixed apnoea, treatment by continuous positive pressure is the most commonly used. This technique consists of permanently applying, via a nasal mask connected by a pipe to a pressure generating apparatus, a low positive relative pressure in the upper respiratory tracts in order to avoid their obstruction.
This pressure prevents the tongue and palate from sticking together. The result is immediate: interrupted respiration is re-established, the lungs receive the oxygen they need and the person sleeps much better.
The optimum value of the pressure corresponds to the minimum allowing the suppression of apnoeas and the oxygen desaturations which result in the blood.
Determination of this optimum pressure is carried out in the laboratory, by subjecting the patient to a polygraph recording, and by progressively raising the level of pressure applied to the patient until the disappearance of respiratory incidents.
The treatment described previously, which consists of applying a constant pressure level to the patient throughout the night, has certain deficiencies.

In fact, the frequency and extent of apnoeas vary during the night according to the stage of sleep the patient is in.
Also, they vary over time as a function of the development of the condition of the patient (gain or loss of weight, absorption of alcohol before going to sleep...).

Therefore, the treatment pressure determined by the prescription is not necessarily adequate subsequently. Now, control recordings cannot be carried out regularly, due to their cost and the significant burden on sleep laboratories, connected with the large number of patients to be treated.

In addition, the patient is subjected to an identical pressure all night, whereas depending on the stages of his sleep, a lower pressure may be sufficient, or a higher pressure may be necessary. Now, the lower the average pressure applied during the night is, the better the MODIFIID PAGE

patient's comfort will be and therefore his acceptance of the treatment, and the more the deleterious effects linked with too high a pressure will be minimised.
Therefore the invention relates to a breathing aid apparatus, in particular for treating sleep apnoea, comprising means for producing a flow of breathable gas under a low positive relative pressure, means for guiding this flow to a respiratory mask, means for acquiring a parameter representative of the respiratory activity of the patient, and automatic adjustment means for increasing the pressure applied at least when the representative parameter is indicative of a hypopnoea, and for reducing the applied pressure when the representative parameter is indicative of normal respiration over a predetermined time.
The term "hypopnoea" encompasses the phenomena of the total disappearance of respiration, and can also include certain phenomena of partial disappearance of respiration, due to a partial obstruction of the upper respiratory tract.
Such an apparatus is known from WO-A-9014121, according to which a respiratory pressure is applied to the patient which is varied during the respiratory cycle in order to give him a maximum value at the start of inspiration with the aim of effecting a sort of forced opening of the respiratory tract at this stage of the cycle. Furthermore, it is envisaged that the applied pressure is modified as a function of respiratory activity. This device is complex and expensive.
In an apparatus known from WO-A-8810108, the speed of an insufflation compressor is adjusted as a function of respiratory activity.
In these two previous apparatuses, in order to carry out the adjustment, respiratory activity is detected by its MODIFIED PAGE

effects, in particular its sonorous effects, on the environment. This prior art is based on the fact that apnoeas or hypopnoeas are frequently indicated by a period of respiratory snoring.

Such a detection is complex to put into operation, is inaccurate and is subject to dysfunctions. In particular, perhaps it is effective for detecting snoring, but if the apnoea or hypopnoea is not preceded by such a forewarning symptom, the whole device is ineffective for correcting the applied pressure.

Therefore the aim of the present invention is to propose a breathing aid apparatus which is both straightforward, more economical and more reliable.
According to the invention, the breathing aid apparatus control is characterized in that it comprises in addition/means for adjusting the operation of a source of breathable gas in order to tend to automatically bring the flow pressure of the gas flow to a set point value which is the same for the inspiration and expiration phases, and in that the automatic adjustment means are means for modifying the pressure set point value, and in that the means for acquiring the representative parameter are means for acquiring the amplitude of the variation of a parameter which varies when the cont r o1 means modify the operation of the source in order to maintain a constant pressure.
According to the invention, the pressure applied during the entire respiratory cycle is adjusted to an approximately constant value. In this way, the excess pressure which tends to become established when the patient expires "against" the pressure produced by the apparatus is eliminated. Resulting from this adjustment is a cyclic variation of activity of the respiratory apparatus, with a stronger activity during J, N-L

MODIFIID PAGE

-4/1- ? 1 38 1 3 2 inspiration and a reduced activity during expiration. This cyclic variation of activity can be detected based on different parameters, for example, speed of the turbine if the breathable gas source is a compressor, flow rate of breathable gas delivered to the patient, etc...
The more intense the respiratory activity of the patient is, the greater the amplitude of these cyclic variations becomes.

This is why it is envisaged according to the invention to detect the said amplitude variations in order to increase the pressure set point when this amplitude drops below a certain threshold beneath which it is considered that a respiratory anomaly exists.

Therefore, the invention uses criteria which are straightforward and easy to use in order to detect the anomalies.

Furthermore, the adjustment which is carried out, consisting of a variation of the pressure set point, is easy to implement with precision.

This process allows hypopnoeas to be put to an end while permanently minimizing the applied pressure.

Preferably, the pressure cannot go below a lower threshold defined by the consultant and set on the apparatus, and of course it cannot exceed the maximum value that the apparatus is capable of delivering, or a maximum value defined by the doctor.
Other characteristics and advantages of the invention will become apparent from the description below, with reference to the non-limitative examples.
According to a broad aspect, the invention provides a breathing aid apparatus, in particular for treating sleep apnoea. The apparatus comprises means for producing a flow of breathable gas under a positive relative pressure, means for leading this flow to a respiratory mask, means for acquiring a parameter representative of the respiratory activity of a patient, and automatic adjustment means for increasing the pressure applied at least when the representative parameter is indicative of a hypopnoea, and for reducing the applied pressure when the representative parameter is indicative of normal respiration over a predetermined time. The breathing aid apparatus is characterized in that the means for acquiring a representative parameter are means for acquiring an amplitude of variation induced by the respiratory activity of the patient, and further include means for acquiring the amplitude of variation of a parameter which is indicative of the flow of breathable gas.
According to another broad aspect, the invention provides a breathing aid apparatus, that includes means for producing a flow of breathable gas to a patient having respiratory activity, means for controlling the pressure of the flow of the breathable gas, and means for calculating an amplitude of variation indicative of the respiratory activity of a patient, wherein the amplitude of variation is a function of a variable measured from.
the means for producing a flow of breathable gas. The breathing aid apparatus further includes detecting means for determining the presence of a hypopnoea from an analysis of the amplitude of variation and adjustment means for increasing the pressure of the flow of breathable gas when said detecting means determines the presence of a hypopnoea.

According to yet another broad aspect, the invention provides a breathing aid apparatus that comprises a compressor, a pressure detector, a comparator, a motor control and a computer. The compressor has a drive motor configured to produce a flow of breathable gas to a patient. The pressure detector is in fluid communication with an outlet of the compressor, and the comparator has a first input, a second input and an output, wherein the pressure detector generates a first signal connected to the first input. The motor control is operably connected to the drive motor of the compressor and generates a second signal indicative of the rotational speed of the drive motor, wherein the motor control accepts the output of the comparator. The computer is configured to accept the second signal from the motor control and to calculate an amplitude of variation based on the second signal to detect the presence of a hypopnoea. The computer further generates a pressure set point connected to the second input to the comparator, such that the set point is calculated to increase the pressure of the flow of breathable gas when the amplitude of variation is indicative of a hypopnoea.

According to still another broad aspect, the invention provides the use of a breathing aid apparatus for treating sleep apnoea that comprises the steps of producing a flow of breathable gas to a patient having respiratory activity, controlling pressure of the flow of the breathable gas, calculating an amplitude of variation indicative of the respiratory activity of the patient, and increasing the pressure of the flow of breathable gas when the amplitude of variation is indicative of a hypopnoea.

In the attached drawings:

- Figure 1 is a diagram of an apparatus according to the invention;

- Figure 2 is a flow chart for the operation of the computer of Figure 1;

- Figures 3 and 4 are diagrams similar to Figure 1 but relating to two other embodiments; and - Figure 5 is a flow chart of the operation of the computer.

The apparatus represented in Figure 1 comprises a compressor 1 capable of producing through its delivery pipe 2 a breathable gas at a positive relative pressure, i.e.

measured relative to atmospheric pressure, which depends on the rotational speed of the drive motor 3. In a non-represented manner, the compressor 1 is of a type which produces the positive relative pressure by a turbine for propelling breathable gas. The delivery pipe 2 is connected to ?0 a nasal mask 4 by a flexible tube 6. The nasal mask 4 is intended to be applied to the patient's face, for example by means of a strap. The mask 4 includes an opening 7 allowing the patient to expire despite the flow in the opposite direction coming from the compressor 1.

A comparator 8 permanently compares the pressure Pm detected in the delivery pipe 2 of the compressor 1 by a pressure detector 9 with a pressure set point PC applied to the other input 11 of the comparator 8. As a function of the result of the comparison, the comparator 8 supplies at its output 12 a signal applied to a motor control device 13 to reduce the rotational speed of the motor 3 when the pressure measured by the detector 9 is greater than the pressure set point, and to increase the rotational speed of the motor 3 and therefore the pressure at the delivery pipe 2 when the pressure measured by the detector 9 is lower than the pressure set point.

In this way, the pressure at the delivery pipe 2 and therefore in the nasal mask 4, is approximately the same during the inspiration phases and during the expiration phases of the patient.

During the inspiration phases, a relative low pressure tends to be created at the delivery pipe 2 of the compressor 1, and maintaining the pressure at the set point value requires an increase in the rotational speed of the motor 3.

On the other hand, during the expiration phases of the patient, an excess pressure tends to be created at the delivery pipe 2, and maintaining the pressure at the set point value requires a decrease in the rotational speed of the motor 3.

Consequently, when the respiration of the patient is normal, the rotational speed of the motor 3 follows a periodical curve.

According to the embodiment in Figure 1, a signal representative of the rotational speed of the motor 3 is applied by the control device 13 to the input 14 of a computer 16 whose function is to analyze the curve of the speed of the motor 3 as a parameter representative of the respiratory activity of the patient, and to modify the pressure set point PC applied to the input 11 of the comparator 8 as a function of the result of this analysis.
In a general fashion, when the analysis of the curve of the rotational speed of the motor reveals a hypopnoea situation, the computer 16 increases the pressure set point.
On the other hand, if the analysis of the curve of the speed of the motor reveals an absence of hypopnoea for a ~:. 10 certain predetermined period of time, the computer reduces by a predetermined amount the pressure set point.
The computer 16 is connected to a manual control 17 allowing the minimum pressure set point Pmin authorized by the doctor for each patient to be adjusted.
There will now be described with reference to Figure 2, the flow chart according to which, essentially, the computer 16 is programmed.
In what follows, by "hypopnoea" is meant the symptom consisting either of an abnormal lowering (for example by 50%) of the respiratory activity, or the symptom of total apnoea consisting of the complete disappearance of respiratory activity.
At the start, the pressure set point Pc is chosen to be equal to Pmin, i.e. the minimum pressure set point chosen using the manual control 17 (stage 18).
In stage 19, the values An-8, An-7, ..., An-1 of the amplitude of the motor speed variation during the eight respiratory cycles before the one which is currently being analyzed, are arbitrarily set equal to a value A0 which is relatively low.
Then, in stage 21, the average of the amplitudes of the eight previous cycles (average M) is calculated and two thresholds S1 and S2 are calculated with for example:
S1 = 0.8 M

S2 = 0.7 M
In stage 22 the extreme values of the rotational speed of the motor are sought.
In order to do this, the rotational speed of the motor at each execution cycle of the program is stored in memory.
A maximum or minimum is only validated if the speed has then varied sufficiently so as to be back from ' this maximum or minimum by a value at least equal to threshold S2.
In other words, as the threshold S2 is greater than half of the average of the previous amplitudes, a given extreme value will only be processed if the speed again then reaches a value beyond that of the average of the speeds. In particular, if respiration stops (total apnoea), the speed of the motor assumes its average value and the previous extreme value is not validated. More. generally, if an amplitude lower than threshold S2 tends to become established, it will no longer be possible to validate the extreme values.
After a period of time T1 equal for example to 10 seconds, this is detected in the following test 23. In the absence of an extreme value for 10 seconds, one follows the path "detection of strong hypopnoea" 24 of the flow chart, in which the four amplitudes An-8 ... An-5 which are the oldest values still in memory are reduced to the relatively low value of A0. The aim of this is to reduce the thresholds S1 and S2 for the next calculation cycle so as to make the resumption of respiratory activity easier to detect.
Returning to test 23, if an extreme value was found within the 10 previous seconds and if this extreme value is the same as that already processed during the previous calculation cycle, one returns to stage 23 in order to search ,. .fi.

for extreme values.
If, on the other hand, the extreme value is new, one passes via stage 26 for calculating the new amplitude An, then, stage 27, storing in memory the amplitude An while simultaneously deleting the oldest amplitude in memory An-8.
In stage 28, the newly-calculated amplitude An is compared with the largest Sl of the two thresholds.
If the newly-calculated amplitude An is greater than threshold S1, one follows normal respiration path 29 which will be described further on.
In the opposite case, i.e. if the amplitude is between thresholds Sl and S2, it is considered that a weak hypopnoea 31 exists.
Whether strong hypopnoea 24 or weak hypopnoea 31 has been recorded, a test 32 is carried out in order to determine whether there was already a hypopnoea during the previous 30 seconds. If the result is negative a number MAP is reset to zero. MAP corresponds to the total increase in pressure in the previous 30 seconds.
If, on the other hand, there was hypopnoea during the previous 30 seconds, the MAP number is not reset to zero.
The following stage 33 consists of adding a relatively high increment to the MAP number if strong hypopnoea was detected, and a relatively low increment if weak hypopnoea was detected. Then, in stage 34, a test is carried out to establish whether the MAP number is greater than 6 cm of water (6hPa). If the result is negative, stage 36, an increment X, being high or low depending on the strength of the hypopnoea, is added to the pressure set point P,. If, on the other hand, MAP exceeds 6hPa, the pressure set point P, is only increased to the extent that the total increase in the previous 30 seconds is equal to 6hPa (stage 37).

The aim of this is to avoid increasing the pressure excessively to treat a single hypopnoea: if an increase of more than 6 cm of water is necessary to treat a hypopnoea, it is because there is some anomaly and it would be better to wake the patient up.
Then, the new pressure set point is applied to the comparator 8 in Figure 1 on the condition that it does not exceed the maximum pressure set point Pmax= If the pressure Pc exceeds Pmax, the set point applied to the comparator 8 is equal to Pmax (stage 38). One is then returned to stage 21 in which the thresholds are calculated. If the strong or weak hypopnoea which was detected during the previous cycle is still not alleviated, the pressure set point will be increased by a new increment and so on until the total 1 5 pressure increase M A P within 30 seconds reaches 6 cm of water or until the hypopnoea is alleviated.
In this way, the amplitude is compared to two different thresholds, one to detect strong hypopnoeas, including total hypopnoeas, and to apply a relatively swift increase in the pressure set point, the other to detect weak hypopnoeas, resulting from a partial obstruction of the upper respiratory tract, and to apply a clearly m i 1 d e r increase in pressure.
One of the important features of the invention consists of analyzing the parameter representative of respiratory activity (the speed of the motor 3) not by comparison with absolute thresholds, but by comparison with the respiratory activity which has just preceded the respiratory anomaly. In fact, it has been noted that respiratory activity varies greatly during sleep, to the extent that an activity which would be considered normal during a certain phase of sleep can correspond to a hypopnoea in another phase of sleep.

Returning to path 29 of the flow chart, this leads to a test 39 for determining whether a time T has passed without detecting a hypopnoea. If the result is negative, one returns to stage 21 in which the thresholds are calculated.
5 If, on the other hand, a time T2, for example equal to 30 minutes, has passed without a hypopnoea, the pressure set point is reduced by, for example, 2 cm of water. In this way one provides an opportunity to bring the pressure applied-to the patient to a lower value if this is possible.

10 However, if the new pressure set point thus became lower than the minimum pressure as set with the manual control 17 of Figure 1, the pressure set point is simply reset equal to the minimum pressure set. Then, once again, one is returned to stage 21 in which the thresholds are calculated.
In the example represented in Figure 3, which will only be described with regard to its differences relative to that of Figure 1, a flow rate detector 41 is placed on the delivery pipe 2 of the compressor 1 whose signal is sent to an input 42 of the computer. On the other hand the computer no longer receives a signal corresponding to the rotational ~.. speed of the motor. It is now the flow rate signal provided by the detector 41 which provides the computer with the parameter representative of the respiratory activity. When the patient inspires, the flow rate detector 41 reveals a higher flow rate than when the patient expires. In other words, the variations in flow rate work in the opposite sense to those of the speed of the motor 3. Apart from that, nothing is changed, and the flow chart of Figure 2 is valid for the embodiment of Figure 3, with the exception that in stage 22 in which the extreme values are sought, the word "speed" must be replaced by the words "flow rate".
The example of Figure 4 corresponds to a simplified -õ - 2 13 8 1 version.
In this example, which will only be described with regard to its differences relative to that of Figure 1, there is no pressure regulation at the delivery pipe 2, i.e., apart from situations of apnoea or hypopnoea, the motor 3 rotates at the same speed whether the patient inspires or expires.
The pressure at the delivery pipe 2 is therefore relatively low when the patient inspires and relatively high when `-he expires. Therefore, the pressure at the delivery pipe 2 constitutes a parameter representative of the respiratory activity and it is, as such, detected by the pressure sensor 9. The computer 16, which receives the pressure signal 9 on an input 43, analyzes the pressure curve and provides the control device 13 of the motor 3 with a signal for increasing the speed of the motor 3 when the variations in pressure indicate a situation of hypopnoea, and for decreasing the speed of the motor 3 when any situation of hypopnoea has not been alleviated within a predetermined period of time, for example 30 minutes.
Figure 5 represents a schematic flow chart according to which the computer 17 of Figure 4 can be programmed.
At the start, the speed V of the motor is adjusted to a value Vmin (stage 44) set with a manual control 46 (figure 4).
Then one passes to stage 47 in which hypopnoeas are detected according to the amplitude of the variations in pressure. This stage can correspond to stages 21 and 22 of Figure 2, except that it is then applied to the pressure instead of being applied to the speed of the motor. In the absence of hypopnoea, one passes via path 48 in which the speed of the motor is reduced by a predetermined value n' if a time T2, for example 30 minutes, has passed without A

-12 213813~

hypopnoea, without however lowering the speed to a value which is less than the set speed Vmin*
In the case of a hypopnoea being detected during a period of time greater than or equal to a value T1 of for example 10 seconds, the speed V is incremented by a predetermined value n, without however allowing the speed to exceed a value Vmax=
Consequently, in this simplified example, only a single degree of intensity of hypopnoea is distinguished and when the hypopnoea is detected, one and the same mode of action is envisaged in every case, i.e. an incrementation of the speed of the motor according to one predetermined step and one only.
Of course, the invention is not limited to the examples as described and represented.
In the computers of the embodiments according to Figures 1 and 3 a program could be envisaged which distinguishes only one type of hypopnoea, or on the other hand, the embodiment according to Figure 4 could be equipped with a program which processes in a different way the weak hypopnoeas and the strong hypopnoeas as was described with reference to Figure 2.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A breathing aid apparatus, in particular for treating sleep apnoea, comprising means for producing a flow of breathable gas under a positive relative pressure, means for leading this flow to a respiratory mask, means for acquiring a parameter representative of the respiratory activity of a patient, and automatic adjustment means for increasing the pressure applied at least when the representative parameter is indicative of a hypopnoea, and for reducing the applied pressure when the representative parameter is indicative of normal respiration over a predetermined time, characterized in that the means for acquiring a representative parameter are means for acquiring an amplitude of variation of a parameter which is indicative of the flow of breathable gas induced by the respiratory activity of the patient.

2. The breathing aid apparatus according to claim 1, characterized in that said automatic adjustment means are means for adjusting the speed of a motor of a compressor for production of the flow of breathable gas.

3. The breathing aid apparatus according to claim 1, characterized in that it furthermore comprises means for controlling operation of a source of breathable gas in order to automatically bring the flow pressure in said flow of breathable gas to a set point value which is the same for inspiration and expiration phases, in that said automatic adjustment means for modifying said set point value of the pressure, and in that said variable, the amplitude of which is acquired by the acquisition means of the representative parameter is a variable which varies when the control means applies modifications to the operation of the source in order to maintain the pressure at a constant magnitude.

4. The breathing aid apparatus according to one of claims 1 to 3, characterized in that said means of acquiring a representative parameter comprise means for detecting the flow rate of the breathable gas.

5. The breathing aid apparatus according to one of claims 1 to 3, characterized in that said means of acquiring a representative parameter comprise means for detecting an operation parameter of a compressor producing the flow of breathable gas.

6. The breathing aid apparatus according to one of claims 1 to 5, characterized in that it comprises comparison means for comparing the amplitude of said variation with at least one threshold calculated from at least one amplitude value relating to at least one previous variation period, and in that said automatic adjustment means automatically increase the applied pressure when the amplitude is below the threshold.

7. The breathing aid apparatus according to claim 6, characterized in that said threshold is calculated from an average amplitude value relating to several prior periods.

8. The breathing aid apparatus according to one of claims 1 to 5, characterized in that it comprises means for comparing the amplitude of said variation with a validation threshold and in that the automatic adjustment means increase the applied pressure when the amplitude remains below the validation threshold for a second predetermined duration time.

9. The breathing aid apparatus according to one of claims 1 to 5, characterized in that it comprises means for comparing the representative parameter with a threshold for weak hypopnoea and a threshold for strong hypopnoea, in that said automatic adjustment means increase the applied pressure by a first incremental adjustment when the parameter is beyond the threshold for strong hypopnoea, relative to the threshold for weak hypopnoea, and by a second incremental adjustment when the parameter is comprised between the two thresholds.

10. The breathing aid apparatus according to one of claims 6 to 9, characterized by means for reducing the threshold after detection of a hypopnoea.

11. The breathing aid apparatus according to one of claims 1 to 10, characterized in that the adjustment means are adapted to increase the pressure by successive incremental adjustments when the representative parameter retains a value indicative of a hypopnoea.

12. The breathing aid apparatus according to claim 11, characterized by comprising means for limiting the increase in pressure permitted for a predetermined time interval.

13. A breathing aid apparatus, comprising:

means for producing a flow of breathable gas to a patient having respiratory activity;

means for controlling pressure of the flow of the breathable gas;

means for calculating an amplitude of variation indicative of the respiratory activity of a patient, wherein the amplitude of variation is a function of a variable measured from said means for producing a flow of breathable gas;

detecting means for determining the presence of a hypopnoea from an analysis of the amplitude of variation;

and adjustment means for increasing the pressure of the flow of breathable gas when said detecting means determines the presence of a hypopnoea.

14. The breathing aid apparatus of claim 13, wherein said adjustment means for increasing the pressure includes means for adjusting the speed of operation of a motor driving a compressor adapted to produce the flow of breathable gas.

15. The breathing aid apparatus of claim 13, wherein said means for producing a flow of breathable gas includes a drive motor operably connected to a compressor.

16. The breathing aid apparatus of claim 15, wherein said means for controlling pressure of the flow of breathable gas includes a motor control operably connected to the drive motor, a pressure detector and a comparator operably connected to the motor control.

17. The breathing aid apparatus of claim 16, wherein said means for calculating an amplitude of variation includes a signal from the motor control indicative of the rotational speed of the drive motor.

18. The breathing aid apparatus of claim 16, wherein said means for calculating an amplitude of variation includes a signal from a flow detector indicative of the flow rate of breathable gas to the patient.

19. The breathing aid apparatus of claim 13, wherein said detecting means includes means for comparing the present amplitude of variation indicative of the respiratory activity of the patient with at least one threshold value calculated from at least one previous amplitude of variation indicative of the respiratory activity of the patient, wherein said adjustment means increases the pressure of the flow of the breathable gas when the amplitude of variation is lower than the threshold value.

20. The breathing aid apparatus of claim 19, wherein the threshold value is calculated from an average amplitude of variation indicative of the respiratory activity of the patient calculated from at least three previous variation periods.

21. The breathing aid apparatus of claim 17, wherein said detecting means includes means for comparing the amplitude of variation with a validation threshold, wherein said adjustment means increases the pressure of the flow of breathable gas when the amplitude of variation remains below the validation threshold for a predetermined period of time.

22. The breathing aid apparatus of claim 13, wherein said detecting means includes means for comparing the amplitude of variation with a first threshold for a weak hypopnoea and a second threshold for a strong hypopnoea, wherein said adjustment means increases the pressure of the flow of breathable gas by a first incremental adjustment when the amplitude of variation is greater than the second threshold for strong hypopnoea, and by a second incremental adjustment when the amplitude is between the first and second thresholds, such that the first incremental adjustment is greater than the second incremental adjustment.

23. The breathing aid apparatus of claim 13, wherein said adjustment means includes means for reducing the pressure of the flow of breathable gas when said detecting means determines the lack of a hypopnoea over a predetermined time.

24. A breathing aid apparatus, comprising:
a compressor having a drive motor and configured to produce a flow of breathable gas to a patient;

a pressure detector in fluid communication with an outlet of said compressor;

a comparator having a first input, a second input and an output, wherein the pressure detector generates a first signal connected to the first input;
a motor control operably connected to the drive motor of said compressor and which generates a second signal indicative of the rotational speed of the drive motor, wherein the motor control accepts the output of the comparator; and a computer configured to accept the second signal from the motor control, the computer further configured to calculate an amplitude of variation based on the second signal and to detect the presence of a hypopnoea, wherein the computer generates a pressure set point connected to the second input to the comparator, such that the set point is calculated to increase the pressure of the flow of breathable gas when the amplitude of variation is indicative of a hypopnoea.

25. The breathing aid apparatus of claim 24, wherein said computer is further configured to compare the amplitude of variation with at least one threshold value calculated from at least one previous variation period, wherein said computer increases the pressure set point when the amplitude of variation is lower than the threshold value.

26. The breathing aid apparatus of claim 25, wherein the threshold value is calculated from an average amplitude value calculated from at least three previous variation periods.

27. The breathing aid apparatus of claim 24, wherein said computer is further configured to compare the amplitude of variation with a validation threshold, wherein said computer increases the pressure set point when the amplitude of variation remains below the validation threshold for a predetermined period of time.

28. The breathing aid apparatus of claim 24, wherein said computer is further configured to compare the amplitude of variation with a first threshold for a weak hypopnoea and a second threshold for a strong hypopnoea, wherein said computer increases the pressure set point by a first incremental adjustment when the amplitude of variation is greater than the second threshold for strong hypopnoea, and by a second incremental adjustment when the amplitude is between the first and second thresholds, such that the first incremental adjustment is greater than the second incremental adjustment.

29. The breathing aid apparatus of claim 24, wherein said computer is further configured to reduce the pressure of the flow of breathable gas when the amplitude of variation is indicative of lack of a hypopnoea over a predetermined time.

30. A breathing aid apparatus, comprising:

a compressor having a drive motor and configured to produce a flow of breathable gas to a patient;
a pressure detector in fluid communication with an outlet of said compressor, wherein the pressure detector generates a first signal;

a flow rate detector in fluid communication with an outlet of said compressor, wherein the flow rate detector generates a second signal;
a comparator having a first input, a second input and an output, wherein the first signal is connected to the first input;
a motor control operably connected to the drive motor of said compressor, wherein the motor control accepts the output of the comparator; and a computer configured to accept the second signal from the flow rate detector, the computer further configured to calculate an amplitude of variation based on the second signal and to detect the presence of a hypopnoea, wherein the computer generates a pressure set point connected to the second input to the comparator, such that the set point is calculated to increase the pressure of the flow of breathable gas when the amplitude of variation is indicative of a hypopnoea.

31. The breathing aid apparatus of claim 30, wherein said computer is further configured to compare the amplitude of variation with at least one threshold value calculated from at least one previous variation period, wherein said computer increases the pressure set point when the amplitude of variation is lower than the threshold value.

32. The breathing aid apparatus of claim 31, wherein the threshold value is calculated from an average amplitude value calculated from at least three previous variation periods.

33. The breathing aid apparatus of claim 30, wherein said computer is further configured to compare the amplitude of variation with a validation threshold, wherein said computer increases the pressure set point when the amplitude of variation remains below the validation threshold for a predetermined period of time.

34. The breathing aid apparatus of claim 30, wherein said computer is further configured to compare the amplitude of variation with a first threshold for a weak hypopnoea and a second threshold for a strong hypopnoea, wherein said computer increases the pressure set point by a first incremental adjustment when the amplitude of variation is greater than the second threshold for strong hypopnoea, and by a second incremental adjustment when the amplitude is between the first and a second thresholds, such that the first incremental adjustment is greater than the second incremental adjustment.

35. The breathing aid apparatus of claim 30, wherein said computer is further configured to reduce the pressure of the flow of breathable gas when the amplitude of variation is indicative of lack of a hypopnoea over a predetermined time.

36. The use of a breathing aid apparatus as defined in claim 1.

37. A breathing aid apparatus, comprising:
means for producing a flow of breathable gas to a patient having respiratory activity;
means for controlling pressure of the flow of the breathable gas;
means for calculating an amplitude of variation indicative of the respiratory activity of a patient, further including means for calculating the amplitude of variation as a function of a variable measured from the means for producing a flow of breathable gas;
detecting means for determining the presence of a hypopnoea from an analysis of the amplitude of variation; and adjustment means for increasing the pressure of the flow of breathable gas when said detecting means determines the presence of a hypopnoea, and for decreasing the pressure of the flow of breathable gas when said detecting means determines the presence of normal breathing.

38. A breathing aid apparatus, comprising:
a compressor having a drive motor and configured to produce a flow of breathable gas to a patient;
a pressure detector in fluid communication with an outlet of said compressor;
a comparator having a first input, a second input and an output, wherein the pressure detector generates a first signal connected to the first input;
a motor control operably connected to the drive motor of said compressor and which generates a second signal indicative of the rotational speed of the drive motor, wherein the motor control accepts the output of the comparator; and a computer configured to accept the second signal from the motor control, the computer further configured to calculate an amplitude of variation based on the second signal and to detect the presence of a hypopnoea, wherein the computer generates a pressure set point connected to the second input to the comparator, such that the set point is calculated to increase the pressure of the flow of breathable gas when the amplitude of variation is indicative of a hypopnoea, and to decrease the pressure of the flow of breathable gas when the amplitude of variation is indicative of normal breathing.