WO2001087156A1

WO2001087156A1 - Detection of breathing disturbances

Info

Publication number: WO2001087156A1
Application number: PCT/NO2001/000192
Authority: WO
Inventors: Rolf Kahrs Hansen; Magne Tvinnereim
Original assignee: Medisinsk Registrering Og Analyse As
Priority date: 2000-05-16
Filing date: 2001-05-09
Publication date: 2001-11-22
Also published as: NO20002538D0; NO20002538L; AU2001260810A1

Abstract

This invention relates to a method and an assembly for the detection and analysis of breathing disturbances, which comprises: measuring of pressure in at least one position in the airways and related organs, and generating a signal corresponding to the measured values, measuring of snoring and generating a signal indicating the excistence of snoring, measuring of air flow in at least one position in or in relation to the airways and related organs, and generating a signal corresponding to the measured values, filtering of said signals for generating of filtered signals comprising frequencies between a lower and an upper frequency limit, and detection of the degree of fluctuations in the signals within a chosen interval of time from the snoring started, for the classification of the type and the position of the breathing disturbances.

Description

DETECTION OF BREATHING DISTURBANCES

This invention relates to a method and an assembly for the detection and analysis of breathing disturbances.

Breathing problems caused by obstructions in the airways and related organs, such as snoring, is a common problem, and the symptoms most frequently referred to are snoring, hypersomnia (augmented daytime sleepiness) and apneas, being total or partial breathing stops, which together is named Obstructive Sleep Apnea Syndrome (OSAS) . In OSAS a total breathing stop is called an apnea, while a partial reduction of more than 50% is named a hypopnea, both having at last for more than 10 seconds. The most common and prominent of the abovementioned features is the snoring, which in addition to indicate the potential dangerous desease also is very little socially accepted.

Furthermore, recent studies have shown that slightly augmented airways pressure during sleep and snoring alone can result in problems like those initiated by apneas. By additionally causing lighter sleep stages superimposed on the deep sleep stages, the important brain and body rest is compromised. The result may be multiple changes throughout the organism, such as hypertonia, heart arrhytmias, heart infarctation, hormone changes, brain haemorrhage as well as social disorders, traffic accidents etc. These problems are seen in addition to the utmost social unaccepted snoring, which in fact is the most common reasong for people to seek medical treatment .

Different treatments of snoring and OSAS have been elaborated, among them surgical methods. To be able to obtain satisfactory results, it is, however, mandatory preoperative to get information of where in the airways the obstruction is located, so that the treatment can be applied in the correct region. If for example the snoring or the apneas originate in the lower part of the upper airways, surgery is shown to be unsuccessful. For the same reasons it is also important to be able to classify the cessation, in order to provide the correct remedy. Thus it is an object of this invention to obtain a method and an assembly adapted to measure and classify the cessations in the air flow.

A problem related to performing the measurements, as well as some of the nonsurgical cures or remedies, is that the patient should not be disturbed by the instruments .

Thus it is an additional object of this invention to obtain a measuring method and assembly being able to conduct the measurements essentially without affecting the patients sleep, which in turn might affect the measurements. It is known, e.g. from "pressure recordings in the diagnosis of Obstructive Sleep Apnea Syndrome" , by Magne Tvinnereim, University of Bergen, Norway, 1995, that pressure recordings may be used in the diagnosis of OSAS . If only small fluctuations in pressure at a given point is measured the air flows freely and there is no obstruction. If there is an obstruction the pressure beneath this point will fluctuate as the patient tries to breath.

The known method does, however, not obtain sufficient information about the breathing of the patient, as it would not provide information of cessations below the point of measurement. It is another object of this invention to provide a method and an assembly being capable of indicating the existence of a cessation below the measuring point . The objects of the invention are obtained using a method and an assembly characterized as described in claim 1 and 5, respectively.

In order to provide a compact and, to the patient, as comfortable as possible, instrument and method, the sensors should be as small as possible. A compact air flow sensor may be obtained indirectly by using a temperature sensor. The temperature of the air flow will vary according to its direction, since the air inside the lungs will have a higher temperature than the air drawn in from outside. Also a small contribution may be added as the evaporation from the sensor will be more effective when the air is moving, giving a cooling effect.

For a better understanding of the features and objects of the invention, a more detailed description is given below by use of an example and referring to the enclosed drawings . Figure 1 gives a schematic view of a cross section of a patient with a measuring instrument positioned in the airways and related organs . Figure 2 shows a flow chart illustrating the analysis of the measured signal. Figure 3 illustrates schematically the assembly according to the invention. Figure 1 illustrates the position of an instrument through the patients nose and extending down into the pharynx. The pressure sensors 2 may be positioned in chosen positions along a catheter 1 to detect obstructions in different parts of the pharynx. In the figure the lower end of the catheter 1 and the sensors 2 are positioned in the oesophagus .

The pressure sensors 2 may be of any suitable kind being at least small enough to be mounted on e.g. a catheter to be positioned in the breathing organs. They should also be easy to clean and robust, which may be obtained providing a protective layer of silicone. Preferably the pressure sensors have a sensitivity in the mm H₂0 range. Semiconductor strain gauges are preferred, but capacitive, fibre optic or piezoelectric sensors may also be used.

In a preferred embodiment the sensors are mounted in a Wheatstone bridge configuration, which in addition to high sensitivity allows for temperature compensation.

A temperature sensor 3 (see figure 3) may be positioned externally, with sensor elements in front of both the nose and the mouth, or in the throat. As was the case with the pressure sensors 2 the temperature sensor 3 should be robust and easy to clean. They should have a sensitivity in the desiKelvin range and be able to measure the temperature both of the oral and the nasal air flow, both the temperature of the inhaled air and the temperature of the exhaled air. Many sensors satisfy these requirements, e.g. thermistors, thermocouples and resistance temperature detectors (RTD) . The chosen sensor type may vary depending on the positioning of the sensor and the measurements needed. Snoring - understood as sound emissions during sleep - may be measured using one or more acoustic sensors 4 (see figure 3) , by attaching a vibration sensor to the outside of the throat of the patient, by placing a microphone in the vicinity of the patient or by using one of the pressure sensors extracting the acoustic frequencies using band pass filtering in a per se known way. In both cases band pass filtering followed by rectification and low pass filtering at suitable frequencies, each according to well known techniques, will yield a level proportinal to the generated sound, and remove disturbing signals caused by other sounds made during sleep, based on known parameters of the sound generated when snoring. These parameters may be adjusted according to the specific patient. The classification of apneic events are performed by first filtering the measured signals in order to avoid interfering noise. The signals are preferably band pass filtered at the approximate breathing frequency, for example within a range of 50-500mHz. The temperature signal is also compensated for zero offset by removing the mean value prior to band pass filtering.

In a preferred embodiment the signals are digitized at a chosen frequency f_s, e.g. 5 Hz .

The filtered digital signals within one or more chosen intervals of time are analysed to find the maximum and minimum value, and the difference y in measured value is found. Thus a value is found for each time interval indicating a degree of fluctuation of the measured value.

The time interval may be chosen according to the use of the invention. In the case of classification of apneic events the interval may typically be 10 seconds.

The classification of the apneas using at least one acoustic sensor, one or more pressure sensors and an air flow sensor/temperature sensor, is illustrated in figure 2, and is based upon the fact that an obstruction will lead to a pressure fluctuation below the obstruction, as the patient tries to breath. The air flow will stop in the entire system, and the pressure will not fluctuate above the obstruction. Thus, while normal breathing will be measured as regular, large fluctuations in temperature y_f and small fluctuations in pressure y_p, since the air moves freely in and out of the breathing organs, an obstruction may be indicated if the pressure fluctuates and the temperature variation stops, or is reduced. By using more than one pressure sensor along the catheter different positions of obstructions may be indicated.

The criterion for indicating a cessation of air flow may be chosen according to the standard deviation S_y of the signals. A cessation in the temperature signals, and thus a cessation in air flow, is defined when y_t < 0.3χS_yt, and similarly a cessation in the pressure signals is defined when y_p < 0.3xS_yp. A marked pressure fluctuation may be indicated when y_p -- 0.3 S_yp. The factor 0.3 is based on experience and comparative tests with conventional methods for sleep analysis.

Referring to the example shown in figure 2, if a cessation in air flow CF₁₀ is detected for at least 10 seconds and if all pressure signals reveal cessation of pressure fluctuations CP₁₀ in the same time window, the event is classified as a central apnea CA.

If a cessation in air flow CF₁₀ is detected for 10 seconds, but the cessation of pressure fluctuations CP₅ only last for 5 seconds, the apnea is classified as mixed MA if it is followed by a pressure fluctuations PF_S for at least 5 seconds .

Reduced breathing, hypoapnea H, has been detected if reduced temperature fluctuations RF₁₀ defined as y_t < 0.5xS_yt, are detected for at least 10 seconds.

In all the cases a level analysis of the signals may be performed. Snoring is a symptom indicating an increase in breathing resistance and is defined as acoustic energy above a threshold, the threshold being well above the background noise level. The acoustic signal is converted to an electrical signal using a suitable transducer, e.g. a microphone or vibration sensor, being band pass filtered. The envelope curve is digitized and stored at the same rate as the other signals. If snoring is detected the pressure gradients are computed as well as the location of the maximum obstruction, the latter being performed by level analysis. The analysis done during snoring may be excactly the same as when the hypopnea is detected. The snoring can be chosen and set as acoustic source level limit by the user of the analysis software .

Figure 3 illustrates schematically an assembly according to one embodiment of the invention, in which a number of pressure sensors 2 one temperature sensor 3 and a microphone 4 are connected to the apneagraph 5 which stores the signals in a RAM-card 6. The RAM-card may be connected to a computer 7, which may be of any suitable kind being capable of performing the necessary analysis. As mentioned above the pressure sensors 2 are located at different positions in the oesophagus. This provides a possibility to find the position of the possible obstructions, which provides a more detailed classification of the apneas. While the use of one pressure 2 and one air flow 3 sensor will provide a possibility to classify the type of apnea, the embodiment shown in figure 3 will provide a possibility to find the position of the problem.

If a cessation of air flow is detected for at least 10 seconds and if the oesophageal sensor does not reveal cessation of pressure fluctuations in the same time window, the event may be classified as an obstructive apnea. This obstructive event is caused by pharyngeal collapse in the segment between sensors with no (or restricted) pressure fluctuations and the adjacent distal transducer with augmented fluctuations.

If all pressure signals reveal cessation of pressure fluctuation for at least 5 seconds and this period is followed by a period of at least 5 seconds cessation of air flow, but with marked pressure fluctuations in phyranx, the event is classified as a mixed apnea, i.e. a mix of a central and obstructive apnea.

An acoustic sensor is also connected to the assembly in figure 3. This sensor may also be contained in the central apneagraph if it is to be positioned in the same room as the patient.

Claims

C l a i m s

1. Method for the detection and analysis of breathing disturbances, c h a r a c t e r i z e d in that it comprises : measuring of pressure in at least one position in the airways and related organs, and generating a signal corresponding to the measured values, acoustic measuring of snoring and generating a signal indicating the existence or amplitude of the snoring, and measuring the duration of said snoring, measuring of air flow in at least one position in or in relation to the airways and related organs, and generating a signal corresponding to the measured values, filtering of said pressure, snoring and air flow signals for generating of filtered signals comprising frequencies between a lower and an upper frequency limit, based on the measured snoring and detection of the degree of fluctuations in said pressure and air flow signals within a chosen interval of time for the classification of the type and the position of the breathing disturbances .

2. Method according to claim 1, c h a r a c t e r i z e d in detection of the highest and the lowest value for each of the pressure and air flow signals within the chosen time interval and calculation of the difference between them for the evaluation of the peak to peak amplitude of the fluctuations, and comparison of the fluctuations at each position for the classification of the breathing disturbances .

3. Method according to^" claim 1 or 2 , c h a r a c t e r i z e d in that the fluctuations of the air flow is measured by measuring fluctuations in the temperature of the air.

4. Method according to any one of the preceding claims, c h a r a c t e r i z e d in that the analysis according to the last step in claim 1 is performed in a time interval of at least 10 seconds from the detection of the snoring.

5. Method according to claim 1, c h a r a c t e r i z e d in that the total duration of the snoring is measured.

6. Assembly for the detection and analysis of breathing disturbances, c h a r a c t e r i z e d in that it comprises one or more pressure sensors being adapted to be positioned in the airways and related organs, one or more air flow sensors positioned in relation to or in the airways and related organs, the sensors being capable of generating signals corresponding to the measured values, an acoustic sensor being capable of detecting snoring, means for filtering said acoustic, pressure and air flow signals, generating filtered signals comprising frequencies within a chosen range, and means for calculating the fluctuations in the filtered signals in chosen time intervals for the classification of the type and/or position of the breathing disturbances .

7. Assembly according to claim 6, c h a r a c t e r i z e d in that it comprises means capable of digitizing the said signals from the sensors with a chosen sampling frequency.

8. Assembly according to claim 6 or 7, c h a r a c t e r i z e d in that it comprises means for detecting the highest and the lowest value for each of the pressure and air flow signals within the chosen time interval, and means for calculating the difference between them to find the amplitude of said fluctuations, and means for comparing the fluctuations for the classification of the breathing disturbances.

9. Assembly according to one of the claims 6-8, c h a r a c t e r i z e d in that the air flow sensor comprises a temperature sensor adapted to measure the temperature of the passing air flow.

10. Assemply according to claim 1, c h a r a c t e r i z e d in that it comprises a timing device connected to said acoustic sensor adapted to measure the duration of the snoring and other breathing disturbances .