Snoredog

dsm wrote:In another thread you mentioned about the S8 Vantage using a mic to detect snores. This is info I am keen to learn about as it is not what I understood these machines did.

In FIG. 3, a CPAP apparatus embodying the invention is illustrated. The CPAP unit comprises a motor 20 which drives a blower 21. The speed of the motor 20 is controlled by an electronic speed control unit 23. As an increase in motor speed also increases the blower speed which in turn increases the output air pressure of the blower 21, the speed control unit can be manipulated to vary the output pressure of the blower 21. The CPAP device also includes a snoring detection means 22 wherein sounds are detected by a microphone 11. In its most general form, the snoring detection means 22 is a pressure detection means and microphone 11 is a differential pressure sensor. The snoring detection means 22 is conveniently in the form of the previously described device 10. Electrical impulses are fed from said microphone 11 to an amplifier/filter/processor unit 26 which generates an electrical signal when snoring sounds occur. The motor speed control means is electrically connected to the snoring detection device 22 and increases the speed of the electric motor 20 by an analogue means in response to the electrical signal generated by the snoring detection device. Accordingly, the output pressure of the CPAP unit increases in response to detection of snoring.

When a snore or sequence of snores is detected by the snoring detection means 22 a signal is generated. The speed control unit 23 increases the speed of the fan motor and the output pressure is increased. As snoring is caused by vibration of the soft palate, it is therefore indicative of an unstable airway and, as previously described, is a warning signal of the imminence of upper airway occlusion in patients that suffer obstructive sleep apnea. Snoring is itself undesirable not only as it is a disturbance to others but it is strongly believed to be connected with hypertension. If the resultant increase in CPAP pressure is sufficient to completely stabilize the airway, snoring will cease. If a further snoring sound is detected, the CPAP pressure is increased again. This process is repeated until the upper airway is stabilized and snoring ceases. Hence, the occurrence of obstructive apnea can be eliminated by application of a minimum appropriate pressure at the time of use.

In order to ensure that the CPAP pressure is maintained at a level as low as practicable to prevent the onset of apnea, the preferred embodiment also includes a means to decrease the pressure if an extended period of snore free breathing occurs. For example, this can be done by automatically reducing the CPAP pressure at a gradual rate as long as snoring is not detected. The rate at which the CPAP pressure is decreased in the absence of snoring is preferably much less than the rate at which it is increased when snoring is detected. This can be achieved, for example, by the amplifier/filter/processor unit 26, in the absence of an electronic signal from the microphone 11, continuously gradually reducing the blower speed over a period of time but increasing the blower speed in incremental steps each time a snore is detected by the microphone 11.

StillAnotherGuest wrote:

dsm wrote:In another thread you mentioned about the S8 Vantage using a mic to detect snores. This is info I am keen to learn about as it is not what I understood these machines did.

Although the term "transducer" is more commonly used to describe the device that detects snores, in the past, Mike has frequently used "microphone" in his inventions:

In FIG. 3, a CPAP apparatus embodying the invention is illustrated. The CPAP unit comprises a motor 20 which drives a blower 21. The speed of the motor 20 is controlled by an electronic speed control unit 23. As an increase in motor speed also increases the blower speed which in turn increases the output air pressure of the blower 21, the speed control unit can be manipulated to vary the output pressure of the blower 21. The CPAP device also includes a snoring detection means 22 wherein sounds are detected by a microphone 11. In its most general form, the snoring detection means 22 is a pressure detection means and microphone 11 is a differential pressure sensor. The snoring detection means 22 is conveniently in the form of the previously described device 10. Electrical impulses are fed from said microphone 11 to an amplifier/filter/processor unit 26 which generates an electrical signal when snoring sounds occur. The motor speed control means is electrically connected to the snoring detection device 22 and increases the speed of the electric motor 20 by an analogue means in response to the electrical signal generated by the snoring detection device. Accordingly, the output pressure of the CPAP unit increases in response to detection of snoring.

When a snore or sequence of snores is detected by the snoring detection means 22 a signal is generated. The speed control unit 23 increases the speed of the fan motor and the output pressure is increased. As snoring is caused by vibration of the soft palate, it is therefore indicative of an unstable airway and, as previously described, is a warning signal of the imminence of upper airway occlusion in patients that suffer obstructive sleep apnea. Snoring is itself undesirable not only as it is a disturbance to others but it is strongly believed to be connected with hypertension. If the resultant increase in CPAP pressure is sufficient to completely stabilize the airway, snoring will cease. If a further snoring sound is detected, the CPAP pressure is increased again. This process is repeated until the upper airway is stabilized and snoring ceases. Hence, the occurrence of obstructive apnea can be eliminated by application of a minimum appropriate pressure at the time of use.

In order to ensure that the CPAP pressure is maintained at a level as low as practicable to prevent the onset of apnea, the preferred embodiment also includes a means to decrease the pressure if an extended period of snore free breathing occurs. For example, this can be done by automatically reducing the CPAP pressure at a gradual rate as long as snoring is not detected. The rate at which the CPAP pressure is decreased in the absence of snoring is preferably much less than the rate at which it is increased when snoring is detected. This can be achieved, for example, by the amplifier/filter/processor unit 26, in the absence of an electronic signal from the microphone 11, continuously gradually reducing the blower speed over a period of time but increasing the blower speed in incremental steps each time a snore is detected by the microphone 11.

SAG

The Breathing Pattern Recognition also performs a secondary analysis, based on peak flow, to determine the occurrence of breathing problems like apnea and hypopnea, and detects snoring based on a frequency analysis of a pressure signal.

dsm wrote:I know that these were used in earlier Autos but understood that they were dropped infavour of airflow sensing (for vibrations).

CPAP treatment apparatus comprising...
...a pressure transducer to generate input for said processor...
...wherein said processor is programmed to perform the steps of:

determining a snore measure from said pressure transducer indicative of a level of snoring by the patient;
calculating a snore threshold as a function of said treatment pressure;
calculating an adjustment pressure by an amount that is a function of said snore threshold and said snore measure if said snore measure exceeds said snore threshold...

The flow sensor, located in the AUTOSET SPIRIT unit, enables detection of inspiratory flow limitation and apneas. The pressure sensor, also located in the unit, enables measurement of pressure and snore.

Figure 3: Inspiratory flow/time curve affected by snore
The AutoSet algorithm assigns an arbitrary value between 0.0 and 2.0 to the
average amplitude of the snoring detected for the past 5 breaths. A value of 1.0 is equivalent to approximately 75dBA measured 10cm from the nares. Treatment pressure increases by up to 0.2 cm H2O per second (proportional to the severity of the snore) for snore above 0.2 snore units. When snore is less than 0.2 snore units, therapy is reduced towards the minimum pressure with a 20-minute time constant.

An apnea is defined as a greater than 75% decrease in ventilation. The AutoSet algorithm scores an apnea if the 2-second moving average entilation drops below 25% of the recent time average (time constant 100 seconds) for at least 10 consecutive seconds. Treatment pressure increases based on the duration of the apnea. The pressure will not rise above 10 cm H2O when an apnea is detected, to prevent an inappropriate response to central apneas. Initial pressure increases are rapid, but the rate of increase diminishes as the pressure approaches 10 cm H2O.
When no further apneas are detected, therapy is reduced towards the minimum pressure with a 20-minute time constant.

A hypopnea is defined as a 50 to 75% drop in ventilation. A hypopnea is scored if the 8-second moving average ventilation drops below 50%, but not below 25%, of the recent average for 15 consecutive seconds. In order to avoid falsely responding to central hypopneas, the AutoSet algorithm does not respond to hypopneas but rather to the associated snore or flow limitation.

tangents wrote:Thanks for the tutorial, SWS, very interesting. Do any of the other brands try to detect snoring?

tangents wrote:Thanks, SWS, both for the additional information, and for pointing out my SAG-ging memory! Thanks to you, SAG, for your tutorial.

I read the article on the Respironics Flow Measurements (you just gotta love pv=nRt), and started wondering about Purital Bennett. I found a White paper describing the GoodKnight 420E system, maybe you have already read it. It claims ~95% sensitivity in snoring detection. They also use a pneumotachograph.

I'm still trying to decide which machine to buy, so all this information is good stuff!

Wulfman wrote: Do you snore?

-SWS wrote:

Wulfman wrote: Do you snore?

Thanks, Den!! Don't mind if I do...

<zzzzzzzz... gurgle.... gasp...... choke... once again wide awake>

How about yourself? Care for an after-lunch snore?