WO2010071919A1 - Dispositif d'aide respiratoire - Google Patents

Dispositif d'aide respiratoire Download PDF

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Publication number
WO2010071919A1
WO2010071919A1 PCT/AU2009/001655 AU2009001655W WO2010071919A1 WO 2010071919 A1 WO2010071919 A1 WO 2010071919A1 AU 2009001655 W AU2009001655 W AU 2009001655W WO 2010071919 A1 WO2010071919 A1 WO 2010071919A1
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WO
WIPO (PCT)
Prior art keywords
respiration
stimulation device
subject
vibrator
controller
Prior art date
Application number
PCT/AU2009/001655
Other languages
English (en)
Inventor
Bredge Mccarren
John Eisenhuth
Original Assignee
The University Of Sydney
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2008906567A external-priority patent/AU2008906567A0/en
Application filed by The University Of Sydney filed Critical The University Of Sydney
Publication of WO2010071919A1 publication Critical patent/WO2010071919A1/fr

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H31/00—Artificial respiration or heart stimulation, e.g. heart massage
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H2201/00—Characteristics of apparatus not provided for in the preceding codes
    • A61H2201/50—Control means thereof
    • A61H2201/5002—Means for controlling a set of similar massage devices acting in sequence at different locations on a patient
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H2201/00—Characteristics of apparatus not provided for in the preceding codes
    • A61H2201/50—Control means thereof
    • A61H2201/5007—Control means thereof computer controlled
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H2201/00—Characteristics of apparatus not provided for in the preceding codes
    • A61H2201/50—Control means thereof
    • A61H2201/5058—Sensors or detectors
    • A61H2201/5071—Pressure sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H2201/00—Characteristics of apparatus not provided for in the preceding codes
    • A61H2201/50—Control means thereof
    • A61H2201/5058—Sensors or detectors
    • A61H2201/5084—Acceleration sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H2201/00—Characteristics of apparatus not provided for in the preceding codes
    • A61H2201/50—Control means thereof
    • A61H2201/5058—Sensors or detectors
    • A61H2201/5087—Flow rate sensors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H2230/00—Measuring physical parameters of the user
    • A61H2230/40—Respiratory characteristics
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61H—PHYSICAL THERAPY APPARATUS, e.g. DEVICES FOR LOCATING OR STIMULATING REFLEX POINTS IN THE BODY; ARTIFICIAL RESPIRATION; MASSAGE; BATHING DEVICES FOR SPECIAL THERAPEUTIC OR HYGIENIC PURPOSES OR SPECIFIC PARTS OF THE BODY
    • A61H23/00—Percussion or vibration massage, e.g. using supersonic vibration; Suction-vibration massage; Massage with moving diaphragms
    • A61H23/02—Percussion or vibration massage, e.g. using supersonic vibration; Suction-vibration massage; Massage with moving diaphragms with electric or magnetic drive
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
    • A61M16/021—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes operated by electrical means
    • A61M16/022—Control means therefor
    • A61M16/024—Control means therefor including calculation means, e.g. using a processor
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M2205/00—General characteristics of the apparatus
    • A61M2205/05—General characteristics of the apparatus combined with other kinds of therapy
    • A61M2205/054—General characteristics of the apparatus combined with other kinds of therapy with electrotherapy

Definitions

  • the present invention relates to a respiratory aid device that stimulates the chest wall of a user during respiration to reduce breathlessness.
  • In-phase vibration of the chest wall has been shown to have effects on ventilation and dyspnoea.
  • In-phase vibration has been applied by a vibratory pad to the inspiratory intercostal muscles during inspiration and to the expiratory intercostal muscles during expiration.
  • Both inspiratory and expiratory in-phase vibration have been noted to increase total volume, respiratory flow rates and minute ventilation in normal subjects and patients with chronic obstructive pulmonary disease (COPD).
  • COPD chronic obstructive pulmonary disease
  • Experimental results have also shown increases in arterial oxygenation in patients with COPD. Studies have noted that in patients with spinal-cord injuries (lower cervical, below C4) and COPD patients, functional residual capacity decreased with in-phase vibration.
  • the in-phase vibration decreased the sensation of dyspnoea in asthmatics, normal subjects with hypercapnic and resistant loads and COPD patients at rest and during exercise. Vibration may alter the input from the intercostal muscles that contributes to the sensation of dyspnoea.
  • the increase in ventilation and the improved mechanics and gas exchange may result in a decrease in the muscular effort (afferent information) of breathing and decrease the sensation of dyspnoea. Based on these findings it is possible vibration may increase ventilation and decrease dyspnoea.
  • a respiratory aid device for reducing breathlessness comprising:
  • a stimulation device that in use is positioned externally on the user to apply a mechanical vibration to stimulate intercostal muscles of the user;
  • a system for stimulating the chest wall of a subject during respiration to reduce breathlessness comprising:
  • respiration sensor operable to generate an output signal dependent on respiration of the subject
  • a stimulation device operable to stimulate the chest wall of the subject during respiration
  • a method for stimulating the chest wall of a subject during respiration to reduce breathlessness comprising:
  • a computer program product comprising machine-readable program code recorded on a machine readable recording medium, for controlling the operation of a data processing apparatus on which the program code executes to perform a method of stimulating the chest wall of a subject during respiration comprising:
  • a computer program comprising machine-readable program code for controlling the operation of a data processing apparatus on which the program code executes to perform a method of stimulating the chest wall of a subject during respiration comprising:
  • Fig 1A is a schematic block diagram of a system that includes a respiration sensor to detect respiration and a stimulation device to stimulate a user's chest wall;
  • Fig 1 B shows a schematic diagram of an embodiment of the system of Fig 1A in which the stimulation device is a vibrator;
  • Fig 2 shows a schematic diagram of a system controller for use in the system of Fig 1 B;
  • Fig 3 shows a schematic diagram of a vibrator controller for use in the system of Fig 1 B;
  • Fig 4 is a flow diagram of a method for generating a trigger signal based on an output of a respiration sensor
  • Fig 5A is a flow chart of a method for generating a vibrator drive signal to maintain a vibrator frequency at setpoint;
  • Fig 5B is a flow chart of a method for determining the period of vibration of the vibrator of Fig 1 B;
  • Fig 5C shows a flow chart of a method for generating the vibrator drive signal using fuzzy logic
  • Fig 6A shows an example of fuzzy sets that may be used with the error signal in the method of Fig 5C
  • Fig 6B shows an example of fuzzy sets that may be used with the error rate signal in the method of Fig 5C;
  • Figs 7A and 7B illustrate how membership of the fuzzy sets may be determined for error and error rate signals respectively;
  • Fig 8 shows an example of fuzzy output sets that may be used in the method of Fig 5C.
  • Fig 9 shows how the fuzzy output sets of Fig 8 may be used to generate a crisp output in the method of Fig 5C.
  • a system for providing in-phase stimulation of the chest wall of a subject to reduce breathlessness during respiration.
  • the term 'in-phase' indicates that the inspiratory intercostal muscles are stimulated during inspiration and/or the expiratory intercostal muscles are stimulated during expiration.
  • a vibrator is used to apply a mechanical vibration to the intercostal muscles used in inspiration or expiration.
  • a control method is described for controlling the frequency of vibration of the vibrator.
  • Fig 1A shows a system 1 that includes a respiration sensor 3, which is operable to determine whether the subject is inhaling or exhaling.
  • the respiration sensor 3 is in data communication with a system controller 5 that monitors the subject's respiration and sends control signals to a stimulation device 7 that stimulates the subject's chest wall in phase with the subject's respiration.
  • the stimulation device 7 is a vibrator.
  • other stimulating devices may be used.
  • a transcutaneous electrical neural stimulation (TENS) device may be used to apply an electrical stimulus to the subject's intercostal muscles instead of applying a mechanical vibration.
  • TENS transcutaneous electrical neural stimulation
  • the stimulation applied in the present arrangements is not designed to cause muscle contraction and alter the normal respiration of the subject. Instead, the stimulation provides an enhanced chest wall movement during respiration to assist in reducing breathlessness.
  • Fig 1 B shows a system 2 in which the stimulation device is one or more vibrators 11.
  • the stimulation device is one or more vibrators 11.
  • two control units are provided.
  • a vibrator controller 9 generates a drive signal to maintain the vibrator 11 at a desired frequency of vibration.
  • the system controller 5 monitors the respiration sensor 3 and generates a trigger signal based on the subject's respiration. The trigger signal is provided to the vibrator controller 9.
  • system controller 5 and vibrator controller 9 are provided in separate housings. However, in other arrangements the functions of the system controller 5 and vibrator controller 9 may be combined into a single unit.
  • the controllers may also be housed within a stimulation device 7.
  • the vibrator 11 may be an off-the-shelf vibrator of the type used in mobile phones, for example the VPM2 from www.solarbotics.com. Such a vibrator may be approximately 12mm in diameter and 3mm thick. When 3 volts DC is applied to the vibrator 11 it will generally vibrate at between 172 Hz and 200 Hz.
  • the vibrator unit 11 includes an accelerometer which is operable to sense the frequency of vibration of the vibrator.
  • An example of a suitable accelerometer is the ADXL103 accelerometer manufactured by Analog Devices, which has a maximum range of + 1.7g and a maximum frequency response of 2.5 kHz.
  • the vibrator unit 11 is positioned on the subject's intercostal muscles and held in position by, for example, elasticised straps.
  • the vibration may be applied to the second or third intercostal parasternal spaces by one or more inspiratory vibrators.
  • the vibration may be applied to the seventh to ninth intercostal midaxilliary spaces by one or more expiratory vibrators.
  • the force required to hold the vibrator 11 in place may affect the frequency of vibration of the vibrator.
  • one of the functions of the vibrator controller 9 is to generate a drive signal that maintains the frequency of the vibrator at a specified frequency.
  • More than one vibrator 11 may be used. In one arrangement two vibrators are attached to the subject's inspiratory muscles and two vibrators are attached to the subject's expiratory muscles.
  • the vibrator controller 9 may provide a control signal for each set of vibrators.
  • the respiration sensor 3 is a 100K NTC thermistor that is mounted on a plastic face mask. Air flow through the face mask effectively heats and cools the thermistor in phase with the subject's respiration. A constant current passing through the thermistor allows the voltage across the thermistor to vary with temperature. Monitoring the changing voltage enables the system controller 5 to determine whether the subject is inhaling or exhaling.
  • the thermistor may be attached to nasal prongs or, for example, to an apparatus that may be mounted on the subject's head in a similar fashion to audio headphones with an extension that can be positioned in front of the subject's mouth and nose. A sensor may be mounted on the extension.
  • respiration sensor may also be used, for example using a flow sensor or pressure sensor.
  • Other methods of monitoring respiration can also be used, for example sensing expansion or contraction of the subject's chest wall.
  • Fig 2 shows an example of a system controller 5 that receives input signals from the respiration sensor 3 at input 13.
  • the system controller unit 5 has an on-off switch 21.
  • the controller 5 also includes 2 light-emitting diodes (LEDs) 17, 19.
  • the power LED 17 indicates to the user the battery status of the system controller 5.
  • the LED 17 flashes at 4 Hz to indicate that the battery is good and flashes at 1 Hz to indicate that the battery needs replacing. As the battery state changes from good to low, the LED 17 flash rate may vary between 4 Hz and 1 Hz, providing further indication to the user that the battery may soon need replacing. If the power LED 17 fails to flash then either the battery is flat or a fault has developed in the system.
  • the inspiration LED 19 indicates to the user that the system controller 5 has detected inspiration.
  • the LED 19 lights up continuously for the duration of inspiration. If the LED 19 fails to light up either no inspiration has been detected or a system fault has developed. If inspiration is not detected the following checks may be performed:
  • An additional LED may be provided that indicates when expiration is detected.
  • cables are used for data communication between the components of system 2.
  • other means of data communication may be used, for example wireless RF signals.
  • the controllers 5, 9 may be implemented on a hardware platform incorporating a microprocessor. However, the controller functions may also be implemented as software instructions running on a suitable computing device, for example a personal computer, personal digital assistant (PDA) or mobile phone. It will be appreciated that there are many ways in which the controllers may communicate with the stimulation device 7, for example an analogue connection such as a DAC card, a digital connection such as a USB link or a wireless connection, for example using the Bluetooth protocol.
  • an analogue connection such as a DAC card
  • a digital connection such as a USB link
  • wireless connection for example using the Bluetooth protocol.
  • Fig 4 illustrates a method 40 that may be performed by the system controller 5 to generate a trigger signal for the vibrator controller 9.
  • the input to method 40 is the voltage across the thermistor of the respiration sensor 3.
  • the voltage signal from the thermistor is conditioned.
  • the thermistor voltage signal is initially amplified by a factor of 5 using an instrumentation amplifier in the system controller 5.
  • the resultant amplified signal is then filtered by a high-pass filter (HPF) followed by a low-pass filter (LPF).
  • HPF high-pass filter
  • LPF low-pass filter
  • the HPF has a cut-off frequency of about 0.02 Hz
  • the LPF has a cut-off frequency of about 20 Hz.
  • the two filters each have unity gain.
  • the output of the LPF is then digitised.
  • the digitisation may be achieved using an on-board, 10-bit analog-to-digital converter (ADC) of a microcontroller embedded in the system controller 5 and sampling at 100
  • the slope of the digitised signal is determined, for example by software running on the microcontroller.
  • Each sample of the thermistor signal is compared to the previous sample to determine the rate of change (slope) of the thermistor signal.
  • the average of the last 4 slopes is calculated to determine the sign and the magnitude of the slope. When the magnitude of the slope exceeds a specified threshold and the sign of the slope changes, a new inspiration or expiration cycle has begun.
  • the system controller 5 generates a trigger signal when an inspiration cycle is detected.
  • the trigger signal may be a 3.3 V low-to-high transition pulse whose duration is equal to the duration of the inspiration cycle.
  • the falling edge of the trigger signal may be at the detected start of an expiration cycle.
  • the trigger signal is active (high) when the inspiration LED 19 is on.
  • the trigger signal may be provided to the vibrator controller 9 by means of a cable connected to output 15 of the system controller 5.
  • a similar method may be used to generate a trigger signal when an expiration cycle is detected.
  • the system controller may generate two output signals, one corresponding to an inspiration and another corresponding to an expiration.
  • the system controller 5 may alternatively determine the slope of the thermistor signal by other means such as analog electronics.
  • the controller 5 when the system controller 5 is powered on using the button 21 , the controller 5 initialises various registers used by the microcontroller and enters a low power mode. In the low power mode the system controller is able to service interrupts arising from a timer within the system controller 5. This enables the system's battery status to be monitored and the power status to be updated with only a minimal power drain. The system controller 5 is also able to service an interrupt from the ADC that causes the controller to exit the low power mode, run the slope-detection algorithm and activate the trigger signal if necessary.
  • the printed circuit board (PCB) of the power supply of system controller 5 provides a battery status output, which is monitored by the microcontroller on the main PCB of system controller 5.
  • the microcontroller changes the flash rate of the power LED 17.
  • the flash rate of LED 17 is handled by a timer on board the microcontroller. When the battery voltage is good the power LED 17 flashes at 4 Hz and when the battery is low the flash rate is 1 Hz. In both cases the flash duration is 75ms.
  • Fig 3 shows an example of the vibrator controller 9.
  • the vibrator controller 9 has an input 33 operable to receive the trigger signal from the system controller 5.
  • the vibrator controller also has a power switch 39 and two red LEDs 35, 37.
  • the LED 37 flashes at 4 Hz to indicate that the battery is good and flashes at 1 Hz to indicate that the battery needs replacing. As the battery transitions from good to low the LED 37 flash rate may vary between 4 Hz and 1 Hz providing further indication to the user that the battery will soon need replacing. If the LED 37 fails to flash either the battery is flat or a fault has developed in the system. In one arrangement the vibrator controller uses a 1.5 volt battery.
  • the vibration LED 35 indicates to the user that a vibrator frequency has been detected within a specified range of the frequency setpoint.
  • the setpoint is 100 Hz and the vibration LED 35 is switched on when the measured vibration frequency is within +/- 5% of the setpoint. If the LED 35 fails to light up, either vibration within the specified range has not been detected or a system fault has developed. If the detected vibration frequency is near the limits of the range, the LED 35 may flicker.
  • Fig 5A shows a method 50 of operation of the vibrator controller 9.
  • the vibrator controller 9 When the vibrator controller 9 is powered up, registers used by an on-board microcontroller are initialised and the vibrator controller enters a low power mode. In the low power mode the vibrator controller is able to service interrupts arising from a timer and then return to the low power mode. This enables the system's battery status to be monitored and the power status to be updated with only a minimal power drain.
  • the vibrator controller 9 remains in the low power mode until a rising edge is detected at the trigger input 33 (step 51 ). When the controller 9 detects a rising edge, an interrupt is triggered. On completion of the interrupt service routine the low power mode is exited and in process 53 the vibrator controller sends a vibrator drive signal via the output 31. The drive signal activates the vibrator 11.
  • the vibrator has an associated accelerometer that returns an output signal to the vibrator controller 9.
  • the controller 9 uses the accelerometer signal to determine a cycle period of vibration of the vibrator 11.
  • the rising edge of each vibration of vibrator 11 generates a timer interrupt.
  • the interrupt service routine saves the time measured between rising edges as the period of vibration of the vibrator 11.
  • the accelerometer and the timer provide a frequency sensor.
  • process 59 software running on the vibrator controller 9 generates a vibrator drive signal to drive the vibration frequency towards setpoint or to maintain the frequency at the specified setpoint.
  • the vibrator controller 9 re-enters the low power mode and waits for the next rising edge from the trigger before repeating the processes of method 50. It will be understood that other setpoints for the vibration control may be used. In addition, different upper and lower bounds on the vibration frequency may be specified. In the described embodiment steps 5, 57 and 59 are performed by software running on a microcontroller on controller 9. However, one or more steps of method 50 may be implemented in other ways, for example using an application specific integrated circuit (ASIC) or field programmable gate array.
  • ASIC application specific integrated circuit
  • the vibrator controller 9 generates a pulse-width modulated (PWM) vibrator drive signal.
  • PWM pulse-width modulated
  • the PWM base frequency and the duty cycle are set by a timer on board the microcontroller.
  • the duty cycle may range from 10 to 100%.
  • Fig 5B shows more detail regarding process 55, in which the vibrator controller 9 determines the cycle period of the measured vibration.
  • the output signal of the accelerometer is conditioned.
  • the accelerometer output is amplified by a factor of 5 before being fed into a unity-gain high-pass filter with a cut-off frequency of 37 Hz.
  • the signal is then applied to a low-pass filter with a cut-off frequency of 160 Hz before being amplified a further 3 times.
  • the amplified signal is fed to a comparator. Hysteresis may be incorporated in the comparator to help reject noise.
  • the output of the comparator is provided to the embedded microcontroller of vibrator controller 9.
  • the conditioned signal output of step 61 enters the microcontroller as a square wave whose frequency is the frequency of vibration of vibrator 11.
  • step 63 the microcontroller uses the conditioned signal to measure the period of vibration.
  • the rising edge of the input signal terminates a timer on board the microcontroller that captures the duration of the previous cycle of vibration.
  • the timer is initialised and restarted to measure the duration of the next cycle.
  • the vibrator controller generates a vibrator drive signal in step 59 to provide the specified vibration frequency.
  • Fig 5C shows an implementation of this control step that uses fuzzy logic. It will be appreciated that other feedback control techniques may also be used to control appropriate operating variables of the stimulation device 7.
  • the setpoint of the vibrator period is 10ms (100 Hz) which is represented by 148h clock cycles, operating at 32768 Hz.
  • the suffix 'h' indicates a hexadecimal number.
  • step 71 the vibrator controller determines an error signal which measures how close the measurement is to the setpoint as follows
  • the error is negative and if the measured value is greater than the setpoint then the error is positive.
  • the vibrator controller also measures an error rate, which is a measure of the rate of change of error and may be obtained as follows:
  • a fuzzification process is implemented that determines the signals' membership of specified fuzzy sets.
  • fuzzy sets are defined for the error to cover the range of frequencies from 8.5ms (118 Hz) to 11.5ms (87 Hz). This range represents 6Oh clock cycles. The desired period corresponds to 148h clock cycles while the minimum and maximum periods are represented by 118h and 178h cycles respectively.
  • an offset of 3Oh is added to the error, resulting in an error range from 0 to 6Oh with the 'zero error' at 3Oh.
  • the defined fuzzy sets for the error signal are illustrated in Fig 6A where the X axis shows a range of errors between Oh and 6Oh. Five fuzzy sets are defined.
  • the zero set (ZE) is triangular and ranges from a value of 0 at an error of 18h to a maximum value of 18h at an error of 3Oh, returning to a value of 0 at an error value of 48h.
  • the positive small (PS) fuzzy set is a triangle with a maximum value of 18h at an error of 48h and a value of Oh at errors of 3Oh and 6Oh respectively.
  • the positive medium (PM) fuzzy set rises linearly from a value of 0 at 48h to a maximum value of 18h.
  • the fuzzy sets negative small (NS) and negative medium (NM) are symmetrically disposed about the zero fuzzy set ZE.
  • the height of the fuzzy sets (18h) represents the degree of membership a crisp input value may have and the location of the set on the horizontal axis is determined by the magnitude of the crisp input value.
  • Y the degree of membership
  • M the slope
  • X error (or error rate)
  • b the intercept on the Y axis.
  • the maximum degree of membership was chosen to be 18h as the slope becomes 1h.
  • one side of the set is defined by the line of equation 3 below and the other side of the set is defined by the line of equation 4 below.
  • the other fuzzy sets are defined in a similar way.
  • the error rate is the difference between consecutive errors and represents the rate of change of error. Since the error difference is always measured at intervals equal to the sampling period (Ts) it is not necessary to explicitly include Ts in the calculation of the error rate.
  • Fig 7 A illustrates how a crisp input is fuzzified to determine membership of the fuzzy sets.
  • the error signal has a value of 5h.
  • the crisp input value intersects the line of MS at a value of 08h and intersects the line of fuzzy set NM at a height of 10h.
  • the crisp error signal 5h belongs to sets NM and NS.
  • the degree of membership of the error value to set NM is 66.7% (10h/18h) and to set NS is 33.3% (08h/18h).
  • Fig 7B illustrates the fuzzification of a crisp input of an error rate of 3Ch.
  • This error rate belongs equally to sets ZE and PS.
  • the degree of membership of the error rate to set ZE is 50% (0Ch/18h) and to set PS is 50% (0Ch/18h).
  • Fuzzification takes a crisp value and determines its degree of membership of the fuzzy sets.
  • the error and error rate may each belong to two sets where membership of set 1 is defined by (set ID 1 , DoM 1 ) and membership of set 2 is defined by (set 2 ID 1 DoM 2).
  • step 75 the vibrator controller performs a fuzzy inference process in which predefined fuzzy rules are applied to determine a fuzzy output value.
  • Fig 8 shows an example of fuzzy output sets that may be used in the calculation of the vibrator drive signal.
  • the sets are labelled:
  • the quantity on the X axis corresponding to each fuzzy output set in Fig 8 represents the number of clock cycles necessary to produce the desired duty cycle of the vibrator 11. For example, for 1 Ch:
  • the output control parameter in this case is the duty cycle of the vibrator drive. If the duty cycle is low the vibrator's frequency is low and its period is longer. If the error is negative the vibrator's period is less (vibrator's frequency is higher) than the set point so the duty cycle of the vibrator drive should be reduced to achieve the set point.
  • Rule 1 is:
  • Table 1 below shows the Fuzzy rules used in the described implantation of step 75.
  • the best estimate of the output may be determined by the process of defuzzification, which is applied by the vibrator controller in process 77.
  • the centre of gravity method of defuzzification is used, utilising the following formula:
  • Fig 9 illustrates the example of defuzzification in which a crisp output of 11 h is calculated, corresponding to input error and error rate signals of 5h and 3Ch respectively.
  • the crisp output generated in process 77 represents a duty cycle.
  • the value is assigned to a register of the timer, thereby changing the duty cycle of the vibrator drive signal to a value that would tend to keep the vibrator's frequency at the specified setpoint.
  • the drive signal is applied to the vibrator 11.
  • the respiratory aid device has been used in a double-blinded, cross over phase 1 (efficacy) repeated measures trial.
  • Subjects undertake two 20-minute cycle sessions during which the order of the placement of the RAD vibrators is randomised.
  • the active position was the third intercostal parasternal space and the sham position was approximately the mid-clavicular line over pectoralis major.
  • the subject's breathlessness was measured every two minutes using the Borg Dyspnoea scale.
  • Seven subjects with severe COPD were recruited and three subjects completed the 20- minute protocol without difficulty.
  • Initial statistical analysis of the results for these subjects indicated that the parasternal stimulation position reduced the sensation of dyspnoea.
  • a flow sensor or pressure sensor may be used in the respiration sensor 3 instead of the thermistor, or elasticised bands around the subject's chest may be used to detect the expansion and contraction of the chest, thereby indicating inspiration and expiration.
  • the vibrator may also be activated in phase with the user's expiration.
  • a vibration protocol may also be specified, for example, the system may activate the vibrator 11 for 1 minute in each 5 minute interval or 1 respiration cycle in 10 respiration cycles.
  • a mode may also be specified in which the vibrator 11 is enabled for random intervals. After a time interval (T), optionally selected by the user, the vibrator is disabled.
  • T time interval
  • the duration of T may be fixed, variable according to a preset range, or random.
  • the vibration protocol may follow a user-selected profile that may be fixed, variable according to preset values, or may include randomly-selected parameters.
  • the operation of the vibrator 11 may also be made dependent on respiration rate or some other physiological variable. For example, if the measured respiration rate or blood oxygen level is above or below a specified threshold, the system 2 can enable the use of the vibrator 11.
  • the vibration setpoint may be variable.
  • a user may be able to select a setpoint in a range of, for example, 80-120 Hz.
  • the setpoint may alternatively be specified in seconds or, for example, as a percentage of a range between fast and slow.
  • the respiration aid system 1 , 2 includes a user interface that allows the user to select various features of the system. For example, the user may select a vibration setpoint or a vibration protocol. The user may also be offered a choice of having the vibration activated in phase with inspiration or expiration or both. The user may, for example, specify a number of stimulation devices to operate.
  • stimulation devices may also be used to induce vibration in the chest wall of the user.
  • the respiratory aid device may be used in conjunction with a ventilator.
  • a patient may be on a mechanical ventilator in intensive care or on non-invasive ventilation at home or in the hospital.
  • the stimulation device 7 may be used to stimulate the intercostal muscles in phase with the operation of the ventilator.
  • the input signal to the system controller 5 may be triggered by the ventilator. That is, rather than measuring the patient's respiration, the input to the system controller 5 corresponds to the action of the ventilator.
  • the respiration sensor 3 may be an arrangement that provides a signal corresponding to the ventilator cycle.
  • the controllers 5, 9 may be implemented as software routines running on the ventilator system.
  • a ventilator may output a drive signal for one or more stimulation devices 7 applied to a patient on the ventilator.

Abstract

L'invention concerne un système pour stimuler la paroi de la cage thoracique d'un patient afin de réduire la dyspnée. Le système comprend un capteur de respiration (3) utilisable pour générer un signal de sortie dépendant de la respiration du patient; un dispositif de stimulation (7) utilisable pour stimuler la paroi de la cage thoracique du patient; et un contrôleur (5) prévu pour surveiller le signal de sortie et pour activer le fonctionnement du dispositif de stimulation en fonction du signal de sortie. Le système assure la stimulation en phase des muscles intercostaux pendant la respiration. Le dispositif de stimulation peut appliquer une vibration mécanique à la paroi de la cage thoracique du patient. Le contrôleur commande la fréquence de la vibration appliquée.
PCT/AU2009/001655 2008-12-22 2009-12-18 Dispositif d'aide respiratoire WO2010071919A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU2008906567 2008-12-22
AU2008906567A AU2008906567A0 (en) 2008-12-22 Respiratory aid device

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