BACKGROUND OF THE INVENTION Asthma is the most common chronic illness of childhood, afflicting approximately 5 million American children. The estimated annual cost of treating asthma in children under 18 years of age is $3.2 billion.

Asthma is the number-one chronic condition causing children to be absent from school and the highest ranked cause of pediatric hospitalizations in the United States.

Worldwide, asthma affects over 100 million people, creating a burden in terms of healthcare costs, lost productivity and reduced participation in family life.

When a child has a serious asthma attack, medical attention is needed immediately. An observant parent will generally have no trouble in recognizing the child's respiratory distress. Mild to moderate asthma attacks, however, are far more common and are more difficult to recognize. Peak flow meters, which measure the peak expiratory airway flow from fully-inflated lungs, can be helpful in providing an early warning of an attack, but they are not always effective and cannot be used with small children and the elderly. The parent may be uncertain as to whether or not to limit the child's activity or to administer medication, and whether it is necessary to bring the child in to the doctor's office or emergency room. As moderate symptoms can turn serious within a short time, parents and caregivers must be alert and take action when needed in response to the child's condition, before it becomes an emergency. On the other hand, bringing the child in for treatment unnecessarily

can be costly, inconvenient and distressing in and of itself.

During an asthma attack, the patient's breathing is typically characterized by wheezing, coughing and other abnormal breath sounds. Doctors listen to these sounds in order to diagnose asthma attacks. PCT patent publication WO 98/14116, which is incorporated herein by reference, describes a phonopneumograph system for automatic analysis of breath sounds. The system uses multiple sensors and complex computation algorithms to classify breath sounds according to type. It is not suitable for home or ambulatory use, however.

Furthermore, there are some asthma attacks, particularly in babies, that cause respiratory distress without manifesting the common pattern of coughing, wheezing and/or other characteristic breath sounds.

SUMMARY OF THE INVENTION It is an object of some aspects of the present invention to provide an improved device for ambulatory analysis of breath sounds.

It is a further object of some aspects of the present invention to provide a method and device for diagnosing the severity of respiratory ailments, and particularly of asthma attacks.

In preferred embodiments of the present invention, an ambulatory device for diagnosis of asthma comprises at least one microphone and processing circuitry. The microphone and circuitry are preferably worn or carried by a patient. Alternatively, the microphone and circuitry are placed next to the patient while the patient is resting or sleeping. The microphone receives acoustic signals responsive to the patient's breathing, which signals are analyzed by the circuitry. The circuitry classifies the signals as belonging to either a moderate to severe asthma attack, requiring medical

attention, or to normal breathing or mild asthma, in which case medical attention is generally not needed.

The device thus resolves the uncertainty of parents and other home caregivers as to whether or not an asthma patient requires medical help at any given time. Because the device is compact and gives a simple, yes/no indication of the severity of the patient's asthma, it is suitable for home use by non-medical personnel, unlike large, complex phonopneumograph systems, such as that described in the above-mentioned PCT publication. The device gives the caregivers an early warning of a possibly severe asthma attack, based on which medical personnel can be consulted and/or treatment administered as needed, in accordance with appropriate guidelines.

The device can subsequently be used to determine whether the administered treatment was effective. Thus, on the one hand, the patient is likely to receive any required care early enough so that emergencies are averted, while on the other hand, unnecessary medication and visits to the doctor or emergency room are avoided.

Although preferred embodiments are described herein with reference to human patients, the present invention may also be applied to detect and diagnose respiratory ailments in animals. The term"subject"as used herein is to be understood as including both humans and animals.

There is therefore provided, in accordance with a preferred embodiment of the present invention, a device for diagnosing the condition of a subject suffering from a respiratory ailment, including: a microphone, which receives acoustic signals responsive to the subject's respiration; and a processor, which analyzes the acoustic signals so as to classify the subject's condition as one that requires immediate medical attention or one that does not.

Preferably, the processor is contained in a case that is carried on the subject's body while the subject is ambulatory.

There is also provided, in accordance with a preferred embodiment of the present invention, a method for diagnosing the condition of a subject suffering from a respiratory ailment, including: receiving acoustic signals responsive to the subject's breath sounds; and analyzing the acoustic signals so as to classify the condition as one that requires immediate medical attention or one that does not.

Preferably, analyzing the acoustic signals includes detecting an asthmatic condition and classifying an asthma attack as mild or moderate to severe. An alarm is provided to a user when the condition is classified as one requiring immediate medical attention.

Preferably, analyzing the acoustic signals includes one or more of the following steps: * Determining the subject's breathing rate; * Finding a relation between an inspiration phase and an expiration phase of the subject's breathing cycle; * Detecting a cough; and * Analyzing a spectrum of the acoustic signals.

In a preferred embodiment, the acoustic signals are received while there is substantially no physical contact between the microphone and the subject's body.

The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic, pictorial illustration showing a patient wearing a device for diagnosis of asthma, in accordance with a preferred embodiment of the present invention; Fig. 2 is a schematic, pictorial illustration showing a patient being monitored by a bedside device for diagnosis of asthma, in accordance with a preferred embodiment of the present invention; Fig. 3 is block diagram that schematically illustrates elements and operation of a control unit of the device of Fig. 1 or 2, in accordance with a preferred embodiment of the present invention; Fig. 4 is a sonogram showing variations in the frequency spectrum of breath sounds received by the device of Fig. 1 or 2 in normal respiration; and Fig. 5 is a sonogram showing variations in the frequency spectrum of breath sounds received by the device of Fig. 1 or 2 during an asthma attack.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 is a schematic, pictorial illustration showing a device 20 worn by a patient 22 for diagnosis of asthma, in accordance with a preferred embodiment of the present invention. Device 20 comprises a microphone 24, which is fixed to the body of patient 22 or is otherwise held in proximity to the patient's face or airway. The microphone preferably has directional characteristics such that it picks up the patient's breathing noises in preference to background noise from the environment. To the extent that the microphone is fixed to the patient's body, it is preferably placed against his chest, back or windpipe area. Optionally, the microphone is not a separate unit as shown in Fig. 1, but is rather contained inside the case of device 20. In an alternative

embodiment, the device includes two microphones: one fixed to the patient's body, and the other inside the case or elsewhere in proximity to the patient's face or airway.

Fig. 2 is a schematic, pictorial illustration showing a device 20'placed at the bedside of patient 22, in accordance with another preferred embodiment of the present invention. Device 20'is functionally very similar to device 20, shown in Fig. 1, and references hereinbelow to one of devices 20 and 20'should generally be understood as applying to the other one, as well.

In the embodiment shown in Fig. 2, there is an optional, removable funnel 25, preferably made of metal, attached to microphone 24 and directed toward patient 22.

The funnel enables the microphone to collect strong audio signals even while the microphone is relatively distant from the patient, so as to avoid disturbing the patient's sleep, for example. Funnel 25 is also helpful in improving the selectivity with which microphone 24 receives the patient's breathing sounds in the presence of background noise. If necessary, however, to overcome background noise or obtain a more accurate reading, funnel 25 can be removed, and microphone 24 can be held near the patient's mouth or in contact with the patient's neck, chest or back. The microphone may also be placed between the patient's bed sheets.

Device 20'further includes a user interface 32, comprising a display 33 and user controls 35, such as a touch pad or set of push buttons, whose function is described further hereinbelow.

Fig. 3 is a block diagram that schematically illustrates functional elements of device 20, in accordance with a preferred embodiment of the present invention. Microphone 24 is coupled to a preamplifier 26, which provides amplified acoustic signals to an

analog input filter 28. Analog signals from the filter are sampled and pre-processed by a digital sampling block 34, which provides a digital signal to a signal processing and recognition block 36. This block, along with a central control block 30 and other elements of device 20, is preferably implemented by software running on a general-purpose microprocessor. Alternatively, some or all of the signal processing functions may be implemented in hard-wired logic or in a programmable digital signal processor, as is known in the art.

Processing and recognition block 36 analyzes the acoustic signals and compares them to predetermined criteria in order to assess the condition of patient 22.

Some of the criteria, such as the patient's respiratory rate, are evaluated based on the acoustic signals alone, whereas more advanced criteria are evaluated by comparing the input acoustic signals to signal spectra and other signal characteristics stored in a database memory 38.

Analysis of the signals preferably includes steps of noise reduction, normalization and spectral analysis, most preferably using a Fast Fourier Transform, as is known in the art.

Preferably, the stored spectra and other characteristics include both normal breath signals and abnormal signals reflecting various types and stages of asthmatic attacks. Most preferably, when device 20 is initially supplied to patient 22, memory 38 includes a library of"standard"signals and signal statistics, reflecting typical breathing and coughing sounds during attacks of varying severity, gathered and averaged over a large number of asthma sufferers. Over time, the memory stores additional, specific signals gathered during normal breathing and asthma attacks suffered by patient 22. Preferably, user controls 35 are used to indicate to device 20 that an asthma attack is in progress, so that

the characteristic signals can be stored and used for later reference.

Over the course of the use of device 20 by patient 22, processing and recognition block 36 learns to recognize the specific characteristics of asthma attacks in the particular patient. Typically, these characteristics include the rate of breathing, the relative duration and amplitude of exhalation and inhalation portions of the breath cycle, the spectrum of breath sounds, and detection of coughing. Preferably, during use of the device, each of the characteristics of the patient's breath sounds is analyzed and classified.

When one or more of the characteristics (or more preferably, two or more characteristics) are indicative of a moderate to severe asthma attack, an alarm is generated by an output control block 40. The alarm is recorded in a record unit 42 and is conveyed to user interface 32 so as to notify the patient or a caregiver that medical assistance should be sought.

Optionally, block 40 also includes a modem or audio output (not shown), which may be coupled to a telephone or other communication line so as to convey the patient's breath sounds to a medical specialist for further diagnostic analysis. Further optionally, record unit 42 records digitized audio signals, particularly signals recorded during asthma attacks, to be played back for the specialist.

Alternatively or additionally, processing and recognition block 36 comprises a neural network, which is gradually modified as it learns the characteristics of the patient's asthma attacks.

Preferably, the alarms generated by block 40 are graduated so as to distinguish, for example, between a normal state, a moderate attack in which medication should be increased or other preliminary steps should be

taken, and a severe attack for which immediate medical attention should be sought. The moderate attack condition may be further subdivided into gradations requiring different sorts or amounts of treatment, such as rest, inhalation and different types or dosages of medication. Early detection of mild attacks by device 20 or 20', and application of suitable treatment, even before the patient experiences discomfort and external symptoms become apparent, can help to prevent deterioration of the patient's condition. The system of alarms and other user outputs provided by the device is also useful in avoiding unneeded medication, in verifying the effectiveness of treatment that is administered when an attack is detected, and in helping caregivers to communicate aspects of the patient's condition to medical personnel. For this last purpose, display 33 may provide a detailed readout, which the caregiver can read over the telephone to the physician, or which may be conveyed electronically, for example, via modem over a telephone line.

Figs. 4 and 5 are sonograms that schematically illustrate spectra of acoustic signals received by device 20. Fig. 4 reflects normal breathing, whereas Fig. 5 illustrates breath sounds received during an asthma attack. The vertical axis in both of the figures corresponds to the frequencies of the signals, shown against a horizontal time axis. Darker areas of the sonogram indicate relatively higher acoustic intensities at the given frequency and time. In Fig. 5, both the vertical and horizontal axes are expanded to show more clearly the spectral characteristics of asthmatic breathing.

As shown in Fig. 4, for example, normal breathing is characterized by regular cyclical phases of inspiration 50 and expiration 52. The spectra of both the

inspiration and expiration phases are similar and include a distribution of both high and low frequencies.

On the other hand, in the spectrum shown in Fig. 5, an expiration phase 62 is markedly longer than an inspiration phase 60. The expiration spectrum is concentrated at low frequencies, indicated a difficulty in exhalation experienced by the patient from whom these readings were taken. This is one of a variety of spectral forms that an asthma attack can assume. These characteristic forms are preferably stored in database 38 and used for reference and triggering of alarms as needed.

A further characteristic of the signals shown in Fig. 5 is the irregularity of the inspiration and expiration phases, particularly as compared with the relative symmetry of the signals in Fig. 4. The irregularity is characteristic of respiratory distress, particularly distress due to asthma. In a preferred embodiment of the present invention, device 20 or 20' identifies asthmatic breathing by detecting asymmetry or irregularity in the spectra of the inspiration and expiration phases and/or in the relative durations or other temporal aspects of the inspiration and expiration phases. The device can thus warn that an asthma attack is occurring or is about to occur even in the absence of an audible difference in breath sounds.

Although in the preferred embodiments described hereinabove, device 20 is shown as being worn by patient 22, whereas device 20 is constructed as a bedside unit, other device configurations will also be evident to those skilled in the art and are considered to be within the scope of the present invention. The principles of the present invention may further be applied to diagnosis of other respiratory ailments, not only in people, but also in animals. It will thus be appreciated that the preferred embodiment described above is cited by way of example, and the full scope of the invention is limited only by the claims.