Surgery – Diagnostic testing – Detecting sound generated within body
Reexamination Certificate
2000-04-21
2002-08-20
Shaver, Kevin (Department: 3736)
Surgery
Diagnostic testing
Detecting sound generated within body
C600S033000
Reexamination Certificate
active
06436057
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatuses for the analysis of patient's coughs. More specifically, this invention relates to methods and apparatuses for the analysis of patient's coughs to aid in diagnosing pulmonary disorders and diseases. This method uses signal analysis techniques to extract quantitative information from recorded cough sound pressure waves. Moreover, the method allows the recordation of cough sound waves while avoiding distortions caused by reflections. The generated data can be used to diagnose pulmonary disorders and diseases as well as track the effectiveness of treatment regimes over time. The method can also be used for screening the general population, or populations at higher risk, so that such pulmonary disorders and diseases can be detected as early as possible so that appropriate treatment can be started as soon as possible.
BACKGROUND OF THE INVENTION
Cough is associated with well over 100 different pulmonary diseases and is one of the most common signs or symptoms of respiratory disease. Even though cough may be an unwanted complication of a pulmonary disease, it has often been used by physicians as an effective diagnostic tool. Since cough sounds are composed of acoustic information which can be altered by lung disease and since cough has essentially the same acoustical characteristics whether performed voluntarily or involuntarily, analysis of voluntary cough sounds has the potential to become a useful noninvasive tool for screening large populations of workers to evaluate their pulmonary function. The use of cough sound analysis to aid in the identification of lung disease has several distinct advantages since testing can be quickly and easily administered while requiring only a minimum amount of technician or patient training.
In order to describe the events that occur during a cough, physiologists have subdivided a cough into 4 different phases (Leith et al., Cough, In:
The Handbook of Physiology, The Respiratory System
edited by A. Fishman, P. T. Macklem and J. Mead, Bethesda, Md., Am. Physiological Society, Sec(3) Chapter 20, 315-336 (1987)). During the initial phase, called the inspiration phase, a variable volume of air is inhaled into the lungs. The second phase, referred to as the compression phase, begins as the glottis closes and the muscles of expiration begin to contract increasing thoracic pressure. The third phase is called the expulsion phase. At the start of the third phase, the glottis opens and gas flows rapidly from the lung. During the fourth and final phase, called the cessation phase, muscle activity is reduced and airflow is diminished.
The physical characteristics of a cough are illustrated in FIG.
1
. Flow from the mouth during a cough is shown in FIG.
1
A. Positive values represent flow from the lungs while negative flow values indicate air flow into the lungs. During the initial phase of a cough (phase I) air flow is negative as air enters the lungs. The volume of air inspired is variable and is said to be a function of the anticipated forcefulness of the cough (Yanagihara et al., “The Physical Parameters of Cough: the Larynx in a Normal Single Cough,”
Acta. Oto
-
laryngol.
61: 495-510 (1966)). As compression of air occurs during phase II of the cough, the glottis closes and airflow ceases. When the glottis reopens, in approximately 200 ms, flow initially increases and then decreases rapidly creating a flow transient. This initial rapid change in flow during phase III is referred to as supramaximal flow and is thought to result from the air rapidly leaving the flexible airway system as the airways compress during the initial part of the expulsion phase of a cough. At the same time that air is leaving the airways during the initial portion of phase III, expiratory flow from the lung periphery rises sharply to maximal flow which is limited by the maximum expiratory flow-volume relationship that is unique for each lung. Air flow leaving the lungs during a cough, therefore, is a summation of the transient air leaving the airways at a supramaximal flow rate and the air leaving the periphery of the lungs at maximal flow. During the cessation phase IV of a cough, airflow from the lungs diminishes and then approaches zero as muscle activity decreases.
FIG. 1B
illustrates a typical sound pressure wave generated by a cough. It has been suggested that the cough sounds are generated during phase III and sometimes during phase IV of a cough. The cough sound, itself, can be subdivided into two and sometimes three parts (Thorpe et al., “Towards a Quantitative Description of Asthmatic Cough Sounds,”
Eur. Respir. J.
5: 685-692 (1992)). The first part of a cough sound is referred to as the initial burst and represents the sound transient that is associated with the glottis opening. The second or middle part corresponds to the interval of near steady, maximal flow coming from the periphery of the lung which occurs with the glottis maximally open. The third part of a cough, called the final burst, is not always present, but is believed to occur in some subjects who close their glottis during the cessation phase of a cough.
Airflow from the lung during a cough and the maximum expiratory flow volume (MEFV) relationship of a lung have much in common. During a forced expiration the airways, which are very flexible cylindrical structures, undergo compression and decrease in cross-sectional area as air rapidly passes through them. As a result, one or more choke points is created in the airway system during maximal gas flow. After a choke point has formed, flow from the lungs becomes independent of the driving pressure. This is important because it implies that airflow through the airway system should become effort independent during the performance of a MEFV maneuver. Once effort independence is reached, the MEFV relationship becomes repeatable. Flow-volume curves recorded during a MEFV maneuver define the limits of flow and volume that can be achieved during most expiratory maneuvers in a given individual. Leith et al. (1987) have stated that a surprisingly modest expiratory effort is required to reach the outer limits of the flow-volume domain for a given individual, making forced expiration a reliable pulmonary function test.
FIG. 2
shows an example of an MEFV curve while expiring with a maximum effort into a spirometer. An example of the flow volume relationship of a lung during a cough is superimposed on the MEFV curve in FIG.
3
. During the initial phase of a cough, air is inspired into the lungs. This is indicated by the increase in lung volume as the operating point on the flow-volume curve moves to the left throughout phase I. During the compression phase, there is no gas flow so phase II is represented by a single point on the diagram. During the initial part of phase III, a supramaximal flow transient is observed as the volume of air in the flexible airways decreases quickly as the airways begin to collapse. Following the very brief flow transient, maximal flow is achieved which approaches the maximal flow reached during the performance of a MEFV maneuver. The events that occur during this portion of the cough are very similar to those that occur during a MEFV maneuver; therefore, it can be assumed that airflow leaving the lung during a cough reaches flow limitation and is reasonably reproducible when successive coughs are performed beginning at the same lung volume. Since the mechanisms producing cough sounds are dependent upon air flow, it seems likely that cough sounds are also reproducible if similar lung histories are followed prior to each cough.
A block diagram of a simple model illustrating how cough sounds are produced is shown in FIG.
4
. It is thought that the acceleration and turbulence of air within the airways caused by the rapid expulsion of air from the lungs generates band limited noise which is then modified by the resonances of the lungs' upper airways and possibly the oral and nasal cavities as air travels toward the mouth. Peaks that occur in the spec
Afshari Aliakbar
Frazer David
Friend Kimberly
Goldsmith William T.
McKinney Walter
Klarquist & Sparkman, LLP
Shaver Kevin
The United States of America as represented by the Department of
Wingood Pamela L.
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