Abstract:
A cardiac rhythm management system provides for ambulatory monitoring of hemodynamic performance based on quantitative measurements of heart sound related parameters for diagnostic and therapeutic purposes. Monitoring of such heart sound related parameters allows the cardiac rhythm management system to determine a need for delivering a therapy and/or therapy parameter adjustments based on conditions of a heart. This monitoring also allows a physician to observe or assess the hemodynamic performance for diagnosing and making therapeutic decisions. Because the conditions of the heart may fluctuate and may deteriorate significantly between physician visits, the ambulatory monitoring, performed on a continuous or periodic basis, ensures a prompt response by the cardiac rhythm management system that may save a life, prevent hospitalization, or prevent further deterioration of the heart.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-pending, commonly assigned Siejko et al. U.S. patent application Ser. No. 10/307,896, entitled “PHONOCARDIOGRAPHIC IMAGE-BASED ATRIOVENTRICULAR DELAY OPTIMIZATION,” filed Dec. 2, 2002, now issued as U.S. Pat. No. 7,123,962, which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     This document relates generally to cardiac rhythm management systems and particularly, but not by way of limitation, to such a system sensing heart sounds for monitoring, diagnosis, and therapy control. 
     BACKGROUND 
     A heart is the center of a person&#39;s circulatory system. It includes a complex electro-mechanical system performing two major pumping functions. The left portions of the heart, including the left atrium and the left ventricle, draw oxygenated blood from the lungs and pump it to the organs of the body to provide the organs with their metabolic needs for oxygen. The right portions of the heart, including the right atrium and the right ventricle, draw deoxygenated blood from the organs and pump it into the lungs where the blood gets oxygenated. These mechanical pumping functions are accomplished by contractions of the myocardium (heart muscles). In a normal heart, the sinus node, the heart&#39;s natural pacemaker, generates electrical signals, called action potentials, that propagate through an electrical conduction system to various regions of the heart to excite myocardial tissues in these regions. Coordinated delays in the propagations of the action potentials in a normal electrical conduction system cause the various regions of the heart to contract in synchrony such that the pumping functions are performed efficiently. Thus, the normal pumping functions of the heart, indicated by hemodynamic performance, require a normal electrical system to generate the action potentials and deliver them to designated portions of the myocardium with proper timing, a normal myocardium capable of contracting with sufficient strength, and a normal electro-mechanical association such that all regions of the heart are excitable by the action potentials. 
     The function of the electrical system is indicated by electrocardiography (ECG) with at least two electrodes placed in or about the heart to sense the action potentials. When the heart beats irregularly or otherwise abnormally, one or more ECG signals indicate that contractions at various cardiac regions are chaotic and unsynchronized. Such conditions are known as cardiac arrhythmias. Cardiac arrhythmias result in a reduced pumping efficiency of the heart, and hence, diminished blood circulation. Examples of such arrhythmias include bradyarrhythmias, that is, hearts that beat too slowly or irregularly, and tachyarrhythmias, that is, hearts that beat too quickly. A patient may also suffer from weakened contraction strength related to deterioration of the myocardium. This further reduces the pumping efficiency. For example, a heart failure patient suffers from an abnormal electrical conduction system with excessive conduction delays and deteriorated heart muscles that result in asynchronous and weak heart contractions, and hence, reduced pumping efficiency, or poor hemodynamic performance. Thus, in addition to ECG, the function of the mechanical system and the electro-mechanical association need to be measured to assess the overall pumping performance of the heart. 
     Characteristics of heart sounds are known to be indicative of various mechanical properties and activities of the heart. Measurements performed with synchronously recorded ECG and heart sounds provide for quantitative indications of the electro-mechanical association. For example, amplitudes of the third heart sound (S 3 ) and fourth heart sound (S 4 ) are related to filling pressures of the left ventricle during diastole. Fundamental frequencies of S 3  and S 4  are related to ventricular stiffness and dimension. Chronic changes in S 3  amplitude is correlated to left ventricular chamber stiffness and degree of restrictive filling. Change in the interval between atrial contraction and S 4  is correlated to the changes in left ventricular end of diastolic pressure. Such parameters, being correlated to the heart&#39;s mechanical properties and electromechanical association, quantitatively indicate abnormal cardiac conditions, including degrees of severity, and need of appropriate therapies. 
     For these and other reasons, there is a need for a system providing for cardiac therapy based on parameters related to heart sounds. 
     SUMMARY 
     A cardiac rhythm management system provides for ambulatory monitoring of hemodynamic performance based on quantitative measurements of heart sound related parameters for diagnostic and therapeutic purposes. Monitoring of such heart sound related parameters allows the cardiac rhythm management system to determine a need for delivering a therapy and/or therapy parameter adjustments based on conditions of a heart. This monitoring also allows a physician to observe or assess the hemodynamic performance for diagnosing and making therapeutic decisions. Because the conditions of the heart may fluctuate and may deteriorate significantly between physician visits, the ambulatory monitoring, performed on a continuous or periodic basis, ensures a prompt response by the cardiac rhythm management system that may save a life, prevent hospitalization, or prevent further deterioration of the heart. 
     In one embodiment, a system includes an acoustic sensor, a cardiac sensing circuit, a heart sound detector, a parameter generator, a processor, and a therapy circuit. The acoustic sensor senses an acoustic energy and produces an acoustic sensor signal indicative heart sounds. The cardiac sensing circuit senses a cardiac signal indicative of cardiac electrical events. The heart sound detector detects selected heart sounds based on the acoustic sensor signal and the cardiac signal. The parameter generator generates values of at least one predetermined parameter related to the selected heart sounds. The processor includes a trending analyzer that produces and analyzes at least one trend related to the selected heart sounds based on the values of the predetermined parameter. The therapy circuit delivers cardiac therapy with at least one therapy parameter determined based on the trend. 
     In another embodiment, an acoustic energy is sensed to produce an acoustic sensor signal indicative heart sounds. One or more cardiac signals indicative of cardiac electrical events are also sensed. Selected heart sounds are detected. Parameter values related to the selected heart sounds and selected cardiac electrical events are generated. Selected parameter values, which are associated with one or more types of the selected heart sounds, are analyzed to produce at least one trend. A therapy, with at least one parameter determined based on the trend, is delivered. 
     In yet another embodiment, a cardiac rhythm management system includes an implantable device. The implantable device includes an acoustic sensor, a cardiac sensing circuit, a gating module, a heart sound detector, a measurement module, and a therapy circuit. The acoustic sensor senses an acoustic energy to produce an acoustic sensor signal indicative heart sounds. The cardiac sensing circuit senses at least one cardiac signal indicative of cardiac electrical events. The gating module generates heart sound detection windows each timed for detection of one of selected heart sounds based on a time of occurrence of one of selected cardiac electrical events. The heart sound detector detects the selected heart sounds. The measurement module generates parameter values related to the selected heart sounds. The therapy circuit delivers a therapy based on the parameter values. 
     This summary is intended not to limit the claimed subject matter, and the scope of the invention is defined by attached claims and their equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily drawn to scale, like numerals describe similar components throughout the several views. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
         FIG. 1  is a block diagram illustrating an embodiment of a heart-sound based hemodynamics monitoring and therapy control system. 
         FIG. 2  is an illustration of an embodiment of a method for detecting selected heart sounds. 
         FIG. 3  is a block diagram illustrating an embodiment of a measurement module of the system of  FIG. 1 . 
         FIG. 4  is a flow chart illustrating an embodiment of a method for hemodynamics monitoring and therapy control using the system of  FIG. 1 . 
         FIG. 5  is an illustration of an embodiment of portions of a cardiac rhythm management system incorporating heart-sound based hemodynamics monitoring and therapy control and portions of an environment in which it is used. 
         FIG. 6  is a block diagram illustrating a specific embodiment of portions of the cardiac rhythm management system of  FIG. 5 . 
         FIG. 7  is a block diagram illustrating another specific embodiment of portions of the cardiac rhythm management system of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. 
     This document discusses, among other things, a cardiac rhythm management system monitoring heart sounds indicative of a heart&#39;s mechanical events related to the heart&#39;s pumping functions and hemodynamic performance to allow, among other things, diagnosis of cardiac conditions and selection of therapies treating the cardiac conditions. The cardiac rhythm management systems include systems having, for example, pacemakers, cardioverter/defibrillators, pacemaker/defibrillators, and cardiac resynchronization therapy (CRT) devices. One specific example of a cardiac rhythm management system that monitors and analyses heart sounds is described in co-pending, commonly assigned Siejko et al. U.S. patent application Ser. No. 10/307,896, entitled “PHONOCARDIOGRAPHIC IMAGE-BASED ATRIOVENTRICULAR DELAY OPTIMIZATION,” filed Dec. 12, 2002, which is hereby incorporated by reference in its entirety. However, it is to be understood that the present methods and apparatuses may be employed in other types of medical devices, including, but not being limited to, drug delivery systems and various types of cardiac monitoring devices. 
     Known and studied heart sounds include the “first heart sound” or S 1 , the “second heart sound” or S 2 , the “third heart sound” or S 3 , the “fourth heart sound” or S 4 , and their various sub-components. S 1  is known to be indicative of, among other things, mitral valve closure, tricuspid valve closure, and aortic valve opening. S 2  is known to be indicative of, among other things, aortic valve closure and pulmonary valve closure. S 3  is known to be a ventricular diastolic filling sound often indicative of certain pathological conditions including heart failure. S 4  is known to be a ventricular diastolic filling sound resulted from atrial contraction and is usually indicative of pathological conditions. The term “heart sound” hereinafter refers to any heart sound (e.g., S 1 ) and any components thereof (e.g., M 1  component of S 1 , indicative of Mitral valve closure). 
     Throughout this document, “heart sound” includes audible and inaudible mechanical vibrations caused by cardiac activity that can be sensed with an accelerometer. Accordingly, the scope of “acoustic energy” in this document extends to energies associated with such mechanical vibrations. 
     Throughout this document, “user” refers to a physician or other caregiver who examines and/or treats a patient using one or more of the methods and apparatuses reported in the present document. Unless noted otherwise, S 1 , S 2 , S 3 , and S 4  refer to the first, second, third, and fourth heart sounds, respectively, as a heart sound type, or as one or more occurrences of the corresponding type heart sounds, depending on the context. 
       FIG. 1  is a block diagram illustrating an embodiment of a heart-sound based hemodynamics monitoring and therapy control system  100 . System  100  includes, among other things, an acoustic sensor  110 , a sensor interface module  120 , a cardiac sensing circuit  112 , a heart sound detector  130 , a parameter generator  140 , a data acquisition timer  118 , a parameter processor  160 , and a therapy circuit  170 . In one embodiment, system  100  is a totally implantable system adapted to be implanted into a patient. In an alternative embodiment, system  100  is an external system that does not include any implantable component. In another alternative embodiment, system  100  includes both implantable and external components. 
     Acoustic sensor  110  senses an acoustic energy or mechanical vibration energy related to cardiac mechanical activities and converts the acoustic energy to an acoustic sensor signal indicative of heart sounds. The acoustic sensor signal is an electrical signal indicative of timing, strength, and frequency characteristics related to the heart sounds. Acoustic sensor  110  is disposed in a heart, or near the heart in a location where the acoustic energy related to the cardiac mechanical activities can be sensed. In one embodiment, acoustic sensor  110  includes an accelerometer disposed in or near a heart. In another embodiment, acoustic sensor  110  includes a microphone disposed in or near a heart. 
     Sensor interface module  120  has a signal input connected to the output of acoustic sensor  110  to receive the acoustic sensor signal. It processes the acoustic sensor signal to prepare for detection of selected type heart sounds. The selected type heart sounds are heart sounds selected for a purpose of monitoring a patient&#39;s hemodynamic performance indicated by the measurable characteristics of these heart sounds. In one specific embodiment, the selected type heart sounds includes S 3  and S 4 , which are indicative of ventricular diastolic hemodynamic performance. Sensor interface module includes a signal conditioning circuit  122 , a digitizer  124 , and a digital filter  126 . Signal conditioning circuit  122  receives the acoustic sensor signal as an analog signal from acoustic sensor  110 , and performs initial conditioning of the acoustic sensor signal. In one embodiment, signal conditioning circuit  122  improves the signal-to-noise ratio of the acoustic sensor signal. It includes an amplifier and a filter to amplify the acoustic sensor signal while reducing the noise therein. In one embodiment, the filter is an analog filter that substantially reduces amplitudes of noises that are not within the frequency spectrum of the selected type heart sounds. In another embodiment, the filter substantially reduces amplitudes of noises as well as components of the acoustic sensor signal that are outside of the frequency range of the selected type heart sounds. Digitizer  124  digitizes the filtered acoustic sensor signal by sampling it at a predetermined rate. In one embodiment, the sampling rate is programmable and determined based on known frequency characteristics of the heart sounds to be detected. In one embodiment, digitizer  124  samples the acoustic sensor signal only during predetermined periods of time where the selected type heart sounds are most likely to be present. This saves electrical energy required for processing the acoustic sensor signal and/or allows a higher resolution of the digitized acoustic sensor signal without substantially increasing the electrical energy required for processing. Energy conservation is of particular importance when system  100  is a totally implantable system or includes implantable components. Digital filter  126  substantially reduces amplitudes for all components of the acoustic sensor signal except the selected type heart sounds, which are to be detected by heart sound detector  130 , thereby enhancing the indications of the selected type heart sounds. In one embodiment, digital filter  126  includes a band-pass filter having cutoff frequencies determined based on the frequency spectrum of the selected type heart sounds. It is to be understood, however, that the cutoff frequencies are dependent on the purpose of detection and need not cover exactly the known spectrum of particular heart sounds. In one specific embodiment, digital filter  126  is band-pass filter having a low cutoff frequency in the range of 5 to 20 Hz and a high cutoff frequency in the range of 30 to 120 Hz selected for the purpose of detecting S 3  and S 4 . One example of a suitable pass band for digital filter  126  for detection of S 3  and S 4  for monitoring ventricular diastolic hemodynamics includes a low cutoff frequency of 10 Hz and a high cutoff frequency of 60 Hz. In one specific embodiment, digital filter  126  is an envelope detector type filter. In one embodiment, digital filter  126  is a programmable digital filter in which at least one of the cutoff frequencies is programmable. This allows a dynamic selection of heart sounds for detection without a need for additional circuitry. 
     Cardiac sensing circuit  112  senses at least one cardiac signal indicative of cardiac electrical events that are needed for detection and measurements related to the heart sounds and/or their components. In one embodiment, the cardiac signal includes a surface ECG signal. In another embodiment, the cardiac signal includes an intracardiac ECG signal that is also referred to as an electrogram. Cardiac sensing circuit  112  includes a sensing amplifier to sense the cardiac signal, a cardiac events detector to detect the cardiac electrical events, and an event marker generator to label each detected cardiac electrical event with an event marker indicative of the timing and type of the detected cardiac electrical event. The detected electrical events include, by not limited to, selected atrial and ventricular contractions. The atrial and ventricular contractions include spontaneous contractions and artificially stimulated contractions. 
     Heart sound detector  130  detects the selected type heart sounds. In one embodiment, heart sound detector  130  detects the selected type heart sounds based on the acoustic sensor signal. In another embodiment, heart sound detector  130  detects the selected type heart sounds based on the acoustic sensor signal and the cardiac signal sensed by cardiac sensing circuit  112 . In one embodiment, heart sound detector includes a gating module  132  and a detection module  134 . Gating module  132  receives the acoustic sensor signal from sensor interface module  120  and the cardiac signal from cardiac sensing circuit  112 . In one embodiment, the cardiac signal received by gating module  132  includes event makers representing the detected cardiac electrical events that allow or facilitate detection of the selected type heart sounds. Gating module  132  generates heart sound detection windows each timed for detection of one of the selected type heart sounds based on a time of occurrence of one of cardiac electrical events.  FIG. 2  illustrates, by way of example, but not by way of limitation, a heart sound detection window. As illustrated in  FIG. 2 , a cardiac signal  200  indicates a heart contraction  202 . An event marker signal  210 , which is a representation of cardiac signal  200 , includes an event marker  212  representing heart contraction  202 . An acoustic sensor signal  230 , simultaneously recorded with cardiac signal  200 , includes an indication of a heart sound  235 . Based on available medical knowledge including statistical information available for an individual patient, heart sound  235  is substantially probable to occur within a time period T 2  which starts after a time period T 1  triggered by event marker  212  representing heart contraction  202 . Thus, gating module  132  generates a heart sound detection window having a duration of T 2  at the end of T 1  following each heart contraction used for detection of the selected type heart sounds. In another embodiment, another heart sound (of a different type than the selected type) substitutes heart contraction  202  to trigger T 1 , and gating module  132  generates the heart sound detection window T 2  at the end of T 1  following each heart sound used for detection of the selected type heart sounds. In one embodiment, the heart sound detection windows are used to conserve energy and/or computational resources of system  100  by limiting the need for detection and subsequent computations to periods within the heart sound detection windows. In another embodiment, it is difficult or practically impossible to differentiate one type of the heart sounds from another by amplitude or frequency spectrum. This necessitates a method of detection that is not based on the amplitude or frequency spectrum of the selected type heart sounds. One feasible method includes the use one or more heart sound detection windows each corresponding to one or more types of heart sounds, thus allowing detections of heart sounds based on their predicted ranges of time of occurrence. Durations of the windows are determined based on an empirical study on the timing of each type of heart sounds relative to a type of cardiac. Heart sound detector  134  detects the selected type heart sounds. In one embodiment, heart sound detector  134  detects the selected type heart sounds within the one or more heart sound detection windows. In one embodiment, heart sound detector  134  includes one or more comparators to detect the selected type heart sounds by comparing the amplitude of the acoustic sensor signal during the one or more heart sound detection windows with one or more predetermined detection thresholds. 
     Following the detections of the selected type heart sounds by heart sound detector  130 , parameter generator  140  makes measurements to generate parameter values of at least one predetermined parameter related to the detected heart sounds. In one embodiment, such a parameter value is measured from one detected heart sound. In another embodiment, the parameter value is calculated based on measurement of several detected heart sounds of the same type. The parameter values indicate the patient&#39;s hemodynamic performance, either directly or after further processing as discussed below. Parameter generator  140  includes a measurement module  150  to make measurements on the acoustic sensor signal. The measurements are timed with the detections of the selected type heart sounds. In one embodiment, measurement module  150  receives the acoustic sensor signal from heart sound detector  130  and the cardiac signal from cardiac sensing circuit  112 .  FIG. 3  is a block diagram that illustrates, by way of example, but not by way of limitation, components of measurement module  150 . As illustrated in  FIG. 3 , measurement module  150  includes a strength detector  351 , a relative strength detector  352 , a duration timer  353 , an electro-mechanical interval timer  354 , a mechanical interval timer  355 , and a frequency analyzer  356 . Strength detector  351  measures amplitudes each associated with a detected heart sound. Relative strength detector  352  determines differences each between amplitudes associated with two detected heart sounds. Duration timer  353  measures durations each associated with a detected heart sound. Electromechanical interval timer  354  measures electro-mechanical time intervals each between a detected heart sound and a cardiac electrical event detected from the cardiac signal. Mechanical interval time  355  measures mechanical time intervals each between two detected heart sounds. Frequency analyzer  356  computes fundamental and/or harmonic frequencies each associated with a detected heart sound. In one embodiment, measurement module  150  calculate one or more parameter values each based on several values of a predetermined parameter measured by one of the components of measurement module  150 . In one specific embodiment, measurement module  150  calculates the one or more parameter values each being an average of the several values of the predetermined parameter. Because of the nature and property of the acoustic sensor, the parameter values output from measurement module  150  may includes those affected by background interference. For example, when the acoustic sensor is an accelerometer, the acoustic sensor signal may indicate a patient&#39;s physical activities in addition to the heart sounds. When the acoustic sensor is a microphone, the acoustic sensor signal may indicate talking and other environment sounds in addition to the heart sounds. Thus, in one embodiment, parameter generator  140  includes a screening module  144  to exclude parameter values resulted from measurements performed when a background noise level exceeds a predetermined threshold. In one embodiment, a noise monitoring module  142  measures the background noise level. In one specific embodiment, noise monitoring module  142  includes an activity sensor that senses a patient&#39;s physical activities and an activity sensor interface module to convert the physical activities to the background noise level. In another specific embodiment, noise monitoring module includes a further sensor interface module coupled to acoustic sensor  110 , which senses the patient&#39;s physical activities in addition to the acoustic energy related to the patient&#39;s cardiac mechanical activities. When acoustic sensor  110  includes an accelerometer, the further sensor interface module includes an activity level detector to produce the background noise level signal indicative of the patient&#39;s physical activities. The activity level as indicated by the acoustic sensor signal has a distinctively higher amplitude than the heart sounds. Thus, the activity level detector distinguishes the patient&#39;s physical activities from the heart sounds by using a predetermined activity level threshold. In one embodiment, parameter generator  140  includes a memory circuit  146  to store the parameter values generated by measurement module  150 . In another embodiment, memory  146  stores only parameters screened by screening module  144 . 
     Data acquisition enabler  118  controls the timing of overall data acquisition by timing the enablement of selected system components including at least one or more of acoustic sensor  110 , sensor interface module  120 , cardiac sensing circuit  112 , heart sound detector  130 , and parameter generator  140 . In one embodiment, data acquisition enabler  118  enables the selected system components in response to an external command, such as given by the user. In another embodiment, data acquisition enabler  118  includes a data acquisition timer to enable the selected system components on a predetermined schedule. In one specific embodiment, the data acquisition timer enables the selected system components on a predetermined periodic basis. In another specific embodiment, if parameter generator  140  is unable to generate required parameter values on the predetermined schedule, for example, because the background noises exceeds the predetermined level when the selected system components are enabled, data acquisition enabler  118  modifies the predetermined schedule by introducing at least one delay to ensure that all the desired parameter values are obtained. 
     Parameter processor  160  processes the parameter values received from parameter generator  140 . In one embodiment, parameter processor  160  includes a statistical processor  162 , a trending analyzer  164 , and an alert signal generator  166 . Statistical processor  162  analyzes the parameter values generated by parameter generator  140  for a predetermined period of time. Trending analyzer  164  produces at least one trend related to the selected type heart sounds. The trend is a hemodynamic performance trend indicative of one or more cardiac conditions. In one embodiment, the trend is a plot of parameter values of one selected parameter related to the detected heart sounds over a predetermined period of time. In another embodiment, the trend is a plot of values derived for the parameter values as a result of the statistical process over the predetermined period of time. Alert signal generator  166  generates an alert signal indicative of a presence of the one or more cardiac conditions indicated by the at least one trend. In one embodiment, alert signal generator  166  includes a comparator. The comparator has a first input to receive the at least one trend, a second input representative of a predetermined threshold level, and an output indicative of the presence of the one or more clinical conditions when the at least one trend exceeds the predetermined threshold level. In one further embodiment, alert signal generator  166  includes a threshold generator that generates an adaptive threshold level based on at least one previously produced trend, such that the predetermined threshold is dynamically adjustable based on the patient&#39;s changing cardiac conditions. 
     Therapy circuit  170  includes, by way of example, but not by way of limitation, one or more of a pacing circuit, a defibrillation circuit, a cardiac resynchronization circuit, and a drug delivery circuit. It includes a therapy controller to execute a predetermined therapy algorithm that times therapy deliveries based on the processed cardiac signal and acoustic sensor signal. In one embodiment, the therapy controller receives at least one of selected parameter values generated by parameter generator  140 , the at least one trend generated by trending analyzer  164 , and the alert signal generated by alert signal generator  166 , based on which it produces or adjusts one or more therapy parameters. 
       FIG. 4  is a flow chart illustrating an embodiment of a method for hemodynamics monitoring and therapy control using system  100 . At  400 , data acquisition for the hemodynamics monitoring and therapy control begins. In one embodiment, the data acquisition begins as system  100  is activated. In one embodiment, the data acquisition begins in response to a user command. In another embodiment, the data acquisition begins at a predetermined time or upon a predetermined triggering event. In one embodiment, the date acquisition lasts for a predetermined duration after it begins. In one specific embodiment, the data acquisition begins on a predetermined periodic basis and lasts for a predetermined duration. 
     At  402 , acoustic sensor  110  senses the acoustic energy related to cardiac mechanical activities and converts the acoustic energy to an acoustic sensor signal indicative heart sounds. In one embodiment, acoustic sensor  110  senses an acceleration indicative of the acoustic energy. 
     At  410 , sensor interface module  410  processes the acoustic sensor signal to prepare for heart sound detection. In one embodiment, the acoustic sensor signal is amplified and filtered to increase its signal-to-noise ratio. Then, the acoustic sensor signal is digitized to the form of binary data. The digitized acoustic sensor signal is filtered to enhance indications of the selected type heart sounds. In one embodiment, the digitized acoustic sensor signal is filtered with at least one cutoff frequency determined based on the frequency spectrum of the selected type heart sounds. 
     At  420 , heart sound detector  130  generates heart sound detection windows each timed for detecting one of the selected type heart sounds. The heart sound detection windows are each triggered by one of selected cardiac electrical events detected from the cardiac signal sensed at  404 . In one embodiment, the selected cardiac electrical events include at least one of spontaneous or artificially stimulated atrial and ventricular contractions. In one embodiment, the selected cardiac electrical events are each represented by a predetermined event marker. In one specific embodiment, At  425 , the selected type heart sounds are detected. In one embodiment, each of the selected type heart sounds is detected when the amplitude of the acoustic sensor signal exceeds a predetermined threshold level. 
     At  430 , parameter generator  140  generates the parameter values of at least one parameter related to the detected heart sounds based on the acoustic sensor signal produced at  400  and/or the cardiac signal sensed at  404 . Such parameter values include, by way of example, but not by way of limitation, one or more of (i) an amplitude associated with one or one selected type of the selected type heart sounds; (ii) a relative strength being differences between amplitudes associated with two or two selected types of the selected type heart sounds; (iii) a duration associated with one or one selected type of the selected type heart sounds; (iv) an electro-mechanical time intervals between one or one selected type of the selected type heart sounds and one or one type of selected type cardiac electrical events; (v) a mechanical time interval between two or two selected types of the selected type heart sounds; and (vi) a fundamental or harmonic frequency associated with one or one selected type of the selected type heart sounds. In one embodiment, parameter values related to S 3  and/or S 4  are measured and/or calculated for the purpose of monitoring ventricular diastolic hemodynamic performance. The parameter values of one or more of the following parameters are generated: (i) peak amplitude of S 3 ; (ii) time of onset of S 3  relative to onset of S 2 ; (iii) duration of S 3 ; (iv) fundamental frequency if S 3 ; (v) time of occurrence of S 3  relative to the subsequently adjacent atrial contraction; (vi) peak amplitude of S 4 ; (vii) time interval between atrial contraction and the subsequently adjacent S 4 ; (viii) fundamental frequency of S 4 ; (ix) duration of S 4 ; (x) time of occurrence of S 4  relative to the subsequently adjacent ventricular contraction; and (xi) amplitude of S 4  relative to amplitude of S 3 . In one embodiment, parameter generator  140  screens out noisy values of the parameter values measured at  435 . Such noisy values include parameter values measured when the background noise level exceeds a predetermined threshold. In one embodiment, the patient&#39;s physical activities are sensed at  406  to produce an activity level signal indicative of the background noise level. In one specific embodiment, the activity level signal is derived from the same acoustic sensor signal from which the selected type heart sounds are detected. This is possible because the patient&#39;s physical activities are typically indicated with amplitudes that are distinctively higher than the amplitudes of the selected type heart sounds. 
     At  440 , the parameter values are stored in memory circuit  146  or other storage medium. In one embodiment, system  100  uses the parameter values directly to control delivery of at least one therapy with at least one therapy parameter being a function of the parameter values. In another embodiment, the parameter values are further processed and analyzed by system  100  for monitoring, diagnosis, and/or therapy control purposes. In yet another embodiment, the stored parameter values are transferred to another system, such as a computer separated from system  100 , for further processing and/or analysis. 
     At  450 , parameter processor  160  statistically processes the parameter values. The statistical process includes analyzing the parameter values of the at least one parameter related to the detected heart sounds in relation to historical values of that parameter measured during a predetermined period of time. The outcome of the statistical process reveals changes in cardiac conditions reflected in the characteristics of the selected type heart sounds. In one embodiment, the outcome of the statistical process reveals changes in ventricular diastolic filling patterns during the predetermined period of time. In one specific embodiment, the predetermined period of time ranges from 1 day to 3 months. 
     At  460 , parameter processor  160  produces at least one hemodynamic performance trend related to the selected type heart sounds. In one embodiment, parameter processor  160  produces the at least one trend based on the outcome of the statistical analysis. In one embodiment, one or more trends quantitatively present one or more ventricular diastolic filling pattern changes during a predetermined duration. In one embodiment, parameter processor  160  plots the parameter values of the at least one parameter related to the detected heart sounds versus time. In another embodiment, parameter processor  160  statistically processes the parameter values of the at least one parameter related to the detected heart sounds and plots the result. At  465 , the one or more trends are analyzed for indication of cardiac conditions. In one embodiment, the values of each trend are compared to a predetermined threshold level, and a predefined cardiac condition is indicated when any value exceeds the predetermined threshold level. In one embodiment, the predetermined threshold level is determined based on at least one previously produced trend. 
     At  475 , an alert signal is generated when a cardiac condition is indicated by the at least one hemodynamic performance trend at  470 . The alert signal notifies the user of the cardiac condition that may need medical attention. In one embodiment, the cardiac condition requires delivery of a therapy. In another embodiment, the alert signal indicates a need for changing one or more therapy parameters. 
     In one embodiment, a therapy is delivered in response to the alert signal at  480 . The therapy includes one or more of, for example, a pacing therapy, a defibrillation therapy, a cardiac resynchronization therapy, any other electrical stimulation therapy, and a drug therapy. The type of the therapy as therapy parameters are determined based on the at least one trend and/or selected values of the at least one parameter related to the detected heart sounds. In one specific embodiment, therapy circuit  170  delivers the therapy. In another embodiment, one or more therapy parameters are adjusted in response to the alert signal, and the new therapy parameters are determined based on the at least one trend and/or the selected values of the at least one parameter related to the detected heart sounds. In an alternative embodiment, the therapy delivery or the therapy parameter adjustments are not dependent on the alert signal. The at least one trend and/or the selected values of the at least one parameter related to the detected heart sounds directly determine the need for the therapy delivery or the therapy parameter adjustments. 
     Many embodiments combining the present method with available medical knowledge will be apparent to those of skill in the art. In one example, the fundamental frequency (also referred to as the pitch) of S 3  is correlated to the stiffness of the left ventricular wall during the rapid filling phase of diastole. The wall stiffness is proportional to diastolic pressure in the left ventricle and to the thickness of the left ventricular wall. Therefore, an increase in the pitch of S 3  is used to indicate one or more of an elevated left ventricular filling pressure and a thickened left ventricular wall. The elevation of the left ventricular filling pressure and/or the increase of the left ventricular wall thickness may reach a degree, represented by predetermined thresholds of S 3  fundamental frequency, that requires an application of adjustment of a therapy. In another example, the amplitude of S 3  is directly related to the rate of deceleration of blood flow into the left ventricle during the rapid filling phase of diastole. An increase in amplitude of S 3  can be used to indicate an elevation of left atrial filling pressure, an increase in stiffness of the left ventricle, or both, which represent a restrictive filling pattern associated with heart failure. Therefore, the trend of S 3  amplitude is useful in monitoring cardiac mechanical properties related to heart failure. In yet another example, the elevated filling pressures cause pulmonary edema. Thus, a physician determines the need of a drug therapy to relieve the elevated pressures based on one or more trends of parameters related to S 3 . These are a few examples, among many possible embodiments, illustrating how system  100  is used. In general, trends of any of the measured parameter values can be used individually, jointly, and/or in combination with other trends related to cardiac functions. 
       FIG. 5  is an illustration of an embodiment of portions of a cardiac rhythm management system  599  and portions of an environment in which it is used. System  599  incorporates a heart-sound based hemodynamics monitoring and therapy control system such as system  100 . In one embodiment, cardiac rhythm management system  599  includes an implanted system  505 , an external system  580 , and a telemetry link  570  providing for communication between implanted system  505  and external system  580 . Implanted system  505  includes an implanted device  506  and a lead system  508 . Implanted device  506  is implanted within a patient&#39;s body  502  and coupled to the patient&#39;s heart  501  via lead system  508 . Examples of implanted device  506  include pacemakers, cardioverter/defibrillators, pacemaker/defibrillators, cardiac resynchronization devices, and drug delivery devices. External system  580  is a patient management system including an external device  585  in proximity of implanted device  502 , a remote device  595  in a relatively distant location, and a telecommunication system  590  linking external device  585  and remote device  595 . An example of such a patient management system is discussed in Hatlestad et al., “ADVANCED PATIENT MANAGEMENT FOR DEFINING, IDENTIFYING AND USING PREDETERMINED HEALTH-RELATED EVENTS,” application Ser. No. 10/323.604, filed on Dec. 18, 2002, assigned to Cardiac Pacemakers, Inc., the specification of which is incorporated herein by reference in its entirety. In one embodiment, telemetry link  570  is an inductive telemetry link. In an alternative embodiment, telemetry link  570  is a far-field radio-frequency telemetry link. In one embodiment, telemetry link  570  provides for data transmission from implanted device  506  to external device  585 . This may include, for example, transmitting real-time physiological data acquired by implanted device  506 , extracting physiological data acquired by and stored in implanted device  506 , extracting therapy history data stored in implanted device  506 , and extracting data indicating an operational status of implanted device  506  (e.g., battery status and lead impedance). In a further embodiment, telemetry link  570  provides for data transmission from external device  585  to implanted device  506 . This may include, for example, programming implanted device  506  to acquire physiological data, programming implanted device  506  to perform at least one self-diagnostic test (such as for a device operational status), and programming implanted device  506  to deliver at least one therapy. 
     In one embodiment, programming implanted device  506  includes sending therapy parameters to implantable device  506 . The therapy parameters provide an improved hemodynamic performance for a patient by delivering cardiac pacing pulses to the patient&#39;s heart. In one embodiment, the therapy parameters providing for the improved hemodynamic performance are determined by monitoring one or more ventricular diastolic hemodynamics as indicated by parameters related to heart sounds such as S 3  and S 4 . Such parameters indicate the heart&#39;s mechanical activities and electro-mechanical association. In one specific embodiment, the acquisition of values of such parameters, the processing of the parameter values, and the subsequent determination of the therapy parameters are performed by system  100 , as discussed above with reference to  FIGS. 1-3 . 
       FIG. 6  is a block diagram illustrating a specific embodiment of portions of cardiac rhythm management system  599 . In this embodiment, system  100  is substantially included within implanted device  506 . System  100  includes, as discussed above with reference to  FIG. 1 , acoustic sensor  110 , sensor interface module  120 , cardiac sensing circuit  112 , heart sound detector  130 , parameter generator  140 , data acquisition timer  118 , parameter processor  160 , and therapy circuit  170 . Implanted device  506  also includes, among other things, an implant telemetry module  672  and an implant antenna  674  to provide implanted device  506  with telemetry capability allowing it to communicate with external system  580  via telemetry link  570 . In one embodiment, therapy circuit  170  includes a therapy controller that executes a predetermined therapy control algorithm to determine whether to deliver a therapy or adjust one or more therapy parameters based on the one or more of the heart sound-related parameter values generated by parameter generator  140  and trends and alert signal generated by parameter processor  160 . 
     External system  580  includes, among other things, an external antenna  676 , an external telemetry module  678 , a controller  682 , and a user interface  684 . In one embodiment, external telemetry module  678  and external antenna  676  are included in external device  585  to provide external system  580  with capability of communicating with implanted device  506  through telemetry link  570  and external device  585 . Controller  682  controls telemetry operation of external system  580 , processes signals received from implanted device  506  for presentation on user interface  684 , and processes user commands entered through user interface  684  for transmission to implanted device  506 . In one embodiment, one or more of the heart-sound related parameter values, trends, and alert signal, as discussed above, are acquired by system  100  and telemetered to external system  580  via telemetry link  570 . Controller  682  executes a predetermined therapy control algorithm to determine whether to deliver a therapy or adjust one or more therapy parameters based on the one or more of the heart sound-related parameter values, trends, and alert signal. 
     In one embodiment, system  100  is completely within a hermetically sealed can that houses at least portions of implanted device  506 . Housing acoustic sensor  110  in the can has the advantage of minimizing the background noise associated with physical movements of the sensor, especially when acoustic sensor  110  includes an accelerometer. In another embodiment, acoustic sensor  110  is attached to a lead of lead system  508 . This allows disposition of acoustic sensor  110  in or near heart  501  such that it is near the mechanical activities being the sources of the heart sounds of interest. 
     To include substantially the whole system  100  within implanted device  506  provides for the advantage of a self-contained implantable cardiac rhythm management system incorporating heart-sound based therapy control. In one embodiment, the heart-sound based therapy control using system  100  is able to function without telemetry link  570 , for example, when the patient is outside the range of the telemetry communication. Implanted device  506  determines, without the intervention of the user or controller  682 , whether to deliver a therapy or adjust one or more therapy parameters based on the one or more of the parameter values, trends, and alert signal generated within itself by system  100 . 
       FIG. 7  is a block diagram illustrating another specific embodiment of portions of cardiac rhythm management system  599 . In this embodiment, system  100  is partially included within implantable device  506  and partially included in external system  580 . In one specific embodiment, parameter processor  160  is within external system  580 , and the remaining components of system  100  are within implanted device  506 . Parameter values generated by parameter generator  140  are telemetered to external system  580  via telemetry link  570  for further processing by parameter processor  160 . In one embodiment, parameter processor  160  is included in external device  585 . In an alternative embodiment, parameter processor  160  is included in remote device  595 . 
     In one embodiment, the parameter values are telemetered as they are generated. In another embodiment, parameter values are first stored in memory circuit  146 . Data acquisition enabler  118  times transmission of the parameter values in response to a command from external device  580  or on a predetermined schedule. 
     To include parameter processor  160  in external system  580  avoids placing the demand of energy and circuit resources required by parameter processor  160  in implanted device  506 , which is subject to design restraints including power and size limitations. The advantages also include the feasibility of updating parameter processing algorithms used by parameter processor  160  without the need of replacing implanted device  506 . 
     It is to be understood that the above detailed description is intended to be illustrative, and not restrictive. For example, system  100  may be incorporated into any implanted or external medical device providing for ECG and heart sound monitoring. Other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.