Method and system for determining fluid status based on a dynamic impedance surrogate for central venous pressure

Abstract

A method and system are provided for determining fluid status with a central venous system of a heart. Dynamic impedance (DI) data and static impedance (SI) data are collected over multiple cardiac cycles (CC) for a persistent time period of interest (POI). The DI and SI data are collected along a central venous (CV) vector that extends through a superior vena cava (SVC). The DI and SI data are analyzed to obtain DI long-term variation (LTV) information and SI LTV information, respectively, and to detect whether the DI LTV information and the SI LTV information include decreasing persistent trends in the DI and SI data. When decreasing persistent trends are detected in the DI and SI data, an overload output is generated to indicate that the heart is experiencing a volume overload state. The DI and SI data represent a surrogate for central venous pressure.

What is claimed is: 
     
         1 . A method for determining fluid status with a central venous system of a heart, the method comprising:
 collecting dynamic impedance (DI) data and static impedance (SI) data over multiple cardiac cycles (CC) for a persistent time period of interest (POI), the DI and SI data collected along a central venous (CV) vector that extends through a superior vena cava (SVC);   analyzing the DI and SI data, collected over the persistent time POI, to obtain DI long-term variation (LTV) information and SI LTV information, respectively;   detecting whether the DI LTV information and the SI LTV information include decreasing persistent trends in the DI and SI data; and   when decreasing persistent trends are detected in the DI and SI data, generating an overload output indicating that the heart is experiencing a volume overload state.   
     
     
         2 . The method of  claim 1 , wherein the DI and SI data represent a surrogate for central venous pressure such that when a decreasing persistent trend is detected a fluid status corresponds to the volume overload state. 
     
     
         3 . The method of  claim 1 , wherein the overload output indicates that an interior dimension of the SVC is expanding over the LT time period of interest. 
     
     
         4 . The method of  claim 1 , wherein the analyzing operation further comprises:
 analyzing at least one morphologic characteristic from the DI and SI data to obtaining DI and SI central venous (CV) indicators for each cardiac cycle, the DI and SI CV indicators representative of a feature of interest within the DI and SI data, respectively; and   analyzing the DI and SI indicators to obtain the LTV information.   
     
     
         5 . The method of  claim 1 , wherein the DI LTV information corresponds to changes in dynamic impedance over the persistent time period of interest that extends over at least one of hours, days or weeks. 
     
     
         6 . The method of  claim 1 , further comprising:
 analyzing the DI and SI data, collected over a transient time period of interest, to obtain DI short-term variation (STV) information;   determining whether the DI STV information includes an increasing or decreasing ST trend in the DI data; and   when a decreasing ST trend exists in the DI data, generating a stroke volume (SV) output indicating that the heart is experiencing a decrease in stroke volume.   
     
     
         7 . The method of  claim 1 , further comprising, over multiple cardiac cycles, changing at least one IMD therapy parameter setting and repeating the collecting, analyzing and detecting operations to obtain a collection of DI LTV information and the SI LTV information associated with different IMD therapy parameter settings. 
     
     
         8 . The method of  claim 1 , further comprising, based on the overload output, determining a select level for the at least one IMD therapy parameter setting that provides at least one of i) heart rate paced, ii) pacing mode (options include DDD, DOO, VVI, VOO, AAI and AOO), iii) a select peak to peak amplitude, iv) a select minimum amplitude, v) a select DI change per unit time (dZ/dt), vi) a select slope, vii) a select ventricular filling time, or viii) a select ventricular emptying time, of the DI data when plotted over time. 
     
     
         9 . The method of  claim 1 , wherein the collecting of DI data includes utilizing an IMD case electrode and at least one of an SVC electrode, an IVC electrode and an RA electrode to define the CV vector and to collect the DI and SI data. 
     
     
         10 . The method of  claim 1 , wherein the analyzing the DI data includes determining, as a morphologic characteristic, at least one of i) a peak to peak (P-P) amplitude, ii) a minimum amplitude, iii) a minimum DI change per unit time (dZ/dt), iv) slope and v) area under the curve, vi) time features from fiducial points of the DI data over the CC. 
     
     
         11 . The method of  claim 1 , wherein the CV vector extends through at least one of the SVC, RA or IVC. 
     
     
         12 . A system for determining fluid status with a central venous system of a heart, the system comprising:
 inputs configured to receive dynamic impedance (DI) data and static impedance (SI) data that is collected over multiple cardiac cycles (CC) for a persistent time period of interest (POI), the DI and SI data collected along a central venous (CV) vector that extends through a superior vena cava (SVC);   an impedance analysis (IA) module configured to analyze the DI and SI data, collected over the persistent time POI, to obtain DI long-term variation (LTV) information and SI LTV information, respectively; and   a trend detection (TD) module configured to detect when the DI LTV information and the SI LTV information include decreasing persistent trends in the DI and SI data, the trend detection module configured to generate an overload output indicating that the heart is experiencing volume overload when the trend detection module detects the decreasing persistent trend in the DI and SI data.   
     
     
         13 . The system of  claim 12 , wherein the DI and SI data represent a surrogate for central venous pressure such that when the trend detection module detects the decreasing persistent trend, a fluid status in the CV system corresponds to a volume overload state. 
     
     
         14 . The system of  claim 12 , wherein the overload output indicates that an interior dimension of the SVC is expanding over the LT time period of interest by more than a predetermined CV expansion threshold. 
     
     
         15 . The system of  claim 12 , wherein the analysis module is further configured to:
 analyze at least one morphologic characteristic from the DI and SI data to obtaining DI and SI central venous (CV) indicators for each cardiac cycle, the DI and SI CV indicators representative of a feature of interest within the DI and SI data, respectively; and   analyze the DI and SI indicators to obtain the LTV information.   
     
     
         16 . The system of  claim 12 , wherein the DI LTV information corresponds to changes in dynamic impedance over the persistent time period of interest that extends over at least one of hours, days or weeks. 
     
     
         17 . The system of  claim 12 , whether the analysis module is further configured to analyze the DI and SI data, collected over a transient time period of interest, to obtain DI short-term variation (STV) information; and the trend detection module is further configured to determine whether the DI STV information includes an increasing or decreasing ST trend in the DI data, when a decreasing ST trend exists in the DI data, the trend detection module configured to generate a stroke volume (SV) output indicating that the heart is experiencing a decrease in stroke volume. 
     
     
         18 . The system of  claim 12 , further comprising a therapy control module configured to change at least one IMD therapy parameter setting, over multiple cardiac cycles, and repeat the collecting, analyzing and detecting operations to obtain a collection of DI LTV information and the SI LTV information associated with different IMD therapy parameter settings. 
     
     
         19 . The system of  claim 12 , further comprising a therapy control module configured to determine, based on the overload output, a select level for the at least one IMD therapy parameter setting that provides at least one of i) heart rate paced, ii) pacing mode (options include DDD, DOO, VVI, VOO, AAI and AOO), iii) a select peak to peak amplitude, iv) a select minimum amplitude, v) a select DI change per unit time (dZ/dt), vi) a select slope, vii) a select ventricular filling time, or viii) a select ventricular emptying time, of the DI data when plotted over time. 
     
     
         20 . The system of  claim 12 , further comprising a lead coupled to the inputs, the lead including an IMD case electrode and at least one of an SVC electrode, an IVC electrode and an RA electrode to define the CV vector and to collect the DI and SI data. 
     
     
         21 . The system of  claim 12 , wherein the analysis module is configured to analyze the DI data by determining, as a morphologic characteristic, at least one of i) a peak to peak (P-P) amplitude, ii) a minimum amplitude, iii) a minimum DI change per unit time (dZ/dt), iv) slope v) area under the curve, and vi) time features from fiducial points of the DI data over the CC. 
     
     
         22 . The system of  claim 12 , wherein the analysis module is configured to receive patient state information indicating at least one of a select activity state and a select posture position of a patient, the analysis module configured to control the inputs to collect the DI data only when the patient state information satisfies a patient state threshold.