System and method of impedance cardiography and heartbeat determination
First Claim
1. A method of processing a time-derivative, thoracic impedance signal generated from a patient to identify events in the time-derivative impedance signal associated with beats of the patient'"'"'s heart, the method comprising the steps of:
- generating a time-frequency distribution of data from the time-derivative impedance signal for a selected portion of the time-derivative impedance signal spanning a single heartbeat of the patient; and
identifying a time of occurrence of at least one cardiac event in the selected portion of said time-derivative impedance signal from the time-frequency distribution.
4 Assignments
0 Petitions
Accused Products
Abstract
Cardiac monitoring is disclosed in which thoracic impedance and EKG signals are gathered and processed for improved resolution and accuracy. EKG signals are adaptively processed by digitizing, filtering, differentiating and raising the resultant differential by a power greater than one to emphasize changes in the slope of the EKG signal. Blocks of the thus processed EKG data are analyzed to identify peak amplitude and to compare spacing between peak amplitude adaptively to more accurately identify R wave peaks. Stroke volume is determined from a thoracic impedance signal and its time derivative. Preferably, a time-frequency distribution is taken of the time derivative thoracic impedance signal after low- and high-pass filtering to identify B and X wave events in the signal which are used to determine ventricular ejection time and dz/dtmin for a determination of heart stroke volume by conventional methods. Alternatively, stroke volume is determined by a new relationship between a product of a pair of impedances simultaneously sensed on opposing sides of a patient'"'"'s heart at the peak of a heartbeat.
-
Citations
30 Claims
-
1. A method of processing a time-derivative, thoracic impedance signal generated from a patient to identify events in the time-derivative impedance signal associated with beats of the patient'"'"'s heart, the method comprising the steps of:
-
generating a time-frequency distribution of data from the time-derivative impedance signal for a selected portion of the time-derivative impedance signal spanning a single heartbeat of the patient; and identifying a time of occurrence of at least one cardiac event in the selected portion of said time-derivative impedance signal from the time-frequency distribution. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
-
-
27. A method of determining stroke volume of a patient'"'"'s heart from thoracic impedance measurements comprising the steps of:
-
applying a fluctuating excitation current to the patient through a first pair of electrodes located on opposing upper and lower sides of the patient'"'"'s heart; generating from a second pair of electrodes located on opposing sides of the patients'"'"'s heart between the first pair of electrodes a first signal related to impedance of the patient at a first electrode of the second pair and a second signal related to impedance of the patient at a second electrode of the second pair; identifying an impedance from each of the first and second signals occurring simultaneously with one heartbeat of the patient; and multiplying together the identified impedances of each of the first and second signals to estimate a cardiac parameter at least related to stroke volume of the patient'"'"'s heart during the one heartbeat. - View Dependent Claims (28)
-
-
29. A method of determining stroke volume of a patient'"'"'s heart from the thoracic impedance measurements comprising the steps of:
-
applying a fluctuating excitation current to the patient through a first pair of electrodes located on opposing upper and lower sides of the patient'"'"'s heart; generating from a second pair of electrodes located on opposing sides of the patients'"'"'s heart between the first pair of electrodes, a first signal indicative of absolute impedance of the patient at only the first electrode of the second pair and a second signal indicative of absolute impedance of the patient at only the second electrode of the second pair; identifying two individual values, one from each of the first and second signals, indicating two absolute impedances occurring at one instant at the first and second electrodes of the second pair during one heartbeat of the patient; and multiplying together the two identified individual values to generate a product value proportional to each of the two absolute impedances at the one instant to estimate a cardiac parameter at least related to stroke volume of the patient'"'"'s heart during the one heartbeat.
-
-
30. In a system for processing a time-derivative thoracic impedance signal generated from a patient to identify events in the time-derivative signal associated with the beats of the patient'"'"'s heart, the improvement comprising:
memory means for at least temporarily storing a time-derivative thoracic impedance signal and processor means coupled with the memory means for generating a time-frequency distribution of data from the time-derivative thoracic impedance signal for a selected portion of the time-derivative thoracic impedance signal spanning a single heartbeat of the patient and for identifying a time of occurrence of at least one cardiac event in the selected portion of the time-derivative thoracic impedance signal from the time-frequency distribution.
Specification