System and method of impedance cardiography and heartbeat determination

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.

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.