Systems and methods for determining cardiac output
A system is provided including a thoracic bio-impedance or bio-reactance (TBIR) analysis module, a photoplethysmograph (PPG) analysis module, and a cardiac output module. The TBIR module is configured to obtain TBIR information from a TBIR detector, and the PPG analysis module is configured to obtain PPG information from a PPG detector. The cardiac output module is configured to determine the cardiac output of a patient using the TBIR information and the PPG information.
1. A method for determining a cardiac output of a patient comprising:
obtaining a thoracic bio-impedance or bio-reactance (TBIR) signal from a TBIR detector configured to detect TBIR activity of the patient;
electronically measuring a voltage of the TBIR signal to determine an impedance value;
determining a first cardiac output value for the patient from a change in the impedance value over a heart cycle;
obtaining a photoplethysmographic (PPG) signal from a PPG detector configured to detect PPG activity of the patient;
calculating a ratio of first and second peaks in the PPG signal;
determining a second cardiac output value for the patient from the ratio;
determining, at a processor, a subsequent cardiac output of the patient from the first and second cardiac output values.
2. The method of claim 1 , wherein the subsequent cardiac output of the patient is determined using at least one of a comparison or a combination of the first and second cardiac output values.
3. The method of claim 2 , further comprising:
obtaining TBIR signal quality information corresponding to a quality of the TBIR signal; and
obtaining PPG signal quality information corresponding to a quality of the PPG signal;
wherein the at least one of the comparison or the combination is performed using the TBIR signal quality information and the PPG signal quality information.
4. The method of claim 1 , wherein
determining the first cardiac output value includes using a pulse rate determined at least in part from the PPG signal.
5. The method of claim 1 , further comprising obtaining blood pressure information from a blood pressure detector, wherein
determining the second cardiac output value includes using the blood pressure information obtained from the blood pressure detector.
6. The method of claim 1 , wherein the subsequent cardiac output of the patient is determined using a combination of the first and second cardiac output values.
7. The method of claim 6 , wherein the combination comprises a weighted combination.
8. The method of claim 7 , wherein a weight for the weighed combination is based on one or more signal quality metrics of the TBIR signal or the PPG signal.
9. The method of claim 1 , wherein the subsequent cardiac output of the patient is determined using a comparison of the first and second cardiac output values.
10. The method of claim 3 , wherein the TBIR signal quality information comprises a signal to noise ratio.
11. The method of claim 3 , wherein the TBIR signal quality information comprises a presence or amount of artifact.
12. The method of claim 3 , wherein the TBIR signal quality information comprises information about a positive end expiratory pressure.
13. The method of claim 3 , wherein the TBIR signal quality information comprises a physiologic condition of the patient.
14. The method of claim 3 , wherein the TBIR signal quality information comprises an amount of match between the obtained TBIR signal and an expected characteristic of the TBIR signal.
15. The method of claim 3 , wherein the PPG signal quality information comprises a signal to noise ratio.
16. The method of claim 3 , wherein the PPG signal quality information comprises a presence or amount of artifact.
17. The method of claim 3 , wherein the PPG signal quality information comprises a physiologic condition of the patient.
18. The method of claim 3 , wherein the PPG signal quality information comprises an amount of match between the obtained PPG signal and an expected characteristic of the PPG signal.
19. The method of claim 1 , wherein the subsequent cardiac output of the patient is determined using a selection of the first cardiac output value or the second cardiac output value.
20. The method of claim 1 , wherein determining the first cardiac output value from the change in the impedance value comprises utilizing an empirically derived relationship.
21. The method of claim 1 , wherein determining the second cardiac output value from the ratio comprises utilizing an empirically derived relationship.
22. The method of claim 1 further comprising obtaining blood pressure information from a blood pressure detector, and using the blood pressure information to determine the subsequent cardiac output of the patient.