Methods and apparatus for visually representing a cardiac status of a patient

• US 8,968,207 B2
• Filed: 04/13/2009
• Issued: 03/03/2015
• Est. Priority Date: 04/15/2008
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Cohen, Richard J.
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): WESTON, TIFFANY C
• Application Number:
  US12/601,027
• Publication Number:
  US 20100249612A1
• Time in Patent Office: 2,150 Days
• Field of Search: 600481-490
• US Class Current: 600/485
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence

Abstract

Method and apparatus are provided for computing signals related to cardiac output from physiologic input signals related to circulatory pressures or flows. Method and apparatus are provided for constructing a transforming filter and applying said filter to the physiologic input signals in order to obtain a signal proportional to phasic cardiac output or time-averaged cardiac output. This invention provides a means for real-time monitoring of cardiac output and stroke volume which is of great clinical importance but not otherwise feasible by present techniques.

Claims

1. A computer-facilitated method for visually representing to a medical practitioner a cardiac status of a patient so as to facilitate a determination by the medical practitioner of 1) a need for a cardiac-related intervention and/or 2) an effect of a prior cardiac-related, intervention, the method comprising:

A) measuring, via a sensing device coupled to the patient, a circulatory parameter of the patient so as to provide, as an output of the sensing device, a physiologic input signal related to a circulatory pressures of the patient;

B) electronically converting the physiologic input signal from the sensing device, via an analog-to-digital converter coupled to the sensing device, to a plurality of digital samples of the physiologic input signal related to the circulatory pressure of the patient;

C) electronically processing at least some of the plurality of digital samples of the physiologic input signal, via at least one computer coupled to the analog-to-digital converter, to construct a transforming filter to transform the plurality of digital samples of the physiologic input signal based at least in part on one or more periods of time corresponding to diastole of the heart of the patient during which the aortic valve or the pulmonary valve of the heart of the patient is closed;

D) electronically applying the transforming filter, via the at least one computer, to at least some of the plurality of digital samples of the physiologic input signal to compute a cardiac output signal proportional to a phasic cardiac output of the patient, the phasic cardiac output corresponding to a flow across the aortic valve or the pulmonary valve of the heart of the patient, wherein;

the cardiac output signal has a sufficient time resolution to reflect variations in the flow across the aortic valve or the pulmonary valve within a single cardiac cycle; and

in C), the transforming filter is constructed so that, when the transforming filter is applied in D) to the at least some of the plurality of digital samples of the physiologic input signal, the cardiac output signal is reduced during the one or more periods of time corresponding to diastole of the heart of the patient, subject to a normalization constraint on a gain of the transforming filter; and

E) electronically displaying, on a display device coupled to the at least one computer, a visual representation of the cardiac output signal computed in D) to provide the cardiac status of the patient to the medical practitioner and thereby facilitate the determination by the medical practitioner of the need for the cardiac-related intervention and/or the effect of the prior cardiac-related intervention.

2. The method of claim 1, wherein:

the physiologic input signal relates to a systemic arterial pressure or a pulmonary arterial pressure; and

the normalization constraint requires that a dc gain of the transforming filter be inversely proportional to a quantity related to a corresponding systemic vascular resistance or pulmonary vascular resistance.

3. The method of claim 1, wherein C) comprises:

C1) electronically processing the at least some of the plurality of digital samples of the physiologic input signal, via the at least one computer, to determine a quantity related to a systemic vascular resistance or a pulmonary vascular resistance of the patient, based at least in part on one or more periods of time corresponding to systole of the heart of the patient during which the aortic valve or the pulmonary value of the heart of the patient is open; and

C2) electronically constructing, via the at least one computer, the transforming filter to transform the plurality of digital samples of the physiologic input signal based at least in part on

     1) the quantity related to the systemic vascular resistance or the pulmonary vascular resistance of the patient as determined in C1) and

     2) the one or more periods of time corresponding to diastole of the heart of the patient,

wherein C1) comprises determining a value for the quantity related to the systemic vascular resistance or the pulmonary vascular resistance by;

C1a) calculating a width of a waveform relating to the phasic cardiac output of the patient based on the at least some of the plurality of digital samples of the physiologic input signal taken over one or more cardiac cycles of the patient; and

C1b) calculating the value for the quantity related to the systemic vascular resistance or the pulmonary vascular resistance that reduces the width of the waveform.

4. The method of claim 3, further comprising computing a value of a quantity proportional to the systemic vascular resistance or the pulmonary vascular resistance from the value of the quantity related to the systemic vascular resistance or the pulmonary vascular resistance.

5. The method of claim 4, further comprising:

time-averaging the at least some of the plurality of digital samples of the physiologic input signal; and

dividing the time-averaged digital samples of the physiologic input signal by the value of the quantity proportional to the systemic vascular resistance or the pulmonary vascular resistance.

6. The method of claim 4, further comprising:

dividing the at least some of the plurality of digital samples of the physiologic input signal by the value of the quantity proportional to the systemic vascular resistance or the pulmonary vascular resistance to compute a plurality of quotient values; and

time-averaging at least some of the plurality of quotient values.

7. The method of claim 4, further comprising constructing a signal proportional to vascular resistance, via the at least one computer, by repeating the step of computing the value of the quantity proportional to vascular resistance to sequential epochs of one or more cardiac cycles.

8. The method of claim 7, further comprising the step of electrically displaying, on the display device, a visual representation of the signal proportional to vascular resistance.

9. The method of claim 8, wherein the visual representation of the signal proportional to vascular resistance is displayed in real-time.

10. The method of claim 3, wherein the transforming filter implements the functional inverse of an expected cardiac-output-to-central-pressure transfer function.

11. The method of claim 3, wherein an impulse-response function of the transforming filter is the functional inverse of an exponentially decaying impulse-response function having a time constant proportional to the systemic vascular resistance or the pulmonary vascular resistance.

12. The method of claim 3, wherein the transforming filter is defined by an equation having a form:

13. The method of claim 12, wherein x is related to a peripheral arterial pressure P^a of the patient as measured by the sensing device, y represents a scaled arterial flow relating to the phasic cardiac output of the patient, and the width of the waveform relating to the phasic cardiac output of the patient is given by:

14. The method of claim 3, further comprising using the value of the quantity related to the systemic vascular resistance or the pulmonary vascular resistance to determine the dc gain of the transforming filter.

15. The method of claim 1, wherein the transforming filter is a linear filter having adjustable coefficients.

16. The method of claim 1, wherein the transforming filter is a convolution of two filters, including:

a first filter to transform at least some of the plurality of digital samples of the physiologic input signal into a central pressure signal; and

a second filter to transform the central pressure signal into the cardiac output signal proportional to the phasic cardiac output.

17. The method of claim 16, wherein:

a dc gain of the first filter is constant; and

the second filter has a known form based at least in part on a quantity related to a systemic vascular resistance or a pulmonary vascular resistance of the patient.

18. The method of claim 1, wherein the transforming filter is a convolution of two filters, including:

a first filter constituted by a linear filter having adjustable coefficients, wherein a dc gain of the first filter is constant; and

a second filter defined by an equation having a form;

19. The method of claim 1, wherein the physiologic input signal relates to a systemic arterial pressure or a pulmonary arterial pressure.

20. The method of claim 1, wherein:

the sensing device is noninvasively coupled to the patient; and

the physiologic input signal relates to a systemic arterial pressure.

21. The method of claim 1, wherein the physiologic input signal relates to at least one of:

a peripheral arterial pressure, wherein the sensing device comprises at least one of an intra-arterial catheter and a noninvasive transducer;

a pulmonary arterial pressure, wherein the sensing device comprises an intravascular catheter; and

a measurement of a volume of an ear-lobe of the patient, wherein the sensing device comprises means of measuring at least one of optical density and infra-red density of the earlobe.

22. The method of claim 1, wherein the visual representation of the cardiac output signal is at least one of a graphical representation and an alphanumerical representation.

23. The method of claim 1, wherein the visual representation of the cardiac output signal is displayed in real-time on the display device.

24. The method of claim 1, further comprising:

F) obtaining a measurement of absolute cardiac output in the patient;

G) electronically processing the cardiac output signal, via the at least one computer, to compute an average value of the cardiac output signal;

H) electronically determining, via the at least one computer, a calibration constant based at least in part on the measurement of absolute cardiac output from F) and the corresponding average value of the cardiac output signal from G); and

I) electronically applying the calibration constant to the cardiac output signal to compute a normalized cardiac output signal proportional to the absolute phasic cardiac output of the patient.

25. The method of claim 1, further comprising:

electronically processing the cardiac output signal over a period of time, via the at least one computer, to compute a time-averaged value of the cardiac output signal proportional to a time-averaged phasic cardiac output of the patient.

26. The method of claim 1, wherein C comprises:

time-averaging the at least some of the plurality of digital samples of the physiologic input signal; and

constructing a modified form of the transforming filter so that, when the transforming filter is applied in D) to the time-averaged digital samples of the physiologic input signal, the cardiac output signal is proportional to a time-averaged phasic cardiac output of the patient.

27. The method of claim 1, wherein the cardiac output signal is proportional to a time-averaged phasic cardiac output.

28. The method of claim 27, wherein in E), the visual representation of the cardiac output signal is displayed in real-time.

29. The method of claim 27, further comprising the step of normalizing the cardiac output signal by using one or more independent methods of measuring absolute cardiac output.

30. The method of claim 1, wherein the circulatory pressure of the patient is referenced to atmospheric pressure, central venous pressure, pulmonary venous pressure, esophageal pressure, and/or a pressure measured in another intrathoracic location.

31. The method of claim 1, wherein each of the one or more periods of time corresponding to diastole of the heart of the patient is computed based at least in part on a first time corresponding to a preceding onset of systole of the heart of the patient and a second time corresponding to a following onset of systole of the heart of the patient.

32. The method of claim 1, wherein the transforming filter involves a nonlinear component.

33. A computer-facilitated method for visually representing to a medical practitioner a cardiac status of a patient over a sequence of one or more cardiac cycles of the heart of the patient so as to facilitate a determination by the medical practitioner of 1) a need for a cardiac-related intervention and/or 2) an effect of a prior cardiac-related intervention, the method comprising:

A) measuring, via a sensing device coupled to the patient, a circulatory parameter of the patient so as to provide, as an output of the sensing device, a physiologic input signal related to a circulatory pressure of the patient;

B) electronically converting the physiologic input signal from the sensing device, via an analog-to-digital converter coupled to the sensing device, to a plurality of digital samples of the physiologic input signal related to the circulatory pressure of the patient;

C) electronically processing at least some of the plurality of digital samples of the physiologic input signal, via at least one computer coupled to the analog-to-digital converter, to construct a transforming filter to transform the plurality of digital samples of the physiologic input signal based at least in part on one or more periods of time corresponding to diastole of the heart of the patient during which the aortic valve or the pulmonary valve of the heart of the patient is closed;

D) electronically applying the transforming filter, via the at least one computer, to at least some of the plurality of digital samples of the physiologic input signal to compute a cardiac output signal proportional to a phasic cardiac output of the patient, the phasic cardiac output corresponding to a flow across the aortic valve or the pulmonary valve of the heart of the patient, wherein;

the cardiac output signal has a sufficient time resolution to reflect variations in the flow across the aortic valve or the pulmonary valve within a single cardiac cycle; and

in C), the transforming filter is constructed so that, when the transforming filter is applied in D) to the at least some of the plurality of digital samples of the physiologic input signal, the cardiac output signal is reduced during the one or more periods of time corresponding to diastole of the heart of the patient, subject to a normalization constraint on a gain of the transforming filter;

E) electronically processing the cardiac output signal, via the at least one computer, to integrate the cardiac output signal over one or more periods of time corresponding to systole of the heart of the patient during which the aortic valve or the pulmonary valve of the heart of the patient is open, to compute a sequence of one or more values respectively proportional to one or more stroke volumes for corresponding cardiac cycles of the heart of the patient; and

F) electronically displaying, on a display device coupled to the at least one computer, a visual representation of the one or more values computed in E) and respectively proportional to the one or more stroke volumes for corresponding cardiac cycles of the heart of the patient to provide the cardiac status of the patient to the medical practitioner and thereby facilitate the determination by the medical practitioner of the need for the cardiac-related intervention and/or the effect of the prior cardiac-related intervention.

34. A system for visually representing to a medical practitioner a cardiac status of a patient so as to facilitate a determination by the medical practitioner of 1) a need for a cardiac-related intervention and/or 2) an effect of a prior cardiac-related intervention, the system comprising:

a sensing device to measure a circulatory parameter of the patient so as to provide, as an output of the sensing device, a physiologic input signal related to a circulatory pressure of the patient;

an analog-to-digital converter coupled to the sensing device to electronically convert the physiologic input signal from the sensing device to a plurality of digital samples of the physiologic input signal related to the circulatory pressure of the patient;

at least one computer coupled to the analog-to-digital converter to;

A) electronically process at least some of the plurality of digital samples of the physiologic input signal to construct a transforming filter to transform the plurality of digital samples of the physiologic input signal based at least in part on one or more periods of time corresponding to diastole of the heart of the patient during which the aortic valve or the pulmonary valve of the heart of the patient is closed; and

B) electronically apply the transforming filter to at least some of the plurality of digital samples of the physiologic input signal to compute a cardiac output signal proportional to a phasic cardiac output of the patient, the phasic cardiac output corresponding to a flow across the aortic valve or the pulmonary valve of the heart of the patient, wherein;

in B), the cardiac output signal has a sufficient time resolution to reflect variations in the flow across the aortic valve or the pulmonary valve within a single cardiac cycle; and

in A), the transforming filter is constructed so that, when the transforming filter is applied to the at least some of the plurality of digital samples of the physiologic input signal in B), the cardiac output signal is reduced during the one or more periods of time corresponding to diastole of the heart of the patient, subject to a normalization constraint on a gain of the transforming filter; and

a display device coupled to the at least one computer to electronically display a visual representation of the cardiac output signal computed by the at least one computer to provide the cardiac status of the patient to the medical practitioner and thereby facilitate the determination by the medical practitioner of the need for the cardiac-related intervention and/or the effect of the prior cardiac-related intervention.

35. The system of claim 34, wherein:

the physiologic input signal relates to a systemic arterial pressure or a pulmonary arterial pressure; and

the normalization constraint requires that a dc gain of the transforming filter be inversely proportional to a quantity related to a systemic vascular resistance or a pulmonary vascular resistance.

36. The system of claim 34, wherein in A) the at least one computer:

A1) electronically processes the at least some of the plurality of digital samples of the physiologic input signal to determine a quantity related to a systemic vascular resistance or a pulmonary vascular resistance of the patient, based at least in part on one or more periods corresponding to systole of the heart of the patient during which the aortic valve or the pulmonary value of the heart of the patient is open; and

A2) electronically constructs the transforming filter to transform the plurality of digital samples of the physiologic input signal based at least in part on

     1) the quantity related to the systemic vascular resistance or the pulmonary vascular resistance of the patient from A1) and

     2) the one or more periods of time corresponding to diastole of the heart of the patient, wherein

in A1), the at least one computer determines a value for the quantity related to the systemic vascular resistance or the pulmonary vascular resistance by;

A1a) calculating a width of a waveform relating to the phasic cardiac output of the patient based on the at least some of the plurality of digital samples of the physiologic input signal taken over one or more cardiac cycles of the patient; and

A1b) calculating the value for the quantity related to the systemic vascular resistance or the pulmonary vascular resistance that reduces the width of the waveform.

37. The system of claim 36, wherein the at least one computer computes a value of a quantity proportional to the systemic vascular resistance or the pulmonary vascular resistance from the value of the quantity related to the systemic vascular resistance or the pulmonary vascular resistance.

38. The system of claim 37, wherein the at least one computer:

time averages the at least some of the plurality of digital samples of the physiologic input signal; and

divides the time averaged digital samples of the physiologic input signal by the value of the quantity proportional to the systemic vascular resistance or the pulmonary vascular resistance.

39. The system of claim 37, wherein the at least one computer:

divides the at least some of the plurality of digital samples of the physiologic input signal by the value of the quantity proportional to the systemic vascular resistance or the pulmonary vascular resistance to compute a plurality of quotient values; and

time-averages at least some of the plurality of quotient values.

40. The system of claim 37, wherein the at least one computer:

constructs a signal proportional to vascular resistance by repeating the step of computing the value of the quantity proportional to vascular resistance to for sequential epochs of one or more cardiac cycles.

41. The system of claim 40, wherein the display device electronically displays a visual representation of the signal proportional to the systemic vascular resistance or the pulmonary vascular resistance.

42. The system of claim 41, wherein the display device displays the visual representation of the signal proportional to the systemic vascular resistance or the pulmonary vascular resistance in real-time.

43. The system of claim 36, wherein the transforming filter implements the functional inverse of an expected cardiac-output-to-central-pressure transfer function.

44. The system of claim 36, wherein an impulse-response function of the transforming filter is the functional inverse of an exponentially decaying impulse-response function having a time constant proportional to the systemic vascular resistance or the pulmonary vascular resistance.

45. The system of claim 36, wherein the transforming filter is defined by an equation having a form:

46. The system of claim 45, wherein x is related to a peripheral arterial pressure P^a of the patient as measured by the sensing device, y represents a scaled arterial flow relating to the phasic cardiac output of the patient, and the width of the waveform relating to the phasic cardiac output of the patient is given by:

47. The system of claim 36, wherein the at least one computer uses the value of the quantity related to the systemic vascular resistance or the pulmonary vascular resistance to determine the dc gain of the transforming filter.

48. The system of claim 34, wherein the transforming filter is a linear filter having adjustable coefficients.

49. The system of claim 34, wherein the transforming filter is a convolution of two filters, including:

a first filter to transform at least some of the plurality of digital samples of the physiologic input signal into a central pressure signal; and

a second filter to transform the central pressure signal into the cardiac output signal proportional to the phasic cardiac output.

50. The system of claim 49, wherein:

a dc gain of the first filter is constant; and

the second filter has a known form based at least in part on a quantity related to a systemic vascular resistance or a pulmonary vascular resistance of the patient.

51. The system of claim 34, wherein the transforming filter is a convolution of two filters, including:

a first filter constituted by a linear filter having adjustable coefficients, wherein a dc gain of the first filter is constant; and

a second filter defined by an equation having a form;

52. The system of claim 34, wherein the physiologic input signal relates to a systemic arterial pressure or a pulmonary arterial pressure.

53. The system of claim 34, wherein:

the sensing device is to be noninvasively coupled to the patient; and

the physiologic input signal relates to a systemic arterial pressure.

54. The system of claim 34, wherein the physiologic input signal relates to at least one of:

a peripheral arterial pressure, wherein the sensing device comprises at least one of an intra-arterial catheter and a noninvasive transducer;

a pulmonary arterial pressure, wherein the sensing device comprises an intravascular catheter; and

a measurement of a volume of an ear-lobe of the patient, wherein the sensing device comprises means of measuring at least one of optical density and infra-red density of the earlobe.

55. The system of claim 34, wherein the visual representation of the cardiac output signal is at least one of a graphical representation and an alphanumerical representation.

56. The system of claim 34, wherein the display device displays the visual representation of the cardiac output signal in real-time.

57. The system of claim 34, wherein the at least one computer:

obtains a measurement of absolute cardiac output in the patient;

electronically processes the cardiac output signal to compute an average value of the cardiac output signal;

electronically determines a calibration constant based at least in part on the measurement of absolute cardiac output and the corresponding average value of the cardiac output signal; and

electronically applies the calibration constant to the cardiac output signal to compute a normalized cardiac output signal proportional to the absolute phasic cardiac output of the patient.

58. The system of claim 34, wherein the at least one computer:

electronically processes the cardiac output signal over a period of time to compute a time-averaged value of the cardiac output signal proportional to a time-averaged phasic cardiac output of the patient.

59. The system of claim 34, wherein the at least one computer:

time-averages the at least some of the plurality of digital samples of the physiologic input signal; and

constructs a modified form of the transforming filter so that, when the transforming filter is applied to the time-averaged digital samples of the physiologic input signal, the cardiac output signal is proportional to a time-averaged phasic cardiac output of the patient.

60. The system of claim 34, wherein the cardiac output signal is proportional to a time-averaged phasic cardiac output.

61. The system of claim 60, wherein in E), the visual representation of the cardiac output signal is displayed in real-time.

62. The system of claim 60, wherein the at least one computer normalizes the cardiac output signal by using one or more independent methods of measuring absolute cardiac output.

63. The system of claim 34, wherein each of the one or more periods of time corresponding to diastole of the heart of the patient is computed based at least in part on a first time corresponding to a preceding onset of systole of the heart of the patient and a second time corresponding to a following onset of systole of the heart of the patient.

64. The system of claim 34, wherein the transforming filter involves a nonlinear component.

65. A system for visually representing to a medical practitioner a cardiac status of a patient over a sequence of one or more cardiac cycles of the heart of the patient so as to facilitate a determination by the medical practitioner of 1) a need for a cardiac-related intervention and/or 2) an effect of a prior cardiac-related intervention, the system comprising:

a sensing device to measure a circulatory parameter of the patient so as to provide, as an output of the sensing device, a physiologic input signal related to a circulatory pressure of the patient;

an analog-to-digital converter coupled to the sensing device to electronically convert the physiologic input signal from the sensing device to a plurality of digital samples of the physiologic input signal related to the circulatory pressure of the patient;

at least one computer coupled to the analog-to-digital converter to;

A) electronically process at least some of the plurality of digital samples of the physiologic input signal to construct a transforming filter to transform the plurality of digital samples of the physiologic input signal based at least in part on one or more periods of time corresponding to diastole of the heart of the patient during which the aortic valve or the pulmonary valve of the heart of the patient is closed;

B) electronically apply the transforming filter to at least some of the plurality of digital samples of the physiologic input signal to compute a cardiac output signal proportional to a phasic cardiac output of the patient, the phasic cardiac output corresponding to a flow across the aortic valve or the pulmonary valve of the heart of the patient, wherein;

in B), the cardiac output signal has a sufficient time resolution to reflect variations in the flow across the aortic valve or the pulmonary valve within a single cardiac cycle; and

in A) the transforming filter is constructed so that, when the transforming filter is applied to the at least some of the plurality of digital samples of the physiologic input signal in B), the cardiac output signal is reduced during the one or more periods of time corresponding to diastole of the heart of the patient, subject to a normalization constraint on a gain of the transforming filter; and

C) electronically process the cardiac output signal to integrate the cardiac output signal over one or more periods of time corresponding to systole of the heart of the patient during which the aortic valve or the pulmonary valve of the heart of the patient is open, to compute a sequence of one or more values respectively proportional to one or more stroke volumes for corresponding cardiac cycles of the heart of the patient; and

a display device coupled to the at least one computer to electronically display a visual representation of the one or more values computed in C) and respectively proportional to one or more stroke volumes for corresponding cardiac cycles of the heart of the patient to the medical practitioner and thereby facilitate the determination by the medical practitioner of the need for the cardiac-related intervention and/or the effect of the prior cardiac-related intervention.

66. A computer-facilitated method for visually representing to a medical practitioner a cardiac status of a patient so as to facilitate a determination by the medical practitioner of 1) a need for a cardiac-related intervention and/or 2) an effect of a prior cardiac-related intervention, the method comprising:

A) measuring, via a sensing device coupled to the patient, a circulatory parameter of the patient so as to provide, as an output of the sensing device, a physiologic input signal related to a circulatory pressure of the patient;

B) electronically converting the physiologic input signal from the sensing device, via an analog-to-digital converter coupled to the sensing device, to a plurality of digital samples of the physiologic input signal related to the circulatory pressure of the patient;

C) electronically processing at least some of the plurality of digital samples of the physiologic input signal, via at least one computer coupled to the analog-to-digital converter, to construct a transforming filter to transform the plurality of digital samples of the physiologic input signal based at least in part on one or more periods of time corresponding to diastole of the heart of the patient during which the aortic valve or the pulmonary valve of the heart of the patient is closed;

D) electronically applying the transforming filter, via the at least one computer, to at least some of the plurality of digital samples of the physiologic input signal to compute a cardiac output signal proportional to a phasic cardiac output of the patient, the phasic cardiac output corresponding to a flow across the aortic valve or the pulmonary valve of the heart of the patient, wherein;

the cardiac output signal has a sufficient time resolution to reflect variations in the flow across the aortic valve or the pulmonary valve within a single cardiac cycle; and

in C), the transforming filter is constructed so that, when the transforming filter is applied in D) to the at least some of the plurality of digital samples of the physiologic input signal, the cardiac output signal is reduced during the one or more periods of time corresponding to diastole of the heart of the patient; and

E) electronically displaying, on a display device coupled to the at least one computer, a visual representation of the cardiac output signal computed in D) to provide the cardiac status of the patient to the medical practitioner and thereby facilitate the determination by the medical practitioner of the need for the cardiac-related intervention and/or the effect of the prior cardiac-related intervention.