SYSTEM AND METHOD FOR EVALUATING CARDIAC PUMPING FUNCTION

Abstract

A system for evaluating a cardiac pumping function includes an oximeter which is attached to a patient for the purpose of recording a pulse oximeter waveform. A computer is connected to the oximeter to receive metric information from the waveform. With this information, the computer determines the value and location of a second derivative acceleration, d.sup.2A/dt.sup.2 in the waveform, which indicates the rate of rise/fall of the waveform. A comparator in the computer then compares this with the value and location of maximum second derivative acceleration, d.sup.2A/dt.sup.2, in earlier waveforms. With this comparison, the computer identifies a trend which can be clinically used to evaluate the efficacy of a cardiac pumping function.

Claims

1. A system for evaluating a cardiac pumping function which comprises: an oximeter adapted to be attached to a patient to monitor a pulse oximeter waveform of the patient; a computer connected to the oximeter for receiving metric information from the pulse oximeter waveform as input for calculating the rate of rise of the pulse oximeter waveform per unit time, wherein the rate of rise is mathematically expressed as a second derivative; a comparator included with the computer for comparing each pulse oximeter waveform with the immediately preceding waveform to calculate the second derivative and identify a maximum value therefor; and a display for showing changes in the maximum value of the second derivative to determine the state of the cardiac pumping function.

2. The system of claim 1 wherein each pulse oximeter waveform has a time interval that begins at a time t.sub.o and ends at a time t.sub.e, with a plurality of time segments Δt therebetween, wherein each time segment Δt of the pulse oximeter waveform has a respective amplitude A, and wherein the mathematical expression for the second derivative is d.sup.2A/dt.sup.2 and has a respective value for each time segment Δt.

3. The system of claim 1 wherein the computer calculates the second derivative of A over the entire time interval from t.sub.o to t.sub.e at each time segment Δt.

4. The system of claim 3 wherein the magnitude of the second derivative of A is identified for each time segment Δt.

5. The system of claim 4 wherein a location for the maximum value of the second derivative is compared with the value of the second derivative at the same location in the immediately preceding waveform to determine a trend in the value of the second derivative.

6. The system of claim 5 wherein a rise in the value of the second derivative is indicative of an improving cardiac pumping function and a drop in the value of the second derivative is indicative of a worsening cardiac pumping function.

7. The system of claim 6 wherein the maximum value of the second derivative occurs during a plurality of time segments Δt immediately following t.sub.o.

8. A method for evaluating a cardiac pumping function which comprises the steps of: attaching an oximeter to a patient to monitor a pulse oximeter waveform of the patient; providing metric information received from the pulse oximeter waveform as input to a computer for calculating the rate of rise of the pulse oximeter waveform per unit time; expressing the rate of rise of the pulse oximeter waveform mathematically as a second derivative; and comparing a maximum value of the second derivative to a previously calculated value of the second derivative to determine the state of the cardiac pumping function.

9. The method of claim 8 wherein each pulse oximeter waveform has a time interval that begins at a time t.sub.o and ends at a time t.sub.e, with a plurality of time segments Δt therebetween, wherein each time segment Δt of the pulse oximeter waveform has a respective amplitude A, and wherein the mathematical expression for the second derivative is d.sup.2A/dt.sup.2 and has a respective value for each time segment Δt.

10. The method of claim 9 further comprising the step of calculating the second derivative of A over the entire time interval from t.sub.o to t.sub.e at each time segment Δt.

11. The method of claim 10 further comprising the step of identifying a time segment Δt having a maximum value of the second derivative of A in the pulse oximeter waveform.

12. The method of claim 11 further comprising the step of comparing the location for the maximum value of the second derivative with the value of the second derivative at the same location in the immediately preceding waveform to determine a trend in the value of the second derivative.

13. The method of claim 12 wherein a rise in the second derivative is indicative of an improving cardiac pumping function and a drop in the second derivative is indicative of a worsening cardiac pumping function.

14. The method of claim 13 wherein the maximum value of the second derivative occurs during a plurality of time segments Δt immediately following t.sub.o.

15. A non-transitory, computer-readable medium having executable instructions stored thereon that direct a computer system to perform a process for evaluating a cardiac pumping function, the medium comprising instructions for: receiving metric information from a pulse oximeter waveform as input to a computer for calculating the rate of rise of the pulse oximeter waveform per unit time; expressing the rate of rise of the pulse oximeter waveform mathematically as a second derivative; and comparing a maximum value of the second derivative to a previously calculated value of the second derivative to determine the state of the cardiac pumping function.

16. The medium of claim 15 wherein the pulse oximeter waveform has a time interval that begins at a time t.sub.o and ends at a time t.sub.e, with a plurality of time segments Δt therebetween, wherein each time segment Δt of the pulse oximeter waveform has a respective amplitude A, and wherein the mathematical expression for the second derivative is d.sup.2A/dt.sup.2 and has a respective value for each time segment Δt.

17. The medium of claim 16 further comprising instructions for: calculating the second derivative of A over the entire time interval from t.sub.o to t.sub.e at each time segment Δt; and identifying a time segment Δt having a maximum value of the second derivative of A in the pulse oximeter waveform.

18. The medium of claim 17 further comprising an instruction for comparing the location for the maximum value of the second derivative with the value of the second derivative at the same location in the immediately preceding waveform to determine a trend in the value of the second derivative.

19. The medium of claim 18 further comprising an instruction for displaying a rising trend in the second derivative as indicative of an improving cardiac pumping function and a dropping trend in the second derivative as indicative of a worsening cardiac pumping function.

20. The medium of claim 19 wherein the maximum value of the second derivative occurs during a plurality of time segments Δt immediately following t.sub.o.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:

[0012] FIG. 1 is a schematic presentation of components of a system for evaluating a cardiac pumping function in accordance with the present invention;

[0013] FIG. 2 is a graph of a portion of a pulse oximeter waveform showing a mathematical first derivative expression for the velocity (i.e., slope) of the waveform;

[0014] FIG. 3A is a graph showing a mathematical second derivative expression for the acceleration (i.e., rise) of the waveform;

[0015] FIG. 3B is a graph showing a mathematical second derivative expression for the deceleration (i.e., fall) of the waveform; and

[0016] FIG. 4 is a composite graph showing the rise and fall of a pulse oximeter waveform resulting respectively from a positive second derivative (rise) and a negative second derivative (fall).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring initially to FIG. 1 a system for evaluating a cardiac pumping function is shown and is generally designated 10. As shown, the system 10 includes an oximeter 12 which can be connected with a patient 14 for the purpose of monitoring blood flow characteristics of the patient 14. FIG. 1 also shows that the system 10 includes a computer 16 which is attached to the oximeter 12, and that the computer 16 includes a differentiator 18 and a comparator 20. A display 22 is provided to present clinical results of measurements from the oximeter 12 that are pertinent to the blood flow characteristics of the patient 14. Specifically, these blood flow characteristics are based on measurements of a pulse oximeter waveform 24 (see FIG. 2) that is obtained by the oximeter 12.

[0018] Operationally, the oximeter 12 is typically connected with a finger 26 of the patient 14 to measure and record the physical characteristics of the patient's pulse oximeter waveform 24. The obtained measurements are then transmitted as metric information to the computer 16 via an electronic connection 28. Of particular interest for the present invention are mathematical expressions which are based on this metric information. Specifically, these mathematical expressions are first and second derivatives which are generated by the differentiator 18 in the computer 16. More specifically, the mathematical expressions are pertinent to changes in the pulse oximeter waveform 24.

[0019] FIG. 2 is a graphical presentation of an exemplary portion of a pulse oximeter waveform 24 whereon a change in the amplitude A of the pulse oximeter waveform 24 is shown as a function of time. Mathematically, such a change is expressed as ΔA/Δt (dA/dt). This expression is referred to as a first derivative, which establishes the “slope” of the waveform 24. The expression ΔA/Δt, or dA/dt, is also commonly often referred to as the “velocity” of the waveform 24.

[0020] Graphically, a change in the amplitude, ΔA, of the waveform 24 is shown in FIG. 2 to occur between points 30 and 32 during the time interval Δt between t.sub.1 and t.sub.2. In accordance with the present invention, this first derivative dA/dt, that occurs during the time interval t.sub.1 to t.sub.2, is used by the comparator 20 of computer 16 for comparison with the first derivative of the waveform 24 during the immediately subsequent same time interval Δt between t.sub.2 and t.sub.3. As disclosed below, this comparison is done to determine an acceleration of amplitude A of waveform 24.

[0021] Another mathematical expression of interest for the present invention is the second derivative of the pulse oximeter waveform 24, d.sup.2A/dt.sup.2. This derivative expresses the time rate of change of the first derivative. It is also commonly referred to as the “acceleration” of the pulse oximeter waveform 24. This second derivative, i.e. acceleration, is of singular importance for the system 10 as it mathematically expresses the rise and/or fall of the waveform 24 as a function of time. Stated differently, as a practical consequence, the rise and fall of a waveform 24 is indicative of the volume of blood flow; with a rise being indicative of improved blood flow for the patient 14, and a fall (or drop) being indicative of a worsening of his/her blood flow condition.

[0022] In FIG. 3A, the line curve 34 represents an increasing second derivative (+d.sup.2A/dt.sup.2), which indicates an acceleration in the magnitude of A. On the other hand, the line curve 36 in FIG. 3B represents a decreasing second derivative (−d.sup.2A/dt.sup.2), which indicates a deceleration in the magnitude of A. The consequences of these accelerations and decelerations are shown in FIG. 4.

[0023] The pulse oximeter waveform 24 shown in FIG. 4 is representative of a constant waveform 24 in which the amplitude A of the waveform 24 has neither accelerated nor decelerated. However, when the comparator 20 in computer 16 detects a second derivative change in the amplitude A, the display 22 presents a visual indication of the change. Specifically, as shown in FIG. 4 an acceleration will show on the display 22 as a movement of the waveform 24 toward a raised position shown for a waveform 24′. A deceleration, however, will show on the display 22 as a movement of the waveform 24 toward a lower position shown for a waveform 24″. As noted above, these movements provide valuable information to an attending physician at the time of care for an immediate response, if needed.

[0024] While the particular System and Method for Evaluating Cardiac Pumping Function as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.