The present invention pertains to systems and methods for monitoring and evaluating a cardiac pumping function. More particularly, the present invention pertains to systems and methods that evaluate cardiac pumping functions which are based on dynamic changes in blood pulse waveforms measured by an oximeter. The present invention is particularly, but not exclusively, useful for evaluating cardiac pumping functions by comparing the maximum second derivatives from a sequence of successive pulse oximeter waveforms, to assess the rise or fall of the waveforms as being indicative of the efficacy of the cardiac pumping function.
A pulse oximeter waveform is well known in the pertinent art as a graphical indication of the blood pressure response to a heart muscle function. Specifically, a pulse waveform shows the change in the amplitude A of blood pressure during a single contraction of the heart muscle. These waveforms are relatively short in duration and are, therefore, typically presented and considered as a continuous succession of pulse waveforms.
When considered individually each pulse waveform provides visual information of the velocity at which the amplitude A of the waveform is increasing or decreasing. Mathematically, this information is referred to as a first derivative, dA/dt. In addition to first derivative changes in velocity, pulses may also exhibit a rise or fall in amplitude of the entire waveform. This rise and/or fall of the waveform provides information about the acceleration of the waveform's amplitude A and is mathematically referred to as a second derivative, d2A/dt2.
At the point of care, e.g., during surgery, information regarding changes in a heart muscle function can be quite helpful. Specifically, by monitoring a second derivative for the rise and/or fall of pulse waveforms, medical personnel can determine the beneficial or detrimental effect surgical activity may have had on heart muscle function. With this information, appropriate corrective action can be taken. In the event, it is obvious that corrective action, if needed, must be taken as soon as possible, i.e., immediately.
With the above in mind, it is an object of the present invention to provide a system and method for immediately evaluating a cardiac pumping function. Another object of the present invention is to provide a system and method for evaluating heart muscle function to determine when immediate corrective action may be advisable. Yet another object of the present invention is to provide a system and method for evaluating a cardiac pumping function by monitoring the acceleration of the pulse oximeter waveform as indicated by the second derivative of its amplitude, d2A/dt2. Still another object of the present invention is to provide a system and method for monitoring a cardiac pumping function which is simple to use, is easy to manufacture, and is comparatively cost effective.
A system and method for evaluating a cardiac pumping function requires attaching an oximeter to a patient to monitor a pulse oximeter waveform of the patient. A computer is then connected to the oximeter for receiving metric information from the pulse oximeter waveform. This metric information is received directly from the computer as input for calculating the rate of rise or fall of the pulse oximeter waveform per unit time. Mathematically, the rate of rise/fall of a pulse oximeter waveform is expressed as a second derivative of the waveform's amplitude A, d2A/dt2. This second derivative is particularly important because it immediately provides an early detection, from a single pulse waveform, of an indication in trends for the overall heat muscle function.
A comparator, which is included with the computer, compares each pulse oximeter waveform with the immediately preceding waveform to calculate the second derivative d2A/dt2. Furthermore, the computer identifies a maximum value for the second derivative and its location in the pulse oximeter waveform. This value and location information is then compared with similar value and location information obtained from earlier pulse oximeter waveforms to identify a trend with which to evaluate a cardiac pumping function.
In detail, each pulse oximeter waveform has a time interval that begins at a time to and ends at a time te. A plurality of time segments Δt can be identified between to and te with each time segment Δt having a respective amplitude A. There are two mathematical expressions of interest here for describing a change in A with respect to each time segment ΔA. The first expression is a velocity term which describes a change in the value of A as a function of time. Mathematically, this velocity term is a first derivative which is expressed as “dA/dt”. Stated differently, in the context of the present invention, the first derivative, dA/dt, describes the slope, i.e., shape, of the pulse oximeter waveform. The second expression of interest is an acceleration term that describes a change of the velocity term as a function of time. Mathematically this acceleration term is a second derivative which is expressed as, “d2A/dt2”. In the context of the present invention, the second derivative, d2A/dt2, describes the rise and fall of the pulse oximeter waveform. As a practical consideration, it is the second derivative that is indicative of blood flow volume and thus, the efficacy of a cardiac pumping function.
For the present invention, the value and location of a maximum second derivative is determined for each consecutive pulse oximeter waveform. The value and location for the maximum second derivative of each pulse oximeter waveform is then compared with the value and location of the maximum second derivative in the immediately preceding waveform. The purpose here is to determine a trend in the value of successive second derivatives for a comparative evaluation that is helpful for determining the efficacy of a cardiac pumping function.
For the evaluation of a cardiac pumping function, a rise in the value of the second derivative is indicative of an improving function. On the other hand, a drop in the value of the second derivative is indicative of a worsening function. Most likely the maximum value of the second derivative for each pulse oximeter waveform occurs during a plurality of time segments Δt immediately following to. In any event, the present invention envisions the use of a visual display for showing trends in the maximum value of the second derivative, to thereby determine the efficacy of the cardiac pumping function.
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:
Referring initially to
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.
Graphically, a change in the amplitude, ΔA, of the waveform 24 is shown in
Another mathematical expression of interest for the present invention is the second derivative of the pulse oximeter waveform 24, d2A/dt2. 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.
In
The pulse oximeter waveform 24 shown in
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.
This divisional application claims priority to U.S. patent application Ser. No. 17/580,300, filed Jan. 20, 2022. The entire contents of application Ser. No. 17/580,300 are hereby incorporated by reference herein.
Number | Date | Country | |
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Parent | 17580300 | Jan 2022 | US |
Child | 19017712 | US |