Patent Application
20220328178
The present invention pertains generally to blood pressure and blood flow monitoring systems. More particularly, the present invention pertains to systems and methods that continuously provide comprehensive information regarding the efficacy of a patient's heart muscle function. The present invention is particularly, but not exclusively, useful for periodically calibrating an oximeter with contemporaneous blood pressure measurements, taken by a sphygmomanometer, to continuously display information from the oximeter regarding a patient's heart rate, blood flow and blood pressure in a clinical environment.
An oximeter is a medical device that is well known for its ability to accurately indicate a patient's local blood flow characteristics. Specifically, an oximeter can record the sinusoidal characteristics of a blood flow waveform that provide both temporal and amplitude values. Of particular concern for the present invention are the magnitudes of sequential peak amplitudes and the time interval between these peak amplitudes in the blood flow waveform. With this information, a patient's heart rate and blood flow volume can be determined. These characteristics alone, however, do not indicate another important physical measurement, namely: blood pressure.
In a clinical environment it is important to have as much timely information as possible, for both a patient's blood flow and for his/her blood pressure. Collectively, this information is both interdependent and interrelated. However, unlike an oximeter which can be automatically operated continuously to record a blood flow waveform, the operation of a sphygmomanometer to measure blood pressure is labor intensive and can be realistically employed only intermittently. Heretofore, this operational disconnect has, for the most part, been tolerated.
A consequence of the interrelationship between the blood flow waveform and blood pressure is the fact there are three separately measurable characteristics of particular importance. These characteristics are variable and include: 1) the peak amplitude A of a pulse in the blood flow waveform; 2) the time interval Δt between these peak amplitudes (i.e., “heart rate”); and 3) blood pressure P. When considered together, collectively, these variables can lead to clinical conclusions that might otherwise have been missed.
With the above in mind, it is an object of the present invention to provide an oximeter which can be periodically calibrated, using a sphygmomanometer, to simultaneously provide continuous blood pressure readings with blood flow waveform information. Yet another object of the present invention is to incorporate heart rate information (±Δt) together with blood flow data (±ΔA) and blood pressure measurements (±ΔP) to provide a more comprehensive display presentation for clinical personnel with which to assess a patient's condition. Still another object of the present invention is to conduct continuous noninvasive blood pressure monitoring to elucidate new data concerning normal and abnormal states to greatly increase the diagnostic power and patient safety in the clinical environment. Another object of the present invention is to provide a system for continuously monitoring a patient's clinical condition which is easy to install, is simple to operate and which is comparatively cost effective.
In accordance with the present invention, a system and method for continuously monitoring blood pressure in the vasculature of a patient requires a comparative interface between blood flow and blood pressure in the patient's vasculature. To do this, it is necessary to initially establish a steady-state condition for the relationship between a patient's blood flow measurement A and his/her blood pressure reading P. This steady-state condition is then used as input for a computer. In an operation of the system, the patient's blood flow waveform is continuously monitored, and continuously compared with a predetermined operational model. Based on this comparison, the blood flow waveform is used as a basis for displaying a corresponding blood pressure reading for the patient.
To establish a steady-state condition, a sphygmomanometer is used to obtain a blood pressure reading Pmeasured. As is common practice, Pmeasured defines the difference between a Psystolic pressure and a Pdiastolic pressure. This blood pressure reading Pmeasured is then used to calibrate a blood flow measurement Acalibrated. More specifically, Acalibrated is concurrently obtained by an oximeter together with Pmeasured from a sphygmomanometer. Importantly, Pmeasured and Acalibrated are established simultaneously while the patient is in a steady state condition. The respectively identified Pmeasured and Acalibrated are then used as computer input to establish the patient's steady state condition for a computer operation.
After it has been calibrated, the oximeter is used to continuously monitor a local blood flow waveform of the patient. This waveform is typically sinusoidal, with each pulse in the waveform having a unique peak amplitude A. Also, the waveform will have a time interval Δt between the peak amplitude of each pulse and the peak amplitude of the immediately preceding pulse in the waveform. Thus, the waveform identifies a computer input that includes both a heart rate based on Δt and a blood flow volume based on both Δt and A. With this information the computer then employs a predetermined operational model that correlates changes in blood flow ±ΔA with changes in blood pressure ±ΔP.
In detail, for a constant blood flow condition, the predetermined operational model can be mathematically expressed as A=P/R, where R is a factor representing the patient's vascular resistance to blood flow. In this ratio relationship, changes in blood flow ±ΔA and changes in blood pressure ±ΔP are equated to each other for correlation purposes as ±ΔA/Acalibrated≈±ΔP/Pmeasured. Importantly, the correlation of blood flow with blood pressure in this operational model is made relative to the previously established steady-state condition. For this purpose the steady state condition can be expressed as (ΔP)base=Psystolic−Pdiastolic.
For the present invention, a display unit is provided for displaying blood pressure variations ±ΔP corresponding to variations in the blood flow waveform ±ΔA. As noted above, this correspondence is made in accordance with the operational model having a constant (ΔP)base. Also, for the purpose of assessing blood flow in the patient's vasculature, the display unit will show whether there are any consequent changes in heart rate ±Δt that are associated with concurrently measured ±ΔA. Specifically, the display unit selectively presents ±ΔP in the context of either a first operational state wherein Δt is constant, or a second operational state wherein Δt is variable.
In the first operational state, Δt is constant and, to maintain a proper mathematically constant blood flow relationship, R is varied whenever A is varied in the operational model A=P/R. Specifically, with a +ΔA there will be a comparable change in R>1, and with a −ΔA there will be a comparable change in R<1. In the short term, this relationship can be considered valid because R is anatomically slow to vary. On the other hand, R may become a factor over a relatively longer term.
In the second operational state, Δt is variable, and R remains constant to maintain the operational relationship between ±ΔA and ±ΔP. Despite this fact, ±ΔA and ±ΔP may vary somewhat. In this latter case, recalibration may be necessary. Thus, in each operational state the operational model will determine a blood pressure P for display that may include important clinical information pertinent to the patient's condition.
Additional features for the present invention envision the use of a monitor for recording variations of ±ΔA and ±Δt in the blood flow waveform during a predetermined time duration. These measurements can then be compared with earlier measurements to determine whether ±ΔA and ±Δt have sufficiently stabilized during the predetermined time duration to identify a new value for the blood flow (e.g., A′). If so, the steady state condition should be recalibrated. For this purpose, the present invention envisions using a sphygmomanometer to periodically obtain new blood pressure readings P′measured to recalibrate a new value for the blood flow A′ as A′calibrated for use with P′measured to identify a new steady state condition for the patient.
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
The purposes of the oximeter 16 and the sphygmomanometer cuff 18 are respectively of a type well known in the industry. Specifically, the sphygmomanometer cuff 18 is used to take periodic blood pressure readings, P, from the patient 20 that will include both a systolic pressure, Psystolic, and a diastolic pressure, Pdiastolic. The oximeter 16, on the other hand, is used to identify a blood flow waveform 26 such as is shown in
In
A consequence of changes in the respective magnitudes of ΔA and Δt is that as one increases the other typically decreases. As disclosed above, for purposes of the present invention, a steady state is established when the patient 20 is resting. With the patient 20 resting, a base relationship is created where A=P/R is constant, and R=1. In this base relationship (ΔA/sec)base=(ΔP)base=0. Nevertheless, when the patient 20 has a short-term episode with a ±ΔA the relationship ΔA=ΔP is still considered acceptable, at least in the short term. The consequence of this is best appreciated with reference to
Examples for an operation of the present invention are provided below. In both of these examples, the steady state case is presented when R, in the expression A=P/R, is constant, with R=1. This situation is such that (ΔA/Δt)base≈ΔP/R»±ΔP. Also, it must be appreciated that (ΔP)base will be determined on a case-by-case basis and will vary accordingly.
By way of example, consider an operational model being established where (ΔP)base=ΔPsystolic−ΔPdiastolic=120−60=60 and where, ΔPsystolic is approximated at ⅘ΔP, and ΔPdiastolic is approximated at ⅕ΔP. Moreover, it is important to recognize that when there is an increase in Δt there will be a drop in P. And vice-versa, when there is a decrease in Δt there will be a rise in P.
In accordance with the expression A=P/R, for an increase in heart rate by a factor of 2 (i.e., Δt decreases by ½), R in the expression A=P/R must also be considered equal to 2. Thus, ΔP=(ΔP)base/2=30 for a decrease in ΔP. Thus, for this example, (ΔP)display will equal [120−⅘(30)]/[60−⅕(30)] 96/54.
In accordance with the expression A=P/R, for a decrease in heart rate by a factor of 15% (i.e., Δt increases by a factor of 1/0.85=1.18), R in the expression A=P/R must also be considered equal to 0.85. Thus, ΔP=(ΔP)base/0.85=60/0.85=70.1) for an increase in ΔP. Thus, for this example, (ΔP)display will equal [120+4/5(70.1)]/[60+1/5(70.1)]=176/74.
In
Still referring to
With reference to
In the circumstance when Δt is variable (block 44) the model 48 for Pbase is evaluated as disclosed above. As also disclosed above, the result of this evaluation is shown on the display 14. On the other hand, when Δt is considered a constant (block 46) the variable R is evaluated for a possible recalibration (block 50) of the expression A=P/R or for sounding an alarm 54. In the event recalibration is implemented, the steady state SS for Pmeasured and Acalibrated with a new (ΔP)base is established using the oximeter 16 and the sphygmomanometer 18. This action is indicated by action block 52.
While the particular System and Method for Correlating Pulse Oximetry Waveform Signals with Blood Pressure 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 application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/172,270, filed Apr. 8, 2021. The entire contents of Application Ser. No. 63/172,270 are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63172270 | Apr 2021 | US |
