Determining arterial pressures
An example autoregulation monitoring system includes processing circuitry configured to receive a blood pressure signal indicative of a blood pressure of a patient; determine a derivative of at least a portion of the blood pressure signal; determine, based on the derivative, a characteristic arterial pressure (CAP) value; determine, based on the CAP value, an autoregulation value of the patient; and output a signal indicative of the autoregulation value of the patient.
1 . A method comprising:
generating, by blood pressure sensing circuitry, a blood pressure signal comprising a blood pressure waveform indicative of fluctuating blood pressure values of the patient through cardiac cycles of the patient;
receiving, by processing circuitry within a housing of an autoregulation monitoring device, the blood pressure signal from the blood pressure sensing circuitry;
removing, by the processing circuitry, erroneous portions of the blood pressure signal by selecting a subset of data points of the blood pressure signal;
determining, by the processing circuitry, characteristic arterial pressure (CAP) values from the selected subset of data points of the blood pressure signal, wherein the CAP values are a representation of arterial pressure over time and are different from the blood pressure values of the patient;
receiving, by the processing circuitry, an oxygen saturation signal indicative of an oxygen saturation of the patient;
determining, by the processing circuitry, an upper limit of autoregulation based on the CAP values and the oxygen saturation signal and a lower limit of autoregulation based on the CAP values and the oxygen saturation signal;
generating, by the processing circuitry, a graph comprising an intact autoregulation zone between the upper limit of autoregulation and the lower limit of autoregulation, and an impaired autoregulation zone extending above the upper limit of autoregulation, or below the lower limit of autoregulation, or both; and
controlling, by the processing circuitry, a user interface to display the blood pressure signal overlaid onto the graph and
tracking, on the graph, changes over time in the displayed blood pressure, the intact autoregulation zone, and the impaired autoregulation zone.
2 . The method of claim 1 , wherein determining the CAP values comprises determining a maximum value or a minimum value of a derivative of the selected subset of data points of the blood pressure signal during a systolic upstroke, a systolic decline, or a diastolic runoff of the blood pressure of the patient.
3 . The method of claim 1 , wherein determining an autoregulation status comprises determining, by the processing circuitry, a correlation index (ChOx) based on a correlation between the CAP values and the oxygen saturation signal.
4 . The method of claim 1 , wherein determining an autoregulation status comprises:
determining a gradient of the CAP value over a period of time;
determining a gradient of the oxygen saturation signal over the period of time; and
determining, based on co-trending of the gradient of the CAP value and the gradient of the oxygen saturation signal, the autoregulation status of the patient.
5 . The method of claim 1 , wherein the erroneous portions of the blood pressure signal comprise one or more of morphological anomalies, noise, or clipped portions.
6 . The method of claim 1 , wherein determining the CAP values comprises determining a rate of change between consecutive data points of the subset of data points.
7 . A system comprising:
a graphical user interface;
blood pressure sensing circuitry configured to generate a blood pressure signal comprising a blood pressure waveform indicative of fluctuating blood pressure values of the patient through cardiac cycles of the patient; and
processing circuitry within a housing of an autoregulation monitoring device, wherein the processing circuitry is configured to:
receive the blood pressure signal from the blood pressure sensing circuitry;
remove erroneous portions of the blood pressure signal by selecting a subset of data points of the blood pressure signal;
determine characteristic arterial pressure (CAP) values from the subset of data points, wherein the CAP values are a representation of arterial pressure over time and are different from the blood pressure values of the patient;
correlate the CAP values with an oxygen saturation signal of the patient to produce a correlation index;
determine an upper limit of autoregulation and a lower limit of autoregulation based on the correlation index;
generate a graph comprising an intact autoregulation zone extending between the upper limit of autoregulation and the lower limit of autoregulation, and an impaired autoregulation zone extending above the upper limit of autoregulation, or below the lower limit of autoregulation, or both; and
control the graphical user interface to display indications of the blood pressure values overlaid onto the graph.
8 . The system of claim 7 , wherein the CAP values comprise a maximum value or a minimum value of a derivative of the selected subset of data points of the blood pressure signal during a systolic upstroke, a systolic decline, or a diastolic runoff of the blood pressure of the patient.
9 . The system of claim 7 , wherein the processing circuitry being configured to correlate the CAP values with the oxygen saturation signal comprises being is configured to:
determine a gradient of the CAP values over a period of time;
determine a gradient of the oxygen saturation signal over the period of time; and
co-trend the gradients.
10 . The system of claim 7 , wherein the erroneous portions of the blood pressure signal comprise one or more of morphological anomalies, noise, or clipped portions.
11 . The system of claim 7 , wherein the upper limit of autoregulation and the lower limit of autoregulation comprises a respective upper and lower blood pressure value at which the correlation index is less than a threshold value.
12 . The system of claim 7 , wherein the processing circuitry is configured to, during a patient monitoring session:
update the lower limit of autoregulation, the upper limit of autoregulation, or both based on the CAP values and the oxygen saturation signal; and
update the graph to reflect the update to the lower limit of autoregulation, the upper limit of autoregulation, or both.
13 . The system of claim 7 , wherein the upper limit of autoregulation and the lower limit of autoregulation on the graph change over time.
14 . A method for medical monitoring, comprising:
generating, from a blood pressure sensor, a blood pressure signal comprising fluctuating blood pressure values of a patient through cardiac cycles of the patient;
transmitting the blood pressure signal to an autoregulation monitor;
discarding, by the autoregulation monitor, portions of the blood pressure signal comprising one or more of an anomaly, noise, or error;
selecting a subset of a remaining portion of the blood pressure signal, the subset being contained within a single cardiac cycle;
determining, from the selected subset, a characteristic arterial pressure (CAP) value representative of arterial pressure;
repeating the discarding, selecting, and determining for subsequent cardiac cycles of the patient to produce a CAP curve;
correlating the CAP curve with an oxygen saturation signal of the patient to identify an autoregulation status of the patient; and
displaying a graph of blood pressure over time, the graph comprising an intact autoregulation zone and an impaired autoregulation zone and a blood pressure line overlaid on the graph.
15 . The method of claim 14 , wherein determining the CAP value comprises determining a derivative of the selected subset.
16 . The method of claim 14 , wherein the oxygen saturation signal comprises a regional oxygen saturation (rSO2) in a cerebral region of the patient.
17 . The method of claim 14 , wherein correlating the CAP curve and the oxygen saturation signal of the patient comprises comparing a gradient of the CAP curve with a gradient of the oxygen saturation signal.
18 . The method of claim 14 , wherein correlating comprises generating a correlation index between zero and one, and wherein the intact autoregulation zone extends between a lower limit of autoregulation and an upper limit of autoregulation, wherein:
the lower limit is based on a lowest blood pressure value at which the correlation index is less than a threshold value, and
the upper limit is based on a highest blood pressure value at which the correlation index is less than the threshold value.