Yes, you can use cuff pressure data to determine blood pressure. Both the Go Direct® Blood Pressure Sensor (GDX-BP) and the Blood Pressure Sensor (BPS-BTA) use the oscillometric method for calculating parameters. See the sensor booklets of each sensor for a description of this method. This method is widely used in cuff sensors and is accurate at predicting mean arterial pressure. This method calculates diastolic and systolic blood pressure based on the peak oscillatory amplitude, which coincides with the mean arterial pressure. Systolic blood pressure is calculated at 57% of the peak oscillatory amplitude. Diastolic blood pressure is calculated at 74% of the peak oscillatory amplitude. See specific instructions below.
You will need to do several calculations to find the parameters manually. Specific instructions for each parameter are given below. The parameters should be calculated in the order presented.
For the Go Direct® Blood Pressure Sensor (GDX-BP) you will need to activate the oscillations channel. The Blood Pressure Sensor (BPS-BTA) provides the oscillations by default in Logger Pro. Please note that you will only be able to proceed with these calculations by using Logger Pro with the Blood Pressure Sensor, or using Graphical Analysis or Graphical Analysis Pro with the Go Direct Blood Pressure Sensor.
Collect Blood Pressure data from the sensor. Verify that you have both the Cuff Pressure and Oscillations on the graphs in your application.
Find the oscillatory peak with the greatest amplitude. This should be the peak of the bell-shaped curve for the oscillatory peaks. Find the time that this peak occurred and then find the corresponding time on the cuff pressure trace. The pressure at this time on the cuff pressure trace should give you the mean arterial pressure (MAP). Write this value down (time and pressure) for future use. Refer to these values as Peak time and MAP.
To calculate systolic pressure do the following;
1) Fit a line to the oscillatory peak data. Click and drag from the beginning of peaks to the largest peak in the data. Make sure you select data that includes (just goes past) the tallest point/peak. Perform a linear fit to oscillation peaks data.
2)Write down the equation for the line. You are going to use this function to find systolic blood pressure. You need to find the X intercept first. Remember that where Y=0, Xi = -b/m. Using this formula solve for Xi.
3)Now you are going to find the point (time) on this line that corresponds to 57% of the entire line. The pressure that occurs at this time is the systolic blood pressure. Solve for systolic blood pressure time using the following equation, Tsp = Xi + 0.57 (Peak time – Xi). Record this value.
4) Using the Examine function, find the time on the cuff pressure trace that corresponds to the value you just calculated (Tsp). Find the pressure at this time on the cuff pressure trace. This pressure should be very close to the systolic blood pressure that was calculated by the software.
To calculate diastolic pressure do the following;
1) Remove the linear fit from the oscillatory peak data. Fit a new line from the largest peak (which corresponds to MAP) to the end of the peaks. Make sure that you select a little data just before the tallest peak.
2)Write down the equation for the line. You are going to use this equation to find diastolic blood pressure. Find the X intercept first. Remember that where Y=0, Xi = -b/m. Using this formula, solve for Xi. Since the slope is negative this time, you are going to get a positive number.
3)Now find the point (time) on this line that corresponds to 74% of the entire line. The pressure that occurs at this time is the diastolic blood pressure. Solve for diastolic blood pressure time using the following equation, Tdp = Xi – (0.74)(Xi-Peak time). Record this value.
4) Find the time on the cuff pressure trace that corresponds to the value you just calculated (Tdp). Find the pressure at this time on the cuff pressure trace. This pressure should be very close to the diastolic blood pressure that was calculated by the software.
Pulse rate is calculated by counting the number of oscillatory peaks and then dividing by the duration of the record that the software found the peaks. Click and drag across the trace for the oscillatory peaks and find the duration of the trace. Count the number of pulses during the trace and divide by the duration to get the pulse rate. Multiply by 60 to get beats per minute. This value should be very close to what the software calculated for pulse rate.
If you need a data set to practice on, one is provided. Calculations from this data set are presented below.
The largest oscillatory peak occurs at 60.72 s. The pressure at this time is 84-85 mmHg. This is very close to the values reported for mean arterial pressure by Logger Pro and Graphical Analysis 4.
For systolic pressure, fitting a line from the beginning of the data to the tallest oscillatory peak should provide a slope of 0.04017 mmHg/s with Y intercept is 0.3180. Solving for Xi you should get -8.48 s. Solving for Tsp = -8.48 + 0.57((60.72-(-8.48)) = 30.96 s. The pressure on the cuff trace that occurs at this time is 117-118 mmHg.
For diastolic pressure, fitting a line from the tallest peak to the end of the oscillatory peak data should provide a slope of -0.06156 and y intercept of 6.659 mmHg. Solving for Xi you should get 108.27 s. Solving for Tdp = 108.27 – (0.74)(108.27-60.72) = 73.083 s. The pressure on the cuff trace that occurs at this time is 70-71 mmHg.
For pulse rate. The number of oscillatory pulses in the record is 78. The duration from the first to last pulse is 81 seconds. 78/81 = 0.96 pulses/s. To get beats per minute. 0.96 * 60 = 58 beats per minute.