Haemodynamic monitor with improved filtering
There is provided a device and method of filtering outliers from physiological values. The method comprises: (a) populating a window with n physiological values taken, in sequence, from a sequence of physiological values, wherein n is a positive integer; (b) determining whether the variability in the physiological values within the window is less than a predetermined threshold; (c) responsive to the variability in the physiological values within the window being less than a predetermined threshold, determining that the window comprises no outliers, and/or responsive to the variability in the physiological values within the window not being less than a predetermined threshold, determining that the window comprises at least one outlier.
1. A method for filtering outliers from regular physiological values, the method being implemented by a device comprising a controller, the method comprising:
(i) filtering outliers from a sequence of haemodynamic values of a patient to generate a filtered sequence of haemodynamic values, the filtered sequence of haemodynamic values generated by:
(a) populating a window with n haemodynamic values taken, in sequence, from the sequence of haemodynamic values, wherein n is a positive integer;
(b) determining whether a variability in the haemodynamic values within the window is less than a predetermined threshold;
(c) responsive to the variability in the haemodynamic values within the window being less than the predetermined threshold, outputting an indication that the window comprises no outliers, and/or responsive to the variability in the haemodynamic values within the window not being less than the predetermined threshold, outputting an indication that the window comprises at least one outlier;
(d) responsive to the variability in the haemodynamic values within the window being less than the predetermined threshold, updating the window by moving the window on by x haemodynamic values in the sequence, wherein x is a positive integer that is less than n divided by two, and repeating steps (b) and (c) based on the updated window; and
(e) responsive to the variability in the haemodynamic values within the window not being less than the predetermined threshold, updating the window by moving the window on by z haemodynamic values in the sequence, wherein z is a positive integer equal to n or equal to n minus x, and repeating steps (b) and (c) based on the updated window; and
(ii) calculating a stroke volume variation or a pulse pressure variation of the patient based on the filtered sequence of haemodynamic values.
2. The method of claim 1 wherein populating the window with n haemodynamic values from the sequence of haemodynamic values comprises selecting n minus x sequential haemodynamic values that have previously been confirmed to not be outliers and selecting the next x haemodynamic values from the sequence.
3. The method of claim 2 wherein selecting the window of n haemodynamic values from the sequence of haemodynamic values comprises:
populating the window with n earlier haemodynamic values taken, in sequence, from the sequence of haemodynamic values;
determining that the variability in the n earlier haemodynamic values is less than the predetermined threshold; and
moving the window on by x haemodynamic values in the sequence.
4. The method of claim 3 further comprising, responsive to the determination that the variability in the n earlier haemodynamic values is less than the predetermined threshold, outputting an indication that the n earlier haemodynamic values do not comprise an outlier.
5. The method of claim 1 wherein:
outputting the indication that the window comprises at least one outlier comprises outputting an indication that the final x values in the sequence within the window comprise at least one outlier; or
outputting the indication that the window comprises no outliers comprises outputting an indication that the final x values in the sequence within the window are not outliers.
6. The method of claim 1 , wherein the filtered sequence of haemodynamic values are generated by performing further operations comprising (f) responsive to the variability of the haemodynamic values within the updated window not being less than the predetermined threshold, selecting n further haemodynamic values by moving the window on by x haemodynamic values in the sequence and repeating steps (b) and (c) based on the further haemodynamic values within in the window.
7. The method of claim 1 , further comprising, responsive to the variability of the haemodynamic values within the updated window not being less than the predetermined threshold, outputting an indication that the first x haemodynamic values in the sequence within the updated window comprise an outlier.
8. The method of claim 1 wherein z is a positive integer equal to n minus x and the filtered sequence of haemodynamic values are generated by performing further operations comprising (g) responsive to the window being updated by moving the window on by z haemodynamic values in the sequence, and responsive to the variability of the haemodynamic values within the updated window being less than the predetermined threshold, outputting an indication that the updated window comprises a step-wise change.
9. The method of claim 8 wherein outputting an indication that the updated window comprises a step-wise change comprises outputting an indication that the first x values in the sequence within the updated window comprise a step-wise change.
10. The method of claim 1 wherein the variability is the coefficient of variation.
11. The method of claim 1 wherein the sequence of haemodynamic values relates to a single haemodynamic parameter, each haemodynamic value of the sequence of haemodynamic values corresponding to a respective cardiac cycle of a chronologically ordered set of cardiac cycles, and wherein cardiac cycles not corresponding to outliers are determined to be regular cardiac cycles.
12. The method of claim 10 , wherein calculating the stroke volume variation or the pulse pressure variation of the patient is performed over each respiratory cycle of the patient.
13. The method of claim 1 further comprising changing n and/or x and repeating the method from step (a).
14. A device, comprising:
a controller configured to:
(i) filter outliers from a sequence of haemodynamic values of a patient to generate a filtered sequence of haemodynamic values, the filtered sequence of haemodynamic values generated by:
(a) populating a window with n haemodynamic values taken, in sequence, from the sequence of haemodynamic values, wherein n is a positive integer;
(b) determining whether a variability in the haemodynamic values within the window is less than a predetermined threshold;
(c) responsive to the variability in the haemodynamic values within the window being less than the predetermined threshold, outputting an indication that the window comprises no outliers, and/or responsive to the variability in the haemodynamic values within the window not being less than the predetermined threshold, outputting an indication that the window comprises at least one outlier;
(d) responsive to the variability in the haemodynamic values within the window being less than the predetermined threshold, updating the window by moving the window on by x haemodynamic values in the sequence, wherein x is a positive integer that is less than n divided by two, and repeating steps (b) and (c) based on the updated window; and
(e) responsive to the variability in the haemodynamic values within the window not being less than the predetermined threshold, updating the window by moving the window on by z haemodynamic values in the sequence, wherein z is a positive integer equal to n or equal to n minus x, and repeating steps (b) and (c) based on the updated window; and
(ii) calculate a stroke volume variation or a pulse pressure variation of the patient based on the filtered sequence of haemodynamic values.
15. A computer readable medium comprising instructions that, when executed by a computer, cause the computer to perform operations comprising:
filtering outliers from a sequence of haemodynamic values of a patient to generate a filtered sequence of haemodynamic values, the filtered sequence of haemodynamic values generated by:
(a) populating a window with n haemodynamic values taken, in sequence, from the sequence of haemodynamic values, wherein n is a positive integer;
(b) determining whether a variability in the haemodynamic values within the window is less than a predetermined threshold;
(c) responsive to the variability in the haemodynamic values within the window being less than the predetermined threshold, outputting an indication that the window comprises no outliers, and/or responsive to the variability in the haemodynamic values within the window not being less than the predetermined threshold, outputting an indication that the window comprises at least one outlier;
(d) responsive to the variability in the haemodynamic values within the window being less than the predetermined threshold, updating the window by moving the window on by x haemodynamic values in the sequence, wherein x is a positive integer that is less than n divided by two, and repeating steps (b) and (c) based on the updated window; and
(e) responsive to the variability in the haemodynamic values within the window not being less than the predetermined threshold, updating the window by moving the window on by z haemodynamic values in the sequence, wherein z is a positive integer equal to n or equal to n minus x, and repeating steps (b) and (c) based on the updated window; and
(ii) calculating a stroke volume variation or a pulse pressure variation of the patient based on the filtered sequence of haemodynamic values.