A subspace decomposition approach toward recognizing valid pulsatile signals

Abstract

Following recent studies, the automatic analysis of intracranial pressure (ICP) pulses appears to be a promising tool for the prediction of critical intracranial and cerebrovascular pathophysiological variations during the management of many neurological disorders. A pulse analysis framework has been recently developed to automatically extract morphological features of ICP pulses. The algorithm is capable of enhancing the quality of ICP signals, recognizing valid (not contaminated with noise or artifacts) ICP pulses and designating the locations of the three ICP sub-peaks in a pulse. This paper extends the algorithm by proposing a singular value decomposition (SVD) technique to replace the correlation-based approach originally utilized in recognizing valid ICP pulses. The validation of the proposed method is conducted on a large database of ICP signals built from 700 h of recordings from 67 neurosurgical patients. A comparative analysis of the valid ICP recognition using the proposed SVD technique and the correlation-based method demonstrates a significant improvement in terms of (1) accuracy (61.96% reduction in the false positive rate while keeping the true positive rate as high as 99.08%) and (2) computational time (91.14% less time consumption), all in favor of the proposed method. Finally, this SVD-based valid pulse recognition can be potentially applied to process pulsatile signals other than ICP because no proprietary ICP features are incorporated in the algorithm.

Figure 1

Representative examples of valid and non-valid (influenced by noise and artifacts) ICP pulse signals. Panel A displays an example of a valid ICP pulse with the three well established subcomponents. Panels B through F display non-valid ICP pulse signals resulted from wrong QRS detection, coughing, patient's movement, sensor detachment and contamination by high frequency noise, respectively.

Figure 2

A histogram of the mean ICP values of the 1440 pulses in the original reference library used for the correlation based approach.

Figure 3

(a) Singular value spectrum of the matrix A constructed from the original reference library 1440 ICP pulses. (b) Plot of E_K (percentage of the total energy in the space define by the first K singular vector of matrix A for the original ICP pulse reference library.

Figure 4

Receiver operator characteristic (ROC) curves of recognizing valid ICP pulse for different values of I = [6 18 54 162], each curve is generated by a two-fold cross validation and systematically changing the coefficient C = [10 5 4 3 2 1 0 −5 −10] in dB.

Figure 5

Receiver operator characteristic (ROC) curves of recognizing valid ICP pulse using 67-fold cross validation under the correlation based method in MOCAIP and the proposed SVD based method for Î = 18. For the correlation based method, r₂ = 0.9 and r₁ was systematically changing as [1 0.99 0.97 0.95 0.92 0.9 0.85 0.8 0.5]. For the proposed SVD based method, the coefficient values are the same as the one used in Figure 4.