Signal processing studies on the quantification of the shape of the compound muscle action potential

Abstract

The compound muscle action potential (CMAP) in patients with a demyelinating neuropathy, is dispersed. This term refers to a prolonged duration and secondly an appearance with a ragged and irregular outline. Whilst the prolonged duration can be measured, there is no metric for the ragged and irregular appearance. The aim of this thesis is to provide a quantification for the ragged and irregular appearance, sometimes referred to as desynchronisation. Two novel metrics based upon the Poincaré recurrence plot have been developed to assess the smoothness or raggedness of the CMAP. These are the ratio of the line length of the Poincaré plot to the spread of the Poincaré plot along the line of identity and the number of crossings of the Poincaré plot along the line of identity; named as the Poincaré ratio, the “Crossings” metric respectively. The numerical methods required to generate the Poincaré plot, the Poincaré ratio and the “Crossings” metric are provided in chapter 2. Chapter 3 goes on to demonstrate that these metrics are elevated in demyelinating neuropathy. Chapter 4 indicates that the degree of abnormality of the Poincaré metrics are related to the clinical impression of the “raggedness” of the waveforms of experienced clinical neurophysiologists. Chapters 5 and 6 have argued that the Poincaré metrics provide additional information to the established metrics of distal motor latency and amplitude of the CMAP. This is shown through comparison of the CMAP of patients with median nerve pathology at the wrist which also causes an increased distal motor latency, and with motor neurone disease that also causes a drop in the amplitude of the CMAP. In chapter 7, the technical difficulties in translating these findings into clinical tools are discussed. The sampling frequency and the low pass filter settings can affect the Poincaré metrics, suggesting that the jitter of high frequency components contribute to the Poincaré metrics. Chapter 8 uses a cross-correlation function to compare the CMAP acquired from proximal and distal stimulation of the same nerve; and provided information additional to the change of the amplitude of the CMAP.