Quantitative assessment of lumbar dural mater pulsations using granger causality testing for spinal dynamics

Spinal disorders lead to paralysis, numbness, pain, etc., due to nerve compression within the spinal canal, affecting quality of life (QOL). Identifying nerve compression is vital for accurate diagnosis. The pulsation of the dura mater, which contains cerebrospinal fluid (CSF) from the choroid plexus, is sometimes evaluated with ultrasound during surgery. Despite its clinical relevance, the physical characteristics of this pulsation remain largely unexplored due to advancements questioning traditional bulk flow theories. This study aimed to analyze the dynamics of dura mater pulsation for a better understanding of these characteristics. Dura mater pulsation was captured using ultrasound at the lumbar spine level in healthy volunteers lying prone. Simultaneously, electrocardiography (ECG), respiratory volume, and respiratory motion were measured. Seasonal Trend Loess (STL) decomposition was employed to decompose the seasonal trends of respiratory and cardiac cycles for comparison with ECG and respiratory data. Both time and frequency domain analyses were conducted, and causal relationships were estimated using Granger causality. The seasonal components of both the respiratory cycle and respiration, as well as the cardiac cycle and heartbeats, exhibited matched spectral peaks and periodicity. Plotting the original dura mater pulsation waveform and the residual component spectra revealed a decreasing trend resembling the 1/f fluctuations typical of vital signals such as heartbeats. While no direct causal relationship between respiration, heartbeats, and dura mater pulsation was found, Granger causality was demonstrated by extracting cardiac and respiratory cycle components from the dura mater pulsation using STL decomposition. The presence of Granger causality between the seasonal components of the respiratory and cardiac cycles and dura mater pulsation implies their interrelated dynamics. However, the absence of direct causality between respiration, heartbeats, and dura mater pulsation, combined with the complex nature of vital signals indicated by 1/f fluctuations in the residual components, necessitates focused analyses on specific periods.