Poincare plots and symbolic dynamics patterns of left ventricular function parameters extracted from echocardiographic acoustic quantification

Throughout the echocardiographic acoustic quantification technique, a non-invasive estimate of left ventricular volume (VV) is obtained and acquired in real-time. An automated algorithm is applied to extract the beat-by-beat values of ventricular function parameters. Their beat-by-beat variability has been recently studied, together with heart period (RR) variability, by spectral techniques. In this study, we propose to investigate this variability by nonlinear techniques, such as Poincare plots (PPS) and symbolic dynamics (SyD) patterns. A group of 17 normal young subjects (NY, 25 ± 1 years) and a group of 12 normal old subjects (NO, 64 ± 2 years) were studied to observe if this approach could be able to detect modifications in VV function connected with the ageing process. Differences in RR, peak filling and peak ejection rate were evidenced by PPs indexes. SyD analysis evidenced different patterns: in RR a change from increasing/decreasing in NY to alternating pattern in NO was found, together with a change in SV pattern from random in NY to alternating in NO. Consistent alternating patterns were found in VV derivative parameters. In conclusion, PPs and SyD patterns seemed able to evidence differences between NY and NO ventricular function, otherwise not captured by linear analysis techniques.