Changes induced by tilting on Poincare plots and symbolic dynamic patterns of HRV compared to spectral indexes in post-MI and normal subjects

Short-term heart rate variability (HRV) analysis in supine and tilting conditions is commonly performed using linear methods, while nonlinear techniques are usually applied to long-term time series. We investigated in post-myocardial infarction patients and normal subjects the changes induced by tilting on quantitative indexes derived from Poincare plots and symbolic dynamics patterns and compared these changes to those observed using classical spectral parameters. We found that Poincare indexes provide more sensitive information than spectral indexes in assessment of changes of cardiac autonomic outflow, following the tilting maneuver in post-MI patients and although symbolic dynamics indexes were not able to detect these changes, they clearly indicated a structurally different pattern of HRV between normal and pathological subjects.