Validation of Sympathetic Activity Index from Heartbeat series: a Preliminary Study on Pre-ejection periods

Abstract

Reliable estimates of cardiac sympathetic activity may not be retrieved from spectral analysis of heart rate variability (HRV) series due to overlap with vagal activity in the low-frequency (0.04-0.14Hz) band. Recently, we proposed a HRV-based index, namely the Sympathetic Activity Index (SAI), which may provide instantaneous estimates of sympa-thetic activity through an orthonormal Laguerre expansion of heartbeat interval series. In this preliminary study, we further validate SAI by performing a correlation analysis with sympathetic- related pre-ejection period (PEP) measurements. Using data gathered from 17 healthy volunteers during a virtual-reality emotional elicitation, results indicate a group-wise SAI-PEP correlation of 0.216 (p < 0.001), with an intra-subject correlation as high as 0.852 (p < 10−6). These findings further support the use of SAI as a proxy measure for the non-invasive, instantaneous estimation of cardiac sympathetic activity.