Cardiac Autonomic Indices (Toichi CSI / CVI) from the Poincare Plot

Computes the cardiac sympathetic and vagal indices (Toichi et al., 1997) from RR interval data. The indices are read off the Poincare plot's \(4\times\)SD bounding box: the long axis \(L = 4\,\mathrm{SD2}\) and the short axis \(T = 4\,\mathrm{SD1}\).

csi: Cardiac Sympathetic Index, \(L/T\) (= SD2/SD1); rises with sympathetic predominance.
cvi: Cardiac Vagal Index, \(\log_{10}(L\times T)\); rises with parasympathetic (vagal) activity.
csi_modified: Modified CSI, \(L^2/T\), a more sensitive sympathetic marker (Jeppesen et al., 2014) used in seizure detection.

Here SD1 is the universal beat-to-beat term (\(\mathrm{SDSD}/\sqrt2\)) and SD2 is the geometric (paired-projection) long-term term, matching the convention in which the Toichi indices are defined (as in NeuroKit2's hrv_nonlinear); this SD2 differs by a small \(O(1/n)\) amount from the analytical closed-form SD2 reported by ecgHRVpoincare.

Usage

ecgHRVautonomic(rr)

Arguments

rr: A data.frame with columns channel, rr_ms, and time_sec, as returned by ecgRRintervals.

Value

A data.frame with one row per channel and the columns channel, csi, cvi, and csi_modified. Columns are NA for channels with fewer than three RR intervals.

References

Toichi, M., Sugiura, T., Murai, T., & Sengoku, A. (1997). "A new method of assessing cardiac autonomic function and its comparison with spectral analysis and coefficient of variation of R-R interval." Journal of the Autonomic Nervous System, 62(1-2), 79–84.

Jeppesen, J., et al. (2014). "Using Lorenz plot and Cardiac Sympathetic Index of heart rate variability for detecting seizures for patients with epilepsy." IEEE EMBC, 4563–4566.

Examples

set.seed(1)
n <- 300
time_sec <- cumsum(rep(0.85, n))
rr_ms <- 850 + 30 * sin(2 * pi * 0.1 * time_sec) + rnorm(n, sd = 15)
rr <- data.frame(channel = 1L, rr_ms = rr_ms, time_sec = time_sec)
ecgHRVautonomic(rr)
#>   channel      csi      cvi csi_modified
#> 1       1 1.920725 3.951332     251.6887