cvi

Cardiac Vagal Index

Definition

Cardiac vagal index. Formally: log10(SD1 * SD2 * 16).

What does normal look like?

Fitted normative prior: Normal(μ = 4.274, σ = 0.4393), KS p = 7.4e-16, n = 61715.

Empirical distribution over the pooled nsrdb+nsr2db normative windows (360-beat windows, 120-beat stride), overlaid with the fitted Normal prior density. Vertical lines mark the median and the 5–95% range.

Normal-range summary (pooled nsrdb+nsr2db)

n varies by feature only through per-window validity over the full pooled nsrdb+nsr2db table (n up to 61 715; e.g. sampen/mse drop windows where the statistic is undefined). ulf is the one exception: a 360-beat (~5 min) window contains no ULF-band power, so it uses a long-window NSRDB-only extraction (see its own page).

Use cases

• Cardiac vagal index from Lorenz-plot geometry (Toichi et al. 1997).
• Parasympathetic-tone screening alongside CSI.
• Autonomic-function assessment.

Applications by area

Evidence is reported at the measure-family level; a specific variant may not be the exact index measured in every cited study.

Clinical

Coverage: individual papers. A small, scattered literature with no pooled meta-analysis.

CSI/CVI (Toichi 1997) separates sympathetic/parasympathetic contributions from a single short ECG without pharmacological blockade; reported clinical uses include psychiatric autonomic dysfunction (CVI drops with worsening psychosis) and epilepsy (CSI spikes distinguish epileptic from psychogenic non-epileptic seizures, though the companion CVI measure does not discriminate the same comparison).

Dominant reported direction: CSI up / CVI down under acute stress or pathology; the two halves of the index do not always agree.

Key references: (Toichi et al., 1997); (Jeppesen et al., 2014); (Jeppesen et al., 2016).

Sports & peak performance

Coverage: individual papers. A small, scattered literature with no pooled meta-analysis.

The one on-topic study (elite football) found CVI differs significantly by playing position but not between athletes and non-athlete controls as a whole: a weaker, more qualified version of the classic "athletes have higher vagal tone" story than the RMSSD-based literature tells; otherwise CSI/CVI appear mainly in methodological papers illustrating exercise/postural-change tracking.

Dominant reported direction: position-dependent; no clear athlete-vs.-control effect at the whole-group level.

Key references: (Toichi et al., 1997).

Contemplative practice

Coverage: sparse or none. Essentially no dedicated application literature found.

No study computes CSI/CVI exactly as Toichi (1997) defined them in a meditation/mindfulness/yoga-breathing population; the same Poincaré-geometry construct appears in meditation studies under other names (SD1/SD2 ratio, ad hoc indices), so the literal CSI/CVI label is essentially absent from this domain even though the underlying geometry is well studied.

Dominant reported direction: no data harvested under this name.

Key references: (Toichi et al., 1997).

See the effect-distribution meta-analysis page for the harvested per-study effect sizes/p-values behind these domain summaries (docs/zoo_gen/effect_stats.csv).

Resources

Resource-intensity rank ◍◍◌◌◌ low is measured: median wall-clock time and allocations over a 360-beat window on synthetic realistic RR (docs/zoo_gen/bench_resources.jl; full grid in resource_bench.csv).

Cold = fresh memoization caches (builds every shared representation from scratch); warm = shared representations (diff, periodogram, Poincaré coords, DFA fluctuation) already cached, so only this feature is recomputed. The tier is derived from the cold cost; see Geometric subgraph (Poincaré coords / RR histogram + reductions). Warm (shared representation cached) is 7× cheaper.

Citation

Cardiac vagal index (log₁₀ 16·SD1·SD2), Toichi et al. (1997).

Seminal reference(s): (Toichi et al., 1997).

See the References page for the full bibliography.