During spontaneous breathing for 3 min in the supine position: | | |

Mean NN | ms | The mean of all normal-to-normal (sinus rhythm) R-R intervals* |

SDNN | ms | The standard deviation of all normal-to-normal (sinus rhythm) R-R intervals* |

LF power | ms^{2} | Low-frequency power, in absolute units: energy in the power spectrum between 0.04 and 0.12 Hz* |

HF power | ms^{2} | High frequency power, in absolute units: energy in the power spectrum between 0.12 and 0.40 Hz* |

LF/(LF + HF) | | The ratio of low-frequency power to the sum of the low- and high-frequency power* |

During six deep breaths for 1 min in the supine position: | | |

EI difference | ms | The mean expiration-inspiration difference in R-R intervals over the six consecutive breaths† |

BRS | ms/mmHg | A measure of baroreflex sensitivity, computed as gain, i.e., ratio of the energy, in the cross-spectrum of systolic blood pressure and R-R intervals and the energy in the power spectrum of the R-R interval, all between 0.05 and 0.15 Hz and with a squared coherence (γ^{2}) of 0.5 or higher‡ |