Table 1—

Overview of the seven measures of cardiovascular autonomic function

MeasureUnitDefinition
During spontaneous breathing for 3 min in the supine position:
 Mean NNmsThe mean of all normal-to-normal (sinus rhythm) R-R intervals*
 SDNNmsThe standard deviation of all normal-to-normal (sinus rhythm) R-R intervals*
 LF powerms2Low-frequency power, in absolute units: energy in the power spectrum between 0.04 and 0.12 Hz*
 HF powerms2High 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 differencemsThe mean expiration-inspiration difference in R-R intervals over the six consecutive breaths
 BRSms/mmHgA 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 (γ2) of 0.5 or higher
  • *

    * See reference no. 14;

  • see reference no. 12;

  • see reference no. 21.