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Table 2 Heart rate variability frequency domain measures when supine and during head-up tilt, with and without a respiratory acidosis induced by inhalation of 5%CO2 in normoxic air

From: Indirect measures of human vagal withdrawal during head-up tilt with and without a respiratory acidosis

Supine Head-up tilt
TPLN VLFLN LFLN HFLN LFNU HFNU LF:HF TPLN VLFLN LFLN HFLN LFNU HFNU LF:HF
Room air
 8.21 7.23 6.88 6.66 52.36 44.01 2.49 8.37 7.21 7.14 6.02 66.58 24.05 4.09
 (0.68) (0.89) (0.64) (1.11) (21.93) (21.57) (3.94) (1.05) (0.83) (1.01) (1.25) (19.49) (13.90) (3.05)
5%CO2
 8.93 6.91 7.24 8.17* 22.97* 69.23* 0.38* 8.27 7.09 6.79 6.79* 40.45* 47.64* 1.31*
 (0.88) (0.54) (1.10) (1.17) (11.54) (15.37) (0.26) (1.08) (0.94) (1.26) (1.55) (21.41) (21.11) (1.43)
  1. Reported values are mean (SD) following transformation with natural logarithm function (LN), or normalised (NU) for total power (TP) of the spectrum between 0 and 0.5 Hz
  2. Very low frequency (VLF): 0–0.04 Hz, low frequency (LF): 0.04–0.15 Hz, high frequency (HF): 0.15–0.4 Hz
  3. * P < 0.03 between room air and 5%CO2
  4. P < 0.03 between supine and head-up tilt