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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
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