Table 2.

Baseline spectral analysis of heart rate and blood pressure variability

	All Controls	All POTS	Pots ↓ETCO2	POTS nlETCO2
Total HRV	2,838 ± 470	1,066 ± 119*	835 ± 118*	1,208 ± 125*#
LF HRV	754 ± 143	379 ± 65*	247 ± 58*	479 ± 96*#
HF HRV	1,444 ± 297	389 ± 51*	339 ± 106*	428 ± 62*
Total BPV	10.3 ± 2.0	11.8 ± 1.3	9.4 ± 1.8	13.1 ± 1.7
LF BPV	2.5 ± 0.3	3.0 ± 0.3	2.9 ± 0.4	3.0 ± 0.3
HF BPV	1.5 ± 0.2	1.3 ± 0.1	1.5 ± 0.2	1.3 ± 0.2
Alpha index	20.5 ± 2.1	15.4 ± 2.0	10.9 ± 2.0*	17.3 ± 2.1#

Pearson’s correlation was used to assess the linear associations for the spectral analyses. Comparison of study groups on baseline spectral analysis of heart rate and blood pressure variability was conducted using independent t tests for all postural tachycardia syndrome (POTS) vs. controls and for each POTS subgroup vs. controls. Similarly, independent t tests were used for comparing each POTS subgroup. For these univariable tests, there was no adjustment for multiple comparisons. P values are unadjusted for multiple comparisons. HF BPV, high-frequency blood pressure variability; HF HRV, high-frequency heart rate variability; HRV, heart rate variability; LF BPV, low-frequency blood pressure variability; LF HRV, low-frequency heart rate variability; POTS-↓ETCO₂, postural tachycardia syndrome with low end-tidal carbon dioxide; POTS-nlETCO₂, postural tachycardia syndrome with normal upright end-tidal carbon dioxide.

^*P < 0.05 compared with all controls; #P < 0.05 ↓ETCO₂ compared with POTS nlETCO₂.