Table 3. Interbeat interval in the frequency domain.

	Maneuver	Sex	LF (s2) (0.04–0.15 Hz)	HF (s2) (0.14–0.4 Hz)	LF/HF	rF (s2) $\sqrt{{\text{LF}}^2+{\text{HF}}^2}$	slope PSD (s2)	β
Control	Supine	F	6 ± 3	9 ± 3	0.7 ± 0.2	11 ± 4	-0.6 ± 0.5
		M	7 ± 3	10 ± 4	0.7 ± 0.3	12 ± 4	-1.0 ± 0.4
	Standing up	F	10 ± 3	11 ± 4	0.9 ± 0.3	15 ± 4	-0.8 ± 0.6
		M	12 ± 5	11 ± 3	1.2 ± 0.3	16 ± 6	-1.1 ± 0.9
	Breathing at 0.1 Hz	F	16 ± 7	12 ± 6	1.5 ± 0.4	20 ± 9	-1.2 ± 0.4	0.29 ± 0.07
		M	15 ± 5	10 ± 4	1.5 ± 0.4	18 ± 6	-1.2 ± 0.3	0.3 ± 0.1
Achalasia	Supine	F	4 ± 2	5 ± 3* (p = 0.01)	0.8 ± 0.2	6 ± 4* (p = 0.002)	-0.3 ± 0.9
		M	5 ± 1*	7 ± 1* (p = 0.02)	0.7 ± 0.2	9 ± 2* (p = 0.007)	-0.4 ± 0.8 * (p = 0.01)
	Standing up	F	4 ± 2*	4 ± 2*(p = 0.0005)	1.0 ± 0.2	6 ± 3* (p = 0.0001)	-0.5 ± 0.7
		M	8 ± 3*	6 ± 1* (p = 0.003)	1.4 ± 0.4	10 ± 3* (p = 0.01)	-0.8 ± 0.6 * (p = 0.02)
	Breathing at 0.1 Hz	F	14 ± 6	6 ± 1* (p = 0.03)	2.5 ± 0.9* (p = 0.02)	15 ± 6	-1.7 ± 0.7 * (p = 0.02)	0.3 ± 0.1
		M	18 ± 4	6 ± 2* (p = 0.04)	3.1 ± 0.7* (p = 0.01)	19 ± 4	-1.7 ± 0.7 * (p = 0.02)	0.3 ± 0.2

* indicates statistically significant difference with respect to control (p value <0.05).