Table 3. Main cardiovascular and FOT parameters at baseline (room air) and neck suction at 0.1 and 0.2 Hz. For all conditions breathing frequency is 15 breaths•min^-1.

	Control (15 bpm)	Neck suction (0.1 Hz)	Neck suction (0.2 Hz)	Paired t-test or ANOVA
RR0.1 Hz, ln-Power	5.96 (0.65)	7.02 (0.92)	-	< 0.001
RR0.2 Hz, ln-Power	5.98 (1.09)	-	6.37 (1.10)	0.042
Mean RR interval, ms	769 (102)*	792 (89)*	782 (93)	0.031
RR-SD, ms	31 (13)*	47 (19)* §	36 (13)§	< 0.001
RMSSD, ms	32 (13)*	44 (15)* §	36 (12)§	0.003
SBP, mm Hg	124 (23)	126 (24)	123 (19)	0.711
DBP, mm Hg	69 (17)	72 (14)	70 (15)	0.593
SaO2, %	98 (1)	98 (1)	98 (1)	0.937
TO2I, %	64 (8)	64 (6)	64 (6)	0.721
R5, cm H2O∙s∙L-1	2.00 (0.68)	2.18 (0.62)	2.24 (0.67)	0.059
R19, cm H2O∙s∙L-1	2.22 (0.76)	2.35 (0.63)	2.43 (0.66)	0.128
VT, L	1.23 (0.51)	1.28 (0.44)	1.30 (0.49)	0.424
$\dot{\mathrm{V}}$ E L∙min-1	18.74 (7.59)	19.09 (6.45)	8.06 (7.24)	0.451
CO2-ET, mm Hg	33.51 (3.81)¶	32.65 (3.49)§	30.70 (4.71)§ ¶	< 0.001

RR interval: interval between two RR wave peaks; RR-SD: standard deviation of RR interval; SBP and DBP: systolic and diastolic pressures, respectively; SaO₂: oxygen saturation; TO₂I: Tissue Oxygen Index; R₅ and R₁₉, inspiratory resistance at 5 and 19 Hz, respectively; V_T: tidal volume; $\dot{\mathrm{V}}$ _E: minute ventilation; CO_2-ET: carbon dioxide end-tidal. Data are mean ± SD. RR0.1 Hz and RR0.2 Hz are expressed as natural logarithm of power spectra of RR interval at 0.1 and 0.2 Hz, respectively. t-test was used to compare RR0.1 between control and Neck suction (0.1 Hz), and to compare RR0.2 between control and Neck suction (0.2 Hz). ANOVA was used for all the other parameters that were compared for the three conditions.

*: p<0.05 between Neck suction (0.1 Hz) and Control by post-hoc analysis

^¶: p<0.05 between Neck suction (0.2 Hz) and Control by post-hoc analysis

^§: p<0.05 between Neck suction (0.1 Hz) and Neck suction (0.2 Hz) by post-hoc analysis.