Table 2.

Time domain responses to progressive lower body negative pressure (LBNP) to presyncope (PS) in high tolerant (HT) and low tolerant (LT) subjects.

	LBNP Stage		LMM P-Value
	0	PS 1-min	Time	Tolerance	Interaction
HR, bpm
HT	61.8 ± 8.2	117.6 ± 14.9^*^,†	<0.0001	0.01	<0.0001
LT	65.5 ± 7.0	99.3 ± 21.4^*
SAP, mmHg
HT	128.1 ± 11.8	94.9 ± 5.8^*	<0.0001	0.81	0.63
LT	127.7 ± 8.7	96.1 ± 7.2^*
MAP, mmHg
HT	94.0 ± 8.8	76.4 ± 5.7^*	<0.0001	0.59	0.50
LT	94.0 ± 8.0	74.8 ± 5.8^*
SV, ml
HT	91.6 ± 19.6	40.3 ± 10.2^*	<0.0001	0.43	0.02
LT (n = 20)	89.4 ± 18.6	48.2 ± 15.4^*
Mean MCAv, cm/s
HT	62.0 ± 12.3	45.0 ± 9.5^*	<0.0001	0.35	0.54
LT	66.4 ± 15.7	47.8 ± 15.3^*
etCO₂, mmHg
HT	39.6 ± 4.2	28.6 ± 5.5^*	<0.0001	0.29	0.71
LT (n = 20)	40.5 ± 4.0	30.2 ± 7.4^*
Respiratory Rate, breaths/min
HT	14.3 ± 4.6	15.3 ± 7.0	0.65	0.89	0.11
LT (n = 20)	15.4 ± 4.3	13.7 ± 4.5

Data are presented as absolute means ± SD. LMM, linear mixed model; HR, heart rate; SAP, systolic arterial pressure; MAP, mean arterial pressure; SV, stroke volume; MCAv, middle cerebral artery velocity; etCO₂, end tidal carbon dioxide. PS-1 time point refers to the 1-min prior to pre-syncope. A two-factor linear mixed model analysis with repeated measures from baseline to PS-1 was performed, followed by Holm-corrected post-hoc tests for multiple comparisons (run on the least squared means generated by the linear mixed model analysis).

P ≤ 0.004 compared to baseline within a group.

^†

P ≤ 0.001 between HT and LT groups. Exact P values are reported for all comparisons.