Table 1.

Patient demographics

	Groups			Subgroups
	HUT(−)	HUT(+)	P Value	POTS	OH	Syncope	P/S	P Value
n	18	30		7	5	8	10
Sex, male/female	3/15	9/21		3/4	1/4	1/7	4/6
Age, yr	15 ± 0.4	15 ± 0.4	NS	14.7 ± 0.5	14.4 ± 1.3	15.3 ± 1.0	16 ± 0.6	NS
Weight, kg	63 ± 3.9	57.9 ± 2.6	NS	60.4 ± 7.9	57.8 ± 6.1	52.6 ± 4.3	60.6 ± 3.6	NS
Body mass index	24.7 ± 1.5	21.2 ± 0.7	0.03*	21.2 ± 1.8	22.1 ± 2.1	20.8 ± 1.2	21.1 ± 0.9	NS
Time on HUT	45.6 ± 0.2a	27.4 ± 2.4b	<0.0001	41.4 ± 3.3c	31.8 ± 6.8d	17.7 ± 2.6e	23.2 ± 2.9f	<0.0001
								<0.0001a vs. e
								<0.01a vs. f
								<0.05c vs. e

All values are expressed as exact numbers (n) or means ± SE. Subjects with a normal response to head-up tilt (HUT) [HUT(−) subjects] had a negative HUT, and subjects with an abnormal response to HUT [HUT(+) subjects] had a positive HUT. Unpaired t-tests were used to assess differences between HUT(−) and HUT(+) subjects. One-way ANOVAs were used to assess differences between HUT(+) subgroups. There were no differences in age or weight between groups. HUT(+) subjects had a lower body mass index than HUT(−) subjects. HUT(+) subjects were unable to sustain HUT for the full 45-min HUT. Syncope subjects sustained the least amount of time on HUT, which was significantly less time than HUT(−) and postural orthostatic tachycardia syndrome (POTS) subjects. POTS/syncope (P/S) subjects also sustained less time on HUT compared with HUT(−) subjects.

OH, orthostatic hypotension; NS, not significant.

^aHUT(−),

^bHUT(+),

^cPOTS,

^dOH,

^esyncope, and

^fP/S.