Table 2.

Steady-state hemodynamics and respiratory condition

	Horizontal	−10° HDT	−30° HDT	P Value
HR, beats/min	61 ± 9	60 ± 8	61 ± 8	0.748	(A)
Mean ABPHeart, mmHg	81 ± 6	80 ± 7	81 ± 8	0.520	(A)
Mean ABPMCA, mmHg	80 ± 6	82 ± 7	91 ± 8*†	<0.001	(A)
Amplitude of mean ABPHeart, mmHg	21 ± 7	20 ± 7	19 ± 8	0.382	(A)
Mean MCAV, cm/s	64 ± 13	65 ± 9	63 ± 10	0.467	(A)
nCPP, mmHg	72 ± 6	73 ± 6*	79 ± 8*§	<0.001	(A)
CVRi, mmHg/cm/s	1.16 ± 0.24	1.14 ± 0.17	1.28 ± 0.23#§	0.001	(A)
Resp-R, breaths/min	15 ± 3	15 ± 3	15 ± 4	0.821	(F)
${\text{Sp}}_{{\text{O}}_{\text{2}}}$, %	98 ± 1	98 ± 1	98 ± 1	0.598	(A)
$\mathrm{E}{\mathrm{T}}_{\mathrm{C}{\mathrm{O}}_2}$, Torr	38 ± 3	38 ± 2	38 ± 2	0.346	(A)

Values represent means ± SD. P values are obtained from one-way repeated-measures analysis of variance (A) or Friedman repeated-measures analysis of variance on ranks (F). *P < 0.001 compared with horizontal (Tukey’s test). †P < 0.001 compared with −10° HDT (Tukey’s test). #P < 0.01 compared with horizontal (Tukey’s test). §P < 0.01 compared with −10° HDT (Tukey’s test). CVRi, cerebrovascular resistance index; $\mathrm{E}{\mathrm{T}}_{\mathrm{C}{\mathrm{O}}_2}$, end-tidal carbon dioxide pressure; HDT, head-down tilt; Horizontal, horizontal supine position (0°); HR, heart rate; mean ABP_Heart, mean arterial blood pressure at heart level; mean ABP_MCA, mean arterial blood pressure at middle cerebral artery level; mean MCAV, mean cerebral blood velocity in the middle cerebral artery; nCPP, noninvasive cerebral perfusion pressure; Resp-R, respiratory rate; ${\text{Sp}}_{{\text{O}}_{\text{2}}}$, arterial oxygen saturation.