Lower body negative pressure identifies altered central vein characteristics without accompanying changes to baroreflexes in astronauts within hours of landing

Figures

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  Figure 1. Example preflight data acquisitions from Constant (Left) and Random (Right) LBNP Protocols in one subject showing SBP (mmHg), DBP (mmHg), HR (bpm), TPR (mmHg.min/l), CVP (cmH2O), and LBNP pressure (mmHg). Data collection periods in Constant LBNP were nominally 5-min for instrumentation and baseline then 2-min at each LBNP including ultrasound scan times.

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  Figure 2. Group changes in cardiovascular variables with increasing negative pressure, displayed here as mean group values during the last 30 s of each period without LBNP and each LBNP intensity. Therefore, the LBNP ‘0’ includes data from all periods without LBNP during the constant and random LBNP protocol. Preflight (black circles with solid line) and postflight (grey triangles with dashed line). Data shown as mean ± SD in 7 participants for: HR (A), SBP (B), DBP (C), SV (D) and in 5 participants for TPR (E), and CVP (F). †Significant effect of LBNP, †p < 0.05, ††p < 0.01, †††p < 0.001, ††††p < 0.0001. #Significant effect of spaceflight, ##p < 0.01. The slight horizontal offset exists to aid visualisation.

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  Figure 3. Repeated Measures Correlations for CVP vs TPR (A and B), CVP vs SV (C and D), CVP vs IVC ø (E and F), and CVP vs PV ø (G and H). Preflight data with solid lines (A,C,E,G) left, and Postflight data with dashed lines (B,D,F,H) right, are shown as circles representing Shuttle astronauts (black circles with solid line) and triangles representing Soyuz astronauts (black triangles with dashed line). Colour represents individual participants. For 2 of the 7 participants, only data taken from the Constant Protocol is plotted for CVP vs TPR and CVP vs SV, due to poor CVP quality during the Random LBNP Protocol.

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  Figure 4. Vein ø shown as a function of CVP for the inferior vena cava (IVC) (A) and portal vein (PV) (B), and the ratio for IVCø/CVP (C) and PVø/CVP (D) (mean ± SD) at different LBNP intensities in preflight (black circles) and postflight (open circles). Two-way ANOVA identified significant interaction effects for both veins (p = 0.0268 for IVCø/CVP and p = 0.005 for PVø/CVP). Post-hoc Bonferroni testing identified significant differences between preflight and postflight groups at − 10 mmHg and − 20 mmHg LBNP. **p < 0.01, ***p < 0.001. The slight horizontal offset exists to aid visualisation.

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  Figure 5. Calculated Step Responses (ARMA analyses) of CVP → TPR (A), DBP → TPR (B), SBP → HR (C) and CVP → HR (D). Preflight (solid line and dark shading) and postflight (dashed line and pale shading). No differences in plateau values or time to 95% plateau values were noted.