5-Day Bed Rest: Portal and Lower Limb Veins With and Without Artificial Gravity Countermeasures

Abstract

Purpose: The objective of the study was to evaluate the effect of short-term, head-down bed rest (HDBR), with and without artificial gravity countermeasures, on splanchnic and lower limb vein properties.

Methods: Data were collected from 12 men before and after 5 d of continuous -6° HDBR without countermeasures (CON) and with two artificial gravity countermeasure protocols: 30-min continuous centrifugation (AG1), and 30-min intermittent centrifugation (AG2). Portal (PV), tibial (TibV), and gastrocnemius (GastV) veins were investigated by echography supine and after 30 min of head-up tilt.

Results: After HDBR, there was no change in PV, TibV, or GastV cross-sectional area at rest in any of the three conditions. In response to tilt, GastV and TibV area increased (168±141% and 192±124%, respectively) with no change in this response post-HDBR in any of the experimental conditions (P>0.05). PV area decreased with tilt (-33±13%) and was not different pre- to post-HDBR in the CON or AG1 conditions. However, there was a greater reduction in PV area in the AG2 group post-HDBR (-32±10% pre, -49±9% post-HDBR, P=0.003).

Conclusions: Calf veins were not significantly affected by 5 d of HDBR and did not appear to be negatively impacted by the artificial gravity countermeasures over this time period. In addition, the intermittent protocol resulted in better splanchnic vasoconstriction in response to head-up tilt, which may have contributed to a better maintenance of orthostatic tolerance post-HDBR.