Peripheral arterial and venous response to tilt test after a 60-day bedrest with and without countermeasures (ES-IBREP)

Abstract

We quantified the impact of 60-day head-down bed rest (HDBR) with countermeasures on arterial and venous response to tilt.

Methods: Twenty-one males: 7 control (Con), 7 resistive vibration exercise (RVE) and 7 Chinese herb (Herb) were assessed. Subjects were identified as finisher (F) or non-finishers (NF) at the post-HDBR 20-min tilt test. The cerebral (MCA), femoral (FEM) arterial flow velocity and leg vascular resistance (FRI), the portal vein section (PV), the flow redistribution ratios (MCA/FEM; MCA/PV), the tibial (Tib), gastrocnemius (Gast), and saphenous (Saph) vein sections were measured by echography and Doppler ultrasonography. Arterial and venous parameters were measured at 3-min pre-tilt in the supine position, and at 1 min before the end of the tilt.

Results: At post-HDBR tilt, MCA decreased more compared with pre-HDBR tilt in the Con, RVE, and Herb groups, the MCA/FEM tended to decrease in the Con and Herb groups (not significant) but remained stable in the RVE gr. FRI dropped in the Con gr, but remained stable in the Herb gr and increased in the RVE gr. PV decreased less in the Con and Herb groups but remained unchanged in the RVE gr. MCA/PV decreased in the Con and Herb groups, but increased to a similar extent in the RVE gr. Gast section significantly increased more in the Con gr only, whereas Tib section increased more in the Con and Herb groups but not in the RVE gr. The percent change in Saph section was similar at pre- and post-HDBR tilt.

Conclusion: In the Con gr, vasoconstriction was reduced in leg and splanchnic areas. RVE and Herb contributed to prevent the loss of vasoconstriction in both areas, but the effect of RVE was higher. RVE and Herb contributed to limit Gast distension whereas only RVE had a protective effect on the Tib.

Figure 1. Percentage change in flow velocity in the middle cerebral artery (MCA) from the supine to tilt positions.

The MCA was measured by Doppler ultrasonography as detailed in the Materials and Methods section. Percentage change in flow velocity in the MCA from the supine to tilt positions was significantly increased after 60-day HDBR in all groups (P<0.05).

Figure 2. Percentage change in the flow velocity of the femoral artery (FEM) from supine to tilt positions.

The FEM was measured by Doppler ultrasonography as detailed in the Materials and Methods section. The percent change in FEM from supine to tilt positions post-HDBR was similar to pre-HDBR in Con, RVE and Herb groups.

Figure 3. Percentage change in resistance in the femoral artery (FRI) from supine to tilt positions.

FRI response decreased in the Con gr (p<0.05), increased in the RVE gr (p<0.05) and was maintained in the Herb gr. RVE and Herb contributed to maintain vasoconstrictive responses at the leg level but the effect of RVE was greater.

Figure 4. Percentage change in flow in the portal vein flow (PV) from supine to tilt positions.

The PV was measured by echography as detailed in the Materials and Methods section. The percent change in the PV from supine to tilt positions decreased less post-HDBR in Con and Herb groups (p<0.05), but there was no change in the RVE gr. RVE contributed to maintain splanchnic vasoconstriction in response to tilt-induced fluid shift.

Figure 5. Ratio of flow of the cerebral vein to portal vein (MCA/PV).

The cerebral-to-splanchnic flow ratio confirmed that only RVE countermeasures contributed to redistribute the cardiac output in favor of the brain area.

Figure 6. “FEM S” femoral systolic velocity changes were in the same proportion as stroke volume.

There was no significant difference in the drop in FEM S (i.e., stroke volume) pre- and post-HDT tilt. Differences in vasomotor responses between the groups were not related to changes in cardiac output. This confirmed that each area provides a specific response that is due to local morphological or functional disturbances.

Figure 7. Percentage changes in gastrocnemius (GAST) section from supine to tilt positions.

Gast section was measured by echography as detailed in the Materials and Methods section. The percent change in Gast section from supine to tilt positions was increased more post-HDBR in the Con gr. RVE and Herb contributed to limit Gast distension, with the effect of Herb being greater.

Figure 8. Percentage change in the tibial vein (Tib) section from supine to tilt positions.

The Tib section was measured by echography as detailed in the Materials and Methods section. The percent change in Tib section from supine to tilt positions was significantly increased (P<0.05) post-HDBR in Con and Herb groups, but not in the RVE gr. Only RVE CM contributed to maintain vein distension at the pre-HDBR level.