Portal vein cross-sectional area and flow and orthostatic tolerance: a 90-day bed rest study.

Abstract

The objective of this study was to evaluate the changes in the portal vein cross-sectional area (PV CSA) and flow during a stand test associated with orthostatic intolerance. Eighteen subjects underwent a 90-day head-down tilt (HDT) bed rest at 6 degrees: 9 controls (Con) and 9 with flywheel exercise countermeasures (CM). At post-HDT, nine subjects (5 CM, 4 Con) were tolerant, and nine were intolerant. The PV CSA was measured by echography. We found that at HDT day 85, the PV CSA at rest had increased less in the CM subjects than in the Con (+12 vs. +27% from pre-HDT supine; P < 0.05), whereas it increased similarly in tolerant and intolerant subjects (23 and 16%, respectively). Two days after the HDT, there was a decrease in the PV CSA supine compared with the pre-HDT PV CSA supine that was similar for all groups (Con: -11%, CM: -21%; tolerant: -10%, intolerant: -16%; P < 0.05). The PV CSA decreased significantly less from supine to standing in the Con than in the CM group (-2 vs. -10% compared with the pre-HDT stand test; P < 0.05). The PV CSA also decreased significantly from supine to standing compared with the pre-HDT stand test in the tolerant group but not in the intolerant group (-20 vs. +2%; P < 0.05). From these findings, we conclude the following. 1) Because the portal vein is the only output from the splanchnic vascular area, we suggest that the lower reduction in the PV CSA and flow associated with orthostatic intolerance was related to a lower splanchnic arterial vasoconstriction. 2) The flywheel exercise CM helped to reduce the distention of the splanchnic network at rest and to maintain partially the splanchnic vasoconstriction, but it did not reduce the orthostatic intolerance.

Aortic, cerebral and lower limb arterial and venous response to orthostatic stress after a 60-day bedrest

“…This suggests that the femoral flow was reduced more than cerebral flow and that the regulating systems (baro-reflexes, cerebral auto-regulation, local leg and splanchnic vasoconstriction) were still operational in this group even after long-term HDBR. This was also observed during supine LBNP or stand tests after long duration HDBR (Arbeille et al 2005(Arbeille et al , 2008b.…”

28-Day hindlimb unweighting reduces expression of Rho kinase and inhibits its effects in femoral artery of rat

“…Results from multiple human spaceflight [7] and bed rest studies [1,2,9] have demonstrated the adaptational changes of the arterial vasculature in both real and simulated microgravity, which could possibly contribute to postflight orthostatic intolerance. Animal studies applying mice experiencing real spaceflight [28] and tailsuspended hindlimb unweighting (HU) rats [10,18,24,34,35] also give support to the involvement of microgravity-induced vascular responsiveness adaptations in postflight orthostatic intolerance.…”

Postsynaptic α 1 -Adrenergic Vasoconstriction Is Impaired in Young Patients With Vasovagal Syncope and Is Corrected by Nitric Oxide Synthase Inhibition

“…Splanchnic hyperemia occurs in real or simulated microgravity (bedrest in man, hindlimb suspension in rats) where it is associated with orthostatic intolerance, adrenergic hyporeactivity 41;42 , and enhanced microvascular production of NO through increased transcription of NOS isoforms 43;44 . Increased NO has been reported in both postural tachycardia syndrome and VVS 45–47 but those results are controversial due to measurement methods and lack of subsetting 46 .…”