Submitted on May 14, 2008
Revised on August 18, 2008
Accepted on August 20, 2008
INSUFFICIENT FLOW REDUCTION DURING LBNP IN BOTH SPLANCHNIC AND LOWER LIMB AREAS IS ASSOCIATED WITH ORTHOSTATIC INTOLERANCE AFTER BEDREST
Philippe Arbeille1*, P. Kerbeci2, L. Mattar, J. Kevin Shoemaker3, and Richard L. Hughson4
1 UMPS University Hospital Tours
2 Universit de Tours
3 University of Western Ontario
4 University of Waterloo
* To whom correspondence should be addressed. E-mail: arbeille{at}med.univ-tours.fr.
We quantified the impact of a 60-day head-down tilt bed rest (HDBR) with countermeasures on the arterial response to supine lower body negative pressure (LBNP). Twenty-four women [8 Control (Con), 8 Exercise+LBNP (Ex-Lb) and 8 Nutrition (Nut)] were studied during LBNP (0 to -45mmHg) before (pre) and at HDBR day 55 (HDBR-55). Left ventricle diastolic volume (LVDV) and mass, flow velocities in the cerebral (MCA flow) and femoral (FEM flow) arteries, portal vein cross-sectional area (PORTAL flow) and lower limb resistance (FRI) were measured. Muscle sympathetic nerve activity (MSNA) was measured in the fibular nerve. Subjects were identified as finisher (F) or non-finisher (NF) of the 10-min post-HDBR tilt test. At HDBR-55, LVDV, Mass, and PORTAL flow were decreased from pre HDBR (p<0.05) in Con and Nut only. During LBNP at HDBR-55 FEM and PORTAL flow decreased less while leg MSNA increased similarly compared to pre HDBR in Con, Nut and NF, 11 of 13 NF showed smaller LBNP-induced reductions in both FEM and PORTAL flow (less vasoconstriction), while 10 of 11 F maintained vasoconstriction in either one or both regions. The relative distribution of blood flow in cerebral versus portal and femoral beds during LBNP [MCA flow/(FEM+PORTAL flow)] increased or reduced less than 15% from pre in 10 of 11 F, but decreased more than 15% from pre in 11 of 13 NF. Abnormal vasoconstriction in both portal and femoral vascular areas was associated with orthostatic intolerance. The vascular deconditioning was partially prevented by Ex-Lb.
