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

The objective of this study is to assess by echography and Doppler the Cerebral (Vmca), Aortic (Vao) and Femoral (Vfem) arterial flow velocity and calf vein (Tibial, Gastrocnemius) section (Tib, Gast) during orthostatic intolerance (OI) test after a 60-day, head down tilt bed rest (HDBR). Twenty-four women (25-40 years) underwent a 60-day HDBR at -6°: eight as control (Con), eight with exercise against lower body negative pressure (Ex-Lb) and eight with nutrition supplement (Nut). Before and after (R0) HDBR, all subjects underwent a 10-min, 80° tilt followed by progressive LBNP until presyncope. After the post-HDBR Tilt + LBNP test, two groups were identified: finishers (F, n = 11) who completed the Tilt and non-finishers (NF, n = 13). A higher percentage decrease in Vao flow, higher percentage distension of Tib vein and a lack of increase in Vmca/Vfem ratio during the post-HDBR Tilt + LBNP compared to pre-HDBR were correlated to OI, but not all of these abnormal responses were present in each of the NF subjects. Abnormal responses were more frequent in Con and Nut than in Ex-Lb subjects. (1) HDBR did not affect the cardiac, arterial and venous responses to the orthostatic test to the same extent in each subject. (2) Exercise within LBNP partially preserved the cardiovascular response to Tilt, while Nutrition supplementation had no efficacy. (3) Cerebral/femoral flow ratio and aortic flow were the parameters most closely related to OI. (4) Reduction in aortic flow was not the major hemodynamic change preceding syncope.

Insufficient flow reduction during LBNP in both splanchnic and lower limb areas is associated with orthostatic intolerance after bedrest.

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-LBNP), and 8 nutrition (Nut) subjects] were studied during LBNP (0 to -45 mmHg) before (pre) and on HDBR day 55 (HDBR-55). Left ventricle diastolic volume (LVDV) and mass, flow velocities in the middle cerebral artery (MCA flow) and femoral artery (femoral flow), portal vein cross-sectional area (portal flow), and lower limb resistance (femoral resistance index) were measured. Muscle sympathetic nerve activity (MSNA) was measured in the fibular nerve. Subjects were identified as finishers or nonfinishers 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 the Con and Nut groups only. During LBNP at HDBR-55, femoral and portal flow decreased less, whereas leg MSNA increased similarly, compared with pre-HDBR in the Con, Nut, and NF groups; 11 of 13 nonfinishers showed smaller LBNP-induced reductions in both femoral and portal flow (less vasoconstriction), whereas 10 of 11 finishers maintained vasoconstriction in either one or both regions. The relative distribution of blood flow in the cerebral versus portal and femoral beds during LBNP [MCA flow/(femoral + portal flow)] increased or reduced < 15% from pre-HDBR in 10 of 11 finishers but decreased > 15% from pre-HDBR in 11 of 13 nonfinishers. Abnormal vasoconstriction in both the portal and femoral vascular areas was associated with orthostatic intolerance. The vascular deconditioning was partially prevented by Ex-LBNP.

WISE-2005: tibial and gastrocnemius vein and calf tissue response to LBNP after a 60-day bed rest with and without countermeasures.

The objective of this study was to quantify by echography the changes in the intramuscular [gastrocnemius (Gast)] and nonintramuscular [posterior tibial (Tib)] calf veins cross-sectional area (CSA) and the superficial tissue thickness (STth) in response to lower body negative pressure (LBNP) after 60-day head-down bed rest (HDBR). Twenty-four healthy women (25-40 yr) were divided into three groups: control (Con), treadmill-LBNP and flywheel (Ex-Lb), nutrition (Nut; protein supplement). All underwent a LBNP (0 and -45 mmHg) before and on day 55 of HDBR. Subjects were identified as finisher (F) or nonfinisher (NF) of a 10-min tilt test after 60 days of HDBR. There were no differences in resting CSA of the Tib and Gast veins on HDBR day 55 compared with pre-HDBR for the Ex-Lb, Con and Nut, or the F groups; however, for NF both the Tib and Gast vein CSA at rest were significantly smaller after HDBR. At -45 mmHg LBNP, Tib and Gast CSAs were not significantly different from before HDBR in all groups (Ex-Lb, Con, Nut, F, NF). However, percent change in CSA of both veins from rest to -45 mmHg LBNP was significantly greater in the Con and Nut groups compared with Ex-Lb, and also NF compared with F. Similarly, the percent increase in STth on going from rest to -45 mmHg was higher after HDBR in the Con and Nut groups compared with Ex-Lb, as well as NF compared with F. These results showed that the Ex-Lb countermeasure minimized the bed rest effect on leg vein capacitance (CSA percent change) and STth increase during LBNP, whereas Nut had no effect and that higher leg vein and superficial tissue capacitance were associated with reduced orthostatic tolerance.

WISE 2005: stroke volume changes contribute to the pressor response during ischemic handgrip exercise in women.

The mechanism of the pressor response to small muscle mass (e.g., forearm) exercise and during metaboreflex activation may include elevations in cardiac output (Q) or total peripheral resistance (TPR). Increases in Q must be supported by reductions in visceral venous volume to sustain venous return as heart rate (HR) increases. Therefore, this study tested the hypothesis that increases in Q, supported by reductions in splanchnic volume (portal vein constriction), explain the pressor response during handgrip exercise and metaboreflex activation. Seventeen healthy women performed 2 min of static ischemic handgrip exercise and 2 min of postexercise circulatory occlusion (PECO) while HR, stroke volume and superficial femoral artery flow (Doppler), blood pressure (Finometer), portal vein diameter (ultrasound imaging), and muscle sympathetic nerve activity (MSNA; microneurography) were measured followed by the calculation of Q, TPR, and leg vascular resistance (LVR). Compared with baseline, mean arterial blood pressure (MAP) (P < 0.001) and Q (P < 0.001) both increased in each minute of exercise accompanied by a approximately 5% reduction in portal vein diameter (P < 0.05). MAP remained elevated during PECO, whereas Q decreased below exercise levels. MSNA was elevated above baseline during the second minute of exercise and through the PECO period (P < 0.05). Neither TPR nor LVR was changed from baseline during exercise and PECO. The data indicate that the majority of the blood pressure response to isometric handgrip exercise in women was due to mobilization of central blood volume and elevated stroke volume and Q rather than elevations in TVR or LVR resistance.

Arterial and venous response to Tilt with LBNP test after a 60 day HDT bedrest (WISE study).

UNLABELLED: The objective was to quantify the Cerebral, and Femoral arterial hemodynamics as well as the calf vein section changes induced by a Tilt up test continuing with a Tilt plus LBNP after a 60 day HDT (WISE). METHOD: 24 healthy volunteers (25-40 y) underwent a 60 day HDT (-6 degree) bedrest: 8 as Control (Co), 8 with Exercise (Ex: treadmill under LBNP and flywheel), 8 with Nutrition (Nut: daily protein supplement). At R+0 all of them underwent a 10 min 80 degree Tilt up test, to which several LBNP period of 3 min were added (from -10 to -50 mmHg by steps of 10 mmHg) until presyncopal stage. Cerebral and Femoral flow changes were assessed by Doppler. Posterior Tibial, and Gastrocnemian vein were investigated by echography. RESULTS: At Post HDT 10 min Tilt: cerebral flow decreased similarly in the 3 groups, but more in the non finishers than in the finishers, while the femoral decreased similarly in all groups. Leg vascular resistance and cerebral/femoral flow ratio increased less in the Co and Nut gr than in the Ex gr, and also in the non finishers than in the finishers. Percent increase in Gastrocnemian and Tibial section was higher in Co and Nut gr than in Ex gr, and in non finishers than in finishers. CONCLUSION: Non exercise and non finisher subjects showed a lack of leg vasoconstriction, and a higher calf vein distensibility at post HDT Tilt test.

WISE 2005: vascular responses to 60-day bed rest in women.

WISE-2005 studied 24 women during a 60-day head down bed rest (HDBR) who look part in an exercise countermeasure (LBNP-treadmill plus flywheel, EX) and no-exercise (No-EX). We conducted a series of experiments to explore changes in cardiovascular function and the ability of EX to prevent these changes. Resting arterial diameter in the arm was not affected but the leg arteries (femoral and popliteal) were significantly reduced in Np-EX, but was increased in EX. In this study we report on drug stimulated responses with sublingual nitroglycerin and infused isoproterenol. Heart rate increased in response to nitroglycerin with larger increases in No-EX after HDBR. Likewise during isoproterenol infusion the HR increase was greater after HDBR in the No-EX group. In all cases, the higher HR was associated with lower stroke volume in No-EX while stroke volume was protected in EX. These data do not support a change in sensitivity of beta-adrenergic receptors after HDBR. The leg vascular resistance decreased in response to isoproterenol and it decreased to a greater extent in No-EX than EX. These data were consistent with observations of lower leg vascular resistance during orthostatic challenge tests after HDBR. We conclude that consistent changes in cardiovascular function in the No-EX were detected by different methods that point to mechanisms contributing to orthostatic intolerance after HDBR.

Tibial and gastrocnemian vein response to LBNP after a 60 day bedrest with and without counter-measures (WISE study).

UNLABELLED: The objective was to quantify calf vein cross section area (CSA) maximal enlargement and the percent change in response to LBNP (lower body negative pressure) after a 60 day bedrest. METHOD: The 24 healthy volunteers (25-40 y) of the WISE 60 day HDT(-6 degree) bedrest, were divided into 3 groups: Control (Co), Exercise countermeasure (Ex: treadmill under LBNP and flywheel), Nutrition (Nut: daily protein supplement). All were studied at -45mmHg LBNP pre and at HDT day 55. Posterior Tibial (Tib), and Gastrocnemian (Gast) vein were investigated by echography using an echographic probe fixed at the upper and posterior part of the calf. From the post HDT CSE test the subjects were identified as finisher or non finisher to the 10-min tilt tolerance test. RESULTS: At LBNP-45mmHg, the maximal enlargement of the Tib and Gast veins remained constant pre, and at HDT day 55 in all group (Co, Ex, Nut, finisher, non finisher). For both veins there was a higher vein distension (percent change from supine rest to -45mmHg) in Co and Nut group compared to Ex group despite the maximal distension was similar in all groups. Also the vein distension was higher in non finisher than in finisher. CONCLUSION: The maximal distension of the vein were not affected nor by HDT nor by CM. The Ex counter-measure minimized the bed rest effect on leg vein distensibility (percent CSA change) while the Nut countermeasure had no effect. Higher leg vein distensibility was associated with reduced orthostatic tolerance.

Effect of the elastic compression stockings on the calf veins and tissues during a simulated orthostatic test (LBNP).

UNLABELLED: The objective of the present study was to quantify the effects of elastic compression stockings (ECS) on the leg hemodynamics, the venous return (flow and distensibility) and on the leg superficial tissue thickness. MATERIAL & METHODS: 10 healthy women were submitted to LBNP (Lower Body Negative Pressure) tests without then with ECS (French pressure class 1, 2 and 3). The subject was instrumented with Doppler and echographic probes for assessing the femoral artery, the external saphenous and the gastrocnemian vein. RESULTS: 1) At -40 mmHg the heart rate and blood pressure didn't change significantly with or without ECS. 2) The lower limb vascular resistance increased by 20 to 25% (p<0.01) from the initial values (i.e. without depressure) without or with class 1 or 2 ECS, while it increased less (13%, p<0.01) with class 3 ECS. 3) With ECS, the gastrocnemian vein area was reduced by 10 to 15% (p<0.01) from the initial values, in proportion to the ECS class. 4) The maximal distension (cross section) of this vein at -40 mmHg remained similar with or without ECS, but the percent change in vein distension was significantly higher with ECS than without. 5) Only without ECS, the distance between the external saphenous vein and the skin increased by 13% at -40 mmHg (p<0.01) from the initial values (increase of the calf peripheral area by 11% p<0.01). With ECS, there was no increase in distance nor area during LBNP. CONCLUSION: ECS had no effect on the main arterial hemodynamics and venous cross section area, while it prevented liquid stowage into the superficial tissue.

Assessment of the calf vein cross section change during stand-test after a 90 day bed rest by echography.

OBJECTIVE: To evaluate the contribution of the calf veins distension during stand test to orthostatic intolerance (OI). METHOD: The population consisted of a control group (Co, n=9) and an exercise (Fly-Wheel) counter-measure group (CM, n=9). Calf vein cross section area was assessed by echography during pre and post HDT stand-tests. RESULTS: Tibial, and muscular vein section at rest did not change during HDT in both groups. From supine to standing, the Tibial and muscular vein section increased significantly more at post HDT in non tolerant subjects, compare to pre HDT (tibial V: +122% from pre-HDT, muscular V: +145% p<005). In tolerant subjects the vein cross section increase from supine to stand was similar pre and post HDT. CONCLUSION: Fly-Wheel CM, did not reduce OI. High calf vein section increase at post-HDT stand-test compare to pre-HDT was significantly correlated with OI but not with CM.

Influence of eye closing on the cardiovascular response to stand test on stable and unstable platforms.

UNLABELLED: Check if the stimulation of the leg muscles and neuro-sensorial system during stand test influence the cardiovascular response to stand test pre and post a 7 d HDT (4 subjects). METHODS: After 20 min supine, the subject stood for 10 min, and closed the eyes for 1 min. Then he stayed 2 min stand up on ant-posterior or lateral unstable platform and closed the eyes for 30 sec. The cerebral and lower limb flow were assessed by Doppler (skin fixed sensors) and also the cerebral to femoral flow ratio (CFR). RESULTS: All 4 subjects were tolerant, CFR increased similarly pre and post HDT. Post HDT eye closing increased leg muscle activity, and femoral flow increased more than pre HDT, on ant-post unstable platform. The trace of the body foot pressure point was much longer post HDT on the ant-post platform. CONCLUSION: Post HDT neuro-sensorial disadaptation may contribute to reduce the orthostatic tolerance at least in absence of visual references.