Consequences of reduced umbilical and increased foetal cerebral flow during malaria crisis on foetal behaviour.

The objectives of this study were (a) to evaluate the sensitivity and specificity of foetal Doppler indices for the prediction of abnormal foetal heart rate (aFHR) at delivery after malaria crisis and (b) to test Doppler parameters against crisis duration for predicting aFHR. Every day during the malaria crisis, the umbilical and cerebral vascular resistance indices were measured by Doppler. These indices allowed evaluation of the amplitude of the foetal flow redistribution induced by malaria (C/U=cerebral resistance/umbilical resistance ratio), the duration of the flow redistribution period and the hypoxic index (mean %C/U change x crisis duration). It was found that the mean duration of the flow redistribution period was: 7 +/- 2 days, mean C/U change -7% +/- 4, hypoxic index -56 +/- 37, prematures 35%, and aFHR 17%. An hypoxic index > 150 predicted occurrence of aFHR with high sensitivity and specificity (100%/91%). The highest foetal flow disturbance (max %C/U) and the duration of the period with flow disturbance (> 7 days) predicted aFHR at delivery with a sensitivity of 10% and 40% and a specificity of 77% and 78%. It was concluded that the hypoxic index was more predictive of aFHR at delivery than the amplitude or the duration (i.e. crisis duration) of the foetal flow redistribution.

Effect of human head flexion on the control of peripheral blood flow in microgravity and in 1 g.

This study evaluated, in six healthy subjects, whether head flexion, which stimulates the vestibular system and the tonic neck receptors, interferes with cardiovascular regulation. Arterial parameters were measured continuously using a pulsed Doppler ultrasound probe during parabolic flights with subjects either in the supine craned-head position (control) or in the supine anterior neck flexion bent-neck position. Exposure to 0 g induced a fluid shift towards the head (stroke volume +8%, P<0.05). Compared to the control situation the mean (SD) blood flow in the femoral artery decreased [ -10 (9)% vs +1 (10)%; P<0.05], and the ratio cerebral artery:femoral artery blood flow ( : ) increased [+8 (14)% vs -4 (7)%; P<0.05], in the bent-neck position. Thus, neck flexion without otolith loading (subject in 0 g) favoured cerebral perfusion during the exposure to 0 g. The return to 1 g, even in the supine position, induced a fluid shift towards the lower limbs. From 0 to 1 g, reduced less [ +6 (8)% vs -1 (8)%; P<0.05], and the : decreased more [-11 (9)% vs 0 (10)%; P<0.05], in the bent-neck position than in the control position. Thus the redistribution of peripheral blood flow in response to the fluid shift towards the legs was less efficient in the bent-neck position. In 0 g environment the passive flexion of the neck (neck receptor stimulation only) increased resistance in the femoral artery [ R(fa) +20 (21)%; P<0.05] and reduced the [-15(10)%; P<0.07] which increased the redistribution of flow towards the brain [; +12 (7)%; P<0.07]. This response was of lower amplitude when both otoliths and neck muscle were stimulated (neck flexion in 1 g) [ R(fa)+9 (7)%, P<0.05; -9 (12), NS; : 0 (12), NS]. We suggest that otolith and neck muscle stimulation (by neck flexion) trigger opposite vascular effects in response to a fluid shift towards the legs.

Influence of otoliths and neck muscle receptors on peripheral hemodynamic regulation.

To evaluate the cardiovascular changes induced by otoliths and neck mechanoreceptors stimulation during head movements, nine subjects in supine prone position performed passive head-down neck flexion (P.Ext) and head up P.Extension (P.Flex) As the lower limbs vasoconstricted from P.Ext to P.Flex, it is suggested that the otoliths stimulation towards the base of the head (like in standing position) contribute to reduce the vasoconstriction whereas when stimulated towards the top of the head (head flexion) they increase it.

Venous stagnation induced by 7 days in HDT, in the cerebral, ophthalmic, renal and splanchnic territories.

The scientific objectives was to quantify the vascular changes in the brain, eye fundus, renal parenchyma, and splanchnic network. Heart, portal, jugular, femoral veins were investigate by Echography. The cerebral mesenteric, renal and ophthalmic arteries were investigated by Doppler. Eye fundus vein an papilla were investigated by optical video eye fundus. The left ventricle volume decreased as usual in HDT. The cerebral and ophthalmic vascular resistances didn't change whereas the eye fundus papilla and vein, and the jugular vein increased. These arterial and venous data confirm the existence of cephalic venous blood stasis without sign of intracranial hypertension. On the other hand the kidney volume increased which is in agreement with blood flow stagnation at this level. At last the mesenteric vascular resistance decreased and the portal vein section increased in HDT which is in favor of an increase in flow and flow volume through the splanchnic area.

Effect of the thigh-cuffs on the carotid artery diameter jugular vein section and facial skin edema: HDT study.

OBJECTIVE: To evaluate the distal arterial, venous and skin changes in a group using thigh cuffs during daytime and in a control group. METHOD: Cardiac, arterial, venous parameters were measured by echography and Doppler. Skin thickness was measured by high frequency echography. RESULTS & DISCUSSION: Head down position induced plasma volume reduction, increased cerebral resistance, reduced lower limb resistance. The jugular vein increased whereas the femoral and popliteal veins decreased. All these changes were already observed in previous HDT. Common carotid diameter decreased, Front head skin thickness increased and Tibial skin thickness decreased. Eight hours with thigh cuffs increased the cardiac and carotid sizes which is in agreement with the plasma volume increase. Conversely they reduced the cerebral vascular resistance, jugular section and front head edema which may explain the sensation of comfort reported by the subjects. At the lower limb level the thigh cuffs restored the skin thickness to pre-HDT level but enlarged markedly the femoral and popliteal veins. HR, BP, CO, TPR did not change.

Effect of a venotonic agent on the main arteries and veins during a 5 day HDT.

OBJECTIVE: To evaluate the cardiac, arterial and venous effect of a venotonic drug (Cirkan "Ck") administrated orally daily to 6 subjects in HDT position during 5 days. These subjects underwent a second 5d HDT without Ck treatment one month later. Pre and post HDT the subjects were submitted to a stand test. METHOD: The cardiovascular parameters were measured by echography and Doppler. RESULTS AND DISCUSSION: The Cirkan treatment contributed to reduce the increase in cerebral resistance, and to maintain the lower limb resistance at a higher level than on controls. It reduces the vein section at the extremities (Jugular, femoral) and in the central vein system connected to the right heart (sub hepatics). On the other hand it increases the portal vein section which means that the blood stagnation at the splanchnic level is increased. Despite these arterial and venous significant modifications the clinical and ECG and Blood pressure response to the Stand test was similar in both groups.

Doppler measurement of cerebral and lower limb flow during a lower body negative pressure test for predicting orthostatic intolerance.

OBJECTIVE: To quantify the cardiovascular response to an orthostatic test for predicting orthostatic intolerance. METHODS: Cerebral and lower limb arterial flow and resistance were assessed by Doppler ultrasonography during lower body negative pressure (7 minutes each at -25 and -45 mm Hg). Cardiovascular deconditioning was induced by 42 days in head-down tilt at -6 degress (7 subjects) and 6-month spaceflights (10 cosmonauts). RESULTS: Orthostatic intolerance during a stand test was observed in 57% of the head-down-tilt subjects and 83% of the cosmonauts. At the lower body negative pressure after head-down tilt and during or after flight, the average cerebral flow velocity and vascular resistance did not change significantly from before head-down tilt and before flight. Conversely, there was a lack of lower limb arterial vasoconstriction (-24% from before head-down tilt and -43% from before flight; P < .01), and the cerebral-femoral flow ratio increased less (-27% from before head-down tilt and -52% from before flight; P < .01). The lack of vasoconstriction was more pronounced in intolerant subjects (-25% from before head-down tilt and -48% from before flight) compared with tolerant subjects (-22% from before head-down tilt and -14% from before flight; P > .01). Also, the lack of a cerebral-femoral flow ratio increase was more pronounced in intolerant subjects (-49% from before head-down tilt and -55% from before flight; P < .01) than in tolerant subjects (-1% from before head-down tilt and -33% from before flight; P < .01). The cerebral flow deficit at the lower body negative pressure before head-down tilt was greater than 8% in 3 of the 4 intolerant head-down-tilt subjects and less than 8% in the 3 tolerant subjects. The 3 cosmonauts who were intolerant after flight had a preflight cerebral flow deficit greater than 8%, whereas the tolerant cosmonaut had a cerebral flow deficit less than 8%. CONCLUSION: Lack of lower limb vasoconstriction and a lower cerebral-femoral flow ratio during lower body negative pressure in disadapted subjects were associated with orthostatic intolerance. A cerebral flow deficit during lower body negative pressure before disadaptation allowed measurement of the predisposition of the subjects to become intolerant.

Adaptation of the left heart, cerebral and femoral arteries, and jugular and femoral veins during short- and long-term head-down tilt and spaceflights.

The objective of this investigation was to identify the major cardiovascular changes induced by exposure to real or simulated Og (spaceflights: 6, 14, 21 and 25 days, and 6 months; head down tilt, HDT: 10 h, 4, 5, 7, 30 and 42 days), with a minimum of counter-measures. The following cardiovascular data were measured by echocardiography and Doppler ultrasonography: left ventricle end-diastolic volume (LVDV), stroke volume (SV), cardiac output (CO), ejection fraction (EF), middle cerebral artery flow velocity (Qca), femoral artery flow velocity (Qfa), cerebral vascular resistance (Rca), femoral vascular resistance (Rfa), jugular vein cross-sectional area (Ajv), femoral vein cross-sectional area (Afv), heart rate (HR), and mean blood pressure (MBP). LVDV remained decreased compared to pre-HDT or pre-flight levels after 1 week of spaceflight or HDT (-8 to -13%, P<0.05), EF did not change. HR tended to increase (5-10%) during spaceflight and HDT, whereas MBP tended to decrease during flight, but did not change in HDT. These findings are consistent with the existence of a moderate and stable hypovolemia. Qca and Rca fluctuated between +10 and -10% from pre-HDT or pre-flight values, and always showed opposing variations. There was no significant decrease in cerebral perfusion. Lower-limb resistance (Rfa) remained decreased (-5% to -18%, P<0.05) throughout the flights or HDT after week 1. Ajv remained significantly enlarged (+40% P < 0.05) after 1 week in spaceflight or in HDT. Afv was enlarged in spaceflight after week 1 (+15% to +35%, P<0.05), whereas it decreased after 4-5 days of HDT (-20% to -35%, P<0.05). The cardiovascular system reached a new and stable equilibrium during flight and HDT within less than 1 week. With the exception of the femoral vein, there was no significant difference in either the amplitude or the time course of the cardiovascular changes in both situations after 1 week.

Cardiac, cerebral & lower limb hemodynamic changes, during HDT (5 days to 42 d) & space flights (7 days to 6 months).

The objective was to identify the major cardiovascular changes induced by exposure to real or simulated 0 g (spaceflights: 6 days, 14 d, 21 d, 25 d, 6 months; Head Down Tilt: 10 h, 4 d, 5 d, 7 d, 30 d, 42 d), with a minimum of countermeasure (Daily exercise in space, no exercise in HDT).

3D realtime echography and echography assisted by a robotic arm for investigating astronauts in the ISS from the ground.

As human will stay for long duration in isolated sites like ISS there will be a need to perform quick and reliable diagnosis to evaluate the gravity of the pathology in presence of clinical symptoms. Many pathological situations (abnormal heart rate, pericardic collection, mitral prolaps, cholecystis, renal lithiasis, normal and ectopic pregnancies, ovarian cyst, acute appendicitis, phlebitis ... ) may occur even if all the astronauts are absolutely normal and healthy preflight. Ultrasound echography and Doppler are non invasive methods easy to use in space and very well adapted and used in routine for such diagnosis at the hospital. The objective of the present project was to design a method that guarantee a reliable echographic diagnostic in an isolated site (space station or earth site) by a Medical Doctor located at the expert site that should be the Nasa control center for ISS. It is supposed that there is only a non sonographer person in the isolated site and that the transmission system (audio, video, numeric..) is the only link between the 2 sites. Two options are proposed: (a) A 3D realtime acquisition echograph that can record quickly all the echos of a volume containing the organ suspected to have a lesion, all these echo information being sent to the ground and processed by the ground experts, (b) A robotic arm that hangs the echo probe in the isolated site tele-operated (through sattelite network) from the ground by an expert in clinical ultrasound. (As the expert moves the joystick of his ground computer the robotic arm reproduces the same movements on the probe).

Doppler monitoring of the vascular resistance in the lower limbs during dipyridamole test in preparation for myocardial tomoscintigraphy.

OBJECTIVE: the aim of this work was to quantify the intensity of the vasodilation induced by dipyridamole used to simulate a stress test during a myocardial tomoscintigraphy. METHODS: Doppler measurements of the femoral artery and the thoracic aorta were made on 26 patients (11 men, 15 women), using transducers attached to the skin, measurements being performed every 2 min during the 10 min of the stress test. The following parameters were measured: (a) the vascular resistance index of the lower limbs defined as R(fa)=D/S with S and D, respectively, the maximum amplitude of the systolic wave and the maximum amplitude of the diastolic reflux measured on the Doppler femoral spectrogram; (b) the aortic and femoral blood flows obtained from the mean velocity on the Doppler spectrogram. RESULTS: 14 of the 26 patients (54%) showed a significant vasodilation (i.e. a decrease of R(fa) of more than 10%). Eighty-seven percent of the patients with a positive myocardial scintigraphy showed a vasodilation. Sixty-six percent of patients who had prior vasodilator treatment showed no vasodilation. A slight decrease in blood pressure was observed for vasodilated patients but also for non-vasodilated patients. The aortic flow increased slightly for all patients. CONCLUSIONS: Doppler monitoring of femoral vascular resistance is a useful method for quantifying the dipyridamole-induced vasodilation, and hence the stress level upon which the diagnostic efficiency of myocardial scintigraphy is depending. Our study demonstrates that testing with dipyridamole was inconclusive in 66% of patients who had already vasodilator treatment.

Evaluation of left ventricular systolic function by 3D echocardiography: a comparative study with X-ray angiography and radionuclide angiography.

OBJECTIVE: the aim of this study was to evaluate left ventricular systolic function by 3D ultrasound as compared to with radionuclide and X-ray angiographies. METHODS: one hundred and four patients were examinated by 3D ultrasound (3D-US) but only 72 examinations were successful. Thirty patients were investigated by 3D-US, M-mode US or bidimensional (2D) US, and X-ray angiography (group I) and 42 patients were investigated by 3D-US, M-mode, or 2D, and radionuclide angiography (group II). RESULTS: the correlation between ejection fraction (EF) evaluated by 3D-US and reference methods was found to be good and similar for the two groups (r=0.75; P<10(-4) for group I and r=0.76; P<10(-4) for group II). The correlation between EF calculated by conventional 2D-US and by reference methods was lower (r=0.60; P=0.04 for group I and r=0.54; P=0.001 for group II). The correlation between EF evaluated by 3D- and 2D-US was modest (r=0. 55; P=0.001 for the whole group). The correlation between 3D-US left ventricle end-diastolic volume (EDV) and end-systolic volume (ESV) and those evaluated by X-ray angiography was also modest (r=0.33; NS for EDV and r=0.60; P<10(-4) for ESV). The correlations between EDV and ESV in 3D-US, and those evaluated from radionuclide angiography were fairly good and in the same range (r=0.76; P<10(-4) and r=0.87; P<10(-4)). CONCLUSION: the 3D-US system using a rotating probe in an apical view is valuable for evaluation of left ventricular systolic function.

Cardiac, arterial and venous adaptation to weightlessness during 6-month MIR spaceflights with and without thigh cuffs (bracelets).

The objectives of this investigation were to study the effects of thigh cuffs (bracelets) on cardiovascular adaptation and deconditioning in 0 g. The cardiovascular parameters of six cosmonauts were measured by echocardiography, Doppler, and plethysmography, during three 6-month MIR spaceflights. Measurements were made at rest during preflight (-30 days), inflight (1, 3-4, and 5-5.5 months) without cuffs (morning) and after 5 h with cuffs, and during postflight (+3 and +7 days). Lower-body negative pressure (LBNP) measurements were performed 1 day after each resting session. Inflight values of left ventricle end-diastolic volume and stroke volume measured without the thigh cuffs (-8 to -24% and -10 to -16%, respectively, both P < 0.05) were lower than corresponding preflight values. The jugular and femoral vein cross-sectional areas (Ajv and Afv, respectively) were enlarged (Ajv: by 23-30%, P < 0.001; Afv: by 33-70% P < 0.01). The renal and femoral vascular resistances (Rra and Rfa, respectively) decreased (Rra: by -15 to -16%, P < 0.01; Rfa: by -5 to -11%, P < 0.01). Inflight, the thigh cuffs reduced the Ajv (by -12 to -20%, P < 0.02), but enlarged the Afv (Afv: by 9-20%, P < 0.02) and increased the vascular resistance (Rra: by 8-13%, P < 0.05; Rfa: by 10-16%, P < 0.01) compared to corresponding inflight, without-cuffs values. During LBNP (-45 mmHg, where 1 mmHg = 133.3 N/ m2), Rfa and the ratio between cerebral and femoral blood flow (Qca/Qfa) increased less inflight and postflight (+25% for Rfa and +30% for Qca/Qfa) than during preflight (60% for Rfa and 75% for Qca/Qfa, P < 0.01). This reduced vasoconstrictive response and less efficient flow redistribution toward the brain was associated with orthostatic intolerance during postflight stand tests in all of the cosmonauts. The calf circumference increased less inflight and postflight (6% P < 0.05) than preflight (9% P < 0.05). The vascular response to LBNP remained similarly altered throughout the flight. The thigh cuffs compensated partially for the cardiovascular changes induced by exposure to 0 g, but did not interfere with 0 g deconditioning.

Real-time 3-D ultrasound acquisition and display for cardiac volume and ejection fraction evaluation.

The objective of this study was to test if three-dimensional (3-D) ultrasound (US) provides accurate determination of the cardiac volumes and ejection fraction. The 3-D device (Model 1-Volumetrics, ) is a 3-D acquisition system using a 2-Mhz matrix probe that insonates the whole cardiac volume in a 4-chamber view and collects the entire backscattered US echoes from this volume within one cardiac cycle. The complete 3-D US information stored in the memory can then be cut into 2-D views of any arbitrary orientation. For volume determination, the best 4-chamber view was selected into the memory, then 6 transverse views were displayed at different depths along the ventricle long axis, and the contour of the ventricle was drawn on each of these views. The left ventricle volume in diastole (LVDV) and the ejection fraction (EF) obtained by 3-D US were compared with those from x-ray and isotopic angiographies, and 2-D echo-time motion (2-D Echo-TM). The variations in stroke volume (SV) during a stand test, measured by 3-D US, and aortic Doppler were compared. The correlation between EF evaluated from 3-D US and x-ray or isotopic angiographies was found to be good (r = 0.80 p < 0.001; r = 0.86 p < 0.001), but lower with 2-D Echo-TM (r = 0.59 p < 0.001). For LVDV, the correlation was acceptable with x-ray angiography (r = 0.75 p < 0.001), but much lower with isotopic angiography and 2-D Echo-TM (r = 0.47 p < 0.001; r = 0.55 p < 0.001). A good correlation was also found between the SV changes measured by 3-D US and aortic Doppler (r = 0.79 p < 0.001).

Influences of thigh cuffs on the cardiovascular system during 7-day head-down bed rest.

Thigh cuffs, presently named "bracelets," consist of two straps fixed to the upper part of each thigh, applying a pressure of 30 mmHg. The objective was to evaluate the cardiac, arterial, and venous changes in a group of subjects in head-down tilt (HDT) for 7 days by using thigh cuffs during the daytime, and in a control group not using cuffs. The cardiovascular parameters were measured by echography and Doppler. Seven days in HDT reduced stroke volume in both groups (-10%; P < 0.05). Lower limb vascular resistance decreased more in the cuff group than in the control group (-29 vs. -4%; P < 0.05). Cerebral resistance increased in the control group only (+6%; P < 0.05). The jugular vein increased (+45%; P < 0.05) and femoral and popliteal veins decreased in cross-sectional area in both groups (-45 and -8%, respectively; P < 0.05). Carotid diameter tended to decrease (-5%; not significant) in both groups. Heart rate, blood pressure, cardiac output, and total resistance did not change significantly. After 8 h with thigh cuffs, the cardiac and arterial parameters had recovered their pre-HDT level except for blood pressure (+6%; P < 0.05). Jugular vein size decreased from the pre-HDT level (-21%; P < 0.05), and femoral and popliteal vein size increased (+110 and +136%, respectively; P < 0.05). The thigh cuffs had no effect on the development of orthostatic intolerance during the 7 days in HDT.

Accuracy of the main Doppler methods for evaluating the degree of carotid stenoses (continuous wave, pulsed wave, and color Doppler).

OBJECTIVE: To compare the accuracy of the main Doppler methods for quantifying the degree of carotid stenoses in 133 patients. METHOD: seven parameters were measured: maximum velocity (V.max) inside the stenosis (by pulsed wave [PW]), grade and index of spectral disturbance (STI) at the outlet of the stenosis (by PW and continuous wave [CW]), ratio of velocities I(IC/CC) in the internal and common carotid (by PW), and ratio of vessel cross-section and residual lumen area (%Color) inside the stenosis (color Doppler). The reference methods were the grades of spectral disturbance and the STI (by CW), already validated against endarterectomy specimens. CONCLUSION: For poststenosis measurements, a high correlation was found between the grades or STI measured by PW and CW (reference method). The measurement of these parameters was easier in PW mode. For intrastenotic velocity, the increase in V.max was not proportional to the degree of stenosis, and V.max showed large fluctuations for the same degree of stenosis. I(IC/CC) also showed large fluctuations for the same degree of stenosis. The correlation was poor for these two parameters, which could only be used for detecting two groups of stenosis: >75% or >90% in area. Color Doppler (conventional and power) routinely overestimated the degree of stenosis by 10%-15% but correlated better with the reference method and was more accurate and reproducible than V.max. A special procedure can be used to avoid this overestimation and improve the accuracy of the color Doppler.

Effect of the thigh-cuffs on the carotid artery diameter jugular vein section and facial skin edema: HDT study.

Thigh cuffs, currently named "bracelets", consist of 2 straps fixed to the upper part of each thigh, applying a pressure of approximately 30 mmHg. Initially the thigh cuffs were designed and used to improve th comfort of the cosmonauts during their stay in zero g. Except a reduction of the "puffy face" aspect no other morphological nor hemodynamic significant change was reported even when the cosmonauts weared these thigh cuffs inflight for 10h per day during several weeks or months. The objective was to evaluate the distal arterial, venous and skin changes in a group of 8 subjects in HDT for 7 days and using thigh cuffs 8h during daytime, and in a control group also in HDT for 7d but not using cuff.

Femoral to cerebral arterial blood flow redistribution and femoral vein distension during orthostatic tests after 4 days in the head-down tilt position or confinement.

The first objective of this study was to confirm that 4 days of head-down tilt (HDT) were sufficient to induce orthostatic intolerance, and to check if 4 days of physical confinement may also induce orthostatic intolerance. Evidence of orthostatic intolerance during tilt-up tests was obtained from blood pressure and clinical criteria. The second objective was to quantify the arterial and venous changes associated with orthostatic intolerance and to check whether abnormal responses to the tilt test and lower body negative pressure (LBNP) may occur in the absence of blood pressure or clinical signs of orthostatic intolerance. The cerebral and lower limb arterial blood flow and vascular resistance, the flow redistribution between these two areas, and the femoral vein distension were assessed during tilt-up and LBNP by ultrasound. Eight subjects were given 4 days of HDT and, 1 month later, 4 days of physical confinement. Tilt and LBNP test were performed pre- and post-HDT and confinement. Orthostatic intolerance was significantly more frequent after HDT (63%) than after confinement (25%, P < 0.001). Cerebral haemodynamic responses to tilt-up and LBNP tests were similar pre- and post-HDT or confinement. Conversely, during both tilt and LBNP tests the femoral vascular resistances increased less (P < 0.002), and the femoral blood flow reduced less (P < 0.001) after HDT than before HDT or after confinement. The cerebral to femoral blood flow ratio increased less after HDT than before (P < 0.002) but remained unchanged before and after confinement. This ratio was significantly more disturbed in the subjects who did not complete the tilt test. The femoral superficial vein was more distended during post-HDT LBNP than pre-HDT or after confinement (P < 0.01). In conclusion, 4 days of HDT were enough to alter the lower limb arterial vasoconstriction and venous distensibility during tilt-up and LBNP, which reduced the flow redistribution in favour of the brain in all HDT subjects. Confinement did not alter significantly the haemodynamic responses to orthostatic tests. The cerebral to femoral blood flow ratio measured during LBNP was the best predictor of orthostatic intolerance.

Cardiovascular echographic and Doppler parameters for the assessment of orthostatic intolerance.

OBJECTIVE: To quantify the hemodynamic changes associated with orthostatic intolerance. METHODS: The aortic flow, the cerebral and lower limb arterial flow and resistance, the flow redistribution between these two areas, and the femoral vein distension were assessed during two orthostatic tests (tilt-up and LBNP:lower body negative pressure) by echography and doppler. Eight subjects stayed 4 days in HDT (head down tilt) in order to induce orthostatic intolerance, and 1 month later, 4 days in confinement. Tilt and LBNP were performed pre- and post-HDT and confinement. RESULTS: Orthostatic intolerance was significantly more frequent after HDT (63%) than after confinement (25%). At rest, the stroke volume was significantly decreased after HDT (-16%, P<0.01) but not after confinement. Cardiac and cerebral hemodynamic responses to tilt-up and LBNP were similar pre- and post-HDT or confinement. Conversely, during both tilt and LBNP the femoral resistances increased less (P<0.002), and the femoral flow reduced less (P<0.001) after HDT than before HDT or after confinement. The cerebral to femoral flow ratio increased less after HDT than before (P<0.002) but remained unchanged before and after confinement. This ratio was significantly more disturbed on the tilt test non-finisher subjects. The femoral superficial vein was more distended during post-HDT LBNP than pre-HDT or after confinement (IP<0.01). In conclusion, 4 days in HDT were enough to alter the lower limb arterial and venous response to tilt-up and LBNP and reduced the flow redistribution in favor of the brain in all subjects. Confinement did not alter significantly the hemodynamic response to orthostatic tests. CONCLUSION: The femoral resistance index, and the cerebral to femoral flow ratio measured by doppler during LBNP were the best predictors for orthostatic intolerance.

Cardiac hemodynamics at rest and during LBNP after 4 days and 6 weeks in HDT.

The first objective was to assess the left ventricle function at rest, at the end of a short term (4 days) HDT, and at the end of a long term (6 weeks) HDT. The second objective was to check if these short and long HDT induced any abnormal cardiac hemodynamic response to LBNP (lower body negative pressure) test that could be related to orthostatic intolerance.