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.

[Doppler monitoring of fetal circulation from multiple arteries over several days to improve evaluation of fetal prognosis]. / Monitoring Doppler de la circulation foetale sur plusieurs artères et sur plusieurs jours pour une meilleure prédiction du devenir foetal.

Intrauterine growth retardation and fetal hypoxia are currently related to placental insufficiency. Fetal biometry assessed by echography is entirely adapted to follow the growth and integrity of the principal fetal organs. Hypoxia induces an hemodynamic adaptation which can be detected and quantified by Doppler. The objective of this article is to review the evolution of the fetal Doppler practice for the last 20 years and especially to show that isolated Doppler measurement and only from one site (umbilical or cerebral or aortic) have a moderate negative predictive value of fetal outcome, compared to the study of the fetal hemodynamic evolution (degradation) from several sites and during several days. We will insist on the fact that (a) umbilical Doppler only gives information on placental blood flow and this information does not reflect neither the adaptation to hypoxia nor the consequences of this adaptation, (b) cerebral Doppler accounts for the vascular response to the pO(2) reduction but it does not allow to predict the consequences of this response, (c) the simultaneous study of the placental hemodynamic time course degradation and the cerebral vascular response to hypoxia allows quantification of the cumulative deficit of fetal oxygenation during this period and evaluation the adverse consequences of a sustained flow redistribution toward the brain. Finally, if cerebral vasodilation in response to hypoxia can be considered as a physiological compensatory mechanism, it is associated after several days to the appearance of irreversible fonctional (abnormal fetal heart rate) or organic (cerebral lesions) abnormalities. Adverse effects of this process are illustrated during episodes of acute hypoxia (malaria crisis of several days) or during sustained exposure of the fetus to hypoxia (pregnancy-induced hypertension).

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.

Fetal vascular response to maternal deep-vein thrombosis and subsequent heparin therapy.

The fetal umbilical and cerebral Doppler changes were recorded in a 27-year-old primigravida referred at 38 weeks for the treatment of an iliofemoral vein thrombosis. On admission and in comparison to a previous Doppler assessment systematically performed during growth scan at 37 weeks, the umbilical resistance index (URI) demonstrated an increase of 19%, the cerebral resistance index (CRI) a reduction of 15% and the cerebral-umbilical (C/U) ratio a decrease of 29% reaching the lowest value of 1.05. Under intravenous heparin therapy, Doppler normalisation was observed within 1 week and the mother delivered a healthy, non-hypoxemic baby by caesarean section at 39 weeks and 2 days. This observation suggests that deep-vein thrombosis (DVT) may, in some cases, be responsible for transient fetal hypoxia. Moreover, treatment with intravenous heparin had a direct beneficial effect on the fetus as it improved placental hemodynamics and fetal oxygenation.

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).

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.