Changes In Blood Flow Velocity Research Articles

Оценка латерализации церебральной гемодинамики при выполнении вербальных мнестических заданий методом функциональной транскраниальной допплерографии

There are the preliminary results of the research of interhemispheric asymmetry of cerebral hemodynamics during the performance of auditory-verbal and visual memory tasks with the use of functional transcranial doppler ultrasound (fTCD). The fTCD is considered as a non-invasive and objective method for assessment the dominant hemisphere for verbal functions. The aim of two experiments was to analyze the effect of a) different types of verbal and nonverbal tasks and b) the conditions of the mnestic activity performance (memorize and recognize) on the changes of blood flow velocity in left and right hemispheres in 62 healthy subjects. There are preliminary results of possible application fTCD to identify the dominant hemisphere for speech functions with combination of concrete verbal cognitive tasks and condition of its presentation.

Hypertonic saline: a brief overview of hemodynamic response and anti-inflammatory properties in head injury.

Hypertonic saline: a brief overview of hemodynamic response and anti-inflammatory properties in head injury.

Pregnany-dependent blood flow velocity changes in lower extermities veis in venous insufficiency

Venous insufficiency in pregnancy is associated witch an increased risk of complications. The aim of the study was to analyse the venous system changes of the lower limbs during pregnancy and puerperium with or without venous insufficiency The research was carried out on pregnant women divided into two groups according to the presence or lack of venous insufficiency The venous system was examined four times: between 11-14th, 18-22nd, 28-32nd gestational week and at the 6th week of puerperium. The doppler examination included the measurement of the blood flow velocity in selected deep veins of the lower limbs: common femoral vein, the superficial femoral vein and the popliteal vein. Consecutively the changes in the blood flow velocity during pregnancy and puerperium were compared between groups and finally to the results obtained in the 1st trimester The analysis of the blood flow showed that the blood flow velocity was statistically lower in the group with venous insufficiency Velocity changes in time showed, in majority of cases, a substantial reduction in the blood flow velocity in the third trimester in both groups. This blood flow velocity increases during the puerperium and does not differ from those observed in the first trimester Thus, the tendency of changes in the blood flow velocity were similar in character in both groups. The pregnancy related changes in venous system of lower extremities showed the reduction of blood flow velocity with advancing gestational age and were more evident in pregnancy complicated by venous insufficiency

Simultaneous imaging of blood flow dynamics and vascular remodelling during development.

Normal vascular development requires blood flow. Time-lapse imaging techniques have revolutionised our understanding of developmental biology, but measuring changes in blood flow dynamics has met with limited success. Ultrasound biomicroscopy and optical coherence tomography can concurrently image vascular structure and blood flow velocity, but these techniques lack the resolution to accurately calculate fluid forces such as shear stress. This is important because hemodynamic forces are biologically active and induce changes in the expression of genes important for vascular development. Regional variations in shear stress, rather than the overall level, control processes such as vessel enlargement and regression during vascular remodelling. We present a technique to concurrently visualise vascular remodelling and blood flow dynamics. We use an avian embryonic model and inject an endothelial-specific dye and fluorescent microspheres. The motion of the microspheres is captured with a high-speed camera and the velocity of the blood flow in and out of the region of interest is quantified by micro-particle image velocitymetry (µPIV). The vessel geometry and flow are used to numerically solve the flow physics with computational fluid dynamics (CFD). Using this technique, we can analyse changes in shear stress, pressure drops and blood flow velocities over a period of 10 to 16 h. We apply this to study the relationship between shear stress and chronic changes in vessel diameter during embryonic development, both in normal development and after TGFβ stimulation. This technique allows us to study the interaction of biomolecular and biomechanical signals during vascular remodelling using an in vivo developmental model.

Morphological and Biomechanical Differences in the Elastase and AngII apoE(-/-) Rodent Models of Abdominal Aortic Aneurysms.

An abdominal aortic aneurysm (AAA) is a potentially fatal cardiovascular disease with multifactorial development and progression. Two preclinical models of the disease (elastase perfusion and angiotensin II infusion in apolipoprotein-E-deficient animals) have been developed to study the disease during its initiation and progression. To date, most studies have used ex vivo methods to examine disease characteristics such as expanded aortic diameter or analytic methods to look at circulating biomarkers. Herein, we provide evidence from in vivo ultrasound studies of the temporal changes occurring in biomechanical parameters and macromolecules of the aortic wall in each model. We present findings from 28-day studies in elastase-perfused rats and AngII apoE−/− mice. While each model develops AAAs specific to their induction method, they both share characteristics with human aneurysms, such as marked changes in vessel strain and blood flow velocity. Histology and nonlinear microscopy confirmed that both elastin and collagen, both important extracellular matrix molecules, are similarly affected in their levels and spatial distribution. Future studies could make use of the differences between these models in order to investigate mechanisms of disease progression or evaluate potential AAA treatments.

Perioperative anesthesia information provided by transcranial doppler ultrasound

Background Transcranial doppler (TCD) is an examination for cerebral blood flow dynamics characteristics.It can be used to monitor the change of cerebral blood flow velocity in the process of anesthesia and the formation of blood clots,to provide information for brain protection.It has the advantages of easy operation,real-timing and continuous monitoring.Objective To introduce the application and progress of TCD in perioperation recently.Content TCD can provide relevant information,such as blood flow velocity,pulse rhythm change,vascular stenosis and thrombosis,intracranial pressure,etc.Trend With lots of advantages,TCD for perioperative period has broad prospects in the future. Key words: Transcranial doppler; Anesthesia; Cerebral blood flow

Ready-to-Use Supplementary Food Supplements Improve Endothelial Function, Hemoglobin and Growth in Tanzanian Children with Sickle Cell Anaemia: The Vascular Function Intervention Study (V-FIT), a Random Order Crossover Trial

Introduction: Endothelial function is impaired in sickle cell anemia (SCA) and may be prognostic of severity of pathophysiology underlying many complications. Poor nutritional status is documented in SCA in all income settings, yet no strategies exist to improve nutrition. Poor nutritional status and hemoglobin predict death and hospitalization in Tanzanian SCA patients (Cox, et al. Haematologica 96, 2011, Makani et al. PloSONE 6, 2011). The objectives are to determine the combined effect of two ready-to-use-supplementary food (RUSF) interventions on the primary endpoints of endothelial function, assessed by flow mediated dilatation (FMD), growth and body composition and hemoglobin (secondary endpoint).Methods: Tanzanian children (N=119) (HbSS) aged 8-11.9 years were enrolled in V-FIT (ISRCTN74331412/NCT01718054) in Aug to Nov 2012. Children received in random order a daily RUSF providing 500 kcal, 1 RDA of vitamins and minerals & 1mg folate (Nutriset, France), plus weekly anti-malarial prophylactic chloroquine syrup (150/225mg base) (Wallace manufacturing chemicals, UK), or a vascular-RUSF (RUSFv) fortified with arginine and citrulline (average 0.2g/kg/d & 0.1g/kg/d) plus daily chloroquine syrup (3mg base/kg/d). Patients and investigators were blind to the different interventions. Each intervention was received for 4 months with 4 month washout periods on either side (Figure 1A). Clinic visits were conducted at baseline and at the end of each intervention/washout period when endothelium-dependent and -independent vasodilatation were assessed (Donald et al. JACC 51, 2008), plus height, weight and body composition by impedance (Tanita BC418). Random effects models were used, adjusting for repeated measures within individuals. In multivariable analyses models were a priori adjusted for gender. Possible temporal effects were modelled via Fourier transformation of visit dates and included in models for growth and hemoglobin. Effects of the interventions on FMDmax were adjusted for arterial diameter before vasodilation induction, which was negatively correlated with FMDmax and for magnitude of reactive hyperaemia during induction of vasodilation, which was not correlated with FMDmax.Results: 115/119 (60% male; mean age at enrolment 10.0, 95% CI 9.8 – 10.2 years) enrolled patients completed the trial and all clinic visits. Endpoints at baseline and the adjusted and unadjusted effects of the interventions are shown in Table 1. FMDmax, baseline brachial diameter, absolute change in blood flow velocity during reactive hyperemia, hemoglobin, height velocity, weight and lean mass gain all increased on the RUSF (Fig 1B-F).Discussion: We demonstrate that providing extra protein, energy and micronutrients improves hemoglobin, vascular endothelial function and growth. It is possible that the effects observed are limited to the RUSFv, and/or from unadjusted for temporal effects. Unblinded analysis of the effect of RUSFv vs. RUSF on these endpoints, plasma amino acids and arginase are planned. Currently the only intervention for children with SCA is hydroxyurea, which although it improves hemoglobin and reduces hemolysis, does not appear to affect growth while its effect on vascular physiology is unknown (Wang et al. J Pediatr 140, 2002). In addition to specific nutrients, general improvement in nutrition may result in improvement in important intermediate endpoints in SCA. Future research should investigate effects of nutritional supplementation on clinical endpoints.Abstract 4087. Table 1Endpoints at enrolment and combined effect of RUSF interventions.Baseline N=119RUSF coefficient [95% CI]P-valueAdjusted RUSF coefficient [95% CI]Adjusted P-valueEndothelial function, mean [SD]FMDmax %7.66 [3.37]0.66 [0.15 – 1.17]0.0110.98 [0.42 – 1.54]0.001Baseline brachial diameter, mm2.61 [0.35]0.05 [0.03 – 0.09]<0.001--Reactive hyperemia absolute, m/s0.69 [0.22]0.034 [0.004 – 0.065]0.026--Anemia, mean [95% CI]Hemoglobin, g/dl7.5 [7.3 – 7.7]0.29 [0.20 – 0.37]<0.0010.34 [0.22 – 0.46]<0.001Anthropometry, mean [95% CI]Height cm126.5 [125.2 – 127.8]----Linear growth velocity, cm/yr-0.46 [0.08 – 0.83]0.0180.51 [0.01 – 1.02]0.053Weight, kg22.8 [22.1 – 23.5]----Weight gain, kg/yr-1.37 [0.83 – 1.91]<0.0011.98 [1.25 – 2.73]<0.001Whole body fat free mass, kg18.6 [18.1 – 19.1]----Fat free mass gain, kg/yr-0.89 [0.48 – 1.30]<0.0010.93 [0.36 – 1.50]0.001 [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Changes in cerebral blood flow velocity in supine and sitting position in patients with aneurysmal subarachnoid hemorrhage

Early mobilization in intensive care units (ICU) provides respiratory, neurological and cardiovascular benefits in hospitalized patients. However, the orthostatic effects of changing from a supine to a sitting position may interfere with cerebral hemodynamics of patients with aneurysmal subarachnoid hemorrhage (aSAH). To describe the changes in mean cerebral blood flow velocity (MCBFV) in supine and sitting position, in adult patients with aSAH, with asymptomatic vasospasm (AVS) or without vasospasm (VS) at a neurosurgical ICU. Descriptive case series study in 21 patients with aSAH, both with and without VS. They were positioned in a supine 30° position and then seated at the edge of bed for six minutes. MCBFV was measured by transcranial Doppler (TCD), and hemodynamic variables in both positions were registered. After this basal assessment and for 21 days after the episode of SAH, patients were seated once a day and signs of VS were recorded. No significant changes in MCBFV or hemodynamic variables were detected during position changes, except for an increase in heart rate in the sitting position. No patient with AVS at the onset, had symptomatic VS during the 21 days of follow up when patients were seated. Among patients with a normal MCBFV at baseline, five patients (24%) had VS at a mean of three days after the first time that they were seated on the edge of bed. Sitting patients at the edge of the bed is a safe mobilization alternative for patients who suffered aSAH who did not have VS or had AVS.

Possible influences of exercise-intensity-dependent increases in non-cortical hemodynamic variables on NIRS-based neuroimaging analysis during cognitive tasks: Technical note.

[Purpose]Functional near-infrared spectroscopy (fNIRS) provides functional imaging of cortical activations by measuring regional oxy- and deoxy-hemoglobin (Hb) changes in the forehead during a cognitive task. There are, however, potential problems regarding NIRS signal contamination by non-cortical hemodynamic (NCH) variables such as skin blood flow, middle cerebral artery blood flow, and heart rate (HR), which are further complicated during acute exercise. It is thus necessary to determine the appropriate post-exercise timing that allows for valid NIRS assessment during a task without any increase in NCH variables. Here, we monitored post-exercise changes in NCH parameters with different intensities of exercise.[Methods]Fourteen healthy young participants cycled 30, 50 and 70% of their peak oxygen uptake (Vo2peak) for 10 min per intensity, each on different days. Changes in skin blood flow velocity (SBFv), middle cerebral artery mean blood velocity (MCA Vmean) and HR were monitored before, during, and after the exercise.[Results]Post-exercise levels of both SBFv and HR in contrast to MCA Vmean remained high compared to basal levels and the times taken to return to baseline levels for both parameters were delayed (2-8 min after exercise), depending upon exercise intensity.[Conclusion]These results indicate that the delayed clearance of NCH variables of up to 8 min into the post-exercise phase may contaminate NIRS measurements, and could be a limitation of NIRS-based neuroimaging studies.

Simultaneous Analysis of Far Infrared Signals From Periorbital and Nostril Areas for Nonintrusive Lie Detection: Performance From Real Case Study

This paper highlights our simultaneous analysis of two-dimensional far-infrared data around the two periorbital and the nostril areas for nonintrusively evaluating the deception level of the subject. In our proposed approach, measured changes in maximum skin temperatures around two periorbital regions are converted to the change in the relative blood flow velocity. A signature of the respiration pattern is also simultaneously determined in terms of the ratio of the measured maximum and minimum temperatures in the nostril area. Our simultaneous analysis of these two far-infrared signatures is similar to the standard polygraph test in that more than one of our involuntary reflexes is examined at once. Our two-year field test study covers 18 examination tests on subjects who are suspected in involving in real crime cases in Thailand. Based on our automatic baseline classification and scoring criteria, we obtain a promising classification rate of 88.9%, which is about 10% improvement compared to our analysis using far-infrared data from either the periorbital or nostril area alone.

Attenuated cerebral vasodilatory capacity in response to hypercapnia in college-aged African Americans.

African Americans (AAs) have increased risk for cardiovascular, cerebral vascular and metabolic disease, including hypertension, stroke, coronary artery disease, metabolic syndrome and type II diabetes, relative to Caucasian Americans (CAs). While it is accepted that endothelial function is impaired in AAs, less is known regarding their cerebral vasodilatory capacity in response to hypercapnia. We hypothesized that AAs have a reduction in the total range of change in cerebral blood flow velocity (CBFV) measured in the middle cerebral artery and an index of cerebral vascular conductance (CVCI) in response to changes in the partial pressure of end-tidal carbon dioxide () during rebreathing-induced hypercapnia when compared with CAs. Twenty-one healthy, college-aged AA (10 male) and 21 age- and sex-matched CA (10 male) subjects participated in this study. A four-parameter logistic regression was used for curve fitting the responses of CBFV and CVCI relative to changes in . The total ranges of change in CBFV (101 ± 18 versus 69 ± 23%; P < 0.001) and CVCI (83 ± 21 versus 58 ± 21%; P < 0.001) as well as the maximal increase in CBFV (205 ± 24 versus 169 ± 24%; P < 0.001) and CVCI (188 ± 30 versus 154 ± 19%; P < 0.001) were reduced during hypercapnia in AAs relative to CAs despite a similar increase in (change, 15 ± 3 versus 15 ± 3 mmHg; P = 0.65). In conclusion, these data indicate that AAs have attenuated cerebral vascular capacity to respond to hypercapnia when compared with CAs.

A comparison of dynamic cerebral autoregulation across changes in cerebral blood flow velocity for 200 s.

Objectives: The dynamic interaction between blood pressure (BP) and cerebral blood flow velocity (CBFV) is not fully understood, especially for CBFV changes lasting longer than 50 s. The interaction between BP and CBFV is relatively well characterized for periods <50 s using transfer function (TF) estimations of phase, gain, and coherence. We used TF estimations to compare the phase and gain for periods >50 s with those for periods <50 s.Materials and Methods: BP and CBFV (of the middle cerebral artery) were simultaneously recorded in 23 healthy subjects (10 men, 13 women, mean age 35 ± 10 years) under normo- and hypocapnia (induced by hyperventilation). TF and coherence estimations were based on Welch's periodogram method with a windowing of 200 s (frequency resolution, 0.005 Hz, corresponding to a period of 200 s). Means of the phase, gain, and coherence were calculated over frequency periods of 0.005–0.02 Hz (sVLF), 0.02–0.07 Hz (VLF), 0.07–0.15 Hz (LF), and 0.15–0.40 Hz (HF) and analyzed using the t-test and Pearson correlation.Results: Compared with the VLF range, normo- and hypocapnia phases were slightly but significantly lower in sVLF, while gain and coherence were not different. Hypocapnia induced significant (mostly p < 0.01) phase increases and gain decreases as well as coherence decreases in all frequency ranges. The phase and gain correlated significantly (−0.87 < r > −0.99) (p < 0.001) and inversely in all frequency ranges <0.15 Hz under both respiratory conditions. In some instances, the phase indicated disturbed autoregulation.Conclusion: In the frequency range <0.15 Hz, the phase and gain correlate highly and linearly with high consistency. The phase, gain, and coherence were similar in sVLF and VLF ranges. The phase was slightly lower in the sVLF range than in the VLF range. Notably, the data suggest that autoregulatory failure may occur in healthy persons.

Assessment of Cerebrovascular Reactivity during Resting State Breathing and Its Correlation with Cognitive Function in Hypertension

Background: Hypertension is associated with cognitive deficits, particularly executive function, and decreased cerebral microvascular responsiveness to CO₂ (CO₂ vasoreactivity). The relation between CO₂ vasoreactivity and executive function is not known. Protocols to assess CO₂ vasoreactivity are cumbersome and require inhaling a CO₂-enriched gas. We explored the ability to measure CO₂ vasoreactivity using end-tidal CO₂ fluctuations during normal breathing and the association of this measure with cognitive function in hypertension. Methods: Executive function (Trail-Making Test parts A/B), memory, attention and blood flow velocity (BFV) in the middle cerebral artery using transcranial Doppler were measured in hypertensive subjects who were tapered off their treatment for 3 weeks. BFV was measured while sitting and normally breathing for 5 min, followed by breathing 5% CO₂ gas and hyperventilation for 2 min each. We calculated CO₂ vasoreactivity as the rate of BFV change from hypoventilation to hyperventilation, and as a model-derived measure using the normal breathing data. The latter was derived using nonlinear principal dynamic modes (PDM), which modelled the dynamic effect of fluctuations in end-tidal CO₂ and blood pressure upon BFV during normal room-air respiration. Multiple regression analyses were used to correlate cerebral hemodynamics with cognitive measures. Results: Data were collected from 41 individuals with hypertension (mean age 71 years, 24% African Americans, 61% women, off antihypertensive therapy). Lower CO₂ vasoreactivity was associated with a worse executive function test score using both calculation methods: p value using the hyper/hypoventilation data was 0.04 and from the PDM analysis was 0.009. PDM calculations showed a stronger correlation with executive function (0.41 vs. 0.21 using the hyper/hypoventilation data). There were no associations with memory or attention measures. There was a weak but statistically significant correlation between the two calculation methods of CO₂ vasoreactivity (R² = 14%, p = 0.02). Conclusion: This study suggests that the decrease in CO₂ vasoreactivity in hypertension is associated with lower executive function. This may offer new insight into the vascular underpinning of cognitive decline in hypertension. We demonstrate that calculating CO₂ vasoreactivity is possible during normal breathing. If replicated in future studies, this may offer a more convenient clinical way to assess CO₂ vasoreactivity in hypertension and cognitive disorders.

Impaired cerebrovascular reactivity in the early phase of subarachnoid hemorrhage in good clinical grade patients does not predict vasospasm.

Subarachnoid hemorrhage (SAH) alters cerebrovascular reactivity (CVR) to carbon dioxide (CO2), which may be related to an increased risk of delayed ischemic neurological deficits (DINDs). We report the results of bedside CVR testing in the acute phase of SAH in good clinical grade patients without established vasospasm or signs of DIND. Eighteen patients with SAH and 26 healthy subjects underwent CVR testing using transcranial Doppler with standardized changes in CO₂. None of the patients had clinical or radiological evidence of vasospasm or DIND at time of testing. A CVR index was calculated as the change in the middle cerebral artery blood flow velocity (MCAv) divided by the change in the end-tidal CO₂partial pressure (PCO₂), ∆ MCAv/Δ PCO₂, and values were compared with controls. SAH patients had lower CVR when compared with normal controls (p = 0.0001 and p = 0.0094, respectively). Impaired CVR was not correlated with future vasospasm (p = 0.2). Patients with SAH had significantly lower CVR indexes compared with healthy controls. Although impaired CVR was present in 50 % of the patients early after SAH, no correlation with later occurrence of DINDs was found.

Advice on Lifestyle Changes (Diet, Red Wine and Physical Activity) Does Not Affect Internal Carotid and Middle Cerebral Artery Blood Flow Velocity in Patients with Carotid Arteriosclerosis in a Randomized Controlled Trial

Background: A Mediterranean diet, with and without small daily amounts of red wine, and physical activity reduce the risk of cerebrovascular disease and improve cognition. An increase in cerebral blood flow may be the underlying mechanism. Under normal conditions, cerebral blood flow velocity changes in the internal carotid arteries and in large basal cerebral arteries correlate closely with cerebral blood flow changes, as the diameter of these vessels hardly changes and only the smaller vessels downstream change their diameter. Methods: A prospective randomized controlled trial was performed in 108 patients with carotid atherosclerosis (mean age 64 years, 67% men, 66% on statin therapy). Half of them were advised to follow a polyphenol-rich modified Mediterranean diet including 1-2 tomatoes, 3-5 walnuts and a bar of dark chocolate (25 g) a day and to perform moderate physical exercise for 30 min/day (lifestyle changes). Within these two groups, half of the patients were randomized either to avoid any alcohol or to drink 100 ml of red wine (women) or 200 ml of red wine (men) daily. Bilateral middle cerebral and internal carotid blood flow velocity (peak systolic, peak end-diastolic and mean) was measured at baseline and after 4 and 20 weeks using colour-coded duplex ultrasound. Insonation depth and insonation angle were used to identically place the sample volume during follow-up investigations. A general linear model with Tukey-Kramer adjustment for multiple comparisons was used to assess the primary end points. For the analysis we used the mean values of the right and left artery. Results: Neither lifestyle changes nor red wine had an effect on peak systolic, peak end-diastolic or mean cerebral blood flow velocity. Conclusions: Advice on lifestyle changes, including a modified polyphenol-rich Mediterranean diet, a glass of red wine daily and physical exercise, did not affect middle cerebral and internal carotid blood flow velocity in our patient group with carotid atherosclerosis. An increase in cerebral blood flow is thus unlikely to be the cause of the reduced risk of cerebrovascular disease and improved cognitive functioning described in the literature. One possible explanation for the fact that blood flow velocity was not affected by red wine, diet and physical activity advice is that two thirds of our patients were already on statin therapy. Statins increase cerebral blood flow and vasomotor reactivity via nitric oxide.

Hemodynamic monitoring of middle cerebral arteries during cognitive tasks performance.

The aim of this study was to obtain temporal pattern and hemispheric dominance of blood flow velocity (BFV) changes and to assess suitability of different cognitive tasks for monitoring of BFV changes in the middle cerebral arteries (MCA). BFV were recorded simultaneously in MCA during performance of phonemic verbal fluency test (pVFT), Trail Making Tests A and B (TMTA and TMTB) and Stroop tests in 14 healthy, right-handed volunteers aged 20-26 years. A significant increase of BFV in both MCA was obtained during performance of all cognitive tasks. Statistically significant lateralization was found during performance of Stroop test with incongruent stimuli, while TMTB was found to have the best activation potential for MCA. Our findings specify TMTB as the most suitable cognitive test for monitoring of BFV in MCA.

An In Vivo Rat Model of Artery Buckling for Studying Wall Remodeling

Theoretical modeling and in vitro experiments have demonstrated that arterial buckling is a possible mechanism for the development of artery tortuosity. However, there has been no report of whether artery buckling develops into tortuosity, partially due to the lack of in vivo models for long-term studies. The objective of this study was to establish an in vivo buckling model in rat carotid arteries for studying arterial wall remodeling after buckling. Rat left carotid arteries were transplanted to the right carotid arteries to generate buckling under in vivo pressure and were maintained for 1 week to examine wall remodeling and adaptation. Our results showed that a significant buckling was achieved in the carotid arterial grafts with altered wall stress. Cell proliferation and matrix metalloprotinease-2 (MMP-2) expression in the buckled arteries increased significantly compared with the controls. The tortuosity level of the grafts also slightly increased 1 week post-surgery, while there was no change in vessel dimensions, blood pressure, and blood flow velocity. The artery buckling model provides a useful tool for further study of the adaptation of arteries into tortuous shapes.

Postnatal changes in cerebral blood flow velocity in term intra-uterine growth-restricted neonates

Background:Intra-uterine growth-restricted (IUGR) fetuses are prone to hypoxic changes in the brain and neurodevelopmental sequelae in later life. Chronic hypoxaemia may also lead to polycythaemia in the fetal and neonatal period.Aim:To evaluate venous haematocrit and cerebral blood flow velocity (CBFV) in term IUGR neonates in the immediate postnatal period.Methods:This was a prospective observational study of 54 clinically healthy term IUGR neonates as cases and 50 term, appropriate-for-gestational-age (AGA), healthy neonates as controls. IUGR was defined as birthweight <10th per centile for gestational age. Neonates with perinatal asphyxia, sepsis and other systemic diseases were excluded. Resistance index (RI), pulsatility index (PI), peak systolic velocity (PSV) and vascular diameter were measured in the internal carotid, vertebral and middle cerebral arteries by transcranial colour Doppler ultrasound between 48 and 72 hours of life, along with the estimation of venous haematocrit. Neonates were observed for development of any complications until discharge and followed up clinically and radiologically for a minimum 6 months.Results:Significantly higher resistance (RI and PI) and lower PSV was recorded in all the cerebral arteries of the IUGR than the AGA group whereas no difference was observed in vascular diameters. Mean haematocrit was significantly higher in the IUGR than in the AGA group [55·7 (4·22) vs 45·1 (2·79) g/dl]. Haematocrit was positively correlated with RI and PI, and negatively correlated with PSV. After discharge, three infants in the IUGR group showed hypertonia and delayed developmental milestones along with hypoxic changes in MRI of the brain.Conclusions:Compared with their AGA counterparts, higher venous haematocrit and lower CBFV were observed in clinically healthy, term IUGR neonates during the early neonatal period. Delayed developmental milestones and hypoxic changes were detected by MRI in three infants. Since the study was limited by its sample size, larger studies are required to document the clinical significance of decreased CBFV and its usefulness as a marker of poor prognosis for future neurodevelopment.

Cerebrovascular function and cognition in childhood: a systematic review of transcranial doppler studies

BackgroundThe contribution of cerebrovascular function to cognitive performance is gaining increased attention. Transcranial doppler (TCD) is portable, reliable, inexpensive and extremely well tolerated by young and clinical samples. It enables measurement of blood flow velocity in major cerebral arteries at rest and during cognitive tasks.MethodsWe systematically reviewed evidence for associations between cognitive performance and cerebrovascular function in children (0-18 years), as measured using TCD. A total of 2778 articles were retrieved from PsychInfo, Pubmed, and EMBASE searches and 25 relevant articles were identified.ResultsMost studies investigated clinical groups, where decreased blood flow velocities in infants were associated with poor neurological functioning, and increased blood flow velocities in children with Sickle cell disease were typically associated with cognitive impairment and lower intelligence. Studies were also identified assessing autistic behaviour, mental retardation and sleep disordered breathing. In healthy children, the majority of studies reported cognitive processing produced lateralised changes in blood flow velocities however these physiological responses did not appear to correlate with behavioural cognitive performance.ConclusionPoor cognitive performance appears to be associated with decreased blood flow velocities in premature infants, and increased velocities in Sickle cell disease children using TCD methods. However knowledge in healthy samples is relatively limited. The technique is well tolerated by children, is portable and inexpensive. It therefore stands to make a valuable contribution to knowledge regarding the underlying functional biology of cognitive performance in childhood.

Visually evoked blood flow responses and interaction with dynamic cerebral autoregulation: Correction for blood pressure variation

Visually evoked flow responses recorded using transcranial Doppler ultrasonography are often quantified using a dynamic model of neurovascular coupling. The evoked flow response is seen as the model's response to a visual step input stimulus. However, the continuously active process of dynamic cerebral autoregulation (dCA) compensating cerebral blood flow for blood pressure fluctuations may induce changes of cerebral blood flow velocity (CBFV) as well. The effect of blood pressure variability on the flow response is evaluated by separately modeling the dCA-induced effects of beat-to-beat measured blood pressure related CBFV changes.Parameters of 71 subjects are estimated using an existing, well-known second order dynamic neurovascular coupling model proposed by Rosengarten et al. [1], and a new model extending the existing model with a CBFV contributing component as the output of a dCA model driven by blood pressure as input.Both models were evaluated for mean and systolic CBFV responses. The model-to-data fit errors of mean and systolic blood pressure for the new model were significantly lower compared to the existing model: mean: 0.8%±0.6 vs. 2.4%±2.8, p<0.001; systolic: 1.5%±1.2 vs. 2.2%±2.6, p<0.001. The confidence bounds of all estimated neurovascular coupling model parameters were significantly (p<0.005) narrowed for the new model.In conclusion, blood pressure correction of visual evoked flow responses by including cerebral autoregulation in model fitting of averaged responses results in significantly lower fit errors and by that in more reliable model parameter estimation. Blood pressure correction is more effective when mean instead of systolic CBFV responses are used. Measurement and quantification of neurovascular coupling should include beat-to-beat blood pressure measurement.