Orientational order induced by a polymer network in the isotropic phase of liquid crystal.

We studied the paranematic ordering induced by a polymer network in the isotropic phase of a liquid crystal (LC) that occurs in polymer-stabilized cells with bend configuration of the LC director (π cells) fabricated via photopolymerization of photoreactive monomer RM 82 added in small concentrations (3-5 wt %) to a nematic LC [4-cyano-4'-pentylbiphenyl (5CB)] when low voltage was applied across the cell. The polymer network formed in the nematic phase of the LC consists of fine fibrils that are aligned along the LC director and thus mirror the bend deformation of the LC at the time of polymerization. When heated to temperatures above the nematic-to-isotropic (N-I) phase transition such highly ordered polymer network anchors LC molecules providing ordering of the LC around the fibrils which results in unusually high optical retardation of the cell, R_{cell}. We present a theoretical model that relates R_{cell} to the degree of order of the fibrils, the anchoring energy of the LC molecules on the surface of the polymer fibrils, and the fibril radius r_{0}. Fitting of the experimental R_{cell}(T) curves with the developed model reveals correlation of r_{0} with the nematic correlation length ξ_{0} which characterizes penetration of the nematic order in the isotropic phase of the LC. Accepting ξ_{0} as a material constant of about 1 nm leads to a very small radius of the fibrils, r_{0}∼1nm, which is also supported by other reported experimental data. High optical retardation and fast electro-optical response of the cells at the temperatures deep into the isotropic phase point toward the enhancement of the polymer-induced paranematic order by a well-oriented layer of LC molecules that are absorbed on the surface of fibrils. Application of high voltage at the isotropic phase temperatures results in high variations of the optical retardation of the cells. Characteristic on and off response times were about 10-100 µs, independent of the cell gap. Combination of large voltage-driven changes of the optical retardation occurring in the low-viscosity isotropic state with switching times that are at least two orders of magnitude shorter than the typical relaxation times of the cells operating in the nematic phase make such polymer-stabilized π cells very promising for application in fast electro-optical switches and light modulators.

Comparative study of the anchoring strength of reactive mesogens and industrial polyimides used for the alignment of liquid crystals.

We measured the Rapini-Papoular polar anchoring strength coefficient W for 4^{'}-pentyl-4-cyanobiphenyl (5CB) on alignment layers formed by the reactive mesogen photopolymers RM 257, RM 82, and RM 84 [4,4^{'}-bis(acryloyl)biphenyl] (by Merck). These materials are commonly used for the photostabilization of the liquid crystal (LC) director in the bulk as well as at the surface of the LC layer via the formation of a loose polymer network that captures the director orientation. We developed a method of fabrication of alignment layers from these polymers, and estimated W from the measurements of the optical retardation as a function of applied voltage in uniformly aligned cells. We found that RM 257 yielded W of about 6×10^{-4}J/m^{2}, whereas RM 82 and RM 84 provided anchoring strengths of about 2×10^{-4} and 4×10^{-4}J/m^{2}, respectively. Subsequent heating of the sample either destroyed the alignment layer, or substantially decreased W to about 1×10^{-4}J/m^{2}, which was comparable to the anchoring strength of weakly rubbed commercial polyimides.

Single-cell gene expression analysis reveals diversity among human spermatogonia.

STUDY QUESTION: Is the molecular profile of human spermatogonia homogeneous or heterogeneous when analysed at the single-cell level? SUMMARY ANSWER: Heterogeneous expression profiles may be a key characteristic of human spermatogonia, supporting the existence of a heterogeneous stem cell population. WHAT IS KNOWN ALREADY: Despite the fact that many studies have sought to identify specific markers for human spermatogonia, the molecular fingerprint of these cells remains hitherto unknown. STUDY DESIGN, SIZE, DURATION: Testicular tissues from patients with spermatogonial arrest (arrest, n = 1) and with qualitatively normal spermatogenesis (normal, n = 7) were selected from a pool of 179 consecutively obtained biopsies. Gene expression analyses of cell populations and single-cells (n = 105) were performed. Two OCT4-positive individual cells were selected for global transcriptional capture using shallow RNA-seq. Finally, expression of four candidate markers was assessed by immunohistochemistry. PARTICIPANTS/MATERIALS, SETTING, METHODS: Histological analysis and blood hormone measurements for LH, FSH and testosterone were performed prior to testicular sample selection. Following enzymatic digestion of testicular tissues, differential plating and subsequent micromanipulation of individual cells was employed to enrich and isolate human spermatogonia, respectively. Endpoint analyses were qPCR analysis of cell populations and individual cells, shallow RNA-seq and immunohistochemical analyses. MAIN RESULTS AND THE ROLE OF CHANCE: Unexpectedly, single-cell expression data from the arrest patient (20 cells) showed heterogeneous expression profiles. Also, from patients with normal spermatogenesis, heterogeneous expression patterns of undifferentiated (OCT4, UTF1 and MAGE A4) and differentiated marker genes (BOLL and PRM2) were obtained within each spermatogonia cluster (13 clusters with 85 cells). Shallow RNA-seq analysis of individual human spermatogonia was validated, and a spermatogonia-specific heterogeneous protein expression of selected candidate markers (DDX5, TSPY1, EEF1A1 and NGN3) was demonstrated. LIMITATIONS, REASONS FOR CAUTION: The heterogeneity of human spermatogonia at the RNA and protein levels is a snapshot. To further assess the functional meaning of this heterogeneity and the dynamics of stem cell populations, approaches need to be developed to facilitate the repeated analysis of individual cells. WIDER IMPLICATIONS OF THE FINDINGS: Our data suggest that heterogeneous expression profiles may be a key characteristic of human spermatogonia, supporting the model of a heterogeneous stem cell population. Future studies will assess the dynamics of spermatogonial populations in fertile and infertile patients. LARGE SCALE DATA: RNA-seq data is published in the GEO database: GSE91063. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Max Planck Society and the Deutsche Forschungsgemeinschaft DFG-Research Unit FOR 1041 Germ Cell Potential (grant numbers SCHO 340/7-1, SCHL394/11-2). The authors declare that there is no conflict of interest.

Oxygen depletion in coastal seas and the effective spawning stock biomass of an exploited fish species.

Environmental conditions may have previously underappreciated effects on the reproductive processes of commercially exploited fish populations, for example eastern Baltic cod, that are living at the physiological limits of their distribution. In the Baltic Sea, salinity affects neutral egg buoyancy, which is positively correlated with egg survival, as only water layers away from the oxygen consumption-dominated sea bottom contain sufficient oxygen. Egg buoyancy is positively correlated to female spawner age/size. From observations in the Baltic Sea, a field-based relationship between egg diameter and buoyancy (floating depth) could be established. Hence, based on the age structure of the spawning stock, we quantify the number of effective spawners, which are able to reproduce under ambient hydrographic conditions. For the time period 1993-2010, our results revealed large variations in the horizontal extent of spawning habitat (1000-20 000 km(2)) and oxygen-dependent egg survival (10-80%). The novel concept of an effective spawning stock biomass takes into account offspring that survive depending on the spawning stock age/size structure, if reproductive success is related to egg buoyancy and the extent of hypoxic areas. Effective spawning stock biomass reflected the role of environmental conditions for Baltic cod recruitment better than the spawning stock biomass alone, highlighting the importance of including environmental information in ecosystem-based management approaches.

Severity of coronary artery disease but not degree of coronary stenosis is correlated to cerebrovascular reactivity.

BACKGROUND: A decade difference in peak incidences of coronary and cerebral ischemia assumes a protection of the brain vasculature. Therefore, we hypothesize that early indicators of cerebrovascular disease such as parameters of the neurovascular coupling show a higher correlation to coronary artery disease than morphologic parameters. METHODS: Stenotic degree (%) of coronary arteries (RCA, LCA, LAD, RCX) was determined together with the Gensini score by angiography in 96 patients (80 men; 62 +/- 10 years), which were grouped according to disease severity (sclerosis, 1-vessel disease (VD), 2-VD, 3-VD). Presence of internal carotid artery stenosis and left ventricular ejection fraction (LVEF) were established with duplex sonography. Resting and visually evoked hemodynamic responses were measured with transcranial Doppler ultrasound in both posterior cerebral arteries and expressed in terms of control system parameters. These were gain, natural frequency, attenuation, and rate time. Group differences and correlations between stenosis and parameters of vasoreactivity were tested. RESULTS: Groups differed in stenotic degree of coronary arteries, Gensini score, LVEF, carotid artery stenosis, resting flow velocity, and evoked responses (gain, p < 0.005; attenuation, p < 0.05). Stenosis of each coronary artery and LVEF were correlated to carotid artery stenosis but no association was found to cerebrovascular parameters. Only severity of coronary artery disease and the Gensini score were associated with disturbed cerebrovascular reactivity. Carotid artery stenosis was associated with decreased cerebrovascular parameters (attenuation, p < 0.05; rate time, p < 0.01). CONCLUSIONS: Although atherosclerosis is a systemic disease our data support concepts of a heterogeneous distribution of the disease indicating protection of brain vessels.

Healthcare-associated hepatitis C virus transmission among patients in an abdominal organ transplant center.

BACKGROUND: De novo hepatitis C virus (HCV) infection among transplant patients is rarely recognized but can have severe consequences. We investigated the scope, source, and mode of HCV transmission within a transplant center after incident HCV infection was identified in 2 patients who had liver transplantation in late 2006. METHODS: Patients were interviewed, and transplant logs, medical records, and staff practices were reviewed to identify opportunities for HCV transmission. Infection via receipt of blood or organs was evaluated. Molecular epidemiology was used to determine the relatedness between persons with incident and chronic HCV infection. RESULTS: HCV from infected blood or organ donors was ruled out. Among the 308 patients who underwent transplant in 2006, no additional incident HCV infections were identified. Eighty-five (28%) had pre-transplant chronic HCV infection; 13 were considered possible HCV source patients based upon shared days on the inpatient unit, nursing assignment, or invasive procedures in common with incident HCV case-patients. Viral isolates from 1 HCV source patient and 1 incident case-patient were found to be highly related by quasispecies analysis, confirming patient-to-patient HCV transmission. Possible modes of transmission identified were the improper use of multidose vials, sharing of blood-contaminated glucometers, and touch contamination. CONCLUSION: Sporadic transmission or endemic levels of HCV transmission might be overlooked in a setting with high HCV prevalence, such as liver transplant units, where multiple, repeated opportunities for patient-to-patient HCV transmission can occur. Surveillance through pre- and post-transplant screening is necessary to identify incident HCV infection in this setting. Constant, meticulous attention must be paid to maintaining aseptic technique and good infection control practices to eliminate HCV transmission opportunities.

Apigenin-induced nitric oxide production involves calcium-activated potassium channels and is responsible for antiangiogenic effects.

BACKGROUND: The dietary flavonoid apigenin (Api) has been demonstrated to exert multiple beneficial effects upon the vascular endothelium. The aim of this study was to examine whether Ca(2+)-activated K(+) channels (K(Ca)) are involved in endothelial nitric oxide (NO) production and antiangiogenic effects. METHODS: Endothelial NO generation was monitored using a cyclic guanosine monophosphate radioimmunoassay. K(Ca) activity and changes of the intracellular Ca(2+) concentration [Ca(2+)](i) were analyzed using the fluorescent dyes bis-barbituric acid oxonol, potassium-binding benzofuran isophthalate, and fluo-3. The endothelial angiogenic parameters measured were cell proliferation, [(3)H]-thymidine incorporation, and cell migration (scratch assay). Akt phosphorylation was examined using immunohistochemistry. RESULTS: Api caused a concentration-dependent increase in cyclic guanosine monophosphate levels, with a maximum effect at a concentration of 1 mum. Api-induced hyperpolarization was blocked by the small and large conductance K(Ca) inhibitors apamin and iberiotoxin, respectively. Furthermore, apamin and iberiotoxin blocked the late, long-lasting plateau phase of the Api-induced biphasic increase of [Ca(2+)](i). Inhibition of Ca(2+) signaling and the K(Ca) blockade both blocked NO production. Prevention of all three (NO, Ca(2+), and K(Ca) signaling) reversed the antiangiogenic effects of Api under both basal and basic fibroblast growth factor-induced culture conditions. Basic fibroblast growth factor-induced Akt phosphorylation was also reduced by Api. CONCLUSIONS: Based on our experimental results we propose the following signaling cascade for the effects of Api on endothelial cell signaling. Api activates small and large conductance K(Ca), leading to a hyperpolarization that is followed by a Ca(2+) influx. The increase of [Ca(2+)](i) is responsible for an increased NO production that mediates the antiangiogenic effects of Api via Akt dephosphorylation.

Elevated Lipoprotein(a) does not promote early atherosclerotic changes of the carotid arteries in young, healthy adults.

BACKGROUND: Elevated levels of Lipoprotein(a) [Lp(a)] have been linked to an increased risk of ischemic cardiovascular events. Yet the mechanism by which Lp(a) might contribute to this increased risk is not clear. METHODS: To elucidate whether high plasma levels of Lp(a) contribute to the development of early atherosclerotic vessel wall changes, the intima-media thickness of the common carotid arteries [CCA-IMT] of 151 healthy young volunteers without additional relevant cardiovascular risk factors was measured by high-resolution ultrasound. Plasma concentrations of Lp(a) were quantified and other established risk factors, such as body mass index [BMI], plasma levels of cholesterol, triglycerides and homocysteine, were determined. Furthermore, the carotid arteries were examined for the presence of plaques and stenoses. RESULTS: Univariate analysis showed a significantly negative correlation of CCA-IMT with HDL cholesterol and positive correlations with age, BMI, total and LDL cholesterol, triglycerides and even with homocysteine, but not with Lp(a). When the study population was dichotomized according to Lp(a) levels, no statistically significant differences in CCA-IMT could be detected between persons with plasma Lp(a)<300mg/l or >or=300mg/l, respectively. CONCLUSION: Our data suggest that elevated Lp(a) levels alone do not contribute to increased cardiovascular risk by promoting early atherogenesis in vivo.

Embolia de líquido amniótico; caso clínico con sobrevida y revisión del tema / Amniotic fluid embolism; clinical case with survived and review of the subject

La embolia de líquido amniótico (ELA) es una de las complicaciones obstétricas menos frecuentes, pero de mayor mortalidad. Presentamos un caso de ELA ocurrido en un hospital tipo cuatro en condiciones de aislamiento. Mujer de 21 años, multípara, con parto de término, feto macrosómico, desgarro extenso de cuello uterino y shock hipovolémico. El episodio fue superado con el aporte de volumen, sangre total y reparación quirúrgica. Durante el puerperio inmediato inició abruptamente un cuadro de hipotensión e insuficiencia respiratoria. La radiografía de tórax fue compatible con distress respiratorio del adulto, planteándose ELA. La paciente fue conectada a ventilación mecánica y se realizó tratamiento consistente en soporte vital, corticoterapia las primeras 48 horas y drogas vasoactivas. Luego de tres días de evolución fue extubada y trasladada a un centro de mayor complejidad para evaluación cardiológica. Permaneció hospitalizada por dos día más y fue dada de alta en controles ambulatorios al octavo día sin secuelas. La ELA debe considerarse en todo cuadro de shock, hipoxia y/o coagulopatía del periparto. El tratamiento se orienta a mantener los parámetros vitales, aunque la causal inmunológica que se postula en la actualidad, hace posible la existencia de terapias específicas en el futuro.

Upregulation of GP IIb/IIIa receptors during platelet activation: influence on efficacy of receptor blockade.

INTRODUCTION: GP IIb/IIIa inhibitor doses high enough to inhibit platelet macroaggregation may not completely prevent formation of microaggregates. Platelets contain an internal pool of GP IIb/IIIa receptors which externalizes with activation and supports microaggregation. This study assesses microaggregation in the presence of the two GP IIb/IIIa inhibitors abciximab and tirofiban. METHODS: Citrated whole blood was preincubated with abciximab (5 microg/ml), tirofiban (50 ng/ml), or saline as control and activated with TRAP (5 microM) or ADP (2 microM) at 37 degrees C under constant stirring. Microaggregate formation and receptor expression were determined with flow cytometry. RESULTS: Within few seconds after TRAP-activation the platelet count dropped from 266,000/microl to 20,000/microl, the number of microaggregates increased from 3700/microl to 10,100/microl and the mean number of GP IIb/IIIa receptors increased from 53,000 to 65,000/platelet. With TRAP+abciximab the platelet count dropped from 259,000 to 113,000/microl, microaggregates increased from 2500 to 9300/microl, GP IIb/IIIa receptors from 56,000 to 77,000/platelet. Platelet microaggregate formation was reversible. With TRAP and tirofiban platelet count dropped to only 190,000/microl, there was no increase in platelet microaggregates, receptors increased to 66,000/platelet. Platelet activation with ADP gave similar results. CONCLUSIONS: During the early phase of activation additional GP IIb/IIIa receptors externalize to the platelet surface. Abciximab does not block these new receptors sufficiently to prevent microaggregate formation. However, the number of unblocked receptors is not high enough to maintain a stable aggregate, microaggregation is reversible. With tirofiban there is no microaggregate formation, possibly because the inhibitor rapidly binds to newly externalized receptors.

Análisis de operación de cesárea y su indicación en Hospital Hanga Roa: Isla de Pascua entre 1996-2000 / Analysis of the cesarean section and their indication of the hospital Hanga Roa, Isla de Pascua in the period 1996-2000

La operación cesárea ha tenido un incremento constante en sus cifras desde la década de los 60, llegando Chile a ser el país con cifras más elevadas a nivel latinoamericano. Como parte del territorio chileno se encuentra la Isla de Pascua, que presenta una situación particular debido a su lejanía geográfica y a que el hospital está a cargo de médicos generales. Es por eso que se ha querido analizar las tasas de cesárea y sus indicaciones en el período 1996-2000, para dar una visión general de cómo se comporta esta frecuente cirugía en un lugar aislado de las redes de atención y la tecnología.

Evaluation of the VIDAS Listeria (LIS) immunoassay for the detection of Listeria in foods using demi-Fraser and Fraser enrichment broths, as modification of AOAC Official Method 999.06 (AOAC Official Method 2004.06).

A multilaboratory study was conducted to compare the VIDAS LIS immunoassay with the standard cultural methods for the detection of Listeria in foods using an enrichment modification of AOAC Official Method 999.06. The modified enrichment protocol was implemented to harmonize the VIDAS LIS assay with the VIDAS LMO2 assay. Five food types--brie cheese, vanilla ice cream, frozen green beans, frozen raw tilapia fish, and cooked roast beef--at 3 inoculation levels, were analyzed by each method. A total of 15 laboratories representing government and industry participated. In this study, 1206 test portions were tested, of which 1170 were used in the statistical analysis. There were 433 positive by the VIDAS LIS assay and 396 positive by the standard culture methods. A Chi-square analysis of each of the 5 food types, at the 3 inoculation levels tested, was performed. The resulting average Chi square analysis, 0.42, indicated that, overall, there are no statistical differences between the VIDAS LIS assay and the standard methods at the 5% level of significance.

Hernia diafragmática con riñón intratorácico / Diaphragmatic hernia with intrathoracic kidney

Las hernias diafragmáticas congénitas son un defecto poco común, diagnosticadas generalmente en las primeras horas de vida. Su diagnóstico en la etapa adulta es poco frecuente. La ectopia renal intratorácica es una patología aún más rara, y la asociación de ésta con un defecto diafragmático no llega al 0,3 por ciento de los casos. Se comunica un caso de una paciente de 40 años en la que se diagnostica mediante radiografía de tórax y TAC de tórax y abdómen la presencia de una hernia de Bochdaleck derecha asociada a riñón intratorácico ipsilateral.

[Embolization therapy of an arteriovenous fistula after percutaneous lithotripsy in combination with angioplasty of an ipsilateral kidney arterial stenosis]. / Embolisationstherapie einer arteriovenösen Fistel nach perkutaner Nephrolitholapaxie in Kombination mit der Angioplastie einer ipsilateralen Nierenarterienstenose.

We describe successful selective coil embolization therapy in a patient with renal hemorrhage caused by iatrogenic pseudoaneurysm after percutaneous nephrostomy and lithotripsy. In the same session, an incidentally detected severe renal artery stenosis that had caused moderate hypertension was treated by balloon angioplasty. No complications occurred. Coaxial micro-catheter technique and platinum microcoils were used for embolization and allowed targeted occlusion of the bleeding renal artery and preserved the surrounding renal parenchyma. Bleeding was controlled immediately and hematuria disappeared after embolization therapy.

Deciphering a subgroup of breast carcinomas with putative progression of grade during carcinogenesis revealed by comparative genomic hybridisation (CGH) and immunohistochemistry.

Distinct parallel cytogenetic pathways in breast carcinogenesis could be identified in recent years. Nevertheless, it remained unclear as to which tumours may have progressed in grade or which patterns of cytogenetic alteration may define the switch from an in situ towards an invasive lesion. In order to gain more detailed insights into cytogenetic mechanisms of the pathogenesis of breast cancer, the chromosomal imbalances of 206 invasive breast cancer cases were characterised by means of comparative genomic hybridisation (CGH). CGH data were subjected to hierarchical cluster analysis and the results were further compared with immunohistochemical findings on tissue arrays from the same breast cancer cases. The combined analysis of immunohistochemical and cytogenetic data provided evidence that carcinomas with gains of 7p, and to a lesser extent losses of 9q and gains of 5p, are a distinct subgroup within the spectrum of ductal invasive grade 3 breast carcinomas. These aberrations were associated with a high degree of cytogenetic instability (16.6 alterations per case on average), 16q-losses in over 70% of these cases, strong oestrogen receptor expression and absence of strong expression of p53, c-erbB2 and Ck 5. These characteristics provide strong support for the hypothesis that these tumours may develop through stages of well- and perhaps intermediately differentiated breast cancers. Our results therefore underline the existence of several parallel and also stepwise progression pathways towards breast cancer.

Molecular cytogenetic investigations of synchronous bilateral breast cancer.

BACKGROUND: Bilaterality in breast cancer is a rare event and together with an early onset of disease points towards inheritance of the disease. However, most cases seem to occur sporadically, either in a synchronous or metachronous manner. METHODS: Thirty two invasive carcinomas and one in situ carcinoma from 16 patients with synchronous, bilateral breast cancer were investigated by means of comparative genomic hybridisation (CGH) and polymerase chain reaction based multiplex microsatellite analysis. The results were analysed conventionally and were also subjected to a biomathematical cluster analysis. RESULTS: On average, bilateral breast cancer cases showed a low number of genetic alterations, a low frequency of genetic amplifications, and a high rate of chromosomal 16q losses. A distinct, characteristic genetic alteration associated with bilateral breast disease could not be found. Although two tumour pairs appeared to be related using biomathematical processing for microsatellite analysis, this result was reproduced by CGH data processing in one patient only. CONCLUSIONS: Most synchronous, bilateral breast cancer cases seem to represent independent tumours rather than metastatic events. Nevertheless, the possibility of a specific susceptibility remains.

[Acute myocardial infarction in premenopausal women]. / Akuter Myokardinfarkt bei prämenopausalen Frauen.

UNLABELLED: Prospective, systematic studies of the pathophysiology and prognosis of premenopausal women vs young men who suffer an acute myocardial infarction (MI) and are treated with direct angioplasty are scarce. METHODS AND RESULTS: A total of 782 consecutive and unselected patients who presented with an acute ST-elevation MI within 12 h of symptom onset underwent immediate angiography to guide direct angioplasty. Using this therapeutic approach clinical characteristics, angiographic observations, and short- and long-term prognosis were analyzed in a sub-group of 31 premenopausal women and compared to 192 young men with acute MI. Premenopausal women account for 4% of individuals with acute MI and for 15% (31/205) of all women. Men of the same age range make up 25% (192/782) of all MI patients (p<0.001). Three or more classic risk factors were present in 20/31 women. Young women presented later than men. Angiography demonstrated a coronary occlusion in 27/31 women (88%) but in 98% of young men (p<0.02). Direct PTCA was successful in all premenopausal women and in 179/185 men (97%, p=ns). Predischarge EF was 57% in women and 54% in men (p=ns). After 4 years of follow-up, all women had survived as compared to a 95% survival in young men. Major cardiac events had occurred in 50% of persons of either gender. CONCLUSION: Premenopausal women account for 4% of individuals and for 1/6 of all female patients who presented with acute MI within 12 h of onset. Hospital admittance is delayed in young women. MI was caused by (atherosclerotic) coronary occlusion in most young women and in virtually all young men. Short- and long-term survival of premenopausal women is favorable after direct PTCA for acute MI and not different than men from the same age group.

Contrast media effect on cerebral blood flow regulation after performance of cerebral or coronary angiography.

OBJECTIVE: The immediate hemodynamic effects of contrast agents are well documented. Less is known about their longer-lasting effects. We investigated the later effect of iopromide on the neurovascular coupling mechanism after the performance of cerebral or coronary angiography. Neurovascular coupling is a fine-tuned and reliable mechanism adapting cerebral blood flow to cortical activity. When performing a visual stimulation and measuring the resultant flow velocity change in the posterior cerebral artery transcranial Doppler has been used to determine vascular integrity. METHODS: The visually evoked blood flow velocity response in the posterior cerebral artery was measured with transcranial Doppler before, 1-2 h after and the day after angiography. The overshoot of the flow velocity response and the stable flow velocity level at the end of the stimulation phase were used to compare the different conditions. RESULTS: A significantly diminished overshoot was found 1-2 h after angiography only in patients undergoing cerebral angiography. The stable blood flow velocity levels at the end of the stimulation phase remained unchanged in all cases. CONCLUSIONS: Our finding demonstrates effects of contrast media on dynamic blood flow regulation of the cerebral vasculature 1-2 h after application of direct contrast agent suggesting a possible concentration effect of the contrast agent. However, since the relative blood flow velocity increase under stable blood flow conditions remained constant, this dynamic alteration does not cause a reduction in cerebral blood flow.