Membrane microdialysis: Evaluation of a new method to assess splanchnic tissue metabolism

OBJECTIVE: Measuring peritoneal lactate concentrations could be useful for detecting splanchnic hypoperfusion. The aims of this study were to evaluate the properties of a new membrane-based microdialyzer in vitro and to assess the ability of the dialyzer to detect a clinically relevant decrease in splanchnic blood flow in vivo. DESIGN: A membrane-based microdialyzer was first validated in vitro. The same device was tested afterward in a randomized, controlled animal experiment. SETTING: University experimental research laboratory. SUBJECTS: Twenty-four Landrace pigs of both genders. INTERVENTIONS: In vitro: Membrane microdialyzers were kept in warmed sodium lactate baths with lactate concentrations between 2 and 8 mmol/L for 10-120 mins, and microdialysis lactate concentrations were measured repeatedly (210 measurements). In vivo: An extracorporeal shunt with blood reservoir and roller pump was inserted between the proximal and distal abdominal aorta, and a microdialyzer was inserted intraperitoneally. In 12 animals, total splanchnic blood flow (measured by transit time ultrasound) was reduced by a median 43% (range, 13% to 72%) by activating the shunt; 12 animals served as controls. MEASUREMENTS AND MAIN RESULTS: In vitro: The fractional lactate recovery was 0.59 (0.32-0.83) after 60 mins and 0.82 (0.71-0.87) after 90 mins, with no further increase thereafter. At 60 and 90 mins, the fractional recovery was independent of the lactate concentration. In vivo: Abdominal blood flow reduction resulted in an increase in peritoneal microdialysis lactate concentration from 1.7 (0.3-3.8) mmol/L to 2.8 (1.3-6.2) mmol/L (p = .006). At the same time, mesenteric venous-arterial lactate gradient increased from 0.1 (-0.2-0.8) mmol/L to 0.3 (-0.3 -1.8) mmol/L (p = .032), and mesenteric venous-arterial Pco2 gradients increased from 12 (8-19) torr to 21 (11-54) torr (p = .005). CONCLUSIONS: Peritoneal membrane microdialysis provides a method for the assessment of splanchnic ischemia, with potential for clinical application.

Inverse thermodilution with conventional pulmonary artery catheters for the assessment of cerebral, hepatic, renal, and femoral blood flow

Assessment of regional blood flow changes is difficult in the clinical setting. We tested whether conventional pulmonary artery catheters (PACs) can be used to measure regional venous blood flows by inverse thermodilution (ITD). Inverse thermodilution was tested in vitro and in vivo using perivascular ultrasound Doppler (USD) flow probes as a reference. In anesthetized pigs, PACs were inserted in jugular, hepatic, renal, and femoral veins, and their measurements were compared with simultaneous USD flow measurements from carotid, hepatic, renal, and femoral arteries and from portal vein. Fluid boluses were injected through the PAC's distal port, and temperature changes were recorded from the proximally located thermistor. Injectates of 2 and 5 mL at 22 degrees C and 4 degrees C were used. Flows were altered by using a roller pump (in vitro), and infusion of dobutamine and induction of cardiac tamponade, respectively. In vitro: At blood flows between 400 mL . min-1 and 700 mL . min-1 (n = 50), ITD and USD correlated well (r = 0.86, P < 0.0001), with bias and limits of agreement of 3 +/- 101 mL . min-1. In vivo: 514 pairs of measurements had to be excluded from analysis for technical reasons, and 976 were analyzed. Best correlations were r = 0.87 (P < 0.0001) for renal flow and r = 0.46 (P < 0.0001) for hepatic flow. No significant correlation was found for cerebral and femoral flows. Inverse thermodilution using conventional PAC compared moderately well with USD for renal but not for other flows despite good in vitro correlation in various conditions. In addition, this method has significant technical limitations.

Comparison of mesencephalic free-floating tissue culture grafts and cell suspension grafts in the 6-hydroxydopamine-lesioned rat

Ventral mesencephalon (VM) of fetal rat and human origin grown as free-floating roller-tube (FFRT) cultures can survive subsequent grafting to the adult rat striatum. To further explore the functional efficacy of such grafts, embryonic day 13 ventral mesencephalic tissue was grafted either after 7 days in culture or directly as dissociated cell suspensions, and compared with regard to neuronal survival and ability to normalize rotational behavior in adult rats with unilateral 6-hydroxydopamine (6-OHDA) lesions. Other lesioned rats received injections of cell-free medium and served as controls. The amphetamine-induced rotational behavior of all 6-OHDA-lesioned animals was monitored at various time points from 18 days before transplantation and up to 80 days after transplantation. Tyrosine hydroxylase (TH) immunostaining of the histologically processed brains served to assess the long-term survival of grafted dopaminergic neurons and to correlate that with the behavioral effects. Additional cultures and acutely prepared explants were also fixed and stored for histological investigation in order to estimate the loss of dopaminergic neurons in culture and after transplantation. Similar behavioral improvements in terms of significant reductions in amphetamine-induced rotations were observed in rats grafted with FFRT cultures (127%) and rats grafted with cell suspensions (122%), while control animals showed no normalization of rotational behavior. At 84 days after transplantation, there were similar numbers of TH-immunoreactive (TH-ir) neurons in grafts of cultured tissue (775 +/- 98, mean +/- SEM) and grafts of fresh, dissociated cell suspension (806 +/- 105, mean +/- SEM). Cell counts in fresh explants, 7-day-old cultures, and grafted cultures revealed a 68.2% loss of TH-ir cells 7 days after explantation, with an additional 23.1% loss after grafting, leaving 8.7% of the original number of TH-ir cells in the intracerebral grafts. This is to be compared with a survival rate of 9.1% for the TH-ir cells in the cell-suspension grafts. Immunostaining for the calcium-binding proteins calretinin, calbindin, and parvalbumin showed no differences in the neuronal expression of these proteins between the two graft types. In conclusion, we found comparable dopaminergic cell survival and functional effects of tissue-culture grafts and cell-suspension grafts, which currently is the type of graft most commonly used for experimental and clinical grafting. In this sense the result is promising for the development of an effective in vitro storage of fetal nigral tissue, which at the same time would allow neuroprotective and neurotrophic treatment prior to intracerebral transplantation.

Fetal ventral mesencephalon of human and rat origin maintained in vitro and transplanted to 6-hydroxydopamine-lesioned rats gives rise to grafts rich in dopaminergic neurons

Free-floating roller tube cultures of human fetal (embryonic age 6-10 weeks post-conception) and rat fetal (embryonic day 13) ventral mesencephalon were prepared. After 7-15 days in vitro, the mesencephalic tissue cultures were transplanted into the striatum of adult rats that had received unilateral injections of 6-hydroxydopamine into the nigrostriatal bundle 3-5 weeks prior to transplantation. Graft survival was assessed in tyrosine hydroxylase (TH)-immunostained serial sections of the grafted brains up to post-transplantation week 4 for the human fetal xenografts and post-transplantation week 11 for the rat fetal allografts. D-amphetamine-induced rotation was monitored up to 10 weeks after transplantation in the allografted animals and compared with that of lesioned-only control animals. All transplanted animals showed large, viable grafts containing TH-immunoreactive (ir) neurons. The density of TH-ir neurons in the human fetal xenografts and in rat fetal allografts was similar. A significant amelioration of the amphetamine-induced rotation was observed in the animals that received cultured tissue allografts. These results promote the feasibility of in vitro maintenance of fetal human and rat nigral tissue prior to transplantation using the free-floating roller tube technique.

Effects of GDNF pretreatment on function and survival of transplanted fetal ventral mesencephalic cells in the 6-OHDA rat model of Parkinson's disease

Transplantation of fetal dopaminergic (DA) neurons offers an experimental therapy for Parkinson's disease (PD). The low availability and the poor survival and integration of transplanted cells in the host brain are major obstacles in this approach. Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor with growth- and survival-promoting capabilities for developing DA neurons. In the present study, we examined whether pretreatment of ventral mesencephalic (VM) free-floating roller tube (FFRT) cultures with GDNF would improve graft survival and function. For that purpose organotypic cultures of E14 rat VM were grown for 2, 4 or 8 days in the absence (control) or presence of GDNF [10 ng/ml] and transplanted into the striatum of 6-hydroxydopamine-lesioned rats. While all groups of rats showed a significant reduction in d-amphetamine-induced rotations at 6 weeks posttransplantation a significantly improved graft function was observed only in the days in vitro (DIV) 4 GDNF pretreated group compared to the control group. In addition, no statistical significant differences between groups were found in the number of surviving tyrosine hydroxylase-immunoreactive (TH-ir) neurons assessed at 9 weeks posttransplantation. However, a tendency for higher TH-ir fiber outgrowth from the transplants in the GDNF pretreated groups as compared to corresponding controls was observed. Furthermore, GDNF pretreatment showed a tendency for a higher number of GIRK2 positive neurons in the grafts. In sum, our findings demonstrate that GDNF pretreatment was not disadvantageous for transplants of embryonic rat VM with the FFRT culture technique but only marginally improved graft survival and function.

The role of brand marketing in snowboarding: A comparative study of Switzerland and New Zealand

Introduction: Brands play an essential role in the organizational structure of snowboarding by sponsoring athletes, arranging events, contributing to product development and developing long-term partnerships with other key actors. However, the specialities of their role in scene sports, such as creating identities, networking and brand marketing strategies, have not been extensively researched. This study aims to provide an analysis of the function of brands within the snowboarding subculture by comparing how the sport is organized in Switzerland and New Zealand. Sociological theories of subcultures (Hitzler & Niederbacher, 2010) and social networks (Stegbauer, 2008) are used to defi ne the structures of the sport, whereas marketing and branding theories (Adjouri & Stastny, 2006) help to understand the role of the brands. Snowboarding will be defi ned as an alternative sports subculture based on characteristics such as aesthetics, adventure and new resources of performance (Schwier, 2006). Such a defi nition also begs for a novel form of analyzing its organization. Unlike more conventional structures, the organization of snowboarding allows a variety of actors to get involved in leading the sport. By portraying and encouraging differentiated identities and lifestyles, athletes provide a space for other actors to fi nd their place within the sport (Wheaton, 2005). According to Stegbauers network theory, individual actors are able to obtain high positions and defi ne their identity depending on their ties to actors and networks within the subculture (Stegbauer, 2008). For example, social capital, contacts within the sport and insider knowledge on subculture-related information enable actors to get closer to the core (Hitzler & Niederbacher, 2010). Actors who do not have close networks and allies within the subculture are less likely to engage successfully in the culture, whether as an individual or as a commercial actor (Thorpe, 2011). This study focuses on the organizational structure of snowboarding by comparing the development of the sport in Switzerland and New Zealand. An analysis of snowboarding in two nations with diverse cultures and economic systems allows a further defi nition of the structural organization of the sport and explains how brands play an important role in the sport. Methods: The structural organization of the sport will be analyzed through an ethnographic approach, using participant observation at various leading events in Switzerland (Freestyle.ch, European Open) and New Zealand (World Heli Challenge, New Zealand Open, New Zealand Winter Games). The data is analyzed using grounded theory (Glaser & Strauss 1967) and gives an overview of the actors that are playing an important role in the local development of snowboarding. Participant observation was also used as a tool to get inside the sport culture and opened up the possibility to make over 40 semi-structured qualitative expert interviews with international core actors from 11 countries. Obtaining access to one actor as a partner early on helped to get inside the local sport culture. The ‘snowball effect’ allowed the researcher to acquire access, build trust and conduct interviews with experts within the core scene. All the interviewed actors have a direct infl uence on the sport in one or both countries, which permit a cross-analysis. The data of the interviews was evaluated through content analysis (Mayring 2010). The two methods together provided suffi cient data to analyze the organizational structure and discuss the role of brand marketing within snowboarding. Results: An actors mapping by means of a center-periphery framework has identifi ed fi ve main core groups: athletes, media representatives, brand-marketing managers, resort managers and event organizers. In both countries the same grouping of actors were found. Despite possessing different and frequently multiple roles and responsibilities, core actors appear to have a strong common identifi cation as ‘snowboarders’, are considered to be part of the organizational elite of the sport and tend to advocate similar goals. The author has found that brands in Switzerland tend to have a larger impact on the broader snowboarding culture due to a number of factors discussed below. Due to a larger amount of snowboarders and stronger economic power in Europe, snowboarders are making attempts to differentiate themselves from other winter sports, while competing with each other to develop niche markets. In New Zealand, on the other hand, the smaller market enables more cooperation and mutual respect within snowboarders. Further they are more closely linked to other winter sports and are satisfi ed with being lumped together. In both countries, brands have taken up the role of supporting young athletes, organizing competitions and feeding media with subculture-related content. Brands build their image and identity through the collaboration with particular athletes who can represent the values of the brand. Local and global communities with similar lifestyles and interests are being built around brands that share a common vision of the sport. The dominance of brands in snowboarding has enabled them with the power to organize and rule the sport through its fan base and supporters. Brands were defi ned by interviewees as independent institutions led by insiders who know the codes and symbols of the sport and were given trust and credibility. The brands identify themselves as the engines of the sport by providing the equipment, opportunities for athletes to get exposure, allowing media to get exclusive information on activities, events and sport-related stories. Differences between the two countries are more related to the economic system. While Switzerland is well integrated in the broader European market, New Zealand’s geographical isolation and close proximity to Australia tends to limit its market. Further, due to different cultural lifestyles, access to resorts and seasonal restrictions, to name a few, the amount of people practicing winter sports in New Zealand is much smaller than in Switzerland. However, this also presents numerous advantages. For example, the short southern hemisphere winter season in New Zealand enables them to attract international sports athletes, brands and representatives in a period when Europe and North America is in summer. Further, the unique snow conditions in New Zealand and majestic landscape is popular for attracting world renowned photo- and cinematographers. Another advantage is the less populated network as it provides the opportunity for individuals to gain easier access to the core of the sport, obtain diverse positions and form a unique identity and market. In Switzerland, on the other hand, the snowboarding network is dense with few positions available for the taking. Homegrown brands with core recognition are found in both countries. It was found that the Swiss brands tend to have a larger impact on the market, whereas in New Zealand, the sport is more dependent on import products by foreign brands. Further, athletes, events and resorts in New Zealand are often dependent on large brand sponsorships from abroad such as from brand headquarters in the Unites States. Thus, due to its location in the centre of Europe, Swiss brands can take advantage of brands which are closer in proximity and culture to sponsor athletes and events. In terms of media coverage, winter sports in New Zealand tend to have a minor coverage and tradition in local mass media, which leads to less exposure, recognition and investment into the sport. This is also related to how snowboarding is more integrated into other winter sports in New Zealand. Another difference is the accessibility of the ski resort by the population. While in Switzerland the resorts are mostly being visited by day-travelers, ‘weekend warriors’ and holiday makers, the location of the resorts in New Zealand make it diffi cult to visit for one day. This is in part due to the fact that Swiss ski resorts and villages are usually the same location and are accessible through public transportation, while the ski resorts in New Zealand have been built separately from the villages. Further, the villages have not been built to accommodate to high tourist arrivals. Thus, accommodation and food facilities are limited and there is a lack of public transportation to the resorts. Discussion: The fi ndings show that networks and social relations combined with specifi c knowledge on scene-related attributes are crucial in obtaining opportunities within the sport. Partnerships as well as competition between these different actors are necessary for core acceptance, peer credibility and successful commercial interests. Brands need to maintain effective marketing strategies and identities which incorporate subcultural forms of behavior and communication. In order to sustain credibility from its fans, athletes and other snowboarding actors, brands need to maintain their insider status through social networks and commercial branding strategies. The interaction between all actors is a reciprocated process, where social capital, networks and identities are being shared. While the overall structure of snowboard subcultures in Europe and New Zealand are similar, there are some distinct characteristics which make each one unique. References Adjouri, N. & Stastny, P. (2006). Sport-Branding: Mit Sport-Sponsoring zum Markenerfolg. Wiesbaden: Gabler. Glaser, B. & Strauss, K. (1967). The discovery of grounded theory: Strategies for qualitative research. Chicago: Aldine. Hebdige, D. (2009). Subculture; The meaning of style. New York: Routledge. Hitzler, R. & Niederbacher, A. (2010). Leben in Szenen: Formen juveniler Vergemeinschaftung heute. Wiesbaden: Verlag für Sozialwissenschaften. Mayring, P. (2010). Qualitative Inhaltsanalyse: Grundlagen und Techniken. Weinheim: Beltz. Schwier, J. (2006). Repräsentationen des Trendsports. Jugendliche Bewegungskulturen, Medien und Marketing. In: Gugutzer, R. (Hrsg.). body turn. Perspektiven der Soziologie des Körpers und des Sports. Bielefeld: transcript (S. 321-340). Stegbauer, C. (2008). Netzwerkanalyse und Netzwerktheorie. Ein neues Paradigma in den Sozialwissenschaften. Wiesbaden: VS Verlag für Sozialwissenschaften. Thorpe, H. (2011). Snowboarding bodies in theory and practice. Basingstoke: Palgrave Macmillan. Wheaton, B. (2005). Understanding lifestyle sports; consumption, identity and difference. New York: Routledge.

Neural correlate of spatial presence in an arousing and noninteractive virtual reality: an EEG and psychophysiology study

Using electroencephalography (EEG), psychophysiology, and psychometric measures, this is the first study which investigated the neurophysiological underpinnings of spatial presence. Spatial presence is considered a sense of being physically situated within a spatial environment portrayed by a medium (e.g., television, virtual reality). Twelve healthy children and 11 healthy adolescents were watching different virtual roller coaster scenarios. During a control session, the roller coaster cab drove through a horizontal roundabout track. The following realistic roller coaster rides consisted of spectacular ups, downs, and loops. Low-resolution brain electromagnetic tomography (LORETA) and event-related desynchronization (ERD) were used to analyze the EEG data. As expected, we found that, compared to the control condition, experiencing a virtual roller coaster ride evoked in both groups strong SP experiences, increased electrodermal reactions, and activations in parietal brain areas known to be involved in spatial navigation. In addition, brain areas that receive homeostatic afferents from somatic and visceral sensations of the body were strongly activated. Most interesting, children (as compared to adolescents) reported higher spatial presence experiences and demonstrated a different frontal activation pattern. While adolescents showed increased activation in prefrontal areas known to be involved in the control of executive functions, children demonstrated a decreased activity in these brain regions. Interestingly, recent neuroanatomical and neurophysiological studies have shown that the frontal brain continues to develop to adult status well into adolescence. Thus, the result of our study implies that the increased spatial presence experience in children may result from the not fully developed control functions of the frontal cortex.

Virtual reality and the role of the prefrontal cortex in adults and children

In this review, the neural underpinnings of the experience of presence are outlined. Firstly, it is shown that presence is associated with activation of a distributed network, which includes the dorsal and ventral visual stream, the parietal cortex, the premotor cortex, mesial temporal areas, the brainstem and the thalamus. Secondly, the dorsolateral prefrontal cortex (DLPFC) is identified as a key node of the network as it modulates the activity of the network and the associated experience of presence. Thirdly, children lack the strong modulatory influence of the DLPFC on the network due to their unmatured frontal cortex. Fourthly, it is shown that presence-related measures are influenced by manipulating the activation in the DLPFC using transcranial direct current stimulation (tDCS) while participants are exposed to the virtual roller coaster ride. Finally, the findings are discussed in the context of current models explaining the experience of presence, the rubber hand illusion, and out-of-body experiences.

Modulating presence and impulsiveness by external stimulation of the brain

BACKGROUND "The feeling of being there" is one possible way to describe the phenomenon of feeling present in a virtual environment and to act as if this environment is real. One brain area, which is hypothesized to be critically involved in modulating this feeling (also called presence) is the dorso-lateral prefrontal cortex (dlPFC), an area also associated with the control of impulsive behavior. METHODS In our experiment we applied transcranial direct current stimulation (tDCS) to the right dlPFC in order to modulate the experience of presence while watching a virtual roller coaster ride. During the ride we also registered electro-dermal activity. Subjects also performed a test measuring impulsiveness and answered a questionnaire about their presence feeling while they were exposed to the virtual roller coaster scenario. RESULTS Application of cathodal tDCS to the right dlPFC while subjects were exposed to a virtual roller coaster scenario modulates the electrodermal response to the virtual reality stimulus. In addition, measures reflecting impulsiveness were also modulated by application of cathodal tDCS to the right dlPFC. CONCLUSION Modulating the activation with the right dlPFC results in substantial changes in responses of the vegetative nervous system and changed impulsiveness. The effects can be explained by theories discussing the top-down influence of the right dlPFC on the "impulsive system".

European undergraduate curriculum in geriatric medicine developed using an international modified Delphi technique.

INTRODUCTION the rise in the number of older, frail adults necessitates that future doctors are adequately trained in the skills of geriatric medicine. Few countries have dedicated curricula in geriatric medicine at the undergraduate level. The aim of this project was to develop a consensus among geriatricians on a curriculum with the minimal requirements that a medical student should achieve by the end of medical school. METHODS a modified Delphi process was used. First, educational experts and geriatricians proposed a set of learning objectives based on a literature review. Second, three Delphi rounds involving a panel with 49 experts representing 29 countries affiliated to the European Union of Medical Specialists (UEMS) was used to gain consensus for a final curriculum. RESULTS the number of disagreements following Delphi Rounds 1 and 2 were 81 and 53, respectively. Complete agreement was reached following the third round. The final curriculum consisted of detailed objectives grouped under 10 overarching learning outcomes. DISCUSSION a consensus on the minimum requirements of geriatric learning objectives for medical students has been agreed by European geriatricians. Major efforts will be needed to implement these requirements, given the large variation in the quality of geriatric teaching in medical schools. This curriculum is a first step to help improve teaching of geriatrics in medical schools, and will also serve as a basis for advancing postgraduate training in geriatrics across Europe.

Lernzielkatalog für die studentische Lehre im Fachbereich „Geriatrie“ an Fakultäten für Humanmedizin.

Zusammenfassung Die Betreuung geriatrischer Patientinnen und Patienten setzt, nebst einer entsprechenden Haltung, fundierte Kenntnisse in Diagnostik und Behandlung praktisch aller medizinischen Fachgebiete voraus. Daher ist es wichtig, dass die Kompetenz von Studierenden der Humanmedizin im Bereich Geriatrie entsprechend gefördert wird. Bis heute hat jedoch die studentische Ausbildung im Fach Geriatrie an vielen europäischen Universitäten einen unklaren oder untergeordneten Stellenwert. Als ersten Schritt zur Förderung der Lehre in der Geriatrie hat die Europäische Facharztvereinigung Geriatrie (UEMS-GMS) in einem Delphi-Prozess einen Lernzielkatalog entwickelt. Dieser Katalog enthält die Mindestanforderungen mit spezifischen Lernzielen (Wissen, Fertigkeiten und Haltungen), welche die Studierenden der Humanmedizin bezüglich Geriatrie bis zum Abschluss des Medizinstudiums erwerben sollen. Zur Förderung der Implementierung dieses neuen, kompetenzbasierten Lernzielkatalogs an den deutschsprachigen Universitäten wurde eine an den Sprachgebrauch des „DACH-Raums“ (Deutschland, Österreich und Schweiz) angepasste deutsche Version erstellt. Im vorliegenden Beitrag wird diese Übersetzung vorgestellt. Die Fachgesellschaften für Geriatrie aus Deutschland, Österreich und der Schweiz empfehlen den medizinischen Fakultäten der jeweiligen Länder, diesen Katalog umzusetzen.