Effect of Cardiac-Cycle-Synchronized Selective Vagal Stimulation on Heart Rate and Blood Pressure in Rats

Introduction

Activation of the baroreflex system through the selective vagal nerve stimulation (sVNS) may become a treatment option for therapy-resistant hypertension, which is a frequently observed problem in the antihypertensive therapy. In previous studies, we used continuous sVNS to lower blood pressure (BP) without major side effects in a rat model. As continuous stimulation is energy consuming and sVNS could be implemented in an antihypertensive stimulator, it was the aim of this study to investigate the efficacy of pulsatile, cardiac-cycle-synchronized sVNS (cssVNS) on the reduction of BP.

Methods

A multichannel cuff electrode was wrapped around the left vagal nerve in six male Wistar rats under Isoflurane anesthesia. BP was recorded in the left carotid artery. An electrocardiogram (ECG) was obtained via subcutaneous needle electrodes. The aortic depressor nerve fibers in the vagal nerve bundle were selectively stimulated with 18 parameter settings within a window of 15–30 ms after the R-peak in the ECG. The stimulation paradigm included every heartbeat, every second heart beat, and every third heart beat. BP and heart rate were initially recorded over 10 min.

Results

Using cssVNS, BP could be significantly reduced over 30 min and maintained at this level. While the highest BP reduction was seen during cssVNS at every heartbeat with minimal bradycardia, less—yet significant—BP reduction was seen during cssVNS at every second or third heartbeat without causing detectable bradycardia.

Conclusion

cssVNS can chronically reduce BP in rats avoiding measurable bradycardic side effects. This energy-efficient technique might allow the implementation of sVNS using an implantable device to permanently lower BP in patients.

Funding

The study was funded by Bundesministerium fur Bildung und Forschung/German Federal Ministry of Education and Research among the call “Individualisierte Medizintechnik” under the grant number FKZ 13GW0120B.

     

Quantitative analysis of bile acids in human plasma by liquid chromatography-electrospray tandem mass spectrometry: a simple and rapid one-step method.

Bile acids play a pivotal role in the metabolism of cholesterol and lipids. Their blood concentrations are important prognostic and diagnostic indicators of hepatobiliary and intestinal dysfunction. This class of molecules comprises a heterogeneous group of compounds with a common cholesterol scaffold. Recently, the introduction of liquid chromatography coupled to tandem mass spectrometry methods has revealed an innovative path in the quantisation of specific bile acids in biological specimens. A robust and sensitive method has been developed based on high performance liquid chromatography separation coupled to an electrospray triple-quadrupole mass spectrometer. Human plasma samples were analysed on a C18 reverse-phase column. The elution profiles were monitored in multiple reaction-monitoring mode, quantifying and identifying each analyte by its own unique precursor to product patterns. A linear correlation over a broad range of bile acid concentrations (0.1-100 microM) was observed. The average recovery period for all of the analysed bile acids was 98 +/- 3%. Intra-day and inter-day precision averages were 2% and 5.4%, respectively. The determination was achieved within a single chromatographic run for all unconjugated, glycine- and taurine-conjugated isomeric forms of bile acids. As a proof of principle this method has been validated on a small subset of cholestatic patients (n = 7) and compared to appropriate clinical controls (n = 10). Based upon our encouraging experimental results, the described HPLC separation coupled to tandem mass spectrometry method for the analysis of bile acids in biological samples is deemed a robust and accurate procedure. Consequently, we propose this technique as a suitable candidate method for the identification and quantitation of bile acids in routine analysis.     

Analysis of B cell subsets following pancreatic islet cell transplantation in a patient with type 1 diabetes by cytometric fingerprinting

Manual gating of bivariate plots remains the most frequently used data analysis method in flow cytometry. However, gating is operator-dependent and cumbersome, particularly with the increasing complexity of modern multicolor immunophenotyping data. A method that can remove operator bias, enable systematic and thorough analysis of complex high-dimensional data, correlate temporal changes in different subsets and lead to biomarker discovery is needed. Here we apply such a method, called cytometric fingerprinting (CF), to data obtained on peripheral blood B cells from an adult patient with type-1 diabetes who underwent pancreatic islet transplantation. We establish that CF can be used to analyze longitudinal trends in immunophenotypic data, and show that results from CF are comparable to those obtained with traditional gating methods. Both methods reveal the appearance of transitional B cells and subsequent accumulation of more mature B cells following immunosuppression and transplantation. This pattern is consistent with a temporally ordered process of B cell auto-reconstitution. We also show the comparative efficiency of fingerprinting in recognizing relative changes in B cell subsets with respect to time, its ability to couple the data with statistical methods (agglomerative clustering) and its potential to define novel subsets.     

Virtual palpation of skeletal landmarks with multimodal display interfaces

The 3D location of skeletal landmarks on CT datasets is an important procedure, used in many research and clinical contexts. The standard procedure involves the segmentation of the CT images, the creation of a 3D surface bone model, and the location of the landmarks on this surface. However, the segmentation is time-consuming and requires skilled operators and sophisticated software. The aim of the present study is to evaluate the efficacy of a multimodal display interface to direct volumetric interactive visualization in performing a virtual palpation task. An expert operator used the CT dataset of a patient's thigh region to locate 14 femoral skeletal landmarks. This operation was repeatedly performed using different CT data representation; the accuracy and repeatability were compared to those achievable with the conventional procedure based on the segmented 3D surface. When a multimodal display interface (formed by an orthogonal slice, RXCT and interactive isosurface views) was used to perform the virtual palpation directly on the CT data, the average coordinates of the landmarks did not differ significantly from those located on the 3D surface, and the measurement repeatability was actually better with the multimodal display of the volumetric data than with the 3D surface. Thus, we can conclude that skeletal virtual palpation can be performed directly on the CT dataset, as far as the virtual palpation is performed with a multimodal display interface.     

In vitro and in vivo evaluation of acellular diaphragmatic matrices seeded with muscle precursors cells and coated with VEGF silica gels to repair muscle defect of the diaphragm

In this work, a bioartificial system consisting of VEGF-loaded porous silica gel and myoblasts cultured on acellular diaphragmatic matrix (ADM) has been implanted to repair a surgically created diaphragmatic defect in Lewis rats. ADMs exerted a strong angiogenic response on chorio-allantoic membrane. Cytotoxicity, VEGF release and matrix erodibility in vitro tests demonstrated that the silica support was nontoxic and that the VEGF bioactivity was maintained after matrix entrapment and it was released within a timeframe that can be modulated by synthesis parameters. Different grafts composed by ADMs with and without autologous male myoblasts or/and VEGF-loaded porous silica gel have been implanted to repair previously created diaphragmatic defects in female Lewis rats. Patches composed of ADMs and myoblasts appeared well preserved until 8 weeks, and contained multinucleated cells and cholinergic fibers. At 8 weeks, the implanted cells were still present inside the patches. The disappointing results obtained when VEGF was delivered by porous silica gel were probably due to an abnormal angiogenic response following an excess of local growth factor concentration. Taken together, these results confirmed that our matrices contained biologically active angiogenic factors which were per se sufficient to induce neo-vessels formation, thus allowing the survival of implanted myoblasts.