Average reference recording from the vagal nerve reveals an evoked indirect response

The vagal nerve conveys information from and to many organs, including the heart. The components of the compound action potentials (CAPs) recorded from the vagal nerve give information about the different fiber types present. In this paper, we show that with the average reference recording method an additional component can be measured. This component is missed when using a tripolar recording method. Recordings were made in anesthetized pigs. Results show that there is an indirect component in the CAP of the cervical vagal nerve. This component comes from the periphery most likely from the heart

12-segment cuff is superior to ring cuff for sensing and stimulation of cardiac fibers in the vagal trunk

Introduction: The vagal nerve is involved in reflexive control of the heart. We would like to sense vagal activity originating from cardiac sensory neurons, and influence cardiac parameters by electrical stimulation of the vagal nerve. The ability of the 12-segment cuff to influence and sense cardiac fibers in the vagal trunk will be compared with the ring cuff. Methods: Experiments were performed in twelve pigs. At the cervical level three cuff electrode configurations were placed on the left vagal nerve for recording and stimulation. The cuffs were 15 mm long and had three circular Pt/Ir electrode contacts with (Fig. 1b). In seven pigs, the third cuff was replaced with a cuff with 12 segments instead of three rings (Fig. 1a). ECG and left ventricular pressure were also recorded. Sensing In twelve pigs sensing was done with a ring cuff and in seven also with a 12-segment cuff. ENG was band-pass filtered at 100-2000Hz, rectified and low-pass filtered at 10Hz, resulting in the envelope of the ENG. Mean activity was removed to obtain only the variations within a cardiac cycle. An ensemble average was determined from 260 cycles of ENG signal, centered on R-tops of the ECG. A signal was identified as cardiac-modulated if the 95%-CI of the ensemble average had a deviation from zero. Stimulation In five pigs the maximal amplitude (300µs, 50Hz) was determined at which, during stimulation with the ring electrode, no coughing occurred. Next in these five pigs, stimulation with this setting was repeated with the ring cuff and the 12-segment cuff. Results: A significantly cardiac-modulated vagal signal was measured in 6/7 pigs with the 12-segment cuff and in 6/12 pigs with the ring cuff. The effect of electrical stimulation on left ventricular pressure was significantly greater when stimulating with the 12-segment cuff than with the ring cuff (p = 0.03). A significant difference was not reached for R-R (p = 0.2) and left ventricular contractility (p = 0.07). Conclusion: The 12-segment cuff seems superior to the ring cuff, considering selective sensing and stimulation of the cardiac fibers in the cervical vagal trunk

An evoked indirect response in the cervical vagal nerve

The response of fibers in the vagal nerve, evoked by electrical stimulation, has been studied in both animals and humans. These compound action potentials (CAPs) consist of components coming from thick, myelinated fibers to thin, unmyelinated fibers. In our study, the possibility is addressed of an indirect component in the CAP which is involved in reflexive control. By using multiple, consecutive electrode sites along the cervical vagal nerve, both the direction and the velocity along the nerve of the CAPs can be analyzed. This information can be used to distinguish direct from indirect components. In this way an indirect component was revealed

Cold trapped atoms detected with evanescent waves

We demonstrate the in situ detection of cold 87 Rb atoms near a dielectric surface using the absorption of a weak, resonant evanescent wave. We have used this technique in time of flight experiments determining the density of atoms falling on the surface. A quantitative understanding of the measured curve was obtained using a detailed calculation of the evanescent intensity distribution. We have also used it to detect atoms trapped near the surface in a standing-wave optical dipole potential. This trap was loaded by inelastic bouncing on a strong, repulsive evanescent potential. We estimate that we trap 1.5 x 10 4 atoms at a density 100 times higher than the falling atoms.Comment: 5 pages, 3 figure

An atom interferometer enabled by spontaneous decay

We investigate the question whether Michelson type interferometry is possible if the role of the beam splitter is played by a spontaneous process. This question arises from an inspection of trajectories of atoms bouncing inelastically from an evanescent-wave (EW) mirror. Each final velocity can be reached via two possible paths, with a {\it spontaneous} Raman transition occurring either during the ingoing or the outgoing part of the trajectory. At first sight, one might expect that the spontaneous character of the Raman transfer would destroy the coherence and thus the interference. We investigated this problem by numerically solving the Schr\"odinger equation and applying a Monte-Carlo wave-function approach. We find interference fringes in velocity space, even when random photon recoils are taken into account.Comment: 6 pages, 5 figures, we clarified the semiclassical interpretation of Fig.

A rainbow of cold atoms caused by a stochastic process

We report direct observation of a rainbow caustic in the velocity distribution of ^{87}Rb atoms, bouncing inelastically on an evanescent-wave atom mirror. In contrast to known examples, this caustic is caused by a stochastic process, namely a spontaneous Raman transition during the bounce. The results are in good agreement with a classical calculation. We observed that although energy is extracted from the atoms, the phase-space density is in most cases not increased

Guiding of cold atoms by a red-detuned laser beam of moderate power

We report measurements on the guiding of cold $^{87}$Rb atoms from a magneto-optical trap by a continuous light beam over a vertical distance of 6.5 mm. For moderate laser power ($<$85 mW) we are able to capture around 40% of the cold atoms. Although the guide is red-detuned, the optical scattering rate at this detuning ($\approx$70 GHz) is acceptably low. For lower detuning ($<$30 GHz) a larger fraction was guided but radiation pressure starts to push the atoms upward, effectively lowering the acceleration due to gravity. The measured guided fraction agrees well with an analytical model.Comment: final version, 6 pages, incl. 6 figure

Observation of modified radiative properties of cold atoms in vacuum near a dielectric surface

We have observed a distance-dependent absorption linewidth of cold $^{87}$Rb atoms close to a dielectric-vacuum interface. This is the first observation of modified radiative properties in vacuum near a dielectric surface. A cloud of cold atoms was created using a magneto-optical trap (MOT) and optical molasses cooling. Evanescent waves (EW) were used to observe the behavior of the atoms near the surface. We observed an increase of the absorption linewidth with up to 25% with respect to the free-space value. Approximately half the broadening can be explained by cavity-quantum electrodynamics (CQED) as an increase of the natural linewidth and inhomogeneous broadening. The remainder we attribute to local Stark shifts near the surface. By varying the characteristic EW length we have observed a distance dependence characteristic for CQED.Comment: 6 pages, 6 figures, some minor revision

Vagal nerve stimulation started just prior to reperfusion limits infarct size and no-reflow

Vagal nerve stimulation (VNS) started prior to, or during, ischemia has been shown to reduce infarct size. Here, we investigated the effect of VNS when started just prior to, and continued during early, reperfusion on infarct size and no-reflow and studied the underlying mechanisms. For this purpose, swine (13 VNS, 10 sham) underwent 45 min mid-LAD occlusion followed by 120 min of reperfusion. VNS was started 5 min prior to reperfusion and continued until 15 min of reperfusion. Area at risk, area of no-reflow (% of infarct area) and infarct size (% of area at risk), circulating cytokines, and regional myocardial leukocyte influx were assessed after 120 min of reperfusion. VNS significantly reduced infarct size from 67 ± 2 % in sham to 54 ± 5 % and area of no-reflow from 54 ± 6 % in sham to 32 ± 6 %. These effects were accompanied by reductions in neutrophil (~40 %) and macrophage (~60 %) infiltration in the infarct area (all p < 0.05), whereas systemic circulating plasma levels of TNFα and IL6 were not affected. The degree of cardioprotection could not be explained by the VNS-induced bradycardia or the VNS-induced decrease in the double product of heart rate and left ventricular systolic pressure. In the presence of NO-synthase inhibitor LNNA, VNS no longer attenuated infarct size and area of no-reflow, which was paralleled by similarly unaffected regional leukocyte infiltration. In conclusion, VNS is a promising novel adjunctive therapy that limits reperfusion injury in a large animal model of acute myocardial infarction