The size, number, and distribution of nerve endings around and within the human epiglottis, focusing on tracheal intubation maneuvers.

The aim of this study was to examine the distribution of nerve endings in the mucosa, submucosa, and cartilage of the epiglottis and the vallecula area and to quantify them. The findings could inform the choice of laryngoscope blades for intubation procedures. Fourteen neck slices from seven unembalmed, cryopreserved human cadavers were analyzed. The slices were stained, and cross and longitudinal sections were obtained from each. The nerve endings and cartilage were identified. The primary metrics recorded were the number, area, and circumference of nerve endings located in the mucosa and submucosa of the pharyngeal and laryngeal sides of the epiglottis, epiglottis cartilage, and epiglottic vallecula zone. The length and thickness of the epiglottis and cartilage were also measured. The elastic cartilage of the epiglottis was primarily continuous; however, it contained several fragments. It was covered with dense collagen fibers and surrounded by adipose cells from the pharyngeal and laryngeal submucosa. Nerve endings were found within the submucosa of pharyngeal and laryngeal epiglottis and epiglottic vallecula. There were significantly more nerve endings on the posterior surface of the epiglottis than on the anterior surface. The epiglottic cartilage was twice the length of the epiglottis. The study demonstrated that the distribution of nerve endings in the epiglottis differed significantly between the posterior and anterior sides; there were considerably more in the former. The findings have implications for tracheal intubation and laryngoscope blade selection and design.

Microscopy of structures surrounding typical acupoints used in clinical practice and electron microscopic evaluation of acupuncture needles.

Although the general functionality and structures of acupoints have been studied, there has been little insight into their underlying morphology and physical characteristics. We describe the microanatomical structures surrounding acupoints, the electron microscopic appearance of the needles, and the physical effects of acupuncture needling on the fascia. We injected heparinized blood solution through thin needles at seven known and commonly used "sweat acupoints" in eight fresh, unembalmed, cryopreserved human cadavers to mark the needle positions, and later, during histological examination, to identify them. After the solution was injected, samples were dissected and prepared for histological examination. We examined 350 cross-sections of five different paraffin wax sections from each acupoint microscopically. Acupuncture needles were photographed and superimposed on the cross-sectioned tissues at similar magnifications. Needles were also examined under a scanning electron microscope to judge the roughness or smoothness of their surfaces. A greater conglomeration of nerve endings surrounded the acupoints than in tissues more than 1-3 cm distant from them. Nerve endings and blood vessels were in close contact with a complex network of membranes formed by interlacing collagen fibers, and were always enclosed within those collagen membranes. Nerve endings were found within hypodermis, muscles, or both. Scanning electron microscopy demonstrated the three-dimensional shapes and sizes of the needles, and the degree of roughness or smoothness of their polished external surfaces. We demonstrate a delicate arrangement of nerve endings and blood vessels enclosed within complex collagen membrane networks at acupoints within the hypodermis and muscle. This arrangement could explain why needling is an essential step in the acupuncture process that provides favorable outcomes in clinical practice.

A reliable septum exists between the lateral cord and medial and posterior cords in the costoclavicular region: Clinical and microanatomical considerations in brachial plexus anesthetic blockade.

BACKGROUND AND OBJECTIVES: The ultrasound-guided proximal infraclavicular costoclavicular block (PICB) appears popular but its results are inconsistent. We sought an accurate demonstration of septae formed between the brachial plexus cords. METHODS: We performed in-plane, lateral-to-medial PICBs on 120 patients and recorded images. Once the most superficial lateral cord component was entered, a 0.4-0.6 mA current was applied to confirm needle placement; 5 ml of local anesthetic (LA) solution was then injected and its spread was observed and recorded. As the needle was advanced, the presence or absence of a hyperechoic linear structure was noted before the deeper compartment was reached, specifically looking for the possible displacement of such a septum. RESULTS: Upon initial scanning, a septum was observed in 67 of the 120 patients (46.2%). However, there was clear displacement of a linear septum between the lateral cord compartment and the medial and posterior cord compartments that prevented spread between the compartments in 94.16% of patients. Piercing the septum evoked motor responses from the medial or posterior cord. The same anatomical regions were studied microanatomically by analyzing cross-sections obtained with the same approach angle as the ultrasound probe. CONCLUSIONS: Intraplexus fascial septae that bundled the medial and posterior cords into one compartment and separated them from the lateral cord were demonstrated and confirmed microanatomically. This suggests the need for two separate injections (or two separate catheter placements for continuous peripheral nerve blockade) into the superficial and deep compartments to ensure LA spread around all three cords of the brachial plexus at this level.

Spatial-Temporal Signals and Clinical Indices in Electrocardiographic Imaging (II): Electrogram Clustering and T-wave Alternans.

During the last years, attention and controversy have been present for the first commercially available equipment being used in Electrocardiographic Imaging (ECGI), a new cardiac diagnostic tool which opens up a new field of diagnostic possibilities. Previous knowledge and criteria of cardiologists using intracardiac Electrograms (EGM) should be revisited from the newly available spatial-temporal potentials, and digital signal processing should be readapted to this new data structure. Aiming to contribute to the usefulness of ECGI recordings in the current knowledge and methods of cardiac electrophysiology, we previously presented two results: First, spatial consistency can be observed even for very basic cardiac signal processing stages (such as baseline wander and low-pass filtering); second, useful bipolar EGMs can be obtained by a digital processing operator searching for the maximum amplitude and including a time delay. In addition, this work aims to demonstrate the functionality of ECGI for cardiac electrophysiology from a twofold view, namely, through the analysis of the EGM waveforms, and by studying the ventricular repolarization properties. The former is scrutinized in terms of the clustering properties of the unipolar an bipolar EGM waveforms, in control and myocardial infarction subjects, and the latter is analyzed using the properties of T-wave alternans (TWA) in control and in Long-QT syndrome (LQTS) example subjects. Clustered regions of the EGMs were spatially consistent and congruent with the presence of infarcted tissue in unipolar EGMs, and bipolar EGMs with adequate signal processing operators hold this consistency and yielded a larger, yet moderate, number of spatial-temporal regions. TWA was not present in control compared with an LQTS subject in terms of the estimated alternans amplitude from the unipolar EGMs, however, higher spatial-temporal variation was present in LQTS torso and epicardium measurements, which was consistent through three different methods of alternans estimation. We conclude that spatial-temporal analysis of EGMs in ECGI will pave the way towards enhanced usefulness in the clinical practice, so that atomic signal processing approach should be conveniently revisited to be able to deal with the great amount of information that ECGI conveys for the clinician.

Spatial-Temporal Signals and Clinical Indices in Electrocardiographic Imaging (I): Preprocessing and Bipolar Potentials.

During the last years, Electrocardiographic Imaging (ECGI) has emerged as a powerful and promising clinical tool to support cardiologists. Starting from a plurality of potential measurements on the torso, ECGI yields a noninvasive estimation of their causing potentials on the epicardium. This unprecedented amount of measured cardiac signals needs to be conditioned and adapted to current knowledge and methods in cardiac electrophysiology in order to maximize its support to the clinical practice. In this setting, many cardiac indices are defined in terms of the so-called bipolar electrograms, which correspond with differential potentials between two spatially close potential measurements. Our aim was to contribute to the usefulness of ECGI recordings in the current knowledge and methods of cardiac electrophysiology. For this purpose, we first analyzed the basic stages of conventional cardiac signal processing and scrutinized the implications of the spatial-temporal nature of signals in ECGI scenarios. Specifically, the stages of baseline wander removal, low-pass filtering, and beat segmentation and synchronization were considered. We also aimed to establish a mathematical operator to provide suitable bipolar electrograms from the ECGI-estimated epicardium potentials. Results were obtained on data from an infarction patient and from a healthy subject. First, the low-frequency and high-frequency noises are shown to be non-independently distributed in the ECGI-estimated recordings due to their spatial dimension. Second, bipolar electrograms are better estimated when using the criterion of the maximum-amplitude difference between spatial neighbors, but also a temporal delay in discrete time of about 40 samples has to be included to obtain the usual morphology in clinical bipolar electrograms from catheters. We conclude that spatial-temporal digital signal processing and bipolar electrograms can pave the way towards the usefulness of ECGI recordings in the cardiological clinical practice. The companion paper is devoted to analyzing clinical indices obtained from ECGI epicardial electrograms measuring waveform variability and repolarization tissue properties.

Vulnerability of different nerves to intrafascicular injection by different needle types and at different approach angles: a mathematical model.

BACKGROUND AND OBJECTIVES: We assume that intrafascicular spread of a solution can only occur if a large enough portion of the distal needle orifice is placed inside the fascicle. Our aim is to present and evaluate a mathematical model that can calculate the theoretical vulnerability of fascicles, analyzing the degree of occupancy of the needle orifice in fascicular tissue by performing simulations of multiple positions that a needle orifice can take inside a cross-sectional nerve area. METHODS: We superimposed microscopic images of two routinely used nerve block needles (22-gauge, 15° needle and 22-gauge, 30° needle) over the microscopic images of cross-sections of four nerve types photographed at the same magnification. Fascicular tissue that was overlapped between 80% and 100% by a needle orifice was considered at risk to possible intrafascicular injection. The effect of three angular approaches was evaluated. RESULTS: There were statistical differences between the vulnerability of fascicular tissue depending on nerve type, the bevel angle of the needle and the angle approach. Fascicular vulnerability was greater in nerve roots of the brachial plexus after using a 22-gauge 30° needle, as was choosing a 45° angle approach to the longitudinal axis of the nerve. CONCLUSIONS: Our results suggest that clinicians may want to consider needle insertion angle and bevel type as they perform peripheral nerve blocks. Furthermore, researchers may want to consider this mathematical model when estimating vulnerabilities of various nerves, needle types and angles of approach of needles to nerves.

A new approach to the intracardiac inverse problem using Laplacian distance kernel.

BACKGROUND: The inverse problem in electrophysiology consists of the accurate estimation of the intracardiac electrical sources from a reduced set of electrodes at short distances and from outside the heart. This estimation can provide an image with relevant knowledge on arrhythmia mechanisms for the clinical practice. Methods based on truncated singular value decomposition (TSVD) and regularized least squares require a matrix inversion, which limits their resolution due to the unavoidable low-pass filter effect of the Tikhonov regularization techniques. METHODS: We propose to use, for the first time, a Mercer's kernel given by the Laplacian of the distance in the quasielectrostatic field equations, hence providing a Support Vector Regression (SVR) formulation by following the principles of the Dual Signal Model (DSM) principles for creating kernel algorithms. RESULTS: Simulations in one- and two-dimensional models show the performance of our Laplacian distance kernel technique versus several conventional methods. Firstly, the one-dimensional model is adjusted for yielding recorded electrograms, similar to the ones that are usually observed in electrophysiological studies, and suitable strategy is designed for the free-parameter search. Secondly, simulations both in one- and two-dimensional models show larger noise sensitivity in the estimated transfer matrix than in the observation measurements, and DSM-SVR is shown to be more robust to noisy transfer matrix than TSVD. CONCLUSION: These results suggest that our proposed DSM-SVR with Laplacian distance kernel can be an efficient alternative to improve the resolution in current and emerging intracardiac imaging systems.

Arrhythmia Mechanism and Scaling Effect on the Spectral Properties of Electroanatomical Maps With Manifold Harmonics.

INTRODUCTION: Spatial and temporal processing of intracardiac electrograms provides relevant information to support the arrhythmia ablation during electrophysiological studies. Current cardiac navigation systems (CNS) and electrocardiographic imaging (ECGI) build detailed 3-D electroanatomical maps (EAM), which represent the spatial anatomical distribution of bioelectrical features, such as activation time or voltage. OBJECTIVE: We present a principled methodology for spectral analysis of both EAM geometry and bioelectrical feature in CNS or ECGI, including their spectral representation, cutoff frequency, or spatial sampling rate (SSR). METHODS: Existing manifold harmonic techniques for spectral mesh analysis are adapted to account for a fourth dimension, corresponding to the EAM bioelectrical feature. Appropriate scaling is required to address different magnitudes and units. RESULTS: With our approach, simulated and real EAM showed strong SSR dependence on both the arrhythmia mechanism and the cardiac anatomical shape. For instance, high frequencies increased significantly the SSR because of the "early-meets-late" in flutter EAM, compared with the sinus rhythm. Besides, higher frequency components were obtained for the left atrium (more complex anatomy) than for the right atrium in sinus rhythm. CONCLUSION: The proposed manifold harmonics methodology opens the field toward new signal processing tools for principled EAM spatiofeature analysis in CNS and ECGI, and to an improved knowledge on arrhythmia mechanisms.

Automatic supporting system for regionalization of ventricular tachycardia exit site in implantable defibrillators.

Electrograms stored in Implantable Cardioverter Defibrillators (ICD-EGM) have been proven to convey useful information for roughly determining the anatomical location of the Left Ventricular Tachycardia exit site (LVTES). Our aim here was to evaluate the possibilities from a machine learning system intended to provide an estimation of the LVTES anatomical region with the use of ICD-EGM in the situation where 12-lead electrocardiogram of ventricular tachycardia are not available. Several machine learning techniques were specifically designed and benchmarked, both from classification (such as Neural Networks (NN), and Support Vector Machines (SVM)) and regression (Kernel Ridge Regression) problem statements. Classifiers were evaluated by using accuracy rates for LVTES identification in a controlled number of anatomical regions, and the regression approach quality was studied in terms of the spatial resolution. We analyzed the ICD-EGM of 23 patients (18±10 EGM per patient) during left ventricular pacing and simultaneous recording of the spatial coordinates of the pacing electrode with a navigation system. Several feature sets extracted from ICD-EGM (consisting of times and voltages) were shown to convey more discriminative information than the raw waveform. Among classifiers, the SVM performed slightly better than NN. In accordance with previous clinical works, the average spatial resolution for the LVTES was about 3 cm, as in our system, which allows it to support the faster determination of the LVTES in ablation procedures. The proposed approach also provides with a framework suitable for driving the design of improved performance future systems.

Implantable defibrillator electrograms and origin of left ventricular impulses: an analysis of regionalization ability and visual spatial resolution.

INTRODUCTION: The implantable cardioverter-defibrillator (ICD) electrogram (EG) is a documentation of ventricular tachycardia. We prospectively analyzed EGs from ICD electrodes located at the right ventricle apex to establish (1) ability to regionalize origin of left ventricle (LV) impulses, and (2) spatial resolution to distinguish between paced sites. METHODS AND RESULTS: LV electro-anatomic maps were generated in 15 patients. ICD-EGs were recorded during pacing from 22 ± 10 LV sites. Voltage of far-field EG deflections (initial, peak, final) and time intervals between far-field and bipolar EGs were measured. Blinded visual analysis was used for spatial resolution. Initial deflections were more negative and initial/peak ratios were larger for lateral versus septal and superior versus inferior sites. Time intervals were shorter for apical versus basal and septal versus lateral sites. Best predictive cutoff values were voltage of initial deflection <-1.24 mV, and initial/peak ratio >0.45 for a lateral site, voltage of final deflection <-0.30 for an inferior site, and time interval <80 milliseconds for an apical site. In a subsequent group of 9 patients, these values predicted correctly paced site location in 54-75% and tachycardia exit site in 60-100%. Recognition of paced sites as different by EG inspection was 91% accurate. Sensitivity increased with distance (0.96 if ≥ 2 cm vs 0.84 if < 2 cm, P < 0.001) and with presence of low-voltage tissue between sites (0.94 vs 0.88, P < 0.001). CONCLUSIONS: Standard ICD-EG analysis can help regionalize LV sites of impulse formation. It can accurately distinguish between 2 sites of impulse formation if they are ≥2 cm apart.