Intestinal Intramural Vascular Anastomoses

Introduction: Present surgical techniques are rarely relying on intestinal intramural vascular anastomoses; however, this could open new limits in reconstructive surgery. Our aim was to study the efficacy of the antimesenteric and the longitudinal intramural vascular anastomoses in a porcine model. Material and Methods: Five minipigs were used. Antimesenteric anastomoses: jejunal loops were detubularized by cutting along the antimesenteric line (Control), in the middle between the mesenteric and antimesenteric border (Group 1) and close to the mesenteric line (Group 2). Mucosal microcirculation (red blood cell velocity, perfusion rate) was recorded with orthogonal polarization spectral imaging (Cytoscan A/R) at the long edge of the detubularized bowel. Longitudinal anastomoses: records were made on a continuous jejunal loop following antimesenteric incision, detubularization, and subsequent ligation of 2, 4, and 6 neighboring vasa recta in the middle of the loop. The same study was repeated on the free end of completely divided jejunal segments with ligation of 2, 4, or 6 vasa recta. Results: Antimesenteric anastomoses: There was no statistically significant difference in red blood cell velocity and perfusion rate between Control and Groups 1 and 2. Longitudinal anastomoses: The red blood cell velocity dropped significantly, while the perfusion rate did not change significantly after ligation of 4 vasa recta in the continuous loop. In the loop with a free end, however, both parameters decreased significantly after ligation of four vessels. Conclusion: It is safe to rely on antimesenteric intramural anastomoses but strong limitation of longitudinal intramural vascular anastomoses should be considered in intestinal reconstructions.     

Localization of Click Trains and Speech by Cats: the Negative Level Effect

Although localization of sound in elevation is believed to depend on spectral cues, it has been shown with human listeners that the temporal features of sound can also greatly affect localization performance. Of particular interest is a phenomenon known as the negative level effect, which describes the deterioration of localization ability in elevation with increasing sound level and is observed only with impulsive or short-duration sound. The present study uses the gaze positions of domestic cats as measures of perceived locations of sound targets varying in azimuth and elevation. The effects of sound level on localization in terms of accuracy, precision, and response latency were tested for sound with different temporal features, such as a click train, a single click, a continuous sound that had the same frequency spectrum of the click train, and speech segments. In agreement with previous human studies, negative level effects were only observed with click-like stimuli and only in elevation. In fact, localization of speech sounds in elevation benefited significantly when the sound level increased. Our findings indicate that the temporal continuity of a sound can affect the frequency analysis performed by the auditory system, and the variation in the frequency spectrum contained in speech sound does not interfere much with the spectral coding for its location in elevation.     

Impact of scanning density on spectral domain optical coherence tomography assessments in neovascular age‐related macular degeneration

Purpose: To determine the effect of optical coherence tomography (OCT) B‐scan density on the qualitative assessment of neovascular age‐related macular degeneration (AMD). Methods: Data were collected from 59 patients imaged with Topcon 3D OCT‐1000 (128 B‐scans × 512 A‐scans). Custom software was used to generate less dense subsets of scans: 1/16 (eight B‐scans), 1/8 (16 B‐scans), 1/4 (32 B‐scans) and 1/2 (64 B‐scans). At each B‐scan density, scans were assessed for cystoid spaces, subretinal fluid (SRF), subretinal tissue (SRT) and pigment epithelium detachment (PED). For each sampling density, sensitivity, specificity and predictive values were calculated using the full volume scan (128 B‐scans) as the reference standard. Results: For cystoid spaces, the detection sensitivity was 76.3% at 1/16 density; this rose to 89.5% with a 1/4 density. For SRF, the detection sensitivity was 75.0% at a 1/16 density; this increased to 91.1% with 1/4 density. For PED, even at the lowest sampling density (1/16) the detection sensitivity was 86.4%; this rose to 94.9% at 1/4 density. For SRT, detection sensitivity at a 1/16 density was 64.7% and only rose above 90% with the densest sampling subset (1/2). Conclusions: Use of scanning protocols with reduced sampling densities resulted in decreased detection of key features of neovascular AMD; despite this, a sampling density reduced to 1/4 appeared to allow accurate assessment for most features. Current management of neovascular AMD is dependent on qualitative assessment of OCT images; with the recent proliferation of OCT systems, optimization and standardization of scanning protocols may be of value.     

Tracking voice change after thyroidectomy: application of spectral/cepstral analyses

This study evaluates the utility of perioperative spectral and cepstral acoustic analyses to monitor voice change after thyroidectomy. Perceptual and acoustic analyses were conducted on speech samples (sustained vowel /ɑ/ and CAPE-V sentences) provided by 70 participants (36 women and 34 men) at four study time points: prior to thyroid surgery and 2 weeks, 3 months and 6 months after thyroidectomy. Repeated measures analyses of variance focused on the relative amplitude of the dominant harmonic in the voice signal (cepstral peak prominence, CPP), the ratio of low-to-high spectral energy, and their respective standard deviations (SD). Data were also examined for relationships between acoustic measures and perceptual ratings of overall severity of voice quality. Results showed that perceived overall severity and the acoustic measures of the CPP and its SD (CPPsd) computed from sentence productions were significantly reduced at 2-week post-thyroidectomy for 20 patients (29% of the sample) who had self-reported post-operative voice change. For this same group of patients, the CPP and CPPsd computed from sentence productions improved significantly from 2-weeks post-thyroidectomy to 6-months post-surgery. CPP and CPPsd also correlated well with perceived overall severity (r = ?0.68 and ?0.79, respectively). Measures of CPP from sustained vowel productions were not as effective as those from sentence productions in reflecting voice deterioration in the post-thyroidectomy patients at the 2-week post-surgery time period, were weaker correlates with perceived overall severity, and were not as effective in discriminating negative voice outcome (NegVO) from normal voice outcome (NormVO) patients as compared to the results from the sentence-level stimuli. Results indicate that spectral/cepstral analysis methods can be used with continuous speech samples to provide important objective data to document the effects of dysphonia in a post-thyroidectomy patient sample. When used in conjunction with patient's self-report and other general measures of vocal dysfunction, the acoustic measures employed in this study contribute to a complete profile of the patient's vocal condition.     

Acoustic Cues for Sound Source Distance and Azimuth in Rabbits, a Racquetball and a Rigid Spherical Model

There are numerous studies measuring the transfer functions representing signal transformation between a source and each ear canal, i.e., the head-related transfer functions (HRTFs), for various species. However, only a handful of these address the effects of sound source distance on HRTFs. This is the first study of HRTFs in the rabbit where the emphasis is on the effects of sound source distance and azimuth on HRTFs. With the rabbit placed in an anechoic chamber, we made acoustic measurements with miniature microphones placed deep in each ear canal to a sound source at different positions (10–160 cm distance, ±150° azimuth). The sound was a logarithmically swept broadband chirp. For comparisons, we also obtained the HRTFs from a racquetball and a computational model for a rigid sphere. We found that (1) the spectral shape of the HRTF in each ear changed with sound source location; (2) interaural level difference (ILD) increased with decreasing distance and with increasing frequency. Furthermore, ILDs can be substantial even at low frequencies when distance is close; and (3) interaural time difference (ITD) decreased with decreasing distance and generally increased with decreasing frequency. The observations in the rabbit were reproduced, in general, by those in the racquetball, albeit greater in magnitude in the rabbit. In the sphere model, the results were partly similar and partly different than those in the racquetball and the rabbit. These findings refute the common notions that ILD is negligible at low frequencies and that ITD is constant across frequency. These misconceptions became evident when distance-dependent changes were examined.     

Spectral Analysis of the High Resolution QRS Complex During Exercise-Induced Ischemia

Background: The effect of acute myocardial infarction and regional ischemia on the frequency content of the ECG signal has been described by several investigators. In the present study, the feasibility of assessing changes in the QRS spectrum during exercise testing, and whether these changes are related to the occurrence of ischemia were examined. Methods: Spectral analysis of the high resolution ECGs from leads V₃, V₄, V₅, and V₆ were performed in two groups of male subjects before, during, and following treadmill exercise testing. Group A included 32 coronary artery disease (CAD) patients, with arteriographically proven >75% obstruction of at least two main coronary arteries, and group B included 30 healthy subjects, without history or symptoms of CAD. Signal averaging and filtering techniques were used in order to enhance the signal-to-noise ratio of the recorded ECGs. The power spectrum of the averaged QRS waveform for the different stages of the exercise testing was computed using a Fast Fourier Transform, and the slope of the linear regression line was found in the frequency range 7.81–249.92 Hz on the plot of log((amplitude)²) versus log(frequency). Results: Regression line slopes immediately after peak exercise were significantly lower for the CAD group than for the healthy subjects in 3 of the 4 examined leads. No significant changes in slopes were found between the two groups at rest or during late recovery. Comparing the differences between slopes at different stages of the test revealed that the difference between postexercise slope and rest slope has lower mean values for the CAD group in all four leads, with a significant difference in lead V6, and for the difference between postexercise slope and recovery slope, lower mean values were found for the CAD group in all four leads, with a significant difference in V5 and V6. Conclusions: These findings indicate that ischemic changes affect the power spectrum of the QRS complex, and result in a steeper regression line on a log-log scale.     

Nile Red fluorescence spectroscopy reports early physicochemical changes in myelin with high sensitivity

The molecular composition of myelin membranes determines their structure and function. Even minute changes to the biochemical balance can have profound consequences for axonal conduction and the synchronicity of neural networks. Hypothesizing that the earliest indication of myelin injury involves changes in the composition and/or polarity of its constituent lipids, we developed a sensitive spectroscopic technique for defining the chemical polarity of myelin lipids in fixed frozen tissue sections from rodent and human. The method uses a simple staining procedure involving the lipophilic dye Nile Red, whose fluorescence spectrum varies according to the chemical polarity of the microenvironment into which the dye embeds. Nile Red spectroscopy identified histologically intact yet biochemically altered myelin in prelesioned tissues, including mouse white matter following subdemyelinating cuprizone intoxication, as well as normal-appearing white matter in multiple sclerosis brain. Nile Red spectroscopy offers a relatively simple yet highly sensitive technique for detecting subtle myelin changes.

Myelin is a highly ordered, lipid-rich extension of glial cell membrane that facilitates rapid and efficient saltatory conduction of action potentials along axons in the central and peripheral nervous systems. The stability of myelin membranes critically depends on its molecular composition (1–3). Although myelin is maintained roughly at a ratio of 70:30% lipid to protein (4), lipid membranes are highly fluid; changes in lipid composition are defining characteristics of myelin development (5), homeostasis in the adult, and aging in rodents (6, 7), as well as primates (8). Shifts in lipid composition also occur in inflammatory demyelinating disorders like multiple sclerosis (MS) (9, 10). Lipids are even theorized to be targets of immune attacks in autoimmune disorders, a role previously ascribed to proteins (11). Key roles for lipids notwithstanding, tools to interrogate biochemical changes to myelin lipids have largely been restricted to in vitro systems.Once thought to be inert, myelin is now known to be a chemically and structurally dynamic element (12). Specific combinations of proteins and lipids induce formation and compaction of multilamellar vesicles that resemble myelin (13), underscoring the importance of correct chemical composition for assembly. Conversely, alterations in these molecular proportions promote decompaction and myelin vesiculation (3, 14). The polarity of lipid species in cell membranes influences their packing properties and therefore stability (15). Governed by competing thermodynamic forces of lipid curling and hydrocarbon packing (16), myelin sheaths lie at the critical edge of bilayer stability and thus are susceptible to factors in the environment. Indeed, the myelin integrity theory of MS rests on the outsized influence of environmental forces on myelin stability and function (17). Therefore, methods for detecting physicochemical changes in myelin lipid composition in situ would greatly enhance our understanding of early events in myelin development, as well as myelin damage in disease states, with important implications for therapies designed to prevent myelin loss in MS and other demyelinating disorders.The study of myelin lipid biochemistry poses unique challenges (18). Traditional analytical methods, such as thin-layer chromatography and high-performance liquid chromatography (19), depend on tissue homogenization that eliminates informative spatial relationships. Imaging lipid mass spectrometry (20) preserves spatial relationships, but submicron resolution has yet to be realized, and reproducibility at the level of sample preparation remains problematic (21). Coherent anti–Stokes Raman scattering microscopy provides high-resolution, label-free imaging of lipids in histological samples (22), but this method lacks sensitivity and requires expertise in nonlinear optics as well as highly specialized hardware. Finally, fluorescent lipophilic dyes, though widely available and easy to use, have traditionally been employed to detect lipid-rich structures in only a qualitative manner. Conventional fluorescence microscopy is therefore unable to detect subtle shifts in lipid biochemistry. By contrast, Nile Red (NR) is a fluorescent dye that is well situated to report changes in the chemical polarity of cell membranes and myelin, being both lipophilic (23, 24) and differentially fluorescent depending on solvent environment (i.e., exhibits solvatochromism) (25). The current study uses NR fluorescence spectroscopy to identify polarity shifts as an early manifestation of myelin disease prior to overt demyelination. We show that this technique reports subtle biochemical changes in myelin, resulting in a method that is a very sensitive marker of incipient myelin injury.     

Does the autonomic nervous system play a role in the development of insulin resistance? A study on heart rate variability in first‐degree relatives of Type 2 diabetes patients and control subjects

AIMS: To investigate dysregulation of the autonomic nervous system as a potential mechanism for early insulin resistance in the development of Type 2 diabetes. METHODS: Thirteen healthy individuals with first-degree relatives with Type 2 diabetes (R) were compared with 14 control subjects without family history of diabetes (C), matched for age, body mass index and sex. An oral glucose tolerance test and a hyperinsulinaemic euglycaemic clamp were performed. Analysis of heart rate variability during rest, controlled breathing, an orthostatic manoeuvre and a standardized physical stress (cold pressor test (CPT)), were used to evaluate the activity of the autonomic nervous system. RESULTS: Fasting blood glucose, HbA1c and serum insulin were similar in the R and C groups. The M-value, reflecting insulin sensitivity, did not differ significantly between the groups. Total spectral power and high-frequency power were lower in R during controlled breathing (P = 0.05 and P = 0.07, respectively), otherwise there were no significant differences between R and C in heart rate variability. However, low-frequency (LF)/high-frequency (HF) spectral power ratio during CPT, reflecting sympathetic/parasympathetic balance, was negatively associated with insulin sensitivity (r = -0.53, P = 0.006). When all subjects were divided into two groups by the mean M-value, the low M-value group displayed an overall higher LF/HF ratio (P = 0.04). HF power was lower in the low M-value group during controlled breathing and CPT (P = 0.01 and P = 0.03, respectively). CONCLUSION: An altered balance of the parasympathetic and sympathetic nervous activity, mainly explained by an attenuated parasympathetic activity, might contribute to the development of insulin resistance and Type 2 diabetes.