Gregory O’Grady

High-resolution mapping of in vivo gastrointestinal slow wave activity using flexible printed circuit board electrodes: methodology and validation.

High-resolution, multi-electrode mapping is providing valuable new insights into the origin, propagation, and abnormalities of gastrointestinal (GI) slow wave activity. Construction of high-resolution mapping arrays has previously been a costly and time-consuming endeavor, and existing arrays are not well suited for human research as they cannot be reliably and repeatedly sterilized. The design and fabrication of a new flexible printed circuit board (PCB) multi-electrode array that is suitable for GI mapping is presented, together with its in vivo validation in a porcine model. A modified methodology for characterizing slow waves and forming spatiotemporal activation maps showing slow waves propagation is also demonstrated. The validation study found that flexible PCB electrode arrays are able to reliably record gastric slow wave activity with signal quality near that achieved by traditional epoxy resin-embedded silver electrode arrays. Flexible PCB electrode arrays provide a clinically viable alternative to previously published devices for the high-resolution mapping of GI slow wave activity. PCBs may be mass-produced at low cost, and are easily sterilized and potentially disposable, making them ideally suited to intra-operative human use.

Origin, propagation and regional characteristics of porcine gastric slow wave activity determined by high‐resolution mapping

Background  The pig is a popular model for gastric electrophysiology studies. However, its normal baseline gastric activity has not been well characterized. High‐resolution (HR) mapping has recently enabled an accurate description of human and canine gastric slow wave activity, and was employed here to define porcine gastric slow wave activity.

High‐resolution spatial analysis of slow wave initiation and conduction in porcine gastric dysrhythmia

Background  The significance of gastric dysrhythmias remains uncertain. Progress requires a better understanding of dysrhythmic behaviors, including the slow wave patterns that accompany or promote them. The aim of this study was to use high‐resolution spatiotemporal mapping to characterize and quantify the initiation and conduction of porcine gastric dysrhythmias.

Comparison of filtering methods for extracellular gastric slow wave recordings.

Background Extracellular recordings are used to define gastric slow wave propagation. Signal filtering is a key step in the analysis and interpretation of extracellular slow wave data; however, there is controversy and uncertainty regarding the appropriate filtering settings. This study investigated the effect of various standard filters on the morphology and measurement of extracellular gastric slow waves.

Falling-edge, variable threshold (FEVT) method for the automated detection of gastric slow wave events in high-resolution serosal electrode recordings.

High resolution (HR) multi-electrode mapping is increasingly being used to evaluate gastrointestinal slow wave behaviors. To create the HR activation time (AT) maps from gastric serosal electrode recordings that quantify slow wave propagation, it is first necessary to identify the AT of each individual slow wave event. Identifying these ATs has been a time consuming task, because there has previously been no reliable automated detection method. We have developed an automated AT detection method termed falling-edge, variable threshold (FEVT) detection. It computes a detection signal transform to accentuate the high ‘energy’ content of the falling edges in the serosal recording, and uses a running median estimator of the noise to set the time-varying detection threshold. The FEVT method was optimized, validated, and compared to other potential algorithms using in vivo HR recordings from a porcine model. FEVT properly detects ATs in a wide range of waveforms, making its performance substantially superior to the other methods, especially for low signal-to-noise ratio (SNR) recordings. The algorithm offered a substantial time savings (>100 times) over manual-marking whilst achieving a highly satisfactory sensitivity (0.92) and positive-prediction value (0.89).

The gastrointestinal electrical mapping suite (GEMS): software for analyzing and visualizing high-resolution (multi-electrode) recordings in spatiotemporal detail

BackgroundGastrointestinal contractions are controlled by an underlying bioelectrical activity. High-resolution spatiotemporal electrical mapping has become an important advance for investigating gastrointestinal electrical behaviors in health and motility disorders. However, research progress has been constrained by the low efficiency of the data analysis tasks. This work introduces a new efficient software package: GEMS (Gastrointestinal Electrical Mapping Suite), for analyzing and visualizing high-resolution multi-electrode gastrointestinal mapping data in spatiotemporal detail.ResultsGEMS incorporates a number of new and previously validated automated analytical and visualization methods into a coherent framework coupled to an intuitive and user-friendly graphical user interface. GEMS is implemented using MATLAB®, which combines sophisticated mathematical operations and GUI compatibility. Recorded slow wave data can be filtered via a range of inbuilt techniques, efficiently analyzed via automated event-detection and cycle clustering algorithms, and high quality isochronal activation maps, velocity field maps, amplitude maps, frequency (time interval) maps and data animations can be rapidly generated. Normal and dysrhythmic activities can be analyzed, including initiation and conduction abnormalities. The software is distributed free to academics via a community user website and forum (http://sites.google.com/site/gimappingsuite).ConclusionsThis software allows for the rapid analysis and generation of critical results from gastrointestinal high-resolution electrical mapping data, including quantitative analysis and graphical outputs for qualitative analysis. The software is designed to be used by non-experts in data and signal processing, and is intended to be used by clinical researchers as well as physiologists and bioengineers. The use and distribution of this software package will greatly accelerate efforts to improve the understanding of the causes and clinical consequences of gastrointestinal electrical disorders, through high-resolution electrical mapping.

The bioelectrical basis and validity of gastrointestinal extracellular slow wave recordings

•  Extracellular recording techniques are commonly used to measure bioelectrical activity. However, the validity of gastrointestinal extracellular recordings has recently been challenged. •  In this joint experimental and modelling study, slow waves were recorded during contractile inhibition, biphasic and monophasic slow wave potentials were recorded simultaneously, and the biophysical basis of extracellular potentials was modelled with comparison to experimental data. •  The results showed that in vivo extracellular techniques reliably recorded slow waves in the absence of contractions, and potentials recorded using conventional serosal electrodes (biphasic) were concordant in phase and morphology with those recorded using suction electrodes (monophasic). •  Modelling further demonstrated that the morphology of experimental recordings is consistent with the biophysics underlying slow wave depolarisation. •  In total, these results demonstrate that gastrointestinal extracellular recordings are valid when performed and analysed correctly, reliably representing bioelectrical slow wave events. Motion suppression is not routinely required for in vivo extracellular studies.

Gastrointestinal extracellular electrical recordings: fact or artifact?

Extracellular electrical recordings underpin an important literature of basic and clinical motility science. In the November 2011 edition of Neurogastroenterology and Motility, Sanders and colleagues reported that contraction artifacts could be recorded from in vitro murine gastric tissues using extracellular electrodes, and that true extracellular bioelectrical activity could not be detected when the contractions were suppressed. The authors interpret their findings to mean that previous extracellular studies have generally assayed contraction artifacts, rather than bioelectrical activity, and suggest that movement suppression is an obligatory control for extracellular experiments. If their interpretation is correct, these claims would be significant, requiring a reinterpretation of many studies, and posing major challenges for future in vivo and especially clinical work. However, a demonstration that motion artifacts can be recorded from murine in vitro tissue does not necessarily mean that other extracellular studies also represented artifacts. This viewpoint evaluates a recently published by Sanders and colleagues in light of the competing literature, and finds a considerable volume of evidence to support the veracity of GI extracellular electrical recordings. It is reasoned from biophysical principles, technical considerations, and experimental studies that motion artifacts cannot explain GI extracellular electrical recordings in general, and that bioelectrical fact and artifact can be readily and reliably distinguished in most contexts. Calls for obligatory motion suppression for extracellular studies are therefore not supported. However, the artifacts recorded by Sanders and colleagues nevertheless serve as a reminder that educated caution is needed when recording, filtering and interpreting extracellular data.

Anatomical registration and three-dimensional visualization of low and high-resolution pan-colonic manometry recordings

Background  Colonic propagating sequences (PS) are important for the movement of colonic content and defecation, and aberrant PS patterning has been associated with slow transit constipation. However, because these motor patterns are typically recorded over long periods (24 h +), the visualization of PS spatiotemporal patterning is difficult. Here, we develop a novel method for displaying pan‐colonic motility patterns.

Effect of Nasogastric Tube Feeding vs Nil per Os on Dysmotility in Acute Pancreatitis: Results of a Randomized Controlled Trial

BACKGROUND Evidence from animal studies suggests that gastrointestinal motility is impaired in acute pancreatitis. Enteral nutrition, and more specifically nasogastric tube feeding, has emerged as a key treatment modality in patients with acute pancreatitis, but its effect on motility has not been investigated in this setting. The aim was to validate the Gastroparesis Cardinal Symptom Index (GCSI) in patients with acute pancreatitis and determine the effect of nasogastric tube feeding on GCSI. METHODS The study design was a randomized controlled trial. Patients were allocated to nasogastric tube feeding or nil per os within 24 hours of hospital admission. GCSI data from before randomization to 72 hours after randomization were analyzed. The test-retest reliability analysis was used to calculate Cronbachs α. RESULTS Seventeen patients were randomized to nasogastric tube feeding and 18 to nil per os. Overall, the total GCSI score significantly decreased over the study (F = 8.537; P = .001) but was not significantly different between the 2 study groups during hospitalization (F = 1.159; P = .322). However, patients on nasogastric tube feeding did show improved appetite compared with nil per os (F = 3.526; P = .036). The GCSI was found to be a reliable tool in the setting of acute pancreatitis (Cronbachs α = 0.852). CONCLUSIONS Nasogastric tube feeding does not appear to affect dysmotility symptoms in acute pancreatitis as measured by the GCSI, although appetite improved. Use of the simple, noninvasive, and inexpensive GCSI tool to evaluate motility is recommended in future clinical trials in pancreatology.