L K Cheng

University of Auckland, Окленд, Auckland, New Zealand

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Publications (43)69.29 Total impact

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    ABSTRACT: Background: Colorectal resections alter colonic motility, including disruption of control by neural or bioelectrical cell networks. The long-term impact of surgical resections and anastomoses on colonic motor patterns has, however, never been assessed accurately. Fibreoptic high-resolution colonic manometry was employed to define motility in patients who had undergone distal colorectal resection. Methods: Recruited patients had undergone distal colorectal resections more than 12 months previously, and had normal bowel function. Manometry was performed in the distal colon (36 sensors; 1-cm intervals), with 2-h recordings taken before and after a meal, with comparison to controls. Analysis quantified all propagating events and frequencies (cyclical, short single, and long single motor patterns), including across anastomoses. Results: Fifteen patients and 12 controls were recruited into the study. Coordinated propagating events directly traversed the healed anastomoses in nine of 12 patients with available data, including antegrade and retrograde cyclical, short single and long single patterns. Dominant frequencies in the distal colon were similar in patients and controls (2-3 cycles/min) (antegrade P = 0·482; retrograde P = 0·178). Compared with values before the meal, the mean(s.d.) number of dominant cyclical retrograde motor patterns increased in patients after the meal (2·1(2·7) versus 32·6(31·8) in 2 h respectively; P < 0·001), similar to controls (P = 0·178), although the extent of propagation was 41 per cent shorter in patients, by a mean of 3·4 cm (P = 0·003). Short and long single propagating motor patterns were comparable between groups in terms of frequency, velocity, extent and amplitude. Conclusion: Motility patterns and meal responses are restored after distal colorectal resection in patients with normal bowel function. Coordinated propagation across healed anastomoses may indicate regeneration of underlying cellular networks. These data define colorectal surgical recovery and provide a foundation for evaluating patients with postoperative dysfunction.
    No preview · Article · Jan 2016 · British Journal of Surgery
  • P Du · A Hameed · T R Angeli · C Lahr · T L Abell · L K Cheng · G O'Grady
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    ABSTRACT: Gastric contractions are coordinated by slow waves, generated by interstitial cells of Cajal (ICC). Gastric surgery affects slow wave conduction, potentially contributing to postoperative gastric dysfunction. However, the impact of gastric cuts on slow waves has not been comprehensively evaluated. This study aimed to define consequences of surgical excisions on gastric slow waves by applying high-resolution (HR) electrical mapping and in silico modeling. Patients undergoing gastric stimulator implantation (n = 10) underwent full-thickness stapled excisions (25 × 15 mm, distal corpus) for histological evaluation, enabling HR mapping (256 electrodes; 36 cm(2) ) over and adjacent to excisions. A biophysically based in silico model of bidirectionally coupled ICC networks was developed and applied to investigate the underlying conduction mechanisms and importance of excision orientation. Normal gastric slow waves propagated aborally (3.0 ± 0.2 cpm). Excisions induced complete conduction block and wavelets that rotated around blocks, then propagated rapidly circumferentially distal to the blocks (8.5 ± 1.2 vs normal 3.6 ± 0.4 mm/s; p < 0.01). This 'conduction anisotropy' homeostatically restored antegrade propagating gastric wavefronts distal to excisions. Excisions were associated with complex dysrhythmias in five patients: retrograde propagation (3/10), ectopics (3/10), functional blocks (2/10), and collisions (1/10). Simulations demonstrated conduction anisotropy emerged from bidirectional coupling within ICC layers and showed transverse incision length and orientation correlated with the degree of conduction distortion. Orienting incisions in the longitudinal gastric axis causes least disruption to electrical conduction and motility. However, if transverse incisions are made, a homeostatic mechanism of gastric conduction anisotropy compensates by restoring aborally propagating wavefronts. Complex dysrhythmias accompanying excisions could modify postoperative recovery in susceptible patients. © 2015 John Wiley & Sons Ltd.
    No preview · Article · Aug 2015 · Neurogastroenterology and Motility
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    ABSTRACT: Background High-resolution (HR) extracellular mapping allows accurate profiling of normal and dysrhythmic slow wave patterns. A current limitation is that cables traverse the abdominal wall or a natural orifice, risking discomfort, dislodgement or infection. Wireless approaches offer advantages, but a multi-channel system is required, capable of recording slow waves and mapping propagation with high fidelity.MethodsA novel multi-channel (n = 7) wireless mapping system was developed and compared to a wired commercial system. Slow wave signals were recorded from the porcine gastric and intestinal serosa in vivo. Signals were simultaneously acquired using both systems, and were filtered and processed to map activation wavefronts. For validation, the frequency and amplitude of detected events were compared, together with the speed and direction of mapped wavefronts.Key ResultsThe wireless device achieved comparable signal quality to the reference device, and slow wave frequencies were identical. Amplitudes of the acquired gastric and intestinal slow wave signals were consistent between the devices. During normal propagation, spatiotemporal mapping remained accurate in the wireless system, however, during ectopic dysrhythmic pacemaking, the lower sampling resolution of the wireless device led to reduced accuracy in spatiotemporal mapping.Conclusions & InferencesA novel multichannel wireless device is presented for mapping slow wave activity. The device achieved high quality signals, and has the potential to facilitate chronic monitoring studies and clinical translation of spatiotemporal mapping. The current implementation may be applied to detect normal patterns and dysrhythmia onset, but HR mapping with finely spaced arrays currently remains necessary to accurately define dysrhythmic patterns.
    No preview · Article · Jan 2015 · Neurogastroenterology and Motility
  • R.J. Vyas · J. Gao · L.K. Cheng · P. Du
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    ABSTRACT: Gastrointestinal (GI) electrical activity is generated by pacemaker cells called the interstitial cells of Cajal (ICC), which are located throughout the GI tract. An extended description of the variations of ICC may help improve our understanding of digestive functions. The main aim of this study is to create an image-based structural model of an extended ICC network. Feature extraction techniques were applied to dual-stained images of ICC to obtain cell distribution, fiber orientation and connectivity. In a sample image, 20 nuclei were isolated and the cell bodies were joined perpendicular to each other in a grid-like network with two principal axes orientated at approximately 20 and 80 degrees to the vertical axis. An extended virtual network model was developed to resemble the cell count and orientation. In conclusion, an extended image-based virtual ICC network was generated. This network model can be adapted to generate the ICC network structure required for large-scale GI electrical simulations and to predict the functional significance of ICC loss in diseases.
    No preview · Article · Jan 2014 · IFMBE proceedings
  • S. Sathar · G. O’grady · M.L. Trew · L.K. Cheng
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    ABSTRACT: Gastric pacing has been investigated for modulating gastric motility in diseased states. However, to advance this field, new pacing protocols are needed that directly improve gastric motility while increasing the efficiency of existing pacing devices. This study presents a mathematical tissue model for investigating slow wave entrainment during pacing and its comparison with experimental data gathered by highresolution electrical mapping. The model was used to predict the effect anisotropic conductivities on slow wave entrainment, and the effect of gastric pacing on ectopic dysrhythmias. A diffusion based slow wave propagation model was used, with cell activity modeled as a finite-state machine. Initially, normal slow-wave antegrade propagation was modeled in accordance with experimental data. Then, these simulation parameters were applied to compare the model, in tandem with experimental studies in which an external pacing signal entrains native slow wave activity. The effect of different pacing frequencies on entrainment was demonstrated. Finally, this model was also used for simulating the effect of external stimuli for entraining a distal ectopic focal pacemaker. Two cases were studied with different fiber directions. The results showed that the pacing frequency and orientation of the fibers relative to the stimulation and ectopic site plays a critical role in gastric pacing efficacy.
    No preview · Article · Jan 2014 · IFMBE proceedings
  • M.Z. Ul Haque · P. Du · L.K. Cheng · M.D. Jacobs
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    ABSTRACT: The intra-epidermal nerve fibre (IENF) network in the skin of the foot generates the sensory nerve action potentials (SNAP). Variations in the conduction velocity (CV) of the SNAP can be recorded to identify diabetic neuropathies. A computational model of the IENF network of the foot may provide a suitable platform to investigate small fibre neuropathy by determining SNAP and CV at different stages of disease and in different regions of the foot. In this work, we demonstrate the development of an anatomically realistic model of the IENF network in the skin of the whole foot and also an IENF network with localized neuropathy. A Monte Carlo algorithm was used to generate the bifurcated IENF network tree based on IENF density (IENFD). In addition, this model demonstrates an initial perturbed IENF network at the lateral region just above the little toe of the foot based on IENFD at this region, to simulate small fibre neuropathy. This generated model will be used in forthcoming studies to integrate the structural and functional consequences of small fibre neuropathy.
    No preview · Article · Jan 2014 · IFMBE proceedings
  • P. Du · L.K. Cheng
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    ABSTRACT: Propulsion of content through the digestive tract is due to the coordinated contractions and relaxations of the smooth muscles in the gut wall. The motility of the gastrointestinal tract is underpinned by an electrophysiological event called slow wave activity. Many other physiological factors, such as neural and hormonal factors, also present a significant level of regulation on both slow waves and motility. In recent years, high-resolution electrical mapping has yielded significant insight to the organization of slow wave activity in-vivo, both in normal as well as pathological conditions. One significant experimental finding has been the description of slow wave dysrhythmias recorded from patients with clinically significant digestive diseases such as diabetic and idiopathic gastroparesis. Accompanying these new findings regarding slow wave activity is a series of mathematical models that have been applied to perform predictive simulations capable of giving further insights to the mechanistic behaviors of slow waves under different physiological conditions. In particular, the multi-scale modeling approach has been utilized to great success to integrate experimental data from multiple recording modalities and infer the relationship between slow waves and gastrointestinal functions. Ultimately, the research efforts aim to develop a "virtual stomach" for simulation of how food is digested and how different pathological factors can influence digestive health.
    No preview · Article · Jan 2014 · IFMBE proceedings
  • S. Sathar · G. O’Grady · M.L. Trew · L.K. Cheng
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    ABSTRACT: Gastric pacing has been investigated for modulating gastric motility in diseased states. However, to advance this field, new pacing protocols are needed that directly improve gastric motility while increasing the efficiency of existing pacing devices. This study presents a mathematical tissue model for investigating slow wave entrainment during pacing and its comparison with experimental data gathered by highresolution electrical mapping. The model was used to predict the effect anisotropic conductivities on slow wave entrainment, and the effect of gastric pacing on ectopic dysrhythmias. A diffusion based slow wave propagation model was used, with cell activity modeled as a finite-state machine. Initially, normal slow-wave antegrade propagation was modeled in accordance with experimental data. Then, these simulation parameters were applied to compare the model, in tandem with experimental studies in which an external pacing signal entrains native slow wave activity. The effect of different pacing frequencies on entrainment was demonstrated. Finally, this model was also used for simulating the effect of external stimuli for entraining a distal ectopic focal pacemaker. Two cases were studied with different fiber directions. The results showed that the pacing frequency and orientation of the fibers relative to the stimulation and ectopic site plays a critical role in gastric pacing efficacy.
    No preview · Article · Jan 2014 · IFMBE proceedings
  • L K Cheng · P Du · G O'Grady
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    ABSTRACT: A key discovery in gastrointestinal motility has been the central role played by interstitial cells of Cajal (ICC) in generating electrical slow waves that coordinate contractions. Multielectrode mapping and multiscale modeling are two emerging interdisciplinary strategies now showing translational promise to investigate ICC function, electrophysiology, and contractions in the human gut.
    No preview · Article · Sep 2013 · Physiology
  • J H K Kim · P Du · L K Cheng
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    ABSTRACT: The use of cutaneous recordings to non-invasively characterize gastric slow waves has had limited clinical acceptance, primarily due to the uncertainty in relating the recorded signal to the underlying gastric slow waves. In this study we aim to distinguish and quantitatively reconstruct different slow wave patterns using an inverse algorithm. Slow wave patterns corresponding to normal, retrograde and uncoupled activity at different frequencies were imposed on a stomach surface model. Gaussian noise (10% peak-to-peak) was added to cutaneous potentials and the Greensite-Tikhonov inverse method was used to reconstruct the potentials on the stomach. The effectiveness of the number or location of electrodes on the accuracy of the inverse solutions was investigated using four different electrode configurations. Results showed the reconstructed solutions were able to reliably distinguish the different slow wave patterns and waves with lower frequency were better correlated to the known solution than those with higher. The use of up to 228 electrodes improved the accuracy of the inverse solutions. However, the use of 120 electrodes concentrated around the stomach was able to achieve similar results. The most efficient electrode configuration for our model involved 120 electrodes with an inter-electrode distance of 32 mm.
    No preview · Article · Aug 2013 · Physiological Measurement
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    ABSTRACT: Background: Slow-waves modulate the pattern of small intestine contractions. However, the large-scale spatial organization of intestinal slow-wave pacesetting remains uncertain because most previous studies have had limited resolution. This study applied high-resolution (HR) mapping to evaluate intestinal pacesetting mechanisms and propagation patterns in vivo. Methods: HR serosal mapping was performed in anesthetized pigs using flexible arrays (256 electrodes; 32 × 8; 4 mm spacing), applied along the jejunum. Slow-wave propagation patterns, frequencies, and velocities were calculated. Slow-wave initiation sources were identified and analyzed by animation and isochronal activation mapping. Key results: Analysis comprised 32 recordings from nine pigs (mean duration 5.1 ± 3.9 min). Slow-wave propagation was analyzed, and a total of 26 sources of slow-wave initiation were observed and classified as focal pacemakers (31%), sites of functional re-entry (23%) and circumferential re-entry (35%), or indeterminate sources (11%). The mean frequencies of circumferential and functional re-entry were similar (17.0 ± 0.3 vs 17.2 ± 0.4 cycle min(-1) ; P = 0.5), and greater than that of focal pacemakers (12.7 ± 0.8 cycle min(-1) ; P < 0.001). Velocity was anisotropic (12.9 ± 0.7 mm s(-1) circumferential vs 9.0 ± 0.7 mm s(-1) longitudinal; P < 0.05), contributing to the onset and maintenance of re-entry. Conclusions & inferences: This study has shown multiple patterns of slow-wave initiation in the jejunum of anesthetized pigs. These results constitute the first description and analysis of circumferential re-entry in the gastrointestinal tract and functional re-entry in the in vivo small intestine. Re-entry can control the direction, pattern, and frequency of slow-wave propagation, and its occurrence and functional significance merit further investigation.
    Full-text · Article · Mar 2013 · Neurogastroenterology and Motility
  • J H K Kim · A J Pullan · L K Cheng
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    ABSTRACT: One approach for non-invasively characterizing gastric electrical activity, commonly used in the field of electrocardiography, involves solving an inverse problem whereby electrical potentials on the stomach surface are directly reconstructed from dense potential measurements on the skin surface. To investigate this problem, an anatomically realistic torso model and an electrical stomach model were used to simulate potentials on stomach and skin surfaces arising from normal gastric electrical activity. The effectiveness of the Greensite-Tikhonov or the Tikhonov inverse methods were compared under the presence of 10% Gaussian noise with either 84 or 204 body surface electrodes. The stability and accuracy of the Greensite-Tikhonov method were further investigated by introducing varying levels of Gaussian signal noise or by increasing or decreasing the size of the stomach by 10%. Results showed that the reconstructed solutions were able to represent the presence of propagating multiple wave fronts and the Greensite-Tikhonov method with 204 electrodes performed best (correlation coefficients of activation time: 90%; pacemaker localization error: 3 cm). The Greensite-Tikhonov method was stable with Gaussian noise levels up to 20% and 10% change in stomach size. The use of 204 rather than 84 body surface electrodes improved the performance; however, for all investigated cases, the Greensite-Tikhonov method outperformed the Tikhonov method.
    No preview · Article · Jul 2012 · Physics in Medicine and Biology
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    ABSTRACT: Gastric slow waves propagate aborally as rings of excitation. Circumferential propagation does not normally occur, except at the pacemaker region. We hypothesized that (i) the unexplained high-velocity, high-amplitude activity associated with the pacemaker region is a consequence of circumferential propagation; (ii) rapid, high-amplitude circumferential propagation emerges during gastric dysrhythmias; (iii) the driving network conductance might switch between interstitial cells of Cajal myenteric plexus (ICC-MP) and circular interstitial cells of Cajal intramuscular (ICC-IM) during circumferential propagation; and (iv) extracellular amplitudes and velocities are correlated. An experimental-theoretical study was performed. High-resolution gastric mapping was performed in pigs during normal activation, pacing, and dysrhythmia. Activation profiles, velocities, and amplitudes were quantified. ICC pathways were theoretically evaluated in a bidomain model. Extracellular potentials were modeled as a function of membrane potentials. High-velocity, high-amplitude activation was only recorded in the pacemaker region when circumferential conduction occurred. Circumferential propagation accompanied dysrhythmia in 8/8 experiments was faster than longitudinal propagation (8.9 vs 6.9 mm s(-1) ; P = 0.004) and of higher amplitude (739 vs 528 μV; P = 0.007). Simulations predicted that ICC-MP could be the driving network during longitudinal propagation, whereas during ectopic pacemaking, ICC-IM could outpace and activate ICC-MP in the circumferential axis. Experimental and modeling data demonstrated a linear relationship between velocities and amplitudes (P < 0.001). The high-velocity and high-amplitude profile of the normal pacemaker region is due to localized circumferential propagation. Rapid circumferential propagation also emerges during a range of gastric dysrhythmias, elevating extracellular amplitudes and organizing transverse wavefronts. One possible explanation for these findings is bidirectional coupling between ICC-MP and circular ICC-IM networks.
    No preview · Article · Jul 2012 · Neurogastroenterology and Motility
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    J H K Kim · A J Pullan · L A Bradshaw · L K Cheng
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    ABSTRACT: Electrogastrograms (EGG) and magnetogastrograms (MGG) provide two complementary methods for non-invasively recording electric or magnetic fields resulting from gastric electrical slow wave activity. It is known that EGG signals are relatively weak and difficult to reliably record while magnetic fields are, in theory, less attenuated by the low-conductivity fat layers present in the body. In this paper, we quantified the effects of fat thickness and conductivity values on resultant magnetic and electric fields using anatomically realistic torso models and trains of dipole sources reflecting recent experimental results. The results showed that when the fat conductivity was increased, there was minimal change in both potential and magnetic fields. However, when the fat conductivity was reduced, the magnetic fields were largely unchanged, but electric potentials had a significant change in patterns and amplitudes. When the thickness of the fat layer was increased by 30 mm, the amplitude of the magnetic fields decreased 10% more than potentials but magnetic field patterns were changed about four times less than potentials. The ability to localize the underlying sources from the magnetic fields using a surface current density measure was altered by less than 2 mm when the fat layer was increased by 30 mm. In summary, results confirm that MGG provides a favorable method over EGG when there are uncertain levels of fat thickness or conductivity.
    Preview · Article · Mar 2012 · Physiological Measurement
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    ABSTRACT: The need for in vivo wireless acquisition of biological signals is emerging in various medical fields. Electrophysiological applications including recording myoelectric signals in-vivo gastric electrical activity (GEA) to study gastric dysmotility, electrocorticography (ECoG) to study pain, and transcranical motor evoked potentials (TcMEP) for intraoperative neurophysiological monitoring of spinal cord integrity require physically miniaturized devices with low power consumption and capability of implantation. These systems should provide reliable communication in real time with sufficient data rates. We have developed three telemetric systems for GEA, ECoG and TcMEP applications based on a common transceiver platform but with different design considerations. Each has been successfully validated in appropriate animal models, to demonstrate the feasibility of wireless acquisition of key electrophysiological signals.
    Full-text · Conference Paper · Jul 2011
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    ABSTRACT: 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. High-resolution mapping was performed on healthy fasted weaner pigs under general anesthesia. Recordings were made from the gastric serosa using flexible arrays (160-192 electrodes; 7.6mm spacing). Dysrhythmias were observed to occur in 14 of 97 individual recordings (from 8 of 16 pigs), and these events were characterized, quantified and classified using isochronal mapping and animation. All observed dysrhythmias originated in the corpus and fundus. The range of dysrhythmias included incomplete conduction block (n=3 pigs; 3.9±0.5cpm; normal range: 3.2±0.2cpm) complete conduction block (n=3; 3.7±0.4cpm), escape rhythm (n=5; 2.0±0.3cpm), competing ectopic pacemakers (n=5, 3.7±0.1cpm) and functional re-entry (n=3, 4.1±0.4cpm). Incomplete conduction block was observed to self-perpetuate due to retrograde propagation of wave fragments. Functional re-entry occurred in the corpus around a line of unidirectional block. 'Double potentials' were observed in electrograms at sites of re-entry and at wave collisions. Intraoperative multi-electrode mapping of fasted weaner healthy pigs detected dysrhythmias in 15% of recordings (from 50% of animals), including patterns not previously reported. The techniques and findings described here offer new opportunities to understand the nature of human gastric dysrhythmias.
    Full-text · Article · Jun 2011 · Neurogastroenterology and Motility
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    ABSTRACT: Stomach contractions are initiated and coordinated by electrical events termed slow waves, and slow wave abnormalities contribute to gastric motility disorders. Recently, flexible printed circuit board (PCB) multi-electrode arrays were introduced, facilitating high-resolution mapping of slow wave activity in humans. However PCBs with gold contacts have shown a moderately inferior signal quality to previous custom-built silver-wire platforms, potentially limiting analyses. This study determined if using silver instead of gold contacts improved flexible PCB performance. In a salt-bath test, modestly higher stimulus amplitudes were recorded from silver PCBs (mean 312, s.d. 89 µV) than those from gold (mean 281, s.d. 85 µV) (p < 0.001); however, the signal-to-noise ratio (SNR) was similar (p = 0.26). In eight in vivo experimental studies, involving gastric serosal recordings from five pigs, no silver versus gold differences were found in terms of slow wave amplitudes (mean 677 versus 682 µV; p = 0.91), SNR (mean 8.8 versus 8.8 dB; p = 0.94) or baseline drift (NRMS; mean 12.0 versus 12.1; p = 0.97). Under the prescribed conditions, flexible PCBs with silver or gold contacts provide comparable results in vivo, and contact material difference does not explain the performance difference between current-generation slow wave mapping platforms. Alternative explanations for this difference and the implications for electrode design are discussed.
    Full-text · Article · Mar 2011 · Physiological Measurement
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    ABSTRACT: 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. Fasted pigs underwent HR mapping following anesthesia and laparotomy. Flexible printed-circuit-board arrays were used (160-192 electrodes; spacing 7.62 mm). Anterior and posterior surfaces were mapped simultaneously. Activation times, velocities, amplitudes and frequencies were calculated, and regional differences evaluated. Mean slow wave frequency was 3.22 ± 0.23 cpm. Slow waves propagated isotropically from the pacemaker site (greater curvature, mid-fundus). Pacemaker activity was of higher velocity (13.3 ± 1.0 mm s(-1)) and greater amplitude (1.3 ± 0.2 mV) than distal fundal activity (9.0 ± 0.6 mm s(-1), 0.9 ± 0.1 mV; P < 0.05). Velocities and amplitudes were similar in the distal fundus, proximal corpus (8.4 ± 0.8 mm s(-1), 1.0 ± 0.1 mV), distal corpus (8.3 ± 0.8 mm s(-1), 0.9 ± 0.2 mV) and antrum (6.8 ± 0.6 mm s(-1), 1.1 ± 0.2 mV). Activity was continuous across the anterior and posterior gastric surfaces. This study has quantified normal porcine gastric slow wave activity at HR during anesthesia and laparotomy. The pacemaker region was associated with high-amplitude, high-velocity slow wave activity compared to the activity in the rest of the stomach. The increase in distal antral slow wave velocity and amplitude previously described in canines and humans is not observed in the pig. Investigators should be aware of these inter-species differences.
    Full-text · Article · Oct 2010 · Neurogastroenterology and Motility
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    ABSTRACT: The aim of this study was to obtain detailed information regarding the three-dimensional structure of the gastro-oesophageal region, and, in particular, the fiber orientation of the different muscle layers of the junction. This was achieved by a study of an en bloc resection of the gastro-oesophageal junction (GOJ) harvested from a human cadaver. The excised tissue block was suspended in a cage to preserve anatomical relationships, fixed in formalin and embedded in wax. The tissue block was then processed by a custom-built extended-volume imaging system to obtain the microstructural information using a digital camera which acquires images at a resolution of 8.2 microm/pixel. The top surface of the tissue block was sequentially stained and imaged. At each step, the imaged surface was milled off at a depth of 50 microm. The processing of the tissue block resulted in 650 images covering a length of 32.25 mm of the GOJ. Structures, including the different muscle and fascial layers, were then traced out from the cross-sectional images using color thresholding. The traced regions were then aligned and assembled to provide a three-dimensional representation of the GOJ. The result is the detailed three-dimensional microstructural anatomy of the GOJ represented in a new way. The next stage will be to integrate key physiological events, including peristalsis and relaxation, into this model using mathematical modeling to allow accurate visual tools for training health professionals and patients.
    Full-text · Article · Apr 2010 · Clinical Anatomy
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    P Du · S Li · G O'Grady · L K Cheng · A J Pullan · J D Z Chen
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    ABSTRACT: Gastric electrical stimulation (GES) involves the delivery of electrical impulses to the stomach for therapeutic purposes. New GES protocols are needed that are optimized for improved motility outcomes and energy efficiency. In this study, a biophysically based smooth muscle cell (SMC) model was modified on the basis of experimental data and employed in conjunction with experimental studies to define the effects of a large range of GES protocols on individual SMCs. For the validation studies, rat gastric SMCs were isolated and subjected to patch-clamp analysis during stimulation. Experimental results were in satisfactory agreement with simulation results. The results define the effects of a wide range of GES parameters (pulse width, amplitude, and pulse-train frequency) on isolated SMCs. The minimum pulse width required to invoke a supramechanical threshold response from SMCs (defined at -30 mV) was 65 ms (at 250-pA amplitude). The minimum amplitude required to invoke this threshold was 75 pA (at 1,000-ms pulse width). The amplitude of the invoked response beyond this threshold was proportional to the stimulation amplitude. A high-frequency train of stimuli (40 Hz; 10 ms, 150 pA) could invoke and maintain the SMC plateau phase while requiring 60% less power and accruing approximately 30% less intracellular Ca(2+) concentration during the plateau phase than a comparable single-pulse protocol could in a demonstrated example. Validated computational simulations are an effective strategy for efficiently identifying effective minimum-energy GES protocols, and pulse-train protocols may also help to reduce the power consumption of future GES devices.
    Full-text · Article · Sep 2009 · AJP Gastrointestinal and Liver Physiology

Publication Stats

512 Citations
69.29 Total Impact Points

Institutions

  • 1999-2014
    • University of Auckland
      • • Auckland Bioengineering Institute
      • • Department of Surgery
      • • Department of Engineering Science
      Окленд, Auckland, New Zealand
  • 2003-2013
    • Vanderbilt University
      • Department of Surgery
      Нашвилл, Michigan, United States