Qualitative behavioral assessment of dogs with acute pain.

Free Choice Profiling (FCP) methodology allows observers to qualitatively assess animal behavior using their own vocabulary. This study aims to investigate the ability of 3 different observer groups to recognize pain-related emotions in 20 dogs using FCP methodology, and to compare FCP data with the Glasgow Composite Pain Scale-Short Form (GCPS- SF) scores. The observer groups consisted of 10 dog owners, 10 veterinary students and 10 veterinarians. Ten healthy ("healthy") dogs and 10 dogs showing clinical signs of pain ("pain") were filmed, and the resulting 20 footages were shown to observers who were blind to the pain-related nature of the study. All observers described and scored animals' emotional expression using FCP; then, students and veterinarians scored all dogs using GCPS- SF. FCP data were analyzed using Generalized Procrustes Analysis (GPA). Spearman correlation coefficient (ρ) was used to determine the correlation among observer groups' FCP scores of the first two FCP dimensions (DIM1 and DIM2), and to compare GCPS-SF scores with FCP scores for the students and veterinarian observer groups. Each observer group reached a significant (p < 0.001) good consensus profile. "Healthy" dogs were mainly described as "quiet" and "lively", while the majority of "pain" dogs were considered "in pain" and "suffering". The correlation among FCP scores was high between owners' DIM1 and students' DIM1 (ρ = -0.86), owners' DIM2 and students' DIM2 (ρ = 0.72) and students' DIM2 and vets' DIM1 (ρ = 0.70). The correlation between GCPS-SF scores and FCP scores was high for students' DIM2 (ρ = 0.77) and for veterinarians' DIM1 (ρ = 0.92). Qualitative methods such as FCP could be used in association with semi-quantitative methods to evaluate the effect of pain on animal emotional expression. Observers' cultural background and personal experience did not substantially affect qualitative behavioral assessment in dogs with acute somatic pain.

Exploring oxygen reserve index for timely detection of deoxygenation in canine patients recovering from anesthesia.

Pulse oximetry (SpO2) identifies a decrease in the partial pressure of oxygen (PaO2) when it falls below 80 mmHg, while oxygen reserve index (ORi), a dimensionless index ranging from 0 to 1, detects PaO2 changes between 100 and 200 mmHg. This study investigates the usefulness of ORi in detecting impending deoxygenation before traditional SpO2. Fifty-one dogs undergoing anesthesia were mechanically ventilated maintaining a fraction of inspired oxygen of 0.50 and an ORi of 1. Animals were classified according to their body condition score (BCS) as normal-fit (BCS 4-5/9), overweight (BCS 6-7/9), or obese (BCS 8-9/9). At the end of the procedure, dogs were placed in sternal recumbency, and after 10 min disconnected from the ventilator and maintained in apnea. ORi added warning time was determined at various ORi values as the time difference in reaching SpO2 of 95% from ORi of 0.9 and 0.5, compared to the SpO2 warning time from SpO2 of 98%. During apnea, ORi decreased before noticeable SpO2 changes. An ORi of 0.9 anticipated an SpO2 of 95% in normal-fit dogs by 87 (33-212) [median (range)] seconds or in those with a BCS ≥ 6/9 by 49 (7-161) seconds. Regardless of the BCS class, the median time from ORi of 0.5 to SpO2 of 95% was 30-35 s. ORi declined from 0.9 to 0.0 in 68 compared to 33 s between normal-fit and obese dogs (p < 0.05). In dogs, ORi added warning time could facilitate timely intervention, particularly in obese patients.

Non-invasive assessment of oxygenation status using the oxygen reserve index in dogs.

BACKGROUND: The oxygen reserve index (ORi) is a real-time, continuous index measured with multi-wavelength pulse CO-oximetry technology. It estimates mild hyperoxemia in humans, which is defined as a partial pressure of oxygen (PaO2) level between 100 and 200 mmHg. The objectives of this study were to assess the correlation between ORi and PaO2, as well as to determine its ability in detecting mild hyperoxemia in dogs. METHODS: This prospective observational study enrolled 37 anaesthetised and mechanically ventilated dogs undergoing elective procedures. Simultaneous measurements of ORi and PaO2 were collected, using a multi-wavelength pulse CO-oximeter with a probe placed on the dog's tongue, and a blood gas analyser, respectively. A mixed-effects model was used to calculate the correlation (r2) between simultaneous measurements of ORi and PaO2. The trending ability of ORi to identify dependable and proportional changes of PaO2 was determined. The diagnostic performances of ORi to detect PaO2 ≥ 150 mmHg and ≥ 190 mmHg were estimated using the area under the receiver operating characteristic curve (AUROC). The effects of perfusion index (PI), haemoglobin (Hb), arterial blood pH and partial pressure of carbon dioxide (PaCO2) on AUROC for PaO2 ≥ 150 mmHg were evaluated. RESULTS: A total of 101 paired measurements of ORi and PaO2 were collected. PaO2 values ranged from 74 to 258 mmHg. A strong positive correlation (r2 = 0.52, p < 0.001) was found between ORi and PaO2. The trending ability ORi was 90.7%, with 92% sensitivity and 89% specificity in detecting decreasing PaO2. An ORi value ≥ 0.53 and ≥ 0.76 indicated a PaO2 ≥ 150 and ≥ 190 mmHg, respectively, with ≥ 82% sensitivity, ≥ 77% specificity and AUROC ≥ 0.75. The AUROC of ORi was not affected by PI, Hb, pH and PaCO2. CONCLUSIONS: In anaesthetised dogs, ORi may detect mild hyperoxaemia, although it does not replace blood gas analysis for measuring the arterial partial pressure of oxygen. ORi monitoring could be used to non-invasively assess oxygenation in dogs receiving supplemental oxygen, limiting excessive hyperoxia.

Oxygen Reserve Index as a Tool to Monitor Four Techniques of Oxygen Supplementation at Different Flow Rates in Dogs Sedated with Dexmedetomidine and an Opioid.

Respiratory dysfunction often decreases arterial oxygen content. Four common oxygen delivery techniques-flow-by, nasal prongs, a tight-vented mask, and a tight mask connected to a Venturi valve-were evaluated for their effectiveness in increasing the oxygen reserve index (ORi), a dimensionless index of oxygen content that provides additional information compared to traditional pulse oximetry (SpO2) during hyperoxia (PaO2 100-200 mmHg), and that ranges from 0 to 1. Thirty-two dogs sedated with dexmedetomidine and an opioid were evenly divided into four groups based on the technique for oxygen administration. Each dog received oxygen at 1, 2, and 3 L/min by a single technique, and the amount of inhaled oxygen (FiO2) was measured at the level of the cervical trachea. At each flow rate, ORi and SpO2 were recorded. The flow-by method minimally increased the FiO2, and ORi reached its highest value only in 3 out of 8 dogs at the maximum flow rate. Other methods exhibited direct correlations between the oxygen flow rate and ORi (p < 0.001). These methods effectively increased FiO2 and ORi, with over half of the values exceeding 40% and 0.4, respectively. The tight-vented mask showed variable increases in FiO2, ranging between 22 and 90%. Despite method-dependent variations, all devices increased SpO2 > 98% as the FiO2 increased (p = 0.002). In conclusion, nasal prongs and the mask connected to the Venturi valve showed the highest correlation between the oxygen flow rate and the ORi. These results suggest that using these two techniques in conjunction with ORI can help in optimizing oxygen therapy.

Salmonella Enteritidis Fatal Septicemia with Meningoencephalitis in a Tiger (Panthera tigris) Cub.

A 15-day-old, female, captive Panthera tigris cub was hospitalized after developing severe hyperthermia, depression, and lack of appetite. The clinical condition rapidly worsened, and the tiger cub died in 72 h after the onset of neurological symptoms, septic shock, and multiple organ dysfunction syndrome. The postmortem main gross findings consisted of a severe and diffuse bilateral fibrino-suppurative meningoencephalitis and ventriculitis, mild fibrinous and sero-hemorrhagic polyserositis and cystitis, severe pulmonary edema, and hemorrhages. Microscopically, the meninges, ependyma, and choroid plexuses were diffusely expanded by abundant infiltration of neutrophils and macrophages, with multifocal fibrinous exudation. Histiocytic interstitial pneumonia, fibrinous and neutrophilic polyserositis, and pyelocystitis were also observed. Vascular thrombosis with multifocal vasculitis and vascular necrosis were frequently observed. Aerobic and anaerobic cultures performed on the brain, lungs, intestine, kidneys, and in pericardial effusion reported the presence of Salmonella enterica subsp. enterica serovar Enteritidis. Environmental and nutritional contamination were identified as putative sources of infections. To the best of the authors' knowledge, this is the first report of Salmonella Enteritidis septicemia with meningoencephalitis in a tiger cub, which highlights the need to further investigate the cause of acute perinatal death to reduce the risk of infectious disease outbreaks.

Efficacy of Intra-Operative Topical Wound Anaesthesia to Mitigate Piglet Castration Pain-A Large, Multi-Centred Field Trial.

Piglet castration results in acute pain and stress to the animal. There is a critical need for effective on-farm methods of pain mitigation. Local anaesthesia using Tri-Solfen® (Animal Ethics Pty Ltd., Melbourne, Australia), a topical local anaesthetic and antiseptic formulation instilled to the wound during surgery, is a newly evolving on-farm method to mitigate castration pain. To investigate the efficacy of Tri-Solfen®, instilled to the wound during the procedure, to alleviate subsequent castration-related pain in neonatal piglets, we performed a large, negatively controlled, randomised field trial in two commercial pig farms in Europe. Piglets (173) were enrolled and randomised to undergo castration with or without Tri-Solfen®, instilled to the wound immediately following skin incision. A 30 s wait period was then observed prior to completing castration. Efficacy was investigated by measuring pain-induced motor and vocal responses during the subsequent procedure and post-operative pain-related behaviour in treated versus untreated piglets. There was a significant reduction in nociceptive motor and vocal response during castration and in the post-operative pain-related behaviour response in Tri-Solfen®-treated compared to untreated piglets, in the first 30 min following castration. Although not addressing pain of skin incision, Tri-Solfen® is effective to mitigate subsequent acute castration-related pain in piglets under commercial production conditions.

Oxygen reserve index as a noninvasive indicator of arterial partial pressure of oxygen in anaesthetized donkeys: a preliminary study.

OBJECTIVE: To evaluate the oxygen reserve index (ORI) as a noninvasive estimate of the PaO2 during moderate hyperoxaemia [100-200 mmHg (13.3-26.6 kPa)], and to determine ORI values identifying PaO2 > 100, > 150 (20.0 kPa) and > 200 mmHg in anaesthetized donkeys with an inspired fraction of oxygen (FiO2) > 0.95. STUDY DESIGN: Prospective observational study. ANIMALS: A group of 28 adult standard donkeys aged (mean ± standard deviation) 4 ± 2 years and weighing 135 ± 15 kg. METHODS: Donkeys were sedated intramuscularly with xylazine and butorphanol; anaesthesia was induced with ketamine and diazepam and maintained with isoflurane in oxygen. An adhesive sensor probe was applied to the donkey's tongue and connected to a Masimo pulse co-oximeter to determine ORI values. An arterial catheter was inserted into an auricular artery. After ORI signal stabilization, the value was noted and PaO2 determined by blood gas analysis. The Pearson correlation coefficient was used to assess the relationship between ORI and PaO2 for oxygen tension < 200 mmHg (< 26.6 kPa). The Youden index was used to identify the value of ORI that detected PaO2 > 150 and 200 mmHg (20.0 and 26.6 kPa) with the highest sensitivity and specificity. RESULTS: A total of 106 paired measurements were collected. A mild positive correlation was observed between ORI and PaO2 for values < 200 mmHg (26.6 kPa; r = 0.52). An ORI > 0.0, > 0.1 and > 0.3 indicated a PaO2 > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) with negative predictive values > 94%. CONCLUSIONS AND CLINICAL RELEVANCE: ORI may provide a noninvasive indication of PaO2 > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) in anaesthetized donkeys with an FiO2 > 0.95, although it does not replace blood gas analysis for assessment of oxygenation.

EVALUATION OF THE QUALITY OF IMMOBILIZATION AND CARDIORESPIRATORY EFFECTS OF ETORPHINE-MEDETOMIDINE-AZAPERONE COMBINATION IN PLAINS ZEBRAS (EQUUS QUAGGA): A PILOT STUDY.

Five free-ranging male (subadults, n = 3; adults, n = 2) plains zebras (Equus quagga) were immobilized using a combination of etorphine (0.017 mg/kg), medetomidine (0.017 mg/kg), and azaperone (0.24 mg/kg) by means of a blank cartridge-fired projector. Time to recumbency was recorded and a descriptive score used to assess the quality of immobilization, manipulation, maintenance, and recovery. Physiological parameters were recorded at 5-min intervals for 20 min. At the end of the procedure, naltrexone (0.23 mg/kg) was administered intramuscularly and time to standing documented. The combination evaluated in this study allowed for successful immobilization and safe recovery of all animals, including during the subsequent 15 days. Despite the good outcome in this pilot study, as a result of the periodic apneic events and hypercapnia documented in the zebras, the authors suggest that physiological parameters be thoroughly monitored when using this protocol. Further studies are needed to improve upon chemical immobilization protocols in free-ranging plains zebras.

Computational Models for the Mechanical Investigation of Stomach Tissues and Structure.

Bariatric surgery is performed on obese people aiming at reducing the capacity of the stomach and/or the absorbing capability of the gastrointestinal tract. A more reliable and effective approach to bariatric surgery may integrate different expertise, in the areas of surgery, physiology and biomechanics, availing of a strong cooperation between clinicians and engineers. This work aimed at developing a computational model of the stomach, as a computational tool for the physio-mechanical investigation of stomach functionality and the planning of bariatric procedures. In this sense, coupled experimental and numerical activities were developed. Experimental investigations on pig and piglet stomachs aimed at providing information about stomach geometrical configuration and structural behavior. The computational model was defined starting from the analysis of data from histo-morphometric investigations and mechanical tests. A fiber-reinforced visco-hyperelastic constitutive model was developed to interpret the mechanical response of stomach tissues; constitutive parameters were identified considering mechanical tests at both tissue and structure levels. Computational analyses were performed to investigate the pressure-volume behavior of the stomach. The developed model satisfactorily interpreted results from experimental activities, suggesting its reliability. Furthermore, the model was exploited to investigate stress and strain fields within gastric tissues, as the stimuli for mechanoreceptors that interact with the central nervous system leading to the feeling of satiety. In this respect, the developed computational model may be employed to evaluate the influence of bariatric intervention on the stimulation of mechanoreceptors, and the following meal induced satiety.

Effect of three opioid-based analgesic protocols on the perioperative autonomic-mediated cardiovascular response in sheep.

Few reports evaluate the clinical effects of opioids in sheep during experimental surgical procedures. Catecholamine-mediated haemodynamic changes resulting from surgical noxious stimulation are blunted by opioids. The aim of this study was to evaluate the efficacy of three opioid-based analgesic protocols in avoiding a 20% increase in heart rate (HR) and/or mean arterial blood pressure (MAP) during experimental intervertebral disk nucleotomy in sheep. Eighteen female Brogna sheep were anaesthetized with propofol and maintained with a fixed end-tidal isoflurane concentration of 1.5 ± 0.1%. Sheep were assigned to one of three groups that intravenously received methadone 0.3 mg/kg (group M), fentanyl 2 µg/kg followed by 10 µg/kg/h (group F), or buprenorphine 10 µg/kg and 30 minutes later ketamine 1 mg/kg followed by 5 mg/kg/h (group BK). Intravenous fentanyl at 2 µg/kg would have been used for rescue analgesia in case HR and/or MAP had increased. During surgery, HR and MAP values did not increase over 20% in all groups. All animals maintained the percentage change between -4 and 7% for both variables; only one sheep in group BK had an increase in MAP superior to 20% after ketamine administration before surgical stimulation. In group M, HR decreased over time and in group BK, MAP tended to increase during surgery. All the opioid-based protocols tested were able to control the cardiovascular response to noxious stimulation in sheep undergoing spinal surgery, although ketamine may have represented a confounding factor.

Neuromuscular blockade of atracurium in permissive hypercapnic versus normocapnic swine undergoing laparoscopy.

Neuromuscular blocking agents (NMBAs) are commonly used in experimental laparoscopy in swine undergoing carbon dioxide pneumoperitoneum. Hypercapnia may be present and may prolong NMBAs' pharmacologic activity. The aim of this study is to evaluate the effect of permissive hypercapnia on the neuromuscular blockade of atracurium in swine. Six Large White swine weighing 30.5 ± 1.6 kg were sedated with intramuscular ketamine and medetomidine, after which anaesthesia was induced with propofol and maintained with sevoflurane. Atracurium 0.4 mg/kg was administered intravenously and the neuromuscular block monitored by acceleromyography during normocapnic and hypercapnic conditions (PaCO2 range 35-45 mmHg and 60-70 mmHg, respectively). Onset time and time to reach a train of four ratio (TOFR) of 0.7 and 0.9 were recorded. Cardiorespiratory parameters, electrolytes and acid-base status were measured under both conditions. Onset time was similar between the two conditions. Time to reach a TOFR of 0.7 and 0.9 (duration of the neuromuscular block) was longer in hypercapnic compared to normocapnic animals being 1325 ± 300 vs 855 ±111 (p = 0.002) and 1823 ± 434 vs 1218 ± 210 seconds (p = 0.005), respectively. Three hypercapnic swine had a TOF count of 2 and 1 instead of a count of 4 with fade. Permissive hypercapnia was associated with a decrease in pH from 7.444 ± 0.039 to 7.257 ± 0.025 (p < 0.001). No differences were observed for heart rate, end-tidal concentration of sevoflurane, body temperature and arterial haemoglobin saturation. Nonetheless, hypercapnic swine had a statistically significant increase in mean arterial pressure (p = 0.020) and plasma potassium concentration (p = 0.003). The values of PaCO2 achieved during hypercapnia were well tolerated in swine undergoing CO2 pneumoperitoneum for laparoscopy. Permissive hypercapnia increased the duration of the atracurium effect and caused an increase in the intensity of the neuromuscular block in few swine.

Alfaxalone anaesthesia in Lemur catta following dexmedetomidine-butorphanol-midazolam sedation.

OBJECTIVE: To evaluate the clinical effects and quality of sedation, induction, maintenance and recovery in Lemur catta after dexmedetomidine-butorphanol-midazolam sedation and alfaxalone anaesthesia. STUDY DESIGN: Prospective, observational study. ANIMALS: Six male L. catta weighing 3.0 ± 0.6 kg undergoing surgical castration. METHODS: Lemurs were sedated with intramuscular dexmedetomidine (0.015 mg kg-1), butorphanol (0.2 mg kg-1) and midazolam (0.2 mg kg-1). Anaesthesia was induced with intravenous alfaxalone 0.5 mg kg-1 over 60 seconds; further boluses were administered until tracheal intubation was feasible and final dose recorded. Alfaxalone continuous infusion was used to maintain anaesthesia. Atipamezole (0.15 mg kg-1) was administered during recovery. The quality of sedation, induction, intubation, maintenance and recovery was assessed using a scoring system. Physiological parameters were recorded during sedation, maintenance and recovery. RESULTS: Sedation was achieved in 13.6 ± 5.6 minutes and no reactions were observed during handling or venepuncture. The mean dose of alfaxalone required for induction and maintenance was 2.09 ± 0.65 and 0.08 ± 0.02 mg kg-1 minute-1, respectively. Quality of induction, intubation and maintenance was good in almost all animals. Mild self-limiting muscle twitching was observed after alfaxalone administration in three animals. Cardiorespiratory function was stable in all animals but one. One lemur showed respiratory depression and required oxygen administration and manual ventilation. The mean maintenance time was 29.2 ± 7.4 minutes. The mean times from the end of alfaxalone administration to extubation, atipamezole administration and full recovery were: 15.3 ± 8.0, 22.2 ± 4.6 and 60.0 ± 8.4 minutes, respectively. Recovery was considered good in all animals. CONCLUSIONS AND CLINICAL RELEVANCE: Dexmedetomidine-butorphanol-midazolam combination provided reliable sedation and adequate muscle relaxation in L. catta. Alfaxalone proved to be a useful drug for induction and maintenance of anaesthesia and might be considered an option for injectable anaesthesia in lemurs.

Novel stepwise model of intervertebral disc degeneration with intact annulus fibrosus to test regeneration strategies.

Novel preclinical models that do not damage the annulus fibrosus (AF) of the intervertebral disc are required to study the efficacy of new regenerative strategies for the nucleus pulposus (NP). The aim of the study was to characterize a preclinical ovine model of intervertebral disc degeneration (IDD) induced by endplate (EP) damage and repair via the transpedicular approach, with or without partial nucleotomy, while keeping the AF intact. Twelve adult sheep were used. By the transpedicular approach, a 2 mm tunnel was drilled to the NP through the EP. A partial-nucleotomy was performed. The tunnel was sealed using a polyurethane scaffold. Lumbar discs were assigned to different groups: L1-2: nucleotomy; L2-3: EP tunnel; L3-4: nucleotomy + EP repair; L4-5: EP tunnel + repair; L5-6: control. X-Ray and MRI were performed at 0, 1, 3, and 6 months after surgery. Disc height and MRI indexes were calculated. Macro- and micro-morphology were analyzed. Pfirrmann and Thompson grades were assigned. The treated discs exhibited a progressive decrease in NP signal intensity and MRI index, displaying specific grades of degeneration based on the surgical treatment. According to Pfirrmann and Thompson grades different procedures were staged as: EP tunnel + repair: grade-II; EP tunnel: grade-III, nucleotomy + EP repair: grade-IV; nucleotomy: grade-V. A new stepwise model of IDD to study and test safety and efficacy of novel strategies for NP regeneration has been characterized. The different degrees of IDD have been observed similar to Pfirrmann and Thompson grading system. The intact AF allows for loading studies and eliminating the need for AF closure. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2460-2468, 2018.

Endodontic treatment of canine teeth in a cynomolgus monkey ( Macaca fascicularis).

A case of bilateral superior canine tooth pulp necrosis in an 18-year-old male Macaca fascicularis is described . A skull computed tomography scan was performed to confirm the diagnostic suspicion. A successful bilateral endodontic treatment with coronotomy was performed using rotary nickel-titanium instruments. Post-operative dental radiographs confirmed the correct positioning of the sealant. A rapid and excellent clinical recovery was obtained after each surgery. This innovative approach may contribute to improving the quality of root canal treatments provided to non-human primates.

Cardiovascular effects and intraoperative pharmacokinetics of tramadol in sheep undergoing spinal surgery.

OBJECTIVE: To evaluate the pharmacokinetics of two doses of tramadol during isoflurane anaesthesia in sheep and their ability to prevent the cardiovascular response induced by surgical stimulation. STUDY DESIGN: Prospective randomized controlled study. ANIMALS: A total of 12 healthy sheep (mean weight, 47.5±7.9 kg) undergoing lumbar transpedicular intervertebral disk nucleotomy. METHODS: Sheep were sedated with medetomidine, anaesthesia was induced with propofol and maintained with isoflurane at 1.5 vol.%. Baseline heart rate and blood pressure were measured and sheep were randomly assigned an intravenous injection of tramadol (4 or 6 mg kg-1). Fentanyl was injected as rescue analgesic if cardiovascular parameters were increased more than 20% compared to baseline. If those variables were below 20% of baseline, the concentration of isoflurane was gradually decreased until parameters returned to the original value. Blood collections were performed at pre-assigned times, and concentrations of tramadol and O-desmethyltramadol (M1) assessed by high-performance liquid chromatography. RESULTS: Time from premedication to anaesthesia induction, anaesthesia time, propofol dose and intraoperative body temperature were similar between doses. Cardiovascular variables remained between ±20% of baseline value, and no statistical difference was observed between treatments. Regardless of the dose of tramadol administered, arterial blood pressure was statistically higher than baseline 10 minutes after tramadol administration, but it gradually returned to previous values. A two-compartment model and a non-compartment model described the pharmacokinetics of tramadol and M1, respectively. Plasma concentrations of tramadol rapidly decreased in the first 2 hours for both doses with an elimination half-life of more than 40 minutes. The M1 maximum concentration was similar for both doses, and it was detected in plasma after 35 minutes. CONCLUSIONS AND CLINICAL RELEVANCE: Both doses of tramadol provided adequate cardiovascular stability during spinal surgery in sheep. The pharmacokinetic variables may be used to plan the dosage regime during general anaesthesia.

A biomechanical approach to the analysis of methods and procedures of bariatric surgery.

Bariatric surgery includes a variety of procedures that are performed on obese people and aim at decreasing the intake of food and calories. This goal is usually pursued by reducing stomach capacity and/or absorbing capability. Adjustable gastric banding is the most common and successful operation. In general, bariatric surgical procedures are effective, but are often associated with major complications. Surgical procedure and post-surgical conformation of the stomach are usually defined on clinical and surgical basis only. Instead, the optimal configuration should be identified by analyzing the mechanical functionality of the stomach and the surrounding structures, and the relationship between food intake, nutrient adsorption, mechanical stimulation of stomach wall and feeling of satiety. A novel approach to bariatric surgery is required, integrating competences in the areas of biomechanics, physiology and surgery, based on a strong interaction between engineers and clinicians. Preliminary results from coupled experimental and computational investigations are here reported. The analyses aim to develop computational tools for the investigation of stomach mechanical functionality in pre- and post-surgical conformations.

Experimental investigation of the structural behavior of equine urethra.

BACKGROUND AND OBJECTIVE: An integrated experimental and computational investigation was developed aiming to provide a methodology for characterizing the structural response of the urethral duct. The investigation provides information that are suitable for the actual comprehension of lower urinary tract mechanical functionality and the optimal design of prosthetic devices. METHODS: Experimental activity entailed the execution of inflation tests performed on segments of horse penile urethras from both proximal and distal regions. Inflation tests were developed imposing different volumes. Each test was performed according to a two-step procedure. The tubular segment was inflated almost instantaneously during the first step, while volume was held constant for about 300s to allow the development of relaxation processes during the second step. Tests performed on the same specimen were interspersed by 600s of rest to allow the recovery of the specimen mechanical condition. Results from experimental activities were statistically analyzed and processed by means of a specific mechanical model. Such computational model was developed with the purpose of interpreting the general pressure-volume-time response of biologic tubular structures. The model includes parameters that interpret the elastic and viscous behavior of hollow structures, directly correlated with the results from the experimental activities. RESULTS: Post-processing of experimental data provided information about the non-linear elastic and time-dependent behavior of the urethral duct. In detail, statistically representative pressure-volume and pressure relaxation curves were identified, and summarized by structural parameters. Considering elastic properties, initial stiffness ranged between 0.677 ± 0.026kPa and 0.262 ± 0.006kPa moving from proximal to distal region of penile urethra. Viscous parameters showed typical values of soft biological tissues, as τ1=0.153±0.018s, τ2=17.458 ± 1.644s and τ1=0.201 ± 0.085, τ2= 8.514 ± 1.379s for proximal and distal regions respectively. DISCUSSION: A general procedure for the mechanical characterization of the urethral duct has been provided. The proposed methodology allows identifying mechanical parameters that properly express the mechanical behavior of the biological tube. The approach is especially suitable for evaluating the influence of degenerative phenomena on the lower urinary tract mechanical functionality. The information are mandatory for the optimal design of potential surgical procedures and devices.

Urethral lumen occlusion by artificial sphincteric devices: a computational biomechanics approach.

The action induced by artificial sphincteric devices to provide urinary continence is related to the problem of evaluating the interaction between the occlusive cuff and the urethral duct. The intensity and distribution of the force induced within the region of application determine a different occlusion process and potential degradation of the urethral tissue, mostly at the borders of the cuff. This problem is generally considered in the light of clinical and surgical operational experience, while a valid cooperation is established with biomechanical competences by means of experimental and numerical investigation. A three-dimensional model of the urethra is proposed aiming at a representation of the phases of the urethral occlusion through artificial sphincters. Different conformations of the cuff are considered, mimicking different loading conditions in terms of force intensity and distribution and consequent deformation caused in soft tissues. The action induced in the healthy urethra is investigated, as basis for an evaluation of the efficacy and reliability of the sphincteric devices. The problem is characterized by coupled nonlinear geometric and material problem and entails a complex constitutive formulation. A heavy computational procedure is developed by means of analyses that operate within an explicit finite element formulation. Results reported outline the overall response of the urethral duct during lumen occlusion, leading to an accurate description of the phenomenon in the different phases.

Aortic stenting in the growing sheep causes aortic endothelial dysfunction but not hypertension: Clinical implications for coarctation repair.

BACKGROUND: Stent implantation is the treatment of choice for adolescents and adults with aortic coarctation (CoAo). Despite excellent short-term results, 20%-40% of the patients develop arterial hypertension later in life, which was attributed to inappropriate response of the aortic baroreceptors to increased stiffness of the ascending aorta (ASAO), either congenital or induced by CoAo repair. In particular, it has been hypothesized that stent itself may cause or sustain hypertension. Therefore, we aimed to study the hemodynamic and structural impact following stent implantation in the normal aorta of a growing animal. METHODS: Eight female sheep completed the study and a stent was implanted in four. Every 3 mo we measured blood pressure of the anterior and posterior limbs and left ventricular function by echocardiography. Twelve months later invasive pressure was measured under baseline and simulated stress conditions. Expression of genes indicating oxidative stress (OS), endothelial dysfunction (ED) and stiffness, as well as pathological examination were performed in ascending (ASAO) and descending aorta (DSAO). RESULTS: SOD1 and MMP9 gene expression were higher in ASAO of the stented animals, compared to DSAO and controls, while NOS3 was decreased. No differences were found in blood pressure and echocardiographic parameters. No histological differences were found in the aorta of the two groups of animals. CONCLUSIONS: Stent does not affect central and peripheral hemodynamics, cardiac structure and function even in the long term. However, the finding of markers of OS and increased stiffness of ASAO, proximal to the stent, points to molecular mechanisms for increased cardiovascular risk of patients with stented CoAo.

Mechanics of the urethral duct: tissue constitutive formulation and structural modeling for the investigation of lumen occlusion.

Urinary incontinence, often related to sphincter damage, is found in male patients, leading to a miserable quality of life and to huge costs for the healthcare system. The most effective surgical solution currently considered for men is the artificial urinary sphincter that exerts a pressure field on the urethra, occluding the duct. The evaluation of this device is currently based on clinical and surgical competences. The artificial sphincter design and mechanical action can be investigated by a biomechanical model of the urethra under occlusion, evaluating the interaction between tissues and prosthesis. A specific computational approach to urethral mechanics is here proposed, recalling the results of previous biomechanical experimental investigation. In this preliminary analysis, the horse urethra is considered, in the light of a significant correlation with human and in consideration of the relevant difficulty to get to human samples, which anyway represents the future advance. Histological data processing allow for the definition of a virtual and a subsequent finite element model of a urethral section. A specific hyperelastic formulation is developed to characterize the nonlinear mechanical behavior. The inverse analysis of tensile tests on urethra samples leads to the definition of preliminary constitutive parameters. The parameters are further refined by the computational analysis of inflation tests carried out on the entire urethral structure. The results obtained represent, in the light of the correlation reported, a valid preliminary support for the information to be assumed for prosthesis design, integrating surgical and biomechanical competences.