Shuddhadeb Ray

Pore size and pore shape – but not mesh density – alter the mechanical strength of tissue ingrowth and host tissue response to synthetic mesh materials in a porcine model of ventral hernia repair

BACKGROUND Over 100 types of soft tissue repair materials are commercially available for hernia repair applications. These materials vary in characteristics such as mesh density, pore size, and pore shape. It is difficult to determine the impact of a single variable of interest due to other compounding variables in a particular design. Thus, the current study utilized prototype meshes designed to evaluate each of these mesh parameters individually. METHODS Five prototype meshes composed of planar, monofilament polyethylene terephthalate (PET) were evaluated in this study. The meshes were designed to focus on three key parameters, namely mesh density, pore size, and pore shape. The prototype meshes were implanted in the preperitoneal, retrorectus space in a porcine model of ventral incisional hernia repair, and tissue ingrowth characteristics were evaluated after 90 days. Mesh-tissue composite specimens were obtained from each repair site and evaluated via T-peel mechanical testing. Force-displacement data for each T-peel test were analyzed and five characteristics of tissue ingrowth reported: peak force (fp), critical force (fc), fracture energy (Γc), work (W), and work density (Wden). Hematoxylin and eosin (H&E) stained sections of explanted mesh-tissue composites were also assessed for characteristics of tissue response including cellular infiltration, cell types, inflammatory response, extracellular matrix deposition, neovascularization, and fibrosis, with a composite score assigned to represent overall tissue response. RESULTS The medium-weight, very large pore, hexagonal (MWVLH) mesh performed significantly better than the light-weight, medium pore, diamond (LWMD) mesh for all parameters evaluated (fp, fc, Γc, W, Wden) and trended toward better results than the medium-weight, medium pore, diamond (MWMD) mesh for the majority of the parameters evaluated. When the data for the five meshes was grouped to evaluate mesh density, pore size, and pore shape, differences were more pronounced. No significant differences were observed with respect to mesh density, however significant improvement in mechanical strength of tissue ingrowth occurred as pore size increased from medium to very large. In addition, the hexagonal pores resulted in the strongest tissue ingrowth, followed by the square pores, and finally the diamond pores. Scores for several histological parameters were significantly different for these prototype meshes. For example, the MWVLH mesh showed significantly greater tissue ingrowth by neovascularization histological score than MWMD and MWVLS meshes (p<0.05) and significantly less fibrosis than LWMD and MWVLS meshes (p<0.05). CONCLUSION Pore shape and pore size significantly altered the mechanical strength of tissue ingrowth and host-site integration in a porcine model of ventral hernia repair, while mesh density had no effect.

Resting myocardial perfusion quantification with CMR arterial spin labeling at 1.5 T and 3.0 T

BackgroundThe magnetic resonance technique of arterial spin labeling (ASL) allows myocardial perfusion to be quantified without the use of a contrast agent. This study aimed to use a modified ASL technique and T1 regression algorithm, previously validated in canine models, to calculate myocardial blood flow (MBF) in normal human subjects and to compare the accuracy and repeatability of this calculation at 1.5 T and 3.0 T. A computer simulation was performed and compared with experimental findings.ResultsEight subjects were imaged, with scans at 3.0 T showing significantly higher T1 values (P < 0.001) and signal-to-noise ratios (SNR) (P < 0.002) than scans at 1.5 T. The average MBF was found to be 0.990 ± 0.302 mL/g/min at 1.5 T and 1.058 ± 0.187 mL/g/min at 3.0 T. The repeatability at 3.0 T was improved 43% over that at 1.5 T, although no statistically significant difference was found between the two field strengths. In the simulation, the accuracy and the repeatability of the MBF calculations were 61% and 38% higher, respectively, at 3.0 T than at 1.5 T, but no statistically significant differences were observed. There were no significant differences between the myocardial perfusion data sets obtained from the two independent observers. Additionally, there was a trend toward less variation in the perfusion data from the two observers at 3.0 T as compared to 1.5 T.ConclusionThis suggests that this ASL technique can be used, preferably at 3.0 T, to quantify myocardial perfusion in humans and with further development could be useful in the clinical setting as an alternative method of perfusion analysis.

Evaluation of a novel cryoablation system: in vivo testing in a chronic porcine model.

ObjectiveCryoablation is commonly used at present in the surgical treatment of atrial fibrillation (AF). However, there have been few studies examining the efficacy of the commonly used ablation devices. This report compares the efficacy of two cryoprobes in creating transmural endocardial lesions on the beating heart in a porcine model for chronic AF. MethodsIn six Hanford miniature swine, the right atrial appendage and the inferior vena cava were isolated using a bipolar radiofrequency clamp to create areas of known conduction block. A connecting ablation line was performed endocardially via a purse string with the novel malleable 10-cm Cryo1 probe for 2 minutes at −40°C. Additional ablation lines were created with the Cryo1 and the 3.5-cm 3011 Maze Linear probe on the right and the left atrial wall. Epicardial activation mapping was performed before and immediately after ablation as well as 14 days postoperatively. Histologic examination was performed 14 days postoperatively. ResultsTransmural lesions were confirmed in 83/84 cross-sections (99%) for the Cryo1 probe and in 40/41 cross-sections (98%) for the 3011 Maze Linear probe. There was no difference between the devices in lesion width (mean ± SD, Cryo1, 10.7 ± 3.5 mm; 3011, 10.0 ± 3.9 mm; P = 0.31), lesion depth (Cryo1, 4.5 ± 1.7 mm; 3011, 4.6 ± 1.5 mm; P = 0.74), or atrial wall thickness (Cryo1, 4.5 ± 1.8 mm; 3011, 4.7 ± 1.7 mm; P = 0.74). There was a conduction delay across the right atrial ablation line (20 ± 2 milliseconds vs 51 ± 8 milliseconds, P < 0.001) that remained unchanged at 14 days (51 ± 8 milliseconds vs 52 ± 10 milliseconds, P = 0.88). ConclusionsThe Cryo1 probe created transmural lesions on the beating heart, resulting in sustained conduction delay. Both probes had a similar performance in lesion geometry in this chronic animal model.

Evaluation of a novel cryoablation system: in vitro testing of heat capacity and freezing temperatures.

ObjectiveCryoablation has been used to ablate cardiac tissue for decades and has been shown to be able to replace incisions in the surgical treatment of atrial fibrillation. This in vitro study evaluates the performance of a novel cryoprobe and compares it with existing commercially available devices. MethodsA new malleable 10-cm aluminum cryoprobe was compared with a rigid 3.5-cm copper linear probe using in vitro testing to evaluate performances under different thermal loads and with different tissue thicknesses. Radial dimensions of ice formation were measured in each water bath by a high-precision laser 2 minutes after the onset of cooling. Probe-surface temperatures were recorded by thermocouples. Tissue temperature was measured at depths of 4 mm and 5 mm from the probe-tissue interface. Time to reach a tissue temperature of −20°C was recorded. ResultsIce formation increased significantly with lower water-bath temperatures (P < 0.001). Width and depth of ice formation were significantly less for the rigid linear probe (P < 0.012 and P < 0.001, respectively). There was no difference between the probes in the maximal negative temperature reached under different thermal loads or at different tissue depths. The malleable probe achieved significantly lower temperatures at the proximal compared with the distal end (−61.7°C vs −55.0°C, respectively; P < 0.001). A tissue temperature of −20°C was reached earlier at 4 mm than at 5 mm (P < 0.001) and was achieved significantly faster with the 3011 Maze Linear probe (P < 0.021). ConclusionsThe new malleable probe achieved rapid freezing to clinically relevant levels in up to 5-mm–thick tissue. Both probes maintained their performance under a wide range of thermal loads.

Expanded Polytetrafluoroethylene for Chordal Replacement: Preventing Knot Failure.

PURPOSE Expanded polytetrafluoroethylene suture is commonly used for chordal replacement in mitral valve repair, but due to material characteristics, knots can unravel. Our aim was to determine the knot security, including how many throws are necessary to prevent knot failure, with Gore-Tex (W.L. Gore and Associates, Elkton, MD) and the newly available Chord-X (On-X Life Technologies Inc, Austin, TX). DESCRIPTION Knots were evaluated for maximal load based on: number of throws (6, 8, 10, and 12), tension to secure each throw (10%, 50%, and 85%) and suture type (Gore-Tex CV-5 and Chord-X 3-0). A physiologic force of 2 N was used for comparison. EVALUATION We evaluated 240 knots. For all knots, the mean load to failure was 11.1 ± 5.8 N. Failure occurred due to unraveling in 141 knots (59%) at 7.1 ± 4.1 N and to breaking in 99 (41%) at 16.7 ± 2.0 N (p < 0.01). Gore-Tex failed at higher loads (12.6 ± 6.0 N vs 9.5 ± 5.2 N, p < 0.01); however, an equivalent number, 6 Gore-Tex and 6 Chord-X, unraveled at 2 N, all with fewer than 10 throws. CONCLUSIONS Expanded polytetrafluoroethylene has adequate strength to prevent breakage; however, a risk of knot unraveling at physiologic conditions exists when fewer than 10 throws are performed.

Ergonomic analysis of laparoscopic and robotic surgical task performance at various experience levels

IntroductionTraditional laparoscopic surgery (TLS) has increasingly been associated with physical muscle strain for the operating surgeon. Robot-assisted laparoscopic surgery (RALS) may offer improved ergonomics. Ergonomics for the surgeon on these two platforms can be compared using surface electromyography (sEMG) to measure muscle activation, and the National Aeronautics and Space Administration Task Load Index (NTLX) survey to assess workload subjectively.MethodsSubjects were recruited and divided into groups according to level of expertise in traditional laparoscopic (TLS) and robot-assisted laparoscopic surgery (RALS): novice, traditional laparoscopic surgeons (TL surgeons), robot-assisted laparoscopic surgeons (RAL surgeons). Each subject performed three fundamentals of laparoscopic surgery (FLS) tasks in randomized order while sEMG data were obtained from bilateral biceps, triceps, deltoid, and trapezius muscles. After completing all tasks, subjects completed the NTLX survey. sEMG data normalized to the maximum voluntary contraction of each muscle (MVC%), and NTLX data were compared with unpaired t tests and considered significant with a p ≤ 0.05.ResultsMuscle activation was higher during TLS compared to RALS in most muscle groups for novices except for the trapezius muscles. Muscle activation scores were also higher for TLS among the groups with more experience, but the differences were less significant. NTLX scores were higher for the TLS platform compared to the RALS platform for novices.DiscussionTLS is associated with higher muscle activation in all muscle groups except for trapezius muscles, suggesting greater strain on the surgeon. Increased trapezius muscle activation on RALS has previously been documented and is likely due to the position of the eye piece. The differences seen in muscle activation diminish with increasing levels of expertise. Experience likely mitigates the ergonomic disadvantage of TLS. NTLX survey data suggest there are subjective benefits to RALS, namely in the perception of temporal demand. Further research to correlate NTLX data and sEMG measurements, and to investigate whether these metrics affect patient outcomes is warranted.

Ethical considerations in the use of Pernkopf's Atlas of Anatomy: A surgical case study

The use of Eduard Pernkopfs anatomic atlas presents ethical challenges for modern surgery concerning the use of data resulting from abusive scientific work. In the 1980s and 1990s, historic investigations revealed that Pernkopf was an active National Socialist (Nazi) functionary at the University of Vienna and that among the bodies depicted in the atlas were those of Nazi victims. Since then, discussions persist concerning the ethicality of the continued use of the atlas, because some surgeons still rely on information from this anatomic resource for procedural planning. The ethical implications relevant to the use of this atlas in the care of surgical patients have not been discussed in detail. Based on a recapitulation of the main arguments from the historic controversy surrounding the use of Pernkopfs atlas, this study presents an actual patient case to illustrate some of the ethical considerations relevant to the decision of whether to use the atlas in surgery. This investigation aims to provide a historic and ethical framework for questions concerning the use of the Pernkopf atlas in the management of anatomically complex and difficult surgical cases, with special attention to implications for medical ethics drawn from Jewish law.

Ethical Challenges in High-Risk Innovative Surgery

The fields of surgery and anesthesia have storied histories with advances in care fueled by innovation by creative individuals striving to improve the care of their patients. Ethical dilemmas arise when contemplating how to allow innovation to continue for the benefit of future patients while mitigating harm to current patients. In this chapter, we explore ethical issues in high-risk innovative surgery from the perspectives of the key stakeholders: the surgeon, the patient, the anesthesiologist, the medical device industry, and other members of the healthcare team.