The Viscoelastic Behavior of Soft Tissues Must be Accounted for in Stapler Design and Surgeon Technique.

BACKGROUND: Since its adoption as a surgical technique over a half-century ago, stapling has continually undergone improvements, both in the devices used and in our understanding of tissue mechanics. To best design and use stapling devices, it is beneficial to have an intimate knowledge of the response of tissue to compression and stapling dynamics. This paper provides the relevant background in the field of biomechanics, and in particular addresses the viscoelastic behavior of soft tissues under compression. Biomechanics of Stapling: The change in shape of a solid, or strain, is related to the load applied, or stress. Biological tissues are known to have non-linear relationships between stress and strain, and generally the relationships are anisotropic (dependent upon direction). Further complicating matters, there is typically a time-dependency to the relationship for compression and recovery, resulting in viscoelastic behavior. Hence both the amount and rate of compressive force applied can be expected to impact the outcome of stapling. DISCUSSION: The growth of the laparoscopic use of staples has increased the difficulty of device design, as precise control of compression is problematic in extended length staplers. Progressive firing along the cartridge and multi-stage compression have both been found to be beneficial in providing the uniform force needed to produce well-formed staples. Such technical advances can reduce stresses within the stapler, preventing deformation of the stapler arm and undesirable strain in the tissue. Current research includes understanding the effects of changing the rate of compression on staple formation with the hope that further improvements can be achieved in this ever-fruitful method of tissue apposition.

Preclinical quantification of air leaks in a physiologic lung model: effects of ventilation modality and staple design.

PURPOSE: Thoracic air leaks are a common complication following pulmonary resections. Limitations in clinical studies and preclinical models have hindered efforts to understand the pathophysiology of air leaks. With an emphasis on staple-line specific air leaks, we hypothesize that ventilation modality - intraoperative positive pressure vs postoperative negative pressure - and stapler design may play a role in air leaks. METHODS: Using a novel physiologic lung model, air leaks associated with graduated and uniform staple designs were evaluated under positive and negative pressure ventilation, simulating perioperative breathing in porcine lungs. Air leak incidence, air leak volume, and air leak rate were captured along with ventilation pressure and tidal volume. RESULTS: In all cases, negative pressure ventilation was associated with a higher occurrence of leaks when compared to positive pressure ventilation. Lungs leaked more air and at a faster rate under negative pressure ventilation compared to positive pressure ventilation. Graduated staple designs were associated with higher occurrence of leaks as well as larger leak rates when compared to uniform staples. Tissue thickness was not associated with differences in air leaks when tested with appropriate staple heights. CONCLUSION: Using a novel lung model to investigate the pathophysiology of air leaks, we have identified breathing modality and staple design as two important variables that may impact air leaks. This work will help guide device design and drive future studies in human tissue, and it may help inform clinical practice to ultimately improve patient outcomes.

Ex Vivo Modeling of Perioperative Air Leaks in Porcine Lungs.

OBJECTIVE: A novel ex vivo model is described to advance the understanding of prolonged air leaks, one of the most common postoperative complications following thoracic resection procedures. METHODS: As an alternative to in vivo testing, an ex vivo model simulating the various physiologic environments experienced by an isolated lung during the perioperative period was designed and built. Isolated porcine lungs were perfused and ventilated during open chest and closed chest simulations, mimicking intra and postoperative ventilation conditions. To assess and validate system capabilities, nine porcine lungs were tested by creating a standardized injury to create an approximately 250 cc/min air leak. Air leak rates, physiologic ventilation, and perfusion parameters were continuously monitored, while gas transfer analysis was performed on selected lungs. Segmental ventilation was monitored using electrical impedance tomography. RESULTS: The evaluated lungs produced flow-volume and pressure-volume loops that approximated standard clinical representations under positive (mechanical) and negative (physiological) pressure ventilation modalities. Leak rate was averaged across the ventilation phases, and sharp increases in leak rate were observed between positive and negative pressure phases, suggesting that differences or changes in ventilation mechanics may strongly influence leak development. CONCLUSION: The successful design and validation of a novel ex vivo lung model was achieved. Model output paralleled clinical observations. Pressure modality may also play a significant role in air leak severity. SIGNIFICANCE: This work provides a foundation for future studies aimed at increasing the understanding of air leaks to better inform means of mitigating the risk of air leaks under clinically relevant conditions.

Clinical Factors Associated With Remission of Obesity-Related Comorbidities After Bariatric Surgery.

IMPORTANCE: Little is known about comorbidity remission after bariatric surgery during typical clinical care across diverse and geographically distributed populations. OBJECTIVE: To estimate the improvement in obesity-related comorbidities after bariatric surgery and to identify clinical factors associated with these responses using a large representative population of patients. DESIGN, SETTING, AND PARTICIPANTS: This retrospective cohort study included all patients (N = 33,718) with a recorded Current Procedural Terminology code for Roux-en-Y gastric bypass (RYGB) or adjustable gastric banding (AGB) in the MarketScan Commercial Claims and Encounters Medicare Supplemental Databases from January 1, 2005, to June 30, 2010, and who had continuous enrollment from 6 months or more before to 12 months after surgery. MAIN OUTCOMES AND MEASURES: Comorbidities before and after surgery were identified using both diagnoses (from International Classification of Diseases, Ninth Revision [ICD-9] codes) and prescription drug fills. Remission was based on a record of the comorbidity within 6 months before surgery, without record of the condition 18 months after surgery, using both ICD-9 codes and medication fills, as applicable. Multivariable logistic regression models were developed to identify factors associated with remission of diabetes and hypertension. RESULTS: Among the 33,718 patients, 13 comorbidities with at least 1% prevalence before surgery were identified. Both RYGB and AGB led to statistically and clinically significant reductions in these comorbidities; remission rates for all comorbidities were higher after RYGB than AGB. For comorbidities that could be defined using both ICD-9 and prescription drug fill codes, prevalence was higher before and lower after surgery when measured by fill codes. Diagnoses using ICD-9 codes, but not prescription fill codes, increased in the 3 months before surgery. In multivariable logistic regression models for remission of diabetes mellitus after RYGB and AGB, age (RYGB: odds ratio [OR], 0.976; 95% CI, 0.965-0.988 and AGB: OR, 0.982; 95% CI, 0.971-0.933), procedure year (RYGB: OR, 1.11; 95% CI, 1.012-1.218 and AGB: OR, 1.185; 95% CI, 1.039-1.351), preoperative insulin use (RYGB: OR, 0.14; 95% CI, 0.114-0.171; AGB: OR, 0.174; 95% CI, 0.131-0.230), preoperative sulfonylurea use (RYGB: OR, 0.616; 95% CI, 0.505-0.752 and AGB: OR, 0.449; 95% CI, 0.357-0.566), and other antidiabetic medication use (RYGB: OR, 0.747; 95% CI, 0.568-0.981 and AGB: OR, 0.506; 95% CI, 0.359-0.715) were significantly associated with response after both procedures. For remission of hypertension, age (RYGB: OR, 0.964; 95% CI, 0.957-0.972 and AGB: OR, 0.968; 95% CI, 0.959-0.977), number of preoperative antihypertensive medications (RYGB: OR, 0.104; 95% CI, 0.067-0.161 and AGB: OR, 0.239; 95% CI, 0.140-0.408), and preoperative diuretic use (RYGB: OR, 1.729; 95% CI, 1.462-2.045 and AGB: OR, 1.648; 95% CI, 1.380-1.967) were significantly associated with response after both procedures. CONCLUSIONS AND RELEVANCE: Analysis of a large, representative administrative database confirmed established predictors and revealed novel variables associated with comorbidity remission after bariatric surgery. Incorporating these factors into clinical tools to assess an individual patient's risk-to-benefit profile for these procedures could enhance patient selection and the overall use of surgery for the treatment of obesity and metabolic disease.

Gastric plication: preclinical study of durability of serosa-to-serosa apposition.

BACKGROUND: Vertical gastric plication is a novel surgical approach for reducing the stomach capacity. Anterior surface plication and greater curvature plication are variations of vertical gastric plication that reduce the gastric capacity through infolding of the anterior surface or greater curvature of the stomach, respectively. These approaches have been tested, with positive results in a small number of preclinical and clinical trials. A key step toward greater investigation of vertical gastric plication as a viable bariatric procedure would be confirmation that the apposed serosal tissues can be securely and durably bonded. We compared the short-term durability of gastric plications and serosal bonds using a variety of fastening devices and techniques in a university hospital and private company setting. METHODS: A total of 30 anterior surface plication and 8 greater curvature plication procedures were performed using an open or a laparoscopic surgical technique in 38 hound dogs. The fastening devices used were T-tags, buttressed T-tags, 2 types of suture, and 4 types of staple-based fasteners. The density of the fastening devices was varied among the dogs. With 3 exceptions (2 in keeping with the study design and 1 due to complications), the dogs were followed up for 8 weeks. Histologic examinations and tensile testing were performed postmortem. RESULTS: All fastening devices created durable plication folds, except for 1 technique. The only technique that did not produce durable serosa-to-serosa adhesions was a staple/suture combination. Intentional abrasion of the apposed sites had no demonstrable effect on the bonds between the tissues in any group. Increasing the fastener density and number of rows increased the adhesions within the folds. CONCLUSION: Our findings have confirmed the short-term durability and development of dense fibrous appositions of the serosal folds for fastening approaches that create fixed serosal apposition. Additional studies are needed to identify the optimal fastening modality for anterior surface plication, greater curvature plication, and, ultimately, clinical applications of this procedure.

Laparoscopic gastric plication for treatment of severe obesity.

BACKGROUND: Current gastric restrictive procedures include either a prosthetic device or gastric resection. We present the results of a feasibility study using laparoscopic gastric plication for weight loss achieved without stapling or banding. METHODS: After institutional review board approval, 2 methods were used to achieve laparoscopic gastric volume reduction. In the first group (anterior plication [AP]), the anterior gastric wall was folded inward from the fundus to the antrum using 2 rows of running sutures. The greater and lesser curvatures were approximated to create an intraluminal fold of the stomach. In the second group (greater curvature plication [GCP]), the short gastric vessels were divided, and the greater curvature was folded inward, with 2 suture lines to reduce the gastric capacity by a large intraluminal gastric fold. RESULTS: The average preoperative body mass index was 43.3 kg/m(2) (range 36.9-49.0), and 3 patients were men. Of the 15 patients, 9 underwent AP. For the 9 patients who underwent AP, the 6- and 12-month endoscopic evaluations demonstrated comparable-size plications over time, except for in 1 patient, who had a partially disrupted fold. Of the 6 patients who underwent GCP, the 6- and 12-month follow-up endoscopic examinations demonstrated a durable intraluminal fold, except for in 1 patient, with a partial disruption at the distal fold owing to a broken suture. For patients completing 1 year of follow-up, the percentage of excess weight loss was 23.3% ± 24.8% in the AP group (n = 5) and 53.4% ± 22.7% in the GCP group (n = 6). No bleeding or infectious complications developed. The first patient in the GCP group required reoperation and plication reduction owing to gastric obstruction. CONCLUSION: Our initial experience has suggested that a reduction in gastric capacity can be achieved by way of plication of the anterior stomach and greater curvature. The early weight loss results have been encouraging, with better weight loss in patients who underwent GCP. The use of laparoscopic GCP warrants additional investigation as a primary bariatric procedure.

Kinetics of thermal damage to a collagenous membrane under biaxial isotonic loading.

Prior isothermal uniaxial isotonic tests on tendons reveal that higher temperatures hasten the rate of thermal denaturation whereas larger mechanical loads delay it; moreover, these findings suggest a time-temperature-load equivalency whereby similar levels of denaturation, as reflected by tissue shrinkage, can be attained via many combinations of heating time, temperature level, and mechanical loading. Yet, most tissues and organs experience multiaxial loads in vivo, and their microstructure differs significantly from that of tendons, thus, we must also evaluate the effects of multiaxial stresses on the kinetics of denaturation in other tissues. In this paper, we describe a new experimental approach for performing isothermal biaxial isotonic tests on thin sheet-like specimens and we report effects of various thermomechanical loads on the rate and amount of multiaxial shrinkage of bovine epicardium. Consistent with uniaxial studies, epicardial shrinkage generally increased sigmoidally with heating time, and a characteristic heating time revealed increases in the rate of shrinkage with higher temperature and decreases with larger biaxial loads. Although this characteristic time exhibited an Arrhenius-type character, time-temperature-load equivalency was not obtained when scaling time with this metric. General multiaxial thermomechanics is thus too complex to explain via a simple extension of uniaxial findings on tendons and there is a pressing need for more data and an appropriate theoretical framework.