Biomedical subjects
Publications and source records attributed to Michael Rosen.
The successful design of nanofluidic devices for the manipulation of biopolymers requires an understanding of how the predictions of soft condensed matter physics scale with device dimensions. Here we present measurements of DNA extended in nanochannels and show that below a critical width roughly twice the persistence length there is a crossover in the polymer physics.
BACKGROUND: Virtual reality (VR) simulation is a rapidly proliferating adjunct of surgical training. Numerous devices have evolved as educational tools in a variety of fields. Whether these tools can be used for validation of physicians' skills has yet to be determined. The objective of this study was to determine whether the GI Mentor (Simbionix, Lod, Israel) flexible endoscopy simulator construct could distinguish experienced endoscopists from beginners. METHODS: Seventy-five surgical attendings, fellows, and residents were recruited for participation in the study. Two cohorts were used and these groups were selected from 2 separate scientific sessions. Participants completed a standardized questionnaire documenting their endoscopic training and experience. Physicians subsequently were designated as experienced or beginner after their endoscopic training and experience were evaluated. All participants completed 1 of 2 colonoscopic simulations. The GI Mentor objectively evaluated performance on the basis of programmed data points, including the time to reach the cecum, the percentage of mucosa visualized, the completed polypectomy rate, the percentage of time spent in clear view through the lumen, the percentage of time that the patient was in pain, and overall efficiency. RESULTS: In both simulations, experienced endoscopists were more efficient than beginners (.32%/s vs. .26%/s, P=.02; and .53%/s vs. .37%/s, P=.03) and achieved a greater polypectomy rate (78% vs. 43%, P=.03; and 87% vs. 48%, P=.01). Furthermore, experienced endoscopists visualized more of the colonic surface (86% vs. 82%, P=.02) and spent a greater proportion of the time in clear view of the lumen (55% vs. 47%, P=.05) than beginners completing the first simulation. In the second simulation, experienced participants reached the cecum more rapidly than beginners (175 vs. 262 s, P=.01). CONCLUSIONS: The G1 Mentor VR colonoscopy construct appears valid. Significant performance differences were shown between the experienced and beginner cohorts. The beginner participants in this study were all physicians with some degree of endoscopic experience. Therefore, the G1 Mentor distinguished endoscopists of varying experience and exposure. Further validation studies are needed to evaluate the breadth of programs inherent to this simulator and to determine whether it may be used in the future for qualification and certification purposes.
In this experimental study, small intestinal submucosa was implanted as an atrial prosthesis in calves. Echocardiography and histology showed this to be an impermeable prosthesis that develops a neointimal nonthrombogenic surface making it safe for repair of defects in a low-pressure system. Further study with small intestinal submucosa in an intracardiac position is warranted.
HYPOTHESIS: Younger patients with immune thrombocytopenic purpura (ITP) and high preoperative platelet counts successfully respond to laparoscopic splenectomy (LS). DESIGN: Case series. SETTING: Private, tertiary care referral center. PATIENTS: Sixty-seven consecutive patients undergoing LS for ITP between 1995 and 2001. INTERVENTIONS: Laparoscopic splenectomy. MAIN OUTCOME MEASURES: A successful response to LS was defined as a postoperative platelet count greater than 100 x 10(3)/microL without medical therapy. Failures were classified as recurrent or refractory. Patients considered refractory to surgery did not achieve a platelet count greater than 100 x 10(3)/microL without medical therapy. Patients with recurrent ITP initially achieved a platelet count greater than 100 x 10(3)/microL, but thrombocytopenia subsequently recurred. RESULTS: Both univariate and multivariate analyses were performed for 13 preoperative variables to identify factors predictive of success following LS. At a mean follow up of 22 months, 43 patients (64%) had a successful response to LS, 14 (21%) were refractory, and 10 (15%) developed recurrent ITP. By univariate analysis, patients responding to laparoscopic splenectomy were younger (P =.005) and had a higher preoperative platelet count (P =.005). In multivariate analysis, younger age (P =.005) and a higher preoperative platelet count (P =.007) again predicted a successful response to LS. CONCLUSIONS: A successful response to LS for ITP is expected in patients younger than 50 years and in those with preoperative platelet counts greater than 70 x 10(3)/microL. These factors can be incorporated into an equation that yields a splenectomy prediction score, which predicts the success of LS for ITP.
Gastric electrical stimulation (GES) was shown to improve symptoms in patients with gastroparesis. However, the underlying mechanisms remain unclear. This study assessed the influence of various patterns of GES on fasting and postprandial gastric acid secretion and 24-hr gastric pH. Eight healthy dogs were studied and we found that in the fasting state, low-frequency, long-pulse (6/12-cpm, 375-msec, 4-mA) GES at the proximal stomach significantly inhibited the secretion of gastric juice (P < 0.05). No such effect was observed during GES (6/12 cpm) at the distal stomach. In the postprandial period, low-frequency, long-pulse GES at both proximal and distal sites and at both frequencies did not significantly affect gastric acid secretion. High-frequency, short-pulse GES, investigated for obesity (21 Hz, 8 mA, and 250 microsec, with 2 secs on, 3 sec off), at the proximal and distal stomach did not significantly affect the 24-hr gastric pH profile. In conclusion, GES with various stimulation parameters, and at various sites, has little effect on gastric acid secretion. The clinical effects induced by GES at these parameters may not be related to their effect on gastric acid homeostasis.
Morbid obesity is a burgeoning health crisis. Significant morbidity is associated with the current gastric bypass, and, therefore, alternative surgical modalities are desired. A novel minimally invasive surgical technique, endoluminal gastric partitioning, is presented. Ten mongrel dogs underwent endolaparoscopic placement of intragastric mesh. Each circular prosthesis (Surgisis or prolene mesh) was 8 cm in diameter with a 1.5 cm central aperture. The mesh was passed transorally into the gastric lumen and secured with a laparoscopic, intragastric suturing resulting in a 30 to 50 mL proximal gastric reservoir. The operation was successfully completed in all 10 animals. Nine of 10 animals were healthy at the scheduled sacrifice date. In 2 dogs, the intragastric mesh was 100% adherent to the gastric mucosa after 7 days. Four of the final 5 dogs demonstrated some degree of mucosal adherence after 1 week. Endoluminal placement of intragastric mesh appears feasible and safe. Long-term studies are necessary to demonstrate the efficacy and long-term weight loss of this, or alternate intraluminal gastric partitioning techniques.
Pancreatic injury is the most frequent serious morbidity that can occur following laparoscopic splenectomy. The presumed mechanism of injury is direct trauma to the pancreatic tail during hilar dissection or transection with endovascular staplers. It was our aim to study the direct application of topical sealants to a pancreatic injury to prevent a pancreatic leak. A porcine model of pancreatic injury in a normal pancreas was developed. Fourteen animals underwent midline laparotomy and subtotal (8 cm) distal pancreatectomy. The pancreas was sharply divided and minimal cauterization used. A (1/4)-inch round Jackson Pratt drain was secured to the pancreatic stump in all animals. The control group (n = 7) underwent no further treatment. Two groups underwent treatment with a sealant. Group 1 (n = 3) had a hydrogel applied to the pancreatic remnant. Group 2 (n = 4) had a biodegradable sealant of PEG (polyethylene glycol)-collagen formulation applied to the pancreatic stump by aerosol. During the postoperative period, animals were fed 2.2 lb/d of a high fat (10% lard) diet to stimulate pancreatic exocrine function. Total daily drain outputs were recorded, and drain amylase content and serum amylase concentration were measured on postoperative days 3, 7, and 10. A significant pancreatic leak was defined as a drain to serum amylase content of greater than 3:1. Animals were killed on day 10 and explored for undrained fluid collections. The pancreas was removed for histologic evaluation. Control and treatment groups were compared using repeated measures ANOVA of log-transformed data. All animals survived until elective necropsy. In group 1, average total drain outputs were not significantly less than the controls (125 mL versus 269; P = .66). The mean drain/serum amylase concentration on days 3, 7, and 10 were not significantly different between group 1 and the control group. Group 2 had significantly less overall average drainage output than controls (40 mL versus 269 mL; P = .0006). Furthermore, group 2 had a significant reduction in pancreatic leaks on days 3, 7, and 10 as measured by mean drain/serum amylase concentration. No undrained fluid collections were identified at autopsy. Based on our experimental porcine model, a novel collagen-based, biodegradable hydrogel can prevent a ductal leak following pancreatic injury. These encouraging data have fostered application by aerosol treatment to the hilar bed at laparoscopic splenectomy to diminish capsular disruption from mechanical injury.
This study determined the most efficient parameters of low-frequency/long-pulse gastric electrical stimulation (GES) required to entrain gastric slow waves and also evaluated the effect of entrainment and high-frequency, short-pulse GES on gastric electrical activity (GEA). Nine dogs were fitted with stimulation wires along the greater curvature. Entrainment was observed in six or seven animals, with long-pulse GES at six cycles per minute (cpm), at various combinations of current and pulse width and was directly related to the energy delivered. Entrainment was observed in four to seven animals, with GES at 12 cpm, and the maximal driven frequency was 6 cpm. Entrainment did not significantly increase the dominant power of GEA. High-frequency, short-pulse GES, using pulse trains of 14 Hz, 5 mA, and 330 micros, with 0.1 s on and 5 s off, and pulse trains of 40 Hz, 10 mA, and 330 micros, with 2 s on 3 s off, did not affect variables of GEA. We conclude that acute low-frequency GES but not high-frequency, short-pulse GES can entrain slow waves; the power of slow waves is not affected by either type of stimulation.
Endoscopic treatment of GERD is still in its infancy, however the potential benefits of an endoscopic treatment for GERD are great. These procedures can be performed on an outpatient basis, without the risks of general anesthesia. The absence of abdominal incisions eliminates the morbidity of wound infections and hernia formation. The procedures are certainly less painful than laparoscopic or open surgery for reflux disease. These procedures might even be more cost effective than long-term acid suppression. These benefits make endoscopic treatment for reflux disease an appealing alternative. While the ideal endoscopic therapy has not been developed, all of these approaches have promise for the future and with further study the role of endoscopic therapy for GERD will continue to be defined.
OBJECTIVE: It has been reported that electrical stimulation at the distal stomach can disrupt intrinsic gastric electrical activity and delay gastric emptying. Gastric dysrhythmia and impaired gastric emptying are associated with upper gastrointestinal symptoms and weight loss. The purpose of this study was to evaluate the effect of low-frequency/long-pulse gastric electrical stimulation (GES), at proximal and distal stomach, on canine gastric emptying, food intake, and body weight. RESEARCH METHODS AND PROCEDURES: Eight dogs were surgically implanted with four pairs of electrodes along the greater curvature and a gastric tube at the dependent part of the stomach. Liquid gastric emptying at baseline, during proximal and distal GES at 6 cycles per minute, was assessed first by a dye dilution technique. Proximal and distal GES were then randomly delivered during feeding for 10 consecutive days, and food intake and body weight were recorded daily. RESULTS: There was no significant difference in gastric emptying parameters among the various sessions. The mean daily food consumption was significantly reduced during both sessions of GES, resulting in significant immediate weight loss. Percentage weight loss was comparable between both sessions of GES. DISCUSSION: Short-term GES significantly reduced canine food intake and weight. This effect may not be related to changes in gastric emptying. GES may have a potential role in the treatment of obesity.
Paraesophageal hernias are typically associated with symptoms and can sometimes lead to life-threatening complications. We recommend laparoscopic surgical repair for patients with symptomatic paraesophageal hernias. This article explains why and presents a general overview of the laparoscopic repair of paraesophageal hernias and its merits relative to open surgical repair.
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HYPOTHESIS: Laparoscopic splenectomy (LS) is the procedure of choice for elective splenectomy. Splenomegaly may preclude safe mobilization and hilar control using conventional laparoscopic techniques. Hand-assisted LS (HALS) may offer the same benefits of minimally invasive surgery for splenomegaly while allowing safe manipulation and splenic dissection. DESIGN: A retrospective review of patients with splenomegaly undergoing conventional LS or HALS was performed. SETTING: Tertiary care referral center. PATIENTS: Hand-assisted LS was performed at the start of the operation for patients with splenomegaly; splenomegaly was determined by palpation of the splenic tip extending to the midline or the iliac crest, or by a craniocaudal splenic length of greater than 22 cm. Splenomegaly was defined as a splenic weight of greater than 700 g after morcellation. MAIN OUTCOME MEASURES: Patient demographic characteristics, operative indications, splenic weight after morcellation, morbidity, mortality, and clinical outcomes were evaluated. RESULTS: Forty-five patients with splenomegaly were identified: 31 underwent standard LS and 14 underwent HALS. The HALS group had significantly larger spleens than the conventional LS group (mean weight, 1516 vs 1031 g; P =.02). Mean operative time (177 vs 186 minutes; P =.89), estimated blood loss (602 vs 376 mL; P =.17), and length of hospital stay (5.4 vs 4.2 days; P =.24) and complication rates (5 [36%] of 14 vs 5 [16%] of 31; P =.70) were similar between the HALS and the standard LS groups. No perioperative mortality occurred. CONCLUSIONS: Hand-assisted LS is a safe and efficacious procedure for these extremely difficult cases. Hand-assisted LS provides the benefits of a minimally invasive approach in cases of splenomegaly.
BACKGROUND: Laparoscopic cholecystectomy has replaced open cholecystectomy for the treatment of gallbladder disease. However, certain cases still require conversion to open procedures. Identifying these patients at risk for conversion remains difficult. This study identifies risk factors that may predict conversion from a laparoscopic to an open procedure. METHODS: From January 1996 to January 2000, a total of 1,347 laparoscopic cholecystectomies were performed at the Cleveland Clinic Foundation (CCF). A retrospective analysis of 34 parameters including patient demographics, clinical history, laboratory data, ultrasound results, and intraoperative details was performed. Stepwise, multivariate logistic regression was used to determine those variables predicting conversion of laparoscopic cholecystectomy. RESULTS: Seventy-one (5.3%) laparoscopic cholecystectomies required conversion. Multivariate analysis revealed that for all cases, a white blood cell count >9 (2.9 greater odds ratio [OR] of conversion P = 0.006) and a gallbladder wall thickness >0.4 cm (7.2 OR, P <0.001) predicted conversion to open cholecystectomy. However, when patients with acute cholecystitis were evaluated only a body mass index >30 kg/m(2) (5.6 OR, P = 0.02) predicted conversion. For patients undergoing elective cholecystectomy, a body mass index >40 kg/m(2) (33.1 OR, P = 0.01) and a wall thickness >0.4 cm (24.7 OR, P <0.004) predicted conversion. Finally, an ASA >2 (5.3 OR, P = 0.01) predicted conversion in patients undergoing nonelective cholecystectomies. CONCLUSIONS: Obese patients with acute cholecystitis undergoing laparoscopic cholecystectomy have an increased chance of conversion. Likewise, patients with multiple comorbid diseases undergoing nonelective laparoscopic cholecystectomy are more likely to require conversion. Finally, in an elective laparoscopic cholecystectomy, morbidly obese patients with chronic cholecystitis and a thickened gallbladder wall are more likely to require conversion. These factors can help counsel patients undergoing laparoscopic cholecystectomy with regards to the probability of conversion to an open procedure.
BACKGROUND: Porcine small intestinal submucosa (SIS) biograft is used as a bioscaffold for regeneration of a variety of tissues. To date, SIS has not been used as a biliary tract graft. The purpose of this study was to evaluate the feasibility of using SIS as a scaffold for bile duct tissue regeneration in a canine model. METHODS: Fifteen, 25- to 35-kg mongrel dogs underwent midline laparotomy and exposure of the common bile duct. Nine dogs had a longitudinal choledochotomy and a 2- x 1-cm elliptical patch of 4-ply SIS placed using 6-0 polypropylene suture. Six dogs had the anterior two thirds of the bile duct resected and a 2- to 3-cm tubularized 4-ply SIS interposition graft placed. Dogs were killed at intervals ranging from 2 weeks to 5 months. Before killing, liver function tests (alkaline phosphatase [U/L] and total bilirubin [mg/dL]) were evaluated, cholangiograms were performed, and the bile duct was examined histologically. RESULTS: Fourteen out of 15 dogs survived and were healthy at the time of killing. The one failure was a result of a bile leak in a patched animal. The SIS showed signs of incorporation with infiltration of native fibroblasts, blood vessels, and biliary mucosa within 2 weeks. Within 3 months the SIS graft was replaced with native collagen covered with a biliary epithelium. No changes occurred at 5-month follow-up. One animal with an interposition graft developed a stricture at the proximal anastomosis within 2 months. In the remaining dogs, liver enzymes were normal, and the caliber of the common bile duct remained normal. CONCLUSIONS: SIS can be used for regeneration of bile duct tissue in a canine model. In 13 of 15 dogs SIS resulted in regeneration of canine common bile duct when used as a patch or as an interposition graft. The potential for the use of SIS as a patch for biliary stricturoplasty, or as an interposition graft for repair of complex biliary injuries is encouraging.
OBJECTIVE: The purpose of this study is to compare the cosmetic outcome of scalp wound closure with staples to traditional skin sutures. METHODS: A prospective, randomized trial was conducted using a convenience sample of children (aged 1-16 y) with simple scalp lacerations admitted to the pediatric emergency department. After parental consent was obtained, patients were randomly assigned to either a stapling or suturing procedure. A trained attending physician completed the procedure following a standard protocol. Based on previously published data, a sample size of 18 patients per group was calculated to give 85% power to detect a 10% difference on a visual analogue scale (VAS) score (two-sided alpha 0.05). Initial outcome of wound healing at 7 to 10 days and final cosmetic outcome after 6 to 18 months were estimated using a VAS. Cosmetic outcome was assessed by a physician blinded to the procedure. Data were analyzed using SPSS (Version 8.02; SPSS Inc., Chicago, IL). The VAS scores for the two treatment groups were compared using the two-tailed Student t test. Analysis of age, race, mode of injury, time interval, and size of the wound were performed to estimate the strength of the association of VAS score with the treatment, adjusted for the covariates. RESULTS: A total of 42 patients were enrolled. Of the 42, 38 (90.5%) finished the initial follow-up and 31 of those 38 (81.6%) finished the final follow-up. There were no significant demographic differences between groups at recruitment and first follow-up. Among those patients who completed the final follow-up, 15 underwent stapling, and 16 underwent suturing. There were no significant demographic or baseline differences between the groups. Procedure time was significantly lower in the stapling group (P = 0.001). Final follow-up evaluations were completed in 12 +/- 4 months. The mean VAS scores at first and final follow-up were 78.75 +/- 16.16 and 96.31 +/- 8.06 for the suturing group and 86.67 +/- 9.76 and 97 +/- 7.02 for the stapling group (P = 0.17). There remained no significant difference in the final follow-up VAS score between groups when adjusted for covariates. CONCLUSION: Stapling appears to be a fast and cosmetically acceptable alternative to suturing for simple scalp lacerations.
Cardiac memory is an altered T wave during sinus rhythm that is induced by a period of ventricular pacing or arrhythmia. The T wave is characterized by a vector that tracks that of the previously paced or arrhythmic QRS complex. Although initially considered a clinical oddity, cardiac memory is of interest both as an example of the general biological property of memory - as studied most extensively in neural tissues - and because of its implications regarding the control of cardiac rhythm. Signal transduction of cardiac memory appears to involve an angiotensin II-regulated pathway initiated by altered stress/strain patterns in the myocardium. The end result is altered density and kinetics of the transient outward current and perhaps other ion currents as well, and an altered transmural gradient for repolarization. The altered repolarization pattern is accompanied by altered responses to specific antiarrhythmic drugs that may be anti- or proarrhythmic.