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Biomedical subjects

Ramon Berguer

Publications and source records attributed to Ramon Berguer.

At least 19 recordsLinked to original sources
PubMed2006

Correction of superior vena cava syndrome with superficial femoral vein juguloatrial bypass.

Several techniques for bypass of the superior vena cava have been described, including spiraled saphenous vein graft, femoral vein graft, and polytetrafluoroethylene graft as conduits. We present two cases of superior vena cava obstruction treated with juguloatrial bypass using harvested superficial femoral vein. We feel that the superficial femoral vein, with its diameter similar to that of the internal jugular vein, provides several advantages compared to other conduits in a juguloatrial bypass.

Adult↗
PubMed2006

Pediatric renovascular hypertension: 132 primary and 30 secondary operations in 97 children.

PURPOSE: This study was undertaken to characterize the contemporary surgical treatment of pediatric renovascular hypertension. METHODS: A retrospective analysis was conducted of the clinical data of 97 consecutive pediatric patients (39 girls, 58 boys), aged from 3 months to 17 years, who underwent operation at the University of Michigan from 1963 to 2006. All but one patient had refractory hypertension not responsive to contemporary medical therapy. Developmental renal artery stenoses accounted for 80% of the renal artery disease, with inflammatory and other ill-defined stenoses encountered less frequently. Splanchnic arterial occlusive lesions affected 24% and abdominal aortic coarctations, 33%. RESULTS: Primary renal artery operations were undertaken 132 times. Procedures included resection beyond the stenosis and implantation into the aorta in 49, renal artery in 7, or superior mesenteric artery in 3; aortorenal and iliorenal bypasses with vein or iliac artery grafts in 40; focal arterioplasty in 10; resection with reanastomosis in 4; operative dilation in 4; splenorenal bypass in 2; and primary nephrectomy in 13 when arterial reconstructions proved impossible. Bilateral renal operations were done in 34 children, and 17 underwent celiac or superior mesenteric arterial reconstructions, including 15 at the time of the renal operation. Thirty patients underwent abdominal aortic reconstructions with patch aortoplasty (n = 19) or thoracoabdominal bypass (n = 11). Twenty-five of the aortic procedures were performed coincidently with the renal operations. Thirty secondary renal artery procedures were done in 19 patients, including nine nephrectomies. Hypertension was cured in 68 children (70%), improved in 26 (27%), and was unchanged in three (3%). Follow-up averaged 4.2 years. No patients required dialysis, and there were no operative deaths. CONCLUSION: Contemporary surgical treatment of pediatric renovascular hypertension emphasizes direct aortic implantation of the normal renal artery beyond its stenosis and single-staged concomitant splanchnic and aortic reconstructions when necessary. Benefits accompany carefully executed operative procedures in 97% of these children.

Adolescent↗
PubMed2006

A biologic basis for asymmetric growth in descending thoracic aortic aneurysms: a role for matrix metalloproteinase 9 and 2.

OBJECTIVE: This study was undertaken to define matrix metalloproteinase (MMP) expression in the anterior and posterior wall of descending thoracic aortic aneurysms (TAAs) and correlate it with specific computed tomography (CT) image sites within the descending thoracic aorta. METHODS: Serial CT images of patients with TAAs were compared with age- and gender-matched normal descending thoracic aortas at levels T4-T12. The mean circumference of the TAAs was 153 mm (n = 12) and 148 mm (n = 11) at T8 and T10, respectively, compared with 75 mm (n = 12) and 75 mm (n = 10) in controls (P < .001). Aortic tissue was collected from a separate set of eight patients undergoing descending TAA resection (processed < or =12 hours of excision) and six cadavers (processed < or =24 hours of death). Tissue collected between the intercostals arteries was defined as posterior wall, and directly opposite was the anterior wall. MMP-9 and MMP-2 messenger RNA (mRNA) extracted from aortic tissue was analyzed by quantitative real time polymerase chain reaction (PCR) and normalized to beta-actin. Immunohistochemistry was performed for MMP-9 and MMP-2. CT aortic measurements and MMP expression were compared by t tests and analysis of variance, respectively. RESULTS: The ratio of arc distance between the intercostals on the posterior wall to total aortic circumference was 0.14 in healthy controls compared with 0.08 in TAAs at vertebral level T8 (P = .001). At T10, the ratio was 0.15 in healthy controls compared with 0.11 in TAAs (P = .001). MMP-9 expression in TAAs was 4.3-fold higher in the anterior wall compared with the posterior wall (P = .03). Conversely, MMP-2 expression in TAAs was 3.2-fold higher in the posterior wall compared with the anterior wall (P = .008). MMP expression was not detected in control cadaver aortas. CONCLUSION: Anterior walls of expanding TAAs grow at a greater rate than the posterior wall, as determined from the lower ratio of intercostal arc distance to total circumference in TAAs. Differential MMP expression appears to be a biologic marker for asymmetric growth in the TAA wall. CLINICAL RELEVANCE: The pathogenesis of thoracic aortic aneurysms (TAAs) is poorly understood. Multiple lines of evidence suggest that matrix metalloproteinases (MMPs), a family of enzymes, are important in aneurysm development. Earlier experiments documented a regional variation of MMP-9 in stimulated rodent aortas, with production greater in the abdominal aorta compared with the thoracic aorta. The present study extends that observation and documents asymmetric aneurysm development in the TAA wall, with increased anterior wall growth in correlation to increased MMP-9 production. An improved understanding of the mechanisms by which MMP production is regulated is critical.

Aortic Aneurysm, Thoracic↗
PubMed2006

Refinements in mathematical models to predict aneurysm growth and rupture.

The growth of aneurysms and eventually their likelihood of rupture depend on the determination of the stress and strain within the aneurysm wall and the exact reproduction of its geometry. A numerical model is developed to analyze pulsatile flow in abdominal aortic aneurysm (AAA) models using real physiological resting and exercise waveforms. Both laminar and turbulent flows are considered. Interesting features of the flow field resulting from using realistic physiological waveforms are obtained for various parameters using finite element methods. Such parameters include Reynolds number, size of the aneurysm (D/d), and flexibility of the aneurysm wall. The effect of non-Newtonian behavior of blood on hemodynamic stresses is compared with Newtonian behavior, and the non-Newtonian effects are demonstrated to be significant in realistic flow situations. Our results show that maximum turbulent fluid shear stress occurs at the distal end of the AAA model. Furthermore, turbulence is found to have a significant effect on the pressure distribution along AAA wall for both physiological waveforms. Related experimental work in which a bench top aneurysm model is developed is also discussed. The experimental model provides a platform to validate the numerical model. This work is part of our ongoing development of a patient-specific tool to guide clinician decision making and to elucidate the contribution of blood flow-induced stresses to aneurysm growth and eventual rupture. These studies indicate that accurately modeling the physiologic features of real aneurysms and blood is paramount to achieving our goal.

Aneurysm↗
PubMed2006

Global expression profiles in human normal and aneurysmal abdominal aorta based on two distinct whole genome microarray platforms.

Abdominal aortic aneurysms (AAA) are the thirteenth cause of death in the United States. The etiology of the disease is yet largely unknown, although several environmental risk factors (e.g., smoking) have been identified and the search for finding genetic risk factors has been initiated. The purpose of our study was to gain insight into the pathobiology of AAA by determining which genes are expressed in the abdominal aorta under either the diseased or normal states, thereby generating the whole-genome-wide expression profiles for these conditions.

Aortic Aneurysm, Abdominal↗
PubMed2006

Modeling pulsatile flow in aortic aneurysms: effect of non-Newtonian properties of blood.

Pulsatile flow in an axisymmetric rigid-walled model of an abdominal aorta aneurysm was analyzed numerically for various aneurysm dilations using physiologically realistic resting waveform at time-averaged Reynolds number of 300 and peak Reynolds number of 1607. Discretization of the governing equations was achieved using a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previously published work on the basis of special cases were performed and found to be in excellent agreement. Our findings indicate that the velocity fields are significantly affected by non-Newtonian properties in pathologically altered configurations. Non-Newtonian fluid shear stress is found to be greater than Newtonian fluid shear stress during peak systole. Further, the maximum shear stress is found to occur near the distal end of AAA during peak systole. The impact of non-Newtonian blood flow characteristics on pressure compared to Newtonian model is found insignificant under resting conditions. Viscous and inertial forces associated with blood flow are responsible for the changes in the wall that result in thrombus deposition and dilation while rupture of AAA is more likely determined by much larger mechanical stresses imposed by pulsatile pressure on the wall of AAA.

Aortic Aneurysm, Abdominal↗
PubMed2005

An ergonomic comparison of robotic and laparoscopic technique: the influence of surgeon experience and task complexity.

BACKGROUND: This study compares the mental and physical workload of laparoscopic and robotic technique while performing simulated surgical tasks in a laboratory setting. MATERIALS AND METHODS: Ten volunteer surgeons performed two tasks in a laparoscopic trainer using laparoscopic (LAP) and robotic (ROB) techniques. Outcome measures included: Task time, task-error, vertical/horizontal arm displacement, percent maximum electromyographic signal from the thenar, forearm flexor, and deltoid muscle compartments, skin conductance, and perceived difficulty and discomfort levels. A two-way repeated-measures ANOVA compared surgical technique and laparoscopic experience level (E = expert, N = novice). RESULTS: For the simple task, ROB technique was slower and had higher errors, and the surgeon's arm was more elevated. For the complex task, ROB electromyographic signal was lower. Stress was lower in both tasks for ROB, but the decrease was not statistically significant. CONCLUSIONS: Robotic technique appears slower and less precise than laparoscopic technique for simple tasks, but equally fast and possibly less stressful for complex tasks. Previous laparoscopic experience has a complex influence on the physical and mental adaptation to robotic surgery.

Adult↗
PubMed2005

Takayasu's arteritis presenting as uveitis in a 5-year-old girl.

A 5-year-old patient presented with uveitis as initial manifestation of Takayasu's arteritis. Our patient is unique not only in the initial presentation but also in the extent of arteritis in the aortic arch and great vessels. This is only the second case reported in the literature with this unusual presentation.

Child, Preschool↗
PubMed2005

Strategies for preventing sharps injuries in the operating room.

With the discovery of AIDS and HIV, the medical community began to widely recognize the dangers of serious illnesses spread-ing through contact with contaminated blood and body fluids. In response, the Centers for Disease Control and other groups have developed guidelines for the operating room to prevent the spread of infection from, for example, accidental needle sticks. Unfortunately, those guidelines are not always strictly followed. This article reviews studies that have examined precautionary practices, including such practices as double gloving, the use of blunt suture needles, and the use of neutral zones for passing sharps. The article also provides related sources for further information.

Accidents, Occupational↗
PubMed2005

Monitor height affects surgeons' stress level and performance on minimally invasive surgery tasks.

This study investigated the effect of monitor height on surgeons' workload and performance during simulated minimally invasive surgery (MIS). Fourteen volunteer subjects (7 experienced, 7 inexperienced) performed a cutting task in a training box at a standard MIS station with the video monitor positioned in random order at, below (-35 degrees), and above (+15 degrees) the subject's eye level. Task time and error, difficulty and discomfort, head orientation, trapezius and neck muscle activity, and skin conductance were recorded. The experienced subjects performed the task faster, with less error, and with less difficulty than did the inexperienced subjects. For the experienced subjects, error decreased when the monitor was lowered. Difficulty and discomfort increased at the high monitor position. As the monitor was lowered, the head pitched forward, and paraspinal cervical muscle activity increased. Variability in sternocleidomastoid activity increased both at the low and high monitor positions. The results show that monitor height affects both performance and workload. The monitor should be lowered to reduce error and task difficulty but not so low as to produce excessive neck flexion.

Adult↗
PubMed2004

The evidence thing.

The methodology of evidence-based medicine (EBM) has become dominant in the clinical field to the detriment of historically validated paradigms. The philosophical background of EBM is considered and the strengths and flaws of its main tools (randomized trials and meta-analysis) are reviewed. The structural format of EBM speaks the language of regulators and health planners, satisfies the needs of the academic-industrial complex, and is favored by editors of medical journals. Specific problems of trials of medical versus surgical therapy are noted. The deductive-numerical approach of EBM is a methodology geared to ascertain the most effective management of a condition when the differences observed between the two entities being considered is small. EBM methodology is unlikely to lead to discovery of new diseases or treatments; the latter derive from alert observation and inductive inference. While its contribution to the rigorous analysis of effectiveness of some therapies is acknowledged, EBM is not the nostrum of clinical research. Observational and inductive clinical intelligence should be stimulated and published because a therapy needs to be invented before it is proven effective. Biomathematicians need to improve nonrandomized methodology as they did for randomized studies.

Evidence-Based Medicine↗
PubMed2004

Elevated expression of matrix metalloproteinase-13 in abdominal aortic aneurysms.

Destructive remodeling of extracellular matrix has been shown to be present in aneurysmal abdominal aorta. We used real-time quantitative reverse transcriptase polymerase chain reaction to determine the relative expression of matrix metalloproteinase-13 (MMP13) in aortic tissue samples from patients who underwent abdominal aortic aneurysm repair operations (n = 36) and from nonaneurysmal autopsy samples (n = 20). The assays were carried out simultaneously in the same reaction tubes for ribosomal 18S RNA to correct for different amounts of input RNA. MMP13 was expressed in all parts of aorta and its expression was elevated in aneurysmal sac. In further studies using MMP13-specific antibody we demonstrated that MMP13 protein was present in the aneurysmal wall.

Aged↗
PubMed2004

Problems facing vascular surgery in 2004.

The most pressing challenges we face in the immediate future are endovascular training for those already in practice and a new educational paradigm for our residents. A number of avenues for training those in practice have been implemented, and newer methods, including computer simulation, are being explored. Vascular training programs should be 3 years in length, include vascular navigation and interventional skills, and follow 3 years of basic general surgical training. These changes in our resident training paradigm can take place only through two avenues: a successful reapplication to the American Board of Medical Specialties for an independent American Board of Vascular Surgery or a full reconfiguration of the training programs for general and vascular surgeons that would have to be spearheaded by the American Board of Surgery. There is skepticism that the latter could take place in the limited time we have left to make the vascular surgery residency attractive to candidates and sufficient in experiential and knowledge content.

Biomedical Research↗
PubMed2004

A simple virtual instrument to monitor surgeons' workload while they perform minimally invasive surgery tasks.

Monitoring the workload of surgeons while they perform minimally invasive surgery (MIS) tasks can help them learn to reduce effort as they improve performance and can help develop better human-technology interfaces for MIS. To monitor workload, we developed a personal computer based virtual instrument (VI) that uses orientation sensors worn on the surgeon's left and right upper arms to measure upper arm flexion, abduction, and outward rotation angles. From these sensors, we compute indices of effort and integrated effort. One effort index is the upper arm elevation angle. The time integral of this index provides a corresponding integrated effort index. A second effort index is hand velocity. Hand trajectory length is the corresponding integrated effort index. We used the workload monitor VI to study 29 volunteer surgeon subjects while they performed a knot-tying task in a laparoscopic trainer at a standard MIS station. For five of these subjects, we also monitored the workload indices while they performed simulated MIS tasks on a virtual reality Procedicus MIST System. For the subject group, integrated effort, but not level of effort, decreased with increased performance. At each performance level, some subjects worked much harder than others, suggesting that these subjects could benefit by learning to reduce their effort levels. The workload measures from the arm sensors augmented the performance measures provided by the MIST system.

General Surgery↗
PubMed2003

A comparison of the physical effort required for laparoscopic and open surgical techniques.

HYPOTHESIS: Performing complex tasks requires greater muscle effort with laparoscopic instruments than with open surgical instruments. DESIGN: A nonrandomized 2-condition trial. SETTING: A semienclosed ergonomics station in the exhibit hall at the Annual Meeting of the Society of American Gastrointestinal Endoscopic Surgeons. SUBJECTS: Twenty-one surgeons volunteered to participate in the study. INTERVENTIONS: Knot tying during 90 seconds, performed first using a laparoscopic technique (ie, axial instruments in a standard laparoscopic trainer) and then using an open technique (ie, 2 hemostats). MAIN OUTCOME MEASURES: Mean and peak surface electromyographic (EMG) signals collected from the thenar compartment, the flexor digitorum superficialis, and the deltoid muscles of the dominant arm. RESULTS: Compared with open knot-tying, laparoscopic tasks resulted in higher average EMG amplitudes in all 3 muscles (thumb, P =.02; forearm flexor, P =.01; and deltoid, P =.01) and higher peak EMG in the thumb (P =.04) and deltoid (P =.02) muscles. Body part discomfort scores were significantly higher during laparoscopic knot-tying for the forearm flexor and deltoid muscles (P =.02 for both). CONCLUSION: Complex manipulative tasks using laparoscopic techniques require substantially higher upper-extremity muscle effort compared with open surgical techniques.

Adult↗