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Biomedical subjects

David L Dawson

Publications and source records attributed to David L Dawson.

11 recordsLinked to original sources
PubMed2007

Vascular surgery: an update.

Caring for patients with vascular illnesses has become increasingly more complex and has changed dramatically over the past 10 years, with a widening array of diagnostic and treatment options. Carotid artery stenting has the potential to become a viable alternative to open surgery in high-risk patients with carotid artery disease (i.e., patients older than 80 years and those with previous neck surgery or irradiation, contralateral carotid artery occlusion, contralateral laryngeal nerve injury, or angina). However, the effectiveness of carotid artery stenting as a therapy is still being evaluated in randomized trials. Endovascular aortic aneurysm repair is an option for patients who desire or require a less invasive modality and who have suitable aortic anatomy. Surgical reconstruction remains the standard treatment for ischemic rest pain and tissue loss (critical limb ischemia). Balloon angioplasty and stenting are treatment options for peripheral vascular disease, although treatment is dependent on the arterial segment or segments involved.

Aortic Aneurysm, Abdominal↗
PubMed2007

Training with simulation improves residents' endovascular procedure skills.

BACKGROUND: Endovascular procedure simulators are now commercially available and in use for physician training. The purpose of this study was to evaluate the role of simulation-based training in vascular surgery residencies. METHODS: Residents from vascular surgery programs in a five-state area were invited to participate in a series of 2-day endovascular training programs that used a high-fidelity endovascular procedure simulator (SimSuite; Medical Simulation Corporation, Denver, Colo), didactic instruction, computer-based training, and tabletop procedure demonstrations. The curriculum covered arteriography and intervention for treatment of aortoiliac, renal, and carotid artery disease. Nine residents participated, with one to three per training session. Each completed an average of 9.5 simulated endovascular cases. Performance on a standardized TransAtlantic Inter-Society Consensus B iliac angioplasty/stenting case was used to assess endovascular skills and knowledge at the beginning of the training program, and this was repeated at the completion of the training. Performance metrics were measured by the simulator, faculty observed trainees' performance of simulated cases, and trainees provided their evaluations of the usefulness of the simulation experiences. RESULTS: Endovascular procedural skills on the standardized iliac intervention case improved after completion of the training program. Compared with performance early on day 1, performance improved (P < or = .05; paired t test): total procedure time decreased 54%, volume of contrast decreased 44%, and fluoroscopy time decreased 48% (mean change from baseline). Selection of angioplasty balloon catheters and stents was improved, and the average number of catheters used and stents deployed decreased, although this did not reach statistical significance. Faculty observation allowed identification of shortcomings of knowledge and skills, including common problems with selection of catheter, balloon, and stent sizes; correct positioning of the sheath; and intraprocedural monitoring. Postcourse evaluations indicated support for the use of simulation in vascular surgery residents' endovascular training. CONCLUSIONS: Training with a simulator, incorporated into an individual or small group learning session, offers a means to learn and realistically practice endovascular procedures without direct risk to patients, with measurable improvements in key performance metrics. How simulation training affects subsequent clinical performance has yet to be established.

Endoscopy↗
PubMed2004

Sonographic detection of pneumothorax and hemothorax in microgravity.

INTRODUCTION: An intrathoracic injury may be disastrous to a crew-member aboard the International Space Station (ISS) if the diagnosis is missed or delayed. Symptomatic or clinically suspicious thoracic trauma is treated as a surgical emergency on Earth, usually with immediate stabilization and rapid transport to a facility that is able to deliver the appropriate medical care. A similar approach is planned for the ISS; however, an unnecessary evacuation would cause a significant mission impact and an exorbitant expense. HYPOTHESIS: The use of ultrasound imaging for the detection of pneumothorax and hemothorax in microgravity is both possible and practical. METHODS: Sonography was performed on anesthetized pigs in a ground-based laboratory (n = 4) and microgravity conditions (0 G) during parabolic flight (n = 4). Aliquots of air (50-500 ml) or saline (10-200 ml) were introduced into the pleural space to simulate pneumothorax and hemothorax, respectively. RESULTS: The presence of "lung sliding" excluded pnemothorax. In microgravity, a loss of "lung sliding" was noted simultaneously in the anterior and posterior sonographic windows after 100 ml of air was introduced into the chest, indicating pneumothorax. The presence of the fluid layer in simulated hemothorax was noted in the anterior and posterior sonographic windows after 50 ml of fluid was injected into the pleural space. During the microgravity phase, the intrapleural fluid rapidly redistributed so that it could be detected using either anterior or posterior sonographic windows. CONCLUSION: Modest to severe pneumothorax and hemothorax can be diagnosed using ultrasound in microgravity.

Animals↗
PubMed2003

Focused Assessment with Sonography for Trauma in weightlessness: a feasibility study.

BACKGROUND: The Focused Assessment with Sonography for Trauma (FAST) examines for fluid in gravitationally dependent regions. There is no prior experience with this technique in weightlessness, such as on the International Space Station, where sonography is currently the only diagnostic imaging tool. STUDY DESIGN: A ground-based (1 g) porcine model for sonography was developed. We examined both the feasibility and the comparative performance of the FAST examination in parabolic flight. Sonographic detection and fluid behavior were evaluated in four animals during alternating weightlessness (0 g) and hypergravity (1.8 g) periods. During flight, boluses of fluid were incrementally introduced into the peritoneal cavity. Standardized sonographic windows were recorded. Postflight, the video recordings were divided into 169 20-second segments for subsequent interpretation by 12 blinded ultrasonography experts. Reviewers first decided whether a video segment was of sufficient diagnostic quality to analyze (determinate). Determinate segments were then analyzed as containing or not containing fluid. A probit regression model compared the probability of a positive fluid diagnosis to actual fluid levels (0 to 500 mL) under both 0-g and 1.8-g conditions. RESULTS: The in-flight sonographers found real-time scanning and interpretation technically similar to that of terrestrial conditions, as long as restraint was maintained. On blinded review, 80% of the recorded ultrasound segments were considered determinate. The best sensitivity for diagnosis in 0 g was found to be from the subhepatic space, with probability of a positive fluid diagnosis ranging from 9% (no fluid) to 51% (500 mL fluid). CONCLUSIONS: The FAST examination is technically feasible in weightlessness, and merits operational consideration for clinical contingencies in space.

Aerospace Medicine↗
PubMed2003

Simple technique to ensure coaxial guidewire positioning for placement of iliac limb of modular aortic endograft.

Endovascular abdominal aortic aneurysm repair using a modular bifurcated stent-graft requires the initial placement of the main component in the infrarenal aorta, followed by insertion of additional iliac stent-graft(s) to exclude aneurysm and to securely affix the device. Placement of the contralateral iliac component within the main bifurcated device is critical in this endovascular procedure, as malpositioning of the contralateral iliac limb can require conversion to open aneurysm repair. A simple adjunctive technique utilizing a rotational maneuver of a pigtail catheter is described. This maneuver reliably confirms the proper placement of the contralateral iliac stent-graft within the main bifurcated device.

Aorta, Abdominal↗
PubMed2002

Iliac artery kinking with endovascular therapies: technical considerations.

Iliac artery tortuosity should be considered when planning endovascular interventions from a femoral approach. Stiff guide wires across tortuous iliac segments can introduce foreshortening and temporary kinking. Recognition of this phenomenon and its implications is important when making anatomic measurements before endovascular device placement, when assessing iliac runoff, and when considering adjunctive procedures after aortoiliac interventions. Two illustrative cases of external iliac artery kinking are presented, one during an abdominal aortic aneurysm endograft procedure and another encountered during stent placement in an external iliac artery dissection. In both cases, the temporary nature of the deformity was recognized, avoiding unnecessary additional intervention.

Aged↗
PubMed2002

Peripheral arterial disease: medical care and prevention of complications.

Peripheral arterial disease (PAD) is a common but under-recognized problem affecting older patients. Intermittent claudication is the most frequent symptom of PAD, although the diagnosis of PAD is often overlooked until the patient presents with limb-threatening ischemia. Importantly, PAD is a marker for generalized atherosclerosis and is closely associated with coronary and cerebrovascular disease. The severity of PAD has been correlated with an increased risk of myocardial infarction, stroke, and cardiovascular death. The recognition and diagnosis of PAD, combined with its appropriate medical management, may well reduce the overall risk of cardiovascular morbidity. When diagnosed early, both exercise and pharmacotherapy can ameliorate symptoms of claudication, augment functional performance, and improve quality of life.

Aged↗
PubMedDate not supplied

Failure of pentoxifylline or cilostazol to improve blood and plasma viscosity, fibrinogen, and erythrocyte deformability in claudication.

Peripheral artery disease is associated with altered blood rheologic properties, including increased viscosity and decreased red blood cell (RBC) deformability. Pentoxifylline and cilostazol are available therapies for intermittent claudication. Improvement of blood viscosity and erythrocyte deformability have been cited as potential mechanisms of action for pentoxifylline. Cilostazol is a new drug with antiplatelet and vasodilating activity, but the mechanism by which it promotes an improvement in walking is not known. This study was performed to evaluate and compare the hemorheologic effects of pentoxifylline and cilostazol on viscosity, fibrinogen levels, and erythrocyte deformability when administered to adults with moderate to severe claudication. A double-blind, controlled study was conducted and included 59 patients (46 male, 13 female; mean age 65 yr) randomized to pentoxifylline 400 mg orally thrice daily (n=20), cilostazol 100 mg orally twice daily (n=19), or placebo (n=20); all subjects were observed for 24 weeks. Walking ability was assessed before, during, and at the conclusion of treatment by standard constant speed, variable grade treadmill testing. Erythrocyte deformability was measured by passage of washed RBCs, 10% hematocrit in phosphate buffered saline (PBS), through a polycarbonate membrane with 4.7 to 5.0 microm pores. Whole blood and plasma viscosity were measured using a cone/plate viscometer at variable shear rates (from 4.5 to 450 sec(-1)). Erythrocyte sedimentation rate was measured by a modified Westergren technique. Fibrinogen was assayed by a commercial reference laboratory. Plasma viscosities did not change significantly in any treatment group. Within-group comparisons demonstrated a significant (p<0.01) drop in whole blood viscosity (week 24 compared with week 0) for cilostazol-treated subjects (at shear rates of 45, 90, 225, and 450 sec(-1)), but these changes were not significantly different from those in the placebo group. There were no significant changes in whole blood viscosity for subjects treated with pentoxifylline or placebo. There were no significant changes in erythrocyte deformability, fibrinogen, or erythrocyte sedimentation rate. A trend toward improved walking distances was noted for both pentoxifylline and cilostazol in comparison with placebo. This trend was not correlated with changes in any underlying rheologic parameter. Ex vivo rheologic characteristics of blood from patients with intermittent claudication are not significantly affected by long-term administration of pentoxifylline or cilostazol. Pentoxifylline did not modulate viscosity or red cell deformability, a finding at variance with its putative mechanism of action. Pentoxifylline cannot be differentiated from cilostazol based on specific hemorheologic effects evaluated in this study. Different mechanisms of action for these medications should be considered.

Adult↗
PubMedDate not supplied

Adjunctive endovascular techniques in the management of postoperative carotid artery pseudoaneurysms--useful armamentarium for vascular surgeons--three case reports.

Postoperative carotid artery pseudoaneurysms are rare. The traditional treatment of choice has been operative repair, which can present a significant technical challenge owing to the reoperative neck inflammation and potential cranial nerve injuries. The authors report 3 cases of postoperative carotid pseudoaneurysms that were successfully managed by use of various adjunctive endovascular techniques. The adjunctive endovascular maneuvers included the following: 1) endoluminal balloon placement for preoperative test occlusion and intraoperative proximal control to facilitate operative dissection in the first patient with a carotid pseudoaneurysm; 2) endoluminal stent-graft placement to exclude a large expanding carotid pseudoaneurysm in the second patient; and 3) endoluminal coil placement along with balloon occlusion to achieve complete hemostasis in the third patient, who presented with a hemorrhaging carotid pseudoaneurysm. Successful outcomes were achieved in all 3 patients by use of adjunctive endovascular techniques. These cases underscore the role of adjunctive endovascular treatment as an armamentarium for vascular surgeons in the treatment of complex carotid pseudoaneurysms.

Aged↗
PubMedDate not supplied

Training in carotid artery stenting: do carotid simulation systems really help?

Virtual reality (VR) simulations have long been used for training in aviation and other professions. High-fidelity endovascular procedure simulators are now available, providing procedure simulations with real-time interactions; two-dimensional graphic displays of angiographic anatomy; mechanical interfaces with guidewires, sheaths, and catheters that provide some degree of haptic feedback; modeling of physiologic and pharmacology responses; and other features. Simulators have been incorporated into training programs for physicians learning carotid artery stenting (CAS). For the first time, US Food and Drug Administration approval of a new device (CAS systems) has included a requirement for physician training that incorporates the use of VR simulators. Early experience has shown that simulation is well accepted by trainees, performance on simulators improves with training and practice, and simulation prior to first performing endovascular procedures can improve clinical performance. Specific to CAS, the value of education programs using simulators appears to be tangible as trained but inexperienced CAS operators have clinical results comparable to those of physicians with extensive CAS experience.

Carotid Stenosis↗