Biomedical subjects

Patrick Han

Publications and source records attributed to Patrick Han.

6 recordsLinked to original sources

PubMed2005

Substrate-mediated intermolecular interactions: a quantitative single molecule analysis.

Long-range intermolecular interactions mediated by the surface are believed to be responsible for many effects in surface science, including molecular ordering, formation of nanostructures, and aligning reactive intermediates in catalysis. Here, we use scanning tunneling microscopy to probe the weak substrate-mediated interactions in benzene overlayers on Au{111} at 4 K. Using an automated procedure to monitor single molecule motion, we are able to quantify the substrate-mediated interaction strength. We explain quantitatively both the kinetics of the benzene motion and the thermodynamics that determine the packing structures benzene adopts in this system in light of these substrate-mediated interactions.

Journal Article↗

PubMed2004

Benzene on Au[111] at 4 K: monolayer growth and tip-induced molecular cascades.

Low-temperature scanning tunneling microscopy has been used to characterize the various structures of submonolayer and near-monolayer coverages of benzene (C6H6) on Au[111] at 4 K. At low coverage, benzene is found to adsorb preferentially at the top of the Au monatomic steps and is weakly adsorbed on the terraces. At near-monolayer coverage, benzene was found to form several long-range commensurate overlayer structures that depend on the regions of the reconstructed Au[111] surface, namely a (radical 52 x radical 52)R13.9 degrees structure over the hcp regions and a (radical 133 x radical 133)R17.5 degrees "pinwheel" structure over the fcc regions. Time-lapse imaging revealed concerted cascade motion of the benzene molecules in the (radical 133 x radical 133)R17.5 degrees pinwheel overlayer. We demonstrate that the observed cascade motion is a result of concerted molecular motion and not independent random motion.

Journal Article↗

PubMed2004

Preliminary experience using the Neuroform stent for the treatment of cerebral aneurysms.

INTRODUCTION: The Neuroform microstent-a flexible, self-expandable, microcatheter-delivered, nitinol stent designed for the treatment of cerebral aneurysms-was recently approved for use in patients. We present the results of our initial experience in using the Neuroform stent to treat patients with cerebral aneurysms, with an emphasis on potential applications, technical aspects of deployment, and associated intra- and periprocedural complications. METHODS: The records of all patients treated with the Neuroform stent were entered prospectively into a database. We assessed the clinical history, indications for stent use, aneurysm dimensions, and technical details of the procedures, including any difficulties with stent placement and/or deployment, degree of aneurysm occlusion, and complications. RESULTS: During a 5-month period, 19 patients with 22 aneurysms were treated with the Neuroform stent. Twenty-five stents were deployed. Five patients had multiple stents placed. Five patients had ruptured aneurysms at the time of treatment. The indications for use were broad-necked aneurysms (n = 13; average neck length, 5.1 mm; average aneurysm size, 9 mm), fusiform or dissecting aneurysms (n = 3), salvage and/or bailout (n = 1), and giant aneurysms (n = 2). Technical problems included difficulty in deploying the stent (n = 6), inability to deploy the stent (n = 1), stent displacement (n = 2), inadvertent stent deployment (n = 1), and coil stretching (n = 1). Twenty-one of the 22 aneurysms were treated. Four aneurysms were stented without additional treatment, and 17 aneurysms were stented and coiled. Of the coiled aneurysms, complete or nearly complete (more than 95%) occlusion was achieved in 6 aneurysms, and partial occlusion was achieved in 11. Two clinically significant adverse events occurred, both of which were sequelae of periprocedural thromboembolic complications. One patient died after thrombolysis was attempted. The other patient made an excellent functional recovery after undergoing successful thrombolysis of a thrombosed basilar artery stent. CONCLUSION: The Neuroform stent is a useful device for the treatment of patients with aneurysms that may not otherwise be amenable to endovascular therapy. In the majority of cases, the stent can be deployed accurately, even within the most tortuous segments of the cerebral vasculature. Although delivery and deployment may be technically challenging, clinically significant complications are uncommon.

Adolescent↗

PubMed2004

Strategies for the management of intraprocedural thromboembolic complications with abciximab (ReoPro).

OBJECTIVE: Most complications related to endovascular neurointerventional procedures are thromboembolic. The objective of this study was to determine whether abciximab, a glycoprotein IIb/IIIa inhibitor, is a safe and effective agent for the treatment of thromboembolic complications encountered during interventional neuroradiological procedures. METHODS: A search of a prospectively maintained database identified 13 patients who were treated for intraprocedural thromboembolic complications with abciximab, either alone or in combination with tissue plasminogen activator, during a 22-month period. RESULTS: Of the 13 patients in our series (10 with aneurysms, 3 with arteriovenous malformations), 12 presented with unsecured vascular lesions, and in 9 cases the lesions were either acutely (<10 d) or subacutely (<6 mo) hemorrhagic. After the identification of a thromboembolic complication, each patient was treated with either intra-arterial (n = 5) or intravenous (n = 8) abciximab. Abciximab was administered intravenously as a 0.25-mg/kg bolus (n = 2), a 0.25-mg/kg bolus followed by a 12-hour 0.125-microg/kg/min infusion (n = 5), or a 12-hour 0.125-microg/kg/min infusion alone (n = 1). Intra-arterial abciximab (3.5-10 mg) was administered directly through a microcatheter positioned in the vicinity of the thrombus (n = 5). Five patients also were administered alteplase. Complete (n = 7) or partial (n = 6) resolution of thrombus was observed in all cases. Five patients had small infarcts in the distribution of the thromboembolic complication. In no case was new or increased hemorrhaging observed after thrombolysis. CONCLUSION: Abciximab (ReoPro), administered either intravenously or intra-arterially, is a viable option for the management of thromboembolic complications encountered during endovascular therapeutic procedures.

Abciximab↗

PubMed2003

Substrate-mediated interactions and intermolecular forces between molecules adsorbed on surfaces.

Adsorbate interactions and reactions on metal surfaces have been investigated using scanning tunneling microscopy. The manners in which adsorbates perturb the surface electronic structure in their vicinity are discussed. The effects these perturbations have on other molecules are shown to be important in overlayer growth. Interactions of molecules with surface steps are addressed, and each molecule's electron affinity is shown to dictate its adsorption sites at step edges. Standing waves emanating from steps are demonstrated to effect transient molecular adsorption up to 40 A away from the step edge. Halobenzene derivatives are used to demonstrate how the surface is important in aligning reactive intermediates.

Adsorption↗

PubMed2003

A reappraisal of angioplasty and stenting for the treatment of vertebral origin stenosis.

OBJECTIVE: To assess the rate of restenosis after vertebral origin angioplasty and stenting (VOAS). METHODS: We reviewed the records of 33 patients (24 men, 9 women; age range, 49-81 yr; mean, 64.5 yr) who underwent VOAS during a period of 5 years and followed each for the development of adverse sequelae through a prospectively maintained database. A neuroradiologist not involved in the stenting procedures assessed original and follow-up angiograms for evidence of restenosis. Restenosis was quantified as insignificant (0-24%), mild (25-49%), moderate (50-74%), or severe (75-100%). RESULTS: Of the 33 patients, 30 presented with transient ischemic attacks or stroke. Most (31 of 33 patients) manifested other brachiocephalic stenoses, including 27 patients with occlusion, hypoplasia, or stenosis of the contralateral vertebral artery. Angiographic follow-up (mean, 16.2 mo) was obtained in 30 patients (2 patients died before follow-up, and 1 refused). Restenosis was mild in seven patients, moderate in eight, and severe in five. The combined rate of moderate-to-severe restenosis was 43.3%. No complications resulted in permanent morbidity. One patient died as a result of a stroke in a different vascular distribution 4 months after VOAS. Another patient died as a result of basilar thrombosis in which emergent stenting had been undertaken in an effort to perform thrombolysis. CONCLUSION: Despite a technical success rate of 97% and a low incidence of complications, VOAS is associated with a high rate of moderate-to-severe restenosis.

Aged↗