Biomedical subjects

Russell Lam

Publications and source records attributed to Russell Lam.

7 recordsLinked to original sources

PubMed2006

Auxin and root initiation in somatic embryos of Arabidopsis.

Somatic embryos of Arabidopsis thaliana can be produced from explants of developing zygotic embryos. Cultivation of explants on maturation medium results in development of three main classes of regenerative structures: adventitious shoots, fused shoots, and complete somatic embryos. The ontogeny and anatomy of these structures was examined using serial plastic sections. Furthermore, two molecular markers were assayed to monitor transcriptional auxin responses and formation of a root meristem in this process: the LENNY allele of PIN4, a transposon insertion creating a fusion to the reporter gene GUS; and DR5::GUS, a synthetic reporter of auxin-induced transcription. In zygotic embryogenesis, PIN4 expression is confined to the center of the root meristem and begins to be detectable by the globular stage of embryogenesis, while DR5::GUS expression marks an "auxin perception maximum" in the more distal regions of the root. Adventitious and fused shoots develop no anatomically recognizable root meristem and do not express either of the two markers at their basal pole. Instead, the vasculature of their axis is directly connected to the vasculature of the explant. By contrast, complete somatic embryos were only loosely attached to the explant, had an anatomically defined root meristem and showed expression of both markers at their root pole. Our results suggest that the establishment of a root meristem in somatic embryos required appropriate auxin levels during the course of their development.

Arabidopsis↗

PubMed2006

Evaluation of the accuracy of a wireless pressure sensor in a canine model of retrograde-collateral (type II) endoleak and correlation with histologic analysis.

BACKGROUND: The utility of intra-aneurysmal pressure determination is dependent on the ability to measure pressure in the presence of endoleak and thrombosis. In this study, the accuracy of a CardioMEMS wireless pressure sensor (CardioMEMS, Atlanta, Ga) transducer in the presence of thrombus associated with type II endoleak was measured. METHODS: Type II endoleaks were created in four mongrel dogs by implanting four collateral arterial side branches (lumbar and caudal mesenteric arteries) as a Carrel patch onto a 3-cm prosthetic polytetrafluoroethylene abdominal aortic aneurysm (AAA). The aneurysm was excluded 2 weeks later from antegrade perfusion by a stent graft. The wireless pressure sensor was positioned in the AAA external to the stent graft. A Konigsberg intraluminal solid-state strain-gauge pressure transducer (Konigsberg Instruments, Pasadena, Calif) that is accurate in the presence of thrombus served as the control to determine AAA pressure. Both of the transducers were implanted on the luminal surface of the aneurysm, 180 degrees opposite from the Carrel patch and endoleak channel. Intra-aneurysmal pressure resulting from the type II endoleak was measured twice daily for 4 weeks using both transducers. A total of 56 pre-exclusion and 224 post-exclusion distinct pressure determinations were made. Intra-aneurysmal pressure was indexed to the systemic pressure that was simultaneously measured by a strain-gauge pressure transducer implanted in the native aorta. Histologic analysis of the aneurysm contents was performed with hematoxylin and eosin. RESULTS: The intra-aneurysmal systolic, mean, and pulse pressures produced by the type II endoleak were significantly lower than systemic pressure in all animals and were < 60% of systemic pressure (P < .001). Close correlation between the wireless transducer and the control strain-gauge transducer was observed (R = 0.83, P < .001). Arteriography and Doppler ultrasound documented retrograde flow through the aneurysm side branches and persistent endoleak patency up to the time of euthanasia. Pathologic analysis demonstrated the endoleak channel to be patent and separated from the transducers by thrombus, which surrounded both transducers. CONCLUSIONS: Intra-aneurysmal pressure generated by type II endoleaks may be accurately measured through thrombus using a wireless pressure sensor in the canine model. The wireless sensor has the potential for clinical applicability in diagnosing and characterizing type II endoleaks.

Angioplasty↗

PubMed2004

Abdominal aortic surgery in patients with human immunodeficiency virus infection.

PURPOSE: Human immunodeficiency virus (HIV) infection is known to cause acquired immune deficiency syndrome, which has been associated with a wide array of cardiovascular pathologies. This report examined the clinical outcome of patients infected with HIV who underwent abdominal aortic reconstruction for aneurysm or occlusive disease. METHODS: Hospital and clinic records of all patients with HIV infection who underwent an abdominal aortic operation were reviewed during an 11-year period. Relevant risk factors and clinical variables were assessed for surgical outcome. RESULTS: Forty-eight HIV patients (mean age 54 +/- 13 years) were identified who underwent abdominal aortic bypass grafting during the study period. Indications for aortic operation included aneurysm (n = 20) and aortoiliac occlusive disease (n = 28). All patients underwent successful aortic reconstructions without intraoperative mortality. Postoperative complications and in-hospital mortality occurred in 16 patients (33%) and 7 patients (15%), respectively. The mean follow-up period was 41 months. Life-table survival rates in aneurysm and occlusive patients at 60 months were 43.2% +/- 5.3% and 46.3% +/- 7.4% (not significant), respectively. Multivariate analysis showed that low CD4 lymphocyte counts (< 200/microL, P <0.05) and hypoalbuminemia (<3.5 g/dL, P <0.05) were risk factors for postoperative complications. CONCLUSION: Perioperative morbidity and mortality rates are high in HIV patients undergoing an abdominal aortic operation. Low CD4 lymphocyte counts and hypoalbuminemia are associated with poor clinical outcomes in HIV patients undergoing abdominal aortic reconstruction.

Adult↗

PubMed2003

Pancreatic islet transplantation: the radiographic approach.

BACKGROUND: Successful pancreatic islet transplantation (PIT) has resulted in several transplant centers wanting to start PIT programs. PIT remains experimental and must be performed safely for its continued use. We describe the radiographic techniques used at our center and their results. METHODS: Between January 17, 2002, and December 16, 2002, 17 percutaneous transhepatic PITs were performed by two interventional radiologists. Ultrasound localization of and guidance to the portal vein (PV) were used. Portosplenography confirmed the position of the PV islet infusion catheter, and PV pressure was documented before, during, and at the completion of PIT. To prevent PV thrombosis, heparin (17.5 U/kg) through the PV infusion catheter and subcutaneous enoxaparin (Lovenox, Aventis Pharmaceuticals, Parsippany, NJ) were administered after PIT. At the completion of PIT, thrombin-saturated Gelfoam (Johnson and Johnson, Summerville, NJ) was embolized into the hepatic parenchymal tract. RESULTS: Percutaneous PV access was achieved in all cases (median number of seeker needle passes=2, range: 1-6), and PIT was performed. In no case was any extrahepatic organ punctured, and sustained PV hypertension was not seen. No patient required transfusion, and it was documented by Doppler ultrasonography that PV thrombosis did not result from PIT. In addition, intraparenchymal and intraabdominal bleeding did not complicate any PIT; 71% and 59% of the patients experienced moderate posttransplant abdominal pain and nausea, respectively. All patients demonstrated a self-limited, asymptomatic posttransplant transaminitis. CONCLUSIONS: We believe that PIT should be performed by a small number of experienced interventional radiologists using ultrasound guidance and posttransplant embolization of the hepatic parenchymal tract.

Diabetes Mellitus, Type 1↗

PubMed2003

A prospective evaluation of interrupted nitinol surgical clips in arteriovenous fistula for hemodialysis.

BACKGROUND: The use of a self-closing nitinol surgical clip (Coalescent Surgical U-Clip) is a novel technique of creating an interrupted vascular anastomosis, which also eliminates the knot tying associated with a conventional vascular anastomosis. The purpose of this study was to compare the clinical outcome of arteriovenous fistulae (AVF) for hemodialysis as constructed using interrupted U-Clip devices and conventional continuous polypropylene sutures. METHODS: We prospectively studied the clinical course of 132 patients (149 access) undergoing either forearm autologous arteriovenous fistula (FAVF, n = 69) or upper arm autologous arteriovenous fistula (UAVF, n = 80) or creations during a 39-month period. Among the FAVF, U-Clips and polypropylene sutures were used in 37 and 32 anastomoses, respectively. Among the UAVF, U-Clips and polypropylene sutures were used in 41 and 30 anastomoses, respectively. Primary patency, complication, and maturation rates were analyzed. RESULTS: Clipped FAVF had an improved maturation rate at 6 weeks (32 of 37, 86%) when compared with sutured FAVF (22 of 32, 69%, P <0.05). There was no difference in the maturation rate among UAVF constructed with either U-Clips or sutures (88% versus 87%, not significant). The primary patency rates at 12, 24, and 36 months were 91%, 84%, and 75% for the clipped FAVF; and 83%, 74%, and 61% for the sutured FAVF (P <0.05) There was no difference in the patency rate of UAVF constructed with either U-Clips or polypropylene sutures at either 12, 24 or 36 moths (91%, 80%, and 75% versus 83%, 77%, and 69%, respectively). CONCLUSIONS: The U-Clips are a viable alternative to sutures for creating vascular anastomosis. It provides a improved maturation and patency rates when compared with the conventional sutured AVF in the forearm. The clinical benefit of the U-Clips may be due in part to the improved compliance created by the interrupted anastomotic technique.

Adult↗

PubMed2003

Acute limb ischemia secondary to myositis-induced compartment syndrome in a patient with human immunodeficiency virus infection.

Myositis, while uncommon, develops more frequently in patients with human immunodeficiency virus infection. We report a case of acute lower leg ischemia caused by myositis in such a patient. Urgent four-compartment fasciotomy of the lower leg was performed, which decompressed the compartmental hypertension and reversed the arterial ischemia. This case underscores the importance of recognizing compartment syndrome as a cause of acute limb ischemia.

Acute Disease↗

PubMed2002

Tyrosinemia.

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Biopsy↗