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Biomedical subjects

M D Liang

Publications and source records attributed to M D Liang.

At least 19 recordsLinked to original sources
PubMed1997

Pharmacodynamics and pharmacokinetics of a 72-hour infusion of 9-aminocamptothecin in adult cancer patients.

PURPOSE: To investigate the pharmacokinetics and pharmacodynamics of 9-aminocamptothecin (9-AC) infused over 72 hours at doses of 5 to 74 micrograms/m2/h. PATIENTS AND METHODS: 9-AC lactone and total (lactone plus carboxylate) plasma concentrations were measured in 44 patients with solid tumors using a high-performance liquid chromatography (HPLC) assay. Fifteen patients underwent extended pharmacokinetic sampling to determine the distribution and elimination kinetics of 9-AC. RESULTS: At steady-state, 8.7% +/- 4.7% (mean +/- SD) of the total drug circulated in plasma as the active 9-AC lactone. Clearance of 9-AC lactone was uniform (24.5 +/- 7.3 L/h/m2) over the entire dose range examined; however, total 9-AC clearance was nonlinear and increased at higher dose levels. In 15 patients treated at dose levels > or = 47 micrograms/m2/h, the volume of distribution at steady-state for 9-AC lactone was 195 +/- 114 L/m2 and for total 9-AC it was 23.6 +/- 10.6 L/m2. The elimination half-life was 4.47 +/- 0.53 hours for 9-AC lactone and 8.38 +/- 2.10 hours for total 9-AC. In pharmacodynamic studies, dose-limiting neutropenia correlated with steady-state lactone concentrations (Css) R2 = .77) and drug dose (R2 = .71). CONCLUSION: Plasma 9-AC concentrations rapidly declined to low levels following the end of a 72-hour infusion and the mean fraction of total 9-AC circulating in plasma as the active lactone was less than 10%. The pharmacokinetics of 9-AC may have a great impact on its clinical activity and should be considered in the design of future clinical trials of this topoisomerase I inhibitor.

Adult↗
PubMed1996

The use of cryopreserved microvenous allografts in the venous system without immunosuppression: an experimental study.

Autogenous vein grafts are currently the number one choice in microsurgical practice for managing vessel length discrepancies. A significant percentage of these grafts is used in the venous system. Allografts may serve as a viable alternative source of vein grafts. Few studies in the past have described the use of cryopreserved vein grafts (1 mm in diameter) in the venous system. In the present study, we cryopreserved the femoral veins of rats and transplanted these across rat species (ACI to Lewis) as interpositional vein grafts into a defect in the femoral vein. Short-term patencies (21 days), expressions of systemic antigenicity, histology, and scanning electron microscopic studies were performed. We obtained 100% patencies with fresh control veins and cryopreserved veins at 21 days.

Animals↗
PubMed1996

Severe neurotoxicity following 5-fluorouracil-based chemotherapy in a patient with dihydropyrimidine dehydrogenase deficiency.

Patients with decreased dihydropyrimidine dehydrogenase (DPD) activity are at increased risk for experiencing serious adverse reactions following 5-fluorouracil (5-FU)-based chemotherapy. Symptoms include severe and potentially life-threatening gastrointestinal toxicity, myelosuppression, and neurological toxicity. In the present study, we describe a 50-year-old Caucasian man who developed severe encephalopathy during his second cycle of 5-FU chemotherapy. The patient remained in a comatose state for 4 days but then showed dramatic improvement in his neurological status following continuous i.v. infusion of thymidine at 8 g/m2/day. Laboratory studies revealed the patient to be severely DPD deficient, as demonstrated by DPD enzyme activity from peripheral blood mononuclear cells being below the lower limit of the 95th percentile of a control population and by Western immunoblot analysis showing undetectable levels of DPD protein. Additional studies revealed a significant defect in pyrimidine catabolism with a 3.3- and 365-fold increase in the levels of uracil in plasma and urine, respectively, compared to normal subjects. Family studies suggest that the inheritance pattern of this syndrome is complex and most consistent with an autosomal recessive trait. This study demonstrates that cancer patients with DPD deficiency are at increased risk for developing severe neurological toxicity secondary to 5-FU chemotherapy, and that infusional thymidine should be considered as a potential rescue agent against this particular host toxicity.

Brain Diseases↗
PubMed1994

Cryopreserved microvascular conduits: current applications and future prospects.

Modern cryopreservation techniques have resulted in the clinical use of cryopreserved allograft heart valves and large diameter veins. In addition to these large vascular tissues, there is a need for small-diameter vascular allografts. We review our studies of cryopreserved rat microvenous allografts (1 mm diameter) in both the arterial and venous systems. The clinical utilization of cryopreserved allografts in reconstructive microsurgery and the potential problems associated with the use of allogeneic tissues will be addressed. Further applications for vascular cryopreservation in reconstructive surgery include small-diameter arteries, vascularized tissue flaps, and limbs.

Animals↗
PubMed1994

Local full-thickness skin-graft coverage for the radial forearm flap donor site.

Closure of the radial forearm flap donor site has been achieved by triangulating the defect and using a full-thickness skin graft from the adjacent volar forearm. Coverage of the flexor carpi radialis tendon has been more robust, and the aesthetic results have been superior to split-thickness skin-graft coverage of the forearm flap donor site.

Bandages↗
PubMed1993

The use of cryopreserved venous allografts in microvascular surgery without immunosuppression: an experimental study.

Excellent patency rates are currently established in the use of autogenous veins as interposition vein grafts in microsurgical practice. Allografts may be a viable alternative source of vein grafts. Recent advances in cryobiology have enabled the controlled freezing of tissues with preservation of vital cellular elements. Although several reports have shown the successful use of cryopreserved large-vessel allografts, few have addressed cryopreservation of microvessels (1 to 2 mm in diameter). In this study, the authors have successfully cryopreserved femoral veins in a rat model and transplanted them as interposition vein grafts into arterial defects across major histocompatibility barriers (ACI to Lewis). Short-term patencies (21 days) were determined, and histologic and scanning electron microscopic analysis were performed. Patency of 100 percent was achieved in both fresh control veins and in cryopreserved veins at 21 days.

Animals↗
PubMed1993

The permeability of tissue expanders to bacteria: an experimental study.

Infection is an occasional but serious complication of tissue expansion. Bacteria in many cases are found both inside and outside the expander. The mechanism of how they spread inside and out is not fully understood. In the current study, we have assessed both the expander membranes (n = 28) and the port (n = 42) in terms of leakage and transmission of Staphylococcus aureus in normal expansion (100 percent) and overexpansion (400 percent) in an in vitro model. Our results indicate that the membrane was impermeable to S. aureus, whereas the bacteria were able to migrate freely through the puncture sites in the ports.

Cell Membrane Permeability↗
PubMed1992

Lower extremity reconstruction using a long-cryopreserved venous allograft for free flap venous outflow.

Vein grafts are used frequently in microvascular surgery, but an adequate supply of autogenous veins is not always available. The search for an ideal substitute for autogenous vein continues. We present a case of lower extremity reconstruction made difficult by lack of suitable autogenous vein for venous outflow from a rectus abdominus free flap. A 36 cm cryopreserved allograft saphenous vein was used on an emergency basis for this problem.

Aged↗
PubMed1992

Experimental endoscopic subcutaneous surgery.

Endoscopic techniques have found increasing applications in general surgery. In this article, an attempt has been made to utilize endoscopy via a subcutaneous approach in an experimental pig model for dissection of fat, muscle, and fascia.

Adipose Tissue↗
PubMed1992

The use of high-frequency ultrasound for the dissection of small-diameter blood vessels and nerves.

The Cavitron ultrasonic surgical aspirator has been successfully used in general surgery and neurosurgery. We have explored its use in the dissection of small-diameter blood vessels and nerves (1-2 mm) in a rat model. Our results seem to indicate that this technique may be useful in isolating blood vessels surrounded by fatty tissue without damage to the vessel itself. In this study, however, high-frequency ultrasound did cause significant damage to peripheral nerves.

Animals↗
PubMed1991

Evaluation of facial fat distribution using magnetic resonance imaging.

Magnetic resonance imaging (MRI) provides noninvasive images of facial and neck fat for a variety of conditions. It accurately maps the soft tissues pre- and postoperatively, enabling surgeons to precisely and objectively assess results of soft tissue facial contouring and fat transplantation. The risks of MRI are few. It has the potential to provide aesthetic surgeons with a more "scientific" means of comparing various techniques of fat contouring.

Adipose Tissue↗
PubMed1991

A case of multiple pilar tumors and pilar cysts involving the scalp and back.

The case of a patient with multiple proliferating trichilemmal tumors and trichilemmal cysts of the scalp and back is discussed. The multicentric presentation of this tumor is unusual and, to our knowledge, has not been described previously. The appearance of trichilemmal cysts in association with multiple proliferating trichilemmal tumors suggests a common histogenesis of these two neoplasms. The typical presenting features, histologic description, and recommended treatment for these tumors are reviewed.

Back↗
PubMed1991

Recombinant hirudin--initial observations in reconstructive microsurgery.

Recent advances in microvascular techniques have significantly enhanced the success rate of these procedures. Microvascular free tissue transfers at present have a 85-90% success rate. This, however, still leaves a 10-15% failure rate due primarily to thrombosis of the blood vessels at the anastomotic site. Previous work in the field has shown that anticoagulants such as heparin can reduce the rate of thrombosis. However, heparin can also cause on-site bleeding. Hirudin, a potent thrombin inhibitor of 65 amino acids, is available through recombinant technology. Our current experimental work utilized 75 male Sprague-Dawley rats for assessing the efficacy of hirudinized saline versus saline alone and heparinized saline as an irrigant in a microsurgery model of anastomosis. After exposing the right femoral artery in a standard fashion, the artery was clamped and a standard transverse division of the vessel was made. The vessel ends were irrigated with one of the three solutions then anastomosed. Vessels were observed for patency over a 3-day period. Initial results showed comparable performance of hirudinized saline and heparized saline, both of which were better than saline, for preventing thrombosis. From these initial data, and the reduced bleeding risk associated with hirudin, this agent appears to be a useful anticoagulant in microsurgery.

Anastomosis, Surgical↗
PubMed1990

The use of cryopreserved venous allografts in free tissue transfers--practical and aesthetic considerations.

A case in which multiple cryopreserved allograft saphenous veins were used as vein grafts for a difficult mandible reconstruction with a free tissue transfer is reviewed. Use of allograft veins was recently reported for lower limb vascular reconstruction but not for free tissue transfers. Such grafts may represent a viable alternative to the use of autologous vein grafts and have the potential to decrease operating time and avoid necessary scars.

Adult↗