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Transmural heparin to prevent microvascular thrombosis
P 70
Otolaryngology Head and Neck Surgery
Scientific Sessions- - Monday
8:30 AM
Ischemic Neuropraxla: Preservation of Neural Function by DFMO and Blockade of Preservation by Exogenous Putrescine ALBERTO D. FERNANDEZ, MD (presenter), NEWTON J, COKER, MD, and CHARLES M. HENLEY, PhD, Houston, Tex.
Several studies have implicated a role for the polyamines in mediating ischemic injury in the central nervous system, peripheral nerves, and in other tissues, ot-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase and putrescine biosynthesis, has been shown to reduce the size of cortical infarcts resulting from ischemia. The purpose of this study was to determine if DFMO preserves function in neuropraxic facial nerves and if the neuroprotective effects could be reversed by exogenously administered putrescine. New Zealand rabbits (n = 60) were assigned to three groups: group I, DFMO or saline solution; group II, DFMO and putrescine or saline solution and putrescine; and group III, sham-operated. Groups I and II were treated with saline solution, DFMO, and/or putrescine 1 hour before surgery. An ischemic compressive injury of the facial nerve was induced with a balloon-clamp apparatus for 4 hours at 80 mm Hg. Electroneuronography specifically evaluating the myogenic compound action potential (MCAP) was used to gauge the neuropraxic status of the nerve preoperatively, after dissection, compression, and 4 and 12 hours after clamp removal (reperfusion). MCAP amplitudes decreased significantly in animals treated with saline solution immediately following 4 hours of ischemic compression injury and remained depressed up to 12 hours after reperfusion. In contrast, MCAPs did not significantly decrease in the group treated with DFMO. The neuroprotective effects of DFMO on facial nerve function was reversed by systemic administration of putrescine (8 mg/kg SC), suggesting that polyamine metabolism may play an integral role in mediating neural damage caused by ischemic injury. DFMO may ultimately serve as a means of ameliorating nerve palsy related to edema secondary to infection, trauma or surgical intervention.
August 1996
2 around a femoral vascular pedicle in a rat. The significance of the vascular pedicle, marrow cells, and BMP-2 in the prefabrication of these grafts is also investigated. Material and methods: Five by seven millimeter cylindrical silastic chambers were implanted in the medial thigh of 48 male Lewis rats. The femoral vascular pedicle was mobilized and placed as a flow-through pedicle within the silastic chambers. Bone marrow was harvested from 50 syngeneic Lewis rats, and 1 x 108 cells were placed in each chamber. Twenty micrograms of rhBMP-2 were also placed in the chamber. Forty-eight animals were divided into four groups. Group 1 contained marrow cells and BMP only; group 2 contained marrow cells and vascular pedicle only; group 3 contained BMP and vascular pedicle only; and group 4 contained marrow cells, BMP, and vascular pedicle. Animals in each group were killed at 2, 4, and 6 weeks. The chamber contents were examined and vascular pedicle checked for patency. The contents were processed and 5 micron sections were stained with von Kossa's mineral stain, Goldner's Trichrome, and hematoxylin and eosin for histologic analysis. Results: Chambers with BMP and vascular pedicle only (group 3) did not produce any bone. Chambers containing marrow cells and vascular pedicle formed minimal bone at the periphery and only at 6 weeks (group 2). The chambers with marrow cells, BMP, and vascular pedicle (group 4) formed copious osteoid and woven bone as early as 2 weeks. At 4 weeks, woven and lamellar bone extended to the periphery of the chamber and the graft assumed a precise shape. At 6 weeks, central islands of bone had substantially reabsorbed and only thin lamellar bone remained in the periphery. Conclusions: We have demonstrated that vascularized bone grafts can be prefabricated in very precise shapes using rhBMP-2, marrow osteoprogenitor cells, and a femoral vascular pedicle. Early woven bone formation was seen at 2 weeks time. Remodeling to lamellar bone was completed by 4 weeks. Central resorption of the vascularized bone graft may be due to a lack of mechanical stress during its formation. The role of osteoprogenitor cells and BMP in bone graft formation is discussed. 9:00 AM
8:45 AM
Transmural Heparln to Prevent Mlcrovascular Thrombosis
Prefabrication of Vascularlzed Bone Grafts Using Bone Morphogenetlc Protein and Marrow Osteoprogenltor
LISA A. ORLOFF, MD (presenter), VINEETA PRASAD, BA, ABRAHAM J, DOMB, PhD, and D, EUGENE STRANDNESS, Jr., MD, San Diego, Calif., Jerusalem, Israel, and Seattle, Wash.
Cells JOHN I. SONG, MD (presenter), THOMAS C. CALCATERRA, MD, and NElL FORD JONES, MD, Los Angeles, Calif.
Introduction: The use of vascularized bone grafts in maxillofacial and mandibular reconstruction has greatly expanded reconstructive options. Vascularized fibular and lilac crest bone grafts are the most widely used. A prefabricated vascularized bone graft would allow precise shaping of grafts to fit specific defects and obviate the need for any donor site dissection. The purpose of this study was to fabricate a vascularized bone graft from osteoprogenitor cells and BMP-
Prevention of anastomotic complications is the most important determinant of success in microvascular surgery. Vascular thrombosis is the most significant complication, with catastrophic results that include total flap or tissue necrosis from ischemia or congestion. Thrombosis accounts for up to 20% of m i c r o v a s c u l a r anastomotic failures. An ideal antithrombotic system has yet to be identified. We have developed a promising form of antithrombotic therapy and prophylaxis in the form of controlled release of heparin by transmural delivery from a biodegradable polymer. We have
Otolaryngology Head and Neck Surgery Volume 115 Number 2
studied the effects of transmurally released heparin in a rat microvascular thrombosis model, the venous inversion graft. Anastomotic patency rates in treated and control vessels were compared under experimental conditions that maximized the stringency of the test model through varying the length of the inversion graft segment. Analyses of the mechanism, site, and degree of action of the heparin-polymer, both in vitro and in vivo, were conducted using radiolabeled heparin, implantable Doppler microflow probes, and blood tests that measured anticoagulation status. A highly significant difference was seen between treated and control vessel patency rates, without any systemic anticoagulation. This heparin-polymer system is a safe and effective device for preventing microvascular thrombosis. Further testing of the heparin-polymer in large vessel surgery and in humans is indicated. (We thank the American Academy of Otolaryngology-Head and Neck Surgery Foundation, Inc.. for supporting this research through the Academy Foundation Research Training Award program.) 9:15 AM
Tissue Oxygen Tension Monitoring in Free Bone Transfers JESSE SALMERON, MD (presenter), HUBERTWEINBERG, MD, MARK L. URKEN, MD, MARTIN B. HIRIGOYEN, MD, FRCS, and WEN X. ZHANG, MD, New York, N.Y.
Free vascularized bone transfer has become one of the most widely used techniques in reconstructive surgery and is the procedure of choice for reconstruction of the mandible after excision of tumor. Despite refinement of microsurgical technique, some anastomoses continue to fail (5% to 15%). As such, it is essential that vascular compromise within a bone flap be recognized early if reexploration is to prove successful. The aim of this study was to gain information about the dynamics of tissue oxygenation in osseous free flaps subjected to different types of ischemia. An animal model was used to assess the role of tissue oxygen tension measurement in the clinical postoperative monitoring of vascularized bone transfers. With use of microcatheter pO2 sensors (Licox, Medical Systems) implanted into 10 adult rabbit femurs, we determined the characteristics of tissue oxygen changes within the intramedullary blood supply when the arterial or venous supply to the bone is occluded and when changes occur in systemic oxygenation. The reliability of the method was tested by performing free femoral transfers in eight rabbits with the venous pedicle subjected to thrombogenic conditions according to a model established previously in our laboratory. Results showed that occlusion of either the arterial or venous supply immediately gave rise to a sharp decrease in intramedullary tissue oxygen tension, and no significant difference was found in the rates of decrease. Inspired oxygen caused a marked increase in tissue pO2, which returned to baseline after removal of the stimulus, but no increase was noted when the pedicle was clamped. A decrease in tissue pO2 was also seen with induced venous thrombosis.
Scientific Sessions-- Monday
P 71
Our results indicate that this promising technique could reduce existing flap failure rates by providing a reliable and early indicator of vascular compromise within the transferred bone. (Research supported by the 1995 Combined AAOH&NSF/PSEF grant.) 9:30 t o 10:30 AM
Posters (Session C) See pages P77 to P98 10:30 AM
Prognostic Implication of Loss of Heterozygosity of 4q in Head and Neck Squamous Cell Carcinoma WAYNE M. KOCH, MD (presenter), BENJAMIN GREENBERG, MS, JOSEPH CAUFANO, MD, and DAVID SlDRANSKY, MD, Baltimore, Md.
Head and neck squamous cell carcinoma (HNSCC) theoretically arises from an accumulation of 7 to 10 alterations selected from 50 to 100 potential target genes. The behavior of a tumor may be determined by the spectrum of alterations involved in its development. Although the only known target gene commonly involved in HNSCC is p53, other putative targets may be located in regions of tumor-specific allelic loss. The status of chromosome 4q was assessed in a group of 51 patients with HNSCC who were treated with curative intent using a panel of 18 microsatellite markers. Matched tumor and normal DNA was amplified with use of the polymerase chain reaction followed by electrophoresis and autoradiography. Twenty-nine tumors (57%) had at least partial loss of heterozygosity (LOH) of 4q. Retention of 4q was associated with the presence of nodal metastasis (chi-square = 2.92, p = 0.087). These individuals also had a threefold increased risk of death in the follow-up period compared with those with 4q LOH (hazard ratio = 3.035, 95% confidence interval 1.241, 7.140). Nodal metastasis was also a strong predictor of clinical outcome associated with a sixfold increased risk of death. In multivariate analysis, the significance of 4q LOH was eliminated when adjusted for nodal status. A target tumor-suppressor gone has not been identified in the minimal region of 4q loss in these tumors. However, molecular analysis may be possible before the detection of nodal metastasis in many cases, and thus 4q status may prove to be a valuable prognostic indicator for HNSCC. 10:4,5 AM
Allelic Losson Chromosome 8p and Prognostication of Patients with Supraglottic Laryngeal Cancer JOHN B. SUNWOO, MD (presenter), BRUCE H. HAUGHEY, MB, ChB, SAMIR EL-MOFTY, DMD, PhD, and STEVEN B. SCHOLNICK, PhD, St. Louis, Mo.
The characteristics of any cell are influenced by its genetic constitution (genotype); alterations of that genotype can therefore result in new cellular properties and behaviors. Tumors routinely accumulate such changes during pro-
Otolaryngology Head and Neck Surgery
Scientific Sessions- - Monday
8:30 AM
Ischemic Neuropraxla: Preservation of Neural Function by DFMO and Blockade of Preservation by Exogenous Putrescine ALBERTO D. FERNANDEZ, MD (presenter), NEWTON J, COKER, MD, and CHARLES M. HENLEY, PhD, Houston, Tex.
Several studies have implicated a role for the polyamines in mediating ischemic injury in the central nervous system, peripheral nerves, and in other tissues, ot-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase and putrescine biosynthesis, has been shown to reduce the size of cortical infarcts resulting from ischemia. The purpose of this study was to determine if DFMO preserves function in neuropraxic facial nerves and if the neuroprotective effects could be reversed by exogenously administered putrescine. New Zealand rabbits (n = 60) were assigned to three groups: group I, DFMO or saline solution; group II, DFMO and putrescine or saline solution and putrescine; and group III, sham-operated. Groups I and II were treated with saline solution, DFMO, and/or putrescine 1 hour before surgery. An ischemic compressive injury of the facial nerve was induced with a balloon-clamp apparatus for 4 hours at 80 mm Hg. Electroneuronography specifically evaluating the myogenic compound action potential (MCAP) was used to gauge the neuropraxic status of the nerve preoperatively, after dissection, compression, and 4 and 12 hours after clamp removal (reperfusion). MCAP amplitudes decreased significantly in animals treated with saline solution immediately following 4 hours of ischemic compression injury and remained depressed up to 12 hours after reperfusion. In contrast, MCAPs did not significantly decrease in the group treated with DFMO. The neuroprotective effects of DFMO on facial nerve function was reversed by systemic administration of putrescine (8 mg/kg SC), suggesting that polyamine metabolism may play an integral role in mediating neural damage caused by ischemic injury. DFMO may ultimately serve as a means of ameliorating nerve palsy related to edema secondary to infection, trauma or surgical intervention.
August 1996
2 around a femoral vascular pedicle in a rat. The significance of the vascular pedicle, marrow cells, and BMP-2 in the prefabrication of these grafts is also investigated. Material and methods: Five by seven millimeter cylindrical silastic chambers were implanted in the medial thigh of 48 male Lewis rats. The femoral vascular pedicle was mobilized and placed as a flow-through pedicle within the silastic chambers. Bone marrow was harvested from 50 syngeneic Lewis rats, and 1 x 108 cells were placed in each chamber. Twenty micrograms of rhBMP-2 were also placed in the chamber. Forty-eight animals were divided into four groups. Group 1 contained marrow cells and BMP only; group 2 contained marrow cells and vascular pedicle only; group 3 contained BMP and vascular pedicle only; and group 4 contained marrow cells, BMP, and vascular pedicle. Animals in each group were killed at 2, 4, and 6 weeks. The chamber contents were examined and vascular pedicle checked for patency. The contents were processed and 5 micron sections were stained with von Kossa's mineral stain, Goldner's Trichrome, and hematoxylin and eosin for histologic analysis. Results: Chambers with BMP and vascular pedicle only (group 3) did not produce any bone. Chambers containing marrow cells and vascular pedicle formed minimal bone at the periphery and only at 6 weeks (group 2). The chambers with marrow cells, BMP, and vascular pedicle (group 4) formed copious osteoid and woven bone as early as 2 weeks. At 4 weeks, woven and lamellar bone extended to the periphery of the chamber and the graft assumed a precise shape. At 6 weeks, central islands of bone had substantially reabsorbed and only thin lamellar bone remained in the periphery. Conclusions: We have demonstrated that vascularized bone grafts can be prefabricated in very precise shapes using rhBMP-2, marrow osteoprogenitor cells, and a femoral vascular pedicle. Early woven bone formation was seen at 2 weeks time. Remodeling to lamellar bone was completed by 4 weeks. Central resorption of the vascularized bone graft may be due to a lack of mechanical stress during its formation. The role of osteoprogenitor cells and BMP in bone graft formation is discussed. 9:00 AM
8:45 AM
Transmural Heparln to Prevent Mlcrovascular Thrombosis
Prefabrication of Vascularlzed Bone Grafts Using Bone Morphogenetlc Protein and Marrow Osteoprogenltor
LISA A. ORLOFF, MD (presenter), VINEETA PRASAD, BA, ABRAHAM J, DOMB, PhD, and D, EUGENE STRANDNESS, Jr., MD, San Diego, Calif., Jerusalem, Israel, and Seattle, Wash.
Cells JOHN I. SONG, MD (presenter), THOMAS C. CALCATERRA, MD, and NElL FORD JONES, MD, Los Angeles, Calif.
Introduction: The use of vascularized bone grafts in maxillofacial and mandibular reconstruction has greatly expanded reconstructive options. Vascularized fibular and lilac crest bone grafts are the most widely used. A prefabricated vascularized bone graft would allow precise shaping of grafts to fit specific defects and obviate the need for any donor site dissection. The purpose of this study was to fabricate a vascularized bone graft from osteoprogenitor cells and BMP-
Prevention of anastomotic complications is the most important determinant of success in microvascular surgery. Vascular thrombosis is the most significant complication, with catastrophic results that include total flap or tissue necrosis from ischemia or congestion. Thrombosis accounts for up to 20% of m i c r o v a s c u l a r anastomotic failures. An ideal antithrombotic system has yet to be identified. We have developed a promising form of antithrombotic therapy and prophylaxis in the form of controlled release of heparin by transmural delivery from a biodegradable polymer. We have
Otolaryngology Head and Neck Surgery Volume 115 Number 2
studied the effects of transmurally released heparin in a rat microvascular thrombosis model, the venous inversion graft. Anastomotic patency rates in treated and control vessels were compared under experimental conditions that maximized the stringency of the test model through varying the length of the inversion graft segment. Analyses of the mechanism, site, and degree of action of the heparin-polymer, both in vitro and in vivo, were conducted using radiolabeled heparin, implantable Doppler microflow probes, and blood tests that measured anticoagulation status. A highly significant difference was seen between treated and control vessel patency rates, without any systemic anticoagulation. This heparin-polymer system is a safe and effective device for preventing microvascular thrombosis. Further testing of the heparin-polymer in large vessel surgery and in humans is indicated. (We thank the American Academy of Otolaryngology-Head and Neck Surgery Foundation, Inc.. for supporting this research through the Academy Foundation Research Training Award program.) 9:15 AM
Tissue Oxygen Tension Monitoring in Free Bone Transfers JESSE SALMERON, MD (presenter), HUBERTWEINBERG, MD, MARK L. URKEN, MD, MARTIN B. HIRIGOYEN, MD, FRCS, and WEN X. ZHANG, MD, New York, N.Y.
Free vascularized bone transfer has become one of the most widely used techniques in reconstructive surgery and is the procedure of choice for reconstruction of the mandible after excision of tumor. Despite refinement of microsurgical technique, some anastomoses continue to fail (5% to 15%). As such, it is essential that vascular compromise within a bone flap be recognized early if reexploration is to prove successful. The aim of this study was to gain information about the dynamics of tissue oxygenation in osseous free flaps subjected to different types of ischemia. An animal model was used to assess the role of tissue oxygen tension measurement in the clinical postoperative monitoring of vascularized bone transfers. With use of microcatheter pO2 sensors (Licox, Medical Systems) implanted into 10 adult rabbit femurs, we determined the characteristics of tissue oxygen changes within the intramedullary blood supply when the arterial or venous supply to the bone is occluded and when changes occur in systemic oxygenation. The reliability of the method was tested by performing free femoral transfers in eight rabbits with the venous pedicle subjected to thrombogenic conditions according to a model established previously in our laboratory. Results showed that occlusion of either the arterial or venous supply immediately gave rise to a sharp decrease in intramedullary tissue oxygen tension, and no significant difference was found in the rates of decrease. Inspired oxygen caused a marked increase in tissue pO2, which returned to baseline after removal of the stimulus, but no increase was noted when the pedicle was clamped. A decrease in tissue pO2 was also seen with induced venous thrombosis.
Scientific Sessions-- Monday
P 71
Our results indicate that this promising technique could reduce existing flap failure rates by providing a reliable and early indicator of vascular compromise within the transferred bone. (Research supported by the 1995 Combined AAOH&NSF/PSEF grant.) 9:30 t o 10:30 AM
Posters (Session C) See pages P77 to P98 10:30 AM
Prognostic Implication of Loss of Heterozygosity of 4q in Head and Neck Squamous Cell Carcinoma WAYNE M. KOCH, MD (presenter), BENJAMIN GREENBERG, MS, JOSEPH CAUFANO, MD, and DAVID SlDRANSKY, MD, Baltimore, Md.
Head and neck squamous cell carcinoma (HNSCC) theoretically arises from an accumulation of 7 to 10 alterations selected from 50 to 100 potential target genes. The behavior of a tumor may be determined by the spectrum of alterations involved in its development. Although the only known target gene commonly involved in HNSCC is p53, other putative targets may be located in regions of tumor-specific allelic loss. The status of chromosome 4q was assessed in a group of 51 patients with HNSCC who were treated with curative intent using a panel of 18 microsatellite markers. Matched tumor and normal DNA was amplified with use of the polymerase chain reaction followed by electrophoresis and autoradiography. Twenty-nine tumors (57%) had at least partial loss of heterozygosity (LOH) of 4q. Retention of 4q was associated with the presence of nodal metastasis (chi-square = 2.92, p = 0.087). These individuals also had a threefold increased risk of death in the follow-up period compared with those with 4q LOH (hazard ratio = 3.035, 95% confidence interval 1.241, 7.140). Nodal metastasis was also a strong predictor of clinical outcome associated with a sixfold increased risk of death. In multivariate analysis, the significance of 4q LOH was eliminated when adjusted for nodal status. A target tumor-suppressor gone has not been identified in the minimal region of 4q loss in these tumors. However, molecular analysis may be possible before the detection of nodal metastasis in many cases, and thus 4q status may prove to be a valuable prognostic indicator for HNSCC. 10:4,5 AM
Allelic Losson Chromosome 8p and Prognostication of Patients with Supraglottic Laryngeal Cancer JOHN B. SUNWOO, MD (presenter), BRUCE H. HAUGHEY, MB, ChB, SAMIR EL-MOFTY, DMD, PhD, and STEVEN B. SCHOLNICK, PhD, St. Louis, Mo.
The characteristics of any cell are influenced by its genetic constitution (genotype); alterations of that genotype can therefore result in new cellular properties and behaviors. Tumors routinely accumulate such changes during pro-