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Biomedical subjects

B T Allen

Publications and source records attributed to B T Allen.

54 records · Page 3Linked to original sources
PubMed1989

Mechanisms of vascular graft thrombosis: role of altered canine platelet sensitivity to thromboxane.

Using the standard turbidimetric method of platelet aggregation and quantitation of platelet secretion with 14C-Serotonin, we have examined the responsiveness of the platelets of mongrel dogs to arachidonic acid (AA), and the thromboxane agonist U46619 in the presence and absence of a subthreshold concentration of epinephrine. In response to stimulation with 750 microM AA, the platelets of 18 dogs produced irreversible aggregation (Group I), the platelets of 22 dogs showed, at most, reversible aggregation (Group II), while the platelets of 8 dogs demonstrated no aggregatory response (Group III). In the presence of AA and a subthreshold concentration of epinephrine (0.5 microM), the platelets of all three groups demonstrated enhanced aggregatory and secretory responses although the extent of 14C-Serotonin secretion differed significantly between all three groups. These in vitro differences in platelet aggregation correlate with the in vivo deposition of platelets onto synthetic vascular grafts and the maintenance of graft patency. When stimulated with 0.5 microM U46619 and a subthreshold concentration of epinephrine, the platelets of 97% Group I dogs and 75% of Group II dogs exhibited irreversible aggregation, while the platelets of all Group III dogs showed only reversible aggregation. In addition, significant differences in the extent of 14C-Serotonin secretion to this combination of agonists were observed between groups. Further examination of the specific effects of U46619 on canine platelets revealed that although the aggregatory and secretory responses to U46619 vary between the different canine platelet populations, the threshold concentration of U46619 required to produce platelet shape change is identical among all groups. Quantitation of the stable metabolite of AA produced via the cyclooxygenase pathway, thromboxane B2 (TxB2), revealed no significant differences in the production of TxB2 by the platelets of these different populations upon stimulation with AA. Our results suggest that the mechanisms underlying the differences in responsiveness of canine platelets to AA, are likely due to differences in sensitivity of canine platelets to TxA2, and may be localized to the mechanism responsible for mediating platelet aggregation and secretion in response to TxA2.

Animals↗
PubMed1989

Retroperitoneal versus transperitoneal approach for repair of abdominal aortic aneurysms.

We, as well as other authors, believe that the retroperitoneal approach is an excellent alternative to the transperitoneal route for the repair of abdominal aortic aneurysms. This approach is associated with a significant decrease in pulmonary and cardiac complications and therefore can be used in selected high-risk patients with expanding aneurysms. A well-controlled randomized multicenter trial should answer the question: "Is this approach the surgical access of choice for the elective repair of abdominal aortic aneurysms?"

Adult↗
PubMed1988

Renal autotransplantation: an alternative to standard renal revascularization procedures.

From January 1978 through December 1987, 22 patients underwent 23 renal autotransplantation procedures for the treatment of renovascular hypertension through the retroperitoneal approach. The causes of the renal artery stenosis were as follows: atherosclerosis (15), fibromuscular dysplasia (6), and Takayasu's arteritis (1). Indications for renal autotransplantation were as follow: disease extending into the renal artery branches (10), stenosis of multiple renal arteries (6), atherosclerotic aorta in high-risk patients (4), and stenosis of renal artery in children (2). The mean preoperative blood pressure of 205 +/- 6/109 +/- 3 mm Hg decreased significantly to 139 +/- 4/77 +/- 2 mm Hg (p less than 0.001). The serum creatinine decreased significantly from a mean preoperative level of 2.2 +/- 0.8 mg/dl to a mean postoperative level of 1.4 +/- 0.4 mg/dl (p less than 0.05). Eleven patients with preoperative renal dysfunction had a significant decrease in the serum creatinine from a mean preoperative level of 3.4 +/- 0.3 mg/dl to a mean postoperative level of 1.9 +/- 0.2 mg/dl (p less than 0.001). One operative death occurred as a result of myocardial infarction. There were three postoperative complications, none of which affected the ultimate result in blood pressure or renal function. This experience demonstrates that in selected patients, renal autotransplantation is an excellent alternative in the surgical treatment of renovascular hypertension.

Adolescent↗
PubMed1988

Combined arachidonic acid and ADP platelet inhibition maximizes patency of small-diameter vascular grafts.

Arachidonic acid (AA) and adenosine diphosphate (ADP) are potent stimuli of platelet aggregation. Each agonist may act through separate platelet pathways. In order to evaluate inhibition of ADP and AA on platelet aggregation, we studied the effect of ticlopidine (TC) and aspirin (ASA) alone and in combination on plasma thromboxane levels, platelet deposition, and patency of small-diameter vascular grafts in a canine model. Thirty-four mongrel dogs were classified as thrombosis prone (TP) or thrombosis resistant (TR) on the basis of in vitro platelet aggregation to AA. Four groups were studied: group I, control; group II, TC (100 mg/kg/day); group III, ASA (3 mg/kg/day); and group IV, TC/ASA (same doses). PTFE grafts were implanted bilaterally in the carotid and femoral arteries Ticlopidine inhibited in vitro platelet aggregation to both ADP and AA but had no significant effect on plasma thromboxane (Tx) B2 production. Aspirin inhibited AA-induced platelet aggregation and significantly decreased TxB2 production. Aspirin inhibited AA-induced platelet aggregation and significantly decreased TxB2 levels in both TP and TR animals (p less than 0.01). Although TC and ASA significantly inhibited platelet deposition and improved 1-month patency in both TP and TR animals, maximal patency was achieved in the group in which TC and ASA were combined. We conclude that platelet ADP and AA pathways are important determinants of the thrombogenic potential in vascular graft performance in dogs and that combined inhibition of both pathways achieves maximal vascular graft patency.

Adenosine Diphosphate↗
PubMed1986

Platelet deposition on vascular grafts. The accuracy of in vivo quantitation and the significance of in vivo platelet reactivity.

An in vivo platelet imaging system utilizing indium-111-labeled platelets and technetium-99m-labeled red cells was used to serially study and compare platelet deposition on autologous external jugular vein grafts, autologous arterial grafts, polytetrafluoroethylene (Gore-tex) and two Dacron (Meadox and USCI) small diameter (4mm) vascular grafts implanted end-to-end in canine carotid and femoral arteries. This method of quantitating platelet deposition was validated by correlating deposition measured in vivo with deposition measured directly on explanted grafts (r = 0.94, p less than 0.01). Platelet accumulation on all grafts was greatest immediately after implantation and declined over time. None of the artery or vein grafts thrombosed, and they had the lowest level of platelet deposition at all times. Platelet deposition on Gore-tex grafts was significantly less than on USCI Dacron grafts from 24 hours to 1 month after implantation. There was no statistical difference in 1-month patency among the synthetic graft groups. Synthetic grafts that thrombosed during the first month accumulated significantly more platelets immediately after operation than did those grafts that remained patent. Patent Dacron grafts with low levels of platelet deposition had less thrombotic debris at explantation on the luminal surface than did those grafts with high levels of platelet deposition. Differences in initial platelet deposition appeared to be more a function of platelet reactivity within each dog rather than the material used in graft construction.

Animals↗
PubMed1984

Reduction of platelet deposition on vascular grafts using an antiplatelet graft coating technique.

The systemic use of platelet inhibitors has been shown to improve vascular graft function. In this study a biodegradable coating of polymeric polylactic acid (PLA) containing a microparticulate suspension of aspirin (ASA) 30% by weight, was applied to the lumenal surface of small diameter vascular prostheses to reduce platelet deposition on canine implanted arterial grafts. USCI 4-mm ID Dacron internal velour grafts were used. Coated and contralateral noncoated (control) prostheses were implanted in canine carotid and femoral arteries. Graft performance was assessed by determination of aspirin elution rates, in vivo red cell subtracted 111indium-labeled platelet scans, and post implant platelet aggregation studies. Eighty percent of the aspirin in the coated grafts was released during the first 24 hr of perfusion and approximately 20% of the aspirin remained in grafts after 1 month. In vivo platelet scans documented less platelet deposition on ASA-coated grafts when compared to controls 2 and 24 hr post implant (P less than 0.01, P less than 0.05, respectively). There was no significant difference in platelet deposition on ASA-coated and control grafts at 2 weeks or 1 month post implant. Post implant platelet aggregation studies indicated systemic platelet inhibition for 4-5 days. It was concluded that aspirin incorporation in a polylactic acid coating applied to 4-mm ID vascular prostheses reduced the platelet affinity of Dacron grafts and exerted a temporary local and systemic platelet inhibiting effect.

Animals↗
PubMed1984

Prostaglandin production and platelet reactivity of small-diameter grafts.

This article examines the relationship of platelet deposition to thromboxane and prostacyclin (PGI2) production in arterial autografts (n = 8), para-anastomotic native artery (n = 40), nonseeded control (n = 6), and endothelial cell-seeded (n = 17) small-diameter Dacron grafts implanted in the carotid and femoral arteries of dogs. Platelet deposition was measured by a dual-isotope subtraction platelet-imaging technique that expresses platelet deposition as percent indium excess (%IE). PGI2 and thromboxane assays were performed with the use of an immunoreactive assay. The %IE in the nonseeded grafts was significantly higher than in the seeded prostheses (p less than 0.001). Arterial autografts accumulated significantly less platelets than did seeded grafts (p less than 0.05) or nonseeded grafts (p less than 0.001). The thromboxane A2 (TXA2) production in nonseeded grafts was significantly higher than in seeded grafts (p less than 0.001), arterial autografts (p less than 0.001), or in para-anastomotic native artery (p less than 0.001). The PGI2 production by the arterial autografts was significantly higher than by the nonseeded grafts (p less than 0.005), seeded grafts (p less than 0.001), or para-anastomotic native artery (p less than 0.025). The PGF1 alpha/TXB2 ratio was significantly higher in the arterial autografts when compared with the nonseeded grafts (p less than 0.001), endothelial cell-seeded grafts (p less than 0.001), or para-anastomotic native artery (p less than 0.025). We conclude that platelet deposition can be significantly decreased by endothelial cell seeding of small-diameter grafts. The transmural production of TXA2 by native arteries and prosthetic grafts may have an important influence on platelet deposition and patency.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Influence of endothelial cell seeding on platelet deposition and patency in small-diameter Dacron arterial grafts.

Serial platelet deposition, surface topography, and patency were evaluated in control (N = 28) and endothelial cell-seeded (N = 28) small-diameter (4 mm inner diameter) USCI Dacron grafts implanted in the carotid and femoral arteries of dogs. All dogs received aspirin (325 mg) daily for 2 weeks starting 24 hours prior to graft implantation. Endothelial cell seeding was performed by mixing suspensions of autologous endothelial cells that had been enzymatically harvested from segments of external jugular vein with blood that was used to preclot the prostheses. The platelet deposition on each graft was quantitated by means of indium 111-labeled platelets and technetium 99m-labeled red cells in a dual-isotope platelet-imaging technique. Platelet deposition on seeded grafts 24 hours after implantation was significantly higher than on the controls (p less than 0.05). Two weeks after implantation platelet deposition on seeded prostheses had decreased to a level significantly lower than that on the controls and continued to decline on serial studies up to 7 months. In contrast to seeded grafts, platelet accumulation on control grafts dramatically increased after the withdrawal of aspirin therapy and was associated with a sharp rise in control graft thromboses. Gross and scanning electron microscopic evaluation of endothelial cell-seeded grafts after 1 month indicated complete neointimal coverage, whereas none of the control grafts explanted at 1 month or later exhibited a continuous neointimal lining. Cumulative 7-month patency for seeded prostheses was significantly higher than for the controls (96% and 29%, respectively; p less than 0.001). We conclude that endothelial cell seeding in combination with short-term aspirin therapy is a simple, reliable diameter Dacron prostheses. Abrupt withdrawal of aspirin therapy may be contraindicated in nonseeded control grafts because it results in increased platelet deposition and thrombosis.

Animals↗
PubMed1966

Environmental factors influencing the hyperfine structure of manganous low-temperature electron paramagnetic resonance spectra.

Hyperfine structure is observed in low temperature (T = -180 degrees C) EPR (electron paramagnetic resonance) spectra of a number of solutions containing Mn(++) ions 13, 15) which have characteristics in common with low temperature EPR spectra from biological substances such as mitochondria and microsomes (1-4). This investigation is an attempt to understand the features of these signals in terms of the molecular environment of the manganous ion, and a qualitative explanation for the observations reported here is advanced in terms of the amount of axial distortion of a manganese hydrate in different environments.

Chlorides↗
PubMedDate not supplied

Tc-99m sulfur colloid scintigraphy for detecting perigraft flow following endovascular aortic aneurysm repair: A feasibility study.

PURPOSE: To determine if scintigraphy with Tc-99m sulfur colloid can be used to detect perigraft flow after stent-graft repair of abdominal aortic aneurysm (AAA). METHODS: Twenty-three men and two women aged 56-84 years (mean 71 years) underwent endoluminal AAA repair as part of the EVT Phase II trial [EVT = Endovascular Technologies (Menlo Park, CA, USA)]. Aneurysm size averaged 5.4 cm (range 3-8 cm). Sixteen bifurcated, seven tube, and two aorto-uniiliac grafts were placed. Two days after stent-graft placement, patients underwent both contrast-enhanced computed tomography (CT), including delayed views, and Tc-99m sulfur colloid scintigraphy. RESULTS: Perigraft flow was found in only one patient at completion of angiography. Four additional patients had perigraft flow, discovered during their postoperative follow-up CT. Four patients had leaks at an attachment site and one had retrograde branch flow. Tc-99m sulfur colloid scintigraphy failed to diagnose any of the five leaks prospectively. In two of these patients, however, some abnormal paraaortic activity was noted in retrospect. CONCLUSION: Tc-99m sulfur colloid scintigraphy was unable to demonstrate endoleak with either rapid flow (attachment site leak) or slow filling (branch flow).

Aged↗
PubMedDate not supplied

Selective non-operative management of pseudoaneurysms and arteriovenous fistulae complicating femoral artery catheterization.

Femoral arterial pseudoaneurysms or arteriovenous fistulae may sometimes complicate percutaneous femoral artery catheterization procedures. Most surgeons recommend prompt operative repair because of the unfavorable natural history of pseudoaneurysms or arteriovenous fistulae secondary to violent or accidental arterial trauma. However, the natural history of catheterization-induced pseudoaneurysms and arteriovenous fistulae has not been well documented. Accordingly, we prospectively studied the natural history of 22 pseudoaneurysms, 8 arteriovenous fistulae, and 3 combined lesions, identified by duplex scan in 32 patients following trans-femoral cardiac, peripheral vascular, or vascular access arterial catheterization procedures. Angiographic procedures were performed with the use of 5-8F introducer sheaths. A femoral artery complication was significantly more likely to result from coronary balloon angioplasty (9/304; 3.0%) than from diagnostic cardiac catheterization (21/2476; 0.8%) (p less than 0.003; chi square). Fourteen patients (13 pseudoaneurysms, 1 combined pseudoaneurysm/fistulae) underwent surgical repair. Pain and/or enlarging hematoma resulted in repair within two days of the diagnosis in 8 patients. The need for chronic anticoagulation prompted elective repair in 2 patients. A pseudoaneurysm was repaired in one patient five days following catheterization when it became painful. In three stable patients, asymptomatic pseudoaneurysms were repaired electively during another surgical procedure. There were no operative deaths. One patients (7%) developed a wound infection postoperatively. Eighteen patients (19 arterial lesions: 9 pseudoaneurysms, 8 arteriovenous fistulae, 2 combined pseudoaneurysms/arteriovenous fistulae) with improving symptoms and stable physical signs were followed by serial clinical evaluation and duplex scans. Seventeen of 19 (89%) of these lesions resolved spontaneously within 5-90 days (mean 30.7 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Aneurysm↗
PubMedDate not supplied

Transient obstruction of the internal carotid artery during angiography.

While performing carotid angiography in a 76-year-old man, we found that the right internal carotid artery repeatedly opened and closed during the examination. The patient experienced no related neurologic events. The explanation, confirmed at surgery, was that a flap associated with an atherosclerotic plaque had acted as a ball valve.

Aged↗