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Biomedical subjects

R E Parsons

Publications and source records attributed to R E Parsons.

At least 37 records · Page 2Linked to original sources
PubMed1995

Human transluminally placed endovascular stented grafts: preliminary histopathologic analysis of healing grafts in aortoiliac and femoral artery occlusive disease.

PURPOSE: The purpose of this study was to perform a preliminary histopathologic analysis of explanted human endovascular stented grafts from patients treated for occlusive disease. METHODS: Over a 16-month period, 26 endovascular stented grafts were placed in 21 patients with limb-threatening ischemia caused by aortoiliac or femoral artery occlusive disease. All grafts were inserted through open arteriotomies remote from the region of primary disease. During the follow-up period, two patients died of preexisting heart disease 2 weeks and 7 months after grafting, and a portion of their endovascular grafts were the surrounding artery was explanted. Specimens from five other endovascular grafts were obtained during surgical revision for graft stenosis after 3 and 6 weeks and for outflow artery stenosis after 3, 5, and 6 months. All specimens were formalin fixed and studied with hematoxylin and eosin and trichrome staining and immunohistochemically for factor VIII-related antigen, alpha actin smooth muscle, macrophage antigen (MAC-387) and PC-10 (a mouse monoclonal antibody which specifically recognizes proliferating cell nuclear antigen in paraffin sections). RESULTS: Three weeks after placement of the stented grafts, organizing thrombus was present on both surfaces of the expanded polytetrafluoroethylene (PTFE) grafts. At 6 weeks, evidence of a neointima with overlying endothelium was seen in the perianastomotic region, and 3 months after grafting it was seen 1 to 3 cm from the anastomosis. The specimen explanted at 5 months demonstrated factor VIII-positive cells 8 cm from the anastomosis. The histopathologic condition of the external capsule appeared to vary, depending on the presence or absence of an external wrap on the PTFE graft and on which layer in the arterial wall the graft was inserted. A foreign body reaction characterized by multinucleated giant cells was seen adjacent to wrapped grafts or around those placed in an intraadventitial plane. Grafts inserted within the media were surrounded by orderly, arranged, smooth muscle cells and few mononuclear cells. Extensive smooth muscle cell proliferation (PC-10 activity) was not seen within native artery atherosclerotic plaques peripherally displaced and external to prosthetic endovascular grafts. CONCLUSIONS: These preliminary observations on the healing of PTFE endovascular stented grafts in human beings demonstrate limited plaque hyperplasia and the presence of endothelial cells on the luminal surface remote from the graft-artery anastomosis. It is unclear whether this is a unique manifestation of healing in prosthetic grafts inserted within the walls of arteries.

Actins↗
PubMed1995

Determining the acuteness and stability of deep venous thrombosis by ultrasonic tissue characterization.

PURPOSE: The intent of the study was to determine whether ultrasonic tissue characterization (UTC) could indicate acuteness and stability of deep venous thrombosis (DVT) of the lower extremities. METHODS: Thrombi presenting as filling defects on color Doppler imaging in the common or superficial femoral or popliteal veins in 50 extremities in 45 patients with DVT were studied. Acute DVT was less than 4 days duration, and chronic DVT was greater than 21 days duration. UTC analysis of parameters from the normalized power spectrum of backscattered ultrasound signals from venous filling defects was performed. This spectrum approaches a straight line, and its basic parameters, slope, and Y-intercept are related to scatterer size, concentration, and the square of the scatterer-to-medium acoustic impedances. Ten of the DVT extremities were reexamined at 1 week to assess UTC changes that would indicate thrombus instability. RESULTS: Acute DVT (19 of the 50 extremities) could be distinguished from chronic DVT, mainly on the basis of significantly higher intercept values for the acute group, which were 11.6 relative decibels (dBr) higher than those of the chronic DVT group. Discriminant linear analysis of the two parameters indicated a sensitivity of 94.7% and specificity of 90.3% in correctly diagnosing acute DVT. In a small sample of 10 extremities reexamined at 1 week, acute DVT extremities showed a mean 9.4 dBr decrease in intercept values with no significant change in slope. CONCLUSIONS: UTC distinguished clinically defined acute from chronic DVT. In a small series of extremities, UTC revealed significant instability of acute thrombi in a selected patient population.

Acute Disease↗
PubMed1995

Mismatch repair gene defects in sporadic colorectal cancers with microsatellite instability.

Microsatellite instability has been observed in both sporadic and hereditary forms of colorectal cancer. In the hereditary form, this instability is generally due to germline mutations in mismatch repair (MMR) genes. However, only one in ten patients with sporadic tumours exhibiting microsatellite instability had a detectable germline mutation. Moreover, only three of seven sporadic tumour cell lines with microsatellite instability had mutations in a MMR gene, and these mutations could occur somatically. These results demonstrate that tumours can acquire somatic mutations that presumably do not directly affect cell growth but result only in genetic instability. They also suggest that many sporadic tumours with microsatellite instability have alterations in genes other than the four now known to participate in MMR.

Adult↗
PubMed1994

hMSH2 mutations in hereditary nonpolyposis colorectal cancer kindreds.

It has recently been shown that hereditary nonpolyposis colorectal cancer (HNPCC) is caused by hereditable defects in DNA mismatch repair genes. However, the fraction of HNPCC due to defects in any one repair gene and the nature of these mutations are not known. We analyzed 29 HNPCC kindreds for mutations in the prototype DNA mismatch repair gene hMSH2 by a combination of linkage analysis, polymerase chain reaction-based screening, and sequencing of the coding region. The complete intron/exon structure of the gene was ascertained to facilitate this analysis. The results suggest that at least 40% of classic HNPCC kindreds are associated with germline mutations in hMSH2 and that most of these mutations produce drastic alterations in the predicted protein product.

Amino Acid Sequence↗
PubMed1994

Intimal hyperplasia producing thrombus organization in an experimental venous thrombosis model.

PURPOSE: A venous thrombosis animal model demonstrated similarities between intimal hyperplasia and thrombus organization. This has prompted the evaluation of a hypothesis that intimal hyperplasia may be the mechanism for thrombus organization in veins with normal pressure. METHODS: Thrombi were produced in surgically exposed jugular veins of anesthetized, 18 to 20 kg pigs. Thrombosis was induced by a combination of devascularization, electric injury produced by a low amperage, direct current, and permanent partial ligation (50% diameter reduction). Vein segments were harvested at 0, 1, 2, 7, 14, and 60 days and histologically examined for fibrin, red blood cells, platelets, smooth muscle cells, endothelial cells, elastic fibers, and collagen deposits. RESULTS: Forty vein segments in 20 pigs were evaluated. Luminal thrombi with thickened walls developed in all specimens. All luminal thrombi demonstrated partial spontaneous thrombolysis over the period of observation. Intimal thickening consisting primarily of smooth muscle cells by day 2 was apparent and progressed until about 2 weeks, when collagen deposits became prominent within the neointima. The neointima frequently comprised half the cross-sectional area of the veins. Endothelial cells were present in the intima as single cells or as lining for clefts formed within the thickened intima. CONCLUSIONS: Smooth muscle cell proliferation with collagen deposition characteristic of intimal hyperplasia seemed to be the mechanism of thrombus organization in the experimental thrombosis model used in this study in which extensive stimulation was used to produce thrombosis.

Animals↗
PubMed1993

Effect of perfusion and blood content on ultrasonic backscattering of liver tissue.

The purpose of this study was to determine the effect of blood flow perfusion and red cell content on ultrasonic scattering by liver tissue. Data acquisition for ultrasonic tissue characterization (UTC) employing analysis of the backscattered echoes from the power spectrum was obtained from the same region of pig liver tissue under four conditions: 1) normal perfusion in situ, 2) ischemia in situ in the living pig, 3) ischemia in situ immediately postmortem, and 4) immediately after excision of the liver. Discriminant function analysis was used to evaluate differences in the two basic parameters from the normalized power spectrum: slope and intercept. Normal perfused liver had significantly higher intercept values and lower slope values than liver under the other three conditions. Excised liver showed the lowest intercept and highest slope values (p < 0.01). These experiments indicate that differences in perfusion produce significant differences in ultrasonic scattering by liver tissue (ischemia caused a 3 dB drop in intercept amplitude). Normal or ischemic in vivo and in vitro liver tissue is associated with different patterns of ultrasonic scattering, and scattering data under these various circumstances are not equivalent.

Animals↗
PubMed1993

Ultrasonic tissue characterization of experimental venous intimal hyperplasia.

Ultrasonic tissue characterization (UTC) employing slope and Y-intercept parameters from the normalized power spectrum of backscattered echoes was employed in vivo to study compositional changes in the walls of pig jugular veins in which thrombi were experimentally induced. Light microscopy revealed these changes to be intimal hyperplasia with an early predominance of smooth muscle cells and a later mixture of smooth muscle cells and collagen deposits. UTC distinguished intimal hyperplasia from previously reported data from luminal thrombosis UTC. Furthermore, UTC was able to discriminate between early (predominantly smooth muscle cells) and older (smooth muscle cells plus collagen deposits) intimal hyperplasia. The study suggests that intimal hyperplasia in the experimental model used may be organized thrombus and that UTC may be able to follow both the development of wall changes as well as luminal changes occurring in venous thrombosis.

Animals↗
PubMed1993

Age determination of experimental venous thrombi by ultrasonic tissue characterization.

PURPOSE: The ability of ultrasonic tissue characterization based on radiofrequency signal processing to detect compositional differences in thrombi of varying ages was evaluated in vivo. METHODS: Thrombi were produced in 49 jugular veins of 26 anesthetized 18 to 20 kg pigs by partial ligation and application of direct electric current. Thrombi were imaged 30 minutes after formation and 1, 7, and 14 days later with a color Doppler ultrasound scanner that identified the thrombi, and acquired radio frequency data for ultrasonic tissue characterization analysis. Ultrasonic tissue characterization used two parameters from the normalized power spectrum, slope, and intercept, which are related to scatterer size, scatterer concentration, and acoustic-impedance differences between scatterers and surrounding medium. Previous in vitro studies demonstrated that lower slope and higher intercept values correlated with greater cellularity and more-dense fibrin mesh. Histologic examination was performed for each time period. The values of slope and intercept for each timed observation were compared by a multilinear discriminant analysis. RESULTS: There were no statistical differences between day 0 and day 1. Statistically-significant differences in ultrasonic tissue characterization parameters were seen between all other time intervals with p values < 0.01. Older thrombi tended to demonstrate higher slope and lower intercept values. These ultrasonic tissue characterization changes correlated with a red cell and fibrin-mesh density reduction, which was confirmed by histologic findings and was indicative of partial spontaneous thrombolysis. The degree of spontaneous thrombolysis provides an estimate of the age of thrombi. CONCLUSION: Ultrasonic tissue characterization is capable of distinguishing age differences in thrombi in an animal model and has the potential for noninvasive application in clinical diagnosis.

Animals↗
PubMed1993

Differentiation of breast tumors by ultrasonic tissue characterization.

The ability of ultrasonic tissue characterization to differentiate and classify benign and malignant breast tissues in vivo in patients with palpable breast masses and in vitro in excised breast tissue was evaluated. One-hundred and twenty-four in vivo and 89 in vitro studies were performed using a technique of UTC based on parameters from the power spectrum of backscattered echoes. Sensitivities and specificities for diagnosing carcinoma were 86 and 84% for in vivo studies and 94 and 92% for in vitro studies. These UTC parameters provided threshold values for color-coding breast lesion images. The results of this preliminary investigation suggest that UTC provides a basis for assessing more accurately lesions suspected of being malignant prior to biopsy and possibly for evaluating breast lesions noninvasively.

Breast Neoplasms↗
PubMed1992

Cellularity and fibrin mesh properties as a basis for ultrasonic tissue characterization of blood clots and thrombi.

This in vitro study was designed to evaluate the ability of ultrasonic tissue characterization (UTC) based on power spectrum analysis of backscattered radio-frequency echo signals to distinguish two prominent variables of thrombi: cellularity (primarily red cell content) and fibrin-mesh density. Six types of clots simulating thrombus components were prepared by varying red-cell and platelet concentrations and shear forces during clotting. Data were acquired with a linear-array transducer, digitized, and analyzed in terms of slope and intercept parameters obtained from normalized power spectra of radio-frequency echo signals. Increased cellularity and fibrin-mesh density both produced lower slope and higher intercept values, which permitted statistically significant discrimination of cellularity and mesh density in the six types of clots analyzed. Shearing forces and (to a lesser degree) platelet concentrations increased fibrin-mesh density. This study suggests that UTC based upon the power spectrum of echo signals may be used to detect and follow compositional differences that have clinical relevance in the diagnosis and follow-up of thrombi.

Blood Coagulation↗
PubMed1991

Technique of ultrasonic detection and mapping of abdominal wall adhesions.

A technique for noninvasive ultrasound examination to detect and map abdominal wall adhesions is described. The examination is based on the demonstration of movement of abdominal viscera during real-time imaging. This movement is called viscera slide and either occurs spontaneously as a result of respiratory movement or may be induced by manual compression. Abdominal wall adhesions produce a restriction of viscera slide. Ultrasonic demonstration of restricted viscera slide has been used for the precise localization and mapping of abdominal wall adhesions prior to abdominal surgery. The technique may be particularly useful in providing safe initial access in patients undergoing laparoscopy who are at increased risk for trocar injury of viscera due to abdominal wall adhesions resulting from previous surgery or peritonitis.

Abdominal Muscles↗
PubMed1991

Distribution of St. Louis encephalitis viral antibody in sentinel chickens maintained in Sarasota County, Florida: 1978-1988.

Sentinel chicken flocks monitored arboviral transmission at 12 sites in Sarasota County, Fla., from 1978 through 1988. During this time, 3,452 serum samples were analyzed for hemagglutination inhibition antibody to St. Louis encephalitis virus (SLE) and eastern equine encephalomyelitis virus (EEE). Overall, 91 chickens seroconverted to SLE and three to EEE. The intensity of SLE transmission showed considerable year-to-year variation. Chickens from south-county flocks were more likely to seroconvert to SLE virus than chickens maintained at the north-county sites. The SLE seroconversion rate for midcounty sentinels was intermediate between north- and south-county sites. Chickens were caged in four habitat types: oak hammocks, slash pine-saw palmetto areas, pastures, and urban-residential areas. There was no significant difference in SLE seroconversion rates between habitats.

Animals↗
PubMed1991

Cooperative assembly of simian virus 40 T-antigen hexamers on functional halves of the replication origin.

The cofactor ATP stimulates the formation of T-antigen double hexamers on the simian virus 40 core origin of replication (I. A. Mastrangelo, P. V. C. Hough, J. S. Wall, M. Dodson, F. B. Dean, and J. Horwitz, Nature [London] 338:658-662, 1989). We report here the pathway for the assembly of hexamers and double hexamers on the core origin. ATP triggers the cooperative assembly of hexamers on the early and late halves of the origin even when they are completely isolated. Hexamer assembly nucleates at T-antigen recognition pentanucleotides in the early half of the origin. In intact origins, assembly of the first hexamer on the early half of the origin cooperatively stimulates the assembly of a second hexamer on the adjacent late half of the origin. Thus, monomer-monomer and hexamer-hexamer interactions of T antigen, allosterically activated by ATP, constitute two distinct types of cooperative interaction with the origin. Finally, we show that the assembly of T-antigen hexamers on isolated half origins leads to the same array of structural changes that T antigen induces in intact origins. We conclude that the origin is divided into complementary halves that each promote the assembly of functional T-antigen hexamers.

Adenosine Triphosphate↗
PubMed1991

The zinc finger region of simian virus 40 large T antigen is needed for hexamer assembly and origin melting.

Simian virus 40 large T antigen contains a single sequence element with an arrangement of cysteines and histidines that is characteristic of a zinc finger motif. The finger region maps from amino acids 302 through 320 and has the sequence C-302 L K C-305 I K K E Q P S H Y K Y H-317 E K H-320. Previous genetic analysis has shown that the cysteine and histidine sequences and the contiguous S H Y K Y region in the finger are important for DNA replication in vivo. We show here that representative mutations in either of these elements of the finger prevent the assembly of large T antigen into stable hexamers in vitro. These same mutations have a characteristic effect on the interaction of T antigen with the simian virus 40 core origin of replication. The mutant T antigens bind to the central pentanucleotide domain of the core origin but fail to melt the adjacent inverted repeat domain and to untwist the adenine-thymine domain. These defects would prevent the formation of a replication bubble and the initiation of DNA replication. Finger mutations have lesser effects on the helicase function of T antigen and no observable effect on binding of T antigen to the mouse p53 protein. We propose that the zinc finger region contributes to protein-protein interactions essential for the assembly of stable T-antigen hexamers at the origin of replication and that hexamers are needed for subsequent alterations in the structure of origin DNA. We cannot exclude the possibility that the zinc finger region also makes specific contacts with components of origin DNA.

Amino Acid Sequence↗
PubMed1988

Evaluation of ULV naled applied simultaneously against caged adult Aedes taeniorhynchus and Culicoides furens.

Two experiments were conducted to test application of ULV naled against adult Aedes taeniorhynchus and Culicoides furens exposed simultaneously in cages hung on poles at selected heights and distances from the spray source. ULV spray was released at 0.14 oz active ingredient/acre, droplet size 13.5 micron mmd. In both experiments, insecticide largely carried over the first poles. The greatest mortality occurred at the second pole position, 18.3 and 25.7 m, respectively, from the spray origin, and diminished progressively with increasing distance. Cages at the highest elevation (183 cm) showed the greatest mortality, while those near the ground (15 cm) were substantially less affected. Regression analysis showed that 70% control or better was attained up to a distance (beyond a line 10 m from the release point) of 23 m in the case of Ae. taeniorhynchus and 18 m in the case of C. furens. ULV naled, applied as described, was not particularly effective for control of Ae. taeniorhynchus and C. furens, and was poor for insects exposed in low vegetation.

Aedes↗
PubMed1987

Evaluation of naled applied as a thermal fog against Culicoides furens (Diptera: Ceratopogonidae).

Naled/diesel oil (1:99), applied as a thermal fog, was tested against the biting midge Culicoides furens. The insects were confined in small cages suspended at 4 heights on poles at progressively greater distances from the fog release point. In terms of population survival 24 hr after treatment, a parabolic equation accurately described the regression of percent survival on distance from the release point. If 10% survival is considered as the maximum acceptable, then the equation predicts adequate control up to 19.6 m (64.3 ft) from the fog release point.

Animals↗
PubMed1983

Diagnosis and behavior of juvenile rhabdomyosarcoma.

The main problems in the diagnosis of rhabdomyosarcoma are 1) distinction of undifferentiated examples from other small cell malignancies, especially soft-tissue Ewing's tumor and lymphoma; 2) distinction of spindling examples from fibrosarcoma, leiomyosarcoma, malignant fibrous histiocytoma, polyhistioma, and other sarcomas; 3) recognition of minimal criteria on small samples such as needle biopsy specimens or frozen sections; and 4) recognition of rhabdomyosarcoma in uncommon sites such as bone (mandible), perineum, retroperitoneum, and chest. In 95 pediatric cases diagnosed and treated at Royal Alexandria Hospital for Children--45 after the introduction of combined therapy--minimal diagnostic criteria were assessed. Cross-striations were found in only one third of cases; longitudinal myofibrils were more common and more helpful. There was much overlap between histologic types, and the microscopic patterns had little bearing on prognoses in preadolescent children. Fourteen cases could not be further differentiated ("embryonal sarcoma, probably rhabdomyosarcoma")--nine small-cell tumors; four tumors from genitourinary tract or head for which very small biopsy specimens were available, and one spindling retroperitoneal neoplasm. In all, slight evidence suggested embryonal rhabdomyosarcoma; this evidence included oat-shaped nuclei and, in a few cells, deeply eosinophilic cytoplasm, small elongated processes, or myxoid or alveolar foci--features that exclude lymphoma and Ewing's tumor. In six cases that were originally classified as poorly differentiated or undifferentiated, later material confirmed the presence of rhabdomyosarcoma by showing a predominantly well-differentiated (pleomorphic) or alveolar pattern after therapy. In 14 remaining undifferentiated cases, immunoperoxidase staining with antihuman-myoglobin serum was positive in five. With combined therapy there was 100 per cent survival among patients with paratesticular, limb, and stage I and stage II tumors; considerably improved survival among patients with head and neck, pelvic, and stage III tumors; and 100 per cent mortality among patients with intra-abdominal and stage IV tumors.

Biopsy↗