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Biomedical subjects

G B Davis

Publications and source records attributed to G B Davis.

At least 19 recordsLinked to original sources
PubMed2002

Use of polymer mats in series for sequential reactive barrier remediation of ammonium-contaminated groundwater: laboratory column evaluation.

Large-scale column experiments were undertaken to evaluate the potential of in situ polymer mats (installed in series) to be used as permeable reactive barriers for delivery of oxidants and reductants to induce sequential bioremediation of ammonium-contaminated groundwater (approximately 120mg L(-1) NH4+-N), without bioaugmentation. The strategy was for the first group of polymer mats to deliver oxygen to induce bacterial nitrification of the ammonium to nitrite/ nitrate as the groundwater moved past and for the second group of polymer mats to deliver hydrogen or ethanol, to induce bacterial denitrification of the nitrite/nitrate to produce nitrogen gas. Once purging of the first polymer mat commenced, ammonium concentrations decreased downgradient from the polymer mats. Nitrification rates increased and stabilized over the 6-month experiment, with stable nitrification half-lives in the range 0.07-0.25 days. Nitrification most likely occurred in a biologically active zone at the polymer wall/aqueous interface. With hydrogen delivery via the polymer mats, a denitrification half-life (nitrate plus nitrite removal) of 3.5 days was induced. Denitrification rates were significantly enhanced when ethanol was delivered via a polymer mat, with denitrification half-lives in the range of 0.12-0.34 days. Nitrification/ denitrification rates were maintained for groundwater flow rates up to 300 m yr(-1), suggesting oxygen and ethanol delivery rates via the polymer mats were sufficient not to limit nitrification or denitrification. In soil columns, the polymer mat delivery system provided an effective and reliable technique for delivery of oxygen and hydrogen or ethanol for sequential nitrification/denitrification of ammonium-contaminated groundwater. Scale-up of this concept to a field pilot-scale is currently underway.

Biodegradation, Environmental↗
PubMed2002

Using polymer mats to biodegrade atrazine in groundwater: laboratory column experiments.

Large-scale column experiments were undertaken to evaluate the potential of in situ polymer mats to deliver oxygen into groundwater to induce biodegradation of the pesticides atrazine, terbutryn and fenamiphos contaminating groundwater in Perth, Western Australia. The polymer mats, composed of woven silicone (dimethylsiloxane) tubes and purged with air, were installed in 2-m-long flow-through soil columns. The polymer mats proved efficient in delivering dissolved oxygen to anaerobic groundwater. Dissolved oxygen concentrations increased from <0.2 mg l(-1) to approximately 4 mg l(-1). Degradation rates of atrazine in oxygenated groundwater were relatively high with a zero-order rate of 240-380 microg l(-1) or a first-order half-life of 0.35 days. Amendment with an additional carbon source showed no significant improvement in biodegradation rates, suggesting that organic carbon was not limiting biodegradation. Atrazine degradation rates estimated in the column experiments were similar to rates determined in laboratory culture experiments, using pure cultures of atrazine-mineralising bacteria. No significant degradation of terbutryn or fenamiphos was observed under the experimental conditions within the time frames of the study. Results from these experiments indicate that remediation of atrazine in a contaminated aquifer may be achievable by delivery of oxygen using an in situ polymer mat system.

Atrazine↗
PubMed2002

Modelling of physical and reactive processes during biodegradation of a hydrocarbon plume under transient groundwater flow conditions.

Numerical experiments of non-reactive and reactive transport were carried out to quantify the influence of a seasonally varying, transient flow field on transport and natural attenuation at a hydrocarbon-contaminated field site. Different numerical schemes for solving advective transport were compared to assess their capability to model low transversal dispersivities in transient flow fields. For the field site, it is shown that vertical plume spreading is largely inhibited, particularly if sorption is taken into account. For the reactive simulations, a biodegradation reaction module for the geochemical transport model PHT3D was developed. Results of the reactive transport simulations show that under the site-specific conditions the temporal variations in groundwater flow do, to a modest extent, affect average biodegradation rates and average total (dissolved) contaminant mass in the aquifer. The model simulations demonstrate that the seasonal variability in groundwater flow only results in significantly enhanced biodegradation rates when a differential sorption of electron donor (toluene) and electron acceptor (sulfate) is assumed.

Biodegradation, Environmental↗
PubMed2002

The role of microbial populations in the containment of aromatic hydrocarbons in the subsurface.

A survey of soil gases associated with gasoline stations on the Swan Coastal Plain of Western Australia has shown that 20% leak detectable amounts of petroleum. The fates of volatile hydrocarbons in the vadose zone at one contaminated site, and dissolved hydrocarbons in groundwater at another site were followed in a number of studies which are herein reviewed. Geochemical evidence from a plume of hydrocarbon-contaminated groundwater has shown that sulfate reduction rapidly developed as the terminal electron accepting process. Toluene degradation but not benzene degradation was linked to sulfate reduction. The sulfate-reducing bacteria isolated from the plume represented a new species, Desulfosporosinus meridiei. Strains of the species do not mineralise 14C-toluene in pure culture. The addition of large numbers of cells and sulfate to microcosms did stimulate toluene mineralisation but not benzene mineralisation. Attempts to follow populations of sulfate-reducing bacteria by phospholipid signatures, or Desulfosporosinus meridiei by FISH in the plume were unsuccessful, but fluorescently-labeled polyclonal antibodies were successfully used. In the vadose zone at a different site, volatile hydrocarbons were consumed in the top 0.5 m of the soil profile. The fastest measured rate of mineralisation of 14C-benzene in soils collected from the most active zone (6.5 mg kg(-1) day(-1)) could account for the majority of the flux of hydrocarbon vapourtowards the surface. The studies concluded that intrinsic remediation by subsurface microbial populations in groundwater on the Swan Coastal Plain can control transport of aromatic hydrocarbon contamination, except for the transport of benzene in groundwater. In the vadose zone, intrinsic remediation by the microbial populations in the soil profile can contain the transport of aromatic hydrocarbons, provided the physical transport of gases, in particular oxygen from the atmosphere, is not impeded by structures.

Biodegradation, Environmental↗
PubMed2000

Tumors of the oral cavity and pharynx.

We have compiled all the reported cases of smooth muscle (stromal) tumors of the oral cavity and pharynx from 1884 through 1996. Our collective data included 139 leiomyomas (LM) and 68 leiomyosarcomas (LMS); but because we did not have sufficient information for 13 cases of LM, we report on only 126; and we report on only 66 of 68 cases of LMS. The peak age of incidence was 40 to 49 years for benign tumors and 50 to 59 years for malignant lesions, with the incidence in men slightly predominating over that in women. The most common sites of LM of the oral cavity and pharynx were the lips, tongue, and hard and soft palate. The most common sites of LMS included the maxilla and mandible. More than 40% of LMs presented as an intraoral mass, and more than half were known to be present for longer than 1 year. About 10% presented with pain, difficulty chewing or swallowing, swelling, toothache or loose teeth, or a combination of these symptoms. Patients with LMS were much more likely to have obvious symptoms of shorter duration, and one-third presented with pain or swelling (or both). Other relatively common symptoms of LMS included tenderness, interference with dentures, or an intraoral mass. In this review, there were almost twice as many LMs as LMSs, which was consistent with smooth muscle tumors found in other areas of the gastrointestinal tract.

Adult↗
PubMed2000

Tumors of the esophagus.

This collective review includes all available case reports of smooth muscle (stromal) tumors of the esophagus in the world literature. Compiling this review, we endeavored to examine cumulative and recently collected data of both benign and malignant esophageal smooth muscle tumors found in the literature spanning the period from 1875 to 1996, which totaled 1679 leiomyomas (LMs) and 165 leiomyosarcomas (LMSs). The peak age of occurrence of benign smooth muscle tumors in the esophagus was found to be between the ages of 30 and 59, whereas the highest frequency of malignant tumors was seen later in life, during the decade from age 60 to 69. The most common location of both LMs and LMSs was the lower third of the esophagus. Their patterns of growth differed; LMs were more likely to grow intramurally, and LMSs were predominantly intraluminal. Most patients with LMs presented with dysphagia and pain or discomfort; patients with LMSs additionally commonly complained of weight loss. As with smooth muscle tumors of other areas of the gastrointestinal tract, the duration of symptoms averaged 1 month to 1 year, and malignant tumors grew to larger sizes than benign neoplasms. Approximately one-third of LMSs had metastasized at diagnosis, and there was a 5-year survival rate of approximately 20%.

Adult↗
PubMed2000

Tumors of the stomach.

This collective review includes all available case reports of smooth muscle (stromal) tumors of the stomach in the world literature from 1762 to 1996. It updates our previous review from 1767 to 1959. Overall, we identified 2189 patients with leiomyoma (LM) and 1594 with leiomyosarcoma (LMS). The peak age of incidence of LM was 50 to 59 years, while LMS was most frequently seen between ages 60 and 69. Women were more likely to develop LM, and men more commonly presented with malignant smooth muscle tumors of the stomach. Concerning the patterns of growth, LMs were more likely to grow intraluminally (endogastric), whereas LMSs were predominantly exogastric. The most common site of LMs was on the anterior or posterior wall of the body of the stomach; LMSs were most likely found along the greater curve. The presenting symptoms of both types of smooth muscle tumors were similar; in decreasing order of frequency they were bleeding, pain, palpable mass, and weight loss. Interestingly, there was no correlation between the size of the tumor and signs or symptoms of bleeding, pain, weight loss, or ulceration, although patients with LMSs were more likely to report weight loss than patients with benign tumors. For LMS, there seemed to be no correlation between tumor size or location and rate of metastasis, although the tumors that grew in a dumbbell shape (i.e., both intraluminally and extraluminally) had a higher frequency of metastasis than other growth patterns. Overall, the rate of metastasis at diagnosis was 35.4%, with the liver, spleen, and regional lymph nodes the most common sites.

Age Factors↗
PubMed2000

Tumors of the small intestine.

This collective review includes all available case reports and series of smooth muscle (stromal) tumors of the small intestine in the world literature from 1881 to 1996. We identified 1074 patients with leiomyoma (LM) and 1689 with leiomyosarcoma (LMS). Our purpose was to update our previous review, which encompassed case reports and series from 1881 to 1959, which included 350 LMs and 257 LMSs. The peak incidence of smooth muscle tumors in the small intestine in both male and female patients was between the ages of 50 and 59. Most commonly, the presenting complaint was gastrointestinal bleeding. Computed tomography was found to detect LM and LMS most successfully and had the additional advantage of locating metastatic disease. The jejunum contained the highest numbers of smooth muscle tumors, followed by the ileum and then the duodenum, with malignant lesions in all locations typically attaining larger diameters than benign tumors. The overall rate of metastatic spread of LMS ranged from 24% to 50%, with the liver being most commonly involved. Unlike other sarcomas, both hematogenous and lymphatic spread were common. The 5-year survival of 705 patients with LMS from 22 series was 27. 8%. For both benign and malignant smooth muscle tumors of the small intestine, surgery remains the treatment of choice, with little efficacy reported for irradiation, chemotherapy, or both.

Age Factors↗
PubMed2000

Tumors of the appendix and colon.

This collective review includes all available case reports of smooth muscle (stromal) tumors of the appendix and large intestine in the world literature. When compiling this review, we endeavored to examine cumulative as well as recently collected data on both benign and malignant smooth muscle tumors spanning the period 1875 to 1996. In total, there were reports of 331 leiomyomas (LMs) and 263 leiomyosarcomas (LMSs). The peak age of incidence of LM was 30 to 39 years, and the peak age of incidence of LMSs was 50 to 59 years. The female/male ratio was slightly higher for LM, and the male/female ratio was higher for LMS. The descending colon and sigmoid colon were the most common sites of both benign and malignant smooth muscle tumors. The growth of LMs most often occurred extraluminally, whereas LMSs tended to grow within the lumen of the colon. With both tumor types pain was the most frequent presenting complaint, followed less commonly by complaints of a palpable mass or gastrointestinal bleeding. LMSs tended to be larger at diagnosis than LMs, though the duration of symptoms for both types of tumor was most often reported to be between 1 month and 1 year. Finally, LMSs were found to metastasize mo

Abdominal Pain↗
PubMed2000

Tumors of the rectum and anal canal.

This collective review includes all available case reports of smooth muscle (stromal) tumors of the rectum and anal canal in the world literature. When compiling this review we endeavored to present cumulative and recently collected data of both benign and malignant smooth muscle tumors found in the literature spanning the period from 1881 to 1996, which totaled 432 leiomyomas (LMs) and 480 leiomyosarcomas (LMSs) of the anus and rectum. The peak age of frequency for LMs was 40 to 59 years and 50 to 69 years for LMSs; men were slightly more likely to develop both benign and malignant anorectal smooth muscle tumors than women. Intraluminal growth of both LMs and LMSs was more frequently seen than extraluminal or intramural patterns, and tumors were more likely to be found in the rectum than in the anus. Patients with LMs presented most commonly with gastrointestinal (GI) bleeding, a palpable mass, or anorectal pain. As with smooth muscle tumors in other areas of the alimentary tract, symptoms likely persisted for less than 1 year prior to diagnosis. As was also the case for these neoplasms in other GI locations, LMSs tended to be larger than LMs. Approximately 20% of LMSs reported from 1881 to 1996 had metastasized at diagnoses. The local recurrence rate for resectable tumors was more than 80%, exceeding the propensity of LMSs in other areas of the GI tract to recur.

Adult↗
PubMed1996

Microbial biomass in a shallow, urban aquifer contaminated with aromatic hydrocarbons: analysis by phospholipid fatty acid content and composition.

The city of Perth contains a number of sites that have been contaminated with hydrocarbons due to leakage from petroleum underground storage tanks. Microbial biomass in groundwater and sediment cores from above and below the water table, and from within and outside a plume of hydrocarbon contamination, was examined using phospholipid fatty acid methyl ester analysis. Microbial numbers, calculated from the phospholipid content, ranged from 0.9 x 10(6) to 7.8 x 10(6) 'Escherichia coli equivalent cells' g-1 dry wt of sediment. Over 96% of the microbial biomass was attached to the sediment and the proportion of attached cells did not decrease within the plume of contaminants. The amount of biomass within aquifer samples seemed to be related more to the proximity of the rhizosphere to the shallow aquifer, and other unknown urban inputs, rather than to the effects of the plume of contaminants. Fatty acids common to many bacterial groups dominated within the plume, and as such the analyses gave limited insight into microbial community structure. For site assessment of intrinsic remediation of shallow aquifers in urban areas, estimates of microbial biomass may not provide information that is readily applicable to plume management.

Biomass↗
PubMed1991

Pharmacomechanical thrombolysis and angioplasty in the management of clotted hemodialysis grafts: early and late clinical results.

The results of pharmacomechanical thrombolysis and angioplasty of 121 thrombosed hemodialysis grafts were reviewed. The initial pharmacomechanical method (used in 65 cases) employed clot maceration with hook-shaped catheters and clot lacing with highly concentrated urokinase. The current technique (used in 56 cases) consisted of pulsed-spray injection of urokinase into the clot. All fully treated grafts (117 cases) underwent complete or near-complete thrombolysis, and 93% remained patent after 1 day. Mean time for pulsed-spray lysis was 46 minutes +/- 21. One patient (less than 1%) had gastrointestinal bleeding and received a transfusion; minor complications occurred in 3% of patients. Primary and secondary graft patency rates for both methods at 1 year were 26% and 51%, respectively. While graft age and results of angioplasty did not influence future graft patency, shorter intervals between graft thromboses was predictive of earlier subsequent graft failure. Results suggest that pharmacomechanical thrombolysis and angioplasty provide rapid, consistent, and safe recanalization of clotted hemodialysis grafts and represent a promising additional therapeutic approach to long-term graft management.

Angioplasty, Balloon↗
PubMed1991

Pulsed-spray thrombolysis of arterial and bypass graft occlusions.

Pulsed-spray thrombolysis is accomplished through forceful injection of a spray of highly concentrated urokinase into clot by using catheters with multiple side holes. We previously reported the immediate technical efficacy of the method in eight arterial and 10 bypass graft occlusions. We now describe the clinical efficacy of the method in a second, larger series of 23 native artery occlusions and 25 bypass graft occlusions. Transluminal angioplasty was performed after thrombolysis in 21 of the arteries and 24 of the bypass grafts. Initial thrombolysis was observed in all artery occlusions and all but one bypass graft occlusion with an average time for pulsed-spray lysis of 65 +/- 28 min in native arteries and 93 +/- 38 min in bypass grafts. Recanalization with improvement in symptoms or distal pulses after thrombolysis and angioplasty was achieved in 74% of treated arterial occlusions and 92% of treated graft occlusions. Of the 15 arteries that were recanalized and did not require adjunctive surgery, seven remained patent at 3-28 months follow-up. Nine of 23 recanalized bypass grafts required early adjunctive surgery. Of the nine synthetic and five saphenous vein grafts successfully recanalized and not requiring surgical revision, the mean patency was 4.3 +/- 3.1 months and 3.0 +/- 2.2 months, respectively. Minor complications were seen in 23% of cases. The two major complications (4%) involved one groin hematoma requiring surgery and one episode of gastrointestinal hemorrhage. We conclude that combined pulsed-spray thrombolysis and angioplasty achieve rapid and consistent arterial and graft recanalization with minimal risk. The method offers a favorable alternative to standard thrombolytic therapy of arterial occlusions. In occluded synthetic and vein bypass grafts, the technique is sometimes beneficial, either alone or combined with surgical revision.

Angioplasty, Balloon↗
PubMed1990

A double-blind study of the effectiveness of a high-efficiency particulate air (HEPA) filter in the treatment of patients with perennial allergic rhinitis and asthma.

This study was designed to assess the effectiveness of a high-efficiency particulate air (HEPA) filter in alleviating allergic respiratory symptoms. Thirty-two patients were studied who had symptomatic perennial rhinitis and/or asthma during the fall and winter months and had a positive skin test with house dust or house dust--mite extract. An ENVIRACAIRE room air cleaner was placed in the bedroom for 8 weeks. In a random manner, the active filter was used for 4 weeks and a blank filter for 4 weeks. There was an average 70% reduction in the particulate matter greater than or equal to 0.3 micron with the HEPA filter. In a double-blind design, results were assessed by analysis of the patients' symptom/medication scores and subjective evaluation. For the total study, there was no difference in the total symptom/medication scores or individual symptom scores during the placebo and active-filter periods. Analysis of the last 2 weeks of each filter period in which respiratory infection was absent demonstrated definite differences in total and individual symptoms, suggesting active-filter benefit. Patients' subjective responses also suggested benefit from the filter. The overall impression is that the HEPA filter can reduce allergic respiratory symptoms.

Adolescent↗
PubMed1989

Angiographic embolization of intractable puerperal hematomas.

Puerperal hematomas may not respond to conventional therapy, including vaginal packing, drainage, and hypogastric artery ligation. Two cases are presented in which selective angiographic arterial embolization was used to manage this potentially lethal complication.

Angiography↗
PubMed1988

Perfusion scan findings understate the severity of angiographic and hemodynamic compromise in chronic thromboembolic pulmonary hypertension.

Major vessel chronic thromboembolic pulmonary hypertension is potentially remediable by thromboendarterectomy. The diagnosis often has been delayed because a lung perfusion scan demonstrated modest defects thought to be incompatible with severe vascular obstruction. To define the relationships between perfusion scan abnormalities, angiographic findings, and hemodynamic data, we analyzed 25 consecutive patients with chronic major vessel thromboembolic pulmonary hypertension who subsequently underwent thromboendarterectomy. We found that the perfusion lung scan consistently caused us to underestimate the severity of pulmonary arterial obstruction as defined by pulmonary angiography. Furthermore, there was no significant correlation between the severity of hemodynamic compromise and the extent of obstruction defined by perfusion scan or angiogram. These findings suggest that, when pulmonary hypertension is known or suspected, the diagnosis of correctable, chronic major vessel obstruction should be pursued by angiography and hemodynamic assessment even though the perfusion scan may demonstrate only two segmental defects.

Adult↗
PubMed1987

Thrombosed dialysis grafts: efficacy of intrathrombic deposition of concentrated urokinase, clot maceration, and angioplasty.

Forty-one thrombosed polytetrafluoroethylene hemodialysis grafts in 26 patients were treated by a modified method of fibrinolytic therapy and transluminal angioplasty. The modifications included the use of highly concentrated urokinase, intrathrombic injection of urokinase into mechanically macerated thrombi, use of a crossed two-catheter technique, observation of the patient in the angiography suite during the entire procedure, and transluminal angioplasty to correct underlying stenosis immediately after partial or complete thrombolysis. Lysis was initially successful in 37 (90%) of 41 procedures. Successful treatment, defined as a functional graft for longer than 6 months without intervening surgery, was achieved in 16 (62%) of 26 patients. In comparison with previous transluminal or surgical regimens, this modified method permits marked acceleration of thrombolysis, immediate transluminal angioplasty, and sparing of potential future graft sites.

Angioplasty, Balloon↗