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Tyler Stevens

Publications and source records attributed to Tyler Stevens.

10 recordsLinked to original sources
PubMed2006

The efficiency of endoscopic pancreatic function testing is optimized using duodenal aspirates at 30 and 45 minutes after intravenous secretin.

OBJECTIVES: The endoscopic secretin test (ePFT) takes an hour to perform, limiting its practicality for routine use. We sought to determine which timed endoscopic collections best predict the peak bicarbonate concentration from full hour-long test. METHODS: A cross-sectional study was performed of all ePFTs performed at our institution from 2000 to 2004. We compared 7 theoretical shortened tests [4-single collections (15, 30, 45, or 60 minutes after secretin) and 3-dual collections (15/30, 30/45, 45/60 minutes after secretin)] to the full test and to each other using multivariate linear and Deming regression models. RESULTS: The bicarbonate results of 240 ePFTs were analyzed. The dual 30/45-minute collection was the optimal method based on the closest agreement with the full test (94%). Deming regression reveals the 30/45 estimate to be the best combination from an analytic perspective, owing to its lack of significant proportional bias and minimal constant bias (5.1 mEq/L) as compared to the reference test. Use of the 30/45 method with the adjusted cutpoint 75 mEq/L produces very good specificity (93%) for ruling in exocrine insufficiency. CONCLUSIONS: A dual timed aspiration at 30 and 45 minutes can be used to screen for pancreatic exocrine insufficiency in patients with abdominal pain, simplifying the use of the ePFT in clinical practice.

Abdominal Pain↗
PubMed2006

A randomized crossover study of secretin-stimulated endoscopic and dreiling tube pancreatic function test methods in healthy subjects.

OBJECTIVES: We have developed an endoscopic method of secretin endoscopic pancreatic function testing (ePFT) to simplify duodenal fluid collection. Validation of the ePFT requires a direct comparison to the traditional PFT using a Dreiling tube (DT). Our aim was to compare bicarbonate concentrations [HCO3-] obtained by the ePFT and DT methods in healthy subjects (HS). METHODS: HS were randomized to either DT or ePFT, then crossed over to the other test after a minimum 1-wk washout. An age/weight-based sedation bolus was used for each test. DT protocol: Endoscopic placement of a DT was confirmed by fluoroscopy. After a baseline 15-min collection and administration of IV synthetic secretin, fluid was continuously collected in 15-min aliquots for an hour. ePFT protocol: Endoscopy was performed using a 6-mm endoscope. After gastric aspiration and discard and IV secretin, duodenal aspirates were obtained every 15-min for an hour. Fluid specimens were auto-analyzed for [HCO3-]. RESULTS: Twelve HS were enrolled (6F, mean age 37 yr). The difference in [HCO3-] between the two methods was not significant at the 0-, 30-, 45-, or 60-min collections. An excellent correlation in peak [HCO3-] was observed (R2 = 0.84, p < 0.001). Using a peak [HCO3-] cutpoint 80 mEq/L, there was 100% agreement between the methods; using cutpoint 90 mEq/L, there was 83% agreement. CONCLUSIONS: The accuracy of the ePFT is similar to DT: There were minimal differences in [HCO3-] at each of the timed collections and at peak. There is an excellent correlation in peak [HCO3-] and high level of diagnostic agreement between the tests.

Adult↗
PubMed2004

Electrolyte composition of endoscopically collected duodenal drainage fluid after synthetic porcine secretin stimulation in healthy subjects.

BACKGROUND: Traditional pancreatic function tests are sensitive for the diagnosis of pancreatic exocrine insufficiency but are cumbersome and difficult to perform. A sedationless endoscopic pancreatic function test that has the potential for wide clinical application was developed by us, but data on the results of this method in healthy subjects are lacking. This study analyzed endoscopically collected duodenal fluid from healthy subjects after synthetic porcine secretin stimulation. METHODS: Healthy subjects underwent the sedationless endoscopic pancreatic function test. After secretin stimulation, duodenal aspirates were obtained every 5 minutes for 1 hour. The collected fluid was analyzed for electrolyte concentrations. RESULTS: Sixteen healthy subjects (8 women, 8 men; median age 34.5 years) underwent the endoscopic pancreatic function test. The concentrations of the sodium ([Na+]) and potassium ([K+]) cations remained constant, similar to normal concentrations in plasma (median [Na+], 155 mEq/L; median [K+], 4.3 mEq/L). The concentrations of the bicarbonate ([HCO 3 - ]) and chloride anions increased and decreased, respectively, in an inverse and reciprocal manner, similar to the previously characterized "secretory curve." The median peak [HCO 3 - ] was 108 mEq/L IQR: 99-110). By the 20-minute collection, the [HCO 3 - ] was greater than 80 mEq/L for 94% (15/16) of subjects, the historic cut point for [HCO 3 - ] in studies based on traditional methods of pancreatic function testing. CONCLUSIONS: Endoscopic collection of pancreatic fluid reproduces the anion-cation secretory curve described by prior studies of pancreatic secretory physiology based on traditional collection methods.

Adult↗
PubMed2004

Analysis of pancreatic elastase-1 concentrations in duodenal aspirates from healthy subjects and patients with chronic pancreatitis.

Fecal pancreatic elastase 1 (PE-1) has been advocated as a noninvasive marker of pancreatic function and allows detection of moderate and severe exocrine insufficiency. Few studies have evaluated the utility of measuring PE-1 in duodenal fluid for the diagnosis of pancreatic insufficiency. Our purpose was (1) to determine the feasibility of measuring PE-1 concentrations in duodenal aspirates obtained through our endoscopic pancreatic function test (ePFT) in healthy subjects and patients with chronic pancreatitis (CP) and (2) to determine correlations between duodenal PE-1 concentrations and bicarbonate and lipase concentrations in duodenal fluid. Healthy subjects (HS) and CP patients underwent an ePFT with CCK or secretin. CP was defined as endoscopic retrograde pancreatography (ERP) Cambridge class III-IV, endoscopic ultrasound (EUS) score >5, or presence of pancreatic calcifications on CT scan. Duodenal fluid PE-1, lipase, and bicarbonate concentrations were measured in each study group. Duodenal lipase and bicarbonate concentrations were measured using an autoanalyzer (Roche Diagnostics, Indianapolis, IN). PE-1 was measured using an ELISA (Genova Diagnostics, Asheville, NC). Ten HS and 10 CP patients were studied. In the CCK test the median peak lipase for HS and CP was 1605 and 113 IU/L, respectively (P < 0.008). In the secretin test the median peak bicarbonate for HS and CP was 102 and 40 mEq/L, respectively (p < 0.008). Median PE-1 concentrations for HS and CP were 317 and 63 microg/ml, respectively, after CCK stimulation (p = 0.046) and 87 and 17 microg/ml, respectively, after secretin stimulation (p = 0.033). Statistically significant correlations were found between [PE-1] and peak [lipase] (r = 0.83, P < 0.001), as well as [PE-1] and peak [HCO3(3)-] (r = 0.65, P = 0.037). Conclusions are as follows: (1) PE-1 concentrations can be measured from duodenal fluid obtained by endoscopic aspiration. (2) Duodenal fluid PE-1 concentrations are decreased in CP compared to HS. (3) Duodenal fluid [PE-1] has an excellent correlation with [lipase] and therefore is a marker of acinar cell function. (4) Secretin-stimulated endoscopic function testing with measurement of bicarbonate and PE-1 may provide a simultaneous assessment of both ductal cell and acinar cell function.

Adult↗
PubMed2004

Indicators of clinical response to treatment with six-mercaptopurine or azathioprine in patients with inflammatory bowel disease.

OBJECTIVES: There is some uncertainty regarding how to best dose and therapeutically monitor 6-mercaptopurine or azathioprine in patients with inflammatory bowel disease. The purpose of this study was to assess the relation between clinical response, 6-mercaptopurine metabolite levels, relative leukopenia, and drug dose. METHODS: 60 patients with inflammatory bowel disease who were on stable doses of 6-mercaptopurine or azathioprine for > or = 3 months and who had measurements of 6-mercaptopurine metabolite levels were evaluated. Patients were classified as complete responders (N = 24), partial responders (N = 7), or non-responders (N = 29). RESULTS: Drug dose was associated with clinical response when we analyzed adjusted doses based on molecular drug weight (P = 0.002). 6-Thioguanine levels also were associated with clinical response (P = 0.003) and the maximal difference between responders and non-responders was seen at 6-thioguanine levels greater than 260 pmol/8 x 10(8) RBC. Relative leukopenia, defined as white blood cell count less than either 5.0 or 4.0 K/uL, was not associated with clinical response (P = 0.13 and 0.77 respectively). CONCLUSIONS: 1. Drug dose and 6-thioguanine levels are related to clinical response in patients with inflammatory bowel disease on 6-mercaptopurine or azathioprine. 2. For 6-thioguanine levels, there is a fair amount of overlap, but maximal differentiation between responders and non-responders is seen at levels > 260 pmol/8 x 10(8) RBC. 3. Relative leukopenia does not correlate well with clinical response.

Adult↗
PubMed2004

Pathogenesis of chronic pancreatitis: an evidence-based review of past theories and recent developments.

In the past several decades, four prominent theories of chronic pancreatitis pathogenesis have emerged: the toxic-metabolic theory, the oxidative stress hypothesis, the stone and duct obstruction theory, and the necrosis-fibrosis hypothesis. Although these traditional theories are formulated based on compelling scientific observations, substantial contradictory data also exist for each. Furthermore, the basic premises of some of these theories are directly contradictory. Because of the recent scientific progress in the underlying genetic, cellular, and molecular pathophysiology, there have been substantial advances in the understanding of chronic pancreatitis pathogenesis. This paper will provide an evidence-based review and critique of the traditional pathogenic theories, followed by a discussion of the new advances in pancreatic fibrogenesis. Moreover, we will discuss plausible pathogenic sequences applied to each of the known etiologies.

Animals↗
PubMed2003

Colonoscopy screening in the elderly: when to stop?

OBJECTIVES: The age to begin colorectal cancer (CRC) screening is based on the risk of neoplasia and is published in screening guidelines. The age to stop screening is unknown but should be based, in part, on the same principle. The purpose of this study was to establish whether the prevalence of neoplasia detected by colonoscopy diminished with advancing age, to warrant ceasing colonoscopic screening. METHODS: The endoscopic and pathology reports of all asymptomatic subjects undergoing colonoscopy for the purpose of CRC screening or an evaluation of abdominal pain or change in bowel habits between 1997 and 2000 were reviewed. A multivariate logistic regression analysis was used to assess the effect of age, gender, and indication for examination on the prevalence of neoplasia, as well as on having more than two adenomas, advanced adenomas (tubulovillous, villous, severe dysplasia, or size > or = 1 cm), and invasive cancers. RESULTS: A total of 915 patients were included. Of these, 50% were male, with a mean age of 65 yr (range 50-100). Neoplasia peaked in the seventh decade, with a fall thereafter (p = 0.009). Numerous adenomas, advanced adenomas, and invasive cancers increased with age. The yield for overall neoplasia, advanced adenomas, and more than two adenomas was higher in the screening group than in the symptomatic group. More invasive cancers were found in the symptomatic group compared with the asymptomatic group, but this did not achieve statistical significance (4 vs 1, p = 0.44). CONCLUSIONS: The prevalence of advanced neoplasia continues to increase with age. Subjects undergoing colonoscopy for screening had a greater risk for neoplasia than did subjects with symptoms. There is no decline in yield of advanced neoplasia to justify stopping screening colonoscopy in the elderly.

Age Factors↗