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Biomedical subjects

N Vakil

Publications and source records attributed to N Vakil.

At least 91 records · Page 5Linked to original sources
PubMed1995

A prospective, controlled trial of eight-bit, 16-bit, and 24-bit digital color images in electronic endoscopy.

BACKGROUND AND STUDY AIMS: Digital color information is obtained in "bits" or parcels of information for each color (red, green, blue) of a picture. As the number of bits increases, the amount of color information increases, and more colors can be displayed on a suitable monitor. With eight bits of information, 256 colors can be displayed; with 16 bits, several thousand colors can be displayed; and with 24 bits, more than 16 million colors can be displayed. We sought to determine the minimum requirement for diagnostic-quality endoscopy images in a prospective blinded trial. PATIENTS AND METHODS: Twenty-four bit color images were digitally acquired from the processor using a video card and a personal computer. Ten lesions were chosen to represent the gamut of lesions seen in the upper gastrointestinal tract. Images were simultaneously obtained with decreasing color information (16 and eight bits), and these served as controls. Eleven observers were the test subjects. Six endoscopy nurses, who perform color calibrations, and five endoscopists viewed the images. Eight-bit, 16-bit and 24-bit color images were coded and displayed simultaneously on a high-resolution color monitor (Supermac Technology, Sunnyvale, CA) that can display 16.8 million colors. RESULTS: All images were considered to be of diagnostic quality by the observers, and the area of abnormality was identified and the diagnosis made in all cases. Of 110 viewings of the 24-bit image, on 45 occasions (41%) the viewers could detect no difference between it and the eight-bit and 16-bit images. In 23 (21%), the 24-bit color image was correctly recognized, and on 21 occasions (19%) the 24-bit image was incorrectly identified as eight-bit or 16-bit. Similar data were obtained with viewings of the eight-bit and 16-bit images. CONCLUSIONS: Our results demonstrate that, with current endoscopic technology, 256 colors may be as good as 16 million. Eight-bit color is an acceptable image standard for routine endoscopy.

Endoscopes↗
PubMed1995

Measurement of lesions by endoscopy: an overview.

BACKGROUND AND STUDY AIMS: Endoscopic measurement of lesion size is important in the design and conduct of clinical trials, in determining prognosis and choosing forms of therapy. Endoscopes are constructed with wide-angle lenses that distort the image significantly by creating a relative compression of points in the periphery of the image. METHODS: Published studies on endoscopic lesion measurement were identified using a computerized search of electronic databases (MedLine). RESULTS AND CONCLUSIONS: Currently used clinical methods of estimating lesion size (visual estimation or comparison to a target of known size, e.g., open biopsy forceps) are flawed and inaccurate. Results from studies using image processing or the stereoendoscope are particularly promising for the future.

Digestive System↗
PubMed1995

Treatment of esophageal fistulas with a new polyurethane-covered, self-expanding mesh stent: a prospective study.

OBJECTIVES: Esophagorespiratory fistulas are serious complications of malignant disease in the esophagus and are associated with rapid deterioration and death. Palliation has thus far consisted of insertion of a plastic stent to occlude the fistula opening. Insertion of these stents is associated with a high complication rate. Our aims were to study the efficacy of a new class of metal stents covered with a membrane with regard to fistula occlusion and lumen patency. METHODS: Six consecutive patients with esophagorespiratory fistulas were treated with covered expandable metal stents. RESULTS: In all six patients, no evidence of persisting fistula was seen on contrast radiographs 2 h after stent placement. All patients were able to eat a normal diet after stent insertion and had complete occlusion of their esophagorespiratory fistula. One patient reported pain after the procedure, and the symptoms persisted until death. One patient died of massive hematemesis 5 days after the procedure. Dysphagia scores improved in all patients from a median of 4 to a median of 1, and the Karnofsky score improved from a median of 40% to a median of 65%. Fistulas remained closed until death in all patients. CONCLUSIONS: Covered expandable metal stents are safe and effective in the palliation of esophagorespiratory fistulas.

Aged↗
PubMed1995

Gastroesophageal reflux-induced cough syncope.

Respiratory complications of gastroesophageal reflux disease that have been reported include hoarseness, wheezing, bronchospasm, stridor, laryngitis, and chronic cough. Syncope as a manifestation of gastroesophageal reflux disease-induced cough has not been described in the literature. We present an unusual case of gastroesophageal reflux that resulted in frequent cough-induced syncope. Treatment ultimately consisted of a laparoscopic Nissen fundoplication which resulted in sustained relief from both cough and syncope.

Adult↗
PubMed1994

Liver abscess in Crohn's disease.

Liver abscess is a rare but serious complication of Crohn's disease. Intra-abdominal abscesses, fistulous disease, and metronidazole or steroid therapy have all been reported to be important predisposing factors in the pathogenesis of the disease, and the mortality has been reported to be high. We report six patients who developed a liver abscess as a complication of Crohn's disease. Three patients presented with a liver abscess as the first manifestation of Crohn's disease and two others had quiescent disease at presentation. The diagnosis was delayed by 1-8 wk after the onset of fever because of the paucity of signs indicating a hepatic infection. None of the patients had intra-abdominal abscesses, active fistulas, or metronidazole therapy before the onset of symptoms. The only predisposing conditions identified were two minor skin infections in patients developing staphylococcal liver abscesses. Nonoperative catheter drainage was successful in four of the six patients. One patient required surgical placement of drains, and the patient with the longest delay before diagnosis required hepatic lobectomy because of extensive necrosis. Shaking chills, fever with leukocytosis, and an elevated alkaline phosphatase are suggestive of a liver abscess and should prompt an ultrasound examination. Catheter drainage with antibiotic therapy is effective if the liver abscess is diagnosed before extensive necrosis has occurred. Minor skin infections may predispose to staphylococcal liver abscess in some cases.

Adolescent↗
PubMed1994

Endoscopic imaging technology.

Upper gastrointestinal endoscopy has evolved from semiflexible instruments of large diameter to a generation of high-resolution electronic and fiberoptic instruments of narrow diameter with many diagnostic and therapeutic capabilities. Resolution and color fidelity are important considerations in endoscopy, and advances in technology have resulted in substantial improvements in both over the last decade. Enhancements in electronic imaging techniques and developments in networking will make image transfer and shared data easier in the coming years, and image processing may help refine diagnostic endoscopy.

Computer Systems↗
PubMed1994

Effects of bile duct ligation on calcium excretion in the rat.

In an earlier study we showed that bile duct-ligated rats were highly susceptible to gentamicin nephrotoxicity and that oral calcium administration had a pronounced protective effect. The mechanism by which this occurs is unclear. Because cations compete with gentamicin for tubule binding sites, it has been suggested that the increased susceptibility of the kidney to gentamicin after bile duct ligation might result from decreased cation excretion. The aim of this study was to determine the effect of bile duct ligation on calcium excretion in relation to overall renal function. Male Sprague-Dawley rats underwent bile duct ligation and division. Pair-fed sham-operated rats served as controls. Metabolic and clearance studies were carried out at 3, 5, 7, 14 and 21 days after surgery. Urine output was higher in bile duct-ligated rats, and they excreted more calcium at 3, 5, 7 and 14 days, while excreting less sodium than controls. We conclude that after bile duct ligation, there is increased calcium excretion, which is independent of the abnormality in sodium excretion. Enhanced nephrotoxicity with aminoglycosides in the bile duct-ligated rat model cannot be explained by decreased calcium excretion.

Animals↗
PubMed1993

A controlled trial of an expansile metal stent for palliation of esophageal obstruction due to inoperable cancer.

BACKGROUND: Esophageal obstruction due to cancer can produce debilitating dysphagia. Rapid palliation is usually possible with endoscopic placement of a plastic esophageal prosthesis, but this device has a high rate of complications. A new alternative is a metal-mesh stent that collapses to 3 mm in diameter at placement but can then expand up to 16 mm. METHODS: Patients with esophageal carcinoma (39 patients) or malignant extrinsic obstruction (3 patients) were randomly assigned to treatment with either a plastic prosthesis (16 mm in diameter) or an expansile metal-mesh stent. The patients were evaluated every six weeks until death. The degree of palliation was expressed as a dysphagia score and a Karnofsky performance score. RESULTS: Complications were significantly less frequent with the metal stents than with the plastic prostheses (no complications vs. nine; P < 0.001). The dysphagia and Karnofsky scores improved significantly and to a similar degree in both treatment groups. The most common causes of recurrent dysphagia were migration of the plastic prostheses (five patients) and ingrowth or overgrowth of the metal stents by tumor (five patients). The rates of reintervention were similar in both treatment groups, as were the 30-day mortality rates. The period of hospitalization after placement of a prosthesis was significantly longer in the group given plastic prostheses than in the group given metal stents (mean +/- SE, 12.5 +/- 2.1 vs. 5.4 +/- 1.0 days; P = 0.005). Despite their higher initial cost, the metal stents were cost effective because of the absence of fatal complications and the decrease in the hospital stay. CONCLUSIONS: Expansile metal stents are a safe and cost-effective alternative to conventional plastic endoprostheses in the treatment of esophageal obstruction due to inoperable cancer.

Aged↗
PubMed1993

Transient acoustic cavitation in gallstone fragmentation: a study of gallstones fragmented in vivo.

The mechanism of gallstone fragmentation by shock waves in vivo is uncertain. We used scanning electron microscopy to study 9 partially fragmented stones obtained from 6 patients who underwent lithotripsy and subsequently had surgery because of incomplete fragmentation. Surface characteristics of the stone were studied using scanning electron microscopy and compared to gallstones fragmented in degassed water in vitro and to control stones obtained from patients with uncomplicated cholelithiasis. Characteristic damage caused by transient acoustic cavitation was visible in all stones fragmented in vivo and in vitro as pits 10-100 microns diameter. In these pits, cholesterol crystals were fractured, and the symmetry of crystal boundaries was damaged. In areas of more severe damage, individual pits coalesced to form craters on the stone surface. High magnification of the pit walls revealed cracks, which in some instances radiated out onto the unpitted surface of the stone. We conclude that transient acoustic cavitation plays a role in gallstone fragmentation in vivo through the mechanism of surface pitting and the formation of cracks that radiate outward from the surface pits. Measures to enhance cavitation may improve the results of gallstone lithotripsy.

Adult↗
PubMed1993

A prospective, randomized, controlled trial of metal stents for malignant obstruction of the common bile duct.

Endoscopic insertion of biliary stents is the preferred method of palliation for inoperable malignant biliary obstruction; however, migration and clogging are frequent problems with conventional endoprostheses. We sought to determine if expandable metal stents offer improved palliation compared to conventional stents. Sixty-two patients with common bile duct lesions were randomized to receive polyethylene or metal stents. Stents were placed endoscopically or by the combined percutaneous-endoscopic route. Early results (< 1 month) were similar in both groups. Long-term follow-up (n = 28 polyethylene, median: 5 months; n = 27 metal, median: 5 months) showed a higher stent failure rate in the polyethylene (n = 12; 43%) compared to the metal group (n = 6; 22%). The incidence of cholangitis was significantly higher (p < 0.05) in the polyethylene (n = 10; 36%) compared to the metal group (n = 4; 15%). Life-table analysis showed a significantly reduced incidence of stent failure (p = 0.0035) in the metal stent compared to the polyethylene group. The total duration of hospital stay for treatment of stent related problems was significantly higher in the polyethylene (11.8 +/- 3 days) compared to the metal group (4 +/- 1.9 days; p = 0.02). The costs for retreatment because of stent failure were significantly higher in the plastic (DM 5900 +/- 1516) compared to the metal group (DM 2070 +/- 977). As a result, the overall costs (treatment of stent related complications & stents) were higher in the polyethylene group (DM 6000 +/- 1500).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Plastic endoprostheses versus metal stents in the palliative treatment of malignant hilar biliary obstruction. A prospective and randomized trial.

This prospective and randomized trial sought to compare large-bore plastic endoprostheses (14 French) and self-expanding metal stents (24 French) in the palliative treatment of obstructive jaundice due to biliary hilar malignancies. Twenty patients with Type II-IV (Bismuth classification) hilar obstruction were randomized to treatment with either plastic or metal stents. Both treatment groups were well matched with regard to all assessed clinical criteria before stenting. Stent placement was uniformly successful in the metal group and in 88.9% of the plastic group. Early stent failure (< 30 days) occurred in two patients of the plastic stent group. Longterm (> 30 days), stent failure was observed in 50% of the plastic group and 18.2% of the metal stent group. All differences were not statistically significant. The number of re-interventions required to manage stent-related problems proved to be significantly higher in the plastic group (2.4 +/- 2.6) compared to the metal group (0.4 +/- 0.5). Hospitalization for treatment of stent complications was also significantly higher in the plastic treatment group. The costs calculated for stents and hospital stay for required re-interventions were therefore higher in the plastic stent group. In conclusion, metal stent insertion for palliation of hilar malignancies does not only offer higher success rates and higher patency rates compared to plastic stent insertion, but is also cost-effective since patients require fewer re-interventions.

Aged↗
PubMed1993

In vitro gallstone fragmentation by three piezoelectric lithotripters.

Several different piezoelectric lithotripters have been under clinical investigation for gallstones in the USA. Design differences in the different shock wave generators result in different characteristics for the three devices and different peak pressures at the focus of the lithotripters. Using gallstone families, we sought to study fragmentation in the three lithotripters. A total of 56 gallstones from eight gallstone families were studied. Forty-eight stones were fragmented in three lithotripters (16 in each), Diasonics (Therasonic), EDAP (LT01), and Wolf lithotripter (Piezolith 2300), at maximum power and a rate of 2-2.5 Hz. A total of 500 shocks was applied to each stone in each of the three lithotripters. Gallstone composition was determined by infrared spectroscopy on one stone of each family (8 x 1). Initial stone weight and size were similar in all the three groups. All families consisted of cholesterol stones ( greater than 70% cholesterol). The fraction of the initial stone mass reduced to fragments less than or equal to 2 mm was not significantly different in the three lithotripters (Diasonics [n = 16] = 60 +/- 4%, EDAP [n = 16] = 53 +/- 6%, Wolf [n = 16] = 50 +/- 7%; p = 0.068).(ABSTRACT TRUNCATED AT 250 WORDS)

Cholelithiasis↗
PubMed1992

[Metal or plastic endoprostheses in malignant obstructive jaundice. A randomized and prospective comparison].

In a prospective randomized trial 58 patients (24 men, 34 women, mean age 67 +/- 13 [42-89] years) with inoperable malignant jaundice were treated with synthetic (S; n = 29) or expanding metal endoprostheses (M; n = 29). After endoscopic retrograde cholangiopancreatography patients were divided into a group with hilar (K: n = 7; M: n = 6) or distal involvement (K: n = 22, M: n = 23). In two cases with hilar involvement (28%) a synthetic endoprosthesis could not be implanted, while early prosthesis occlusion (after 2 days) was observed in one case. But in this group it was possible to implant all metal stents. In the group with distal involvement both synthetic and metal endoprostheses were successfully implanted. In the M group the proportion of patients with prosthesis failure (13.6%) was significantly higher than in the S subgroup (40.9%). The cholangitis incidence was 9% in the M group, significantly less (P less than 0.05) than in the K group (40.9%). Duration of hospital stay to treat prosthesis-related complications was significantly less in the M group (average 2.9 days) than the K group (12.9 days). It would be a great advance in palliative tumour treatment if it were possible significantly to reduce, by means of metal stents, the incidence of late cholangitis and the duration of hospital stay necessary to treat late complications. But improvement in the technique of implanting metal stents would be essential before their general use in distal lesions can be recommended.

Adult↗
PubMed1992

Bile composition, microspheroliths, antinucleating activity, and gallstone calcification.

This study examined if abnormalities in bile composition and antinucleating activity are associated with gallstone calcification. Nineteen controls without gallbladder disease and 42 patients with cholesterol stones were studied. Bile was obtained at surgery and analyzed for pH and PCO2, ionized calcium, and total calcium. The pH and carbonate concentrations of gallbladder bile were significantly higher in patients with calcified stones than in patients with noncalcified stones and in controls, resulting in significantly higher levels of the ion product in patients with calcified gallstones. Microspheroliths of calcium carbonate, seen on microscopic examination of bile, predicted stone calcification with a sensitivity of 86%, a specificity of 86%, and a predictive value of 86%. Bile from control subjects completely inhibited precipitation of calcium carbonate from a supersaturated solution, whereas bile from subjects with calcified and noncalcified gallstones did not. It is concluded that gallstone calcification is related to elevated bile pH and carbonate concentrations, resulting in an elevated ion production of calcium carbonate in gallbladder bile. In addition, bile from subjects with calcified and noncalcified gallstones lacks antinucleating activity for calcium carbonate.

Absorption↗
PubMed1992

Technical failure of biliary metal stent deployment in a series of 116 applications.

Biliary metal stents are thought to offer improved long-term palliation of malignant biliary obstruction due to a lower incidence of migration and clogging. Placement of these stents is technically more complicated than that of plastic endoprostheses and requires two experienced physicians. We report the incidence and reasons for apparent malfunction of expandable metal stent deployment (Wallstents and Strecker stents). In 116 applications of 82 Wallstents (endoscopic approach: n = 33, transhepatic approach: n = 49), we observed 19 cases of stent malfunction due to technical problems of stent delivery. In 13 cases (15.8%), the restraining membrane of the Wallstent could not be retracted sufficiently to deliver the stent. There were 6 (17.6%) failures in 34 cases of Strecker stent deployment. In 3 cases, we noted difficult balloon removal, including avulsion of the balloon catheter shaft within the endoscope during attempted balloon removal in one case. In one case, the Strecker stent could only be released partially, requiring subsequent endoscopic extraction. In two patients, only partial expansion of one end of the Strecker stent could be achieved. Given the significant malfunction rate of expandable metal stents during stent delivery, further improvements in the delivery system of the metal stents are required.

Cholestasis, Extrahepatic↗
PubMed1992

Gallstone movement during lithotripsy: mechanisms and effects on fragmentation.

We sought to examine the mechanisms of gallstone movement and its effect on gallstone fragmentation in vitro. Two experiments were performed in four specially constructed phantoms that allowed decreasing degrees of movement during the application of shock waves. Shock waves caused displacement of the stone from the focus, but the stone and its fragments were returned to the focus by streaming movements in the coupling liquid when the volume of surrounding fluid was small. Streaming movements were ineffective in large volumes. Restraining movements of the gallstone did not improve the results of fragmentation. We conclude that radiation force and the streaming motion of the surrounding liquid account for movements of the stone and fragments during lithotripsy. Lithotripsy is more effective when smaller volumes are used because streaming brings fragments back to the focus of the lithotripter. Total immobilization of the stone in the focus of the lithotripter, however, offers no benefit, probably because it inhibits rotational movement of the stone.

Cholelithiasis↗