Search PubMed⌕ Search

Biomedical subjects

G R May

Publications and source records attributed to G R May.

At least 37 records · Page 2Linked to original sources
PubMed1990

Radioisotopic model for investigating thromboembolism in the rabbit.

111Indium (111In)-oxine labeled platelets have been used in a variety of species to assess platelet behavior in vivo. We have shown that 111In-oxine is a suitable label for rabbit platelets and, using a noninvasive technique for the automated, continuous, external imaging of these radiolabeled platelets, we have shown that intravenous adenosine disphosphate (ADP), collagen, platelet activating factor (PAF), and thrombin all elicit dose-related accumulation of platelet-(but not erythrocyte-)associated radioactivity in the thoracic region and a concomitant fall in both the cranial and hindlimb regions of the anesthetized rabbit. Intracarotid (i.c.) ADP, collagen, PAF, and thrombin also produce dose-related increases in platelet-associated radioactivity in the thoracic and decreases in the cranial and hindlimb regions. However, the initial fall in cranial counts induced by i.c. thrombin was followed by a marked increase that was sustained for up to 3 hr. These results suggest this may be a useful model for investigating the mechanisms of platelet activation in the arterial and venous circulations in vivo and may provide a novel model for investigating thromboembolic events in the cerebral circulation.

Adenosine Diphosphate↗
PubMed1990

Safety of same-day sequential extracorporeal shock wave lithotripsy and dissolution of gallstones by methyl tert-butyl ether in dogs.

Passage of stone fragments after extracorporeal shock wave lithotripsy (ESWL) of gallstones has resulted in biliary colic, duct obstruction, and pancreatitis in some patients. Rapid dissolution of these fragments with methyl tert-butyl ether (MTBE) may prevent such side effects and achieve complete clearance of gallstones within hours rather than several months to a year or longer. This study examines the safety of same-day ESWL fragmentation and MTBE dissolution of surgically implanted human gallstones in 15 dogs. The animals were randomly assigned to one of four treatment groups to assess MTBE absorption from the gallbladder and to observe hematology and chemistry profiles after 0, 400, and 1,200 shock waves from a lithotriptor followed by MTBE dissolution therapy. They were sacrificed either immediately after treatment (12 dogs) or 2 weeks later (3 dogs). The results demonstrated that although ESWL causes moderate trauma to the gallbladder, this did not result in increased MTBE absorption or histologic evidence of mucosal disruption. Blood profiles demonstrated an increase in only the level of aspartate aminotransferase. The three dogs that were sacrificed 2 weeks after the combined treatment had no residual evidence of gallbladder injury or remaining stone material. In all animals, severe injury occurred where shock waves passed through lung or air-filled colon. This study suggests that same-day sequential fragmentation of gallstones by ESWL followed by dissolution of stone fragments with use of MTBE may be associated with only mild to moderate and reversible gallbladder trauma and can rapidly achieve clearance of gallstones.

Animals↗
PubMed1990

Endothelin-1 inhibits platelet aggregation in vivo: a study with 111indium-labelled platelets.

1. A non-invasive technique for the scintigraphic determination of 111indium-labelled platelet aggregation stimulated with submaximal doses of adenosine diphosphate (ADP, 56 micrograms kg-1 i.v.), collagen (100 micrograms kg-1 i.v.), platelet-activating factor (PAF, 0.1 microgram kg-1 i.v.) or thrombin (18 iu kg-1 i.v.) was used to investigate the platelet-inhibitory effects of endothelin 1 (ET-1) in anaesthetized rabbits in vivo. 2. ET-1 (1 nmol kg-1 i.v.) inhibited ADP-stimulated platelet aggregation in vivo; a maximum inhibition of 78% of the control value was reached at 3 min, with 45% inhibition at 15 min, and a return to control values at 30 min after injection of the peptide. 3. ET-1 (1 nmol kg-1 i.v.) inhibited in vivo platelet aggregation in response to collagen or PAF by 86% and 52%, respectively, but had no effect on thrombin-induced platelet aggregation. 4. Indomethacin (5 mg kg-1 i.v.) abolished the ET-1-induced inhibition of ADP-stimulated platelet aggregation and significantly potentiated and prolonged the pressor response brought about by ET-1. 5. In conclusion, the data demonstrate that ET-1 potently inhibits platelet aggregation in the anaesthetized rabbit in vivo by releasing a hypotensive and anti-aggregatory cyclo-oxygenase product, presumably prostacyclin, into the circulation.

Adenosine Diphosphate↗
PubMed1989

Dissolution of cholesterol gallbladder stones by methyl tert-butyl ether administered by percutaneous transhepatic catheter.

We treated 75 patients with symptomatic cholesterol gallstones by dissolving the stones with methyl tert-butyl ether (MTBE) instilled into the gallbladder through a percutaneous transhepatic catheter. The MTBE was continuously infused and aspirated manually four to six times a minute, for an average of five hours per day for one to three days; the treatment was monitored by fluoroscopy. The placement of the catheter and the administration of MTBE caused few side effects or complications, and treatment did not have to be stopped in any patient for this reason. In 72 patients there was complete dissolution of stones or more than 95 percent dissolution. Among 21 patients who were completely free of stones after treatment, 4 had recurrence of stone formation 6 to 16 months later. The other 51 patients had residual debris, which spontaneously cleared completely in 15 patients within 6 to 35 months; only 7 with persisting debris have had symptoms. Five of the initial 6 patients treated, but only 1 of the next 69 patients, have required surgery during follow-up periods of 6 to 42 months. We conclude that the dissolution of gallstones by MTBE delivered through a percutaneous transhepatic catheter is a useful alternative to surgery in selected patients with symptomatic cholesterol stones. Further study will be necessary to establish the long-term effectiveness of this treatment and its appropriate role in the management of the various types of gallstones.

Adult↗
PubMed1988

Endothelium-derived relaxing factor inhibits platelet aggregation in human whole blood in vitro and in the rat in vivo.

Carbachol (0.03-10 microM) or histamine (0.06-10 microM) challenge of indomethacin-pretreated rat aortic rings inhibited ADP-induced aggregation of platelets suspended in anticoagulated human whole blood. The maximum inhibition of platelet aggregation achieved with either drug was approximately 50%. No such inhibition was observed in rat aortic rings rubbed to remove endothelial cells or in intact vessels preincubated with nordihydroguaiaretic acid (NDGA, 10 microM), mepacrine (10 microM) or methylene blue (100 microM). Intravenously (i.v.) injected carbachol (0.5-5 micrograms/kg) also inhibited ADP-induced accumulation of 111indium-labelled platelets in the pulmonary circulation of urethane-anaesthetised rats. This effect of carbachol was inhibited by i.v. injected methylene blue (10 mg/kg) but unaffected by indomethacin (3 mg/kg) or hexamethonium (10 mg/kg) suggesting that PGI2 or adrenaline release did not account for the inhibition of platelet activation observed. Similarly, the platelet inhibitory effect of carbachol in vivo was not related to increased pulmonary vascular blood flow (assessed by accumulation of 111indium-labelled erythrocytes) or blood fibrinolytic activity (measured by euglobulin clot bioassay). The present results suggest that endothelium-derived relaxing factor or a like substance inhibits human platelet aggregation in vitro and rat platelet aggregation in vivo.

6-Ketoprostaglandin F1 alpha↗
PubMed1987

Benign postoperative biliary strictures: dilation with fluoroscopic guidance.

Benign postoperative biliary strictures in 74 patients were dilated percutaneously with balloon catheters. In all cases, dilation was performed with fluoroscopic guidance in a radiology suite. Lasting patency following removal of biliary stents occurred in 73% of 49 patients with biliary-enteric anastomotic strictures and in 88% of 25 patients with primary ductal strictures, for an overall success rate of 78%. A successful outcome was more likely if the interval between the last biliary tract surgery and balloon dilation exceeded 2 years. Stricture patency was more easily achieved in patients with primary ductal strictures than in those with biliary-enteric anastomotic strictures. Serious, procedure-related complications were encountered when strictures were dilated transhepatically; these included sepsis in 18 of 65 patients and bleeding due to arteriobiliary communications in seven. No serious complications occurred when strictures were dilated via a T tube track, making this the preferred route if available. Surgeons should be encouraged to leave T tubes in place if postoperative biliary stricture is suspected. Balloon dilation should be strongly considered in patients with benign postoperative strictures in whom surgical repair is difficult.

Adult↗
PubMed1986

Preoperative staging of rectal carcinoma by computed tomography and 0.15T magnetic resonance imaging. Preliminary report.

A prospective study was done on 34 patients using magnetic resonance imaging (MRI) and computed tomography (CT) preoperatively to stage patients with known rectal carcinoma. The study was done to determine the accuracy and clinical usefulness of CT and MRI. The Thoeni staging method was used. Twenty-four of 30 cases were staged correctly by CT. Sixteen of 27 were staged correctly by MRI. CT detected lymph node metastases in six of 15 cases with one false-positive. MRI detected lymph node metastases in two of 15 patients with one false-positive. CT was the preferred examination, and was useful in some cases. These cases included patients with small tumors who were considered for local excision and patients with extensive disease who were candidates for preoperative or intraoperative radiation treatment. MRI demonstrated extensive disease, as did CT in our later cases.

Adult↗
PubMed1986

Diagnosis and treatment of jaundice.

1. CT and sonography are helpful in distinguishing between an obstructing lesion and hepatocellular disease as the cause of jaundice. 2. CT and sonography can demonstrate the level and extent of an obstructing lesion, and can define its nature if a mass more than 1-2 cm is present; sonography is usually the preferred screening study because of its availability, relatively low cost and lack of radiation hazard. 3. PTC or ERCP is useful in the evaluation of jaundice when sonography and CT are equivocal, fail to provide information necessary to establish proper therapy, or are at variance with the clinical impression of obstructive jaundice; in addition to defining obstructions these techniques can detect atrophy, sequestra, stones, abscesses, fistulas, primary sclerosing cholangitis, etc. 4. PBD offers an expedient alternative to surgical decompression in patients with obstructive jaundice, since most cancers that cause biliary obstruction are not resectable for cure at the time of diagnosis.

Adenoma, Bile Duct↗
PubMed1986

Magnetic resonance imaging of osteosarcomas. Comparison with computed tomography.

This study was done to describe the magnetic resonance imaging (MRI) characteristics of osteosarcomas and to determine the clinical usefulness of MRI in the evaluation of patients with these tumors. Ten patients with osteosarcomas were examined with a Picker MRI scanner (0.15 Tesla resistive magnet). All had computed tomograms available for comparison. For demonstrating tumor extent in marrow, MRI was superior to computed tomography (CT) in 60% and about equal to CT in 40%. For defining soft tissue mass, MRI was superior to CT in 40% and about equal to CT in 60%. Direct sagittal and coronal images on MRI and superior contrast differences between tumor and normal tissues with MRI were the reasons for the advantage of MRI in these instances. CT was superior in all cases for demonstrating calcifications. Overall, MRI is better than CT for defining local extent of osteosarcomas. It is of greatest value in the peripheral skeleton, in the medullary canal, and in soft tissues.

Adolescent↗
PubMed1985

Magnetic resonance imaging: application in musculoskeletal infection.

Forty-two patients with clinically suspected osteomyelitis were examined using magnetic resonance imaging (MRI). Twenty-seven patients (64%) had previous surgery or fracture, and 15 (36%) were referred for differentiation of acute osteomyelitis from bone tumors or other pathologic conditions. MRI was compared with computed tomography in 12 cases and with 111In-labeled leukocytes scans in 22. With MRI, 92% of proved infections were detected, and bone and soft-tissue changes were more evident than with routine radiographs, tomography, or computed tomography. In patients with negative cultures and no previous surgery or fracture, it was difficult for MRI to differentiate operative changes from infection. In these patients, 111In-labeled leukocyte images were more specific than MRI.

Adolescent↗
PubMed1985

Cholelitholysis using methyl tertiary butyl ether.

We tested methyl tertiary butyl ether both in vitro and in vivo to evaluate its efficacy as a potential cholesterol gallstone solvent for direct instillation into the human gallbladder or bile duct. Like diethyl ether, methyl tertiary butyl ether is an aliphatic ether with an excellent cholesterol-solubilizing capacity. However, unlike diethyl ether which vaporizes at body temperature, methyl tertiary butyl ether remains a liquid having a boiling point of 55.2 degrees C. In vitro, methyl tertiary butyl ether dissolved human gallstones (40%-94% cholesterol) within 60-100 min. In contrast, monooctanoin, an established gallstone solvent, required greater than 50 h to dissolve similar stones. By direct catheter instillation in 6 dogs, methyl tertiary butyl ether required only 4-16 h to dissolve gallstones surgically implanted in the gallbladder. The dogs tolerated methyl tertiary butyl ether with only minor clinical, biochemical, or histologic effects. We conclude that further evaluation of methyl tertiary butyl ether for dissolution of human gallbladder and biliary duct cholesterol stones is warranted.

Animals↗
PubMed1985

Percutaneous removal of kidney stones: review of 1,000 cases.

We report the results of 1,000 consecutive patients who underwent percutaneous removal of renal and ureteral stones. Removal was successful for 98.3 per cent of the targeted renal stones and 88.2 per cent of the ureteral stones. Complications, evolution and technique are discussed. Percutaneous techniques are an effective way to handle the majority of renal calculi and these techniques will continue to be important as shock wave lithotripsy becomes more widespread in the United States.

Blood Transfusion↗
PubMed1985

Magnetic resonance imaging in a routine clinical setting.

The results of magnetic resonance imaging (MRI) examinations in the first 1,000 consecutive patients who were studied by this technique at our institution were reviewed to determine the disease states encountered, the sensitivity and accuracy of results, and the value of the examination as compared with computed tomography and other imaging procedures. The MRI device was a 0.15-tesla resistive magnet that used a variety of saturation recovery, spin echo, and inversion recovery pulse sequences to produce images. MRI was found equal to or superior to other imaging techniques in most cases. Exceptions included organs or body regions that are prone to excessive respiratory or vascular motion, lesions that necessitate exquisite spatial resolution for diagnosis, and lesions in which angulation of the viewing plane is necessary for optimal depiction. Fresh blood and calcification within a lesion were also difficult to detect with use of MRI.

Adolescent↗