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Biomedical subjects

M H Thomas

Publications and source records attributed to M H Thomas.

At least 37 records · Page 2Linked to original sources
PubMed1991

Confirmation of oxytetracycline, tetracycline and chlortetracycline residues in milk by particle beam liquid chromatography/mass spectrometry.

A method using particle beam liquid chromatography/mass spectrometry was developed for the confirmation of oxytetracycline, tetracycline and chlortetracycline residues in bovine milk. This method is one of the first to apply particle beam technology to the confirmation of animal drug residues in food products for regulatory purposes. The milk is centrifuged, using molecular weight cut-off filters to remove components of 25,000 daltons and above from the milk. The filtrate is passed through a C-18 sample preparation cartridge which retains the tetracyclines. After the columns are washed with water, the tetracyclines are eluted with 0.1 M oxalic acid in methanol and concentrated. The compounds are separated on a Novapak C-18 column with a methanol-oxalic acid-acetonitrile mobile phase. Negative chemical ionization with selective ion monitoring is used to identify the tetracyclines. The procedure was used to confirm the presence of each tetracycline at 100 ng ml-1 in fortified and incurred milk samples.

Animals↗
PubMed1991

Cardiac sympathetic tone in anaesthetized diabetics.

To assess cardiac sympathetic nervous function in diabetics, the heart rates attained following a pharmacological dose of intravenous atropine, 23 micrograms.kg-1, were studied under N2O, isoflurane anaesthesia in diabetics (n = 21) and nondiabetics (n = 30). Atropine-induced heart rate in diabetics was significantly lower than that in nondiabetics (95 +/- 14 (SD) bpm vs 109 +/- 12 bpm, P less than 0.001) and were closely related to preoperative orthostatic diastolic blood pressure change (r = 0.60, P less than 0.01). There was some correlation between the atropine-induced heart rate and preoperative RR-variation in diabetics (r = 0.50, P less than 0.05). The findings suggest that cardiac sympathetic function may also be impaired in diabetics with orthostatic hypotension.

Adolescent↗
PubMed1991

Small bowel function after aortic surgery.

One cause of post-operative morbidity in the elective repair of abdominal aortic aneurysms is the development of a paralytic or 'adynamic' ileus. In a series of 20 consecutive patients undergoing such a procedure, the maintenance of small bowel motility and absorptive capacity in the immediate post-operative period was assessed using barium sulphate and xylose passed down a naso-duodenal tube sited at the time of surgery. This simple study demonstrated that small bowel function was preserved in all cases, and hence that patients could be fed enterally via naso-duodenal tube (in particular using very low residue formulae) rather than using costly parenteral regimens, should an ileus persist.

Aorta, Abdominal↗
PubMed1990

Self protection in surgery: the use of double gloves.

This study assesses the perforation rate of single and double gloves and thus the extent to which double gloving protects the surgeon from diseases transmissible from the patient. We have also investigated whether double gloving offers the patient extra protection by reducing wound sepsis. Two hundred adult hernia repairs were performed, the first 100 single gloved and the second 100 double gloved. Glove perforation rates were not significantly different between single gloves and the outer of the double gloves. Although 46 of 400 outer gloves were perforated there were only 15 inner glove perforations and only eight of these matched the outer perforations. The percentage of operations in which the latex protective barrier was breached was reduced from 31 per cent when the surgeon wore single gloves to 8 per cent with double gloves. Wound sepsis was not increased by glove perforation nor reduced by double gloving. While careful technique remains mandatory we conclude that double gloving offers increased protection to the surgeon operating on high risk infectious cases.

General Surgery↗
PubMed1990

Pseudomembranous colitis after abdominal aortic aneurysm repair.

We report three patients who developed pseudomembranous colitis following aortic aneurysm resection. Colonic ischaemia can occur after such surgery and ischaemic colonic mucosa is known to be more susceptible to damage by bacteria and their toxins. This colonic ischaemia together with the antibiotic prophylaxis used may render aortic aneurysm patients susceptible to pseudomembranous colitis. It is important to distinguish pseudomembranous from ischaemic colitis in these patients as specific and effective drug therapy can be given to those with the pseudomembranous type.

Aged↗
PubMed1990

Stroke volume measurements by electrical bioimpedance and echocardiography in healthy volunteers.

To evaluate the validity of three equations for estimation of thoracic electrical field size in a new bioimpedance algorithm, stroke volume (SV) as calculated by these equations was compared with that calculated by Doppler echocardiography in 48 healthy volunteers, both lean and obese. When the volume of electrically participating tissue was estimated from body height (modified Sramek) or body height corrected for body habitus (Sramek-Bernstein), there was considerable variation between bioimpedance and Doppler stroke volumes. When the volume of electrically participating tissue was estimated from the actual measurement of the height of the thorax and the circumference at the base of the thorax, the variation in SV differences decreased substantially (Sramek equation), although still considerable for clinical use, and there was no relationship between SV thus obtained and body habitus. Analysis of calculated stroke indices derived by our Doppler echocardiographic standard, as compared with values in the literature, revealed a systematic underestimation. We conclude that the original Sramek equation systematically underestimates SV by 15% to 20%, and the modified Sramek and Sramek-Bernstein equations systematically underestimates SV by 15% to 20%, and the modified Sramek and Sramek-Bernstein equations systematically overestimate SV in females by about 15%, but provide SV values in males in the predicted range. Further studies on the current assumption that the electrical field size is a truncated cone may improve precision of the bioimpedance method.

Adult↗
PubMed1989

Bile leaks after simple cholecystectomy.

Drains after cholecystectomy are used commonly to avoid biliary leaks and subsequent peritonitis. Thirty-five patients who had had cholecystectomy without drainage underwent 99mTc-labelled dimethylphenylcarbamoylmethyliminodiacetic acid (HIDA) and ultrasound scans the morning after surgery. Biliary leaks detected by positive HIDA scans occurred in 11 patients. Subhepatic fluid collections were seen on 20 ultrasound scans. There was no relation between biliary leaks and subhepatic collections. Many of the collections were not seen on the HIDA scan, suggesting that they contained blood and not bile. Many of the patients with bile leaks showed no fluid collection. Clinical complications were few and evenly distributed between those with positive and negative scans. We conclude that bile leaks are not an occasional event but occur after 31 per cent of undrained cholecystectomies and that these bile leaks remain clinically unimportant.

Bile↗
PubMed1989

Peripheral somatic sensory neuropathy and skin galvanic response in the feet of patients with diabetes.

The relationship between abnormality in the peripheral sympathetic nervous system (skin galvanic response) and in the peripheral somatic sensory nerve fibers was studied in the lower extremities of 51 patients with diabetes. Deficits in temperature and pain sensations (the small sensory nerve fibers) were related to abnormal sympathetic nervous function (temperature sensation, p less than 0.001; pain sensation, p less than 0.05). The deficits in temperature sensation, in particular, predicted abnormal sympathetic nervous function reliably and vice versa. There was no relationship between deficits in touch and vibration sensations (the large sensory nerve fibers) and abnormal sympathetic nervous function. There was a relationship between skin galvanic response and RR-variation (p less than 0.01). However, abnormality in RR-variation was not related to the deficits in any of the four sensory modalities.

Adult↗
PubMed1988

Surgical glove perforation.

In a study to investigate the incidence and significance of surgical glove perforation, bacterial contamination of surgeons' hands and gloves before and after operation was measured and the gloves tested for damage. Perforations were found in 74 of 582 gloves (12.7 per cent) and occurred in 34.5 per cent of operations. Glove perforation did not influence bacterial counts on the surgeons' hands or on the outside of their gloves. A separate clinical study of 100 adult hernia repairs gave no evidence that perforation increased wound sepsis. After standard pre-operative hand preparation, glove perforations are of no clinical significance to the patient, but their high incidence should alert surgeons to the need for protection against pathogens transmissible during surgery, such as hepatitis B and the human immunodeficiency virus. Protection of the surgeon is the main indication for preoperative change of damaged gloves.

Equipment Contamination↗
PubMed1988

Cholecystectomy: safe or not safe to drain?

The aim of this study was to determine whether drains influenced the size of subhepatic collections following cholecystectomy, and if these had any affect on complications. Eighty-five patients undergoing cholecystectomy had either no drain, a narrow bore suction drain or an open corrugated drain. Subhepatic fluid collections were measured by real time ultrasound on the first and fifth postoperative days, and thereafter if necessary. The volumes of fluid drained were also measured and clinical complications recorded. The subhepatic collections were, on average, the same whether a drain was used or not. Drains produced volumes considerably in excess of any subhepatic collection measured, but they did not appear to warn of biliary leakage. More complications (28%) were seen in the drained group compared with the undrained group (10.5%), and furthermore, the complications did not seem to occur in relation to the larger collections. One patient who had had a corrugated drain correctly placed developed biliary peritonitis. We suggest that drainage of simple cholecystectomy is unnecessary and, if an open drain is used, potentially dangerous.

Adult↗
PubMed1986

Sulfamethazine blood/tissue correlation study in swine.

Seventy market-weight hogs (90 to 113 kg) were used in a feeding study to determine the correlation of serum sulfamethazine concentrations with sulfamethazine concentrations in liver and muscle at time of slaughter. Test groups were fed medicated feeds prepared from commercial medicated premixes containing 110 g of sulfamethazine/metric ton for 30 days. Fifteen days before hogs were slaughtered, test groups were given maintenance feeds containing 1.1 to 13.9 g of sulfamethazine/metric ton and were fed these diets until slaughtered. Comparison of data from positive- and negative-control groups indicated that total withdrawal of sulfamethazine in the feed was not necessary for the liver to contain less than the allowed tolerance of 0.1 mg of sulfamethazine/kg of liver at slaughter. Feed concentrations of up to 2 g of sulfamethazine/metric ton could be tolerated in withdrawal feeds before liver sulfamethazine values exceeded 0.1 mg/kg of liver. Serum/tissue sulfamethazine ratios were erratic in hogs given 1.1 to 2.7 g of sulfamethazine/metric ton, but became less variable in hogs given greater than 5.7 g/metric ton. Feed concentrations greater than 8 g of sulfamethazine/metric ton produced values greater than 0.1 mg/kg of muscle and values of about 0.4 mg/kg of liver. When serum sulfamethazine concentrations alone were used as a predictor for tissue sulfamethazine values, 100% of the liver values exceeded 0.10 mg/kg of liver when sulfamethazine in serum was greater than 0.45 mg/L. However, 57.4% of samples having serum concentrations between 0.10 and 0.45 mg/L had associated sulfamethazine values greater than 0.1 mg/kg of liver. All hogs having serum sulfamethazine concentrations less than 0.1 mg/L had sulfamethazine concentrations less than 0.1 mg/kg of liver.

Animal Feed↗
PubMed1984

Gold vs D-penicillamine double blind study and followup.

We undertook a controlled random double-blind comparing gold and penicillamine. Of the 50 patients with rheumatoid arthritis entered into the study, 34 completed the protocol. We found no significant differences in the clinical results, laboratory variables, or toxicity. Longterm followup of 55 months revealed that a significant number of patients were no longer on either drug. The notable exceptions were those who were felt to be in remission from either drug, and remained on gold, or penicillamine. No toxicity from penicillamine involving known immunological aberration has thus far been encountered.

Adult↗
PubMed1983

Quantitative thin layer chromatographic multi-sulfonamide screening procedure.

In-situ optical scanning of fluorescamine derivatives on thin layer silica gel plates provides a rapid method for the determination of multiple sulfonamides at levels below 0.1 ppm. Sample preparation is minimal. Homogenized liver or muscle is extracted with ethyl acetate and then back-extracted into 0.2M glycine buffer. After pH adjustment, the extract is washed with hexane and extracted with methylene chloride. The organic phase is evaporated to dryness and reconstituted in methanol. Pre-adsorbent layer silica gel plates are used for chromatography. The method has been applied to residues of sulfamethazine, sulfadimethoxine, sulfathiazole, sulfaquinoxaline, and sulfabromomethazine in cattle, swine, turkey, and duck tissues.

Animals↗
PubMed1983

Quantitative thin layer chromatographic multi-sulfonamide screening procedure: collaborative study.

A thin layer chromatographic procedure suitable for detection of multiple sulfonamides at 0.1 ppm was studied in an interlaboratory collaborative study. Sulfamethazine, sulfadimethoxine, and sulfaquinoxaline were variously analyzed in liver and muscle tissues from swine, turkey, and duck. The average recovery for all drugs across all tissues was 95%. The corresponding repeatability and reproducibility were 7.7% and 10.5%, respectively.

Animals↗