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Biomedical subjects

B Dodson

Publications and source records attributed to B Dodson.

16 recordsLinked to original sources
PubMed2003

Gastrointestinal handling of glycosyl [13C]ureides.

OBJECTIVES: Lactose [(13)C]ureide has been proposed as a noninvasive marker for oro-caecal transit time in adults and children. The present study investigates the handling of lactose [(13)C]ureide ((13)C LU) and glucose [(13)C]ureide ((13)C GU) by the gastrointestinal tract and describes the metabolic fates of these substrates and describes the extent of tracer excretion by different routes. STUDY DESIGN AND SUBJECTS: Four subjects underwent five studies in which they ingested a test meal plus (1) no substrate, (2) (13)C LU, (3) (13)C GU, (4) (13)C LU after predosing with unlabelled lactose ureide and (5) (13)C LU after predosing with glucose ureide. Subjects were studied at home with at least 1 week between tests and they all completed the study. Breath was analysed for (13)CO(2) recovery and urine was analysed for total (13)C recovery, (13)C urea recovery and (13)C GU recovery. RESULTS: The profiles and extent of tracer recovery in breath and urine were similar when either (13)C GU or (13)C LU was used, suggesting similar handling of these substrates by the gut. (13)C GU was the major (13)C-enriched species recovered in the urine even when (13)C LU was consumed. Predosing with either lactose ureide or glucose ureide increased the rate of appearance of tracer, but did not alter transit times. CONCLUSIONS: (13)C LU is hydrolysed to (13)C GU in the small intestine with the fraction of (13)C GU appearing in the urine probably limited by small intestinal permeability. Either (13)C LU or (13)C GU can be used to measure oro-caecal transit time.

Adult↗
PubMed2001

Rapid quality control analysis of (13)C-enriched substrate synthesis by isotope ratio mass spectrometry.

There is a growing interest in the use of (13)C-enriched substrates to investigate metabolic processes in humans. The non-invasive nature of (13)C breath tests makes them attractive to clinicians, particularly because they can be safely used in children. The availability of suitable (13)C-enriched substrates can limit the application of this biotechnology. We have used isotope ratio mass spectrometry to assay the chemical purity and isotopic enrichment of substrates that were synthesised to study gut transit and colonic fermentation. Lactose ureide and lactose [(13)C]ureide were synthesised by acid-catalysed condensation of lactose and urea or (13)C urea, respectively. Glucose ureide and glucose [(13)C]ureide were synthesised by similar methods but required an additional purification step to remove urea of crystallisation. Substrates were analysed by standard analytical techniques and combustion isotope ratio mass spectrometry for carbon and nitrogen content and (13)C-enrichment. Monitoring the C/N ratio proved to be a sensitive assay of chemical purity. Analysis of the percentage composition of C and N (and hence O + H) suggested that lactose ureide crystallises as the dihydrate. It was synthesised with approximately 99% chemical purity and with the theoretical enrichment. Glucose ureide was synthesised with approximately 98% chemical purity but with lower than theoretical enrichment.

Breath Tests↗
PubMed2000

(13)C natural abundance in the British diet: implications for (13)C breath tests.

Surprisingly little information is available on the natural abundance of the minor isotope of carbon, (13)C, in common foodstuffs in the British diet. This study therefore aimed to examine the (13)C natural abundance of foodstuffs from a small cross-section of the British diet. The isotopic abundance, delta per mil, was calculated by measurement of the isotope ratio (13)C:(12)C by isotope ratio mass spectrometry. Results from this study were also compared with results from a North American study to highlight the difference in isotopic abundance between Northern European foodstuffs and North American foodstuffs. Such data should prove useful to those planning tracer studies using the stable isotope (13)C where enrichment is measured against a large and variable natural abundance in the body. Minimisation of this basal variation, for example in breath CO(2), can be achieved by controlling dietary intake of foods naturally abundant in (13)C.

Algorithms↗
PubMed1999

Measurement of urinary total 13C and 13C urea by isotope ratio mass spectrometry after administration of lactose [13C]-ureide.

A method of measuring total 13C excreted in urine after oral administration of lactose [13C]-ureide was developed using isotope ratio mass spectrometry. Furthermore, a method to measure 13C urea excreted in the urine was developed. Each urine sample collected over a 24 hour period, after administration of the tracer dose, was analysed for both total 13C and 13C urea. Combustion of the dried urine samples allowed measurement of the total 13C content. Treatment of urine samples with urease (EC 3.5.1.5) and analysis by isotope ratio mass spectrometry of the CO2 evolved allowed measurement of 13C urea in the urine sample. The total 13C and 13C urea content of each urine sample, obtained throughout the protocol, were compared to total 13C and 13C urea contents of a urine sample taken before the test. This allowed calculation of the fraction of tracer incorporated into urea and the fraction of tracer excreted in total. Analyses showed that approximately 15% of the dose administered, in terms of 13C, was recovered in the urine over the sampling period. Further analysis for urinary 13C urea showed that less than 1% of the label was incorporated into urea excreted over the sampling period.

Carbon Isotopes↗
PubMed1999

Identification of motor pathways during tumor surgery facilitated by multichannel electromyographic recording.

OBJECT: The goal of this study was to determine the usefulness of electromyographic (EMG) recording in locating motor pathways near the central sulcus or internal capsule during surgery. METHODS: Multichannel EMG recordings were compared with visual observation of contralateral body movement that was elicited by direct cortical or subcortical stimulation used to identify motor pathways before and during tumor resection. The EMG recordings were more sensitive than visual observation alone in identifying motor responses: in 30% of cases, responses were identified by EMG recording alone at some point during the operation and, in 9% of cases, EMG responses were the only responses observed. Additionally, EMG recordings often detected seizure activity resulting from electrical stimulation of the cortex that could not be appreciated on visual inspection. No new motor deficits were seen postoperatively in 88% of the patients in this series. CONCLUSIONS: Using EMG recording in addition to motor pathway mapping results in greater sensitivity, allowing the use of lower stimulation levels and facilitating detection of stimulation-induced seizure activity.

Adolescent↗
PubMed1997

Venous bleeding during transsphenoidal surgery: its association with pre- and intraoperative factors and with cavernous sinus and central venous pressures.

Venous bleeding during transsphenoidal surgery for resection of pituitary tumors is a common problem that interferes with the performance of the surgical procedure. In this study, data were collected prospectively from 50 patients to determine whether there were pre- or intraoperative factors (e.g., patient demographics, type and grade of pituitary tumor, intraoperative hemodynamics) associated with venous bleeding which might be used to predict its occurrence. In addition, central venous pressure (CVP), and cavernous sinus pressure (CSP) were measured in 13 patients to evaluate the relationship of these pressures to each other and to the severity of venous bleeding. During resection of the pituitary tumor, the severity of venous bleeding was graded as minimal, moderate, or severe, the latter two grades requiring therapeutic intervention. Moderate bleeding requiring intervention occurred in 15 of the 50 patients, and resolved in all cases. Moderate bleeding was not related to CSP or CVP, and no specific associated factor was observed. CSP was not correlated with CVP, and was higher than that predicted from the CVP and the position of the patient or the hydrostatic gravitational pressure gradient. These results suggest that it is not possible to predict in advance which patients will have problems with venous bleeding, but that simple therapeutic maneuvers are effective.

Adult↗
PubMed1997

The effect of clonidine on cerebral blood flow velocity, carbon dioxide cerebral vasoreactivity, and response to increased arterial pressure in human volunteers.

BACKGROUND: Because patients may be taking clonidine chronically or may be receiving it as a premedication before surgery, the authors investigated its effect on cerebral hemodynamics. METHODS: In nine volunteers, middle cerebral artery mean blood flow velocity (Vm) was measured using transcranial Doppler ultrasonography (TCD). CO2 vasoreactivity was measured before clonidine administration (preclonidine), 90 min after clonidine, 5 microg/kg orally, then following restoration of mean arterial pressure (MAP) to the preclonidine level. In addition, Vm was measured after a phenylephrine-induced 30-mmHg increase in MAP. RESULTS: After clonidine administration, Vm decreased from 62 +/- 9 to 48 +/- 8 cm/s (P < 0.01), and MAP decreased from 86 +/- 10 to 63 +/- 5 mmHg (P < 0.01; mean +/- SD). Clonidine decreased the CO2 vasoreactivity slope from 2.2 +/- 0.4 to 1.2 +/- 0.5 cm x s(-1) x mmHg(-1) (P < 0.05); restoring MAP to the preclonidine level increased the slope to 1.60 +/- 0.5 cm x s(-1) x mmHg(-1), still less than the preclonidine slope (P < 0.05). CO2 vasoreactivity expressed as a percentage change in Vm, decreased after clonidine, 3.5 +/- 0.8 versus 2.4 +/- 0.8 %/mmHg (P < 0.05); this difference disappeared after restoration of MAP, 3.1 +/- 1.2 %/mmHg. With a 30-mmHg increase in MAP, Vm increased by 13% before and after clonidine (P < 0.05). CONCLUSIONS: Clonidine, 5 microg/kg orally, decreases Vm and slightly attenuates cerebral CO2 vasoreactivity, therefore decreased cerebral blood flow and mildly attenuated CO2 vasoreactivity should be anticipated.

Adrenergic alpha-Agonists↗