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Biomedical subjects

R A Sutton

Publications and source records attributed to R A Sutton.

At least 19 recordsLinked to original sources
PubMed2003

The use of a reconstructed three-dimensional solid model from CT to aid the surgical management of a total knee arthroplasty: a case study.

The use of a rapid prototyping method was utilised to produce a pre-operative solid model of the proximal tibia in a patient with a massive defect of the medial tibial plateau. The solid model was reconstructed from aligned sequential CT images of the knee. This was then used to determine the level of bone resection of the proximal tibia for the optimum placement of the tibial component of a total knee replacement. This technique gives the surgeon both the three-dimensional anatomical information needed to ascertain whether there is adequate bony support after cutting for the prosthesis, as well as a solid model on which to carry out the proposed surgery, before undertaking the procedure on the patient.

Arthroplasty, Replacement, Knee↗
PubMed2000

Dealing with Cerenkov radiation generated in organic scintillator dosimeters by bremsstrahlung beams.

An organic scintillator detector system has been developed for radiotherapy bremsstrahlung dosimetry. The scintillators are connected to photodiodes by light pipes as the photodiodes must be removed and shielded from the incident radiation. The photodiodes see visible and near-visible light emissions from the scintillator as well as Cerenkov and fluorescence radiation that has been generated and trapped in the scintillator and light pipe. The Cerenkov and fluorescence radiation limits the accuracy of the dosimeter. This work examines a range of methods for diminishing the signal contribution of Cerenkov and fluorescence radiation while optimizing the scintillator signal. Three methods of achieving these goals have been used. They are: reflective coatings on the scintillator, long-wavelength-emitting scintillators used in conjunction with the photodiode, and absorptive filters placed between the light guide and photodiode. The contribution of the Cerenkov radiation to the light seen by the photodiode has been modelled and the model predictions have been tested using bremsstrahlung beams of peak energy between 13 and 20 MV, showing agreement with measurement.

Biophysical Phenomena↗
PubMed2000

Water equivalence of plastic organic scintillators in megavoltage radiotherapy bremsstrahlung beams.

Plastic organic scintillators are often considered 'water equivalent' in megavoltage photon beams as they have similar atomic composition and density to water. Two plastic scintillators are evaluated for their 'water equivalence', using the Burlin cavity theory, in the photon energy range of 200 keV to 20 MeV. The Burlin theory predicts that the two investigated scintillator materials are likely to be 'water equivalent' in the energy range investigated. The prediction of the Burlin theory for one of these scintillators has been confirmed by absorbed dose measurements in bremsstrahlung beams between 13 and 19 MeV.

Calibration↗
PubMed1998

Stones and bones: bone resorption and metabolism in stoneformers.

Abnormalities of bone metabolism and osteopenia (which may be progressive) are features of idiopathic calcium stone disease. This abnormal bone metabolism may be mediated by increased levels of, or responsiveness to, calcitriol or cytokines, including interleukin-1. Bone resorption may be reduced experimentally with bisphosphonates, but for clinical management an appropriate adjustment of dietary calcium intake may be the method of choice to ameliorate bone loss.

Journal Article↗
PubMed1997

Intestinal absorption of trace amounts of aluminium in rats studied with 26aluminium and accelerator mass spectrometry.

1. Until recently studies of intestinal aluminium absorption used pharmacological amounts of stable 27Al. 2. To examine the intestinal absorption of trace amounts of different chemical compounds of aluminium, in the present study we have employed the long half-life isotope of aluminium, 26Al, and accelerator mass spectrometry. Trace amounts of 26Al (2.7-12.1 ng) as the hydroxide, citrate, citrate plus 1 mmol/kg sodium citrate, or maltolate respectively, were administered to four groups of rats (n = 9 per group) by gavage. Blood and urine samples were collected for 5 h and the 26Al content (as a percentage of the administered dose) determined by accelerator mass spectrometry. 3. The 5 h urinary 26Al excretion amounted to 0.1 +/- 0.02, 0.7 +/- 0.2, 5.1 +/- 1.5 and 0.1 +/- 0.1% of administered dose in the four groups respectively. There was a strong positive correlation between peak plasma 26Al (r = 0.98) and urinary 26Al excretion in individual animals (P < 0.001). 4. We conclude that the fractional intestinal absorption of trace oral doses of aluminium hydroxide is at least 0.1% (compared with the previous estimate of 0.01% using large 27Al oral loads). Absorption of aluminium citrate given alone is significantly greater (0.7%) and is further increased to 5% by the accompanying sodium citrate, consistent with an enhancing effect of added citrate upon mucosal aluminium permeability. Aluminium maltolate absorption approximates that of aluminium hydroxide (0.1%).

Aluminum↗
PubMed1995

Influence of electrical stimulation of the tibialis anterior muscle in paraplegic subjects. 2. Morphological and histochemical properties.

In adult paraplegic subjects one tibialis anterior muscle received daily electrical stimulation for 4 weeks at twice the motor threshold to determine changes of morphological and histochemical profiles (this paper) and of contractile properties (preceding paper). Bilateral biopsies, obtained 4 weeks before, and immediately after, electrical stimulation, were studied for fibre type proportions, fibre diameters, oxidative capacity, microvasculature and histopathology. Before stimulation the biopsies showed disuse with increased type 2 fibre proportions and decreased oxidative capacity (succinate dehydrogenase (SDH) activity). The effects of two stimulus patterns were compared. Following stimulation SDH activity increased significantly in all stimulated muscles. Inconsistent changes occurred in fibre type proportions, fibre diameters, capillary density and capillary/fibre ratios. Both stimulus patterns evoked similar results. In five/seven subjects subsarcolemmal vacuolation was observed. Electrical stimulation for 4 weeks at only twice motor threshold improves oxidative capacity, but different stimulus parameters are probably needed for significant fibre type conversion.

Adenosine Triphosphatases↗
PubMed1995

Influence of electrical stimulation of the tibialis anterior muscle in paraplegic subjects. 1. Contractile properties.

In adult paraplegic subjects one tibialis anterior muscle received daily electrical stimulation for 4 weeks at twice motor threshold to determine changes of its contractile properties (this paper) and its morphological and histochemical profiles (following paper). Force, speed of contraction and fatigue resistance were assessed by percutaneous electrical stimulation of the muscle with torque measured about the ankle. Comparative contractile tests were performed on 51 normal adult subjects and new parameters for force measurement proposed, particularly where maximum voluntary contraction cannot be obtained. In paraplegic subjects before stimulation the tibialis anterior muscle showed evidence of disuse with decreased force, faster contraction and relaxation, and reduced fatigue resistance. The effects of two stimulus patterns were compared: 10 Hz, and 10 Hz with 100 Hz bursts. After stimulation contraction was slower, fatigue resistance increased and there was a tendency for force to increase. No differences occurred using the different stimulus patterns. Four weeks later fatigue resistance was partially maintained, while speed of contraction reverted to pre-stimulus levels.

Adult↗
PubMed1994

Magnesium deficiency: pathophysiologic and clinical overview.

Magnesium is an essential cation, involved in many enzymatic reactions, as a cofactor to adenosine triphosphatases. It is critical in energy-requiring metabolic processes, as well as protein synthesis and anaerobic phosphorylation. Serum Mg concentration is maintained within a narrow range by the kidney and small intestine since under conditions of Mg deprivation both organs increase their fractional absorption of Mg. If Mg depletion continues, the bone store contributes by exchanging part of its content with extracellular fluid (ECF). The serum Mg can be normal in the presence of intracellular Mg depletion, and the occurrence of a low level usually indicates significant Mg deficiency. Hypomagnesemia is frequently encountered in hospitalized patients and is seen most often in patients admitted to intensive care units. The detection of Mg deficiency can be increased by measuring Mg concentration in the urine or using the parenteral Mg load test. Hypomagnesemia may arise from various disorders of the gastrointestinal tract, conditions affecting Mg renal handling, or cellular redistribution of Mg. The gastrointestinal causes include the following: protein-calorie malnutrition, the intravenous administration of Mg-free fluids and total parenteral nutrition, chronic watery diarrhea and steatorrhea, short bowel syndrome, bowel fistula, continuous nasogastric suctioning, and, rarely, primary familial Mg malabsorption. The renal causes include Bartter's and Gitelman's syndrome, post obstructive diuresis, post acute tubular necrosis, renal transplantation, and interstitial nephropathy. Many therapeutic agents cause renal Mg wasting and subsequent deficiency. These include loop and thiazide diuretics, aminoglycosides, cisplatin, pentamidine, and foscarnet. Magnesium deficiency is seen frequently in alcoholics and diabetic patients, in whom a combination of factors contributes to its pathogenesis. Hypomagnesemia is known to produce a wide variety of clinical presentations, including neuromuscular irritability, cardiac arrhythmias, and increased sensitivity to digoxin. Refractory hypokalemia and hypocalcemia can be caused by concomitant hypomagnesemia and can be corrected with Mg therapy. The dose and route of administration of Mg in the treatment of hypomagnesemia is dictated by the clinical presentation, the degree of Mg deficiency, and the renal function.

Animals↗
PubMed1994

Renal microangiopathy in the primary antiphospholipid syndrome: a case report with literature review.

We report the case of a 52-year-old male patient with recurrent thrombosis from 'primary antiphospholipid syndrome' who developed renal microangiopathy. Despite anticoagulant therapy with coumadin, serum creatinine progressively increased from 398 to 592 mumol/l and platelets decreased to 43,000. The patient responded to high-dose methylprednisolone and aspirin and the renal function improved. A review of the literature disclosed 4 other cases of association between primary antiphospholipid syndrome and renal microangiopathy. The clinical characteristics of these cases are discussed.

Adult↗
PubMed1994

Enteric and mild hyperoxaluria.

Enteric hyperoxaluria complicates extensive disease or resection of the small intestine in the presence of an intact colon, and is associated with calcium oxalate nephrolithiasis. In addition to hyperoxaluria these patients have a low urine volume, low urinary ionic strength and hypocitraturia. Many forms of treatment have been recommended, but none has been subjected to a prospective clinical trial. Mild idiopathic hyperoxaluria is reported in 8-50% of idiopathic calcium oxalate stoneformers. Several pathophysiological mechanisms have been proposed, including low dietary calcium and possible oxalate transport defects in the gut and/or the kidney. Mild hyperoxaluria, or a high oxalate:calcium ratio in the urine, may be particularly important risk factors for calcium oxalate stone formation; an approach to the correction of these abnormalities is proposed.

Calcium Oxalate↗
PubMed1994

Tissue disposition of 26aluminum in rats measured by accelerator mass spectrometry.

A trace quantity of 26aluminum (26Al) was administered intravenously to 1 normal and 1 uremic rat. After a 3-week period, the animals were sacrificed and samples of bone, muscle, kidney, liver, heart, and brain were analyzed for their 26Al content. In the normal and uremic rats, most of the tissue 26Al was found in bone amounting to 0.9% and 2.0%, respectively, of administered dose/g dry weight of tissue. Much smaller amounts of isotope were found in the other tissues in both animals. In the normal rat, the descending order of 26Al content in other tissues was: kidney, 0.2% > liver, 0.06% > heart, 0.03%, > brain and muscle, 0.02%. In the uremic rat, the same order of tissue 26Al content was found with kidney, 0.37% > liver, 0.06% > heart, 0.02% > brain and muscle, 0.01% per g dry weight of tissue. When expressed per g wet weight of tissue in the 2 animals, a similar order of tissue 26Al content was found. In comparing the amount of 26Al in the bone of the 2 rats, the uremic animal was found to have more than twice that found in the bone of the normal rat when expressed either per g dry or wet weight of bone. However, 26Al content of other tissues was similar in the 2 animals. This suggests that uremic bone may have a greater affinity for aluminum than normal bone, but kidney, liver, brain, heart, and muscle appear to behave similarly in uremic and normal rats in regard to incorporation of a single trace dose of isotope in the 3-week time frame of the present study.

Aluminum↗
PubMed1993

Effect of dietary oxalate and calcium on urinary oxalate and risk of formation of calcium oxalate kidney stones.

Dietary restriction of oxalate intake has been used as therapy to reduce the risk of recurrence of calcium oxalate kidney stones. Although urinary oxalate is derived predominantly from endogenous synthesis, it may also be affected by dietary intake of oxalate and calcium. The risk of increasing urinary oxalate excretion by excessive consumption of dietary oxalate is greatest in individuals with a high rate of oxalate absorption, both with and without overt intestinal disease. Although oxalate-rich foods enhanced excretion of urinary oxalate in normal volunteers, the increase was not proportional to the oxalate content of the food. Only eight foods--spinach, rhubarb, beets, nuts, chocolate, tea, wheat bran, and strawberries--caused a significant increase in urinary oxalate excretion. Restriction of dietary calcium enhances oxalate absorption and excretion, whereas an increase in calcium intake may reduce urinary oxalate excretion by binding more oxalate in the gut. This review of the literature indicates that initial dietary therapy for stone-forming individuals can be limited to the restriction of foods definitely shown to increase urinary oxalate. The effects of oxalate-restricted diets on urinary oxalate should be evaluated by means of laboratory analyses of urine composition. Subsequent long-term therapy can be recommended if beneficial results are obtained from oxalate restriction at an appropriate calcium intake.

Animals↗
PubMed1993

Transient syndrome of inappropriate antidiuretic hormone secretion during pregnancy.

Plasma osmolality normally decreases in early pregnancy, reaching a minimum at approximately 10 weeks and remaining depressed until term. This is associated with a mean decrease of 4 mEq/L in the plasma sodium level, and with an altered threshold for arginine vasopressin (AVP) release and for thirst. We describe a patient who developed more severe hyponatremia (120 mEq/L), which accompanied the development of hypertension and edema at 37 weeks in her fourth pregnancy. Hyponatremia and hypo-osmolality were associated with marked elevation of the plasma AVP level. The hyponatremia and elevated AVP level resolved after the delivery of the infant. To our knowledge, this is the first reported example of transient inappropriate antidiuretic hormone secretion (SIADH) associated with pregnancy.

Adult↗
PubMed1993

Mechanism of polyuria after cisplatin therapy.

Cisplatin is an antineoplastic agent. Several nephrotoxic effects are associated with its use including chronic and acute renal failure, renal magnesium wasting, and polyuria. We have investigated polyuria in groups of rats treated with cisplatin at doses of 2.5 and 5 mg/kg body weight given once weekly for 3 weeks to determine possible mechanisms of this impairment. After cisplatin administration, glomerular filtration rate was reduced and significant increases in sodium and water loss were also seen. These changes were associated with decreases in urinary cAMP. Inner medullary collecting duct (IMCD) cells were removed from these animals and were stimulated with graded doses of vasopressin. Cells from cisplatin-treated rats showed an impaired response in cAMP generation to vasopressin stimulation as compared to cells from normal animals. To determine more precisely the site of impairment, the adenylate cyclase complex of the IMCD cells was further studied with forskolin and NaF. Forskolin was used to probe the catalytic unit activating adenylate cyclase, and NaF the guanine nucleotide regulatory protein (G protein). In response to forskolin, cells from cisplatin-treated rats and normal rats responded similarly in generating cAMP. However, following NaF, the cAMP response was blunted in the cells from the cisplatin rats. These results suggested that the catalytic unit was not injured by cisplatin (forskolin study) but the G protein was (NaF). In conclusion, the present study suggests that the polyuria seen following cisplatin administration is associated with an end-organ resistance to vasopressin manifested by reduced cAMP generation, secondary in part or whole to a defect at the level of the G protein.

Animals↗
PubMed1993

Abnormal renal magnesium handling.

The normal fractional urinary excretion of filtered magnesium is about 5%. In magnesium deficiency in man, the kidneys can normally reduce the 24-hour urinary magnesium excretion to less than 1 mmol (24 mg) via unknown mechanisms, and initially without a fall in plasma magnesium concentration. Renal magnesium wasting may be defined as a urinary excretion greater than 1 mmol/day in the presence of hypomagnesemia (plasma magnesium < 0.7 mmol/l). Congenital renal magnesium wasting occurs in several syndromes including Bartter's syndrome in which it is associated with hypercalciuria, and the defect may be in the thick ascending limb of Henle's loop, and Gitelman's syndrome in which there is hypocalciuria, and the defect may be in the distal convoluted tubule. Other causes of renal magnesium wasting include diabetes mellitus, hypercalcemia and diuretics. Magnesium wasting may also result from various toxicities including those of cis-platinum, in which the biochemical features resemble Gitelman's syndrome, and those of aminoglycosides, pentamidine and cyclosporin. Calcitriol deficiency may also contribute to renal magnesium wasting in some circumstances. Mild hypermagnesemia may occur in familial hypocalciuric hypercalcemia and may reflect abnormal sensitivity of the loop of Henle to calcium and magnesium ions. By contrast, the hypermagnesemia that occurs in chronic renal failure results from the reduced glomerular filtration of magnesium.

Animals↗
PubMed1993

Plasma and urinary oxalate and glycolate in healthy subjects.

High-performance ion chromatography (HPIC) has been widely used for oxalate analysis and, more recently, for glycolate analysis. We describe a procedure for sample preparation in which the plasma ultrafiltrate is acidified during harvesting with a cation-exchange resin, and the chloride is removed before the ion chromatography, which is performed with a newly developed AS10 column. The same ultrafiltrate sample is analyzed for glycolate. For plasma oxalate, the mean recovery of sample in eluted fractions was 95-96%, and intraassay CV was 6.2-8.1%. The reference interval (mean +/- 2 SD) for men was 0.8-3.2 mumol/L and for women, 1.0-2.6 mumol/L. For urinary oxalate, the reference interval for men was 175-560 mumol/day and for women, 107-432 mumol/day. For plasma glycolate, the mean analytical recovery was 96-98%, and the intra-assay CV was 2.4-6.2%. The reference interval for men was 1.9-7.5 mumol/L and for women, 1.4-7.4 mumol/L. For urinary glycolate, the reference interval for men was 0-1400 mumol/day and for women, 91-1001 mumol/day.

Chromatography, High Pressure Liquid↗
PubMed1992

Radiation dose reduction in diagnostic x-ray procedures.

The performance of K-edge filters to modify the x-ray spectrum is investigated experimentally in a variety of clinical situations involving bone/soft tissue imaging, with the aim of improving the optimization between image contrast and patient exposure. The results show that simultaneous improvement of contrast and reduction of exposure is possible for a wide range of patient sizes. For conditions of fixed contrast skin exposure reductions of better than 50% and integrated dose reductions of up to 30% have been achieved with tolerable increases in tube load. Rare earth salt solutions were used as an inexpensive alternative source of K-edge filtration, and their performance was found to be in no way inferior to that of expensive metal foils.

Filtration↗