Search PubMed⌕ Search

Biomedical subjects

T R Overton

Publications and source records attributed to T R Overton.

At least 19 recordsLinked to original sources
PubMed1992

Bone mass measurements in the distal forearm using dual-energy x-ray absorptiometry and gamma-ray computed tomography: a longitudinal, in vivo comparative study.

Indices of bone mass were measured in 23 volunteers weekly over 14-16 weeks using dual-energy x-ray absorptiometry (DEXA) and special-purpose computed tomography (gamma-CT). In vitro, the precision for both systems was excellent (coefficient of variation less than 0.5%). Over 4 months, the precision in vivo (average CV for all subjects) for DEXA measures (BMD, g/cm2, and BMC, g/cm) varied between 0.6 and 1.1%; with gamma-CT it varied from 1.1% for TBD (g/cm3) to 2.2% for CBD (g/cm3). Correlation between the indices of bone mass measured using DEXA and gamma-CT at the ultradistal site was moderate, but these indices were not correlated at the distal third site. When BMD and BMC were derived from the CT index IBD, however, the correlation between these gamma-CT indices and the corresponding DEXA indices was high for both ultradistal and proximal radial sites.

Absorptiometry, Photon↗
PubMed1992

Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography.

Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone "space"), were monitored continuously using gamma-ray computed tomography (gamma-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3-4.7 g of Sr over a period of 110-160 minutes into 20-kg dogs resulted, within 6-8 hours, in an increase of 0.019-0.045 cm-1 (P less than 0.002) in the LAC. Calibration of the gamma-CT system showed that 0.44 mg/cm3 of Sr produced a change of 0.01 cm-1 in the LAC. Using this conversion factor, the Sr concentration in the trabecular bone space resulting from infusion, as measured by flame atomic absorption spectroscopy, agreed with that predicted by the change observed in the LAC. Sr present in the serum and urine was consistent with the changes observed in the LAC over the study period. Control dogs infused with mineral-free solutions showed no change in LAC. Calcium equivalents required to give the changes observed in the LAC using Sr indicate that variations in skeletal turnover in man can be monitored in the peripheral skeleton using gamma-CT.

Animals↗
PubMed1992

Vitamin B12 and folate status of a selected group of free-living older persons.

Vitamin B12 and folate status was determined in 50 male and 47 female free-living subjects (65-77 years) in winter and summer. The mean intake calculated from 3-day food records met the Canadian recommended intake (RNI) for both gender and season, however, probability analysis of dietary data revealed a number of subjects at risk of deficiency. Although the mean plasma levels were within the acceptable range for both vitamins, some 9 to 14% of individual subjects had folate plasma levels below normal. Fewer subjects had subnormal plasma vitamin B12 levels. Although mean values for dietary intake and plasma concentration of folate and vitamin B12 may indicate nutritional adequacy, a proportion of an older population may be at nutritional risk.

Aged↗
PubMed1990

A special purpose x-ray fan-beam CT scanner for trabecular bone density measurement in the appendicular skeleton.

A special purpose x-ray CT scanner with the capability of scanning objects 75-220 mm in diameter with constant relative geometrical resolution has been developed. The data collection scheme for the scanner uses multiple rotations of a linearly shifted, asymmetric fan beam permitting user-defined variable resolution. Details of hardware and the calibration procedures for the scanner are described and the methods used to measure trabecular bone density (TBD) in the peripheral skeleton are outlined. The standard error of estimate (SEE) of a calibration line of pixel value as a function of K2HPO4 concentration was determined to be 0.07%. The short-term, in vivo precision of the TBD determination, by repeated measurements of a volunteer with repositioning between each measurement, was +/- 0.67% (coefficient of variation (CV] with a 50s scan time and a radiation dose of less than 20 mR per slice.

Bone Density↗
PubMed1990

Dental health status and treatment needs of elderly residents of Edmonton, Alberta.

The oral health of 140 independent elderly volunteers, selected from different sections of Edmonton, Alberta, was assessed in conjunction with their nutritional and medical status, in an attempt to evaluate the dental needs of this population. Dental caries was assessed using WHO standards and the CPITN was used in assessing periodontal and gingival health needs. The mean age of the participants was 70.9 +/- 2.6 years. The average time since they had last seen a dentist was 3.0 +/- 6.2 years. Twenty-six percent of the group were edentulous and wore full dentures. An evaluation of denture hygiene and retention showed that 53 per cent of all maxillary and 57 per cent of all mandibular appliances exhibited poor hygiene; 33 per cent and 54 per cent, respectively, had problems with retention and/or occlusion. Only 12 per cent of the group exhibited any sort of mucosal pathology, all of which was related to ill fitting dentures. The total population had a mean of 15.0 +/- 11.1 teeth, only 0.5 of these were decayed, while 8.9 were restored. CPITN scores taken from a total of 511 sextants with standing teeth showed that 16 per cent of the group exhibited bleeding upon probing, 29 per cent had calculus, 13 per cent exhibited pocketing, while 3.6 per cent had deep pockets. Sixty-seven per cent of the population required dental treatment, none of whom needed emergency intervention. Over 49 per cent of the dentate population could benefit from prophylaxis; 16 per cent required more definitive periodontal treatment. Forty-five per cent of the denture population required treatment.

Aged↗
PubMed1987

Performance evaluation of density measurements of axial and peripheral bone with x-ray and gamma-ray computed tomography.

We examined sources of error in bone measurements made with computed tomography (CT) using a whole-body scanner (GE 8800) and a peripheral-bone CT scanner (developed at the University of Alberta). We investigated the influence of various factors on trabecular bone density: homogeneity and noise in the image plane, linearity of calibration, body size, effects of cortical bone, and the image analysis procedure. With the GE 8800 scanner, the precision (SD) of measurements of a single vertebra is expected to be +/- 1.65% (noise: +/- 0.22%, calibration: +/- 1.3%, analysis: +/- 1%); the accuracy, excluding consideration of marrow fat, varied between -2.7 and +7.3% (compact-bone thickness: 2-5%, body size: -2.5 - +1.5%, calibration: -0.47 - +0.77%). With the peripheral-bone CT scanner, the total precision error (+/- 0.53%) was dominated by noise, with only a minor contribution from the analysis procedure (+/- 0.04%); accuracy varied between -0.6 and +3.4% (effect of cortical bone: up to 3.0%; changes in size of object: -0.59 - +0.4%). The magnitude of these errors was determined under 'ideal' conditions, mostly through phantom measurements; therefore, the errors represent optimistic lower limits in clinical application. Furthermore, measurements of density of cortical bone were not reliable for bone thicknesses of less than about 4 mm with the GE 8800 scanner and less than about 1.5 mm with the peripheral scanner.

Absorptiometry, Photon↗
PubMed1979

Treatment of subarachnoid hemorrhage with sodium nitroprusside and phenylephrine: an experimental study.

The effectiveness of simultaneous intravenous sodium nitroprusside and phenylephrine in improving the cerebrovascular disturbances and survival rate after induced subarachnoid hemorrhage (SAH) was studied in the cynomolgus monkey. We measured regional cerebral blood flow (rCBF) using the intra-arterial xenon-133 clearance technique. In our experimental animal model, SAH was associated with a persistent reduction in rCBF, elevation of cerebrovascular resistance (CVR), cerebral vasospasm for the duration of the study (150 minutes), and poor survival. For animals receiving the treatment regime (administered approximately 25 minutes after the induced SAH), rCBF remained low, CVR was high, and cerebral vasospasm was persistent. Survival in this group was the same as that observed for the untreated animals. Simultaneous administration of sodium nitroprusside and phenylephrine was ineffective in improving rCBF, CVR, cerebral vasospasm, or survival after SAH. In the control group (receiving only the treatment and not an intracranial insult), rCBF was below resting levels both during and after therapy, indicating impaired cerebral autoregulation. (Neurosurgery, 5: 688--595, 1979).

Animals↗
PubMed1979

Cerebrovascular responses to subarachnoid blood and serotonin in the monkey.

Preliminary in vitro experiments were performed to determine the serum concentration of serotonin in the monkey, and the ability of cyproheptadine to block serotonin and serum-induced contractions in monkey cerebral arteries. Thirty-four cynomolgus monkeys were subsequently used to study changes in regional cerebral blood flow (CBF) obtained by the intracartoid 133Xe technique, and in the angiographic cerebral arterial caliber resulting from subarachnoid injection of artificial cerebrospinal fluid (CSF), blood, and serotonin. Five animals in each injection group were given 1.0 mg/kg intravenous cyproheptadine (a serotonin-blocking agent) during the post-injection period. Subarachnoid injection of artificial CSF produced no change in CBF or arterial caliber. Post-injection administration of cyproheptadine also had no effect on these parameters. A subarachnoid injection of fresh autogenous blood produced a significant but transient (less than 1 hour) decrease in CBF and moderate vasospasm, which lasted at least 3 hours. This vasospasm was essentially unaffected by intravenous cyproheptadine. The CBF and arterial caliber were unchanged following a subarachnoid injection of serotonin at concentrations (5 x 10(-6)M) present in normal monkey serum. In contrast, 5 x 10(-6) M serotonin invariably produced near maximal contractions in the in vitro cerebral artery preparations. Higher (x10) serotonin concentrations caused a transient CBF response similar to that obtained with blood. However, the cerebral vasospasm induced was of shorter duration than that obtained with blood. These results do not support a major role for serotonin in the production of post-subarachnoid hemorrhage vasospasm. Moreover, our data indicate that in vitro experiments do not reflect the ability of serotonin to constrict cerebral arteries in the intact animal.

Animals↗
PubMed1978

Effects of age on regional residual volume.

Forty-one normal non-smokers between the ages of 20 and 80 were studied to determine if the increased residual volume, known to occur with aging, results from increased residual volume throughout, or only in specific regions of the lung. The subjects were dividied into groups consisting of 20-29, 30-39, 40-49, 50-69, and 70+ yr. Measurements of regional residual volume to regional total lung capacity ratio (RVr/TLCr) were made using zenon-133 and a multidetector analysis system in which five zones (from top to bottom) were analyzed in each lung. Closing volume was also measured. The subjects were in the sitting position for all studies. The results showed regardless of age, the RVr/TLCr was higher at the top than at the bottom of the lung. In addition, the ratio of upper to lower RVr/TLCr was not significantly different between any of the age groups. The results can be explained if airways throughout the lung close at higher volumes as age increases, or if altered emptying sequences within regions occur due to retarded emptying of highly compliant lung regions.

Adult↗
PubMed1978

Cerebral arterial responses to induced hypertension following subarachnoid hemorrhage in the monkey.

Regional cerebral blood flow (rCBF), angiographic cerebral arterial caliber, and cerebrospinal fluid (CSF) pressure were measured in rhesus monkeys to determine the effect of experimentally induced subarachnoid hemorrhage (SAH) on cerebral arterial responses to graded increases in blood pressure. These measurements were also performed in a control group of monkeys subjected to a mock SAH by injection of artificial CSF into the cerebral space. Before subarachnoid injection of blood or artificial CSF, graded increases in mean arterial blood pressure (MABP) to a level 40% to 50% above baseline values had no effect on rCBF. The major cerebral arteries constricted and CSF pressure remained unchanged. Similar responses were observed after injections of artificial CSF. When MABP was increased in animals that had been subjected to subarachnoid injection of blood, rCBF increased and was associated with dilatation of the major cerebral arteries and moderate increases in CSF pressure. These results demonstrate that cerebral arterial responses to increases in blood pressure may be abnormal in the presence of subarachnoid blood. The manner in which abnormal cerebral arterial reactivity, changes in blood pressure, and vasospasm combine to determine the level of cerebral perfusion following SAH is postulated.

Animals↗
PubMed1977

Frequency dependence of ventilation distribution in normal and obstructed lungs.

Differences in regional pulmonary time constant may cause ventilation distribution to vary with breathing frequency and frequency-dependent changes in regional ventilation per unit volume might be expected. We measured the regional distribution of inhaled xenon-133 (133Xe) at 10 and 60 breaths/min in normal subjects and in patients with a clinical diagnosis of chornic bronchitis or asthma. Breathing frequency had no siqnificant effect on ventilation distribution in normals but in patients with chronic bronchitis ventilation decreased in the lower lung regions at 60 breaths/min compared with 10 breaths/min. In six asthmatic patients the lung regions demonstrating the greatest frequency-dependent reductions in ventilation, which were assumed to have the greatest time constants, also showed decreased ventilation-perfusion ratios (V/Q) measured by standard 133Xe techniques. Bronchodilator increased ventilation more than perfusion in these regions and thus V/Q ratio increased toward the normal range. These results imply that measurement of the frequency dependence of regional ventilation provides information about the relative distribution of airway obstruction, and that airway function in the most obstructed lung regions in asthmatics is improved following bronchodilator therapy.

Asthma↗
PubMed1976

Bone demineralization in renal failure: a longitudinal study of the distal femur using photon absorptiometry.

The bone mineral content (BMC) of the lower end of the femur was measured by photon absorptiometry in 87 patients with chronic renal failure. The gamma-ray photon source was Am241. Serial measurements were obtained for up to two years. The mean BMC of the adult patients, comprising: 18 pre-dialysis (CRF), 41 chronic haemodialysis (CHD) and 19 renal transplant (RT) patients were all significantly lower than controls with the exception of the male CRF group. Two adults and one child on chronic haemodialysis showed a significant rate of bone loss (less than 2% per year). In one of these adults the addition of daily oral 1 alpha hydroxycholecalciferol was associated with no further reduction in BMC. Two children and one adult on chronic haemodialysis showed a significant rate of increase in BMC (less than 2% per year). This adult had had a tendency to loss of BMC on standard CHD treatment but after receiving parenteral 1,25 dihydroxycholecalciferol three times weekly showed a significant rate of loss of BMC on serial measurement. Two adults and one child with CRF had a significant rate of increase in BMC on standard treatment.

Adolescent↗
PubMed1976

An automatic bolus injector for use in radiotracer studies of blood flow: design and evaluation.

An electromechanical device is described which automatically injects the radiotracer bolus used in the measurement of cerebral blood flow. It consists of two electronically controlled, solenoid operated syringes, one containing the radiotracer solution and the other heparinized saline. Results are presented which show that use of the automatic bolus injector in place of hand injection leads to an improvement in the precision of measured flow values. Additional advantages of the device are discussed.

Animals↗