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Biomedical subjects

M A Laskey

Publications and source records attributed to M A Laskey.

31 records · Page 2Linked to original sources
PubMed1992

Comparison of the effect of different reference data on Lunar DPX and Hologic QDR-1000 dual-energy X-ray absorptiometers.

We have investigated whether the Lunar DPX (software 3.4) and Hologic QDR-1000 dual-energy X-ray absorptiometers have comparable normal reference databases for the spine and femur of white UK and USA subjects. After conversion for systematic differences in absolute bone density values between the two systems, the reference databases were very similar for the spine in young subjects, but there were clear differences in the femur databases of young females and males of all ages. These differences were confirmed by comparing the percent age-matched and young values determined by the two systems for subjects scanned on both systems. Thus the diagnosis and management of a patient could differ, depending on the system used for the bone density measurements.

Absorptiometry, Photon↗
PubMed1992

The influence of tissue depth and composition on the performance of the Lunar dual-energy X-ray absorptiometer whole-body scanning mode.

To assess the performance of the Lunar dual-energy X-ray absorptiometer (DPX) whole-body scanning mode (software version 3.1), a simple phantom was devised. This had known but variable amounts of lard to represent fat, and water to represent fat-free tissue. The bone mineral content of the phantom remained constant and consisted of the Lunar spine phantom to represent the spine/trunk and a slab of aluminium to represent the head. This phantom was scanned using the whole-body mode by the Lunar DPX to determine bone mineral content (BMC), area, bone mineral density (BMD), and body composition in terms of fat and fat-free tissue. The determinations of total tissue mass were very accurate and precise but fat tissue mass was slightly overestimated (103% of calculated value) and lean tissue mass slightly underestimated (98% of calculated value). The spine and head sections of the phantom were scanned individually using the spine mode and hence by addition the total BMC, area, and BMD of the whole phantom were determined. These results were compared to the bone mineral results obtained using the whole-body mode. The whole-body mode gave higher values for BMC and area than spine-mode measurements (at depths above 10 cm). This discrepancy increased with increasing depths of water (140% and 170% respectively of spine-mode value at soft-tissue depths of 22 cm and 15% fat). The values for BMD of the whole phantom tended to decrease with increasing depths of water and were lower than spine-mode values at tissue depths above 12cm.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1991

Bone mineral content of British and rural Gambian women aged 18-80+ years.

The bone mineral content (BMC) of the mid-shaft radius was measured in 446 rural Gambian and 349 British women aged 18-80+ years using single-photon absorptiometry. The two groups of women differed substantially in habitual calcium intake, calcium requirements for reproduction, physical activity and incidence of minimal-trauma fractures. The relationships of BMC with bone width (BW) and with body weight and height were explored using stepwise multiple regression analysis. The pattern of BMC with age was similar in The Gambia and Britain; BMC increased slightly to a peak at the end of the fourth decade followed by a decrease of about 30% between 40 and 70+ years. Gambian women had significantly lower BMC than British women of the same age (-5.6%, P less than 0.001) but after adjusting for weight, height and BW, the BMC of Gambian women was shown to be slightly higher than that of British women (+2.1%, P less than 0.05).

Absorptiometry, Photon↗
PubMed1991

A semi-automated micromethod for the determination of calcium and phosphorus in human milk.

A simple, semi-automated method for the analysis of calcium and phosphorus in small volumes of human milk is described. Samples are ashed, digested with dilute hydrochloric acid and assayed with commercially available kits on a centrifugal analyser. The precision and accuracy of the method are similar to those of standard manual methods using larger volumes of milk. Analysis of human milk for phosphorus without prior ashing and digestion gives observed concentrations only 30-40% of their true value.

Autoanalysis↗
PubMed1991

Comparative performance in vitro and in vivo of Lunar DPX and Hologic QDR-1000 dual energy X-ray absorptiometers.

The measured absolute bone mineral density values of spine and femur and their precision were compared on two dual energy X-ray absorptiometers, the Lunar DPX and the Hologic QDR-1000. There were systematic differences between the two systems, the Lunar DPX always giving a higher bone density value. The ratio of the mean Lunar DPX/Hologic QDR-1000 bone density measurements obtained in vivo was 1.13 g/cm2 for spine (L2-L4) and 1.20-1.43 g/cm2 for femur measurements. For both systems, short- and long-term precision (coefficient of variation) was below 0.5% for spine in vitro measurements and below 1.5% for neck of femur in vitro measurements. Precision of in vivo measurements was less good, especially for femur measurements. The coefficient of variation of spine measurements was dependent on bone density and deteriorated with decreased bone mineral density and increased body thickness.

Absorptiometry, Photon↗
PubMed1990

Influence of heparin therapy on percutaneous transluminal coronary angioplasty outcome in unstable angina pectoris.

The acute procedural outcome of percutaneous transluminal coronary angioplasty in 304 patients with unstable angina was retrospectively examined with respect to the influence of prolonged preprocedural intravenous heparin therapy. Clinical and angiographic success in 135 patients receiving heparin therapy for greater than or equal to 24 hours was 91% while such success was noted in 81% of patients not treated with heparin (p = 0.02). The incidence of immediate postprocedural thrombotic vessel occlusion was higher in the nonheparin group than in the heparin-treated group (8.3 vs 1.5%, respectively, p less than 0.01). In addition, the overall rate of thromboembolic target and branch or distal vessel occlusion was 12.4% in the nonheparin group and 1.5% in the heparin-treated group (p less than 0.001). Thus, prolonged preprocedural intravenous heparin administration in this well-defined group of patients with unstable angina resulted in an improved procedural success rate and a significant decrease in the risk of abrupt vessel closure. These observations are concordant with current understanding of the pathophysiology of unstable angina.

Aged↗
PubMed1990

Influence of heparin therapy on percutaneous transluminal coronary angioplasty outcome in patients with coronary arterial thrombus.

The clinical and angiographic outcome of 18 patients with coronary thrombus undergoing percutaneous transluminal coronary angioplasty without antecedent heparin therapy was compared to that of a group of 35 patients receiving pre-procedural heparin therapy. The former group had a significant reduction in angiographic success (61 vs 94%, p less than 0.05) and a significant increase in immediate postprocedural thrombotic arterial occlusion (33 vs 6%, p less than 0.05). This difference existed despite equivalent frequencies of antiplatelet therapy. Prolonged intravenous heparin therapy before angioplasty in the setting of coronary thrombus improves the overall success rate and lessens the likelihood of periprocedural coronary arterial thrombosis.

Angiography↗
PubMed1990

Bone mineral content of Gambian and British children aged 0-36 months.

The influence of age, sex and body size on the bone mineral content of the radius (BMC) measured by single-photon absorptiometry has been studied in 134 British and 243 rural Gambian children aged 0-36 months. Growth rates and childhood nutrition, including calcium intakes, were markedly different in the two communities. In both groups BMC increased with age and was higher in boys (8%, P less than 0.001). Adjustment for body size (height, weight, bone width), using multiple regression analysis, removed the age effect and reduced the sex difference to 4% (P less than 0.01). Gambian children had significantly lower BMCs than British children of the same age (P less than 0.001), averaging 11% close to birth and diverging to a calculated difference of 31% at 36 months. The differential was reduced after adjustment for body size but remained significant (P less than 0.01) with BMC values diverging from birth to a predicted difference of 12% at 15 kg body weight. The extent to which these results reflect the low calcium intakes of Gambian children requires further study.

Aging↗
PubMed1990

Breast-milk calcium concentrations during prolonged lactation in British and rural Gambian mothers.

Detailed investigation of breast-milk calcium concentrations during 2 years of lactation have been conducted in Cambridge, UK, and rural Gambia. Mature milk concentrations remained steady for 3 months but declined during months 4-12 by over 25% (p less than 0.001). The pattern was identical in both communities despite differences in breast-feeding practices. Calcium concentrations were not related to feed frequency or breast-milk sodium concentrations, suggesting that breast involution is not responsible for the decrease after 3 months. Breast-milk calcium concentrations were characteristic of the individual, varied twofold between mothers and were independent of maternal age, parity and milk output. Gambian breast-milk contained 19% less calcium than Cambridge milk, throughout lactation (p less than 0.001). The extent to which this reflected the lower calcium intakes of Gambian mothers is unknown. Further studies are required to determine factors regulating breast-milk calcium secretion.

Breast Feeding↗
PubMedDate not supplied

Changes in body fat: measurements by neutron activation, densitometry and dual energy X-ray absorptiometry.

The measurement of body fat in ten subjects (BMI from 22 to 43 kg/m2), and in particular the changes arising from a ketogenic diet, by the techniques of in vivo neutron activation analysis (NAA), densitometry (using two- and four-compartment models) by under water weighing (UWW) and dual energy X-ray absorptiometry (DXA) was compared. The association between techniques for the fat changes was generally high (r = 0.70 to 0.98) and significant (p < 0.05). Assessment of agreement between DXA and the other techniques revealed discrepancies with significant slope and high association (r = -0.81 and -0.64). Whilst NAA and UWW appeared to measure similar changes, DXA underestimated small changes.

Absorptiometry, Photon↗
PubMedDate not supplied

Prediction of body composition in elderly men over 75 years of age.

A comprehensive number of body composition predictions (involving weight, height, skinfold thicknesses, bioelectrical impedance and near-infrared interactance-NIRI) were evaluated against total body water (TBW from isotope dilution), in 23 randomly selected men over 75 years old, and dual-energy X-ray absorptiometry (DXA), in 15 volunteers from this group. Comparisons were made between anthropometric and impedance methods for estimating limb muscle mass (obtained using DXA). Bias and 95% limits of agreement between measured TBW and DXA estimates were -2.1 kg and 3.1 kg, respectively (for fat, 5.4% and 6.1% body weight). Agreement between TBW predictions and reference measurements was remarkably variable, irrespective of whether TBW was predicted from TBW-specific equations or indirectly from estimates of fat or fat-free mass: for predictions using anthropometry, bias ranged from -4.7 kg to 1.6 kg and 95% limits of agreement from bias +/- 3.8 kg to +/- 5.0 kg; using impedance, bias was -8.8 kg to 3.2 kg and 95% limits of agreement were bias +/- 3.6 kg to +/- 7.8 kg; corresponding values for NIRI were -5.3 kg and +/- 5.4 kg. Although some non-age-specific equations appeared valid, age-specific equations generally predicted TBW better. Limb muscle mass (DXA) was predicted better using the segmental impedance method, from indices of limb muscle area (r = 0.76; SEE = 1.9 kg) and volume (r = 0.86; SEE = 1.6 kg), than by anthropometry alone (r = 0.61 and 0.71; SEE = 2.3 kg and 2.1 kg, respectively). In conclusion, some body composition predictions are unacceptable (at least for TBW) in older men, and care is recommended when selecting from these methods or equations. Also, the segmental impedance method is as good as, if not better than, anthropometry alone in predicting limb muscle mass (DXA) in older men.

Absorptiometry, Photon↗
PubMedDate not supplied

An investigation of ethnic differences in bone mineral, hip axis length, calcium metabolism and bone turnover between West African and Caucasian adults living in the United Kingdom.

The aim of the study was to investigate factors relating to calcium and bone metabolism which might explain the low incidence of osteoporotic fracture among Africans. Adult bone mineral status, hip axis length and biochemical indices were investigated in 20 Caucasians (10 male, 10 female) and 19 Gambians (12 male, 7 female) living in the UK. Bone mineral content (BMC), bone mineral density (BMD) and BMC adjusted for bone area, body weight and height (size-adjusted BMC) were measured for the whole-body, lumbar spine, femoral neck, trochanter, radius shaft and radius wrist using dual-energy X-ray absorptiometry. There were no significant differences in whole body or regional BMC; values tended to be lower in the Gambians. Gambian men had higher size-adjusted BMC at the femoral neck (Gambian-British = 21%, 95% CI = 6 to 36%, p < 0.01), associated with a smaller bone area (Gambian-British = -11%, 95% CI = -20 to -2%, p = 0.02). BMD was affected similarly. No other significant differences in BMD or size-adjusted BMC were observed. Gambians had shorter hip axis length (Gambian British, after accounting for sex, = -5%, 95% CI = -9 to -1%, p = 0.02). There were no significant differences in bone turnover (osteocalcin, bone isoenzyme of alkaline phosphatase, urinary deoxypyridinoline) or calciotropic hormone levels (parathyroid hormone, 1,25-dihydroxyvitamin D, calcitonin). Gambian men had lower 25-hydroxyvitamin D concentrations (Gambian = 26.3 SD 12.0 nmol/L, British = 55.5 SD 13.9 nmol/L, p < 0.0001), a difference not seen among the women. Gambian men and women excreted significantly less phosphate and potassium than British subjects by 30-60%; urinary calcium and sodium excretion were similar in the two groups. This study revealed few ethnic differences that could account for the disparity in osteoporotic fracture rates between Africans and Caucasians, with the possible exception of anatomical differences in the hip.

Absorptiometry, Photon↗