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Biomedical subjects

A Horsman

Publications and source records attributed to A Horsman.

At least 55 records · Page 3Linked to original sources
PubMed1987

Isotope computed tomography using cone-beam geometry: a comparison of two reconstruction algorithms.

A CT scanner has been constructed specifically to determine the three-dimensional distribution of bone mineral in the medullary cavities of the radius, ulna and femur. A source of x-rays (153Gd) and a multiwire proportional counter (MWPC) are mounted at opposite ends of a diameter of an annular mounting. The limb is placed on the axis of rotation of the annulus and a series of two-dimensional transmission projections are obtained at equal angular spacings over 360 degrees. The distribution of bone mineral is reconstructed from the projections either by the method of maximum entropy (ME) or by convolution and back projection (CBP). These two methods have been evaluated by reconstructing a single slice of a phantom, representing the forearm, from projections simulated by computer. With a clinically acceptable exposure time, the mean medullary densities of the ulna and radius were determined with systematic errors of less than 3.5% (ME) and 11% (CBP), although for the latter method of reconstruction the systematic error was reduced to less than 2% by increasing the number of views. The mean medullary densities of the ulna and radius were determined with precisions better than 2.5% (ME) and 3.5% (CBP).

Algorithms↗
PubMed1987

Bone mineral content in bronchopulmonary dysplasia.

Fourteen preterm infants who developed bronchopulmonary dysplasia diagnosed radiologically were compared with a group of similar infants who did not. The two groups were of comparable maturity and birth weight. The clinical histories indicated that those infants with bronchopulmonary dysplasia had had longer periods of supplemental oxygen, more frequent treatment with dexamethasone, and a higher mean total dosage of frusemide. Bone mineral content in the mid-forearm was measured by photon absorptiometry at or near the postconceptional age of 40 weeks in all cases; no significant difference was found between the two groups, although both were severely undermineralised when compared with infants born at full term. In both groups mean daily calcium intake (about 70 mg/kg/day) was about half the daily intrauterine accretion of calcium.

Absorption↗
PubMed1986

Measurement of bone mineral content in the human fetus by photon absorptiometry.

A photon absorptiometer designed to measure the bone mineral content (BMC) of the radius and ulna in premature or term babies was used to examine 34 forearm specimens obtained from 25 male and 9 female babies dying before or up to 13 weeks after birth. Gestational age, foot and crown-heel lengths and birth weight were recorded. Radiographic measurements showed that the midshaft of the radius can be located with a positioning error of +/- 1.28 mm (+/- 2 S.E.E.) from the distance between the distal ulnar styloid process and proximal tip of the olecranon, both of which can be palpated in vivo. Scanning at 5 sites showed that effects of positioning errors on BMC measurements are least at the midshaft site. Subsequent measurements of the ash weight of sections of the radius and ulna, centred on the midshaft of the radius, showed that ash weight/unit length can be estimated with a standard error 2.99 mg/cm from scan data.

Birth Weight↗
PubMed1986

Osteoporosis in hypogonadal men: role of decreased plasma 1,25-dihydroxyvitamin D, calcium malabsorption, and low bone formation.

To investigate the pathogenesis of osteoporosis in male hypogonadism we have investigated a heterogeneous group of 13 men with hypogonadism: 7 men (median age 60, range 31-79) with two or more vertebral crush fractures and 6 men (median age 61.5, range 28-76) without vertebral fractures. The group with crush fractures had trabecular and cortical osteoporosis as assessed by Singh grade, iliac crest trabecular bone volume, and metacarpal cortical area/total area. This was accompanied by an altered trabecular architecture with a reduction in number of trabeculae but no change in trabecular width, which contrasts with age-related bone loss in men where there is no reduction in trabecular number but thinning of trabeculae. The fracture group had significantly lower plasma 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations than the nonfracture group, and this was associated with malabsorption of calcium. Irrespective of the presence or absence of osteoporosis, treatment with testosterone led to a significant increase in total and free plasma 1,25(OH)2D and an improvement in calcium absorption measured with radiocalcium and by balance techniques. In addition, urine biochemistry, metabolic balance studies, and bone biopsy suggest that skeletal retention of calcium and bone formation are increased by testosterone treatment. We conclude that male hypogonadism causes both cortical and trabecular osteoporosis and altered trabecular architecture. A major risk factor for the development of osteoporosis is reduction in plasma 1,25(OH)2D, leading to malabsorption of calcium and reduced bone formation.

Adult↗
PubMed1986

Osteopenia of prematurity.

Bone mineral content of the forearm was measured by photon absorptiometry in 17 preterm infants at a postconceptional age of 40 weeks. Radiographs of the forearm were assessed by Koo's method and plasma alkaline phosphatase activity was also measured at this time. Bone mineral content was significantly but weakly correlated with Koo score and was not significantly correlated with alkaline phosphatase activity. Neither of these two commonly used investigations accurately predicts the presence of underlying bone disease. Compared with 15 full term infants the preterm infants had significantly lower values of bone mineral content, palpated ulnar length, and crown-heel length. After adjusting for weight and ulnar length the preterm group still had a significantly lower mean value of bone mineral content than the full term group. Accurate diagnosis of osteopenia of prematurity requires photon absorptiometry, with bone mineral content assessed relative to body weight or ulnar length.

Anthropometry↗
PubMed1985

A prospective trial of the effect of vitamin D supplementation on metacarpal bone loss in elderly women.

The effect on cortical bone loss of treating elderly women with 15,000 IU vitamin D2 weekly was evaluated by sequential radiographic morphometry of the metacarpals. One hundred nine randomly selected women aged 65-74 yr were studied for 2 yr. The women were randomly allocated to control or treated groups taking placebo or vitamin D2 capsules. Hand radiographs and blood samples were obtained at the beginning and end of the trial. Plasma 25-hydroxyvitamin D was measured by radio-competitive protein binding assay. Comparing the treated and control groups, vitamin D treatment significantly raised the plasma 25-hydroxyvitamin D levels (p less than 0.001) and reduced the rate of cortical bone loss (p less than 0.01). The placebo had no measurable effect on the plasma levels.

Aged↗
PubMed1985

A stochastic model of age-related bone loss and fractures.

A stochastic model of age-related bone loss capable of predicting age-specific incidence of fractures has been implemented by Monte Carlo simulation. Each simulation involves aging a large cohort of individuals from 20 to 100 years. Every individual is randomly allocated a particular amount of bone as a young adult, an age of onset of bone loss, and parameter values that determine the subsequent bone loss. Fracture risk is assumed to be zero when the amount of bone is above a global threshold level, increasing progressively as the amount of bone falls below the threshold. From the individual fracture risks, a fracture subpopulation is identified and age-specific incidence evaluated numerically. By adjusting the model parameters, predicted and observed incidences of femoral neck fracture can be closely matched in both sexes by use of a linear function to describe age-related bone loss. For fracture of the distal radius, a close match can be achieved in women by use of an exponential function to describe the bone loss phase. In men, the incidence is independent of age; trauma, rather than the amount of bone in the forearm, appears to be the main determinant of fracture risk.

Adult↗
PubMed1983

The effect of estrogen dose on postmenopausal bone loss.

In order to establish whether the favorable effect of estrogen therapy on postmenopausal bone loss was dose related, we measured sequential changes in the cortical diameters of the metacarpals by radiographic morphometry in 120 normal postmenopausal women who were being treated with ethinyl estradiol in doses ranging from 5 to 50 micrograms daily. There was a net loss of bone at doses below 15 micrograms per day and a net gain at doses of 25 micrograms per day and above. At doses between 15 and 25 micrograms daily, bone was neither gained nor lost. The loss of bone with the low doses was due to expansion of the medullary cavity that was unaccompanied by any change in total bone width. There was no change in bone volume with the intermediate doses because endosteal resorption of bone was offset by periosteal apposition. The net gain of bone with the higher doses occurred because endosteal resorption was totally inhibited but periosteal bone apposition continued. Thus, in postmenopausal women the reduction in the rate of cortical bone loss in response to estrogen therapy depends on the dose administered.

Adult↗
PubMed1983

Mineral content of the forearms of babies born to Asian and white mothers.

Vitamin D deficiency is common in pregnant Asian women. The effect of maternal vitamin D deficiency on fetal skeletal mineralisation was assessed by measuring the bone mineral content of babies born to 45 Asian women, 19 Asian women who had received 1000 units of vitamin D during the last trimester, and 12 white women. The mean cord blood concentrations of 25-hydroxy vitamin D in the three groups were 5.9 +/- SE 0.9 nmol/l (2.4 +/- SE 0.4 ng/ml), 15.2 +/- 3.2 nmol/l (6.1 +/- 1.3 ng/ml), and 33.4 +/- 3.6 nmol/l (13.4 ng/ml), respectively. Despite this wide variation in values there was no significant difference in the bone mineral content (as assessed by photon absorptiometry) of the forearms of babies born to these women. This suggests that mineralization of the fetal skeleton is not impaired in maternal vitamin D deficiency. Craniotabes (skull softening) was present in seven of the 64 Asian babies. The bone mineral content in these babies was not significantly different from that of babies without this sign, and craniotabes should not therefore be taken as an indication of a generalized impairment in skeletal mineralization.

Adult↗
PubMed1983

Estimating total body calcium from peripheral bone measurements.

In a heterogeneous group of 12 male and 30 female patients, total body calcium (TBCa) was measured by neutron activation analysis, and bone mineral content of the distal femur and six regions of the distal radius and ulna were measured by photon absorptiometry. TBCa was an average of 71 g (9%) lower than normal in the females and 119 g (11%) lower than normal in the males. Of the forearm measurements, those of the radial shaft provided the best estimate of TBCa with a standard error of estimation (SEE) of 88 g (14% of the mean value) for female patients alone, and 113 g (16%) for the whole group. The measurement on the femur provided a better estimate with SEE 80 g (13%) for female patients and 90 g (13%) for the whole group. These SEE are comparable with the variability in TBCa between normal subjects, which has a coefficient of variation of the order of 20% in both sexes. A slightly better estimate of TBCa can be obtained by using a multiple regression equation involving both the femur and radial shaft measurements with a SEE of 74 g (12%) for female patients and 81 g (11%) for the whole group. The correlation between the estimated deficit of TBCa and the estimated deficit of bone mineral from the forearm and the femur has been calculated.

Adolescent↗
PubMed1983

Prolonged heparin therapy in pregnancy causes bone demineralization.

The relation of heparin therapy to osteoporosis was assessed in a retrospective analysis of 20 women treated during and after pregnancy with subcutaneous heparin for thromboembolism prophylaxis. The phalangeal cortical area ratio was significantly less after long term therapy (greater than 25 weeks) compared with that after short term therapy (less than 7 weeks). The same trend was found in the metacarpal area ratio, although this did not reach statistical significance. The changes were most marked in a woman who had received heparin also in a previous pregnancy. No correlations were found between duration of therapy and back pain, conventional radiology of lumbar spine or the Singh index of femoral trabecular pattern which were within the normal range in all patients. The findings indicate a dose-related demineralization process associated with prophylactic heparin therapy in pregnancy. The correct methods of and criteria for thromboembolism prophylaxis in pregnancy need critical re-examination.

Adult↗
PubMed1983

Estimation of mechanical properties of the distal radius from bone mineral content and cortical width.

Bone mineral content (BMC) was determined by photon absorptiometry and cortical width (CW) by radiographic morphometry at two levels in 17 radii obtained postmortem from women ranging in age from 39 to 95 years. One level was the region in which Colles' fracture occurs (lower level) and the other about 6 cm from the styloid tip (upper level). Principal compressive strain at a 600-N load, fracture load, compliance, and work/unit length to fracture were measured in longitudinal compression tests. In general, BMC provides more precise estimates of mechanical properties than CW. The correlation coefficient between fracture load and BMC at the lower level was +0.83 (less than 0.001). Between work/unit length to fracture and BMC the coefficient was +0.81 (p less than 0.001).

Absorption↗
PubMed1981

A left/right comparison of sequential bone loss from the metacarpals of postmenopausal women.

The rate of decrease of mean metacarpal cortical width was assessed by sequential radiographic morphometry for each hand separately in a series of 46 right-handed postmenopausal women observed for 222 patient-years. For the left hand, the mean rate was 0.0331 +/- 0.0053 mm/year and for the right, 0.0310 +/- 0.0060 mm/year. The difference between the hands in the rate of decrease was not significant. It is concluded that the higher work load of the dominant hand has no effect on the rate of bone loss from the metacarpals of postmenopausal women.

Aged↗
PubMed1980

Treatment of spinal osteoporosis in postmenopausal women.

Ninety-five postmenopausal women with unequivocably wedged or compressed vertebrae in whom the recognised causes of secondary osteoporosis had been excluded were studied, 41 having no treatment and the rest one or more of six different treatments. The treatment regimens comprised calcium supplements, vitamin D, calcium and vitamin D, ethinyloestradiol or--where oestrogens were contraindicated--norethisterone, 1 alpha-hydroxycholecalciferol (1 alpha-OHD3), or hormones with 1 alpha-OHD3. The seven groups were reasonably comparable in most respects except that the hormone-treated patients were younger and had a higher initial cortical area ratio than the others, and the calcium- and hormone-treated groups had the best initial radio-calcium absorption. The untreated osteoporotic patients lost cortical bone more rapidly than do normal postmenopausal women. Three treatments (calcium, hormones, and 1 alpha OHD3 plus hormones) appear to be useful in modifying the disease, and two treatments (vitamin D and 1 alpha-OHD3) useless or even harmful. Vitamin D and 1 alpha-OHD3 are more safely used in conjunction with oestrogens, which protect bone against resorption, than on their own.

Aged↗