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Biomedical subjects

J R Buchanan

Publications and source records attributed to J R Buchanan.

At least 19 recordsLinked to original sources
PubMed1989

Long-term oral contraceptive use does not affect trabecular bone density.

To determine whether long-term exposure to exogenous estrogen in oral contraceptives influences trabecular bone mass in premenopausal women, we studied 25 closely matched, healthy, premenopausal women, who were recruited from an active obstetrics and gynecology practice. Eleven women had never used oral contraceptives, and 14 women had used oral contraceptives for a minimum of 67 months. All oral contraceptive users had used preparations that provided a minimum of 50 micrograms mestranol per day. Trabecular bone density was determined by quantitative single-energy computerized tomography of the L1-3 lumbar vertebral bodies. Trabecular bone density was similar for both the control group and the oral contraceptive users, 160.6 +/- 6.9 versus 161.2 +/- 7.4 mg/ml, respectively. The power to detect a 15% difference in bone density between these two samples was 0.87. We concluded that long-term, premenopausal oral contraceptive use has no effect on vertebral bone density.

Absorptiometry, Photon↗
PubMed1989

Determination of peak trabecular bone density: interplay of dietary fiber, carbohydrate, and androgens.

To elucidate mechanisms linking nutrition and sex hormones to magnitude of peak trabecular bone density, we studied 11 normal women aged 19-21 y. Trabecular bone density was related inversely to dietary fiber (r = -0.69, p = 0.02) and carbohydrate (r = -0.70, p = 0.02) and directly to serum free-and-albumin-bound testosterone (fab T) (r = -0.70, p = 0.02) and total testosterone (total T) (r = 0.66, p = 0.03). Dietary fiber was correlated negatively with fab T (r = -0.74, p = 0.009), total T (r = -0.70, p = 0.02), and androstenedione (Adione) (r = -0.72, p = 0.01). Controlling for the effect of fab T or Adione weakened the relationship between dietary fiber and bone density and the relationship was no longer statistically significant. Conversely, controlling for sex hormones did not abolish the effect of carbohydrate on bone density. The contributions of fab T and carbohydrate to bone density were independent. These results suggest that dietary fiber may depress serum androgens which in turn decrease trabecular bone density. Carbohydrate may also depress bone density but independently of sex steroid hormones.

Adult↗
PubMed1989

Resources and limitations of medical centers in the United States.

A profile is provided of the range of opportunities and limitations for foreign nationals who seek access to the U.S. health care education and training system. The system is complicated, and entry depends on numerous variables. Facility in the English language is considered a prerequisite. Among opportunities, clinical training is probably most sought in the form of either residencies or clinical fellowships. Many major medical centers are eager to host earnest students and trainees from abroad. Yet such opportunities are limited, since most programs are unable to accept additional trainees once the first year of the program has been filled. Additional residency positions are not likely to be created and funded. In general, the larger academic medical centers tend to be the first to introduce new technologies and newer diagnostic and therapeutic modalities. Other settings may offer better, or at least equally good, environments for other kinds of post-M.D.-degree training. U.S. educational opportunities also exist in health policy and health systems education, nursing education, allied health and non-physician education, and research. All those seeking to study in the United States are urged to consult one of the several agencies that are knowledgeable about the opportunities and requirements for entering the programs offered.

Academic Medical Centers↗
PubMed1988

Early vertebral trabecular bone loss in normal premenopausal women.

The precise timing for the onset of trabecular bone loss in women is a matter of controversy. To address this issue, we studied the relationship between age and vertebral trabecular bone density (measured by computed tomography) in 74 healthy premenopausal women from 18 to 48 years old. We also measured radial cortical bone density (by single photon absorptiometry) in 28 of these subjects. Trabecular bone density levels (milligrams per milliliter, mean +/- standard error of the mean, SEM) were significantly (p less than 0.05) higher in the second (178 +/- 8) and third (171 +/- 6) decades than in the fourth (158 +/- 4) or fifth (140 +/- 12) decades, and were inversely correlated with age (r = -0.39, p = 0.0006), diminishing at a rate of 1.3 mg/ml (0.73%) per year. Radial cortical bone density levels (grams per square centimeter) were similar in the third (0.711 +/- 0.021), fourth (0.721 +/- 0.012), and fifth (0.736 +/- 0.012) decades and were not related to age (r = 0.17, p = 0.39). We conclude that vertebral trabecular bone loss in women commences during or prior to the third decade. In contrast, radial cortical bone density does not decline during the premenopausal years.

Adolescent↗
PubMed1988

Determinants of peak trabecular bone density in women: the role of androgens, estrogen, and exercise.

To elucidate determinants of peak trabecular bone density, we studied the role of androgens, estrogen, and aerobic exercise in 30 women from 18 to 22 years old. The women were divided into three groups: Sedentary, 11 normal women who did not exercise regularly; eumenorrheic, 10 athletes with normal menstrual function; and oligomenorrheic, 9 athletes with exercise-induced oligomenorrhea. All athletes participated in aerobic sports that did not involve selective resistance loading of the back. Serum free and albumin-bound testosterone (fab T), androstenedione (A), and estradiol (E2) were measured on four separate occasions at consecutive 7 day intervals and averaged. Trabecular density was measured by quantitative computed tomography of the lumbar spine. Peak trabecular bone density was related to fab T (r = 0.48, p = 0.007), A (r = 0.40, p = 0.03), and E2 (r = 0.40, p = 0.04). When taken in combination, androgens and estrogen each accounted independently for significant portions of the variance in bone density [fab T and E2 (R2 = 0.38, p = 0.002) and A and E2 (R2 = 0.27, p = 0.01)]. Bone density (mg/ml, mean +/- standard error of the mean, SEM) in the sedentary group (174 +/- 6) was not significantly different from that in the eumenorrheic (183 +/- 12, p = 0.47) or oligomenorrheic (161 +/- 11, p = 0.32) subjects. We conclude that androgens and estrogen function as independent and additive determinants of peak trabecular bone density in young women. The quantitative impact of aerobic exercise (without resistance loading) and exercise-induced menstrual dysfunction appears to be less important than that of the hormones.

Adolescent↗
PubMed1988

Effect of declining renal function on bone density in aging women.

The factors that are responsible for trabecular bone loss in aging women are not completely understood. To evaluate declining renal function as a possible factor, we studied 19 Caucasian women (average age 67) who were from 6 to 41 years postmenopausal. Trabecular bone density was quantitated by computerized tomography of the spine. Serum calcium, phosphorus, and creatinine were normal in all subjects. Creatinine clearance averaged 74 ml/min (range 38-122), decreased with age (r = -0.60, P = 0.003), and was inversely related to serum creatinine (r = -0.51, P = 0.01). Bivariate regression demonstrated that bone density decreased with age (r = -0.59, P = 0.004); controlling for the effect of creatinine clearance weakened this correlation to r = -0.45 (P = 0.03); controlling additionally for 1,25-dihydroxyvitamin D [1,25(OH)2D] and parathyroid hormone (PTH) reduced the correlation coefficient to r = -0.34 (P = 0.11). Bone density also decreased in direct proportion to the decrement in creatinine clearance (r = 0.44, P = 0.03); controlling for the effects of 1,25(OH)2D and PTH reduced this correlation coefficient to r = 0.34 (P = 0.11). These results suggest that occult renal insufficiency may contribute to bone loss in aging women, and that this effect may be mediated in part by 1,25(OH)2D and PTH. In this age group renal function should be assessed by measuring creatinine clearance rather than the serum creatinine concentration since renal insufficiency can be masked by apparently normal circulating creatinine levels.

Aged↗
PubMed1988

Determinants of atraumatic vertebral fracture rates in menopausal women: biologic v mechanical factors.

In menopausal women, the susceptibility to atraumatic vertebral fractures is thought to be governed by both mechanical factors (as represented by bone density) and by biologic factors such as age, body size, and dietary calcium. Whether these biologic factors independently influence fracture rates beyond the effect of bone density is a matter of controversy. To compare the relative importance of mechanical and biologic factors on vertebral fractures, we elucidated the determinants of atraumatic compression fractures in 63 menopausal women who had no chronic diseases other than osteopenia. Trabecular bone density was determined by quantitative computerized tomography of the spine. Fracture frequency was expressed as the number of compressed vertebrae per person between T5 and L4. The analysis showed that fracture frequency, bone density, and the biologic factors were closely interrelated. Fracture frequency was inversely correlated to bone density [R2 (spline model) = .40, P less than .0001], body size (r = -.26, P = .05), and dietary calcium (r = -.28, P = .04), and directly correlated with age (r = .46, P = .0002). Bone density decreased with age (r = -.65, P less than .0001), increased with body size (r = .37, P = .004), and tended to increase with dietary calcium (r = .24, P = .08). After controlling for bone density, there was no perceptible residual relationship between fracture frequency and any of these biologic factors. We conclude that mechanical factors overshadow age, body size, and dietary calcium as determinants of vertebral fracture frequency. The apparent influence of these biologic factors on fracture frequency is explained by their surrogate effects on bone density.

Aged↗
PubMed1988

Effect of excess endogenous androgens on bone density in young women.

To determine whether endogenous androgens influence bone density in young women, we studied 27 normal women and 19 women with androgen excess, as defined by increased serum bioavailable testosterone (bio T) concentrations. The women ranged from 21-48 yr of age. The 2 groups were comparable with respect to age, anthropomorphic measures, nutrition, gynecological history, and serum cortisol and estradiol levels. Trabecular (lumbar) and cortical (radial) bone density were quantitated by computerized tomography and single photon absorptiometry, respectively. Serum obtained during the follicular phase of the cycle was assayed for bio T, total T, dehydroepiandrosterone sulfate, androstenedione (Adione), and 3 alpha-androstanediol glucuronide (3-Adiol-G). Trabecular bone density was significantly higher in the androgen excess group [172 +/- 7 (+/- SE) vs. 153 +/- 5 mg/mL; P = 0.03]; controlling for serum Adione (but not for serum bio T, total T, dehydroepiandrosterone sulfate, or 3 alpha-androstanediol glucuronide, or 3-Adiol-G) abolished this difference. Similarly, serum Adione correlated more strongly than the other androgens with trabecular bone density (r = 0.31; P = 0.03). Average cortical bone density was not higher in the androgen excess group (0.740 +/- 0.014 vs. 0.722 +/- 0.008 g/cm2; P = 0.27). Among the 27 normal women, cortical density was correlated to serum bio T (r = 0.47; P = 0.01) and total T (r = 0.53; P = 0.004), but not to the other androgens. We conclude that supraphysiological levels of endogenous androgens are associated with increased trabecular bone density in young women. Serum Adione appeared to be the best marker for the impact of androgen on trabecular density. Among normal women, cortical bone density was related to serum T.

Adult↗
PubMed1988

Should the patella be resurfaced in total knee arthroplasty? Efficacy of patellar resurfacing.

To assess the long-term efficacy of patellar resurfacing, 100 knees were evaluated in 84 patients. The operations were performed between 1978 and 1982. The follow-up period ranged from 60 to 103 months. The diagnosis was degenerative joint disease (DJD) in 83%, rheumatoid arthritis in 12%, and miscellaneous in 5% of the knees. The implant (47 knees) and nonimplant (53 knees) groups were comparable with respect to age, body size, and length of follow-up period. The analysis revealed equivocal results. Considering all diagnostic categories combined, rest pain was marginally better in the resurfaced group (p = 0.04), but this difference resulted from an unequal distribution of subjects between mild and zero pain categories. Pain with walking, maximum walking distance, ability to climb stairs and rise from a chair, active arc of motion, extensor lag, and quadriceps strength were similar in the two groups. When the DJD group was considered separately, no significant difference emerged. There was little evidence to support a recommendation for routine patellar resurfacing in total knee arthroplasty.

Activities of Daily Living↗
PubMed1988

Complex fracture-dislocation of the metacarpophalangeal joint. Case report.

A complex fracture-dislocation involving the fifth metacarpophalangeal (MCP) joint occurred in a 16-year-old boy approaching skeletal maturity. Roentgenographic examination demonstrated a widened MCP joint and a dorsally displaced Salter-Harris Type III fracture of the metacarpal head. Attempted manipulative closed reduction was unsuccessful. To achieve successful reduction and fixation it was necessary to make a dorsal approach, incise the interposed volar plate longitudinally, and lever it to the anatomic volar position. Successful fixation of the fracture would have been impossible through a volar approach. The Salter-Harris Type III fracture is a surgical problem.

Adult↗
PubMed1988

A comparison of the risk of vertebral fracture in menopausal osteopenia and other metabolic disturbances.

The risk of atraumatic compression fracture in postmenopausal women increases as vertebral trabecular bone density decreases. To determine whether the risk is similar for patients who have other metabolic disorders, we compared eight-nine patients who had various disturbances affecting bone and sixty-three postmenopausal women who had no evidence of underlying disease. Trabecular bone density was measured by quantitative computed tomography of the lumbar spine. The relationship between frequency of fracture and bone density was modeled mathematically with spline threshold, quadratic polynomial, and decaying exponential functions. Analysis of covariance showed that the diagnostic category did not influence the relationship between frequency of fracture and bone density in any of the three models. We concluded that the risk of atraumatic compression fracture, as assessed by measurement of vertebral trabecular bone density using quantitative computerized tomography, is independent of the underlying metabolic disturbance.

Adult↗
PubMed1988

Collegiate women athletes with irregular menses during adolescence have decreased bone density.

We studied six eumenorrheic and 13 oligomenorrheic collegiate women athletes who were matched in all respects other than menstrual histories. There was a significant (P less than .05) association between menstrual regularity and bone density. The severely oligomenorrheic subjects had modestly decreased plasma estrogen levels. These findings support the notion that plasma estrogen levels during adolescence play a significant role in the development of peak adult bone density in women.

Adolescent↗
PubMed1987

Adrenal androgens, sex-hormone binding globulin and bone density in osteoporotic menopausal women: is there a relationship?

The relationships among sex steroids, sex hormone binding globulin (SHBG) and vertebral bone density as measured by computerized tomography were studied in 18 post-menopausal women. A significant negative correlation was found between SHBG binding capacity (SHBG-BC) and bone density. Bone density and the adrenal androgen dehydroepiandrosterone sulfate (DHEAS) declined with age, and SHBG-BC was correlated significantly with DHEAS concentrations. The relationship between SHBG-BC and bone density may be affected by adrenal androgen output.

Adrenal Cortex Hormones↗
PubMed1987

Interrelationships of diet, athletic activity, menstrual status, and bone density in collegiate women.

We undertook a case-control study to examine the effect of nutritional factors on menstrual function and bone density in collegiate athletes. Three groups, matched with respect to age, height, and weight, were studied: eumenorrheic collegiate athletes, oligomenorrheic collegiate athletes, and eumenorrheic sedentary collegiate control subjects. Menarche was delayed in the eumenorrheic (13.1 y) and oligomenorrheic (14.3 y) athletic groups compared with the sedentary control subjects (12.2 y) (p less than 0.05). Average bone density tended (p = 0.10) to be lower in the oligomenorrheic athletes (158 mg/mL) compared with the eumenorrheic athletes (184 mg/mL) or sedentary control subjects (173 mg/mL). Dietary fiber intake was significantly elevated (p less than 0.05) in the oligomenorrheic athletes (5.74 g/d) compared with the eumenorrheic athletes (3.62 g/d) or sedentary control subjects (2.97 g/d). We conclude that increased dietary fiber intake is associated with menstrual dysfunction of these collegiate athletes. These factors may contribute to decreased bone density.

Adult↗
PubMed1987

Declining adrenal androgens: an association with bone loss in aging women.

Bone loss in aging women is a major contributing factor to the onset of osteoporosis. To determine whether a decline in adrenal androgen output might be important in the loss of bone with age, we studied a highly selected group of 14 women, average age 70, and measured adrenal androgens in relationship to trabecular bone density. Dehydroepiandrosterone sulfate (DHEAS) levels were used as a marker of adrenal sex steroid output while quantitative, computerized tomography was used to determine trabecular bone density. Our results showed that both bone density (r = -0.69, P less than 0.01) and DHEAS levels (r = -0.68, P less than 0.01) declined with age, and that DHEAS was positively correlated with bone density (r = 0.66, P = 0.01). These data emphasize the association of declining adrenal sex steroid production with declining bone density during the process of aging.

Adrenal Cortex↗
PubMed1987

Assessment of the risk of vertebral fracture in menopausal women.

The decision to institute prophylaxis in women with menopausal osteopenia is hampered by the absence of quantitative criteria for appraising the risk of fracture in the individual. We have developed standards for assessing the risk of fracture by relating the prevalence of atraumatic vertebral compression fractures to bone density in sixty-five menopausal women, forty-nine to ninety-two years old. To define the upper limit of the spectrum of bone density, we also studied thirty-one young women, seventeen to twenty-two years old. The density of trabecular bone in a vertebral body was determined by quantitative computed tomography and expressed in terms of milligrams per milliliter of dipotassium hydrogen phosphate. Twenty-five of the menopausal women exhibited at least one fracture (range, one to six fractures), and forty had no fracture. The bone density ranged from -9 to sixty-nine milligrams per milliliter in those with fractures and from twelve to 122 milligrams per milliliter in those without a fracture. The densities in the young women averaged 173 milligrams per milliliter and ranged from ninety-five to 248 milligrams per milliliter. The percentage of subjects with fractures increased as the bone density decreased. It was zero per cent in women with a density of seventy milligrams per milliliter or more, 38 per cent in women with a density between fifty and less than seventy milligrams per milliliter, 71 per cent in those with a density between thirty and less than fifty milligrams per milliliter, and 82 per cent in women with a density of less than thirty milligrams per milliliter.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

The effect of endogenous estrogen fluctuation on metabolism of 25-hydroxyvitamin D.

To test the hypothesis that estrogen modulates the metabolism of 25-hydroxyvitamin D (25(OH)D) to 1,25-dihydroxyvitamin D (1,25(OH)2D) and 24,25-dihydroxyvitamin D (24,25(OH)2D), we studied 20 normal premenopausal women at four consecutive weekly intervals during one menstrual cycle. Estrogen stimulation was semiquantitatively defined into baseline, low-grade, or medium-grade categories, based on endogenous estrone and estradiol concentrations. 1,25(OH)2D increased incrementally from baseline levels of 34 +/- 3(SE) pg/ml to 39 +/- 3 pg/ml (P = 0.2) with low-grade estrogen stimulation and to 43 +/- 3 pg/ml (P less than 0.05) with medium-grade estrogen stimulation, while 25(OH)D, 24,25(OH)2D, vitamin D binding protein, parathyroid hormone, calcium, and phosphate did not change. 24,25(OH)2D was correlated to 25(OH)D at baseline (r = 0.65, P less than 0.01) and with low-grade estrogen stimulation (r = 0.62, P less than 0.01), but not with medium-grade stimulation (r = 0.13); these relationships are consistent with the concepts that 25(OH)D is metabolized predominantly to 24,25(OH)2D at low estrogen levels, but not at higher estrogen levels. We conclude that endogenous estrogen elevation promotes formation of 1,25(OH)2D from 25(OH)D, and that it may reciprocally inhibit synthesis of 24,25(OH)2D.

24,25-Dihydroxyvitamin D 3↗