Biomedical subjects

Robert J Ploutz-Snyder

Publications and source records attributed to Robert J Ploutz-Snyder.

6 recordsLinked to original sources

PubMed2006

Maturity and activity-related differences in bone mineral density: Tanner I vs. II and gymnasts vs. non-gymnasts.

This study tests the hypotheses that (1) Tanner I and Tanner II girls comprise distinct maturational cohorts, exhibiting BMD differences that are not explained by age and body size alone; and (2) within these distinct maturational cohorts, BMD is higher in gymnasts than non-gymnasts, independent of age and body size. Premenarcheal artistic gymnasts (n=28) and non-gymnasts (n=28) were evaluated. Fan-beam DXA measured areal BMD (aBMD) at the forearm, femoral neck, and lumbar spine; fat free mass (FFM) was derived from whole-body scans. Height, weight, physical activity and calcium intake were assessed. Group means were compared using ANOVA; ANCOVA was used to adjust for age, height and FFM. For all 3 sites and both maturity levels, gymnasts had higher aBMD than non-gymnasts, independent of age and body size (7.2-20.8%, p<0.04). After adjustment for age, height and FFM, Tanner II gymnasts demonstrated lower aBMD than Tanner I gymnasts at the femoral neck (7.6%, p<0.05); no other maturity group comparisons yielded statistically significant differences independent of age and body size. In conclusion, for both Tanner groups, the osteogenic role of impact activity is evident at all three sites. Trends in Tanner group differences in aBMD were specific to gymnast and non-gymnast activity groups and therefore were not generalizable to all subjects. Overall, aBMD correlations and ANCOVA results differ by activity group, maturity level and site. These results highlight the need to consider both maturity and activity status in studies assessing bone accrual.

Absorptiometry, Photon↗

PubMed2005

Knee extensor isometric unsteadiness does not predict functional limitation in older adults.

OBJECTIVE: To determine how knee extensor steadiness is related to age and difficulty performing everyday tasks. DESIGN: In this cross-sectional study performed at a research laboratory, 50 older adults (age range, (56-95 yrs) performed steadiness testing at 50% of maximum strength and were timed and rated on four tasks of daily living: chair rise, stair ascent and descent, and walk. The independent variables of age, steadiness, and strength-to-weight ratio were entered into regression models with the ratings and time to complete the four everyday tasks as dependent variables. RESULTS: The strength-to-weight ratio was the only significant predictor in the multiple regression models, explaining 29%, 33%, 14%, and 14% of the variance in gait speed and time to complete a chair rise, stair ascent, and stair descent, respectively. Similar results were seen with task ratings. Age was not correlated with steadiness (r = 0.25, P = 0.07). CONCLUSION: This study suggests that knee extensor isometric steadiness performance does not carry over to tasks of everyday living, and older subjects, regardless of age, have similar steadiness values. Because the strength-to-weight ratio predicted the most variance in functional performance, it is recommended that muscle strength be improved to increase function in older adults.

Activities of Daily Living↗

PubMed2005

Advances in digital quantification technique enhance discrimination between mild and advanced liver fibrosis in chronic hepatitis C.

BACKGROUND AND AIMS: The necessity of liver biopsy for staging fibrosis and its quantification in patients with chronic hepatitis C (CHC) remains controversial. Semiquantitative scoring of fibrosis is considered more subjective and less objective than digital quantification by image analysis. However, measurement of fibrosis using digital image analysis is thought to be less reliable in determining early stage fibrosis as compared with advanced fibrosis or cirrhosis. Our aims were to correlate all Ishak stages of fibrosis (0-6) with fibrosis percentage (%) using computerized digital image analysis, and thereby seek to improve discrimination between varying levels of liver fibrosis. METHODS: Fibrosis % data were obtained by image analysis on 164 trichrome-stained liver biopsies from untreated patients with CHC, representing all Ishak stages of fibrosis. RESULTS: Digital analysis of fibrosis % was highly correlated with Ishak scores of fibrosis (Kendall's tau-beta=0.86, P<0.001). Receiver-operator characteristic curves showed reliable discriminative capability of our digital image measurement of fibrosis when compared with semiquantitative assessments of fibrosis. Excellent interobserver reliability was found. CONCLUSIONS: Recent advances in digital quantification of fibrosis have resulted in improved discrimination between the varying stages of liver fibrosis, including mild fibrosis. This method is reproducible, can detect early as well as advanced fibrosis or cirrhosis, may prove to be the best assessment of mild fibrosis, and may be more precise than semiquantitative estimation of changes for monitoring fibrosis progression or regression during clinical therapeutic trials.

Azo Compounds↗

PubMed2002

Functionally relevant thresholds of quadriceps femoris strength.

The purpose of this study was to identify quadriceps femoris strength thresholds below which performance on ambulatory tasks is compromised. A second purpose was to evaluate whether self-reported functioning matches evaluated performance of the activities. Subjects (N = 100; age 73 +/- 0.9 years) participated in isometric knee extension strength tests, performed three functional ambulatory tasks (chair rise, gait speed, and stair ascent and descent), and answered standard survey questions assessing physical function. Significant relationships were observed between functional performance and the ratio of isometric leg extension peak torque to body weight (STR/WT) for each activity (p <.0001). For each activity, thresholds of STR/WT between 3.0 and 3.5 N m/kg were observed, below which the likelihood for success was reduced. Thresholds were determined by calculating the value of STR/WT that minimized the classification error. Individuals with a STR/WT < 3.0 N m/kg are at a substantial risk for impaired function in chair rise, gait speed, and stair ascent and descent. Sensitivity and specificity of STR/WT as a predictor of functional success ranged from 76% to 81% and from 78% to 94%, respectively, depending on activity. This is of clinical significance, as the STR/WT thresholds can identify individuals with preclinical disability (beginning to have difficulty with ambulatory tasks) as opposed to those in whom an outright disability is observed. This may be useful for targeting individuals for strengthening interventions and developing specific intervention goals.

Aged↗

PubMed2002

Responsiveness of hypercalciuria to thiazide in Dent's disease.

Hypercalciuria is the major risk factor promoting stone formation in Dent's disease, also known as X-linked recessive nephrolithiasis, but the effects of diuretics on calcium excretion and other stone risk factors in this disease are unknown. This study examined urine composition in eight male patients with Dent's disease, ages 6 to 49 yr, all of whom were hypercalciuric and had inactivating mutations of CLCN5. Eight males, ages 7 to 34 yr, with idiopathic hypercalciuria (IH) served as controls. Patients were instructed to maintain a consistent intake of sodium, potassium, calcium, and protein. Two consecutive 24-h urine collections were obtained after a baseline period and after 2 wk of chlorthalidone (25 mg), amiloride (5 mg), and the two diuretics in combination, with a week off drug separating the treatment periods in a randomized crossover design. Doses were reduced by half in boys under age 12 yr. Chlorthalidone alone (P < 0.002) and the combination of chlorthalidone and amiloride (P < 0.003) reduced calcium excretion significantly in either patient group. With chlorthalidone, calcium excretion fell to normal (<4.0 mg/kg per d) in all but one patient in each group. Amiloride alone had no significant effect on urinary calcium excretion, in either patient group. In patients with Dent's disease during chlorthalidone therapy, the supersaturation ratios for calcium oxalate and calcium phosphate fell by 25% and 35%, respectively. Mean citrate excretion was reduced by chlorthalidone (P <.04) and by chlorthalidone in combination with amiloride (P <.02). There were no significant differences in the responses to these diuretics between the patient groups in any of the urinary parameters. The intact hypocalciuric response to a thiazide diuretic indicates that inactivation of the ClC-5 chloride channel does not impair calcium transport in the distal convoluted tubule and indicates that thiazides should be useful in reducing the risk of kidney stone recurrence in patients with Dent's disease.

Adolescent↗

PubMed2002

Illusory causation: why it occurs.

Considerable evidence indicates that people overattribute causality to a given stimulus when it is salient or the focus of their attention--the so-called illusory-causation phenomenon. Although illusory causation has proved to be quite robust and generalizable, a compelling explanation for it has not been empirically documented. Four social-attribution studies were conducted to test the hypothesis that illusory causation occurs because salient information is initially registered, or perceptually organized, differently than nonsalient information. The results provide considerable support for the notion that people's literal point of view affects how they initially perceive, or extract, information from an observed interaction, which in turn affects their judgments regarding the causal influence exerted by each interactant.

Adult↗