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PubMed2005

Longitudinal diffusion changes in cerebral hemispheres after MCA infarcts.

Diffusion tensor imaging can be used in vivo to assess the longitudinal and regional microstructural changes occurring after middle cerebral artery (MCA) infarcts in humans. Nine patients were investigated 1 week (D7), 1 (M1), 3 (M3), and 6 months (M6) after the occurrence of an isolated MCA infarction. First, an overall analysis was performed using histograms of mean diffusivity (MD) and fractional anisotropy (FA) in each hemisphere. Thereafter, the regional pattern of diffusion changes was investigated voxel by voxel with statistical parametric mapping 99. In the hemisphere ipsilateral to the infarction, histogram analysis revealed a significant decrease in FA between D7 and M6 associated with a progressive increase in MD from D7 to M3. Remote from the MCA territory, the voxel by voxel analyses detected a significant increase in MD within the thalamus at M3 and M6 and a reduction in FA along the pyramidal tract at M6. In the contralateral hemisphere, between D7 and M6, a significant hemispheric atrophy was observed in association with a global reduction in anisotropy, in the absence of distinctive regional diffusion changes. These results suggest that micro- and macrostructural tissue modifications can be detected with diffusion tensor imaging in regions remote from the ischemic area in both hemispheres.

Adult↗
PubMed2002

Anisotropic conduction properties in canine atria analyzed by high-resolution optical mapping: preferential direction of conduction block changes from longitudinal to transverse with increasing age.

BACKGROUND: Anisotropic conduction properties may provide a substrate for reentrant arrhythmias. We investigated the age-dependent changes of structural and functional anisotropy in isolated right atria from infant (1 to 2 months), young (6 to 12 months), and old (6 to 10 years) dogs. METHODS AND RESULTS: The histology of the mapped atrial tissues (a small subepicardial area, 2.8x4.2 mm) was characterized by an age-dependent increase of myofiber width and fat cell infiltration between myofibers. Cx43 was distributed homogeneously over the entire cell surface in infant dogs, whereas it progressively polarized to the cell termini with increasing age. The activation sequences were analyzed by high-resolution optical mapping using a voltage-sensitive dye. Activation fronts from the pacing site proceeded more rapidly along fiber orientation (longitudinal) than across it (transverse). Infant dogs showed "elliptical" isochrones with a smooth transition between longitudinal and transverse propagation, whereas old dogs had a "square" pattern with a sharp transition. Conduction block occurred predominantly during longitudinal propagation in infant dogs but during transverse propagation in old dogs. The shape of the wave front and the degree of lateral uncoupling seemed to decide the preferential direction of block. A zigzag activation causing an extremely slow transverse conduction was observed only in old dogs. CONCLUSIONS: Along with the age-dependent structural anisotropy, the preferential direction of block changed from longitudinal to transverse in association with a change in the wave front configuration. A zigzag propagation based on lateral uncoupling would predispose the elderly to multiple reentry and a higher incidence of atrial fibrillation.

Action Potentials↗
PubMed2001

The Long Beach Longitudinal Study: evaluation of longitudinal effects of aging on memory and cognition.

This article outlines the purposes, design, and findings of the Long Beach Longitudinal Study, a multipanel study of adults aged 28 through the upper reaches of the life span. The goal of the study is to identify normal short- and long-term longitudinal changes in memory and cognition across adulthood, and to develop models to explain cognitive changes. Descriptive findings of 3- and 16-year longitudinal change patterns are identified, as well as results suggesting the role of cognitive processing resources and intellectual ability in memory change. Change patterns of the oldest-old, who differ from less elderly adults, are discussed.

Adult↗
PubMed2005

The lateral view radiograph for assessment of the tibiofemoral joint space in knee osteoarthritis: its reliability, sensitivity to change, and longitudinal validity.

OBJECTIVE: To evaluate the reliability, validity, and sensitivity to change of tibiofemoral (TF) narrowing on lateral radiographic views. METHODS: In a natural history study of symptomatic knee osteoarthritis (OA), both lateral view and fluoroscopically positioned posteroanterior (PA) semiflexed view radiographs of the knee in 30 degrees of flexion and with weight bearing were obtained at baseline and at 30 months. Test-retest reliability was evaluated using repeat radiographs, with joint space width measured using electronic calipers. All radiographs were scored on a 0-3 scale, and progression of joint space loss was defined as narrowing of the joint space by 1 grade. We evaluated sensitivity to change compared with the PA view. We evaluated validity by examining whether knees with progression showed expected malalignment on full-limb films. RESULTS: Test-retest reliability of the TF joint space using the lateral view had a root mean square error of 0.303 mm, with 92.5% of repeats within 1 mm. More knees showed progression on the lateral view alone (n = 41) than on the PA view alone (n = 27). Compared with knees without joint space loss, knees with medial compartment loss on the lateral view only were more varus malaligned (P < 0.001), while those with lateral compartment loss were more valgus malaligned (P = 0.008). CONCLUSION: In the assessment of TF joint space loss, lateral view radiographs are reliable, valid, and more sensitive to change than fluoroscopically positioned PA radiographs.

Cartilage, Articular↗
PubMed2000

Latent Growth Models of Individual Change: The Case of Newcomer Adjustment.

One commonality to various theoretical frameworks concerning employee work adjustment is change in employee-organization linkages over time, yet few empirical tests of employee work adjustment theories have adequately operationalized change. We develop and test a model of longitudinal change on one particular form of employee adjustment, employee attachment, operationalized in terms of O'Reilly and Chatman's (1986) triparite structure of commitment, using second-order factor (SOF) latent growth modeling (LGM). Results were generally supportive of the theoretical model and illustrate several advantages to using SOF LGM to measure longitudinal change. Copyright 2000 Academic Press.

Journal Article↗
PubMed1993

Life stress and dysphoria: the role of self-esteem and hopelessness.

This study evaluated the hypotheses that the relation between life stress (life events and daily hassles) and longitudinal change in dysphoria would be (a) moderated by self-esteem and (b) mediated by longitudinal change in hopelessness. Eighty undergraduates were first assessed on self-esteem, hopelessness, and dysphoria and then reassessed 3 months later on life events, daily hassles, hopelessness, and dysphoria. Residual change in dysphoria was significantly associated with self-esteem, life stress, and a Self-Esteem X Life Stress interaction. However, inconsonant with predictions, the moderating impact of self-esteem was greatest under conditions of low (vs. high) life stress. Moreover, residual change in hopelessness mediated the relations between residual change in dysphoria and both self-esteem and life stress.

Adolescent↗
PubMed2000

Quantitative assessment of longitudinal metabolic changes in vivo after traumatic brain injury in the adult rat using FDG-microPET.

With the advent and emerging importance of neurobiology and its relation to behavior, scientists desire the capability to apply noninvasive, quantitative imaging of neuronal activity to small rodents. To this end, the authors' laboratory has developed microPET, a high-resolution positron emission tomography (PET) scanner that is capable of performing in vivo molecular imaging at a resolution sufficient to resolve major structures in the rat brain. The authors report in this article that, in conjunction with 2-[18F]fluoro-2-deoxyglucose (FDG), microPET provides accurate rates of cerebral glucose metabolism (59.7 to 108.5 micromol/100 g x min) in conscious adult rats as validated by within-subject autoradiographic measurements (59.5 to 136.2 micromol/100 g x min; r = 0.88; F[1,46] = 168.0; P < 0.001). By conducting repeated quantitative scanning, the authors demonstrate the sensitivity and accuracy of FDG-microPET to detect within-subject metabolic changes induced by traumatic brain injury. In addition, the authors report that longitudinal recovery from traumatic brain injury-induced metabolic depression, as measured by quantitative FDG-microPET, is significantly correlated (r = 0.65; P < 0.05) to recovery of behavioral dysfunction, as assessed by the Morris Water Maze performance of the same rats, after injury. This is the first study to demonstrate that FDG-microPET is quantitative, reproducible, and sensitive to metabolic changes, introducing a new approach to the longitudinal study of small animal models in neuroscience research.

Animals↗
PubMed1995

Longitudinal growth changes in the sagittal relationship of maxilla and mandible.

This is a longitudinal study of the growth pattern in sagittal linear measurements at points A, B, and pogonion relative to the pterygoid vertical plane in a Class I sample. Serial cephalometric radiographs were traced and digitized at ages 6, 12, 18, and 24 years. The results indicated that between the ages of 6 and 24 years there was a total growth increment of 6.07, 7.53, and 11.17 mm at points A, B, and pogonion, respectively, in the female Class I sample and 9.49, 11.65, and 16.21 mm at points A, B, and pogonion, respectively, in the male sample. Although the actual change in length of these measurements was larger in the male subjects than in the female subjects, in terms of percentage of growth increment in each of these three measurements from age 6 to 24 years, the anterior movement at point B relative to point A, and at pogonion relative to points B and A was approximately the same for both male and female subjects. When each of the subjects in both male and female samples was rank-ordered according to the size at age 6 years, considerable individual variation was noticeable for most persons within the group. The individual variation in growth pattern in each of the different measurements continues to raise questions about growth prediction and its application in visual treatment objectives.

Adolescent↗
PubMed1991

A time-series analysis of longitudinal weight changes in two adult women.

This study was conducted to examine individual longitudinal serial trends in body weight of two moderately obese adult women. Self-measured daily weights (over 5000 data points for subject 1 and over 3500 for subject 2) were averaged for each month and analyzed using a time-series analysis approach. The best statistical model for both women indicated a significant upward trend (gain 30 and 22 lb, respectively) interrupted by linear decreases (P less than 0.05) during weight loss programs over the 16- and 10-year observation periods, respectively. The women participated in six and eight weight control programs, respectively, and consistently lost weight, averaging 9.17 +/- 1.85 lb and 8.00 +/- 3.57 lb. Both subjects regained weight after dieting, in a period approximately 2.25 times as long as the diet. Numerous weight fluctuations occurred and one subject lost and then regained 10 percent of her body weight during two 5-year periods. Results are examined in terms of a possible weight increase protection benefit, as well as the deleterious medical potential that may occur with numerous weight loss attempts. Suggestions for future research are provided regarding weight cycling, seasonal variations, set point theory, aging effects, and the use of self-directed weight loss initiatives in conjunction with formal weight reduction programs. This study may serve as a prototype for exploring weight fluctuation using time-series analyses and for further investigating the etiology and clinical management of obesity.

Body Mass Index↗
PubMed2006

Longitudinal anthropometric changes in HIV-infected and HIV-uninfected men.

BACKGROUND: Although morphologic abnormalities are common among HIV-infected persons receiving highly active antiretroviral therapy (HAART), longitudinal comparative body shape changes among HAART-treated HIV-infected men versus HIV-seronegative men of similar age remain unclear. METHODS: Since September 1999, men enrolled in the Multicenter AIDS Cohort Study underwent body mass index (BMI) and circumference measurements of the waist, hip, thigh, and arm at each semiannual visit. Changes in these measurements that occurred between 1999 and 2003 among HIV-infected men were compared with measurements of HIV-seronegative men using linear mixed effects regression models. The HIV-infected men were further stratified by treatment group (no antiretroviral therapy [ART], monotherapy or combination [mono/combo] ART, or HAART). Analyses were adjusted for age, nadir CD4 cell count, and BMI (for circumference measurements). RESULTS: Over the 4-year observation period, mean BMI increased significantly among the 392 HIV-seronegative men (0.12 kg/m/y; P < 0.001) but did not change in the 3 HIV-infected groups (combined n = 661). Mean waist and hip circumferences increased significantly in all groups. Hip circumferences increased more slowly in the HIV-positive HAART-treated group (n = 488) than in the HIV-seronegative group (0.18 vs. 0.49 cm/y; P < 0.001), however, yielding a more rapid increase in the waist/hip ratio in the HIV-positive, HAART-treated group over time (0.005 per year; P < 0.001). CONCLUSIONS: The increased rate of change in waist/hip ratio in HIV-infected men receiving HAART compared with HIV-seronegative men is attributable to slower increases in hip circumference rather than an increased rate of change in waist circumference. These findings underscore the importance of body fat composition changes in the peripheral compartment relative to the central compartment among HIV-infected men receiving HAART.

Anthropometry↗
PubMed1990

The power to detect differences in average rates of change in longitudinal studies.

With considerable current interest in longitudinal epidemiologic studies, little is available regarding sample size requirements. This paper considers a method for analysis of longitudinal data, where one compares the mean rates of change for two or more groups, and proposes a statistic for use in determining sample size requirements. One calculates individual rates of change with least squares estimates of slopes of individuals' responses regressed over time. The assumption of linear change over time, while clearly not applicable for some data, applies to many biological measurements, either as recorded or with some transformation. The variances of these estimated slopes have two components: within-individual variability based on measurement error and length and frequency of follow-up, and true between-individual slope variability. It is assumed that measurement error is the same for all subjects, so that the total variances differ due to differences in follow-up. The question addressed is: when can one use the usual ANOVA F statistic to compare group means of estimated slopes? Expected mean squares demonstrate that this F is appropriate when either group has the same number of subjects, or when each subject has the same length and frequency of follow-up. A procedure for computing power and sample size is presented, where one can specify the maximum detectable difference in any two average slopes. Moment estimation and maximum likelihood estimation of variance components from prior data are discussed.

Humans↗
PubMedDate not supplied

[Influence of photon scattering on the quantification of relative changes in longitudinal brain PET studies with 18F-FDG].

AIM: To study the effect of photon scattering on the quantification of relative changes of 18F-FDG uptake in longitudinal brain PET studies. MATERIALS AND METHODS: Two studies from a numerical Zubal phantom were simulated. One of these was a basal reference study and the other was an activated study showing an increase or decrease in the uptake in a region of the anterior cingulated cortex. SimSET Monte Carlo code was used to simulate PET sinograms. Primary photons, which did not undergo interactions, and scattered photons, which underwent one or more interactions, were stored in separate files to assess the effect of scattering. Reconstruction was carried out using an iterative algorithm based on ordered subsets of projections (OSEM-2D). The relative changes in uptake were calculated from images reconstructed with all the photons (primary and scattered) and from images reconstructed with only primary photons. RESULTS: A linear relationship between the calculated and theoretical values was obtained both for the images reconstructed with all the photons and for those reconstructed with primary photons. Our findings show a relative change recovery of 79% +/- 0.4% for all photons and 91% +/- 0.5% for primary photons only. CONCLUSIONS: Our results highlight subestimation of relative changes of 12% +/- 0.7% when scattered photons are used. Thus the importance of correcting this degradation in order to improve quantification is shown.

Algorithms↗
PubMed1993

On physiological effects of positive and negative life changes--a longitudinal study.

A sample of working men and women were followed longitudinally on four occasions during a year with regard to serum triglycerides, plasma prolactin and systolic and diastolic blood pressure at rest. Participants were asked about life changes that they had gone through during the examination year. They were also asked to rate the importance and the direction (positive and negative, respectively) of the changes. On the basis of this information participants were divided into a no event group (N = 20), a positive event group (N = 11) and a negative event group (N = 11). Statistical analyses revealed that prolactin levels tended to increase in the negative event group whereas blood pressure as well as serum triglycerides increased in the negative event group and decreased in the positive event group.

Adult↗
PubMed2005

Application of micro-CT assessment of 3-D bone microstructure in preclinical and clinical studies.

As the mechanical competence of trabecular bone is a function of its apparent density and 3-D distribution, assessment of 3-D trabecular structural characteristics may improve our ability to understand the pathophysiology of osteoporosis, to test the efficacy of pharmaceutical intervention, and to estimate bone biomechanical properties. We have studied ovariectomy-induced osteopenia in rats and its treatment with agents such as estrogen and sodium fluoride. We have demonstrated that 3-D micro-computed tomography (microCT) can directly quantify mouse trabecular and cortical bone structure with an isotropic resolution of 6 microm(3). MicroCT is also useful for studying osteoporosis in mice and phenotypes of mice with gene manipulation, such as SHIP-knockout mice, which are severely osteoporotic due to increased numbers of hyperresorptive osteoclasts, PTHrP heterozygous-null mice, and mice with Zmpste24 deficiency. MicroCT can quantify osteogenesis in mouse Ilizarov leg-lengthening procedures, osteoconduction in a rat cranial defect model, and structural changes in arthritic rabbits, rats, and mice. In clinical studies, we evaluated longitudinal changes in the iliac crests. Paired bone biopsies from the same premenopausal and postmenopausal women showed the changes in 3-D trabecular structure, such as decreased trabecular thickness, shifting of trabecular model from platelike structure to rodlike structure, and decreased degree of anisotropy were remarkable. Treatment with PTH in postmenopausal women with osteoporosis significantly improved trabecular morphology with a shift toward a more platelike structure, increased trabecular connectivity density, and increased cortical thickness. Paired bone biopsy specimens from the iliac crest in postmenopausal women with osteoporosis before and an average of 2 years after beginning of estrogen replacement therapy demonstrated that posttreatment biopsies showed a significant change in the ratio of plates to rods and statistically insignificant changes in other 3-D trabecular parameters. Thus, microCT can characterize 3-D structure of various animal models, and the longitudinal changes in 3-D bone microarchitectural integrity that deteriorates in the transmenopausal period, is preserved with HRT, and is improved with PTH treatment in postmenopausal women.

Animals↗
PubMed1995

A simulation study of estimators for rates of change in longitudinal studies with attrition.

Many longitudinal studies and clinical trials are designed to compare rates of change over time in one or more outcome variables in several groups. Most such studies have incomplete data because some patients drop out before completing the study. The missing data may induce bias and inefficiency in naive estimates of important parameters. This paper uses Monte Carlo methods to compare the bias and efficiency of several two-stage estimators of the effect of treatment on the mean rate of change when the missing data arise from one of four processes. We also study the validity of confidence intervals and the power of hypothesis tests based on these estimates and their standard errors. In general, the weighted least squares estimator does relatively well, as does an analysis of covariance type estimator proposed by Wu et al. The best estimates of variance components are based on complete cases or maximum likelihood.

Analysis of Variance↗
PubMed1988

Comparing change in longitudinal studies: adjusting for initial value.

Adjustment for initial value may yield misleading results when comparing change over time in two populations. This paper presents a methodology for correcting for the effects of regression to the mean when change over time is regressed on standardized initial level. The results are used to examine the bias introduced by failing to correct for the effects of regression to the mean in the two sample problem. We also examine the implications of adjusting for initial value in certain observational studies. When group assignment is known to be related to initial value, we argue that this adjustment procedure is inappropriate. The results are illustrated using data from a longitudinal study of lung function decline.

Analysis of Variance↗
PubMed2002

Predictors of functional change: a longitudinal study of nondemented people aged 65 and older.

OBJECTIVES: To identify factors associated with functional change in an older population and investigate interactions among selected potential risk factors. DESIGN: A population-based prospective cohort study. SETTING: A random sample was selected from the Group Health Cooperative members in the Seattle area from 1994 to 1996 and followed biennially. PARTICIPANTS: Two thousand five hundred eighty-one people aged 65 and older, cognitively intact at baseline. MEASUREMENTS: Functional status was measured by activities of daily living, instrumental activities of daily living, and performance-based physical function testing. RESULTS: The cohort status at the time of these analyses was: deceased, 391; withdrawn, 179; dementia, 152; and on study, 1,873. The mean follow-up time was 3.4 years. Using linear regressions with Generalized Estimating Equation, selected medical conditions (diabetes mellitus, hypertension, coronary heart disease, cerebrovascular disease (CVD), osteoporosis, arthritis, and cancer), low cognitive function, depression, and smoking were associated with worse functional outcomes. Exercise and moderate alcohol use were associated with better functional outcomes. Over the follow-up period, coronary heart disease, CVD, and depression were associated with increased rates of functional decline. Exercise and moderate alcohol consumption were associated with decreased rates of functional decline. Significant interactions were observed between exercise and coronary heart disease, moderate alcohol use and CVD, and cognition and CVD. CONCLUSIONS: Our study has identified not only risk factors associated with functional decline but also the interactions among these factors. These observations, along with other published research, add to the growing understanding of the underlying process of functional change and could provide a basis to design effective strategies to delay functional decline.

Activities of Daily Living↗
PubMed1991

Adolescent drug use, psychological distress, and physical symptoms.

The longitudinal interrelationships among general drug use, psychological distress, and physical symptoms were investigated in a three wave panel study of a community sample of adolescents interviewed when they were 12, 15, and 18 years of age. Results did not provide any support for the hypothesis that adolescents use drugs in general to cope with pre-existing psychological distress and physical symptoms. In contrast, the results supported the hypothesis that general drug use contributes to physical and psychological impairments over time. However, such drug-induced psychological distress and physical symptoms only occurred in later adolescence (from ages 15 to 18), and no evidence of impairments due to general drug use or specific alcohol use was found in early adolescence (from ages 12 to 15). Psychological distress and physical symptoms influenced each other over time, and physical symptoms partially mediated longitudinal changes in psychological distress. However, general drug use did not mediate any longitudinal changes in psychological distress and physical symptoms.

Adaptation, Psychological↗