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PubMed2002

Increased rate of arthrodesis with strut grafting after multilevel anterior cervical decompression.

STUDY DESIGN: Reconstruction techniques after multilevel anterior cervical decompression were retrospectively compared. OBJECTIVE: To compare radiographic and clinical outcomes of multiple interbody grafting with strut grafting. SUMMARY OF BACKGROUND DATA: Previous studies have reported lower fusion rates for anterior cervical decompressions reconstructed with multiple interbody grafts as opposed to a single strut graft, although these techniques have never been directly compared in a consecutive series of patients who underwent surgery by a single surgeon. METHODS: Over a 20-year period, 190 patients underwent anterior cervical decompression and autogenous grafting without internal fixation and were followed for an average of 68 months. There were 98 two-level and 33 three-level discectomies with interbody grafting. These were compared with 16 one-level, 21 two-level, 20 three-level, and 2 four-level corpectomies with strut grafting. Radiographic and clinical outcomes were compared between the groups by chi2 and rank-sum analysis, respectively. RESULTS: Of the 59 patients who underwent strut grafting, 55 achieved a solid arthrodesis (93%), as compared with 87 of the 131 patients who underwent multiple interbody grafting (66%) (P = 0.0002). There were six cases of graft displacement or extrusion among the 59 patients who had strut grafts, as compared with no graft-related complications among the 131 patients who had interbody grafts (P < 0.0001). More "good" and "excellent" clinical outcomes were found among patients who underwent strut-grafting (88% vs 84%), although the difference was not statistically significant (P = 0.73). However, patients with a pseudarthrosis had significantly poorer clinical outcomes (P < 0.0001). CONCLUSIONS: A much higher fusion rate was achieved after corpectomy and strut grafting than after multilevel discectomy and interbody grafting. Although there were strut graft-related complications, four of these six complications occurred among patients who had a postlaminectomy kyphosis. Because pseudarthrosis resulted in poorer clinical outcomes, strut grafting should be considered after multilevel anterior cervical decompression to increase the likelihood of successful fusion.

Adult↗
PubMed1997

A cost-effective and rational surgical approach to patients with snoring, upper airway resistance syndrome, or obstructive sleep apnea syndrome.

The past decade has seen several innovations in the surgical techniques available for treatment of patients with sleep-disordered breathing. Outpatient techniques such as laser-assisted uvulopalatoplasty (LAUP) and more aggressive procedures designed to address hypopharyngeal and base of tongue obstruction (genioglossus advancement and hyoid myotomy) have been developed and proven successful. We describe the efficacy of LAUP for snoring (72.7%), upper airway resistance syndrome (81.8%), and mild (mean [+/-SD] respiratory disturbance index [RDI] = 12 +/- 8.1) obstructive sleep apnea (41.7%) in 56 patients who underwent 132 LAUP procedures in a 26-month period. Thirty-two patients with more significant obstructive sleep apnea (mean RDI = 41.8 +/- 23.1) underwent multilevel pharyngeal surgery consisting of genioglossus advancement and hyoid myotomy combined with uvulopalatopharyngoplasty. The surgical success rate in this group of patients was 85.7% when commonly accepted criteria were applied. We recommend a stratified surgical approach to patients with sleep-disordered breathing. Progressively worse airway obstruction marked by multilevel pharyngeal collapse and more severe sleep-disordered breathing is treated with incrementally more aggressive surgery addressing multiple areas of the upper airway.

Adult↗
PubMed1999

The progressive nature of peripheral arterial disease in young adults: a prospective analysis of white men referred to a vascular surgery service.

OBJECTIVE: The onset of symptomatic peripheral arterial disease at a young age (premature PAD) has been associated with rapid progression, bypass graft failure, and amputation. This study was performed to document the incidence of these complications and to determine the risk factors for poor outcome in patients with premature PAD. METHODS: This study was designed as a prospective longitudinal analysis, with patients who were ambulatory or hospitalized at a single vascular referral institution. The subjects were 51 white men with onset of PAD symptoms before the age of 45 years (mean age of onset, 41 +/- 0.5 years) and represented consecutive patients who were seen at the vascular surgery service during a 4-year period. Thirty of the study subjects (58%) were recruited during the first 2 years. The main outcome measures were number and type of lower extremity revascularization procedures or amputations that were necessitated during the follow-up period. RESULTS: During a mean follow-up period of 73 +/- 6 months, 15 patients (29%) had PAD that remained stable without interventions and 15 (29%) had PAD that remained stable for a mean of 76 +/- 13 months after a single intervention. Twenty-one patients (41%) required multiple operations or major amputations. In a comparison of the 30 PAD patients whose conditions were stable with or without a single intervention with the 21 PAD patients who required multiple interventions (REDO), there were no differences in smoking, hypertension, diabetes, or dyslipidemias. The REDO group had a younger mean age at the onset of symptoms (39 +/- 1 years vs 43 +/- 2 years; P <.001). At entry, the REDO patients had a higher prevalence of infrainguinal or multilevel disease (57% vs 20%; P =.03), a lower mean ankle brachial index (0. 44 +/- 0.04 vs 0.56 +/- 0.03; P =.02), and more frequent tissue loss (24% vs 0; P =.005). The REDO patients had a higher mean lipoprotein (a) level than did the patients with stable conditions (51 +/- 11 mg/dL vs 27 +/- 5 mg/dL; P =.03), but there were no significant differences in the mean plasma homocysteine levels (19 +/- 2 micromol/L vs 16 +/- 1 micromol/L) or in the proportion of patients with hypercoagulable states (33% vs 30%). The only predictive variables that were selected with stepwise logistic regression analysis were age at onset (P <.002; odds ratio, 1.4; 95% confidence interval, 1.11 to 1.81) and ankle brachial index of less than 0.5 (P <.008; odds ratio, 6.4; 95% confidence interval, 1.5 to 27.3). CONCLUSION: Although 60% of the white men with premature PAD who were referred to a vascular surgery service had conditions that appeared to remain stable, these data show that approximately 40% of the patients will require multiple interventions because of disease progression or bypass graft failure. Clinical indicators, not serum markers, are predictors of poor outcome in patients with premature PAD. The results of this study suggest that patients with onset of PAD before the age of 43 years who have objective evidence of advanced disease are predisposed to multiple interventions.

Adult↗
PubMed1992

Inverse correlation between essential antioxidants in plasma and subsequent risk to develop cancer, ischemic heart disease and stroke respectively: 12-year follow-up of the Prospective Basel Study.

There is accumulating evidence that free radicals may contribute to various diseases such as cancer or cardiovascular disease. Possible health hazards can to some extent be prevented by the body's multilevel defense system against free radicals, which comprises, besides others, antioxidant vitamins. The 12-year mortality follow-up of 2,974 participants of the Basal Study allowed to test the hypothesis that low antioxidant vitamin plasma concentrations (vitamin A, C, E and carotene) were associated with increased death from cancer of various sites and death from atherosclerosis such as ischemic heart disease and stroke, respectively. For the analysis 204 cancer cases, 132 fatalities from ischemic heart disease (IHD) and 31 deaths from cerebral vascular disease were available. Cancer mortality. Overall mortality from cancer was associated with low mean plasma levels of carotene adjusted for cholesterol (p less than 0.01) and of vitamin C (p less than 0.01). Bronchus and stomach cancers were associated with a low mean plasma carotene level (p less than 0.01). Subjects with subsequent stomach cancer had also lower mean vitamin C and lipid-adjusted vitamin A levels than survivors (p less than 0.05). Calculating the relative risk with exclusion of mortality during the first two years of follow-up, low plasma carotene was associated with an increased risk for bronchus cancer (RR 1.8, p less than 0.05), and the small number of stomach cancer cases (RR 2.95, p less than 0.05) low plasma levels of carotene and vitamin A with all cancer types (RR 2.47, p less than 0.01), and low plasma retinol in older subjects (greater than 60 years) with lung cancer (RR 2.17, p less than 0.05). Studies in other cohorts with a poor vitamin E status revealed an increased risk of subsequent cancer at low vitamin E levels as well. It is concluded that low plasma levels of all major essential antioxidants are associated with an increased risk of subsequent cancer mortality. Cardio-vascular mortality. Plasma carotene concentration below quartile 1 was associated with an increased risk for IHD (RR 1.53, p = 0.02). The same was true for low levels of both carotene and vitamin C (RR = 1.96, p = 0.022). The risk of cerebrovascular death was elevated in subjects with low carotene in the presence of low vitamin C plasma concentration (RR 4.17, p less than 0.01). These data confirm and extend recent findings on an inverse correlation of beta-carotene and vitamin C respectively to CVD.(ABSTRACT TRUNCATED AT 400 WORDS)

Antioxidants↗
PubMed2006

Multilevel perspectives on diffusing a physical activity promotion program to reach diverse older adults.

Diffusing research-based physical activity programs in underserved communities could improve the health of ethnically diverse populations. We utilized a multilevel, community-based approach to determine attitudes, resources, needs, and barriers to physical activity and the potential diffusion of a physical activity promotion program to reach minority and lower-income older adults. Formative research using focus groups and individual interviews elicited feedback from multiple community sectors: community members, task force and coalition members, administrators, service implementers, health care providers, and physical activity instructors. Using qualitative data analysis, 47 transcripts (N = 197) were analyzed. Most sectors identified needs for culturally diverse resources, promotion of existing resources, demonstration of future cost savings, and culturally tailored, proactive outreach. The program was viewed favorably, especially if integrated into existing resources. Linking sectors to connect resources and expertise was considered essential. Complexities of such large-scale collaborations were identified. These results may guide communities interested in diffusing health promotion interventions.

Age Factors↗
PubMed1990

Multilevel regulation of surface antigen gene expression in Paramecium tetraurelia.

A family of genes is responsible for production of surface antigenic components of Paramecium tetraurelia. These surface proteins are expressed in a mutually exclusive manner. Individuals rarely display more than one type. However, changes in environmental conditions can cause different surface proteins which replace preexisting types to be expressed. We investigated the nature of regulation of the genes for the A, C, and H surface antigens of P. tetraurelia. A system for in vitro run-on transcription was developed from crude Paramecium extracts and used in this analysis. The genes for surface antigens A and H were controlled at the level of transcription. However, the gene for surface antigen C demonstrated both transcriptional and posttranscriptional control, depending on the serotype being expressed. When animals expressed serotype A, the gene for surface antigen C was not transcribed. However, when animals expressed serotype H, the gene for surface antigen C was actively transcribed and stable surface antigen C mRNA was present in the cells, although surface antigen C was not detectable by serotype testing or by a salt-alcohol extraction method. The kinetics of transformation from serotype H to serotype C were determined by using the in vitro transcription system and monitoring steady-state RNA levels. During the transition, serotype A transcription was detected in run-on transcription experiments, although this RNA did not accumulate. The results indicate that serotype expression is controlled at several levels and that not all serotype genes are controlled in the same manner.

Animals↗
PubMed1996

Reliability and validity of the FIM for persons aged 80 years and above from a multilevel continuing care retirement community.

OBJECTIVE: Development of accurate functional assessment instruments will help clinicians evaluate treatment outcome and plan realistic rehabilitation goals for elderly patients. The reliability, validity, and appropriateness of the Functional Independence Measure (FIM) were examined for a population aged 80 years and more from a multilevel, continuing care retirement community. DESIGN: Forty-nine residents (average age 89.7 years, range 80 to 104 years; 46 women), were randomly selected. SETTING: Subjects were grouped according to their residence in either an Independent community (18 subjects), Sheltered Care (16 subjects), or Skilled Nursing Facility (15 subjects). MEASUREMENTS: Subjects were evaluated twice using the FIM. Motor and cognitive scores were converted into interval measures (logits) using Rasch Analysis with the BIGSTEPS statistical package. Parametric statistical procedures were utilized to further analyze data. RESULTS: FIM motor and cognitive items formed 2 unidimensional and linear subscales. Hierarchical levels of FIM item difficulties were identified. Bladder management, bowel management, and grooming were misfitting motor items. Memory misfit for the cognitive subscale. High test-retest reliability for 45 repeated FIM assessments for the motor, (ICC = .9) and cognitive subscales (ICC = .8) was demonstrated. One way ANOVA for FIM ratings for the 3 groups demonstrated significant differences for both the motor subscale, F(2,46) = 34.71, p < .05, and the cognitive subscales, F(2,46) = 12.42, p < .05. CONCLUSION: Construct validity of the FIM was demonstrated. High test-retest reliability was demonstrated. Environmental context and operational definitions influenced FIM ratings. Subjects' FIM ratings, abilities, and time to complete the locomotor walking item correlated with their current residence in increasingly dependent environments. These findings suggest that with certain caveats, the FIM may be useful as a functional assessment instrument for persons who are 80 or more years old.

Activities of Daily Living↗
PubMed2006

Sociodemographic characteristics of the neighborhood and depressive symptoms in older adults: using multilevel modeling in geriatric psychiatry.

OBJECTIVE: Neighborhood sociodemographic characteristics may be important to the mental health of older adults who have decreased mobility and fewer resources. Our objective was to examine the association between neighborhood context and level of depressive symptomatology in older adults in a diverse geographic region of central North Carolina. METHODS: The sample included 2,998 adults 65 or older residing in 91 census tracts. Depressive symptoms were measured using the Center for Epidemiologic Studies-Depression scale (CES-D). Neighborhoods were characterized by five census-based characteristics: socioeconomic disadvantage, socioeconomic advantage, racial/ethnic heterogeneity, residential stability, and age structure. RESULTS: In ecologic level analyses, level of census tract socioeconomic disadvantage was associated with increased depressive symptoms. To determine whether neighborhood context was associated with depressive symptoms independently of individual characteristics, the authors used multilevel modeling. The authors examined the ability of each of five neighborhood (level 2) characteristics to predict a level 1 outcome (CES-D symptoms) controlling for the effects of individual (level 1) characteristics. Younger age, being widowed, lower income, and having some functional limitations were associated with increased depression symptoms conditional on census tract random effects. However, none of the neighborhood characteristics was significantly associated with depression symptoms, conditional on census tract random effects, either unadjusted or adjusted for individual characteristics. CONCLUSION: Any observed association between neighborhood sociodemographic characteristics and individual depressive symptoms in our sample may reflect the characteristics of the individuals who reside in the neighborhood rather than the neighborhood characteristics themselves. The use of multilevel modeling is important to separate these effects.

Aged↗
PubMed1993

Modelling lactation using an inverse polynomial in a multilevel statistical model.

A method is outlined for modelling the relationship between breast-milk production and time from delivery, suitable for data collected longitudinally. The relationship is described using inverse polynomials. In a two-level model the coefficients are specified as random variables across subjects, allowing within- and between-subject variation to be separately estimated. In a three-level model, day-to-day variation can also be separately estimated. The model is illustrated using data from the Chiang Mai Lactation Project. It allows the use of covariates that vary over time, and provides a method of analysis that is compatible with the practical constraints on the timing of data collection that are inherent in longitudinal studies.

Age Factors↗
PubMed2005

Social capital and young adolescents' perceived health in different sociocultural settings.

We conducted a cross-national study to examine the association between neighbourhood socioeconomic deprivation, social capital and child health in two countries and multiple ethnic groups. For our analysis we used data from (1) the Project on Human Development in Chicago Neighborhoods (PHDCN), USA and (2) the Maastricht Quality of Life study (MQoL), the Netherlands. Both the PHDCN and the MQoL collected data on objective neighbourhood socioeconomic deprivation, subjective neighbourhood social capital (i.e. informal social control, ISC, social cohesion and trust, SC&T), and children's perceived health. For the present analyses, 11- and 12-year olds were selected. Multilevel analyses were conducted using both neighbourhood level and individual-level data. Lower socioeconomic deprivation scores and higher levels of ISC as well as SC&T were associated with higher levels of children's perceived health, in both Maastricht and the Chicago Hispanic subsample, but not in the Chicago non-Hispanic samples. The results suggest that associations between the wider social environment and health outcomes vary across different populations and cross-national contexts.

Chicago↗
PubMed2003

Psychosocial and perceived environmental correlates of physical activity in rural and older african american and white women.

African American and rural older women are among the least active segments of the population. This study, guided by social cognitive theory, examined the correlates of physical activity (PA) in 102 rural older women (41% African American; 70.6 +/- 9.2 years). In bivariate associations, education, marital status, self-efficacy, greater pros than cons, perceived stress, social support, and perceived neighborhood safety were positively associated with PA; age, depressive symptoms, perceived sidewalks, health care provider discussion of PA, and perceived traffic were negatively associated with PA. In a hierarchical regression analysis, the sociodemographic (R(2) = 23%), psychological (IR(2) = 9%), social (IR(2) = 6%), and perceived physical environmental (IR(2) = 9%) sets of variables were significant (p <.05) predictors of PA (model R(2) = 47%). In response to open-ended questions, most women cited individual and social factors as PA barriers and motivators; falls, injuries, and heart attacks were identified most often as risks. These findings support the importance of multilevel influences on PA in older rural women and are useful for informing PA interventions.

Black or African American↗
PubMed2004

Comprehensive focusing analysis of various Fresnel zone plates.

A series-form expression for the individual diffracted field of a general annular ring is derived from the Rayleigh-Sommerfeld diffraction integral. It can be used for the accurate and fast simulation of any diffractive focusing element composed of concentric transparent rings. We present a comprehensive analysis, based on the leading term and the linear superposition principle, of the focusing performances of various Fresnel zone plates. Many problems, such as the equivalent aperture function, the diffraction efficiency, the focal spot pattern, the suppression of higher orders and the appearance of "fractional orders," and the explanation for the appearance of Fraunhofer diffraction patterns, are analytically investigated in detail. Because of the great similarity between Fresnel zone plates and multilevel diffractive lenses, most of the obtained results are also applicable to multilevel diffractive lenses.

Journal Article↗
PubMedDate not supplied

Multilevel modeling of a clustered continuous outcome: nurses' work hours and burnout.

BACKGROUND: Multilevel models were designed to analyze data generated from a nested structure (e.g., nurses within hospitals) because conventional linear regression models underestimate standard errors and, in turn, overestimate test statistics. OBJECTIVES: To introduce 2 types of multilevel models, the random intercept model and the random coefficient model, to describe the correlation among observations within a cluster, and to demonstrate how to identify the superior model. METHOD: The conceptual and mathematical bases for the 2 multilevel model types are presented. Intraclass correlation is defined and assessment of model fit is detailed. An empirical example is presented in which average work hours per week and burnout are analyzed using data from 4,320 staff nurses clustered in 19 hospitals. RESULTS: Average work hours were positively associated with nurse burnout. The multilevel models corrected the problem of underestimated standard errors in conventional linear regression models. Graphs displaying the hospital-level differences illustrated the 2 multilevel model types. Although the multilevel models corrected the underestimation of standard errors, the results did not differ substantively for the conventional or the 2 multilevel models. The intraclass correlation coefficient was .044, indicating that the extent of shared variance among nurses in a hospital was low. The random intercept model fit the data better than did the random coefficient model. CONCLUSIONS: Multilevel models provide a more accurate and comprehensive description of relationships in clustered data than do conventional models, by correcting underestimated standard errors, by estimating components of variance at several levels, and by estimating cluster-specific intercepts and slopes.

Burnout, Professional↗
PubMed2004

Geometric results of anterior cervical plate stabilization in degenerative disease.

STUDY DESIGN: Consecutive case retrospective computerized analysis of lateral radiographs. OBJECTIVES: To investigate the time evolution of the geometry of anterior cervical discectomy and fusion using a new computer-aided measurement technique. SUMMARY OF BACKGROUND DATA: Prior clinical studies have reported benefits and complications of anterior cervical plate stabilization, but have not comprehensively described changes in sagittal geometry following arthrodesis and plating. High fusion success rates have been reported for single-level discectomy and fusion, whereas multilevel procedures have demonstrated lower clinical success rates with increased hardware failure and pseudarthrosis rates. METHODS: Sagittal alignment data were collected from lateral radiographs of 51 patients with 52 operations for single- or multiple-level anterior cervical discectomy and fusion, both with and without anterior cervical plate stabilization. Intervertebral angulation and separation at the operated segments before surgery, immediately after surgery, and at long-term follow-up were compared using a computer-aided technique. RESULTS: Single-level anterior cervical discectomy and fusion with plate stabilization lost 0.9 degrees of the operatively obtained lordosis after surgery compared to 7.5 degrees for single-level fusions with bone alone (P = 0.0001). In multilevel anterior cervical discectomy and fusion, the bottommost level of the anterior cervical discectomy and fusion construct was much more prone to collapse than the remaining levels (mean bottom-level loss of 4.0 degrees vs. mean 0.2 degrees increase at the remaining levels, P < 0.0001). CONCLUSIONS: Anterior cervical plate stabilization helps maintain operatively obtained segmental distraction and lordosis following anterior cervical discectomy and fusion. In multilevel procedures, this study found that postoperative collapse is largely localized to the bottommost level, where hardware failure and pseudarthrosis have been observed most often by others.

Adult↗
PubMed1999

Multilevel modeling and model averaging.

Multilevel modeling, also known as hierarchical regression, generalizes ordinary regression modeling to allow explicit and flexible compromises between simple and complex models. This article provides an elementary introduction to multilevel modeling as a model-averaging technique. Model averaging provides an alternative to model selection, and it emphasizes the role of prior information in finding good models.

Abortion, Spontaneous↗
PubMed2001

[A telemedical multilevel server network system].

Telemedicine is a hot research focus. When we develop the telemedicine system, we find that in China the network condition can not fit the demands of the transregional telemedicine service. In order to improve the poor conditions, we have designed a set of telemedicine system based on distributed multilevel server network model. The paper expounds the structure and the working process of the system, then goes into the technology details in realizing it, finally discusses some relative questions.

Computer Communication Networks↗
PubMed2001

Relating amino acid sequence to phenotype: analysis of peptide-binding data.

We illustrate data analytic concerns that arise in the context of relating genotype, as represented by amino acid sequence, to phenotypes (outcomes). The present application examines whether peptides that bind to a particular major histocompatibility complex (MHC) class I molecule have characteristic amino acid sequences. However, the concerns identified and addressed are considerably more general. It is recognized that simple rules for predicting binding based solely on preferences for specific amino acids in certain (anchor) positions of the peptide's amino acid sequence are generally inadequate and that binding is potentially influenced by all sequence positions as well as between-position interactions. The desire to elucidate these more complex prediction rules has spawned various modeling attempts, the shortcomings of which provide motivation for the methods adopted here. Because of (i) this need to model between-position interactions, (ii) amino acids constituting a highly (20) multilevel unordered categorical covariate, and (iii) there frequently being numerous such covariates (i.e., positions) comprising the sequence, standard regression/classification techniques are problematic due to the proliferation of indicator variables required for encoding the sequence position covariates and attendant interactions. These difficulties have led to analyses based on (continuous) properties (e.g., molecular weights) of the amino acids. However, there is potential information loss in such an approach if the properties used are incomplete and/or do not capture the mechanism underlying association with the phenotype. Here we demonstrate that handling unordered categorical covariates with numerous levels and accompanying interactions can be done effectively using classification trees and recently devised bump-hunting methods. We further tackle the question of whether observed associations are attributable to amino acid properties as well as addressing the assessment and implications of between-position covariation.

Amino Acid Sequence↗
PubMed2007

Using hierarchical models to attribute sources of variation in consumer assessments of health care.

The Consumer Assessments of Healthcare Providers and Systems (CAHPS) Medicare Advantage (MA-CAHPS) survey has provided extensive and uniform data for 8 years on the quality of Medicare health plans in the United States. The complex structure of the data makes hierarchical modelling an appropriate analytic tool. After describing the CAHPS survey and the analytic methods used in standard reports, we review research using two multilevel modelling strategies, each addressing a different aspect of the structure of the CAHPS data. The first fits a 2-level Fay-Herriott-type model to data aggregated by plan to estimate plan-level correlations among summary scores on different items. By forming separate measures for healthier and sicker members of each plan, we were able to determine which items measured distinct dimensions of quality depending on health status. The second analysis evaluated the relative contributions of geography and organizational units to the various quality measures, and the amount of variation over time in each. Geographical variation predominated for aspects of member experiences that are not typically under the direct control of plans, and the geographical effects were very stable over time. Each of the two analyses can be regarded as a simplification for particular objectives of a larger underlying model. Further methodological development is needed to better characterize variation in quality.

Data Interpretation, Statistical↗