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Biomedical subjects

Michael E Miller

Publications and source records attributed to Michael E Miller.

9 recordsLinked to original sources
PubMed2003

Baseline balance and functional decline in older adults with knee pain: the Observational Arthritis Study in Seniors.

OBJECTIVES: To examine the cross-sectional and longitudinal effect of baseline balance, independent of multiple covariates (sociodemographic variables, comorbidities), on self-reported disability and several measures of functional performance. DESIGN: Observational Arthritis Study in Seniors was a community-based longitudinal study. SETTING: Data collection was conducted at an exercise science research laboratory. PARTICIPANTS: A cohort of 245 women and 235 men, aged 65 and older, with self-reported knee pain. MEASUREMENTS: Measurements of balance, self-reported disability, functional performance, strength, sociodemographic characteristics, disease burden (including radiographic knee osteoarthritis (OA)), and functional limitations were obtained on participants at baseline and 30 months. The four outcome measures (self-reported disability, stair climb time, car time, preferred walking speed) were also collected at 15 months. RESULTS: In cross-sectional analyses, baseline balance was significantly associated with each of the four outcome measures before adjusting for baseline knee strength. After adjusting for knee strength, baseline balance remained significantly associated with all functional performance outcomes and self-reported disability. In longitudinal analyses, baseline balance had a significant effect on car-time performance, whereby individuals in the lowest quartile of baseline balance scores declined in a quadratic manner from baseline to Month 30. CONCLUSION: Baseline balance, independent of strength and various other covariates, is an important component of performance for transfer and ambulatory tasks and for self-reported disability. Balance was predictive of change in performance over time only in a task that presented a significant challenge to the lateral mobility/stability of participants. Balance was not predictive of decline in ambulatory performance-based tasks or in self-reported disability.

Age Factors↗
PubMed2002

Phrenic nerve pacing in a tetraplegic patient via intramuscular diaphragm electrodes.

In patients with ventilator-dependent tetraplegia, phrenic nerve pacing (PNP) provides significant clinical advantages compared with mechanical ventilation. This technique however generally requires a thoracotomy with its associated risks and in-patient hospital stay and carries some risk of phrenic nerve injury. We have developed a method by which the phrenic nerves can be activated via intramuscular diaphragm electrodes. In one patient with ventilator-dependent tetraplegia, two intramuscular diaphragm electrodes were implanted into each hemidiaphragm near the phrenic nerve motor points via laparoscopic surgery. The motor points were identified employing a previously devised mapping technique. Because inspired volumes were suboptimal on the right, a second laparoscopic procedure was necessary to position electrodes near the anterior and posterior branches of the right phrenic nerve. During bilateral stimulation, inspired volume was 580 ml. After a reconditioning program of progressively increasing diaphragm pacing, maximum inspired volumes on the left and right hemidiaphragms increased significantly. Maximum combined bilateral stimulation was 1120 ml. Importantly, the patient has been able to comfortably tolerate full-time pacing. If confirmed in additional patients, PNP with intramuscular diaphragm electrodes via laparoscopic surgery may provide a less invasive and less costly alternative to conventional PNP.

Adult↗
PubMed2002

Declines in strength and balance in older adults with chronic knee pain: a 30-month longitudinal, observational study.

OBJECTIVES: To document changes in lower extremity strength and balance over a 30-month period in older adults with chronic knee pain, and to identify relationships among these variables that may prove useful in designing a subsequent clinical intervention trial. METHODS: This longitudinal, 30-month, observational study was designed to examine the association of physical, psychological, social, and environmental factors with severity and progression of physical disability caused by chronic knee pain. This article will focus on 2 physical measures: strength and dynamic balance. The participants were a cohort of 480 adults 65 years of age or older with chronic knee pain. Measurements included: 1) force platform dynamic balance measure of the center of pressure excursion during a forward and subsequent backward lean, 2) isokinetic strength measures of concentric and eccentric knee flexion and extension, and concentric ankle plantar flexion and dorsiflexion, and 3) body mass index and a knee pain scale to measure obesity and knee pain, respectively. RESULTS: A maximum-likelihood analysis revealed an overall significant decline in knee (P < 0.001) and ankle (P = 0.012) strength, and balance (P < 0.001) after a 30-month followup period. Participants with greater knee strength at baseline had less expected decline in balance at followup than their weaker counterparts (4.2% versus 7.7% for the 75th versus 25th percentiles of strength; P = 0.023). However, the absolute decline in balance over 30 months was similar regardless of baseline ankle strength. CONCLUSIONS: Adults age >or=65 years with chronic knee pain experience significant declines in balance and lower extremity strength over a 30-month period. Moreover, greater knee and ankle muscular strength is associated with better balance. Previous studies have shown that weight training is effective in improving balance in older adults with knee osteoarthritis. Taken together, these studies present a strong rationale for incorporating weight training into an exercise prescription for older adults with chronic knee pain.

Aged↗
PubMed2002

Do optimism and pessimism predict physical functioning?

Dispositional optimism has been shown to be related to self-report measures of health and well-being, yet little research has examined the relationship between optimism and more objective measures of functioning. The purpose of this study was to examine the relationship between optimism and pessimism and objective physical functioning. Four hundred eighty community-dwelling older adults with knee pain completed a measure of optimism and pessimism and were observed performing four daily activities (walking, lifting an object, climbing stairs, and getting into and out of a car). Results indicated that pessimism was significantly related to performance on all four tasks (p < .001), while optimism was related to performance only on the walking task (p < .05), after controlling for demographic and health variables.

Activities of Daily Living↗
PubMed2002

Exercise and depressive symptoms: a comparison of aerobic and resistance exercise effects on emotional and physical function in older persons with high and low depressive symptomatology.

This study examines and compares the effect of aerobic and resistance exercise on emotional and physical function among older persons with initially high or low depressive symptomatology. Data are from the Fitness, Arthritis and Seniors Trial, a trial among 439 persons 60 years or older with knee osteoarthritis randomized to health education (control), resistance exercise, or aerobic exercise groups. Depressive symptoms (assessed by the Center for Epidemiologic Studies--Depression scale) and physical function (disability, walking speed, and pain) were assessed at baseline and after 3, 9, and 18 months. Compared with results for the control group, aerobic exercise significantly lowered depressive symptoms over time. No such effect was observed for resistance exercise. The reduction in depressive symptoms with aerobic exercise was found both among the 98 participants with initially high depressive symptomatology and among the 340 participants with initially low depressive symptomatology and was the strongest for the most compliant persons. Aerobic and resistance exercise significantly reduced disability and pain and increased walking speed both, and to an equal extent, in persons with high depressive symptomatology and persons with low depressive symptomatology.

Activities of Daily Living↗
PubMed2002

Mixed effects logistic regression models for multiple longitudinal binary functional limitation responses with informative drop-out and confounding by baseline outcomes.

In the context of analyzing multiple functional limitation responses collected longitudinally from the Longitudinal Study of Aging (LSOA), we investigate the heterogeneity of these outcomes with respect to their associations with previous functional status and other risk factors in the presence of informative drop-out and confounding by baseline outcomes. We accommodate the longitudinal nature of the multiple outcomes with a unique extension of the nested random effects logistic model with an autoregressive structure to include drop-out and baseline outcome components with shared random effects. Estimation of fixed effects and variance components is by maximum likelihood with numerical integration. This shared parameter selection model assumes that drop-out is conditionally independent of the multiple functional limitation outcomes given the underlying random effect representing an individual's trajectory of functional status across time. Whereas it is not possible to fully assess the adequacy of this assumption, we assess the robustness of this approach by varying the assumptions underlying the proposed model such as the random effects structure, the drop-out component, and omission of baseline functional outcomes as dependent variables in the model. Heterogeneity among the associations between each functional limitation outcome and a set of risk factors for functional limitation, such as previous functional limitation and physical activity, exists for the LSOA data of interest. Less heterogeneity is observed among the estimates of time-level random effects variance components that are allowed to vary across functional outcomes and time. We also note that. under an autoregressive structure, bias results from omitting the baseline outcome component linked to the follow-up outcome component by subject-level random effects.

Aged↗
PubMed2002

Cellular basis of diabetic nephropathy: II. The transforming growth factor-beta system and diabetic nephropathy lesions in type 1 diabetes.

Transforming growth factor-beta (TGF-beta) may be critical in the development of diabetic nephropathy (DN), and genetic predisposition is an important determinant of DN risk. We evaluated mRNA expression levels of TGF-beta system components in cultured skin fibroblasts (SFs) from type 1 diabetic patients with fast versus slow development of DN. A total of 125 long-standing type 1 diabetic patients were ranked by renal mesangial expansion score (MES) based on renal biopsy findings and diabetes duration. Patients in the highest quintile of MES who were also microalbuminuric or proteinuric (n = 16) were classified as "fast-track" for DN, while those in the lowest quintile who were also normoalbuminuric (n = 23) were classsified as "slow-track" for DN. Twenty-five normal subjects served as control subjects. SFs were cultured in medium with 25 mmol/l glucose for 36 h. SF mRNA expression levels for TGF-beta1, TGF-beta type II receptor (TGF-beta RII), thrombospondin-1, and latent TGF-beta binding protein-1 (LTBP-1) were measured by real-time RT-PCR. LTBP-1 mRNA expression was reduced in slow-track (0.99 +/- 0.38) versus fast-track patients (1.65 +/- 0.52, P = 0.001) and control subjects (1.41 +/- 0.7, P = 0.025). mRNA levels for TGF-beta1, TGF-beta RII, and thrombospondin-1 were similar in the three groups. Reduced LTBP-1 mRNA expression in SFs from slow-track patients may reflect genetically determined DN protection and suggests that LTBP-1 may be involved in the pathogenesis of DN through the regulation of TGF-beta activity.

Adult↗
PubMed2002

Cellular basis of diabetic nephropathy: 1. Study design and renal structural-functional relationships in patients with long-standing type 1 diabetes.

This study was designed to elucidate the cellular basis of risk of or protection from nephropathy in patients with type 1 diabetes. Entry criteria included diabetes duration of > or =8 years (mean duration, 22.5 years) and glomerular filtration rate (GFR) >30 ml x min(-1) x 1.73 m(-2). Patients were classified, on the basis of the estimated rate of mesangial expansion, as "fast-track" (upper quintile) or "slow-track" (lower quintile). A total of 88 patients were normoalbuminuric, 17 were microalbuminuric, and 19 were proteinuric. All three groups had increased glomerular basement membrane (GBM) width and mesangial fractional volume [Vv(Mes/glom)], with increasing severity from normoalbuminuria to microalbuminuria to proteinuria but with considerable overlap among groups. Vv(Mes/glom) (r = 0.75, P < 0.001) and GBM width (r = 0.63, P < 0.001) correlated with albumin excretion rate (AER), whereas surface density of peripheral GBM per glomerulus [Sv(PGBM/glom)] (r = 0.50, P < 0.001) and Vv(Mes/glom) (r = -0.48, P < 0.001) correlated with GFR. Vv(Mes/glom) and GBM width together explained 59% of AER variability. GFR was predicted by Sv(PGBM/glom), AER, and sex. Fast-track patients had worse glycemic control, higher AER, lower GFR, more hypertension and retinopathy, and, as expected, worse glomerular lesions than slow-track patients. Thus, there are strong relationships between glomerular structure and renal function across the spectrum of AER, but there is considerable structural overlap among AER categories. Given that normoalbuminuric patients may have advanced glomerulopathy, the selection of slow-track patients based on glomerular structure may better identify protected patients than AER alone.

Adult↗