Regional recruitment and differential behavior of motor units during postural control in older adults

Aging is associated with neuromuscular system changes that may have implications for the recruitment and firing behaviors of motor units (MUs). In previous studies, we observed that young adults recruit subpopulations of triceps surae MUs during tasks that involved leaning in five directions: common units that were active during different leaning directions and unique units that were active in only one leaning direction. Furthermore, the MU subpopulation firing behaviors [average firing rate (AFR), coefficient of variation (CoVISI), and intermittent firing] modulated with leaning direction. The purpose of this study was to examine whether older adults exhibited this regional recruitment of MUs and firing behaviors. Seventeen older adults (aged 74.8 ± 5.3 yr) stood on a force platform and maintained their center of pressure leaning in five directions. High-density surface electromyography recordings from the triceps surae were decomposed into single MU action potentials. A MU tracking analysis identified groups of MUs as being common or unique across the leaning directions. Although leaning in different directions did not affect the AFR and CoVISI of common units (P > 0.05), the unique units responded to the leaning directions by increasing AFR and CoVISI, albeit modestly (F = 18.51, P < 0.001). The unique units increased their intermittency with forward leaning (F = 9.22, P = 0.003). The mediolateral barycenter positions of MU activity in both subpopulations were found in similar locations for all leaning directions (P > 0.05). These neuromuscular changes may contribute to the reduced balance performance seen in older adults.NEW & NOTEWORTHY In this study, we observed differences in motor unit recruitment and firing behaviors of distinct subpopulations of motor units in the older adult triceps surae muscle from those observed in the young adult. Our results suggest that the older adult central nervous system may partially lose the ability to regionally recruit and differentially control motor units. This finding may be an underlying cause of balance difficulties in older adults during directionally challenging leaning tasks.

Differential behavior of distinct motoneuron pools that innervate the triceps surae

It has been shown that when humans lean in various directions, the central nervous system (CNS) recruits different motoneuron pools for task completion; common units that are active during different leaning directions, and unique units that are active in only one leaning direction. We used high-density surface electromyography (HD-sEMG) to examine if motor unit (MU) firing behavior was dependent on leaning direction, muscle (medial and lateral gastrocnemius; soleus), limits of stability, or whether a MU is considered common or unique. Fourteen healthy participants stood on a force platform and maintained their center of pressure in five different leaning directions. HD-sEMG recordings were decomposed into MU action potentials and the average firing rate (AFR), coefficient of variation (CoV_ISI), and firing intermittency were calculated on the MU spike trains. During the 30°-90° leaning directions both unique units and common units had higher firing rates (F = 31.31, P < 0.0001). However, the unique units achieved higher firing rates compared with the common units (mean estimate difference = 3.48 Hz, P < 0.0001). The CoV_ISI increased across directions for the unique units but not for the common units (F = 23.65, P < 0.0001). Finally, intermittent activation of MUs was dependent on the leaning direction (F = 11.15, P < 0.0001), with less intermittent activity occurring during diagonal and forward-leaning directions. These results provide evidence that the CNS can preferentially control separate motoneuron pools within the ankle plantarflexors during voluntary leaning tasks for the maintenance of standing balance.NEW & NOTEWORTHY In this study, we demonstrate that the different subpopulations of motor units within the three muscles comprising the ankle plantarflexors behave differently during multidirectional leaning. Our results suggest that the central nervous system has the capability to control distinct subpopulations of motor units to meet the force requirements necessary for leaning. This may allow for a precise, efficient, and flexible control strategy for the maintenance of standing balance.

Being uninsured in 1996 compared to 1987: how has the experience of the uninsured changed over time?

OBJECTIVE

To explore trends in the nonelderly uninsured population between 1987 and 1996 and examine whether the broad disparities in medical care utilization and out-of -pocket spending between the privately insured and uninsured populations that existed in 1987 continued over the following decade.

DATA SOURCES/STUDY DESIGN

Data are from the 1996 Medical Expenditure Panel Survey and the 1987 National Medical Expenditure Survey. We used survey data to create descriptive tables examining the characteristics of the uninsured population and the use of medical services, total and out-of -pocket expenditures, and the burden of out-of -pocket spending for the uninsured and the privately insured in 1987 and 1996. Tabulations are presented by demographic and socioeconomic characteristics.

PRINCIPAL FINDINGS

The composition of the uninsured population changed somewhat between 1987 and 1996, with adults over age 18 and employed persons making up larger proportions of the uninsured in 1996, and the poor and those in fair or poor health making up smaller proportions. There were few changes in utilization of services by the uninsured over this period and no change in mean expenses, but there was an increase in receipt of at least one preventive service (mammograms) and a decline in the proportion of families with high out-of-pocket burden. Disparities in use and expenses that existed between the uninsured and the privately insured in 1987, however, remained in 1996.

CONCLUSIONS

Despite the fundamental changes in the health care system that took place between 1987 and 1996, health care utilization and expenses for the uninsured changed very little. The uninsured are still much less likely to use services than are the privately insured, and they pay for a larger proportion of their medical care expenses out of pocket. There was some improvement in the burden of out-of -pocket spending between 1987 and 1996, but a significant number of the uninsured still have high financial burden.

The Medical Expenditure Panel Survey: a national health information resource

This article describes the Medical Expenditure Panel Survey (MEPS), the third in a series of nationally representative surveys of medical care use and expenditures sponsored by the Agency for Health Care Policy and Research. The MEPS is designed to provide extensive data on the types of health care services American use, how frequently they use them, how much is paid for the services, and who pays for them. It also will provide information on the types and costs of private health insurance available to the U.S. population. The survey is unparalleled in its degree of detail, as well as its ability to link medical care use, payments, and health insurance coverage to specific survey respondents and their families. It allows analysts to examine how individual and family characteristics, including the characteristics of their health insurance, affect medical care use and spending. This article discusses each of the MEPS components, focusing on design enhancements that have been made since the survey was last conducted nearly a decade ago.

Racial and ethnic differences in access to and use of health care services, 1977 to 1996

This article focuses on racial and ethnic disparities in health care, describing both absolute differences and relative changes in access to care and the use of health services among whites, blacks, and Hispanics over the past two decades. Using data from a series of three nationally representative medical expenditure surveys, the authors present descriptive statistics on disparities in access and use between minorities and whites over time. They also use multivariate analyses to isolate the extent to which health insurance and income explain those disparities. The authors find that disparities increased between 1977 and 1996, particularly for Hispanic Americans. Results also show that approximately one half to three quarters of the disparities observed in 1996 would remain even if racial and ethnic disparities in income and health insurance coverage were eliminated.

Reconciling medical expenditure estimates from the MEPS and the NHA, 1996

This article compares 1996 estimates of national medical care expenditures from the Medical Expenditure Panel Survey (MEPS) and the National Health Accounts (NHA). The MEPS estimate for total expenditures in 1996 was $548 billion; whereas, the NHA estimate for personal health care (PHC) in 1996 was $912 billion. Much of this apparent difference, however, arises from differences in scope between MEPS and NHA--rather than from differences in estimates for comparably-defined expenditures. We adjusted the NHA for differences in included populations and types of services covered, finding a much smaller difference between MEPS and a comparably-defined NHA.

A comparison of health care experiences for medicaid and commercially enrolled children in a large, nonprofit health maintenance organization

BACKGROUND

Proponents of Medicaid managed care have argued that this type of care offers the potential to provide mainstream health care for poor children and the elimination of the 2-tier system of care that has long existed for poor and nonpoor children. However, few studies have attempted to assess whether differences in access, utilization, and satisfaction exist between Medicaid and commercially sponsored children who are enrolled in the same managed care plan.

OBJECTIVE

To systematically answer the following research question: Within the same large, nonprofit, group-model health maintenance organization (HMO), how do children enrolled in Medicaid compare with children enrolled commercially across the domains of access, utilization, and satisfaction with care?

METHODS

We compared access, satisfaction, and utilization of services between Medicaid and commercially sponsored children enrolled in Kaiser Permanente of Northern California during 1998 through use of a telephone survey and administrative data. Kaiser Permanente is a nonprofit, integrated, group HMO that serves 2.8 million members in more than 15 counties in northern California. The sample for this survey included 510 Medicaid-enrolled children and 512 commercially enrolled children. An overall response rate of 82% was achieved. Bivariate and multivariate analyses were used to compare Medicaid and commercially enrolled children.

RESULTS

We found few differences between commercial and Medicaid enrollees across the domains of access, utilization, and satisfaction. Where access differences were present (problems in finding a personal care provider, problems getting care overall, and experiencing 1 or more barriers to care), the differences favored Medicaid-enrolled children. That is, Medicaid enrollees were reported to experience significantly fewer access problems and barriers than commercial enrollees, even after adjustment for confounding factors. Only one difference was found between Medicaid and commercial enrollees across the 6 utilization variables examined (volume of emergency department visits), and no differences were found among the 4 satisfaction and 2 global assessments of care received. Taken together, our results suggest that Medicaid-enrolled children experience as good as or better care than their commercially enrolled counterparts. However, there are other possible explanations for our findings. It may be that families of Medicaid-enrolled children hold their care providers to a lower standard than families of commercially enrolled children, given historic inequities in care between poor and nonpoor families. In addition, some degree of selection bias may be present in our sample, although that is true for both the Medicaid and commercial populations.

CONCLUSIONS

Our findings suggest that large commercial HMOs are capable of eliminating the access barriers and stigma traditionally associated with the Medicaid program. However, this conclusion must be tempered with the knowledge that other explanations for our findings may also be at play.

Comparing the medical expenses of children with Medicaid and commercial insurance in an HMO

BACKGROUND

In recent years, growing numbers of children with Medicaid have been enrolled in managed care plans nationwide. Yet, large, commercial managed care plans are increasingly discontinuing their participation in Medicaid because of low Medicaid payment rates.

OBJECTIVE

To compare the healthcare utilization and costs of children with Medicaid and children with commercial insurance within the same health maintenance organization (HMO).

STUDY DESIGN

Retrospective study using electronically captured cost and utilization data.

PATIENTS AND METHODS

We compared the healthcare utilization and costs of children with Medicaid (n = 42,636) and children with commercial insurance (n = 159,651) who were members of the same large, nonprofit HMO at any time between January 1, 1995, and December 31, 1997. Medicaid children were grouped as income eligible, medically needy, and blind or disabled.

RESULTS

The unadjusted costs of income-eligible, Medicaid-insured children were not significantly different from those of commercially insured children. The medically needy were $25 per month more expensive than commercially insured children (P = 0.02), and the blind or disabled were $213 per month more expensive (P < .01). After adjusting for age and sex, income-eligible children were $5 per month more expensive than children with commercial insurance (P = .07), the medically needy were $20 per month more expensive (P = .02), and the blind or disabled were $216 per month more expensive (P < .01).

CONCLUSIONS

The costs of income-eligible, Medicaid-insured children in this HMO were similar to those of commercially insured children, but the costs for the medically needy and the blind and disabled were substantially higher.

The impact of ownership type on nursing home outcomes

This paper examines the sorting of residents between for-profit and nonprofit nursing homes and the health outcomes of those residents conditional on ownership type. Using data from the 1987 National Medical Expenditure Survey, we find evidence of systematic sorting of residents by ownership type, and significant effects of ownership type on outcomes. These results are broadly consistent with the hypothesis that for-profit and nonprofit homes exploit their informational advantages to differing extents in a market characterized by asymmetric information.

Children's health insurance, access to care, and health status: new findings

Despite various policy initiatives, a substantial number of children in the United States remain uninsured, have problems with access to health care, or are in fair or poor health. These difficulties are not evenly distributed across the population. Hispanic children, those whose parents have little education, and those who live in families without an employed parent are at disproportionately high risk of encountering these problems. Although multivariate analyses would be required to disentangle the complex relationships among these factors, these descriptive data reveal the segments of the population to which new health-related programs, such as CHIP-funded state plans, might most productively be directed. Issues concerning children's health are likely to remain on the national policy agenda for some time to come. Because MEPS is a continuing data collection effort, it will enable researchers and policymakers to follow trends in these issues over time. For example, MEPS data will support evaluations at the national level to determine whether children who lack health insurance or a usual source of care will actually face fewer barriers after CHIP-funded programs are implemented. This paper provides a baseline against which to evaluate the impact of CHIP and other policy changes on the health and well-being of America's children.

The effect of Medicaid reimbursement on quality of care in nursing homes

This study uses a nationally representative sample of nursing homes and nursing home residents to examine the effect of Medicaid reimbursement on quality of care. The analysis shows that both reimbursement approach and level affect nursing home quality, as measured by case-mix adjusted staff to resident ratios. The analysis also shows that staffing ratios have a significant impact on resident outcomes, and these impacts vary by professional category of staff. Reimbursement does not have a significant impact on outcomes, however.

The use of hospital emergency departments for nonurgent health problems: a national perspective

The use of the hospital emergency department (ED) for nonurgent health problems has been a subject of considerable controversy, in part because there is no widely accepted definition of "nonurgent." Elimination or substantial reduction in nonurgent ED use is frequently offered as a strategy for reducing health expenditures. Previous studies, often limited to individual hospitals or communities, have limited generalizability and do not permit examination of multiple factors likely to influence nonurgent ED utilization or examination of ED use for nonurgent problems in the context of overall outpatient utilization. This analysis of the 1987 National Medical Expenditure Survey (NMES) provides a nationally representative examination of nonurgent ED utilization that describes the frequency of ED use for nonurgent problems, characteristics of individuals that are associated with an increased likelihood of nonurgent ED use, the use of other outpatient physician services, and expenditures associated with nonurgent ED visits.

Medicaid physician fee levels and children's access to care

This study examines the effects of physician fees on children's use of preventive and illness-related ambulatory physician services under the Medicaid program. Using data from the 1987 National Medical Expenditure Survey (NMES), we examine the effects of Medicaid fee generosity on physician service use and overall ambulatory physician spending. The results indicate that more generous fees are associated with a greater likelihood of having a doctor's office as a usual source of care and a higher number of preventive visits at office-based sites of care. Having a doctor's office as a usual source of care is associated with lower overall ambulatory physician expenditures.

Medicaid policy and the substitution of hospital outpatient care for physician care

This article explores the effects of reimbursement and utilization control policies on utilization patterns and spending for physician and hospital outpatient services under state Medicaid programs. The empirical work shows a negative relationship between the level of Medicaid physician fees relative to Medicare and private fees, and the numbers of outpatient care recipients, suggesting that outpatient care substitutes for physician care in states with low fee levels. In addition, it shows a positive relationship between Medicaid physician fees and outpatient spending per recipient, suggesting that in low-fee states outpatient departments are providing some types of care that could be provided in a physician's office. Finally, the analysis demonstrates that reimbursement and utilization control policies have significant effects in the expected directions on aggregate Medicaid spending for physician and outpatient services.