Superconductivity of alpha-uranium and the role of 5f electrons.

A much sharper and lower superconducting transition has been found for alpha-uranium than any reported previously. A model that explains the unusual volume dependence of alpha-uranium below 43 degrees K and the unusual pressure dependence of its superconducting transition temperature is presented.

Diagnostic testing following screening mammography in the elderly.

BACKGROUND: To provide some sense of the general frequency and timing of diagnostic testing following screening mammography in the United States, we investigated the experience of women screened in the Medicare population. METHODS: By use of Medicare's National Claims History System, we identified a cohort (n=23172) of women 65 years old or older screened during the period from January 1, 1995, through April 30, 1995, and tracked each woman over the subsequent 8 months for the performance of additional breast imaging and biopsy procedures. Using two claims-based definitions for newly detected breast cancer, we also estimated the positive predictive value of screening mammography. RESULTS: For every 1000 women aged 65-69 years who underwent screening, 85 (95% confidence interval [CI]=79-91) had follow-up testing in the subsequent 8 months; 76 (95% CI=71-82) had additional breast imaging, and 23 (95% CI=20-26) had biopsy procedures. Corresponding numbers for women aged 70 years or more were similar. Some women underwent repeated examinations; 13% of those receiving diagnostic mammograms had more than one; 11% of those undergoing biopsy procedures had more than one. About half of the women who underwent a biopsy had the procedure more than 3 weeks after the imaging test upon which the decision to perform a biopsy was presumably made. The estimated positive predictive value of an abnormal screening mammogram (defined as a mammogram that engendered additional testing) was 0.08 (95% CI=0.06-0.10) for women aged 65-69 years and 0.14 (95% CI=0.12-0.16) for women aged 70 years or more. CONCLUSION: Additional testing is a frequent consequence of screening mammography and may require a considerable period of time to come to closure. The need for additional testing, however, is weakly predictive of cancer.

Treatment and health outcomes of women and men in a cohort with coronary artery disease.

BACKGROUND: Women with coronary artery disease are treated differently than men. Although mortality has been studied, functional outcomes for women and men have not been prospectively compared. METHODS: The Manitoba Health Reform Impact Study used hospital databases to identify all residents aged 45 years and older in Manitoba who were hospitalized for a myocardial infarction between October 1, 1991, and September 30, 1992. Cohort members were interviewed twice, an average of 16 and 25 months after hospitalization. Baseline and follow-up measures included treatments (eg, physician visits, diagnostic testing, revascularization, and cardiac medications), physical health status (physical component summary [PCS] score derived from the Medical Outcomes Study Short Form 36), reinfarction, and mortality. RESULTS: Of the 820 patients who completed the initial survey, 31 died during the follow-up period, and 734 completed the follow-up survey. Data were complete for the primary outcome (PCS score) and all relevant covariates for the 677 patients who were included in this study Women constituted 34% of this cohort. Although women had more physician visits during follow-up, they were less likely to have undergone treadmill testing or angiography (odds ratio, 0.68; 95% confidence interval, 0.46-0.99). Women were equally likely to report taking beta-adrenergic blocking agents, but were less likely than men to report the use of aspirin (odds ratio, 0.69; 95% confidence interval, 0.48-0.98). After adjusting for baseline differences in PCS scores, age, income, social supports, and the levels of angina and dyspnea, the PCS score for women declined by 1.4 points, while the score for men improved by 0.2 points (P = .03). During the follow-up period, reinfarction and mortality rates were low overall, but were not different in men and women. CONCLUSIONS: In this cohort of patients with known coronary artery disease, we found less aggressive treatment of coronary artery disease and less use of aspirin among women than among men during 1 year of observation. After controlling for baseline differences, women with coronary artery disease experienced a more rapid decline in physical health status than did men during 1 year of follow-up.

Why are children hospitalized? The role of non-clinical factors in pediatric hospitalizations.

OBJECTIVE: Pediatric medical discharge rates vary widely across hospital service areas, beyond differences explained by chance or disease incidence alone. This study examines the relationship between the characteristics of local medical services and the likelihood of hospitalization. DESIGN: Small area and population-based regression analysis. SETTING: The 72 hospital service areas of Maine, New Hampshire, and Vermont. STUDY POPULATION: The 589,290 (1989) children of Maine, New Hampshire, and Vermont < 15 years of age with 120,806 discharges during 1985 through 1989. MEASUREMENT AND MAIN RESULTS: Using logistic regression and controlling for community income, we found that children residing in zip codes with high per capita bed supply (4.0/1000) had 9% more discharges (odds ratio: 1.09; 99% confidence interval: 1.07, 1.11) compared with children in areas with low per capita bed supply (1.9/1000). Children living 30 minutes from the nearest hospital had 15% fewer medical discharges (odds ratio: 0.849; confidence interval: 0.830, 0.867) than those living in a zip code with a hospital. Residence in one of the three academic medical center hospital service areas resulted in 32% fewer discharges (odds ratio: 0.68; confidence interval: 0.66, 0.70). Similar and statistically significant (P < .01) results were noted for the most common nonperinatal diagnostic categories: asthma/bronchitis (diagnostic related group = 98) and gastroenteritis (diagnostic related group = 184). No effect was noted for femur fracture, a condition for which admission rates equal disease incidence. CONCLUSIONS: The supply and character of medical care are important influences on the likelihood of hospitalization for pediatric medical conditions for which outpatient alternatives are available.

Using administrative data to describe casemix: a comparison with the medical record.

We compared the coding of comorbid conditions in an administrative database to that found in medical records for 485 men who had undergone a prostatectomy. Only a few specific conditions showed good agreement between charts and claims. Most showed poor agreement and appeared more frequently in the chart. A comorbidity index calculated from each of these sources was used to explore the differences in mortality for patients who had undergone transurethral vs open prostatectomy. The claims-based comorbidity index most often underestimated the index from the chart. Proportional hazards analysis showed that models including either comorbidity index were better than those without an index and models with information from both indices were best. No analysis eliminated the effect of type of prostatectomy on long-term mortality. Claims-based measures of comorbidity tend to underrepresent some conditions but may be an acceptable first step in controlling for differences across patient populations.

Influence of patient preferences and local health system characteristics on the place of death. SUPPORT Investigators. Study to Understand Prognoses and Preferences for Risks and Outcomes of Treatment.

OBJECTIVE: To examine the degree to which variation in place of death is explained by differences in the characteristics of patients, including preferences for dying at home, and by differences in the characteristics of local health systems. DESIGN: We drew on a clinically rich database to carry out a prospective study using data from the observational phase of the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT component). We used administrative databases for the Medicare program to carry out a national cross-sectional analysis of Medicare enrollees place of death (Medicare component). SETTING: Five teaching hospitals (SUPPORT); All U.S. Hospital Referral Regions (Medicare). STUDY POPULATIONS: Patients dying after the enrollment hospitalization in the observational phase of SUPPORT for whom place of death and preferences were known. Medicare beneficiaries who died in 1992 or 1993. MAIN OUTCOME MEASURES: Place of death (hospital vs non-hospital). RESULTS: In SUPPORT, most patients expressed a preference for dying at home, yet most died in the hospital. The percent of SUPPORT patients dying in-hospital varied by greater than 2-fold across the five SUPPORT sites (29 to 66%). For Medicare beneficiaries, the percent dying in-hospital varied from 23 to 54% across U.S. Hospital Referral Regions (HRRs). In SUPPORT, variations in place of death across site were not explained by sociodemographic or clinical characteristics or patient preferences. Patient level (SUPPORT) and national cross-sectional (Medicare) multivariate models gave consistent results. The risk of in-hospital death was increased for residents of regions with greater hospital bed availability and use; the risk of in-hospital death was decreased in regions with greater nursing home and hospice availability and use. Measures of hospital bed availability and use were the most powerful predictors of place of death across HRRs. CONCLUSIONS: Whether people die in the hospital or not is powerfully influenced by characteristics of the local health system but not by patient preferences or other patient characteristics. These findings may explain the failure of the SUPPORT intervention to alter care patterns for seriously ill and dying patients. Reforming the care of dying patients may require modification of local resource availability and provider routines.

Variation profiles of common surgical procedures.

BACKGROUND: Rates of many surgical procedures vary widely across both large and small geographic regions. Although variation in health care use has long been described, few studies have systematically compared variation profiles across surgical procedures. The goal of this study was to examine current patterns of regional variation in the rates of common surgical procedures. METHODS: The study population consisted of patients enrolled in Medicare in 1995, excluding those enrolled in risk-bearing health maintenance organizations. Patients ranged in age from 65 to 99 years. Using data from hospital discharge abstracts, we calculated rates of 11 common inpatient procedures for each of 306 US hospital referral regions (HRRs). To assess the relative variability of each procedure, we determined the number of low and high outlier regions (HRRs with rates < 50% or > 150% the national average) and the ratio of highest to lowest HRR rates. RESULTS: Procedures differed markedly in their variability. Rates of hip fracture repair, resection for colorectal cancer, and cholecystectomy varied only 1.9- to 2.9-fold across HRRs (0, 0, and 4 outlier regions, respectively). Coronary artery bypass grafting, transurethral prostatectomy, mastectomy, and total hip replacement had intermediate variation profiles, varying 3.5- to 4.7-fold across regions (8, 10, 16, and 17 outlier regions, respectively). Lower extremity revascularization, carotid endarterectomy, back surgery, and radical prostatectomy had the highest variation profiles, varying 6.5- to 10.1-fold across HRRs (25, 32, 39, and 56 outlier regions, respectively). CONCLUSIONS: Although the use of many surgical procedures varies widely across geographic areas, rates of "discretionary" procedures are most variable. To avoid potential overuse or underuse, efforts to increase consensus in clinical decision making should focus on these high variation procedures.

Effect of hospital volume on in-hospital mortality with pancreaticoduodenectomy.

BACKGROUND: Reports of better results at national referral centers than at low-volume community hospitals have prompted calls for regionalizing pancreaticoduodenectomy (the Whipple procedure). We examined the relationship between hospital volume and mortality with this procedure across all US hospitals. METHODS: Using information from the Medicare claims database, we performed a national cohort study of 7229 Medicare patients more than 65 years old undergoing pancreaticoduodenectomy between 1992 and 1995. We divided the study population into approximate quartiles according to the hospital's average annual volume of pancreaticoduodenectomies in Medicare patients: very low (< 1/y), low (1-2/y), medium (2-5/y), and high (5+/y). Using multivariate logistic regression to account for potentially confounding patient characteristics, we examined the association between institutional volume and in-hospital mortality, our primary outcome measure. RESULTS: More than 50% of Medicare patients a undergoing pancreaticoduodenectomy received care at hospitals performing fewer than 2 such procedures per year. In-hospital mortality rates at these low- and very-low-volume hospitals were 3- to 4-fold higher than at high-volume hospitals (12% and 16%, respectively, vs 4%, P < .001). Within the high-volume quartile, the 10 hospitals with the nation's highest volumes had lower mortality rates than the remaining high-volume centers (2.1% vs 6.2%, P < .01). The strong association between institutional volume and mortality could not be attributed to patient case-mix differences or referral bias. CONCLUSIONS: Although volume-outcome relationships have been reported for many complex surgical procedures, hospital experience is particularly important with pancreaticoduodenectomy. Patients considering this procedure should be given the option of care at a high-volume referral center.

The 3H-leucine tracer: its use in kinetic studies of plasma lipoproteins.

3H-leucine administered as a bolus has been widely used as a tracer in kinetic investigations of protein synthesis and secretion. After intravenous injection, plasma specific radioactivity decays over several orders of magnitude during the first half-day, followed by a slow decay lasting a number of weeks that results from recycling of the leucine tracer as proteins are degraded and 3H-leucine reenters the plasma pool. In studies in which kinetic data are analyzed by mathematical compartmental modeling, plasma leucine activity is generally used as a forcing function to drive the input of 3H-leucine into the protein synthesis pathway. 3H-leucine is an excellent tracer during the initial hours of rapidly decreasing plasma activity; thereafter, reincorporation of recycled tracer into new protein synthesis obscures the tracer data from proteins with slower turnover rates. Thus, for proteins such as plasma albumin and apolipoprotein (apo) A-I, this tracer is unsatisfactory for measuring fractional catabolic (FCR) and turnover rates. By contrast, the kinetics of plasma very-low-density lipoprotein (VLDL)-apoB, a protein with a residence time of approximately 5 hours, are readily measured, since kinetic parameters of this protein can be determined by the time plasma leucine recycling becomes established. However, measurement of VLDL-apoB specific radioactivity extending up to 2 weeks provides further data on the kinetic tail of VLDL-apoB. Were plasma leucine a direct precursor for the leucine in VLDL-apoB, the kinetics of the plasma tracer should determine the kinetics of the protein. However, this is not the case, and the deviations from linearity are interpreted in terms of (1) the dilution of plasma leucine in the liver by unlabeled dietary leucine; (2) the recycling of hepatocellular leucine from proteins within the liver, where recycled cellular leucine does not equilibrate with plasma leucine; and (3) a "hump" in the kinetic data of VLDL-apoB, which we interpret to reflect recycling or retention of a portion of the apoB protein within the hepatocyte, with its subsequent secretion. Because hepatocellular tRNA is the immediate precursor for synthesis of these secretory proteins, its kinetics should be used as the forcing function to drive the modeling of this system. The VLDL-apoB tail contains the information needed to modify the plasma leucine data, to provide an appropriate forcing function when using 3H-leucine as a tracer of apolipoprotein metabolism. This correction is essential when using 3H-leucine as a tracer for measuring low-density lipoprotein (LDL)-apoB kinetics. The 3H-leucine tracer also highlights the importance of recognizing the difference between plasma and system residence times, the latter including the time the tracer resides within exchanging extravascular pools. The inability to determine these fractional exchange coefficients for apoA-I and albumin explains the failure of this tracer in kinetic studies of these proteins. For apoB-containing lipoproteins, plasma residence times are generally determined, and these measurements can be made satisfactorily with 3H-leucine.

Where do elderly veterans obtain care for acute myocardial infarction: Department of Veterans Affairs or Medicare?

OBJECTIVE: To examine Department of Veterans Affairs (VA) and Medicare hospitalizations for elderly veterans with acute myocardial infarction (AMI), their use of cardiac procedures in both systems, and patient mortality. DATA SOURCES: Merging of inpatient discharge abstracts obtained from VA Patient Treatment Files (PTF) and Medicare MedPAR Part A files. STUDY DESIGN: A retrospective cohort study of male veterans 65 years or older who were prior users of the VA medical system (veteran-users) and who were initially admitted to a VA or Medicare hospital with a primary diagnosis of AMI at some time from January 1, 1988 through December 31, 1990 (N = 25,312). We examined the use of cardiac catheterization, coronary bypass surgery, and percutaneous transluminal coronary angioplasty in the 90 days after initial admission for AMI in both VA and Medicare systems, and survival at 30 days, 90 days, and one year. Other key measures included patient age, race, marital status, comorbidities, cardiac complications, prior utilization, and the availability of cardiac technology at the admitting hospital. PRINCIPAL FINDINGS: More than half of veteran-users (54 percent) were initially hospitalized in a Medicare hospital when they suffered an AMI. These Medicare index patients were more likely to receive cardiac catheterization (OR 1.24, 95% C.I. 1.17-1.32), coronary bypass surgery (OR 2.01, 95% C.I. 1.83-2.20), and percutaneous transluminal coronary angioplasty (OR 2.56, 95% C.I. 2.30-2.85) than VA index patients. Small proportions of patients crossed over between systems of care for catheterization procedures (VA to Medicare = 3.3%, and Medicare to VA = 5.1%). Many VA index patients crossed over to Medicare hospitals to obtain bypass surgery (27.6 percent) or coronary angioplasty (12.1 percent). Mortality was not significantly different between veteran-users who were initially admitted to VA versus Medicare hospitals. CONCLUSIONS: Dual-system utilization highlights the need to look at both systems of care when evaluating access, costs, and quality either in VA or in Medicare systems. Policy changes that affect access to and utilization of one system may lead to unpredictable results in the other.

Associations among hospital capacity, utilization, and mortality of US Medicare beneficiaries, controlling for sociodemographic factors.

OBJECTIVE: To explore whether geographic variations in Medicare hospital utilization rates are due to differences in local hospital capacity, after controlling for socioeconomic status and disease burden, and to determine whether greater hospital capacity is associated with lower Medicare mortality rates. DATA SOURCES/STUDY SETTING: The study population: a 20 percent sample of 1989 Medicare enrollees. Measures of resources were based on a national small area analysis of 313 Hospital Referral Regions (HRR). Demographic and socioeconomic data were obtained from the 1990 U.S. Census. Measures of local disease burden were developed using Medicare claims files. STUDY DESIGN: The study was a cross-sectional analysis of the relationship between per capita measures of hospital resources in each region and hospital utilization and mortality rates among Medicare enrollees. Regression techniques were used to control for differences in sociodemographic characteristics and disease burden across areas. DATA COLLECTION/EXTRACTION METHODS: Data on the study population were obtained from Medicare enrollment (Denominator File) and hospital claims files (MedPAR) and U.S. Census files. PRINCIPAL FINDINGS: The per capita supply of hospital beds varied by more than twofold across U.S. regions. Residents of areas with more beds were up to 30 percent more likely to be hospitalized, controlling for ecologic measures of socioeconomic characteristics and disease burden. A greater proportion of the population was hospitalized at least once during the year in areas with more beds; death was also more likely to take place in an inpatient setting. All effects were consistent across racial and income groups. Residence in areas with greater levels of hospital resources was not associated with a decreased risk of death. CONCLUSIONS: Residence in areas of greater hospital capacity is associated with substantially increased use of the hospital, even after controlling for socioeconomic characteristics and illness burden. This increased use provides no detectable mortality benefit.

The development of a survey instrument for community health improvement.

OBJECTIVE: To develop a survey instrument that could be used both to guide and evaluate community health improvement efforts. DATA SOURCES/STUDY SETTING: A randomized telephone survey was administered to a sample of about 250 residents in two communities in Lehigh Valley, Pennsylvania in the fall of 1997. METHODS: The survey instrument was developed by health professionals representing diverse health care organizations. This group worked collaboratively over a period of two years to (1) select a conceptual model of health as a foundation for the survey; (2) review relevant literature to identify indicators that adequately measured the health constructs within the chosen model; (3) develop new indicators where important constructs lacked specific measures; and (4) pilot test the final survey to assess the reliability and validity of the instrument. PRINCIPAL FINDINGS: The Evans and Stoddart Field Model of the Determinants of Health and Well-Being was chosen as the conceptual model within which to develop the survey. The Field Model depicts nine domains important to the origins and production of health and provides a comprehensive framework from which to launch community health improvement efforts. From more than 500 potential indicators we identified 118 survey questions that reflected the multiple determinants of health as conceptualized by this model. Sources from which indicators were selected include the Behavior Risk Factor Surveillance Survey, the National Health Interview Survey, the Consumer Assessment of Health Plans Survey, and the SF-12 Summary Scales. The work group developed 27 new survey questions for constructs for which we could not locate adequate indicators. Twenty-five questions in the final instrument can be compared to nationally published norms or benchmarks. The final instrument was pilot tested in 1997 in two communities. Administration time averaged 22 minutes with a response rate of 66 percent. Reliability of new survey questions was adequate. Face validity was supported by previous findings from qualitative and quantitative studies. CONCLUSIONS: We developed, pilot tested, and validated a survey instrument designed to provide more comprehensive and timely data to communities for community health assessments. This instrument allows communities to identify and measure critical domains of health that have previously not been captured in a single instrument.

Academic health centers and health care reform.

There is increasing support for the proposition that academic health centers have a duty to accept broad responsibility for the health of their communities. The Health of the Public program has proposed that centers become directly involved in the social-political process as advocates for reform of the health care system. Such engagement raises important issues about the roles and responsibilities of centers and their faculties. To address these issues, the authors draw upon the available literature and their experiences in recent health care reform efforts in Minnesota and Vermont in which academic health center faculty participated. The authors discuss (1) the problematic balance between academic objectivity and social advocacy that faculty must attempt when they engage in the health care reform process; (2) the management of the sometimes divergent interests of academic health centers, some of their faculty, and society (including giving faculty permission to engage in reform efforts and developing a tacit understanding that distinguishes faculty positions on reform issues from the center's position on such issues); and (3) the challenge for centers to develop infrastructure support for health reform activities. The authors maintain that academic health centers' participation in the process of health care reform helps them fulfill the trust of the public that they are obligated to and ultimately depend on.

The burden of prevention: downstream consequences of Pap smear testing in the elderly.

CONTEXT: Although cervical cancer is an unusual cause of death among women 65 and older, most elderly women in the US report continuing to undergo periodic Pap smear screening. OBJECTIVE: To describe the incidence of Pap smears and downstream testing among elderly women. SETTING: Claims-based analysis of female Medicare enrollees age 65 and older. METHODS: Using three years of Medicare Part B 5% Files (1995-1997), we differentiated between women undergoing screening Pap smears and those undergoing Pap smears for surveillance of previous abnormalities or Pap smear follow-up. We determined the proportion of elderly women undergoing Pap smear testing and rates of downstream testing and procedures after an initial Pap smear. RESULTS: Four million female Medicare beneficiaries over 65 years underwent Pap smear testing between 1995 and 1997, representing 25% of the eligible population. After adjusting for underbilling for Pap smears under Medicare, 43% of women over 65 are estimated to have undergone Pap smear testing during the 3-year period. The large majority (90%) of Pap smears were for screening, while 10% were done for surveillance or follow-up. For every 1000 women with a screening Pap smear, 39 had at least one downstream intervention within eight months of the initial Pap smear, including seven women who underwent colposcopy and two women who had other surgical procedures. Rates of downstream interventions were considerably higher for women undergoing Pap smear follow-up (302 per 1000 with at least one downstream intervention), and surveillance of previous abnormalities (209 per 1000 with a downstream intervention). CONCLUSION: Cervical cancer screening is widespread among elderly American women, and follow-up testing is not uncommon, particularly among the ten percent of women who appear to be in a cycle of repeated testing. This substantial volume of testing occurs despite the rarity of cervical cancer deaths and unknown benefits of screening in this age group.

The measurement of energy imparted to patients during diagnostic x-ray examinations using the Diamentor exposure-area product meter.

The mean energy imparted to the patient has been proposed as a practical quantity which may be useful for assessing somatic risk in X-ray diagnostic radiology. A technique is described for estimating energy imparted during most common X-ray examinations of the trunk or complete head from a measurement of exposure-area product conveniently provided by the Diamentor transmission ionisation chamber. The necessary energy imparted calibration for the Diamentor has been deduced from consideration of incident spectral energy fluence and Monte Carlo calculations of the fraction of total beam energy imparted to mathematical phantoms representing the patient. The relationship between energy imparted and exposure-area product depends primarily on the applied potential and total filtration of the X-ray beam, and to a lesser extent on voltage waveform and X-ray target angle. Direct measurements of energy imparted to an Alderson Rando phantom for a range of irradiation conditions provided an excellent verification of the technique developed. Using the energy imparted per exposure-area product factors presented, overall uncertainties of less than +/- 15% and +/- 20% should be possible for measurements of energy imparted during examinations of the trunk and head respectively using the Diamentor.

The suitability of different preparations of thermoluminescent lithium borate for medical dosimetry.

The thermoluminescence properties of three different preparations of lithium borate have been studied with specific reference to their use in medical dosimetry. The properties of lithium borate powder doped with copper make it more attractive for low dose measurements than the more conventional phosphor doped with manganese. However, the energy response of the copper-doped material was not quite so suitable as that of the manganese-doped material for measuring doses to tissue at photon energies below 100 keV. It also exhibited appreciable light induced fading.

Hospice use in Medicare managed care and fee-for-service systems.

OBJECTIVE: To examine whether patterns of hospice use by older Medicare beneficiaries are consistent with the differing financial incentives in Medicare managed care (MC) and fee-for-service (FFS) settings. Specifically, are use patterns consistent with incentives that might encourage hospice use for MC enrollees and discourage hospice use for FFS enrollees? STUDY DESIGN: One-year study of hospice use by Medicare beneficiaries dying in 1996. PATIENTS AND METHODS: Medicare enrollment and hospice administrative data were used to examine hospice use before death for all elderly individuals residing in 100 US counties with high MC enrollment in 1996. Age-, sex-, and race-adjusted rate of hospice use and length of stay in hospice are compared between FFS and MC enrollees across and within (when possible) the 100 counties. RESULTS: Rates of hospice use were significantly higher for MC enrollees than for FFS enrollees (26.6 vs 17.0 per 100 deaths; P < .001). These differences persisted within age, sex, and race groups but were not related to area MC enrollment rate or the amount of money paid to managed care organizations. Age-, sex-, and race-adjusted differences were observed in 94 of 100 counties. Length of stay in hospice was marginally longer for MC enrollees than for FFS enrollees (median, 24 vs 21 days; P < .0001). CONCLUSIONS: System of care is an important determinant of hospice use in the elderly Medicare population.

Doses to patients from pantomographic and conventional dental radiography.

The increasing popularity of pantographic dental radiography and particularly its recent use for routine screening of asymptomatic patients have prompted the NRPB to compare the risks to patients from this technique with those from more conventional dental diagnostic procedures. Pantographic equipment from seven manufacturers have been investigated along with five procedures for obtaining similar information using conventional dental X-ray sets. Lithium borate thermoluminescent dosimeters located at 141 sites in the head and neck of a Rando phantom have been used to measure the mean absorbed dose to organs of interest as well as the total energy imparted to the phantom. Relative values of the energy imparted by the various techniques provide an estimate of their relative somatic risk to the patient. Pantomographic techniques were generally found to impart less than half the energy to the phantom than that given by a conventional full-mouth periapical series conducted at 45 kV, and a similar amount of energy to four bitewing intra-oral films. The restriction of the frequency of pantomographic examinations to no more than once per year during adolescence and once per three to five years during adulthood has been shown to involve only a minimal increase in the risk of somatic injury to the patient.

Doses to patients from routine diagnostic X-ray examinations in England.

A collaborative survey between the National Radiological Protection Board and the Hospital Physicists' Association has been conducted to ascertain current levels of exposure for patients undergoing 10 routine types of X-ray examination in England. The main part of this study consisted of measurements on nearly 3200 patients attending 20 randomly selected English hospitals. The energy imparted to each patient was determined from a measurement of the total exposure-area product for the examination. In addition, thermoluminescent dosemeters were attached to the patient's skin to enable the derivation of doses to the major radiosensitive organs, either directly or using appropriate conversion factors calculated for a mathematical phantom by a Monte Carlo technique. Histograms are presented showing the wide distributions often observed in the doses for each type of examination. Mean values of exposure-area product, energy imparted to the patient, entrance skin dose per film and organ dose are reported, together with coefficients of variation. Comparison of the results with those from similar surveys in the UK and abroad is complicated by inconsistencies in the reporting of such data, but substantial differences are sometimes apparent, particularly for the estimates of organ doses. The present measurements will provide a useful baseline for future measurements and will be used to evaluate the collective dose to the population from medical exposures and the radiation risks from the various radiological procedures.

Analysis of the effects of immune cell motility and chemotaxis on target elimination dynamics.

White blood cells of the immune system must encounter specific targets such as bacteria, malignant cells, virus-infected cells or other cells of the immune response in order to carry out their function of protecting the host from infectious and malignant disease. To analyze the dynamics of this process, a mathematical model has been developed for elimination of proliferating targets by a constant population of motile immune system cells in two dimensions. Encounter is assumed to be the rate-limiting step for elimination. This model makes use of a previously derived analysis of single cell-target encounter times, which yields an encounter rate constant that is incorporated into a kinetic conservation equation for target number density. This paper focuses on the influence of directed cell movement, or chemotaxis, as well as other cell motility properties, such as cell speed and persistence, on target elimination dynamics. A particularly significant result is that a given relative decrease in chemotactic responsiveness leads to much more severe deficiencies in target clearance rates for low levels of baseline chemotactic responsiveness than for high levels of baseline responsiveness. The general model results are then applied to the particular example of bacterial clearance from the lung surface by alveolar macrophages. It is shown that moderate levels of macrophage chemotactic responsiveness, similar to those measured in vitro, can account for the experimentally observed rates of bacterial elimination from the lung for typical values of bacterial specific growth rate and alveolar macrophage number density.