Increases in central aortic impedance precede alterations in arterial stiffness measures in type 1 diabetes

OBJECTIVE

Increased pulse pressure has been associated with increased cardiovascular risk in individuals with diabetes. Changes in central aortic properties can increase central pulse pressure and may adversely affect microvascular perfusion and cardiac performance. This study was performed to define early changes in central arterial properties in a group of young individuals with type 1 diabetes.

RESEARCH AND DESIGN METHODS

Seventeen individuals with type 1 diabetes and their nondiabetic control subjects who were participating in the Cardio-Diab Study had arterial stiffness and pulsatile hemodynamics measured with calibrated tonometry and pulsed Doppler. Aortic characteristic impedance (Z(c)) was calculated from the ratio of change in carotid pressure and aortic flow in early systole. Pulse wave velocity (PWV) was assessed from tonometry and body surface measurements.

RESULTS

Duration of type 1 diabetes was 15.3 +/- 0.7 (mean +/- SD) years. In type 1 diabetic subjects, central pulse pressure was elevated (45 +/- 11 vs. 36 +/- 10 mmHg in control subjects, P = 0.02), as was peripheral pulse pressure (54 +/- 13 vs. 43 +/- 10 mmHg, P = 0.002). Z(c) was elevated in type 1 diabetes (179 +/- 57 vs. 136 +/- 42 dynes x s/cm5 in control subjects, P = 0.004), whereas PWV was not different (5.9 +/- 0.9 vs. 5.9 +/- 0.7 m/s in type 1 diabetic vs. control subjects, respectively; NS). There was a moderate correlation between Z(c) and urinary albumin excretion (coefficient 0.39, P = 0.02).

CONCLUSIONS

Z(c) appears to be increased early in type 1 diabetes, before elevation of PWV and is associated with higher pulse pressure, which may contribute to renal microvascular damage in diabetes.

Pulmonary testing using peak flow meters of very low birth weight children born in the perisurfactant era and school controls at age 10 years

We determined lung function at age 10 years in very low birthweight (VLBW, <or=1,500 g) children and controls, and compared the sensitivity to detect subgroup differences by peak expiratory flow (PEF), forced expiratory volume in one second (FEV(1)), forced vital capacity (FVC) and their diurnal variation. VLBW children were recruited across the perisurfactant era at admission to six NICUs in Wisconsin and Iowa, and controls from area classrooms. Two hundred sixty five VLBW children and 360 controls were tested by the Jaeger AM1 peak flow meter at age 10 years. Two hundred six VLBW and 79 controls had additional home monitoring. Abnormality was defined as observed/predicted ratio <0.8 for PEF, FEV(1), and FVC, and by criteria of Pelkonen for diurnal PEF variation. VLBW children were compared to controls, VLBW children with bronchopulmonary dysplasia (BPD) to those without, and those with respiratory conditions to those without. PEF and FEV(1) showed high reproducibility (intraclass correlations, ICC 0.75-0.83). Controls and VLBW children with and without BPD differed significantly on all measures. Baseline test results did not differ across birth years, but PEF variation was less after surfactant availability (P = 0.04). Observed over predicted FEV(1) was the most sensitive in detecting differences between groups (P < 0.001), with mean (s.d.) 0.97 (0.12) for controls, 0.88 (0.14) for VLBW children without BPD, and 0.78 (0.13) for those with BPD. Odds ratios for abnormality were especially high with respiratory medication use during the first 5 years of life, 4.4 (95% CI: 2.0-9.8) for FEV(1) and 5.1 (95% CI: 2.0-13.2) for diurnal PEF variation. Our results show that respiratory abnormalities persist to at least age 10 years for VLBW children born in the surfactant era.

Properties of R(2) statistics for logistic regression

Various R(2) statistics have been proposed for logistic regression to quantify the extent to which the binary response can be predicted by a given logistic regression model and covariates. We study the asymptotic properties of three popular variance-based R(2) statistics. We find that two variance-based R(2) statistics, the sum of squares and the squared Pearson correlation, have identical asymptotic distribution whereas the third one, Gini's concentration measure, has a different asymptotic behaviour and may overstate the predictivity of the model and covariates when the model is mis-specified. Our result not only provides a theoretical basis for the findings in previous empirical and numerical work, but also leads to asymptotic confidence intervals. Statistical variability can then be taken into account when assessing the predictive value of a logistic regression model.

Lower-than-expected prevalence and severity of retinopathy in an incident cohort followed during the first 4-14 years of type 1 diabetes: the Wisconsin Diabetes Registry Study

The authors examined the development of diabetic retinopathy in a population-based cohort of persons with incident type 1 diabetes to investigate the possibility of lowered retinopathy prevalence and severity compared with previous US studies. A total of 474 diabetic persons from Wisconsin were followed from diagnosis through 4-14 years' duration during 1990-2002. Retinopathy was determined by fundus photography at 4, 7, 9, and 14 years' duration. Risk of developing retinopathy was modeled on demographic and diabetes-care characteristics by means of a generalized linear model using the complementary log-log link for interval-censored data. Prevalence of retinopathy increased with duration of diabetes, from 6% at 4 years to 73% at 14 years, and was highest among adults (> or =20 years of age). Risk of developing retinopathy increased with increasing duration, worse glycemic control, and age up to 20 years. Indicators of diabetes care were related to retinopathy through their effect on glycemic control. Improvements in diabetes care leading to better glycemic control may have contributed to the much lower prevalence and less severe retinopathy observed than expected on the basis of a previous report from the same region of Wisconsin. The observed decreased prevalence has important implications for persons with type 1 diabetes, since retinopathy is a serious microvascular complication.

School achievement in a regional cohort of children born very low birthweight

Children born very low birthweight (VLBW, <=1500 g) have historically had lower average school achievement than their normal birthweight peers. However, perinatal care and survival have changed dramatically since prior cohorts accrued, prompting reassessment. Surfactant therapy became generally available 8/1/1990, and the use of ante- and postnatal steroids increased substantially around this time. Standardized test scores and teacher ratings in math, reading, science, and social studies were obtained at age 10 for a cohort of children admitted to six regional NICUs in Wisconsin and Iowa, 8/1/1988 - 6/30/1991. We compared achievement between the VLBW cohort and controls from the same school districts. Among VLBW children, we determined neonatal and early childhood factors associated with achievement on standardized tests (ordinal logistic regression) and teacher ratings (linear regression) and evaluated whether achievement differed by birth year. Compared to population controls, VLBW children's greatest deficits occurred in mathematics. Scores on the standardized math exam and teacher ratings of overall achievement were positively associated with birthweight, social function measured at age five, and socioeconomic status. VLBW children born in the post-surfactant era (after 8/1/1990) had lower achievement on the standardized math exam than children born during the pre-surfactant era of the prior two years. Lower achievement in the post-surfactant era may be due to greater survival among less healthy neonates or increased exposure to postnatal steroids. VLBW children more likely to struggle academically could be identified by early childhood measures, allowing for targeted interventions to mitigate their difficulties.

Validation of a Carotid Intima-Media Thickness Border Detection Program for Use in an Office Setting

BACKGROUND

A unique semiautomated border detection program (BDP) designed for use on a personal computer was evaluated to determine whether: (1) carotid intima-media thickness (CIMT) measurements were bioequivalent to a reference laboratory; and (2) it would allow a novice (NOV) reader with no medical training to accurately and reproducibly measure CIMT.

METHODS

Far-wall CIMT was measured blindly and in duplicate by an experienced and NOV reader using BDP and by a reference laboratory.

RESULTS

Mean CIMT using BDP was bioequivalent to the reference laboratory (two 1-sided T-test, P < .05) with small absolute differences (experienced 0.011 +/- 0.004 mm, NOV 0.022 +/- 0.004 mm). Reproducibility was high, with small coefficients of variation when used by either the experienced (3.1%) or NOV (7.8%) reader.

CONCLUSION

CIMT measurements using BDP were accurate and reproducible. It was mastered easily by a NOV reader and appeared suitable for use in an office setting.

The association of increased total glycosylated hemoglobin levels with delayed age at menarche in young women with type 1 diabetes

CONTEXT

Delayed menarche is associated with subsequent reproductive and skeletal complications. Previous research has found delayed growth and pubertal maturation with type 1 diabetes and poor glycemic control. The effect of diabetes management on menarche is important to clarify, because tighter control might prevent these complications.

OBJECTIVE

The objective of this study was to investigate age at menarche in young women with type 1 diabetes and examine the effect of diabetes management [e.g. total glycosylated hemoglobin (GHb) level, number of blood glucose checks, insulin therapy intensity, and insulin dose] on age at menarche in those diagnosed before menarche.

DESIGN

The Wisconsin Diabetes Registry Project is a follow-up study of a type 1 diabetes population-based incident cohort initially enrolled between 1987 and 1992.

SETTING

This study was performed in 28 counties in south-central Wisconsin.

PATIENTS OR OTHER PARTICIPANTS

The study participants were recruited through referrals, self-report, and hospital/clinic ascertainment. Individuals with newly diagnosed type 1 diabetes, less than 30 yr old, were invited to participate. Of 288 young women enrolled, 188 reported menarche by 2002; 105 were diagnosed before menarche.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

The main outcome measure was age at menarche.

RESULTS

Mean age at menarche was 12.78 yr, compared with 12.54 yr in the United States (P = 0.01). Ages at menarche and diagnosis were not associated. For those diagnosed before menarche, age at menarche was delayed 1.3 months with each 1% increase in mean total GHb level in the 3 yr before menarche.

CONCLUSIONS

Age at menarche was moderately delayed in young women with type 1 diabetes. Delayed menarche could potentially be minimized with improved GHb levels.

A longitudinal measurement error model with a semicontinuous covariate

Covariate measurement error in regression is typically assumed to act in an additive or multiplicative manner on the true covariate value. However, such an assumption does not hold for the measurement error of sleep-disordered breathing (SDB) in the Wisconsin Sleep Cohort Study (WSCS). The true covariate is the severity of SDB, and the observed surrogate is the number of breathing pauses per unit time of sleep, which has a nonnegative semicontinuous distribution with a point mass at zero. We propose a latent variable measurement error model for the error structure in this situation and implement it in a linear mixed model. The estimation procedure is similar to regression calibration but involves a distributional assumption for the latent variable. Modeling and model-fitting strategies are explored and illustrated through an example from the WSCS.

A semiautomated ultrasound border detection program that facilitates clinical measurement of ultrasound carotid intima-media thickness

We have developed a novel, semiautomated carotid intima-media thickness (CIMT) border detection program (AUTO) and evaluated its measurement reproducibility and accuracy. Images from 6 carotid segments were acquired in 50 subjects, for a total of 300 segments. Mean and maximum CIMT values were measured blindly at a reference (REF) lab and in duplicate by experienced (EXP) and novice (NOV) readers using manual (MAN) and AUTO methods. Coefficients of variation for AUTO measurements of mean (3.2%) and maximum (4.1%) CIMT were low, and the AUTO method improved the NOV reader's reproducibility. Compared with the REF lab, mean (0.012 +/- 0.006 mm) and maximum (0.144 +/- 0.006 mm) CIMT biases were small and equivalent to those of the REF lab ( P < .001). The AUTO method shortened reading times by 35% to 46% ( P < .001). We conclude that our novel AUTO CIMT measurement program improved reproducibility and was accurate. Compared with MAN tracing, the AUTO method agreed better with the REF lab and decreased reading time.

Outcomes monitoring of health, behavior, and quality of life after nutrition intervention in adults with type 2 diabetes

OBJECTIVES

To examine changes in health and lifestyle indicators over 6 months in persons with type 2 diabetes mellitus receiving nutrition counseling from a registered dietitian, and to promote dietetics professionals' participation in outcomes monitoring and research.

DESIGN

Prospective, noncontrolled descriptive study.

SUBJECTS

Two hundred forty-four physician-referred adults with type 2 diabetes mellitus from 31 sites who received usual and customary nutrition counseling, and 83 registered dietitians.

MAIN OUTCOME MEASURES

Glycemic control, coronary heart disease risk, self-management behaviors, and quality of life were measured at baseline, 3 months, and 6 months. Dietitians' perceptions of the study were also measured.

STATISTICAL ANALYSIS

Repeated-measures analysis of variance, paired t test, Wilcoxon signed rank test, sign test, Spearman correlation, and chi 2 analysis were conducted.

RESULTS

Weight and glycemic control, coronary heart disease risk, and self-management behaviors improved significantly between baseline and 3 months and baseline and 6 months. Weight, body mass index, and glycosylated hemoglobin value also improved significantly between 3 months and 6 months. Increased time and/or number of sessions with the registered dietitian were associated with weight loss and reduced glycosylated hemoglobin, fasting plasma glucose, total cholesterol, and triglyceride levels. Self-perceived health status and missed workdays were significantly improved at 6 months. Difficulty obtaining current laboratory values, lack of time, and inability to reach subjects for follow-up presented the greatest obstacles for the dietitians.

CONCLUSIONS

Positive outcomes were observed in adults receiving nutrition intervention for type 2 diabetes. Clinical improvements were greatest between baseline and 3 months, with stabilization between 3 months and 6 months, suggesting ongoing intervention is needed to support continued clinical progress. Dietitians found participation in this state affiliate-coordinated research project rewarding.

Cardiovascular Disease, Mortality, and Retinal Microvascular Characteristics in Type 1 Diabetes

BACKGROUND

Diabetic retinopathy and proteinuria, manifestations of microvascular abnormalities, occur early in the course of diabetes mellitus; in contrast, macrovascular cardiovascular complications usually occur later. Retinal vessel characteristics may be informative about risk of cardiovascular disease in persons with diabetes. We evaluated this in a longitudinal cohort study of persons with type 1 diabetes.

METHODS

The population consisted of persons with type 1 diabetes who were receiving care in 11 counties in Wisconsin. Subjects (n = 996) were examined at baseline (1980-1982), and 4, 10, 14, and 20 years later. Evaluations included medical history and measurements of height, weight, blood pressure, and glycosylated hemoglobin. Fundus photographs were graded for diabetic retinopathy at baseline, and the same photographs were graded later for the diameters of retinal blood vessels. At each examination, a history of cardiovascular disease events since the last examination (and prior to baseline) was obtained. Mortality was monitored yearly.

RESULTS

The 20-year age-adjusted cumulative incidences were 18.1% for angina, 14.8% for myocardial infarction, and 5.9% for stroke. Severity of diabetic retinopathy was associated with angina and stroke. Arteriovenous ratio was associated with myocardial infarction. Of 273 deaths, 176 involved heart disease. The severity of retinopathy and arteriovenous ratio was associated with heart disease mortality. Nephropathy was more informative about the cardiovascular end points than were the blood vessel characteristics.

CONCLUSIONS

Incidences of cardiovascular disease, including mortality, were common in people with type 1 diabetes during a 20-year interval. Retinal vascular characteristics were associated with these end points, but this association was confounded by nephropathy.

A measurement error model with a Poisson distributed surrogate

We study a linear model in which one of the covariates is measured with error. The surrogate for this covariate is the event count in unit time. We model the event count by a Poisson distribution, the rate of which is the unobserved true covariate. We show that ignoring the measurement error leads to inconsistent estimators of the regression coefficients and propose a set of unbiased estimating equations to correct the bias. The method is computationally simple and does not require using supplemental data as is often the case in other measurement error analyses. No distributional assumption is made for the unobserved covariate. The proposed method is illustrated with an example from the Wisconsin Sleep Cohort Study.

Relation between intake of vitamins C and E and risk of diabetic retinopathy in the Atherosclerosis Risk in Communities Study

BACKGROUND

The potential protective effect of vitamins C and E against the development of diabetic retinopathy has not been thoroughly evaluated in epidemiologic studies.

OBJECTIVE

The objective was to study the association between prevalent diabetic retinopathy and intake of vitamins C and E in participants of the Atherosclerosis Risk in Communities Study.

DESIGN

A total of 1353 subjects with type 2 diabetes diagnosed between 1993 and 1995 or before were included. Nutrient intake was assessed with a food-frequency and supplement questionnaire administered between 1987-1989 and 1993-1995. Prevalent retinopathy (n = 224) was determined in 1993-1995 from graded fundus photographs.

RESULTS

No association of retinopathy with intake of vitamin C or E from food alone or from food and supplements combined was observed. The odds ratios and 95% CIs for retinopathy for quartile 4 compared with quartile 1 of vitamins C and E intakes from food and supplements combined were 1.1 (0.7, 1.9) and 1.3 (0.8, 2.2), respectively, after adjustment for diabetes treatment and serum glucose. There was a significant interaction of the observed relations with serum glucose concentration (P < 0.05). Additionally, a decreased odds of retinopathy was found among users (reported use > or =3 y before 1993-1995) of vitamin C or E supplements or multisupplements compared with reported use of no supplements: 0.5 (0.3, 0.8), 0.5 (0.2, 0.8), and 0.4 (0.2, 0.9), respectively.

CONCLUSION

No significant overall associations were observed between risk of retinopathy and intake of major dietary antioxidants. The observed association between risk of retinopathy and supplement use may reflect nondietary factors or a possible benefit of supplementation.

Self-rated health among young people with type 1 diabetes in relation to risk factors in a longitudinal study

Care for type 1 diabetes mellitus should both alleviate the physical complications of the disease and improve overall quality of life. The Wisconsin Diabetes Registry, comprising a population-based cohort that is followed longitudinally from diagnosis of type 1 diabetes, provided the authors with a unique opportunity to examine quality of life in children, adolescents, and young adults with type 1 diabetes and its relation to both sociodemographic and clinical risk factors. The authors analyzed data from 1987-2002 with a mean of 10.2 years' duration of diabetes (n = 569). They used ordinal-scaled self-rated global health as a measure of quality of life. In this paper, they propose a random-effects model for drawing inferences on individuals regarding the relation of longitudinally measured quality of life to multiple risk factors. Results showed that male gender, higher parental socioeconomic level, younger age at diabetes diagnosis, shorter diabetes duration, no hospitalization in the preceding 6 months, lower glycosylated hemoglobin level, and questionnaire responses by a person other than the subject were independently associated with better reported health. The authors found that individuals varied in their reported health even after adjustment for all identified risk factors. This could imply either that there is variability in perception even with the same health status or that there are independent unmeasured risk factors for poor health in persons with type 1 diabetes.

The relation of retinal vessel caliber to the incidence and progression of diabetic retinopathy: XIX: the Wisconsin Epidemiologic Study of Diabetic Retinopathy

OBJECTIVE

To describe the relation of retinal arteriolar and venular caliber to the incidence and progression of diabetic retinopathy in people with type 1 diabetes mellitus.

DESIGN

Incidence findings in a population-based study of diabetic retinopathy in Wisconsin. Participants included 996 persons diagnosed as having diabetes mellitus before 30 years of age who took insulin and underwent the baseline examination, 891 in the 4-year follow-up, 765 in the 10-year follow-up, and 634 in the 14-year follow-up. Retinal photographs of 7 standard fields were taken at all examinations. Computer-assisted grading was performed from a digitized image of field 1 to determine the average diameter of retinal arterioles and venules and their ratio. Main outcome measures included incidence and progression of retinopathy, incidence of proliferative retinopathy, and macular edema.

RESULTS

While adjusting for other factors, larger arteriolar (relative risk [RR] for the fourth vs first quartile range, 2.04; 95% confidence interval [CI], 1.20-3.47; test of trend, P =.008) and venular diameters (RR, 2.33; 95% CI, 1.37-3.95; test of trend, P =.005) were associated with greater 4-year progression of retinopathy. Larger venular diameters (RR, 4.28; 95% CI, 1.50-12.19; test of trend, P =.006) but not arteriolar diameters were associated with greater 4-year incidence of proliferative retinopathy. In multivariable analyses, arteriolar and venular calibers were not associated with the 4-year incidence of retinopathy. While adjusting for other factors, arteriolar and venular calibers were not associated with incidence of macular edema at 4 years. There were few associations of arteriolar or venular caliber with the 10- or 14-year incidence or the progression of retinopathy.

CONCLUSIONS

Larger arteriolar and venular caliber, independent of retinopathy severity level, is related to the progression of retinopathy, and larger venular caliber is associated with the 4-year incidence of proliferative retinopathy. Caliber of retinal vessels is not associated with incident retinopathy. These data suggest a quantitative measure of retinal vascular caliber provides additional information regarding risk for progression of retinopathy.

Retinal vascular abnormalities in persons with type 1 diabetes: the Wisconsin Epidemiologic Study of Diabetic Retinopathy: XVIII

PURPOSE

To describe the distribution of retinal vascular characteristics and their correlates in people with type 1 diabetes.

DESIGN

Population-based study with baseline cross-sectional findings.

PARTICIPANTS

Nine hundred ninety-six persons who were diagnosed with diabetes before 30 years of age and who were taking insulin in an 11-county area in south-central Wisconsin participated in the baseline examination from 1980 to 1982. In addition, 225 persons without diabetes participated.

METHODS

Retinal photographs of 7 standard fields were taken; lightbox grading was performed to determine arteriovenous (A/V) nicking and focal retinal arteriolar narrowing. Computer-assisted grading was performed from a digitized image of field 1 to determine central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE), and the arteriole-to-venule ratio (AVR).

MAIN OUTCOME MEASURES

Frequency and distribution of A/V nicking, CRAE, CRVE, AVR, and focal retinal arteriolar narrowing.

RESULTS

In multivariate analyses, retinopathy severity, mean arterial blood pressure, presence of gross proteinuria, glycosylated hemoglobin, and history of cardiovascular disease were associated with CRAE. Retinopathy severity, age, mean arterial blood pressure, duration of diabetes, glycosylated hemoglobin level, and body mass index were associated with CRVE. With the exception of glycosylated hemoglobin, similar factors were associated with AVR. Age (odds ratio [OR] per 10 years, 2.43 and 2.02) and retinopathy severity (OR per level, 1.14 and 1.21) were associated with focal retinal arteriolar narrowing and A/V nicking, respectively. In persons >/=18 years of age, smoking was associated with CRAE, CRVE, and A/V nicking (OR, 2.67), but not with AVR or focal arteriolar narrowing.

CONCLUSIONS

This study documented the frequency and distribution of retinal vascular characteristics and their relationships to various factors in persons with type 1 diabetes.

Postmenopausal Hormone Therapy and Its Association With Cognitive Impairment

BACKGROUND

Cognitive impairment is a common and potentially debilitating medical problem in older women. Postmenopausal hormone therapy (HT) has been associated with better cognitive function, but the literature is conflicting. Results of recent trials suggest that HT is inappropriate for prevention of heart disease, and we sought to determine the role of HT in the risk of cognitive impairment.

METHODS

We measured HT use and cognitive function in a population-based cohort of 1462 postmenopausal women participating in the 5-year follow-up examination for the Epidemiology of Hearing Loss Study in 1998-2000. The cohort was defined in 1987-1988 by residency in Beaver Dam, Wis, and an age of 43 to 84 years. Women had also participated in the Beaver Dam Eye Study baseline examination in 1988-1990. Use of HT was assessed at the Beaver Dam Eye Study baseline (1988-1990), 5-year follow-up (1993-1995), and 10-year follow-up (1998-2000) visits. Cognitive impairment was defined as a low Mini-Mental State Examination score or a reported diagnosis of Alzheimer disease.

RESULTS

Six percent of participants (n = 94) were impaired; these women were significantly older and less educated than those who were unimpaired. In age- and education-adjusted analysis, current HT use was not significantly associated with cognitive impairment (odds ratio, 0.6; 95% confidence interval, 0.2-1.3). Similarly, cognitive impairment was not associated with past HT use or duration of HT use.

CONCLUSION

In this large population-based study, postmenopausal hormone therapy was not significantly associated with better cognitive function.

Relations of serum ascorbic acid and alpha-tocopherol to diabetic retinopathy in the Third National Health and Nutrition Examination Survey

The protective relation of ascorbic acid and alpha-tocopherol to the development of diabetic retinopathy has not been thoroughly evaluated in epidemiologic studies. The association of prevalent diabetic retinopathy with serum ascorbic acid and alpha-tocopherol was studied among participants with type 2 diabetes (>or=40 years) (n = 998) in the Third National Health and Nutrition Examination Survey (1988-1994); 20% of the sample (n = 199) had prevalent retinopathy. The overall odds ratio for retinopathy among participants in quartile 4 compared with quartile 1 for serum ascorbic acid was 1.3 (95% confidence interval: 0.8, 2.3), with a p for trend = 0.60 after adjustment for the confounders of smoking, race, waist/hip ratio, hypertension, and duration of diabetes. The overall odds ratio for retinopathy among participants in quartile 4 compared with quartile 1 for serum alpha-tocopherol was 2.7 (95% confidence interval: 1.6, 4.6), with a p for trend = 0.14 after adjustment for confounders. After removal of supplement users of vitamin C (n = 307) or vitamin E (n = 298), the odds ratio changed direction or was attenuated: adjusted odds ratios for retinopathy among participants in quartile 4 compared with quartile 1 for serum ascorbic acid and alpha-tocopherol = 0.7 (95% confidence interval: 0.3, 1.4) and 1.6 (95% confidence interval: 0.9, 2.9), respectively. In summary, no significant associations were observed between serum levels of major dietary antioxidants and retinopathy. Recent use of supplements for treatment of complications of diabetes may explain the direct associations.

The effect of correction of sleep-disordered breathing on BP in untreated hypertension

OBJECTIVES

To compare BP response to 3 weeks of nasal continuous positive airway pressure (CPAP) in hypertensive patients with and without sleep-disordered breathing (SDB).

DESIGN

A controlled, interventional trial of nasal CPAP in patients with and without SDB.

PARTICIPANTS AND SETTING

Twenty-four men, aged 30 to 60 years, with mild to moderate untreated hypertension recruited from employee health and primary care clinics.

METHODS

Based on in-laboratory polysomnography, 14 hypertensive patients had SDB, defined by five or more episodes of apnea and hypopnea per hour of sleep (apnea-hypopnea index [AHI], > or = 5), and 10 had no SDB (AHI, < 5). We performed 24-h ambulatory BP monitoring on all patients at baseline, during CPAP, and after CPAP treatment. In patients with an AHI > or = 5, nasal CPAP was titrated to reduce the AHI to < 5. Patients with an AHI < 5 received CPAP of 5 cm H(2)O to control for any potential effect of CPAP per se on BP. Both groups received CPAP for 3 weeks.

RESULTS

After adjusting for age and body mass index, the mean nocturnal systolic and diastolic BP changes after CPAP treatment in the SDB group were significantly different from those in the no-SDB group: -7.8 vs +0.3 mm Hg (p = 0.02), and -5.3 vs -0.7 mm Hg (p = 0.03), respectively. There was a similar, although statistically insignificant, difference in the adjusted mean daytime systolic and diastolic BP changes after CPAP treatment between the two groups (-2.7 vs +0.4 mm Hg and -2.3 vs -1.7 mm Hg, respectively).

CONCLUSIONS

Three weeks of nasal CPAP treatment of SDB in hypertensive men caused the lowering of nocturnal systolic and diastolic BP values, suggesting that increased nocturnal BP in persons with hypertension was causally related to the apnea and hypopnea events of SDB.

Relation of blood homocysteine and its nutritional determinants to age-related maculopathy in the third National Health and Nutrition Examination Survey

BACKGROUND

Blood homocysteine and its nutritional determinants folate and cyanocobalamin (vitamin B-12) have been shown to affect the risk of vascular disease. The pathogenesis of age-related maculopathy (ARM) is related to adverse vascular changes.

OBJECTIVE

The objective was to evaluate the associations between homocysteine, its nutritional determinants, and ARM in persons aged >or= 40 y participating in the third National Health and Nutrition Examination Survey.

DESIGN

A nonmydriatic fundus photograph of one eye, taken in a mobile examination center, was used to ascertain ARM status. Phlebotomy was performed for measurement of homocysteine, cyanocobalamin, and erythrocyte folate in participants of phase 2 of the survey (n = 3828). Logistic regressions were used to compute odds ratios and 95% CIs by quintile of serum analyte by using sample weights and jackknife replication methods to adjust for the complex survey design. The final analyses were adjusted for potential risk factors that influenced odds ratios.

RESULTS

Total serum homocysteine, red blood cell folate, and serum cyanocobalamin were unrelated to ARM in the overall sample. However, red blood cell folate was inversely related to one type of early ARM lesion (soft drusen) in non-Hispanic blacks.

CONCLUSIONS

ARM does not appear to be associated with homocysteine or its dietary determinants in this survey. There is a need for further investigation to rule out potential associations in subgroups with low folate status that may not have been detected because of the cross-sectional survey design.

Testing model fit in longitudinal data analysis against alternatives with omitted covariates

Several types of common model misspecifications can be re-formulated as problems of omitted covariates. These include situations with unmeasured confounders, measurement errors in observed covariates and informative censoring. Longitudinal data present special opportunities for detecting omitted covariates that are related to the observed ones differently across time than across individuals. This situation arises with period and cohort effects, as well as with usual formulations of classical measurement error in observed covariates. In this article we focus on testing for the existence of omitted covariates in longitudinal data analysis when models are fit by generalized estimation equations. When omitted covariates are present, specification of the correct link function conditionally on only observed covariates under the alternative usually involves complicated numerical integration. We propose a quasi-score test statistic that avoids the need to fit such alternative models. The statistic is asymptotically chi-square distributed under the null hypothesis of no omitted covariates with degrees of freedom determined by the assumed alternative structure. We study the significance level and the power of the quasi-score test in linear and logistic regression models. The test is then applied to an analysis of excessive daytime sleepiness.

HLA-DR3 and DR4 and their relation to the incidence and progression of diabetic retinopathy

PURPOSE

Cross-sectional data from the Wisconsin Epidemiologic Study of Diabetic Retinopathy indicated that patients with HLA-DR4, but not DR3, were more likely to have prevalent proliferative retinopathy than those without both antigens. We describe the relation of HLA-DR3 and DR4 antigens to the 14-year incidence and progression of diabetic retinopathy and macular edema in this cohort.

DESIGN

A population-based cohort study.

PARTICIPANTS

A probability sample of male and female patients receiving primary care for diabetes in 11 counties of southern Wisconsin.

METHODS

Participants were invited for a baseline examination in 1980 to 1982, with follow-up examinations at 4, 10, and 14 years later. At the 4-year examination, a random sample of participants (n = 428) diagnosed with diabetes before the age of 30 and taking insulin were selected for HLA-DR typing.

MAIN OUTCOME MEASURES

Fourteen-year incidence and progression of diabetic retinopathy and macular edema based on masked stereoscopic fundus photographic grading.

RESULTS

There was no relation between HLA-DR3 and DR4 status with the 14-year incidence and progression of diabetic retinopathy, progression to proliferative retinopathy, and incidence of macular edema. Patients with either HLA-DR3 or DR4 were less likely to progress to proliferative retinopathy compared with those who were negative for both, although these relations were not statistically significant. The associations did not vary after adjusting for hypertension status, baseline retinopathy, and glycosylated hemoglobin levels, or after stratifying by duration of diabetes (less than 10 years vs. 10 years or more) and age at diagnosis of diabetes (less than 15 years vs. 15 years or more). Furthermore, 10-year mortality and 14-year nephropathy rates did not differ by HLA-DR3 or DR4 status, suggesting that selective mortality did not explain the pattern of associations seen.

CONCLUSIONS

In contrast to the initial cross-sectional findings, these data suggest that HLA-DR3 or DR4 status is unrelated to 14-year incidence and progression of diabetic retinopathy. The discrepancy may be related to increasing homogeneity of retinopathy and diminishing power to detect small differences, but it may also reflect the uncertain and inconsistent effects of HLA-DR3 or DR4 on the development and progression of diabetic retinopathy.

Bias adjustment in analysing longitudinal data with informative missingness

The recent biostatistical literature contains a number of methods for handling the bias caused by 'informative censoring', which refers to drop-out from a longitudinal study after a number of visits scheduled at predetermined intervals. The same or related methods can be extended to situations where the missing pattern is intermittent. The pattern of missingness is often assumed to be related to the outcome through random effects which represent unmeasured individual characteristics such as health awareness. To date there is only limited experience with applying the methods for informative censoring in practice, mostly because of complicated modelling and difficult computations. In this paper, we propose an estimation method based on grouping the data. The proposed estimator is asymptotically unbiased in various situations under informative missingness. Several existing methods are reviewed and compared in simulation studies. We apply the methods to data from the Wisconsin Diabetes Registry Project, a longitudinal study tracking glycaemic control and acute and chronic complications from the diagnosis of type I diabetes.

Relationship of dietary fat to age-related maculopathy in the Third National Health and Nutrition Examination Survey

OBJECTIVE

To evaluate the associations between dietary fat and age-related maculopathy (ARM) in persons 40 years or older who participated in the Third National Health and Nutrition Examination Survey.

METHODS

We used a single, nonmydriatic, fundus photograph of 1 eye to ascertain ARM status in 7883 of 11 448 survey participants. Intake of fat was estimated from 24-hour recall, and specific sources of dietary fat were estimated from responses to food frequency questionnaires. Logistic regression was used to compute odds ratios (ORs) and 95% confidence intervals (CIs) that accounted for complex survey design, nonresponse, and potential risk factors for ARM (age, smoking, race, sex, body mass index, history of cardiovascular disease or hypertension, eye color, and sedentary lifestyle). Persons aged 40 to 79 years (n = 7405) were included in analyses for early ARM (n = 644); those 60 years or older (n = 4294) were included in analyses for late ARM (n = 53).

RESULTS

After adjustment for age, race, eye color, and sedentary lifestyle, OR for early ARM was 1.4 (95% CI, 0.9-2.2; P for trend,.10) among persons in high vs low quintiles of total fat intake (percentage of total energy). Associations for specific types of fatty acids (as percentages of caloric intake) were in the same direction and unrelated to ARM. The OR for late ARM was 0.7 (95% CI, 0.2-2.6; P for trend,.60) in persons 60 years or older. Further adjustments for other potential confounders did not significantly affect the ORs.

CONCLUSION

Age-related maculopathy was not significantly associated with dietary fat in this large cross-sectional survey.

Risk factors for frequent and severe hypoglycemia in type 1 diabetes

OBJECTIVE

To determine the risk of frequent and severe hypoglycemia and the associated demographic and clinical risk factors.

RESEARCH DESIGN AND METHODS

Demographic and diabetes self-management factors were measured in 415 subjects followed prospectively for 4-6.5 years of type 1 diabetes duration as participants in a population-based incident cohort. Blood samples were collected up to three times yearly to test glycosylated hemoglobin (GHb) levels. Reports of frequent (2-4 times/week) and severe (lost consciousness) hypoglycemia as well as other diabetes self-management data were collected by questionnaires.

RESULTS

Frequent hypoglycemia was common (33 and 35% of participants reported this on the 4- and 6.5-year questionnaires, respectively), whereas severe hypoglycemia occurred much less often. Better glycemic control (odds ratio [OR] 1.3 per 2% decrease in GHb, 95% CI 1.1-1.5) and more frequent self-monitored blood glucose (1.5 per blood glucose check, 1.3-1.7) were independently related to frequent hypoglycemia. The association of frequent hypoglycemia with intensive insulin therapy increased with age. Better glycemic control (1.5 per 2% decrease in GHb, 1.2-2.0) and older age were related to severe hypoglycemic reactions. No sociodemographic factors other than age increased the risk of hypoglycemia.

CONCLUSIONS

Frequent hypoglycemia was common in a population representing the full range of glycemic control in the community. Intensive insulin management and blood glucose monitoring independently predicted frequent but not severe hypoglycemia. This information may be useful for updating patients such that minor changes in diabetes management might decrease the daily burden of this condition while maintaining intensive insulin therapy.

Respiratory symptoms at age 8 years in a cohort of very low birth weight children

The childhood respiratory consequences of very low birth weight (birth weight < or =1,500 g) are incompletely understood, especially since the introduction of recent changes in neonatal care. To assess prevalence, trends, and risk factors for respiratory symptoms, the authors followed to age 8 years a cohort of 384 very low birth weight children from six regional neonatal intensive care units in Wisconsin and Iowa who were born between August 1, 1988, and June 30, 1991. A control group of 154 Wisconsin schoolchildren was also assembled. Respiratory symptoms in the past 12 months and history of asthma ("asthma ever") were reported by parents on a questionnaire used in the International Study of Asthma and Allergies in Childhood (ISAAC). Control group prevalence resembled ISAAC prevalence worldwide and in Canada, but respiratory symptoms were twice as common among very low birth weight children. With advent of the availability of pulmonary surfactants, the prevalence of wheezing at age 8 decreased from 50% to 16% (p = 0.002) among children with bronchopulmonary dysplasia, but it increased from 14% to 38% among those with milder neonatal respiratory disease. Bronchopulmonary dysplasia, family history of asthma, smoking in the household, and patent ductus arteriosus were predictive of wheezing in the previous 12 months. Antenatal steroid therapy had a borderline-significant protective association with wheezing (odds ratio = 0.56, 95% confidence interval: 0.29, 1.1). There were interaction effects between several of the predictors.

Chronic nasal congestion at night is a risk factor for snoring in a population-based cohort study

BACKGROUND

Nasal congestion at night is thought to have a role in snoring and sleep apnea, but this hypothesis has not previously been tested in a population-based study.

METHODS

Baseline and 5-year follow-up data on self-reported nocturnal nasal congestion and snoring frequency were collected from a population-based sample of 4916 men and women (age range, 30-60 years at baseline) enrolled in the ongoing Wisconsin Sleep Cohort Study. In-laboratory polysomnography was performed on a subset (n = 1032) of the study population to determine the frequency of apnea and hypopnea episodes during sleep. Logistic regression was used to estimate odds ratios for snoring with chronic nasal congestion at night.

RESULTS

Nocturnal nasal congestion frequency was independently associated with snoring frequency in cross-sectional analyses. The odds ratios (adjusted for sex, age, body habitus, and smoking) for habitual snoring with severe (always or almost always) nasal congestion vs none was 3.0 (95% confidence interval, 2.2-4.0). This association was not explained by habitual snorers with frank sleep apnea (ie, >/=5 apnea and hypopnea episodes per hour of sleep). Prospective analyses showed that persons with chronic severe nasal congestion had a high risk of habitual snoring according to the data from the 5-year follow-up survey: the odds ratio for habitual snoring and reporting congestion always or almost always at both baseline and follow-up was 4.9 (95% confidence interval, 2.8-8.8).

CONCLUSIONS

Nocturnal nasal congestion is a strong independent risk factor for habitual snoring, including snoring without frank sleep apnea. Intervention studies are needed to determine if snoring can be reduced with treatment of nasal congestion.

Predictors, prodromes and incidence of postpartum depression

The purpose of this study was to determine the incidence of clinically significant depression occurring between 1 and 4 months postpartum and to investigate whether somatic complaints, subsyndromal depressive symptoms, or birth-related concerns among non-depressed women at 1 month were predictive of postpartum depression. This is a prospective cohort study of 465 women from the Wisconsin Maternity Leave and Health Project (WMLHP). Women who were not depressed at 1 month postpartum were reassessed 3 months later for depression occurring at any time in the interval between 1 and 4 months postpartum. Depression was defined as either meeting the criteria for major depression on the National Institute of Mental Health (NIMH) Diagnostic interview Schedule (DIS) or scoring above 15 on the Center for Epidemiologic Studies Depression Scale (CES-D). Physical symptoms were assessed by an adapted Health Responses Scale. Other measures were developed specifically for the WMLHP. Of 465 women, 27 (5.8%) became clinically depressed between 1 and 4 months postpartum. In a logistic regression analysis, four variables (maternal age, depression during pregnancy, thoughts of death and dying at 1 month postpartum, and difficulty falling asleep at 1 month postpartum) were predictive of depression at 4 months postpartum. Breast-feeding, mode of delivery, family income, parity and mother's education did not predict depression. The existence of subsyndromal depressive symptoms, particularly thoughts of death and dying, may represent a prodromal phase of depression and should alert clinicians to the possibility of future postpartum depression. Women with a history of depression during pregnancy should be monitored for signs of postpartum depression for a minimum of 4 months. Obstetricians are in a unique position during the postpartum check-up to screen women for these predictors of future postpartum depression and possibly to avert the development of a clinically significant depressive episode.

Lutein and zeaxanthin in the diet and serum and their relation to age-related maculopathy in the third national health and nutrition examination survey

Relations of the carotenoids lutein and zeaxanthin in the diet and serum to photographic evidence of early and late age-related maculopathy (ARM) among persons over age 40 years (n = 8,222) were examined. Inverse relations of these carotenoids in the diet or serum to any form of ARM were not observed overall. There was a direct relation of dietary levels to one type of early ARM (soft drusen). However, relations differed by age and race. In the youngest age groups who were at risk for developing early (ages 40-59 years) or late (ages 60-79 years) ARM, higher levels of lutein and zeaxanthin in the diet were related to lower odds for pigmentary abnormalities, one sign of early ARM (odds ratio among persons in high vs. low quintiles = 0.1, 95 percent confidence interval: 0.1, 0.3) and of late ARM (odds ratio = 0.1, 95 percent confidence interval: 0.0, 0.9) after adjustment for age, gender, alcohol use, hypertension, smoking, and body mass index. Relations of these carotenoids to ARM may be influenced by age and race and require further evaluation in separate populations and in prospective studies.

Longitudinal study of moderate weight change and sleep-disordered breathing

CONTEXT

Excess body weight is positively associated with sleep-disordered breathing (SDB), a prevalent condition in the US general population. No large study has been conducted of the longitudinal association between SDB and change in weight.

OBJECTIVE

To measure the independent longitudinal association between weight change and change in SDB severity.

DESIGN

Population-based, prospective cohort study conducted from July 1989 to January 2000.

SETTING AND PARTICIPANTS

Six hundred ninety randomly selected employed Wisconsin residents (mean age at baseline, 46 years; 56% male) who were evaluated twice at 4-year intervals for SDB.

MAIN OUTCOME MEASURES

Percentage change in the apnea-hypopnea index (AHI; apnea events + hypopnea events per hour of sleep) and odds of developing moderate-to-severe SDB (defined by an AHI > or =15 events per hour of sleep), with respect to change in weight.

RESULTS

Relative to stable weight, a 10% weight gain predicted an approximate 32% (95% confidence interval [CI], 20%-45%) increase in the AHI. A 10% weight loss predicted a 26% (95% CI, 18%-34%) decrease in the AHI. A 10% increase in weight predicted a 6-fold (95% CI, 2.2-17.0) increase in the odds of developing moderate-to-severe SDB.

CONCLUSIONS

Our data indicate that clinical and public health programs that result in even modest weight control are likely to be effective in managing SDB and reducing new occurrence of SDB.

Vitamin supplement use and incident cataracts in a population-based study

OBJECTIVE

To determine the relationship between vitamin supplement use and the 5-year incidence of nuclear, cortical, and posterior subcapsular cataract in the Beaver Dam Eye Study cohort.

DESIGN

The 5-year incidence of cataract, determined from slitlamp (nuclear cataract) and retroillumination (cortical and posterior subcapsular cataract) photographs, was assessed in a population-based cohort of persons participating in baseline (1988-1990) and follow-up (1993-1995) examinations. Detailed data regarding the type, dosage, and duration of supplement use were obtained by in-person interviews at follow-up.

PARTICIPANTS

Residents of Beaver Dam, Wis, aged 43 to 86 years, were identified by private census. Of the 3684 participants in both baseline and follow-up examinations, 3089 were eligible for incident cataract analysis in the present study.

RESULTS

Compared with nonusers, the 5-year risk for any cataract was 60% lower among persons who, at follow-up, reported the use of multivitamins or any supplement containing vitamin C or E for more than 10 years. Taking multivitamins for this duration lowered the risk for nuclear and cortical cataracts but not for posterior subcapsular cataracts (odds ratios [95% confidence intervals] = 0.6 [0.4-0.9], 0.4 [0.2-0.8], and 0.9 [0.5-1.9], respectively). Use of supplements for shorter periods was not associated with reduced risk for cataract. Measured differences in lifestyle between supplement users and nonusers did not influence these associations, nor did variations in diet as measured in a random subsample.

CONCLUSIONS

These data add to a body of evidence suggesting lower risk for cataract among users of vitamin supplements and stronger associations with long-term use. However, the specific nutrients that are responsible cannot be ascertained at this time, and unmeasured lifestyle differences between supplement users and nonusers may explain these results. Arch Ophthalmol. 2000;118:1556-1563

Temporal association between hospitalization and rate of falls after discharge

BACKGROUND

Evidence suggests that acute illness and hospitalization may increase the risk for falls.

OBJECTIVE

To evaluate the rate of falls, and associated risk factors, for 90 days following hospital discharge.

METHODS

We consecutively enrolled 311 patients, aged 65 years and older, discharged from the hospital after an acute medical illness and receiving home-nursing services. Patients were assessed within 5 days of discharge for prehospital and current functioning by self-report, and balance, vision, cognition, and delirium by objective measures. Patients were followed up weekly for 13 weeks for falls, injuries, and health care use.

RESULTS

The rate of falls was significantly higher in the first 2 weeks after hospitalization (8.0 per 1000 person-days) compared with 3 months later (1.7 per 1000 person-days) (P =.002). Fall-related injuries accounted for 15% of all hospitalizations in the first month after discharge. Independent prehospital risk factors significantly associated with falls included dependency in activities of daily living, use of a standard walker, 2 or more falls, and more hospitalizations in the year prior. Posthospital risk factors included use of a tertiary amine tricyclic antidepressant, probable delirium, and poorer balance, while use of a cane was protective.

CONCLUSIONS

The rate of falls is substantially increased in the first month after medical hospitalization, and is an important cause of injury and morbidity. Posthospital risk factors may be potentially modifiable. Efforts to assess and modify risk factors should be integral to the hospital and posthospital care of older adults (those aged >/=65 years).

Differentiation of acute cortical and subcortical ischemic stroke by risk factors and clinical examination findings

BACKGROUND

Differentiation between acute cortical and subcortical ischemic stroke may be problematic when cortical stroke presents without obvious cortical deficits such as aphasia, neglect or hemianopia. This study explores stroke risk factors and clinical variables that may assist in this differentiation.

METHODS

Records of consecutive patients with acute ischemic stroke, examined within 72 h of symptom onset, were reviewed. Stroke type was verified by clinical course and follow-up imaging. Stroke risk factors and acute examination findings were compared by odds ratios and positive predictive values for cortical and subcortical stroke.

RESULTS

For 355 patients studied, 237 had cortical stroke and 118 had subcortical stroke. Odds ratios for cortical stroke were highest for atrial fibrillation by EKG (OR = 4.77, CI = 2.08-10.94), recent hospitalization (OR = 4.51, CI = 2.39-8.53) and nonalert mental status (OR = 4.50, CI = 2.29-8.87). Possible cardioembolic condition, ischemic heart disease and peripheral vascular disease were also significant, but hypertension, age and diabetes mellitus were not significantly different for the stroke subtypes. Cortical deficits were absent in 19.4% of cortical stroke patients on initial examination. Predictive models were generated based on the presence or absence of cortical deficits and the interaction of significant risk factors with degree of motor deficit.

CONCLUSIONS

There are clinical features that, in addition to initial examination, may help differentiate cortical from subcortical ischemic stroke. These features may be relevant to both diagnostic and therapeutic approaches to acute stroke.

Problems of older adults living alone after hospitalization

OBJECTIVE

To describe functional deficits among older adults living alone and receiving home nursing following medical hospitalization, and the association of living alone with lack of functional improvement and nursing home utilization 1 month after hospitalization.

DESIGN

Secondary analysis of a prospective cohort study.

PARTICIPANTS

Consecutive sample of patients age 65 and over receiving home nursing following medical hospitalization. Patients were excluded for new diagnosis of myocardial infarction or stroke in the previous 2 months, diagnosis of dementia if living alone, or nonambulatory status. Of 613 patients invited to participate, 312 agreed.

MEASUREMENTS

One week after hospitalization, patients were assessed in the home for demographic information, medications, cognition, and self-report of prehospital and current mobility and function in activities of daily living (ADLs) and independent activities of daily living (IADLs). One month later, patients were asked about current function and nursing home utilization. The outcomes were lack of improvement in ADL function and nursing home utilization 1 month after hospitalization.

RESULTS

One hundred forty-one (45%) patients lived alone. After hospital discharge, 40% of those living alone and 62% of those living with others had at least 1 ADL dependency (P =.0001). Patients who were ADL-dependent and lived alone were 3.3 (95% confidence interval [95% CI], 1.4 to 7. 6) times less likely to improve in ADLs and 3.5 (95% CI, 1.0 to 11. 9) times more likely to be admitted to a nursing home in the month after hospitalization.

CONCLUSION

Patients who live alone and receive home nursing after hospitalization are less likely to improve in function and more likely to be admitted to a nursing home, compared with those who live with others. More intensive resources may be required to continue community living and maximize independence.

Prospective study of the association between sleep-disordered breathing and hypertension

BACKGROUND

Sleep-disordered breathing is prevalent in the general population and has been linked to chronically elevated blood pressure in cross-sectional epidemiologic studies. We performed a prospective, population-based study of the association between objectively measured sleep-disordered breathing and hypertension (defined as a laboratory-measured blood pressure of at least 140/90 mm Hg or the use of antihypertensive medications).

METHODS

We analyzed data on sleep-disordered breathing, blood pressure, habitus, and health history at base line and after four years of follow-up in 709 participants of the Wisconsin Sleep Cohort Study (and after eight years of follow-up in the case of 184 of these participants). Participants were assessed overnight by 18-channel polysomnography for sleep-disordered breathing, as defined by the apnea-hypopnea index (the number of episodes of apnea and hypopnea per hour of sleep). The odds ratios for the presence of hypertension at the four-year follow-up study according to the apnea-hypopnea index at base line were estimated after adjustment for base-line hypertension status, body-mass index, neck and waist circumference, age, sex, and weekly use of alcohol and cigarettes.

RESULTS

Relative to the reference category of an apnea-hypopnea index of 0 events per hour at base line, the odds ratios for the presence of hypertension at follow-up were 1.42 (95 percent confidence interval, 1.13 to 1.78) with an apnea-hypopnea index of 0.1 to 4.9 events per hour at base line as compared with none, 2.03 (95 percent confidence interval, 1.29 to 3.17) with an apnea-hypopnea index of 5.0 to 14.9 events per hour, and 2.89 (95 percent confidence interval, 1.46 to 5.64) with an apnea-hypopnea index of 15.0 or more events per hour.

CONCLUSIONS

We found a dose-response association between sleep-disordered breathing at base line and the presence of hypertension four years later that was independent of known confounding factors. The findings suggest that sleep-disordered breathing is likely to be a risk factor for hypertension and consequent cardiovascular morbidity in the general population.

[Anterior screw fixation for odontoid fractures]

The results of anterior screw fixation of odontoid fractures in 28 patients are presented. There were 27 type II- and 1 type III-injuries. Non-union with persistent instability had to be notified in one patient (3.6 %), secondary posterior C1/2 fusion had to be performed. Incorrect positioning of the screws in the odontoid with penetration of the postero-lateral cortex occurred in 3 patients (10.7 %). Malpositioning of the odontoid after screw fixation was documented in 5 cases (17.9 %). Cardiopulmonary complications had to be treated in 5 patients (17.9 %), 4 patients (14.3 %) died in the postoperative period. 17 patients could be followed up. Only 3 patients (17.8 %) were free of symptoms. A significant limitation in ROM of axial rotation was seen in 44 % of the patients. With anterior screw fixation of the odontoid high fusion rates can be achieved, however the procedure is technically demanding. Regarding the functional outcome, there is no significant difference to other established treatment methods.

Functional assessment of a multicenter very low-birth-weight cohort at age 5 years. Newborn Lung Project

BACKGROUND

Very low-birth-weight newborns (birth weight < or = 1500 g) experience serious neonatal complications, but long-term outcomes are not completely known. Most studies reflect an era of neonatal care that was fundamentally different from the present.

OBJECTIVES

To compare the functional level of very low-birth-weight children before and after surfactant introduction and to relate functional level to clinical and socioeconomic factors.

DESIGN

Inception cohort followed up from birth to an average age of 5 years.

SETTING

Six regional neonatal intensive care units in a contiguous geographic area.

PARTICIPANTS

Four hundred twenty-five very low-birth-weight children, born between August 1, 1988, and June 30, 1991, of 438 located among 626 whose parents provided follow-up information before neonatal intensive care unit discharge.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Diagnosis of cerebral palsy and standardized scores for self-care, mobility, and social function from the Pediatric Evaluation of Disability Inventory.

RESULTS

Cerebral palsy was present in 12.6% of the children, with no change after surfactant introduction. Intraventricular hemorrhage (odds ratio, 2.3 per grade; 95% confidence interval, 1.8-2.8) and bronchopulmonary dysplasia (odds ratio, 2.3; 95% confidence interval, 1.2-4.6) were independently predictive of cerebral palsy and of functional outcome. For self-care, mobility, and social function, 11.7%, 29.5%, and 10.7% of the children, respectively, scored at least 2 SDs below the normative means. Social function was 0.25 to 0.50 normative SDs lower after general surfactant availability than before general surfactant availability.

CONCLUSIONS

While there was no increase in major disability after surfactant introduction, there may have been a decrease in social function associated with the lower neonatal mortality. Most very low-birth-weight children functioned within the normal range in everyday tasks. Several predictors of outcome were identified.

Age-related maculopathy in a multiracial United States population: the National Health and Nutrition Examination Survey III

OBJECTIVE

To investigate the prevalence of and risk factors for age-related maculopathy (ARM) in three racial/ethnic groups: non-Hispanic whites, non-Hispanic blacks, and Mexican-Americans.

DESIGN

A nationally representative population-based, cross-sectional study.

PARTICIPANTS

A total of 8270 persons 40 years of age or older, a sample of the Third National Health and Nutrition Examination Survey.

MAIN OUTCOME MEASURES

Age-related maculopathy was determined by the grading of fundus photographs using a standardized protocol.

RESULTS

The prevalence of any ARM in the civilian noninstitutionalized United States population including those 40 years of age or older was 9.4% (95% confidence interval [CI], 8.2, 10.6) as estimated from the sample. After adjusting for age, there was no difference in the prevalence of early ARM (defined largely by the presence of soft drusen) by ethnic/racial group. However, for the less frequent component lesions of early ARM (increased retinal pigment and retinal pigment epithelial depigmentation), the odds ratios (95% CIs) comparing non-Hispanic blacks to non-Hispanic whites were 0.47 (0.31, 0.74) and 0.59 (0.33, 1.04), respectively, and for comparing Mexican-Americans to non-Hispanic whites, they were 0.41 (0.21, 0.81) and 0.72 (0.44, 1.19), respectively. For late ARM, the odds ratio (95% CI) for non-Hispanic blacks compared to non-Hispanic whites was 0.34 (0.10, 1.18) and for Mexican-Americans compared to non-Hispanic whites, it was 0.25 (0.07, 0.90). Other than age, none of the personal, medical, or physiologic variables studied were statistically significantly associated with any of the ARM endpoints in any of the three races/ethnic groups.

CONCLUSION

Overall, rates of any ARM (including all early and late lesions) are not significantly different among non-Hispanic blacks, Mexican-Americans, and non-Hispanic whites. However, the rates of individual lesions suggest that non-Hispanic whites and Mexican-Americans may be protected against retinal pigment abnormalities and lesions associated with late ARM. There appears to be little influence of personal, medical, and environmental factors studied on these results. Further studies in larger populations of older persons in these ethnic groups would likely clarify these relations.

An estimation method for the semiparametric mixed effects model

A semiparametric mixed effects regression model is proposed for the analysis of clustered or longitudinal data with continuous, ordinal, or binary outcome. The common assumption of Gaussian random effects is relaxed by using a predictive recursion method (Newton and Zhang, 1999) to provide a nonparametric smooth density estimate. A new strategy is introduced to accelerate the algorithm. Parameter estimates are obtained by maximizing the marginal profile likelihood by Powell's conjugate direction search method. Monte Carlo results are presented to show that the method can improve the mean squared error of the fixed effects estimators when the random effects distribution is not Gaussian. The usefulness of visualizing the random effects density itself is illustrated in the analysis of data from the Wisconsin Sleep Survey. The proposed estimation procedure is computationally feasible for quite large data sets.

Risk factors for lack of recovery of ADL independence after hospital discharge

OBJECTIVE

To determine risk factors for lack of recovery of independent functioning after hospitalization for acute medical illness.

DESIGN

Secondary analysis of cohort study of patients receiving home nursing after discharge.

SETTING

Evaluations performed in the home after discharge and 1 month later.

PARTICIPANTS

A total of 73 adults aged 65 years and older who were independent in activities of daily living (ADLs) before hospitalization and dependent at discharge.

MEASUREMENTS

Self-report and objective measures of function, mobility, and cognition.

OUTCOME

Return to independence in ADLs 1 month after discharge.

RESULTS

Fifty-nine percent of patients did not return to previous ADL independence by 1 month postdischarge. The likelihood for not recovering was 87% (95% CI, 70-100%) if a patient had a Mini-Mental State Examination score (MMSE) < 24 at discharge (P = .015). Among patients with good cognition, 85% (95% CI, 66-100%) of those who used an assistive device indoors before hospitalization did not recover (P = .007). Among patients with good cognition and no previous assistive device use, 73% (95% CI, 47-99%) of those with a Timed "Up and Go" of > or = 40 seconds did not recover (P = .012). The likelihood of recovery was high (76%, 95% CI 56-96%) if a patient had no assistive device prehospital, a good MMSE, and a Timed "Up and Go" of < 20 seconds.

CONCLUSION

We hypothesize that a classification strategy using cognition, prehospital mobility, and discharge physical performance will predict patients who are less likely to recover functional independence after hospitalization. If this is validated in future study, it may help clinicians identify patients who are more likely to benefit from additional intervention.

Latent variables, measurement error and methods for analysing longitudinal binary and ordinal data

We explore structural equations with latent variables for modelling between-individual variability and measurement error in the analysis of longitudinal binary and ordinal data. The structural equation formulation provides insight into the assumptions and differences in interpretation of methods that are popular for longitudinal data analysis. Introducing the concept of continuous latent variables makes it clear that marginal and cluster-specific models differ because their predicted variables are scaled to different standard deviations, and that adjustment for measurement error in the outcome involves a change in scale as well. We apply both structural equation modelling and common longitudinal modelling approaches to data from a study of sleep disorders. In the process, we compare results from marginal modelling using an SAS GEE routine (Karim and Zeger, 1988), Qu's GAUSS program (Qu, 1992) for generalized mixed models using GEE, the MIXOR package for cluster-specific mixed effects models (Hedeker and Gibbons, 1994), and LISCOMP for structural models (Muthén, 1988).