Biomedical subjects

Michael D Knudtson

Publications and source records attributed to Michael D Knudtson.

28 records · Page 2Linked to original sources

PubMed2004

Cardiovascular disease, mortality, and retinal microvascular characteristics in type 1 diabetes: Wisconsin epidemiologic study of diabetic retinopathy.

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.

Adolescent↗

PubMed2004

A prospective cohort study of retinal arteriolar narrowing and mortality.

The authors examined the relation of narrowed retinal arteriolar diameters, a marker of hypertensive damage, to mortality in a population-based cohort of 4,926 persons aged 43-84 years living in Wisconsin. A computer-assisted method was used to measure retinal vessel diameters from digitized retinal photographs taken at the baseline examination (1988-1990). These measurements were summarized as the retinal arteriole-to-venule ratio (AVR), with a smaller AVR indicating narrower arterioles compared with venules. Its relation to 10-year mortality was analyzed by using Cox proportional hazards models, adjusting for age, gender, blood pressure, diabetes, and other risk factors. No relation was found between smaller AVR and increased mortality. In relation to the largest AVR quartile, the adjusted relative risks of all-cause mortality were 0.93 for the smallest AVR quartile, 0.71 for the second AVR quartile, and 0.80 for the third AVR quartile. Results were largely similar in analyses of cause-specific mortality (vascular disease and non-vascular-disease mortality) and in subgroups stratified by age, gender, and diabetes and hypertension status. These data contrast with recent studies showing a relation between narrowed retinal arterioles and increased cardiovascular risk, suggesting that further research is needed to understand the systemic associations of retinal microvascular changes.

Adult↗

PubMed2004

Sunlight and the 10-year incidence of age-related maculopathy: the Beaver Dam Eye Study.

OBJECTIVE: To examine the association of sunlight exposure and indicators of sun sensitivity with the 10-year incidence of age-related maculopathy (ARM). DESIGN: Population-based cohort study. PARTICIPANTS: We included persons aged 43 to 86 years at the baseline examination from 1988 to 1990, living in Beaver Dam, Wis, of whom 3684 persons underwent 5-year follow-up and 2764 underwent 10-year follow-up. METHODS: Data on sun exposure and indicators of sun sensitivity were obtained from a standardized questionnaire administered at baseline and/or follow-up. We determined ARM status by grading stereoscopic color fundus photographs using the Wisconsin Age-Related Maculopathy Grading System. MAIN OUTCOME MEASURES: Incidence and progression of ARM. RESULTS: While controlling for age and sex, we found that participants exposed to the summer sun for more than 5 hours a day during their teens, in their 30s, and at the baseline examination were at a higher risk of developing increased retinal pigment (risk ratio [RR], 2.99; 95% confidence interval [CI], 1.18-7.60; P =.02) and early ARM (RR, 2.20; 95% CI, 1.02-4.73; P =.04) [corrected] by 10 years than those exposed less than 2 hours per day during the same periods. In participants reporting the highest summer sun exposure levels in their teens and 30s, the use of hats and sunglasses at least half the time during the same periods was associated with a decreased risk of developing soft indistinct drusen (RR, 0.55; 95% CI, 0.33-0.90; P =.02) and retinal pigment epithelial depigmentation (RR, 0.51; 95% CI, 0.29-0.91; P =.02). Participants who experienced more than 10 severe sunburns during their youth were more likely than those who experienced 1 or no burn to develop drusen with a 250-microm diameter or larger (RR, 2.52; 95% CI, 1.29-4.94 [corrected] P =.01) by the 10-year examination. No relationships were found between UV-B exposure, winter leisure time spent outdoors, skin sun sensitivity, or number of bad sunburns experienced by the time of the baseline examination and the 10-year incidence and progression of ARM or its associated lesions. CONCLUSIONS: Few significant relationships between environmental exposure to light and the 10-year incidence and progression of ARM were found in the Beaver Dam Eye Study. Consistent with results from the baseline and 5-year follow-up examinations, significant associations were found between extended exposure to the summer sun and the 10-year incidence of early ARM and increased retinal pigment. A protective effect of hat and sunglasses use by participants while in their teens and 30s against the 10-year incidence of soft indistinct drusen and retinal pigment epithelial depigmentation was also found, but only in those who reported the highest amount of sun exposure during the same periods.

Adult↗

PubMed2004

Computer-assisted measurement of retinal vessel diameters in the Beaver Dam Eye Study: methodology, correlation between eyes, and effect of refractive errors.

OBJECTIVE: Narrowed retinal arterioles may independently predict cardiovascular disease. We describe a computer-assisted method to measure retinal vessel diameters from digitized fundus photographs in a large population, and examine the correlation of retinal vessel diameters between eyes and whether refractive errors affect these measurements. DESIGN AND POPULATION: Population-based, cross-sectional study in Beaver Dam, Wisconsin (n = 4926; age, 43-84 years). METHODS: Retinal photographs were digitized, and all arterioles and venules located in an area 0.5 to 1 disc diameter from the optic disc were measured with the aid of computer software. MAIN OUTCOME MEASURES: Summary of retinal arteriolar and venular diameters, and the ratio of their diameters (arteriole:venule ratio [AVR]). RESULTS: Correlation between right and left eyes was substantial for retinal arteriolar diameters (Pearson correlation coefficient, rho = 0.71) and venular diameters (rho = 0.74), and moderate for the AVR (rho = 0.49). The inverse association of higher blood pressure and smaller retinal arteriolar diameters was similar using data from either one eye or two eyes; arteriolar diameters decreased by 4.1 microm (right eyes), 4.0 microm (left eyes), and 4.0 microm (mean of both eyes) with each 10-mmHg increase in mean arterial blood pressure. A myopic refraction was associated with smaller retinal vessel diameters; arteriolar diameters decreased by 2.8 microm and venular diameters by 3.3 microm with each -1.0-diopter shift towards myopia. However, the pattern and strength of the association of blood pressure and retinal vessel diameters were not altered by variations in refractive errors. CONCLUSIONS: There is good correlation of retinal vessel diameters between eyes. A myopic refraction is associated with smaller retinal vessel diameters. The association of retinal arteriolar diameters and blood pressure seems similar using data from either one eye or two eyes, and is minimally affected by refraction. These data suggest that measurement of retinal vessel diameters from one eye without regard to its refractive status may provide adequate information indicative of a person's retinal vessel caliber if information from two eyes and refraction is unavailable.

Adult↗

PubMed2004

Life-style correlates of tooth loss in an adult Midwestern population.

OBJECTIVES: To describe life-style correlates of tooth loss in a representative rural American population. METHODS: Information on tooth loss as well as past medical history and life-style factors was obtained in a well-defined cohort of 2,764 persons 53-96 years of age in Beaver Dam, WI (1998-2000). RESULTS: There were 1,992 (68.2%) persons missing some and 447 (15.3%) missing all of their teeth. In univariable analyses, age, cigarette smoking, heavy drinking, education, multivitamin use, and diabetes status were associated with tooth loss. Tooth loss was associated with poorer self-rated health and with difficulty eating solid food and inability to enjoy some food. In multivariable models age, education, smoking, heavy drinking, and diabetes were significantly associated with tooth loss. CONCLUSIONS: Tooth loss is common in older persons and is associated with many risk factors including education, smoking, and heavy drinking. It is possible that modifying these may influence risk of tooth loss.

Adult↗

PubMed2004

Location of lesions associated with age-related maculopathy over a 10-year period: the Beaver Dam Eye Study.

PURPOSE: To describe cumulative incidence and changes in retinal lesions associated with age-related maculopathy (ARM) by location over a 10-year period and to examine the relation of location of those lesions to progression of ARM. METHODS: Persons ranging in age from 43 to 84 years and living in Beaver Dam, Wisconsin, at the time of a census (1987-1988) were examined two to three times over a 10-year period (n = 3684). Drusen area, size, and type; retinal pigment epithelium depigmentation; increased pigment; geographic atrophy; and neovascular macular degeneration were determined in each of nine macular subfields: central, inner and outer superior, inner and outer nasal, inner and outer inferior, and inner and outer temporal by grading of stereoscopic color fundus photographs. Late ARM was defined as presence of either geographic atrophy or neovascular ARM. RESULTS: Lesions were more likely to change or develop in specific locations. Drusen area increased most in the central circle. Compared with other quadrants, drusen greater than 125 micro m in diameter and soft indistinct or reticular drusen were most likely to develop in the superior or temporal quadrants, whereas pigmentary abnormalities were most likely to occur in the nasal or superior quadrants. In general, large drusen, soft indistinct drusen, and pigmentary abnormalities were more likely to develop in the inner circle versus the central and outer circles. The quadrant location of early ARM lesions in 72 persons in whom late ARM developed was generally similar to that in persons who did not have late ARM. However, persons who had geographic atrophy were more likely to have large drusen in the inner circle than in the outer circle, while those who did not have late ARM were more likely to have large drusen in the outer circle. CONCLUSIONS: Lesions associated with early ARM were more likely to develop in specific locations in the macular area, and persons with lesions closer to the fovea may be related to a higher risk of development of late ARM. The quadrant location of early ARM lesions does not appear to add additional information to the risk of development of late ARM.

Adult↗

PubMed2004

Familial aggregation of retinal vessel caliber in the beaver dam eye study.

PURPOSE: To describe familial correlations of retinal vessel measurements. METHODS: A standardized examination and interview was administered to a population-based cohort of adults aged 43-86 years. Blood pressure was measured, and family relationships, current smoking status, and photographs of the retina were obtained. Computer-assisted grading was done to determine central retinal arteriole (CRAE) and venule equivalents (CRVE), and the arteriole-to-venule ratio (AVR) was computed. Familial correlations were calculated using FCOR in the SAGE software package. Analysis was done on the right eye measures for 871 sibling, 341 parent-child, 1362 cousin, 554 avuncular, and 887 spousal pairs. RESULTS: After adjustment for age, gender, mean arterial blood pressure, and current smoking status, the correlations (and 95% confidence interval) between siblings for the CRVE, CRAE, and AVR were 0.23 (0.16, 0.31), 0.20 (0.12, 0.28) and 0.13 (0.05, 0.20), respectively. Parent-child correlations were very similar, and the avuncular correlations were about half as great. The cousin correlations were about half the avuncular correlations. Spousal correlations of 0.03, 0.04, and 0.01 for CRVE, CRAE, and AVR, respectively, were not significantly different from 0. CONCLUSIONS: Retinal vessel equivalents were more highly correlated between relatives than between unrelated individuals. The relative magnitudes of these correlations were likely the result of shared genes. Because the vessel measurements have been shown to be predictive of cardiovascular and other systemic diseases, understanding the determinants of these familial relationships could have important health benefits.

Adult↗

PubMed2003

Revised formulas for summarizing retinal vessel diameters.

Background/Purpose. Recent findings suggest that an objective assessment of retinal vessel caliber from fundus photographs provide information about the association of microvascular characteristics with macrovascular disease. Current methods used to quantify retinal vessel caliber, introduced by Parr(1,2) and Hubbard,(3) are not independent of scale and are affected by the number of vessels. To improve upon these methods we introduce revised formulas for quantifying vessel caliber. Methods. Revised formulas were estimated using retinal vessel measurements from 44 young adults free of hypertension and diabetes. Comparisons between the two methods were done using digitized photographs from 4926 participants at the baseline examination of the Beaver Dam Eye Study (BDES), an ongoing population-based cohort study initiated in 1987. Individual arterioles and venules were measured using semi-automated computer software from which summary measures were calculated. Results. Correlation coefficients between the Parr-Hubbard and revised formulas were high (Pearson correlation coefficients ranging from 0.94 to 0.98). Both arteriolar and venular caliber significantly increased with an increasing number of vessels measured using the Parr-Hubbard formulas (p < 0.001), which in turn affected the relationship to mean arterial blood pressure. To the contrary, the revised formulas were not affected by the number of measured vessels (p > 0.50). Conclusions. We describe revised formulas for summarizing retinal vessel diameters measured from fundus photographs to be used in future studies and analyses. The revised formulas correlate highly with the previously used Parr-Hubbard formulas, but offer the advantages of being more robust against variability in the number of vessels observed, being independent of image scale, and being easier to implement.

Adult↗

PubMed2003

Relationship of measures of frailty to visual function: the Beaver Dam Eye Study.

PURPOSE: To investigate the association of standard measures of frailty to visual acuity and contrast sensitivity. METHODS: Time to walk a measured course, handgrip strength, peak expiratory flow rate, ability to stand from a sitting position without using arms, best-corrected visual acuity, and contrast sensitivity were assessed at the third examination (1998-2000) of the Beaver Dam Eye Study. The study is population-based with the initial census in 1988-1990. RESULTS: All measures of frailty and vision were significantly associated with age (poorer function at older ages). In general, women had poorer function than men in each age category. An "index of frailty" consisting of highest quartile (slowest) gait time, lowest quartile of peak expiratory flow rate, lowest quartile of handgrip strength, and inability to stand from sitting in one try (for those not in a wheelchair) was constructed for women and men. A score of 0 was the minimum amount of frailty, while a score of 4 indicated the maximum amount. Controlling for age, those with no evidence of frailty (score = 0) were likely to have the best visual acuity and best contrast sensitivity, while those with maximum evidence of frailty (score = 4) were likely to have poorest visual acuity and contrast sensitivity. CONCLUSION: Greater frailty was associated with poorer visual functions. Including a measure of visual function when assessing frailty may improve upon the usefulness of an index of frailty in predicting incidence of chronic systemic diseases and survival.

Adult↗

PubMedDate not supplied

Medical records as sources of data on cardiovascular disease events in persons with diabetes.

PURPOSE: The aim of this study is to evaluate medical records as a source of data on cardiovascular disease over a 20-year interval. METHODS: Participants in a population-based cohort of persons with Type 1 diabetes were asked whether they had been told by a doctor that they had several specific cardiovascular events. In addition, they were asked when and where they were hospitalized for myocardial infarction, stroke, surgical procedures, and for other conditions and procedures. The medical care institution was contacted to obtain copies of the relevant hospitalization. RESULTS: Overall, the confirmation of the self-reported events was 86.0% when medical records were obtained. Percent confirmed varied with the diagnosis. Reports of poor circulation in the lower extremities were confirmed in 42.6%, stroke was confirmed in 70%, and coronary bypass surgery was confirmed in 100% of cases. The success of obtaining medical records was greater for those events that were reported to have occurred more recently than those reported further in the past, especially when 10 or more years had elapsed. CONCLUSION: Medical record confirmation of reported cardiovascular events in persons with Type 1 diabetes was high for some events when medical records could be obtained but was lower for "poor circulation" to the legs and stroke possibly related to the lack of specificity of our questions, to incorrect attribution of symptoms by the respondent, or to inaccurate recall of a physician's examination. Medical record confirmation was better for more recent than past events. Therefore, when hard copy documentation is needed, it should be sought within 10 years of the event.

Cardiovascular Diseases↗