Muscatine Heart Study

BACKGROUND:

Longitudinal studies of coronary risk factors beginning in subjects at adult age have shown that hypertension, hypercholesterolemia, and obesity are related to the risk of coronary artery disease and stroke. The Framingham Study has shown, in adults over 30 years of age, a positive association between risk of cardiovascular disease and low density lipoprotein cholesterol, elevated systolic blood pressure and diabetes, and a negative association with high density lipoprotein cholesterol.

In 1971 when the Muscatine Heart Study was initiated, there was preliminary evidence that these processes began in childhood. It was noted that children's lipids, blood pressures, and body size maintained a degree of rank order over time, suggesting that those with high levels were likely to become adults with high levels. Whether elevated levels in children of the accepted adult coronary risk factors were predictive of future cardiovascular disease morbidity and mortality remained an important unanswered question.

No data were available which directly linked overt cardiovascular disease to childhood measures of risk factors. The Muscatine study followed children from their school age years into middle age. This study, for the first time, directly related multiple observations of levels and profiles of change in coronary risk factors during childhood to levels of these risk factors measured at ages when the levels had established predictive significance for the development of premature atherosclerotic heart disease.

The Muscatine Heart Study was funded over the years by a Specialized Center of Research (SCOR) in Arteriosclerosis. The SCOR program was initiated by the NHLBI to expedite the development and application of new knowledge essential for improved diagnosis, treatment, and prevention of arteriosclerosis, ischemic heart disease, hypertension, pulmonary disease, and thrombosis. The Muscatine Heart Study was also funded by R01HL35600.

Several substudies were conducted using the Muscatine study population. The subproject on left ventricular mass in childhood was designed to determine the age/sex distribution of left ventricular mass in children 5-14 years of age and whether elevated left ventricular mass, as demonstrated by echocardiography, could be related to higher ambulatory blood pressure, exercise blood pressure and work capacity, or physical conditioning. The study also determined whether there was a familial aggregation of left ventricular mass, whether it was associated with high blood pressure in parents and whether left ventricular mass in children was associated with increased cardiovascular and all causes mortality in first and second degree relatives.

Two subprojects were conducted on the determinants of blood pressure during childhood. Both investigated factors related to blood pressure in groups of children whose blood pressure patterns had been documented over a period of four to 10 years. Five groups of children were identified for study: a group with persistently high pressure; a group with rising blood pressure; a group with decreasing pressure; a group with persistently low pressure; and a group with labile high blood pressure.

The first subproject studied cardiac output, systemic vascular resistance, echocardiographic dimensions, responses to exercise and to mental stress in these groups of children. The purpose of this study was to define whether there were significant differences in blood pressure control during rest, exercise and mental stress in these groups and to determine whether differences in left ventricular wall mass resulted in these groups. The second subproject studied blood pressure control mechanisms in a free-living sample of these five groups while they consumed usual, high and low salt diets. Measurements were made of baroreflex control, structural component of vascular resistance, and response to mental stress. The purpose of this study was to define whether salt sensitivity existed in school children and how it expressed itself on blood pressure control mechanisms.

Studies were also conducted on apolipoproteins in childhood to determine their role as a risk factor and apolipoprotein A-I and A-II gene polymorphisms and their associations with alterations in high density lipoprotein levels and risk of coronary artery disease.

DESIGN NARRATIVE:

The design was both cross-sectional and longitudinal. Between 1971 and 1986, over 13,000 school age children from 5 to 18 years of age were screened for coronary risk factors. Measurements were made of serum cholesterol, serum triglycerides, blood pressure, height, weight, and skinfold thickness. Beginning in 1980 the graduates of the Muscatine schools who had participated in earlier screens were recruited at ages 23, 28, 33, and 38 years to have their risk factors re-assessed. The oldest graduates were 38 years of age by 1991. The total number of adults was 5,126.

The study completion date listed in this record was obtained from the "End Date" entered in the Protocol Registration and Results System (PRS) record.