Blood pressure in prospective population based cohort of newborn and infant twins.

OBJECTIVE: To describe blood pressure in twins during infancy. DESIGN: Prospective study of cohort of twins. SETTING: Teaching hospital in Florida. SUBJECTS: 166 viable twin pairs born between July 1976 and December 1989. MAIN OUTCOME MEASURES: Blood pressure and body weight at birth, at 14 days, and at 1, 3, 6, 9, and 12 months. RESULTS: Both systolic and diastolic pressure correlated with body weight throughout infancy (at birth r = 0.41, P < 0.001 and r = 0.42, P < 0.001 respectively; at 1 year r = 0.23, P < 0.001 and r = 0.26, P < 0.001 respectively). In infants weighing < 1500 g at birth mean blood pressure rose from about 45/25 mm Hg to 101/55 mm Hg from birth to the age of 1 year, while in infants weighing > 3000 g at birth it rose from 63/39 mm Hg to 100/61 mm Hg; corresponding mean body weights at 1 year were 7.86 kg and 9.88 kg. Differences in birth weight within pairs of monozygotic twins were negatively correlated with such differences in systolic blood pressure at 1 year (r = -0.37, P < 0.01). CONCLUSIONS: Blood pressure and body weights in twins showed strongly positive but generally declining correlations throughout infancy. Twins of lower birth weight showed a more rapid rate of rise in blood pressure during infancy. At 1 year the catch up in blood pressure exceeded that in body weight. Greater differences in birth weights between monozygotic twins were associated with smaller differences in systolic blood pressure at 1 year, suggesting that intrauterine environmental factors related to birth weight are important in determining blood pressure in infancy.

Genetic variance of weight and length in infant twins.

A population-based cohort of 166 twin pairs (67 monozygotic and 99 dizygotic) born at the Jackson Memorial Hospital/University of Miami Medical Center, from July 1, 1976 to December 31, 1980 was identified. Body weight and length were measured at 14 days and at one, three, six, nine, and 12 months of age. Statistically significant genetic variance was found for both body weight and length at each data point. Heritability for body weight increased from 0.28 at 14 days to 0.64 at one year. Corresponding values for body length were 0.16 and 0.48.

Genetic variance of blood pressure levels in infant twins.

A cohort of 166 twin pairs (67 monozygotic and 99 dizygotic) born at the Jackson Memorial Hospital/University of Miami Medical Center between July 1, 1976 and December 31, 1980, was followed from birth to one year of age in order to estimate the genetic variance of blood pressure during the first year of life. The sex-adjusted summary estimate of heritability for systolic blood pressure during all of infancy was 0.22 (p less than 0.001), but statistically significant genetic variance was not found for diastolic blood pressure. When using blood pressures from six to 12 months of age, adjusted for infant sex, heritability was estimated as 0.33 (p less than 0.001) for systolic blood pressure and 0.24 (p = 0.04) for diastolic blood pressure; adjustment for body weight reduced these estimates to 0.27 (p less than 0.001) and 0.17 (p = 0.13), respectively.

Cardiovascular risk factors among children of men with premature myocardial infarction.

The possible association between fasting glucose, cholesterol, triglyceride, blood pressure, and body weight in children and the early occurrence of paternal myocardial infarction (MI) was explored by examination of 91 children of 38 fathers who had experienced MI before they were 50 years old and 86 children of 39 healthy father. The only variables significantly associated with paternal MI were childhood cholesterol (P = .003) and glucose (P = .006). The results are consistent with the hypothesis that elevated childhood cholesterol levels offer a mechanism whereby family history predicts future risk of coronary heart disease.

Retirement and coronary mortality.

Information on several variables, including occupational history and various coronary risk factors, was collected from the wives of 568 married men who died of coronary heart-disease (CHD) and an equal number of matched control subjects. The crude matched-pair relative risk of fatal CHD among men who retired compared with non-retirees was 2.9 (95% confidence limits from 1.9 to 4.9). After adjustment for age and history of hospitalisation for myocardial infarction by means of a paired multiple-logistic regression analysis the relative risk was reduced to 1.8 (range 1.0 to 3.3). These data suggest that retirement and subsequent coronary mortality may be linked.

Effect of Position on Blood Pressure in Infants.

In order to estimate the effect of position on blood pressure measurements during the first year of life, pressures were recorded for 71 infants at one, three, six and twelve months of age in both the propped and lying positions. The position of the infant appeared to have little effect on mean values or upon the correlation of measurements over time. These results favor the use of a position for blood pressure measurement during infancy which places primary importance upon the comfort of the child.

A longitudinal evaluation of blood pressure in children.

Blood pressure levels obtained on two occasions, one year apart, were evaluated among 212 children. An overall correlation of .65 was obtained for systolic pressure and .43 for diastolic pressure. The results suggest that adult levels of correlation are not reached in childhood and that screening programs must consider the relative lability of children's measurements in establishing referral criteria.

Cigarette consumption and deaths from coronary heart-disease.

There is a positive association between cigarette smoking and coronary heart-disease (C.H.D.). In non-fatal myocardial infarction a dose-response relation persists even after the effects of additional variables have been controlled for. The relation between cigarette consumption and deaths from C.H.D. was investigated in a matched-pair case/control study. The overall simple matched-pair risk ratio (R.R.) between current smokers and non-smokers was 1.9 (95% confidence limits 1.5-2.4). For smokers of fewer than 20 cigarettes per day, the R.R. was 1.2; at a level of 21-40 cigarettes per day, the R.R. was 2.3; and for smokers of 41+ cigarettes per day, the R.R. was 4.0. A similar relation was found after adjustment for additional variables. These results suggest that the heaviest smokers could halve their risk of death from C.H.D. by reducing their tobacco consumption to an intermediate level; and that benefit of a similar order would be experienced by smokers of 21-40 cigarettes per day who cut down to less than one pack (20 cigarettes) daily.