Objectives: To determine the genetic and environmental contributions to resting blood pressure, the level of blood pressure during the cold-pressor test and the increase in blood pressure with the cold-pressor test in an adult cohort of normotensive twins.
Design and methods: Ninety-one monozygotic and 41 dizygotic normal twin pairs were recruited by advertisement. The mean age was 34 +/- 14 years (mean +/- SD). Systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate were measured continuously at the finger (using a Finapres device) and verified at the upper arm oscillometrically (using a Dinamap device) every minute. The cold-pressor test was conducted by immersing the non-dominant hand into cold (< 4 degrees C) water for 2 min. Statistical analysis was performed by using the SPSS program; parameters of the quantitative genetic models were estimated by path-analysis techniques using the LISREL 8 program.
Results: Heritability estimates of additive genetic effects were statistically significant for SBP and DBP but not for heart rate during rest and during the cold-pressor test. Furthermore, the path analysis indicated shared as well as specific genetic components both for the blood pressure level at rest and for that during the cold-pressor test. However, the genetic influences on the blood pressure level at rest and on the increase in blood pressure during the cold-pressor test (the blood pressure level during the cold-pressor test minus that during rest) were entirely independent of one another.
Conclusions: A significant genetic covariation exists for SBP and DBP during rest and during the cold-pressor test, as well as a significant genetic variation that is specific to the cold-pressor stress condition. These findings suggest that different genes or sets of genes contribute to blood pressure regulation during rest and to blood pressure reactivity to cold-pressor stress.