The first chapter of this thesis consists in a critical review of the literature on cardiac and cardiac-related autonomic activity, and infant development. Empirical findings are presented on mechanisms of interaction between heart rate and the autonomic nervous system; their relationship with infant development; their genetic and environmental influences; their gender effects; and related quantification issues. / This is followed by a study of 322 5-month-old twin pairs that investigated the genetic and environmental influences on sleeping heart rate and cardiac-related autonomic activity, as indexed by spectral analysis of heart rate variability and response to postural change. The postural change elicited only minor changes in cardiovascular activity, perhaps due to immaturity of the baroreflex. As a result, analyses focused on supine cardiovascular activity. Multivariate genetic modeling indicated that individual differences in sleeping HR and high frequency HR variability were determined by unique environmental and distinct additive genetic factors. These variables, along with low frequency HR variability, were also affected by overlapping familial environmental influences. Familial influences on individual differences in high frequency HR variability were more pronounced for baby girls than boys. Estimates of relative low and high frequency HR variability were determined by common (familial) and unique environmental factors; familial influences on these estimates of HR variability did not overlap with familial influences on sleeping HR. / A second study using the same twin sample is then presented. Its objectives were to investigate the indices of genetic and environmental etiology of individual differences in five month-old twins' HR reactivity and to evaluate the possible overlap, if any, between the familial influences on HR in states of sleep and reactivity. Multivariate genetic modeling showed that the total variance of individual differences was decomposed in the following manner: Sleeping and awake HR were under the influence of shared additive genetic factors; sleeping HR also shared common environmental influences with the absolute power spectrum values; and absolute high frequency power additionally had phenotype-specific additive genetic factors influencing its expression. Relative power spectrum values were under the influence of phenotype-specific common environmental factors. / Overall, these results suggest the presence of important familial (genetic and environmental) influences on heart rate and cardiac-related autonomic activity at five months of age: There is an absence of overlap of these (familial) additive genetic influences but the presence of a partial overlap of the (familial) environmental influences.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.82858 |
| Date | January 2002 |
| Creators | Dubreuil, Etienne |
| Contributors | Pihl, Robert O. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Psychology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001986358, proquestno: AAINQ88453, Theses scanned by UMI/ProQuest. |
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