The relationship of prenatal nicotine exposure and newborn heart rate: Is there a basis for Sudden Infant Death?
Sherman, Jan Wheeler
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Prenatal exposure to cigarette smoke increases the risk of Sudden Infant Death Syndrome (SIDS) by 2 to 4 fold. Although the etiology for this increased risk of SIDS is unknown, nicotine has been shown to cause adverse cardiovascular effects in animal models and adults. This study proposed a relationship between prenatal nicotine exposure and newborn heart rate during the immediate postnatal period of transition. Physiologically, transition is a time of cardiovascular adaptation for the newborn infant. Measuring the newborn heart rate during transition would allow the assessment of fetal drug exposure under the challenging, rather than basal, conditions associated with birth. A total of 130 mother/infant couplets participated in this descriptive, correlational study. Placental cord blood was drawn at the time of delivery and analyzed for cotinine. Cotinine is the primary metabolite of nicotine and is considered to be the best available biomarker to quantify nicotine exposure. The heart rate of the newborn infants was measured every one minute during the immediate postnatal period of transition, the first four hours of life. Statistical analysis, using the Pearson Correlation to test the hypotheses, found statistically significant negative relationships between venous cord blood cotinine levels, maximum heart rate (r = −.271, p = .002), and variance of the heart rate (r = −.206, p = .0 19). The coefficient of determination ascertained that 7% of the heterogeneity in the maximum heart rate and 4% of the heterogeneity of the variance in the heart rate were a result of the linear relationship with the cord blood cotinine. The findings of this study suggest that newborn infants with higher venous cord blood cotinine levels have a limited ability to maximize and vary their heart rate. Cardiac output in the infant is primarily dependent on heart rate. If the infant is unable to maximize cardiac output during times of stress, the infant is at an increased risk for morbidity and possible mortality.