Cardiovascular Autonomic Regulation in Preterm Infants: The Effect of Atropine

Abstract

To study cardiovascular autonomic control, we assessed the effect of atropine on heart rate (HR) and blood pressure (BP) variability in 12 preterm infants (range 26 -32 wk) before intubation for respiratory insufficiency. Spectral power analysis of R-R interval and systolic BP (SBP) series were estimated in a low-frequency (LF; 0.04 -0.15 Hz) and high-frequency (HF; 0.4 -1.5 Hz) band and evaluated for a 10-min period before and a 10-min period after atropine sulfate (0.01 mg/kg). Baroreceptor reflex (BR) functioning was estimated using transfer function analysis at LF (coherence, gain, and phase). Atropine resulted in a significant 12% increase in steady-state HR (p Ͻ 0.01) and unchanged SBP. For R-R interval series, the total spectral power decreased 6-fold (p Ͻ 0.01), which was predominantly due to a reduction in the LF band (16-fold; p Ͻ 0.01). In contrast, we observed a significant increase (25%; p Ͻ 0.05) in total spectral power of SBP series partly as a result of an increase in HF power. The LF power of SBP series was not altered. The median LF transfer gain (BR sensitivity) between SBP and R-R interval decreased from 4.2 to 1.4 ms/mm Hg (p Ͻ 0.01) after atropine. The LF phase relationship (BP leads R-R interval fluctuations bỹ 4 s) was not changed after atropine. In conclusion, even in preterm infants in distress, atropine modulates HR and BP variability, suggesting that BR-mediated parasympathetic control of heart rate is of significance for cardiovascular control at that age. The baroreceptor reflex (BR) is the most important regulatory mechanism in the short-term control of heart rate (HR) and blood pressure (BP). The BR buffers sudden changes in systemic BP by adapting HR and peripheral vascular resistance. These responses of HR and vascular resistance are mediated by the efferent parasympathetic and sympathetic limb of the BR. As both systems are involved, studies on the BR give information on autonomic cardiovascular regulation (1,2).Data about the ontogeny of the BR and functional maturation in the human infant are limited. This is partly caused by the limited experimental (pharmacologic or mechanical) possibilities to challenge the BR in neonates. Passive head-up tilt test has been applied to neonates to measure responses in BP, HR, and limb blood flow to body tilting. In preterm infants (26 -38 wk gestation), passive head-up tilt resulted in significant vasoconstriction of the lower limb with a slight fall in aortic BP and unchanged HR (3). The inadequate ability to maintain BP and the lack of tachycardia suggest that preterm infants lack the full integrated BR response as seen in adults. In term infants, however, a fall in systolic BP (SBP) was observed in conjunction with tachycardia and a fall in limb blood flow, suggesting the presence of active reflex vasoconstriction (4). In a recent study, BR maturation was studied longitudinally in preterm infants, using a beat-to-beat analysis of R-R interval series and noninvasively measured SBP (5). BR sensitivity (the R-R interval change in millisecon...

Premedication for Nonemergent Neonatal Intubations: A Randomized, Controlled Trial Comparing Atropine and Fentanyl to Atropine, Fentanyl, and Mivacurium

“…3,4,6,8,12,13 Previous studies have shown that these potentially adverse effects can be attenuated by using pharmacologic agents. Anticholinergic medication can attenuate the decrease in heart rate (HR), 3,[6][7][8]14 potent analgesics or anesthetic agents can attenuate the hypertensive response, 11 and muscle relaxants have been shown to attenuate the increase in ICP. 3,4,6,8,12 Studies have also shown that using premedication may decrease the time and number of attempts needed to successfully intubate.…”

Cardiovascular Consequences of Preterm Birth in the First Year of Life

“…Atropine increased heart rate without altering systolic blood pressure, decreased HRV, and the decrease in LF power was larger than the decrease in HF power. These findings suggest that although the higher heart rate of preterm infants indicate relatively low vagal tone, the response to provides evidence that that a significant amount of vagal tone is present shortly after birth (Andriessen et al, 2004a). A recent study which followed 31 low risk preterm infants born at 28 weeks PMA to 34 weeks PMA at weekly intervals found no significant changes in the total, HF or ratio of LF/HF HRV components in the group overall.…”

The role of physiological studies and apnoea monitoring in infants

“…[12] Preterm birth has been associated with immaturity of autonomic nervous system control of the cardiovascular system. This is manifest with higher heart rates [13,14], reduced heart rate variability [14][15][16], and decreased baroreflex sensitivity compared to infants born at term. [17,18] After birth at term, heart rate increases initially over the first month of life before declining gradually as a result of an increase in parasympathetic dominance of autonomic control of heart rate.…”