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; 0.4-1.5Hz) 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 < 0.01) and unchanged SBP.For R-R interval series, the total spectral power decreased 6-fold (p < 0.01), which was predominantly due to a reduction in the LF band (16-fold; p < 0.01).In contrast, we observed a significant increase (25%; p < 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 < 0.01) after atropine.The LF phase relationship (BP leads R-R interval fluctuations by ～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.
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