Spectral analysis of heart rate variability and respiration during sleep in cocaine-exposed neonates

This study's objective was to examine the autonomic control of heart rate and respiration during the neonatal period in human infants with prenatal exposure to cocaine. Four-hour daytime recordings of the electrocardiogram (ECG) were obtained from 15 cocaine-exposed and 13 non-exposed full-term neonates at 2 weeks of age during quiet sleep (QS) and active sleep (AS). For each 1-min epoch of sleep, the power spectrum of the R-R intervals was computed from the ECG to obtain the total power (0-2 Hz), and spectral power in the high-frequency (HFP, 0.3-2 Hz), mid-frequency (MFP, 0.1-0.2 Hz), and low-frequency (LFP, 0.03-0.1 Hz) bands. Respiration was also monitored and processed using similar spectral analysis procedures. Cocaine-exposed neonates showed enhanced heart rate variability reflected by an increase in spectral power across all frequency bands. Spectral power in LFP and MFP was higher in cocaine-exposed neonates during both sleep states, but only in HFP during QS. There were no respiratory patterning differences between the groups to account for these findings. The index of sympathovagal balance (LFP + MFP)/HFP, showed no differences between the groups. We conclude that infants exposed to cocaine in utero show differences in the modulation of heart rate reflecting an increase in both vagal and sympathetic influences.

Cardiac and respiratory patterns during sleep in cocaine-exposed neonates

Four-hour recordings of heart rate and respiration during spontaneous sleep and wakefulness were obtained from 17 cocaine-exposed and 14 control infants at 2 weeks of age. The median values for heart and respiratory rate and variability were determined for each 1-min epoch of quiet and active sleep. Overall mean rates and variabilities were determined for each state. The cocaine-exposed infants showed significantly greater sleep state effects on heart rate relative to the control infants. Recency of cocaine exposure was not a factor in the differences; even those cocaine-exposed infants who tested negative for the drug perinatally differed significantly from those who had never been exposed. Heart rate variability was increased in cocaine-exposed infants relative to controls in both sleep states. Respiratory rate and variability were not significantly different in the cocaine-exposed and control infants. These results suggest differences in cardiovascular control in infants of cocaine-abusing mothers compared to infants without cocaine exposure. The mechanism responsible for these differences is unclear and may reflect cocaine-induced changes in the autonomic physiology of developing infants or some indirect effect of maternal cocaine use.

Elevated plasma norepinephrine levels in infants of substance-abusing mothers

Infants of substance-abusing mothers (ISAM) have significant growth and neurodevelopmental abnormalities. The origin of these abnormalities is unknown. We postulated that ISAM have increased sympathetic nervous system tone and altered catecholamine levels. Therefore, we measured plasma norepinephrine, epinephrine, and dopamine levels and the number and receptor affinity of beta-adrenoreceptor binding sites on lymphocytes and alpha-adrenoreceptor binding sites on thrombocytes in 22 otherwise healthy ISAM (age, 2.1 +/- 0.5 months; mean +/- SD) and 15 healthy controls (age, 2.5 +/- 0.8 months). Norepinephrine levels in venous blood were 1.8-fold higher in ISAM than in control infants (6.30 +/- 3.85 nmol/L vs 3.55 +/- 2.45 nmol/L). There were no differences in plasma epinephrine or dopamine levels. There were no differences in the number of binding sites or receptor affinity for beta- and alpha-adrenoreceptors. We conclude that ISAM have elevated circulating norepinephrine levels compared with controls. We speculate that this is associated with increased sympathetic nervous system tone in ISAM and that the absence of adrenoreceptor down-regulation may create catecholamine suprasensitivity.