Biobehavioral pain responses in former extremely low birth weight infants at four months' corrected age.

OBJECTIVE: To compare biobehavioral responses to acute pain at 4 months' corrected age between former extremely low birth weight (ELBW) infants and term-born controls. METHODOLOGY: Measures of facial behavioral and cardiac autonomic reactivity in 21 former ELBW infants (mean birth weight = 763 g) were compared with term-born infants (n = 24) during baseline, lance, and recovery periods of a finger-lance blood collection. Further, painful procedures experienced during neonatal care were quantified in both groups. RESULTS: Overall, behavioral and cardiac autonomic responses to the lance were similar between groups. However, the ELBW group seemed to have a less intense parasympathetic withdrawal in the lance period and a more sustained sympathetic response during recovery than the control group. Further, in the recovery period, two behavioral patterns (early recovery and a late recovery) were apparent among the ELBW group. CONCLUSIONS: Biobehavioral pain responses were similar overall between both groups of infants. Subtle differences were observed in cardiac autonomic responses during the lance period and in behavioral recovery among ELBW infants. Whether these findings represent a long-term effect of early pain experience or a developmental lag in pain response remains unclear. The lack of an overall difference runs counter to previously reported findings of reduced behavioral response in former ELBW infants. biobehavioral pain response, premature infants, repetitive pain, heart rate variability.

The developmental character of cardiac autonomic responses to an acute noxious event in 4- and 8-month-old healthy infants.

Heart rate (HR) has been widely studied as a measure of an individual's response to painful stimuli. It remains unclear whether changes in mean HR or the variability of HR are specifically related to the noxious stimulus (i.e. pain). Neither is it well understood how such changes reflect underlying neurologic control mechanisms that produce these responses, or how these mechanisms change during the first year of life. To study the changes in cardiac autonomic modulation that occur with acute pain and with age during early infancy, the relationship between respiratory activity and short-term variations of HR (i.e. respiratory sinus arrhythmia) was quantified in a longitudinal study of term born healthy infants who underwent a finger lance blood collection at 4 months of age (n = 24) and again at 8 months of age (n = 20). Quantitative respiratory activity and HR were obtained during baseline, lance, and recovery periods. Time and frequency domain analyses from 2.2-min epochs of data yielded mean values, spectral measures of low (0.04-0.15 Hz) and high (0.15-0.80 Hz) frequency power (LF and HF), and the LF/HF ratio. To determine sympathetic and parasympathetic cardiac activity, the transfer relation between respiration and HR was used. At both 4 and 8 months, mean HR increased significantly with the noxious event (p > 0.01). There were age-related differences in the pattern of LF, HF, and LF/HF ratio changes. Although these parameters all decreased (p > 0.01) at 4 months, LF and LF/HF increased at 8 months and at 8 months HF remained stable in response to the noxious stimulus. Transfer gain changes with the lance demonstrated a change from predominant vagal baseline to a sympathetic condition at both ages. The primary finding of this study is that a response to an acute noxious stimulus appears to produce an increase in respiratory-related sympathetic HR control and a significant decrease in respiratory-related parasympathetic control at both 4 and 8 months. Furthermore, with increasing age, the sympathetic and parasympathetic changes appear to be less intense, but more sustained.