Noninvasive assessment of autonomic function in human neonates born at the extremes of fetal growth spectrum

Abstract

Birth weight is associated with adult cardiovascular disease, such that those at both ends of the spectrum are at increased risk. This may be driven in part by modification to autonomic control, a mechanistic contributor to hypertension. However, birth weight is a relatively crude surrogate of fetal growth; and newborn body composition may more accurately identify the "at risk" infant. Accordingly, we sought to determine whether newborns with high or low body fat have altered autonomic control of vasomotor function and cardiac contractility. Body fat was assessed by air-displacement plethysmography <24 h postnatal. Measures of spontaneous baroreflex sensitivity (sBRS), blood pressure variability (BPV), and dP/dt_max variability were compared between newborns categorized according to established body fat percentiles: high body fat (HBF, >90th percentile, n = 7), low body fat (LBF, ≤10th percentile, n = 12), and normal body fat (control, >25th to ≤75th percentile, n = 23). BPV was similar across body fat percentiles; similarly, low frequency dP/dt_max variability was similar across body fat percentiles. sBRS was reduced in HBF compared to controls (11.0 ± 6.0 vs. 20.1 ± 9.4 msec/mmHg, P = 0.03), but LBF did not differ (18.4 ± 6.0 msec/mmHg, P = 0.80). Across the entire body fat spectrum (n = 62), there was a nonlinear association between newborn body fat and sBRS (P = 0.03) that was independent of birth weight (P = 0.04). Autonomic modulation of vasomotor function and cardiac contractility in the newborn did not differ by body fat, but newborns born with high body fat show depressed baroreflex sensitivity.

Keywords: Autonomic function; hypertension; in utero growth; newborn body fat.

Figure 1

Example of blood pressure waveform (A) recorded in a control newborn using the Finapres and (B) dP/dt and (C) dP/dt _max derived from the BP waveform. The dP/dt waveform was generated by applying the slope function to the blood pressure waveform in Spike2. dP/dt _max coincides with the maximum upstroke of the blood pressure waveform during systole.

Figure 2

Estimated power spectral density obtained from a 60‐sec period of dP/dt _max. The y‐axis represents dP/dt _max variability in mmHg²/sec²/Hz and the x‐axis represents frequency in Hz. The bin size was 0.04 Hz. The vertical lines denote the ranges for the very low‐frequency band (<0.04 Hz), the low‐frequency band (0.04–0.16 Hz), the high‐frequency band (0.16–1.1 Hz). Total power is the sum of the area under the curve between 0 and 1.1 Hz.