Endotoxin Effects on Markers of Autonomic Nervous System Function in the Piglet: Implications for SIDS

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Abstract
The hypothesis was tested in 30 newborn piglets that the effects of a low dose of endotoxin (1 µg i.v. bolus; Salmonella abortus equi) would impair autonomic nervous system function. Two tests of autonomic function were performed following external warming (pre-endotoxin) and during endotoxin-generated thermogenesis: (1) analysis of heart rate variability in the time and frequency domains and (2) baroreflex sensitivity measured following intravenous injection of the vasoactive drugs nitroprusside and phenylephrine. Beat-to-beat heart rate variability (SDΔRR) fell by 2.2 ms from 7.0 ms before fever (p < 0.05). Low-frequency spectral power fell by 2.4 ms2 from 4.1 ms2 before fever (p < 0.05). The sensitivity of the baroreflex to changes in blood pressure induced by the vasoactive drugs decreased during fever by 0.72 ms/mm Hg for the nitroprusside test (p < 0.0005) and by 0.31 ms/mm Hg for the phenylephrine test (p < 0.005). These results indicate that in the piglet the balance of autonomic tone is altered and autonomic responsiveness reduced during the thermogenic phase of a fever. These findings are consistent with known risk factors for sudden infant death syndrome.