Characterization of the neonatal heart rate baroreflex during and after ECMO.

Prolonged continuous blood pressure (BP) and heart rate (HR) recordings from neonates of 35 to 42 weeks gestation were studied during and after ECMO. Data segments with significant deviation of BP were extracted for further analysis. The simultaneous changes in BP and HR were compared and the slope of the regression determined baroreflex sensitivity (BRS). Of 464 BP deviations, 98% produced curves with a negative slope consistent with the presence of a baroreflex. The average BRS was -1.0 +/- 0.8 bpm/mmHg (mean +/- S.D.) and curves were steeper during rising BP than falling BP (-1.1 +/- 0.9 beats/min per mmHg versus -0.9 +/- 0.6, P = 0.001). The baroreflex was more sensitive during ECMO than after ECMO to both rising BP (-1.0 +/- 0.5 beats/min per mmHg versus -0.7 +/- 0.5, P = 0.004) and falling BP (-1.0 +/- 0.6 beats/min/mmHg versus -0.7 +/- 0.5, P = 0.04). HR response curves obtained during different BP fluctuations on the same recording had varying threshold, consistent with acute resetting. One infant demonstrated chronic baroreceptor resetting over 3 days to a rise in resting BP. The near-term, critically ill neonate has an active baroreflex which is capable of resetting. ECMO was associated with accentuation of the baroreflex response.