Uncoupling and recoupling of autonomic regulation of the heart beat in pediatric septic shock

Healthy physiological systems exhibit marked signal variability and complex ity, whereas diseased systems generally show a loss of variability, decreas ed complexity ("decomplexification"), and increased regularity. The goal of this study was to evaluate the uncoupling and recoupling phenomenon in chi ldren with septic shock by observing serial changes in heart rate variabili ty metrics. Data were collected from 7 children with septic shock by using the computer system in the Complex Systems Laboratory at Oregon Health Scie nces University. Heart rate time series were constructed and analyzed by us ing the Hales Research System at intervals of 6 h during pediatric intensiv e care unit (PICU) hospitalization. These power spectral values were then p lotted vs. time. Six of seven patients showed an increase over time in low- frequency heart rate power and the low-/high-frequency ratio, whereas high- frequency heart rate power decreased. We also compared the change in mean h eart rate, heart rate standard deviation, and power spectral values during the first 24 h of PICU hospitalization vs. the remainder of the PICU stay ( for the 5 patients with a PICU length of stay > 48 h). Compared to the init ial 24 h in the PICU, low-frequency power and the low-/high-frequency ratio increased, whereas high-frequency power decreased over the course of the i llness. This report shows the potential value of monitoring the uncoupling and recoupling phenomenon in patients with septic shock. Our results are in agreement with other investigators who report evidence of decomplexificati on both in experimental models of sepsis and in clinical studies and provid e direction for further work.