Inappropriate sympathetic activation at onset of septic shock - A spectralanalysis approach

The autonomic cardiovascular control was investigated in 10 patients with s eptic shock, 10 patients with sepsis syndrome, and six tilted healthy subje cts. Overall variability, high- and low-frequency components (AUC, HF, and LF, beats/min(2)/Hz or mm Hg-2/Hz) from heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressures spectra were obtained from 5-min recording s. LFHR/HFHR and the square root of LFSBP/LFHR (alpha) were used as indices of sympathovagal interaction and baroreflex control of the heart, respecti vely. Compared with tilted control subjects and patients with sepsis syndro me, septic shock is characterized by reduction in: (1) HR variability, i.e. , decreased AUC(HR) (p = 0.007), LFHR (p = 0.002), and LFHR/HFHR (p = 0.000 2); (2) DBP variability, i.e., decreased AUC(DBP) (p = 0.003) and LFDBP (p = 0.001), (3) or (p = 0.003). In septic shock, LFHR/HFHR, alpha, and LFDBP correlated with mean blood pressure (r = 0.67, p = 0.04, r = 0.64, p = 0.03 , and r = 0.88, p = 0.0008, respectively), and with plasma norepinephrine l evels (r = -0.65, p = 0.03, r = -0.79, p = 0.006, and r = -0.69, p = 0.03, respectively). In conclusion, onset of septic shock is characterized by hig h concentrations of circulating catecholamines but impaired sympathetic mod ulation on heart and vessels, suggesting that central autonomic regulatory impairment contributes to circulatory failure.