Inappropriate sympathetic activation at onset of septic shock - A spectral analysis approach

The autonomic cardiovascular control was investigated in 10 patients with septic shock, 10 patients with sepsis syndrome, and six tilted healthy subjects. 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 recordings. LFHR/HFHR and the square root of LFSBP/LFHR (alpha) were used as indices of sympathovagal interaction and baroreflex control of the heart, respectively. Compared with tilted control subjects and patients with sepsis syndrome, 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 = 0.0002); (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 levels (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 high concentrations of circulating catecholamines but impaired sympathetic modulation on heart and vessels, suggesting that central autonomic regulatory impairment contributes to circulatory failure.