Spectral analysis of heart period and pulse transit time derived from electrocardiogram and photoplethysmogram in sepsis patients

Sepsis is a potentially lethal condition, and is one of the major causes of death in non-coronary intensive care units. Sepsis syndrome progresses through a number of increasingly severe stages, from systemic inflammatory response syndrome (SIRS) through sepsis, severe sepsis and septic shock. Each stage of sepsis is potentially characterized by differing autonomic nervous system responses. Spectral analysis of cardiovascular variability has been regarded as a possible non-invasive method to study this autonomic regulation, and in this study, the variabilities of heart period (RRi) and pulse transit time (PTT) derived from electrocardiogram and photoplethys-mogram were investigated in three different groups: normal subjects (n = 3D 11), SIRS (n = 3D 7) and severe sepsis patients (n = 3D 16), by computing spectral and cross-spectral measures in the low-frequency (LF) and the high-frequency (HF) ranges. SIRS and severe sepsis patients were found to have lower RRi (p < 0.01), augmented LF power in PTT (p < 0.01) and a lower RRi-PTT ratio (alpha_PTT) in the LF and HF bands (p < 0.01) as compared with the normal subjects, which might indicate a suppression of baroreflex-mediated autonomic control of heart rate and an increased sympathetic influence on ventricular contractility in sepsis. The results have highlighted the potential value of spectral analysis of RRi and PTT variabilities as a non-invasive tool for clinical evaluation of cardiac autonomic regulation in sepsis patients.