Spectral analysis of blood pressure variability in atrial fibrillation: The effect of tilting

Aim of this study was to assess changes of blood pressure (BP) variability spectrum in response to a sympathetic stimulation during a tilt-up stress test. Thirty patients (21 males, 69 ±10 years) with AF were included in the study. Surface ECG and non-invasive beat-to-beat BP were recorded for 10 minutes at rest and during tilt (in 19 patients). The systolic and diastolic BP series were resampled at 1Hz using cubic spline interpolation and spectral analysis was performed using autoregressive (AR) models. The total power was decomposed into M contributions, one for each pole. The poles whose frequency was in the Low Frequency (LF, 0.03-0.15 Hz) or High Frequency (HF, 0.15-0.4 Hz) were selected. LF component power increased during tilt in both systolic and diastolic BP (rest vs. tilt: systolic BP: 6.5 ± 5.3 vs. 13.0 ± 13.4 p<;0.05; diastolic BP: 8.6 ± 4.5 vs. 10.9 ± 9.2 ns). HF component power also increased during tilt, and the HF peak was shifted towards lower frequency values during tilt. Thus, BP spectrum shows LF and HF components even in patient with AF and these components are influenced by a sympathetic stimulus, such as the one induced by a tilt-up stress test. This finding highlights the capability of the autonomic nervous system to modulate periodic LF and HF oscillations in BP variability even in presence of an irregular ventricular electrical and mechanical activity.