Effect of Head-Up/-Down Tilt on ECG Segments and Myocardial Temporal Dispersion in Healthy Subjects

Simple Summary The autonomic nervous system (ANS) modulates the oscillation of electrocardiogram segments and their intervals so much that its balance could be investigated throughout the heart rate variability analysis. It is noteworthy that the ANS is able to modulate the myocardial repolarization phase too. Head-up/-down tilt test modifies acutely the ANS balance by means of a deactivation of the cardiopulmonary reflexes. The present study examines the influence of head-up/-down tilt on a number of ECG segments, assuming that the cardiopulmonary postural reflexes modulate most of the ECG interval oscillations in terms of their lengths and short-period temporal dispersion. The T wave amplitude diminished during head-up tilt and significantly correlated with the left ventricular end-systolic volume. The head-up/-down tilt test acutely modifies the autonomic nervous system balance throughout a deactivation of the cardiopulmonary reflexes. The present study examines the influence of head-up/-down tilt on a number of ECG segments. A total of 20 healthy subjects underwent a 5 min ECG and noninvasive hemodynamic bio-impedance recording, during free and controlled breathing, lying at (a) 0 & DEG;; (b) -45 & DEG;, tilting up at 45 & DEG;, and tilting up at 90 & DEG;. Heart rate variability power spectral analysis was obtained throughout some ECG intervals: P-P (P), P-Q (PQ), P(e)Q (from the end of P to Q wave), Q-R peak (QR intervals), Q-R-S (QRS), Q-T peak (QT(p)), Q-T end (QT(e)), STp, STe, T peak-T end (T-e), and, eventually, the TeP segments (from the end of T to the next P waves). Results: In all study conditions, the Low Frequency/High Frequency(PP) and LFPP normalized units (nu) were significantly lower than the LF/HFRR and LFRRnu, respectively. Conversely, the HFPP and HFPPnu were significantly higher in all study conditions. STe, QT(p,) and QT(e) were significantly related to the PP and RR intervals, whereas the T wave amplitude was inversely related to the standard deviations of all the myocardial repolarization variables and to the left ventricular end-systolic volume (LVEDV). The T wave amplitude diminished during head-up tilt and significantly correlated with the LVEDV.