Variability of the systolic and diastolic electromechanical periods in healthy subjects

Our aims were to assess: 1) the variability of the systolic and diastolic periods, estimated by the electromechanical interval measured from the R wave to the systolic peak of the pressure wave (RPre), and the interval from this peak to the next R wave (PreR), respectively; 2) the effect of two maneuvers on the variability of these periods. ECG, arterial pressure and respiration were recorded from 21 volunteers in three 5-min conditions: supine (S), controlled breathing (CB) and exercise (E). Spectral analysis of RR, RPre, PreR and respiration series was performed to obtain their high (HF) and low (LF) frequency components. Both LF and HF powers of PreR changed in parallel with those of RR intervals. The maneuvers did not affect the LF power of RPre interval (p>;0.05) and had a minimal effect on the HF power; both components were much smaller than those of PreR in S and CB (p<;0.001) but similar during E. The minimal and constant spectral powers of RPre interval and the highly variable components of PreR indicate that the cardiac autonomic modulation is expressed preferentially in the diastolic period rather than in the systolic one.