RT and systolic blood pressure variability after sympathetic stimulation during positive tilt in healthy volunteers

Repolarisation of the left ventricle and blood pressure are mainly influenced by sympathetic tone. The authors investigated RR-, RT-intervals and systolic blood pressure variability by spectral analysis in 18 healthy volunteers in supine and head-up tilt position (90/spl deg/). ECG and peripheral arterial blood pressure were recorded 3 minutes in both positions (respiratory rate 0.26 Hz). Mean values, standard deviation (STD), LF (0.05-0.18 Hz) and HF (0.18-0.32 Hz) areas of the spectra were calculated. After positive tilt mean RR-intervals and RR-variability (HF) decrease. Mean RT-interval decreases and mean systolic blood pressure increases in tilt position. STD and LF of RT and blood pressure increase parallely. HF increases for blood pressure and shows no significant changes for RT-intervals. The increase of LF for the RT-intervals may be due to a sympathetic influence, but also beat to beat changes of the stroke volume and coronary perfusion may be responsible for this effect. The different behaviour of the variability of RR- and RT-intervals indicates that there is no direct coupling between RR- and RT-intervals.<
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