[The effect of sudden changes in the stimulation rate of the heart on peak systolic pressure (author's transl)].

The changes in systolic pressure were studied in 48 patients during artificially (by electrical stimulation) induced sudden increases and consecutive decreases in heart rate. Various patterns could be separated respective to phase A (sudden switch from low (80-120 impulses/min) to higher heart rate (140-180 impulses/min)) and to phase B (sudden switch-back from high to lower (control) beating rate): AI) The systolic peak-pressure of the first contraction after the shortened stimulation interval is very low and often stays ineffective (below the aortic opening pressure). The second contraction develops already a higher pressure than the first one, during the consecutive beats the systolic pressure increases gradually until a new steady state is reached, which is usually lower than the systolic pressure during the foregoing lower beating rate. Sometimes however it can be equal or even higher. Accordingly after an elevation of heart rate arterial mean pressure can drop, stay constant or increase. AII) The systolic peak-pressure of the first contraction after the shortened stimulation interval stays relatively high and drops continuously with the succeeding contractions until a new steady state is reached according to the higher heart rate, it is however always lower than the one at a lower stimulation rate. Therefore arterial mean pressure is always decreased. AIII) Finally we observed changes in arterial systolic pressure in some patients that could not be grouped according to one or to the other pattern described above.- BI) The systolic peak of the first contraction after the switch-back from the high to the lower (control) rate is much higher than that of the last at the higher rate. The peak pressures of the consecutive contractions are then dropping continuously to the new steady-state, that can be higher, equal or lower than that at the higher stimulation rate. BII) ....