SPECTRAL-ANALYSIS OF SYSTOLIC BLOOD-PRESSURE AND HEART-RATE AFTER HEART-TRANSPLANTATION IN CHILDREN

1. The aim of the study was to examine the short-term variability in b lood pressure and heart rate in 19 children who had received heart tra nsplants and in eight normal control children. 2. Blood pressure was d etermined by a finger arterial pressure device. We examined the power spectra for heart rate and systolic blood pressure in the supine and t ilted positions. In addition, we studied the acute changes in blood pr essure and heart rate during active standing. 3. In the transplanted c hildren we could distinguish two groups (groups A and B) in whom heart rate variability differed, although in both it was greatly reduced co mpared with controls (group C). In group A there were no significant f luctuations in the mid-frequency range for heart rate. The gain of the relationship between systolic blood pressure and heart rate was very low and there were virtually no heart rate changes associated with pas sive tilting. 4. By contrast, in group B transplant patients the heart rate variability, as assessed by standard deviation, was about half t hat of normal controls. The power spectra attenuation was greater in t he high-frequency than in the mid-frequency bands, On passive tilting the latter became enhanced, but not the high-frequency variability. On active standing the tachycardic response was about half that of contr ols. The findings suggest some reinnervation involving cardiac sympath etic fibres to a greater degree than the fast-responding vagal fibres. 5. In both groups A and B the drop in systolic blood pressure observed early in active standing was about 4-6 times as great as in controls. One possible mechanism could be the loss of cardiac afferents. 6. Tim e since operation was a critical factor for reinnervation, since all s ubjects from group B were transplanted more than 44 months prior to th e recording. 7. We conclude that in a proportion of children who have received heart transplantation there is a delayed reinnervation of the heart, which probably involves sympathetic effectors rather than the vagus.