Cerebral autoregulatory changes in hypertensive states assessed by beat to beat cerebral blood velocity changes

Abstract

BY BEAT TO BEAT CEREBRAL BLOOD VELOCITY CHANGES KEITH WILLIAMS, FRANCE GALERNEAU, MARIA SMALL, Yale University, Obstetrics & Gynecology, New Haven, Connecticut, Yale University, Obstetrics and Gynecology, New Haven, Connecticut, Yale University, New Haven, Connecticut OBJECTIVE: Recent studies have identified significant changes in cerebral autoregulation in preeclampsia (PET). We chose to examine pulsatile fluctations in in the Middle Cerebral Blood Flow Velocity. (MCBFV) by assessing the beat to beat systolic variation with changes in RR interval and Systolic MCBFV Variability. This study investigates the usefulness as a test of cerebral autoregulation the beat-to-beat changes in MCBFV with changes in RR intervals. STUDY DESIGN: Transcranial Doppler monitoring of the middle cerebral artery (MCA) was performed for 2 minutes on 20 normotensive, 10 PET, 5 chronic hypertensive and 7 Pregnancy Induced Hypertension (PIH) patients were assessed. We measured beat-to-beat systolic, diastolic, and mean MCBFV velocity and RR intervals. Offline using software we calculated the beat-to-beat change in Systolic MCBFV associated with changes RR in each of the groups. In addition the Systolic MCBFV variability was calculated as the square root of the mean of the sum of the squares of differences in Systolic MCBFV between adjacent RR intervals. All continuous data was compared between the four groups using ANOVA with Bonferroni correction. RESULTS: We identified a significant difference the Systolic MCBFV change with the RR interval among the normotensive PET, Chronic Hypertensive and PIH groups (33.6G14.6, vs 16G10.2, vs, 44G14.8, vs 31.9G17.8)(P!.004) There was no significant difference in Systolic MCBFV variability (1.96G63, vs 1.63G.49, vs1.91G.52, vs 1.58G.29)(P!.30). CONCLUSION: We evaluated cerebral function in various pregnant hypertensive states by examining spontaneous fluctuations and rythmicity of RR interval and systolic MCBFV. Our data suggest that in PET unlike chronic hypertension acts to diminish spontaneous beat to beat oscillations in MCBFV. The loss of the dynamic complexity of the variability signal may be an indication of loss of vessel adaptability to continuously changing environmental requirements.