Transfer function analysis of dynamic cerebral autoregulation in preeclampsia

Abstract

Objective: The cerebral circulatory effects of preeclampsia on the latency (phase) and the efficiency (gain) of the cerebral autoregulatory response is unknown. Preeclampsia causes a progressive impairment of the cerebral autoregulatory response. We sought to identify these dynamic cerebral autoregulation changes in preeclampsia.

Study design: We simultaneously measured continuously beat to beat outputs of mean arterial pressure (MAP) (Pilot 9200) and beat to beat, systolic, diastolic, and mean cerebral blood flow (MCBFV) (Nicolet Vascular TCD) for 2min with the patient during supine rest. Five preeclamptic and 5 matched normotensive controls were studied. R-R intervals, MAP, and MCBFV were analyzed in the frequency domain. Data sets were fast Fourier transformed and power spectral densities were calculated. We calculated the phase angle (which represents the temporal relationship between the MAP and mean MCBFV) and the transfer function (amplitude or gain between changes in the MCBFV signal and the MAP signal). All continuous data was compared between the two groups using T tests.

Results: We identified a significant difference between (1) the gain between the normotensive and preeclamptic groups (.29±.07 vs .10±.04) (p<.01, and (2) the phase angle (59±12 vs 129±31), p<.01. The preeclamptic group showed significant decrease in gain but an increase in phase angle).

Conclusion: Preeclampsia paradoxically results in a significant improvement in dynamic cerebral autoregulation as demonstrated by an increase in phase and a decrease in gain. Clinical studies that can systematically assess the progression of these dynamic autoregulation changes are needed.

Keywords: Cerebral autoregulation; Eclampsia; Middle cerebral blood flow velocity; Preeclampsia; Transfer function analysis.