STEP BAROREFLEX RESPONSE IN AWAKE PATIENTS UNDERGOING CAROTID SURGERY- TIME-DOMAIN AND FREQUENCY-DOMAIN ANALYSIS

Step baroreceptor stimulation can provide an insight into the barorefl ex control mechanism, yet this has never been done in humans. During c arotid surgery under regional anesthesia, a step increase in barorecep tor stimulation occurs at carotid declamping immediately after removal of the intra-arterial atheromatous plaque. In 10 patients, the R-R in terval and systolic and diastolic blood pressures (BP) were continuous ly recorded, and signals obtained within the time window from 10 min b efore until 10 min after carotid declamping were analyzed. Mean +/- SD time signals, power spectra, and transfer and coherence functions bef ore and after declamping were calculated. Immediately after carotid de clamping, both heart rate (HR) and BP declined in an exponential-like manner lasting 10.3 +/- 5.9 min, and their power spectra increased in the entire frequency range. Transfer function magnitude and coherence functions between BP and HR increased predominantly in the midfrequenc y region (similar to 0.1 Hz), with no change in phase function. Thus, in carotid endarterectomy patients, step increase in baroreceptor gain elicits a prolonged decline in HR and BP. Frequency analyses support the notion that the baroreflex control mechanism generates the midfreq uency HR and BP variability, although other frequency regions are also affected.