Cerebral blood flow velocity response to induced and spontaneous sudden changes in arterial blood pressure

The influence of different types of maneuvers that can induce sudden change s of arterial blood pressure (ABP) on the cerebral blood flow velocity (CBF V) response was studied in 56 normal subjects (mean age 62 yr, range 23-80) . ABP was recorded in the finger with a Finapres device, and bilateral reco rdings of CBFV were performed with Doppler ultrasound of the middle cerebra l arteries. Recordings were performed at rest (baseline) and during the thi gh cuff test, lower body negative pressure, cold pressor test, hand grip, a nd Valsalva maneuver. From baseline recordings, positive and negative spont aneous transients were also selected. Stability of PCO2 was monitored with transcutaneous measurements. Dynamic autoregulatory index (ARI), impulse, a nd step responses were obtained for 1-min segments of data for the eight co nditions by fitting a mathematical model to the ABP-CBFV baseline and trans ient data (Aaslid's model) and by the Wiener-Laguerre moving-average method . Impulse responses were similar for the right- and left-side recordings, a nd their temporal pattern was not influenced by type of maneuver. Step resp onses showed a sudden rise at time 0 and then started to fall back to their original level, indicating an active autoregulation. ARI was also independ ent of the type of maneuver, giving an overall mean of 4.7 +/- 2.9 (n = 602 recordings). Amplitudes of the impulse and step responses, however, were s ignificantly influenced by type of maneuver and were highly correlated with the resistance-area product before the sudden change in ABP (r = 20.93, P < 0.0004). These results suggest that amplitude of the CBFV step response i s sensitive to the point of operation of the instantaneous ABP-CBFV relatio nship, which can be shifted by different maneuvers. Various degrees of symp athetic nervous system activation resulting from different ABP-stimulating maneuvers were not reflected by CBFV dynamic autoregulatory responses withi n the physiological range of ABP.