Influence of the cold pressor test on the middle cerebral artery circulation

Cold pressor test (CPT) evokes generalized activation of the sympathetic nervous system (SNS). The activity of SNS may be estimated by monitoring the mean blood velocity (v(m)) in the middle cerebral artery (MCA) by using a transcranial Doppler monitoring system (TCD). To determine the response of SNS, we studied the v(m) during CPT. Thirty-four healthy volunteers, 13 female and 21 male (mean age 34 +/- 9.5 years, range 18 to 55 years) participated in our study. The experiment consisted of a 5-min baseline period followed by a 3-min immersion of the right hand in ice water. Blood velocity in both MCA's was monitored by bitemporal 2 MHz probes by using a Multi-Dop X4. MAP and heart rate (HR) were measured simultaneously by a Finapres non-invasive blood pressure monitor and a computerized ECG system. End-tidal CO2 (Et-CO2) was measured with an infrared capnograph. To determine v(m) over a chosen time interval the TCD-8 software was utilized. The results showed that during CPT v(m), MAP, and HR increased significantly (P < 0.01) for 9.8%, 18.5%, and 3.6%, respectively. Et-CO2 did not change significantly (P > 0.05). The increase of v(m) was also significantly higher in the stimulated hemispheres (P = 0.005) regarding to unstimulated ones. The increase of v(m) during CPT was not gender dependent. To establish the association between variables the models of multivariate regression were used. Multiple regression CPT model was significant (P < 0.01) and fitted data moderately well (R2 = 0.28). MAP and Et-CO2 were significant in the model (P < 0.01). It seems that the reactivity of the SNS can be estimated by measuring v(m) with TCD during CPT.