Noninvasive Estimation of Cerebral Perfusion Pressure and Zero Flow Pressure in Healthy Volunteers: The Effects of Changes in End-Tidal Carbon Dioxide

Abstract

Increasing end-tidal CO(2) increases the estimated cerebral perfusion pressure and vice versa. These results are opposite to those expected from the known effects of CO(2) on intracranial pressure. Thus, we support the suggestion that, in the absence of intracranial hypertension, vascular tone remains a major determinant of effective downstream pressure and cerebral perfusion.

Carbon Dioxide Induced Changes in Cerebral Blood Flow and Flow Velocity: Role of Cerebrovascular Resistance and Effective Cerebral Perfusion Pressure

“…Tests for normal distribution of data were performed with the D'Agostino-Pearson omnibus K2 method. Effective cerebral perfusion pressure (CPPe) 5,7 CPPe = MAP-ZFP mm Hg Cerebral vascular resistance (CVR) 5 CVR = CPPe/CBF mm Hg/mL/100 g/min Resistance area product (RAP) 2,10 RAP = inverse slope of the relationship of pressure/flow velocity MCA mm Hg × s/cm Relative carbon dioxide reactivity (CO 2 -R) 18 CO 2 Both CPPe and CVR determine CO 2 reactivity of CBF F Grüne et al…”

“…4 Since the introduction of TCD, a number of methods have been developed to assess CCP noninvasively by extrapolating instantaneous pressure-flow velocity plots (ABP/V MCA ) to zero from continuous recordings or by extrapolation of the ZFP from a linear function given by diastolic, mean, and/or systolic values of pressures and flow velocity. 2,[5][6][7] In a former investigation, we suggested the hypothesis of two Starling resistors in a series connection, one (proximal) at the precapillary level of cerebral resistance vessels (CCP art ) and a second (distal) at the level of collapsible cerebral veins (CCP ven ). The EDP of the cerebral circulation may be determined by CCP art , CCP ven (i.e., ICP), or jugular venous pressure, depending on which one is the highest.…”

“…The reduction of CPPe due to hyperventilation in our patients was clinically relevant, which is in accordance with previous findings. 2,[5][6][7]40 When using TCD, an estimate of vascular resistance can be derived from the ratio between blood pressure and blood flow velocity, which equals the product of the peripheral resistance and the cross-sectional area of the vessel at the site of insonation, the RAP. 10 Up to now, there is no investigation that compared measurements of global CBF and V MCA compare changes in CVR with RAP.…”

“…4 Since the introduction of transcranial Doppler ultrasonography (TCD), a number of methods have been developed to assess CCP by extrapolating instantaneous pressure-flow velocity plots (ABP/V MCA ) to zero or by calculation of the intercept of diastolic, mean, and/or systolic values of pressures and flow velocity. 2,[5][6][7][8] A number of factors other than vascular tone, i.e., central venous pressure and ICP, can also influence the EDP in the cerebral circulation. Consequently, the use of the term 'zero flow pressure' (ZFP) is considered more appropriate than CCP.…”

Transcranial Doppler estimation of cerebral blood flow and cerebrovascular conductance during modified rebreathing

“…For each cycle, the corresponding value for P etC 0 2 and mean values for CBFV, ABP, and HR were measured. Averaging the number of cardiac cycles (usually 6 ) has been applied previously in an attempt to reduce respiratory hemodynamic variability (17). We preferred to identify each respiratory cycle (2 2 ) to derive the breathto-breath CBFV-Petc 0 2 relationship.…”