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Objective: Cerebral critical closing pressure (CrCP) is the arterial pressure (AP) below which small arterial cerebral vessels collapse. Our objective was to estimate cerebral CrCP in 12 severe TBI patients, relating transcranial Doppler flow velocity (FV) and AP data., Methods: FV, intracranial pressure (ICP) and invasive AP were prospectively acquired at 50 Hz. CrCP was estimated using three methods (M): M(1): amplitude ratio of FV/AP first harmonics; M(2): AP axis intersection of the regression line between systolic and diastolic values of FV and AP; M(3): AP axis intersection of the regression line between decreasing AP and FV simultaneous values., Results: There were 12 patients. Frequent negative CrCP values were found. Average M(1):-12 mmHg; M(2):-33 mmHg; M(3):-43 mmHg. Correlation between the three methods was significant (P < 0.01). M(1) showed the lowest range and more positive values. The better limits of agreement (Bland and Altman test) were between M(2) and M(3)., Conclusions: The frequently found negative values do not allow us for the moment, to use any of these three methods for clinical guidance.

Background: Cerebral critical closing pressure (CrCP) is the level of arterial blood pressure (ABP) at which small brain vessels close and blood flow stops. This value is always greater than intracranial pressure (ICP). The difference between CrCP and ICP is explained by the tone of the small cerebral vessels (wall tension). CrCP value is used in several dynamic cerebral autoregulation models. However, the different methods for calculation of CrCP show frequent negative values. These findings are viewed as a methodological limitation. We intended to evaluate CrCP in patients with severe traumatic brain injury (TBI) with a new multiparameter impedance-based model and compare it with results found earlier using a transcranial Doppler (TCD)-ABP pulse waveform-based method.Methods: Twelve severe TBI patients hospitalized during September 2005-May 2007. Ten men, mean age 32 years (16-61). Four had decompressive craniectomies (DC); three presented anisocoria. Patients were monitored with TCD cerebral blood flow velocity (FV), invasive ABP, and ICP. Data were acquired at 50 Hz with an in-house developed data acquisition system. We compared the earlier studied "first harmonic" method (M1) results with results from a new recently developed (M2) "multiparameter method."Results: M1: In seven patients CrCP values were negative, reaching -150 mmHg. M2: All positive values; only one lower than ICP (ICP 60 mmHg/ CrCP 57 mmHg). There was a significant difference between M1 and M2 values (M1 < M2) and between ICP and M2 (M2 > ICP).Conclusion: M2 results in positive values of CrCP, higher than ICP, and are physiologically interpretable. [ABSTRACT FROM AUTHOR]