Detection of Impaired Cerebral Autoregulation Improves by Increasing Arterial Blood Pressure Variability

Abstract

Although the assessment of dynamic cerebral autoregulation (CA) based on measurements of spontaneous fluctuations in arterial blood pressure (ABP) and cerebral blood flow (CBF) is a convenient and much used method, there remains uncertainty about its reliability. We tested the effects of increasing ABP variability, provoked by a modification of the thigh cuff method, on the ability of the autoregulation index to discriminate between normal and impaired CA, using hypercapnia as a surrogate for dynamic CA impairment. In 30 healthy volunteers, ABP (Finapres) and CBF velocity (CBFV, transcranial Doppler) were recorded at rest and during 5% CO 2 breathing, with and without pseudo-random sequence inflation and deflation of bilateral thigh cuffs. The application of thigh cuffs increased ABP and CBFV variabilities and was not associated with a distortion of the CBFV step response estimates for both normocapnic and hypercapnic conditions (P ¼ 0.59 and P ¼ 0.96, respectively). Sensitivity and specificity of CA impairment detection were improved with the thigh cuff method, with the area under the receiver-operator curve increasing from 0.746 to 0.859 (P ¼ 0.031). We conclude that the new method is a safe, efficient, and appealing alternative to currently existing assessment methods for the investigation of the status of CA.

Cerebral Pressure–Flow Relationship in Lowlanders and Natives at High Altitude

“…An alternative interpretation to the reported impairment in the dynamic cerebral pressure-flow relationship at high altitude (HA) is that these observations are influenced by poor BP variability, a limitation of using TFA under spontaneous conditions. 13,14 Induced nonpharmacological elevations in BP variability can be utilized to mitigate this limitation and improve the reliability and interpretation of the TFA metrics. 14 In contrast to lowlanders at HA, we know of only two studies that have examined the cerebral pressure-flow relationship in natives to HA.…”

“…13,14 Induced nonpharmacological elevations in BP variability can be utilized to mitigate this limitation and improve the reliability and interpretation of the TFA metrics. 14 In contrast to lowlanders at HA, we know of only two studies that have examined the cerebral pressure-flow relationship in natives to HA. 15,16 In their first study, Jansen et al 15 assessed the pressure-flow relationship during steady-state hypertensive changes in BP (i.e.…”

The Leicester cerebral haemodynamics database: normative values and the influence of age and sex

“…Using standard procedures (Panerai et al 1998a, Zhang et al 1998, Panerai et al 1998b, Gommer et al 2010, Meel-van den Abeelen et al 2014b, Katsogridakis et al 2013, the coherence function, amplitude (gain) and phase frequency responses were calculated from the auto-and cross-spectra. The coherence function was visually inspected and TFA estimates were only accepted if the coherence was above 0.5 in the frequency range 0.15-0.25Hz where the BP-CBFV relationship can be assumed to be linear (Claassen et al 2016).…”

“…Healthy volunteers were recruited from departmental staff and their relatives and provided informed consent in compliance with local ethics committee approvals for all previous studies (Brodie et al 2009, Haunton 2013, Katsogridakis et al 2013, Saeed et al 2013, Salinet, Panerai & Robinson 2014, Minhas et al 2016. Exclusion criteria included poor insonation of both temporal bone windows and any history of cardiovascular, neurological, or respiratory disease.…”

“…It is also important to be aware that CBFV, EtCO2, CrCP and LF coherence do change with ageing when interpreting results from TFA. Above all, it is well known that PaCO2 is a potent determinant of CBF and also affects dynamic CA (Paulson, Strandgaard & Edvinsson 1990, Aaslid et al 1989, Katsogridakis et al 2013, Minhas et al 2016, Marinoni et al 1998). …”