Can interhemispheric desynchronization of cerebral blood flow anticipate upcoming vasospasm in aneurysmal subarachnoid haemorrhage patients?

Background: Asymmetry of cerebral autoregulation (CA) was demonstrated in patients after aneurysmal subarachnoid haemorrhage (aSAH). A classical method for CA assessment requires simultaneous measurement of both arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV). In this study, we have proposed a cerebral blood flow asymmetry index based only on CBFV and analysed its association with the occurrence of vasospasm after aSAH.

Assessment of Baroreflex Sensitivity Using Time-Frequency Analysis during Postural Change and Hypercapnia.

Baroreflex is a mechanism of short-term neural control responsible for maintaining stable levels of arterial blood pressure (ABP) in an ABP-heart rate negative feedback loop. Its function is assessed by baroreflex sensitivity (BRS)-a parameter which quantifies the relationship between changes in ABP and corresponding changes in heart rate (HR). The effect of postural change as well as the effect of changes in blood O and CO have been the focus of multiple previous studies on BRS.

Applying time-frequency analysis to assess cerebral autoregulation during hypercapnia.

Objective: Classic methods for assessing cerebral autoregulation involve a transfer function analysis performed using the Fourier transform to quantify relationship between fluctuations in arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV). This approach usually assumes the signals and the system to be stationary. Such an presumption is restrictive and may lead to unreliable results.

Phase shift between respiratory oscillations in cerebral blood flow velocity and arterial blood pressure.

We aim to investigate whether phase shift between respiratory oscillations in cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP) is associated with changes in cerebral autoregulation (CA) or reflects the mechano-elastic properties of the cerebrovascular bed. The relationships between respiratory phase shift and slow wave phase shift versus cerebrovascular time constant (the product of cerebrovascular resistance and compliance) and the index of CA (Mx) were analyzed during breathing at 6, 10, and 15 breaths min in 39 volunteers. With increasing respiratory rate the time constant, Mx, and respiratory phase shift decreased, whereas slow wave phase shift increased.

Principles of operation, accuracy and precision of an Eye Surface Profiler.

Purpose: To introduce a newly developed instrument for measuring the topography of the anterior eye, provide principles of its operation and to assess its accuracy and precision.

Methods: The Eye Surface Profiler is a new technology based on Fourier transform profilometry for measuring the anterior eye surface encompassing the corneo-scleral area. Details of technical principles of operation are provided for the particular case of sequential double fringe projection.

Complexity of cerebral blood flow velocity and arterial blood pressure in subarachnoid hemorrhage using time-frequency analysis.

We investigated changes of time-frequency (TF) complexity, in terms of Rényi entropy and a measure of concentration, of middle cerebral blood flow velocity (CBFV) and arterial blood pressure in relation to the development of cerebral vasospasm in 15 patients after aneurysmal subarachnoid hemorrhage. Interhemispheric differences in the period of no vasospasm and vasospasm were also compared. Results show reduced complexity of TF representations of CBFV on the side of aneurysm before vasospasm was identified.