Publications by authors named "Agnieszka Kazimierska"

5 Publications

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Compliance of the cerebrospinal space: comparison of three methods.

Acta Neurochir (Wien) 2021 Apr 14. Epub 2021 Apr 14.

Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK.

Background: Cerebrospinal compliance describes the ability of the cerebrospinal space to buffer changes in volume. Diminished compliance is associated with increased risk of potentially threatening increases in intracranial pressure (ICP) when changes in cerebrospinal volume occur. However, despite various methods of estimation proposed so far, compliance is seldom used in clinical practice. This study aimed to compare three measures of cerebrospinal compliance.

Methods: ICP recordings from 36 normal-pressure hydrocephalus patients who underwent infusion tests with parallel recording of transcranial Doppler blood flow velocity were retrospectively analysed. Three methods were used to calculate compliance estimates during changes in the mean ICP induced by infusion of fluid into the cerebrospinal fluid space: (a) based on Marmarou's model of cerebrospinal fluid dynamics (C), (b) based on the evaluation of changes in cerebral arterial blood volume (C), and (c) based on the amplitudes of peaks P1 and P2 of ICP pulse waveform (C).

Results: Increase in ICP caused a significant decrease in all compliance estimates (p < 0.0001). Time courses of compliance estimators were strongly positively correlated with each other (group-averaged Spearman correlation coefficients: 0.94 [0.88-0.97] for C vs. C, 0.77 [0.63-0.91] for C vs. C, and 0.68 [0.48-0.91] for C vs. C).

Conclusions: Indirect methods, C and C, allow for the assessment of relative changes in cerebrospinal compliance and produce results exhibiting good correlation with the direct method of volumetric manipulation. This opens the possibility of monitoring relative changes in compliance continuously.
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http://dx.doi.org/10.1007/s00701-021-04834-yDOI Listing
April 2021

Cerebrovascular Impedance During Hemodynamic Change in Rabbits: A Pilot Study.

Acta Neurochir Suppl 2021 ;131:283-288

Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.

Introduction: Cerebrovascular impedance describes the relationship between pulsatile changes in arterial blood pressure (ABP) and cerebral blood flow (CBF). It is commonly defined by modulus and phase shift derived from Fourier spectra of ABP and CBF velocity (CBFV) signals under mostly steady-state conditions. The aim of this work was to assess heartbeat-to-heartbeat cerebrovascular impedance at heart rate frequency during controlled changes in mean ABP and intracranial pressure (ICP).

Material And Methods: Recordings of ABP in the femoral artery, transcranial Doppler CBFV in the basilar artery, and subarachnoid ICP were obtained from anesthetized rabbits with induced arterial hypotension (n = 8 rabbits), arterial hypertension (n = 5), or intracranial hypertension (n = 7). Modulus of cerebrovascular impedance (|Z|) was estimated from amplitudes of ABP and CBFV. Phase shift of cerebrovascular impedance (PS) was estimated from time-frequency (TF) representations of phase shift between ABP and CBFV overlaid with a time-variant mask based on the fundamental frequency of ABP.

Results: Both |Z| and PS increased with increasing mean ABP. |Z| decreased with increasing mean ICP, but no change was observed in PS.

Conclusions: The combined beat-to-beat and TF approach allows for the estimation of cerebrovascular impedance during transient hemodynamic changes. |Z| and PS follow the pattern of changes in CPP.
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http://dx.doi.org/10.1007/978-3-030-59436-7_53DOI Listing
January 2021

Analysis of Intracranial Pressure Pulse-Pressure Relationship: Experimental Validation.

Acta Neurochir Suppl 2021 ;131:279-282

Faculty of Electronics and Information Technology, Institute of Electronic Systems, Warsaw University of Technology, Warsaw, Poland.

The slope of linear relationship between the amplitude of pulsations in intracranial pressure (ICP) versus mean ICP has recently been suggested as a useful guide for selecting patients for shunt surgery in normal pressure hydrocephalus (NPH). To better understand how the pathophysiology of cerebral circulation influences this parameter, we aimed to study the relationship between mean pressure and pulsation amplitude in a wide range of conditions affecting cerebrovascular tone and ICP in experimental conditions.We retrospectively analysed experimental material collected previously. Three physiological manoeuvres were studied in 29 New Zealand white rabbits: lumbar infusion with an infusion rate ≤0.2 mL/min to induce mild intracranial hypertension (n = 43), sympathetic blockade to induce arterial hypotension (n = 19), and modulation of the ventilator tidal volume, simultaneously influencing arterial carbon dioxide partial pressure (PaCO) to induce hypocapnia or hypercapnia (n = 17). We investigated whether the slope of the pulse amplitude (AMP)-ICP line depended on PaCO and arterial blood pressure (ABP) changes.We found a linear correlation between AMP-ICP and ICP with positive slope. Regression of slope against mean ABP showed a negative dependence (p = 0.03). In contrast, the relationship between slope and PaCO was positive, although not reaching statistical significance (p = 0.18).The slope of amplitude-pressure line is strongly modulated by systemic vascular variables and therefore should be taken as a descriptor of cerebrospinal fluid dynamics with great care.
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http://dx.doi.org/10.1007/978-3-030-59436-7_52DOI Listing
January 2021

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

Comput Math Methods Med 2019 3;2019:4875231. Epub 2019 Feb 3.

Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology, Wroclaw 50-370, Poland.

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. However, little is known about the influence of the combination of these two factors on dynamic baroreflex response. Furthermore, classical methods used for BRS assessment are based on the assumption of stationarity that may lead to unreliable results in the case of mostly nonstationary cardiovascular signals. Therefore, we aimed to investigate BRS during repeated transitions between squatting and standing in normal end-tidal CO (EtCO) conditions (normocapnia) and conditions of progressively increasing EtCO with a decreasing level of O (hypercapnia with hypoxia) using joint time and frequency domain (TF) approach to BRS estimation that overcomes the limitation of classical methods. Noninvasive continuous measurements of ABP and EtCO were conducted in a group of 40 healthy young volunteers. The time course of BRS was estimated from TF representations of pulse interval variability and systolic pressure variability, their coherence, and phase spectra. The relationship between time-variant BRS and indices of ABP and HR was analyzed during postural change in normocapnia and hypercapnia with hypoxia. In normocapnia, observed trends in all measures were in accordance with previous studies, supporting the validity of presented TF method. Similar but slightly attenuated response to postural change was observed in hypercapnia with hypoxia. Our results show the merits of the nonstationary methods as a tool to study the cardiovascular system during short-term hemodynamic changes.
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http://dx.doi.org/10.1155/2019/4875231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6377966PMC
August 2019

Baroreflex sensitivity and heart rate variability are predictors of mortality in patients with aneurysmal subarachnoid haemorrhage.

J Neurol Sci 2018 11 13;394:112-119. Epub 2018 Sep 13.

Department of Anesthesiology and Intensive Care, Wroclaw Medical University, Wroclaw, Poland.

Object: We aimed to investigate the link between the autonomic nervous system (ANS) impairment, assessed using baroreflex sensitivity (BRS) and heart rate variability (HRV) indices, and mortality after aneurysmal subarachnoid haemorrhage (aSAH).

Methods: A total of 57 patients (56 ± 18 years) diagnosed with aSAH were retrospectively enrolled in the study, where 25% of patients died in the hospital. BRS was calculated using a modified cross-correlation method. Time- and frequency-domain HRV indices were calculated from a time-series of systolic peak intervals of arterial blood pressure signals. Additionally, cerebral autoregulation (CA) was assessed using the mean velocity index (Mxa), where Mxa > 0 indicates impaired CA.

Results: Both BRS and HRV indices were lower in non-survivors than in survivors. The patients with disturbed BRS and HRV had more extensive haemorrhage in the H-H scale (p = .040) and were more likely to die (p = .013) when compared to patients with the intact ANS. The logistic regression model for mortality included: the APACHE II score (p = .002; OR 0.794) and the normalised high frequency power of the HRV (p < <.001; OR 0.636). A positive relationship was found between the Mxa and BRS (R = 0.48, p = .003), which suggests that increasing BRS is moderately strongly associated with worsening CA.

Conclusion: Our results indicated that lower values of HRV indices and BRS correlate with mortality and that there is a link between cerebral dysautoregulation and the analysed estimates of the ANS in aSAH patients.
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http://dx.doi.org/10.1016/j.jns.2018.09.014DOI Listing
November 2018