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Soehle M. Fractal Analysis of the Cerebrovascular System Pathophysiology. ADVANCES IN NEUROBIOLOGY 2024; 36:385-396. [PMID: 38468043 DOI: 10.1007/978-3-031-47606-8_19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/13/2024]
Abstract
The cerebrovascular system is characterized by parameters such as arterial blood pressure (ABP), cerebral perfusion pressure (CPP), and cerebral blood flow velocity (CBFV). These are regulated by interconnected feedback loops resulting in a fluctuating and complex time course. They exhibit fractal characteristics such as (statistical) self-similarity and scale invariance which could be quantified by fractal measures. These include the coefficient of variation, the Hurst coefficient H, or the spectral exponent α in the time domain, as well as the spectral index ß in the frequency domain. Prior to quantification, the time series has to be classified as either stationary or nonstationary, which determines the appropriate fractal analysis and measure for a given signal class. CBFV was characterized as a nonstationary (fractal Brownian motion) signal with spectral index ß between 2.0 and 2.3. In the high-frequency range (>0.15 Hz), CBFV variability is mainly determined by the periodic ABP variability induced by heartbeat and respiration. However, most of the spectral power of CBFV is contained in the low-frequency range (<0.15 Hz), where cerebral autoregulation acts as a low-pass filter and where the fractal properties are found. Cerebral vasospasm, which is a complication of subarachnoid hemorrhage (SAH), is associated with an increase in ß denoting a less complex time course. A reduced fractal dimension of the retinal microvasculature has been observed in neurodegenerative disease and in stroke. According to the decomplexification theory of illness, such a diminished complexity could be explained by a restriction or even dropout of feedback loops caused by disease.
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Affiliation(s)
- Martin Soehle
- Department of Anesthesiology and Intensive Care Medicine, University Hospital Bonn, Bonn, Germany.
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Veraar CM, Rinösl H, Kühn K, Skhirtladze-Dworschak K, Felli A, Mouhieddine M, Menger J, Pataraia E, Ankersmit HJ, Dworschak M. Non-pulsatile blood flow is associated with enhanced cerebrovascular carbon dioxide reactivity and an attenuated relationship between cerebral blood flow and regional brain oxygenation. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2019; 23:426. [PMID: 31888721 PMCID: PMC6937980 DOI: 10.1186/s13054-019-2671-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Accepted: 11/13/2019] [Indexed: 12/16/2022]
Abstract
BACKGROUND Systemic blood flow in patients on extracorporeal assist devices is frequently not or only minimally pulsatile. Loss of pulsatile brain perfusion, however, has been implicated in neurological complications. Furthermore, the adverse effects of absent pulsatility on the cerebral microcirculation are modulated similarly as CO2 vasoreactivity in resistance vessels. During support with an extracorporeal assist device swings in arterial carbon dioxide partial pressures (PaCO2) that determine cerebral oxygen delivery are not uncommon-especially when CO2 is eliminated by the respirator as well as via the gas exchanger of an extracorporeal membrane oxygenation machine. We, therefore, investigated whether non-pulsatile flow affects cerebrovascular CO2 reactivity (CVR) and regional brain oxygenation (rSO2). METHODS In this prospective, single-centre case-control trial, we studied 32 patients undergoing elective cardiac surgery. Blood flow velocity in the middle cerebral artery (MCAv) as well as rSO2 was determined during step changes of PaCO2 between 30, 40, and 50 mmHg. Measurements were conducted on cardiopulmonary bypass during non-pulsatile and postoperatively under pulsatile blood flow at comparable test conditions. Corresponding changes of CVR and concomitant rSO2 alterations were determined for each flow mode. Each patient served as her own control. RESULTS MCAv was generally lower during hypocapnia than during normocapnia and hypercapnia (p < 0.0001). However, the MCAv/PaCO2 slope during non-pulsatile flow was 14.4 cm/s/mmHg [CI 11.8-16.9] and 10.4 cm/s/mmHg [CI 7.9-13.0] after return of pulsatility (p = 0.03). During hypocapnia, non-pulsatile CVR (4.3 ± 1.7%/mmHg) was higher than pulsatile CVR (3.1 ± 1.3%/mmHg, p = 0.01). Independent of the flow mode, we observed a decline in rSO2 during hypocapnia and a corresponding rise during hypercapnia (p < 0.0001). However, the relationship between ΔrSO2 and ΔMCAv was less pronounced during non-pulsatile flow. CONCLUSIONS Non-pulsatile perfusion is associated with enhanced cerebrovascular CVR resulting in greater relative decreases of cerebral blood flow during hypocapnia. Heterogenic microvascular perfusion may account for the attenuated ΔrSO2/ΔMCAv slope. Potential hazards related to this altered regulation of cerebral perfusion still need to be assessed. TRIAL REGISTRATION The study was retrospectively registered on October 30, 2018, with Clinical Trial.gov (NCT03732651).
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Affiliation(s)
- Cecilia Maria Veraar
- Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care Medicine, Department of Anaesthesia, Intensive Care Medicine, and Pain Medicine, Vienna General Hospital, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria
| | - Harald Rinösl
- Department of Anaesthesia and Intensive Care Medicine, LKH Feldkirch, Feldkirch, Austria
| | - Karina Kühn
- Department of Anaesthesia, Intensive Care Medicine and Pain Medicine, Klinikum Traunstein, Traunstein, Germany
| | - Keso Skhirtladze-Dworschak
- Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care Medicine, Department of Anaesthesia, Intensive Care Medicine, and Pain Medicine, Vienna General Hospital, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria
| | - Alessia Felli
- Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care Medicine, Department of Anaesthesia, Intensive Care Medicine, and Pain Medicine, Vienna General Hospital, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria
| | - Mohamed Mouhieddine
- Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care Medicine, Department of Anaesthesia, Intensive Care Medicine, and Pain Medicine, Vienna General Hospital, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria
| | - Johannes Menger
- Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care Medicine, Department of Anaesthesia, Intensive Care Medicine, and Pain Medicine, Vienna General Hospital, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria
| | - Ekaterina Pataraia
- Department of Neurology, Vienna General Hospital, Medical University of Vienna, Vienna, Austria
| | - Hendrik Jan Ankersmit
- Division of Thoracic Surgery, Department of Surgery, Vienna General Hospital, Medical University of Vienna, Vienna, Austria
| | - Martin Dworschak
- Division of Cardiothoracic and Vascular Anaesthesia and Intensive Care Medicine, Department of Anaesthesia, Intensive Care Medicine, and Pain Medicine, Vienna General Hospital, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
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Zhang Y, Chan GSH, Tracy MB, Hinder M, Savkin AV, Lovell NH. Detrended fluctuation analysis of blood pressure in preterm infants with intraventricular hemorrhage. Med Biol Eng Comput 2013; 51:1051-7. [PMID: 23716182 DOI: 10.1007/s11517-013-1083-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Accepted: 05/07/2013] [Indexed: 11/30/2022]
Abstract
Very preterm infants are at high risk of death and serious permanent brain damage, as occurs with intraventricular hemorrhage (IVH). Detrended fluctuation analysis (DFA) that quantifies the fractal correlation properties of physiological signals has been proposed as a potential method for clinical risk assessment. This study examined whether DFA of the arterial blood pressure (ABP) signal could derive markers for the identification of preterm infants who developed IVH. ABP data were recorded from a prospective cohort of 30 critically ill preterm infants in the first 1-3 h of life, 10 of which developed IVH. DFA was performed on the beat-to-beat sequences of mean arterial pressure (MAP), systolic blood pressure (SBP) and pulse interval, with short-term exponent (α1, for timescale of 4-15 beats) and long-term exponent (α2, for timescale of 15-50 beats) computed accordingly. The IVH infants were found to have higher short-term scaling exponents of both MAP and SBP (α1 = 1.06 ± 0.18 and 0.98 ± 0.20) compared to the non-IVH infants (α1 = 0.84 ± 0.25 and 0.78 ± 0.25, P = 0.017 and 0.038, respectively). The results have demonstrated that fractal dynamics embedded in the arterial pressure waveform could provide useful information that facilitates early identification of IVH in preterm infants.
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Affiliation(s)
- Ying Zhang
- School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, NSW 2052, Australia.
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