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Cortical blood flow autoregulation revisited using laser Doppler perfusion imaging
Linköping University, Department of Medical and Health Sciences, Anesthesiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Neuroscience and Locomotion, Oto-Rhiono-Laryngology and Head & Neck Surgery. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medical and Health Sciences, Anesthesiology. Linköping University, Department of Biomedicine and Surgery, Plastic Surgery, Hand Surgery and Burns. Linköping University, Faculty of Health Sciences.
2002 (English)In: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 176, no 4, 255-262 p.Article in journal (Refereed) Published
Abstract [en]

Methods of laser Doppler perfusion monitoring (LDPM) and imaging (LDPI) have been validated and found useful for measurements of brain blood flow in several studies. The present work was undertaken to examine the cortical blood flow autoregulatory phenomenon as it has lately been questioned and claimed to be method-dependent and related to sample volume. Spatial variations in cerebral cortical blood flow (CBFcortex) in the pressure range 20–140 mmHg (static cerebral autoregulation; caval block/angiotensin infusion) were studied in six mechanically ventilated (hypocapnic, normocapnic and hypercapnic) pigs anaesthetized with propofol and fentanyl. Although the cortical blood flow values sampled were highly heterogeneously distributed, they were strongly pressure-dependent as well as CO2-dependent (P < 0.001). A cumulative cerebral blood flow (CBF)–pressure (MAP) plot comprising all values obtained indicated a pressure range between 70 and 120 mmHg where CBF remained almost constant. However, at the local level in the cortex (mm2) the same type of ‘classic’ autoregulatory flow : pressure graphs (FPG) were found in only a few of the cases of the cortical areas examined (n = 96). Alterations in blood PaCO2 saturation did not affect the pressure : flow relationship at low perfusion pressures, whereas at normal or above normal values, and as anticipated, hypercapnia considerably increased CBF (P < 0.001). ‘Classic’ autoregulatory FPGs were found only when all values sampled were clustered together, whereas, as a new finding, data are presented indicating that autoregulatory capacity is lacking at the local level at some cortical surface areas.

Place, publisher, year, edition, pages
2002. Vol. 176, no 4, 255-262 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-25358DOI: 10.1046/j.1365-201X.2002.01034.xLocal ID: 9800OAI: diva2:245687
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2012-09-28Bibliographically approved
In thesis
1. Intrinsic and extrinsic protection of the brain
Open this publication in new window or tab >>Intrinsic and extrinsic protection of the brain
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The brain is a complex organ and critically dependent on its oxygen metabolism and blood supply. The purpose of the present study was twofold: firstly to design, evaluate, and adopt a physiologically stable experimental model for repeated measurements of cerebral cortical microvascular perfusion by a new laser Doppler technique (experimental part (I) - intrinsic model). Secondly, to examine the complication rates of a brief period of hypothermia for protection of the brain in patients who  were operated on for subarachnoid aneurysms (clinical part (II) - extrinsic model).

Method. Part I. In contrast to conventional laser Doppler flowmetry, the laser Doppler perfusion imager (LDPI) creates a two-dimensional map of the tissue perfusion in an area of up to 120 x 120 mm, comprising 4096 measurement points. Measurements were made in a closed cranial window in ventilated anaesthetised pigs (n=25). Provocations that altered cerebral blood flow (CBF) were those that can occur during anaesthesia and critical care, including varying arterial concentration of carbon dioxide and mean arterial blood pressure (MABP), and those caused by different types (isoflurane and sevoflurane) and concentrations (minimum alveolar concentration, MAC, 0.3-1.2) of volatile anaesthetics.

Part II. The feasibility and complication rates of rapidly-induced moderate hypothermia in 359 operations were examined prospectively. The complications that we sought were: altered haemostasis, infections, haemodynamic instability, and increased need for postoperative ventilatory support. Hypothermia was produced by cold (4°C) intravenous infusions and convective cooling. This lowered the body temperature at a mean (SD) 4 (0.4)oC h1 to 32.5 (0.4)oC. The body temperature returned to normal in all patients by 5 (2) hours postoperatively.

Results. Part I. Cortical CBF was distributed highly heterogeneously and it was strongly dependent on MABP, as well as concentrations of CO2 During decreasing MABP the lower limit of autoregulation varied locally in the cortex and the 'classic' autoregulatory pressure-flow relation was present in only a few areas. Alterations in PaC02 concentration did not affect the pressure-flow relation at low perfusion pressures, whereas at normal or above normal values, hypercapnia increased CBF considerably (p < 0.001). CBF was not affected by the anaesthetic (isoflurane or sevoflurane) or dose (MAC 0.3-1.2) used.

Part II. Perioperative and postoperative complications itcluded: circulatory instability (10%), arrhythmias (5%), abnormalities of coagulation, need for blood transfusions (47%), infections (8%), and puhnonary complications including infiltrates or oedema while on ventilatory support (27%). There was no correlation between the extent of hypothermia and any of the complications. However, there was a strong correlation (p < 0.001) between the incidence of complications and the severity of the underlying neurological disease as assessed by the Hunt and Hess score.

Conclusion Part I. The LDPI method was useful and relevant for measurement of cortical CBF in this experimental model. 'Classic' autoregulatory patterns were found only when all values sampled wereclustered together, whereas the autoregulatory capacity is often lacking at the local level in the cortex. Volatile anaesthestics (isoflurane and sevoflurane) in the doses 0.3 - 1.2 (MAC) did not affect the regulation of CBF in this model. Part II. Moderate hypothermia can be achieved within 1 hour of induction of anaesthesia and seems to be safe as far as the risks of perioperative and postoperative complications are concerned.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 76 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 897
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-31533 (URN)17332 (Local ID)91-85299-07-3 (ISBN)17332 (Archive number)17332 (OAI)
Public defence
2005-05-21, Berzeliussalen, Hälsouniversitetets bibliotek, Campus US, Linköpings Universitet, Linköping, 09:00 (Swedish)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-09-28Bibliographically approved

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