Trial Lecture – time and place
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Adjudication committee
- First opponent: Associate Professor Caroline A. Rickards , UNT Health Science Center, Texas, USA
- Second opponent: Professor Eirik Skogvoll, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology
- Third member and chair of the evaluation committee: Professor Leiv Arne Rosseland, Faculty of Medicine, University of Oslo
Chair of the Defence
Professor II Jo Kramer-Johansen, Faculty of Medicine, University of Oslo
Principal Supervisor
Associate Professor Maja Elstad, Faculty of Medicine, University of Oslo
Summary
Cerebral blood flow (CBF) is regulated by several overlapping mechanisms to ensure adequate nutrient and oxygen supply to the brain. Cerebral metabolism, arterial partial pressure of carbon dioxide (PaCO2) and mean arterial blood pressure (MAP) are important regulators. In the clinical setting, changes in cerebral perfusion may result in brain damage. We assessed CBF response to hypovolemia (lower body negative pressure, LBNP) and positive pressure ventilation (PPV); the role of the respiratory sinus arrhythmia in CBF regulation; CBF response and dynamic cerebral autoregulation during isometric handgrip and head-down tilt; CBF changes during laparoscopic surgery and pneumoperitoneum. Healthy volunteers and day-surgery patients were recruited. Blood velocity in the internal carotid artery (ICA) and cardiorespiratory variables were recorded. The ICA diameter was used to calculate ICA blood flow. Non-parametric statistics, mixed-models and frequency analyses (transfer function and wavelets) were used. Cardiac output (CO) reductions (LBNP) led to CBF reductions despite preservation of mean arterial blood pressure (MAP). In addition, PPV led to a reduction in respiratory sinus arrhythmia and an increase in respiration-related ICA blood flow variability. During laparoscopy, CBF was reduced in response to MAP and CO reductions. Such a reduction in cerebral perfusion may predispose more fragile patients to cerebral ischemia. CBF did not change despite CO and MAP elevations during isometric handgrip and head down tilt. Dynamic cerebral autoregulation was not disturbed by submaximal isometric exercise or head-down tilt despite the sustained cardiovascular responses to exercise. Cerebral circulation may thus compensate for increases in CO, but not completely for CO reductions. Respiratory sinus arrhythmia may act as a short term regulatory mechanism that minimizes ICA blood flow variability.
Additional information
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