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Cerebral microvascular changes are influenced by intracranial pressure (ICP) as well as mean arterial blood pressure (MAP). The mechanism maintaining blood flow despite changes in either pressure is called cerebral autoregulation. This mechanism is known to be impaired in many diseases, including traumatic brain injury and stroke. Maintaining adequate cerebral blood flow and autoregulation is known to improve long term patient outcomes. However, the influence on the microvasculature and autoregulation of blood pressure vs. fluid increase, hence intracranial pressure, is not well understood. Furthermore, while blood pressure changes can readily be measured, intracranial pressure sensors are invasive and there is a need to overcome this invasiveness. We have recently shown that changes in cerebral perfusion pressure, which is the difference between blood pressure and intracranial pressure, can be correlated to total hemoglobin concentration, as measured non-invasively with near-infrared spectroscopy (NIRS) in non-human primates. These results showed that non-invasive intracranial pressure monitoring should be possible by means of vascular changes as measured with NIRS. In order to quantify autoregulation and differentiate between blood pressure and fluid increase driven vascular changes, we collected data on non-human primates. The primates’ brains were cannulated to induce rapid changes in ICP. Exsanguination was performed to reduce blood pressure. Data was collected with a combined frequency domain NIRS (OxiplexTS, ISS Inc.) and diffuse correlation spectroscopy (DCS) system for measuring hemoglobin concentration changes as well as blood flow changes, respectively. We will present on the experimental implementation as well as data analysis for quantifying cerebral autoregulation.
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