![]() ![]() They concluded that the glymphatic circulation was unlikely, as the high resistance of the pathway would prevent sufficient flow. Recently, the resistance of the glymphatic system under normal conditions was estimated by Faghih & Sharp. This potential link, between infusion tests and the glymphatic system, has not yet been explored. Thus, such tracer experiments may in fact be viewed as infusion tests. In these experiments, tracers are typically infused in the CSF in rodents at a rate of 0.34–2 μL/min, with a resulting pressure increase of 0.1–2.5 mmHg. The main bulk of evidence for the glymphatic pathway has been established via in-vivo rodent experiments. The glymphatic pathway continues through AQP-4 channels, through extracellular spaces (ECS) and eventually reaching the venous PVS. In the glymphatic circulation, CSF moves through the subarachnoid space (SAS) along arteries and dives into the brain along arterial paravascular spaces (PVS). Glymphatic dysfunction has been hypothesized to contribute to development in neurodegenerative disorders, traumatic brain injury and stroke. Therefore, this waste clearance system has been named the glymphatic system, where the “g” indicates that glial cells play an important role. The purpose of this circulation is to clear solutes from deep inside the brain, thus taking the role of the lymphatic system within the central nervous system wich is abscent of lymphatic vessels. Here, paravascular spaces, extensions of the Virchow–Robin spaces, play an active role in brain-wide CSF circulation in conduits that runs in parallel with the vasculature. More recently, an alternative CSF circulation has been proposed – the glymphatic circulation. The main outflow route is assumed to be the arachnoid granulations (AG) in accordance with the traditional view of the third circulation where CSF is produced in the choroid plexus and absorbed through AG as proposed by Cushing in 1925. The procedure has a well developed theoretical foundation as well as corresponding mathematical models (see for an overview). Typically, a constant infusion rate of 1.5 ml/min results in an ICP pressure increase by around 10–25 mmHg, and the calculated R out parameter is commonly used as a supplementary parameter in the selection of patients for shunt surgery. During infusion of artificial cerebrospinal fluid (CSF), intracranial pressure (ICP) is monitored, and a CSF outflow resistance ( R out) is calculated. Infusion testing is a standard procedure to assess whether patients with normal pressure hydrocephalus (a type of dementia) would benefit from shunt surgery. ![]()
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