engleski

Pulse pressure in regulation of intracranial fluid volume

Oncotic pressure of plasma proteins and hydrostatic pressure in capillary (Pc) and interstitial fluid (Pi)are regulators of filtration and reabsorption of water across the capillary wall as expressed in Starling equation. In this equation Pc and Pi are taken as avareged, constant values, which may not be justified. Passage of ions and various substances across the wall of cerebral capillaries is regulated and restricted so that osmotic pressure (oncotic is an extremely small part of it) is the main homeostatic regulator of the water shift from blood to brain interstitial fluid (ISF) and cerebrospinal fluid (CSF), and vice versa. However, these osmotic pressures on both sides of the capillary wall are the same so that they cancel each other. Hydrostatic pressures in ISF and CSF are the same and they show high systolic-diastolic cyclic change(pulse pressure). Furthermore, it was shown that the volume of 3H-water is absorbed across the capillary wall in brain vetricles due to hydraulic conductivity of the capillaries. On hte basis of these data we propose that CSF/ISF puls epressure is instrumental in absorption of fluid volume from CSF/ISF into venous capillaries during "CSF systole", while during "brain systole" water is filtered from arterial capillaries into ISF/CSF. Thus, we suggest that cyclic changes in pulse pressure exert fine tuning of intracranial fluid volume from second to second. Furthermore, it appears that Pc and Pi in Starling equation should not be taken as avareged, constant values since they change continuosly over systolic. diastolic cycle.

Starling's hypothesis; pulse pressure; intracranial fluid volume; CSF systole; brain systole

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