Dynamic compression of the cerebral vasculature induced by changes of pleural pressure during mechanical ventilation

Previously, the authors have reported that during normal tone the intracranial pressure (ICP) and arterial blood pressure (ABP) recordings are not similar and as the cerebrovasculature dilates the corresponding ICP and ABP recordings become progressively similar (see IEEE Trans. Biomed. Engng., vol 42, 1995; Acta Neurochirngica Supplementum 71, p. 285-8, 1998). Furthermore, estimates of pial venous blood flow reveal that flow during the expiration phase of ventilation was found to be uniformly higher than flow during inhalation flow for all states of vascular dilation. The purpose of this study was to develop a preliminary test of the premise that cyclic compression of the cerebral capillary bed and venules occurs during positive pressure ventilation and it causes the corresponding cyclic variation of the ICP baseline recording during normal tone. Furthermore, this cyclic compressional effect progressively reduces as tone is lost and correspondingly the cyclic variation of the ICP baseline recording becomes diminished. As a result the ICP recording becomes strongly correlated with the ABP recording. Preliminary analysis of pial venous blood flow characteristics and measures of anatomical changes of the pial vasculature during ventilation support the authors premise