Investigation of the Effects of Hypocapnia upon Cerebral Haemodynamics in Normal Volunteers and Anaesthetised Subjects by near Infrared Spectroscopy (NIRS)

Abstract

The effect of alterations in arterial carbon dioxide tension (PaCO2) upon the cerebral blood vessels was first described in 1930 by Wolff and Lennox and quantified in 1948 by Kety and Schmidt. Since then many studies have investigated this relationship in terms of cerebral blood flow (CBF) (Novack et al 1953, Severinghaus et al 1967, Grubb et al 1974.) and volume (CBV)(Greenberg et al 1978, Artru 1984). CBV has not been as closely studied as CBF because of the paucity of measurement techniques. Since arterial PCO2 is frequently maintained at an artificially low level during anaesthesia for neurosurgery, to reduce intracranial pressure, it is of interest to measure the changes in cerebral haemodynamics as well as to describe the time course. 133Xenon washout and positron emission tomography (PET) are relatively invasive and can only provide measurements intermittently. Near infrared spectroscopy (NIRS) has been used to quantify the response of CBV to altered PaCO2 (CBVR) in newborn infants and is capable of measuring changes in CBV at 0.5 second intervals. The purpose of this study was to quantify both the extent and the duration of the haemodynamic response to an alteration in PaCO2 in anaesthetised patients and healthy volunteers.KeywordsCerebral Blood FlowCerebral Blood VolumeNear Infrared SpectroscopyArterial Carbon Dioxide TensionConscious SubjectThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.