Automatic end-tidal gas sampling system for non-invasive rCBF measurements.

Non-invasive measurements of regional cerebral blood flow (133Xe inhalation or IV injection) require knowledge of the arterial 133Xe concentrations, which is usually estimated from the end-tidal expiration. An automated sampling system is described for measurement of end-tidal 133Xe concentration that can be used in both spontaneously breathing and mechanically ventilated patients. A comparison is made between the automatic sampling system and manual measurements performed on a continuous gas sample.