Pulmonary function affects the quantification of rCBF by non-invasive xenon methods.

Area of Science:

• Neurology
• Medical Imaging
• Physiology

Background:

• Non-invasive xenon methods (133-xenon inhalation, Xe/CT, 133-xenon IV) are crucial for assessing regional cerebral blood flow (rCBF).
• These methods rely on arterial xenon concentration curves, often estimated from end-tidal curves, to calculate rCBF using the Kety equation.
• Cerebrovascular circulation diseases necessitate accurate rCBF evaluation.

Purpose of the Study:

• To investigate the impact of impaired pulmonary gas exchange on end-tidal and arterial xenon concentration curves.
• To quantify the deviations in calculated rCBF values when using end-tidal versus arterial xenon curves.
• To assess how pulmonary function influences the accuracy of non-invasive rCBF measurements.

Main Methods:

• Simultaneous measurement of end-tidal and arterial xenon concentration curves in nine anesthetized pigs.
• Induction of impaired pulmonary gas exchange (lung atelectasis, pulmonary artery occlusion).
• Computer simulations to calculate rCBF deviations using different input functions.

Main Results:

• Impaired pulmonary gas exchange significantly delayed the arterial xenon concentration curve relative to the end-tidal curve.
• Time constants for arterial curve delay varied with pulmonary condition (11.9s normal, 21s atelectasis, 19.7s occlusion).
• Computer simulations revealed statistically significant rCBF underestimation influenced by pulmonary gas exchange, rCBF levels, tissue partition coefficients, and inhalation protocols.

Conclusions:

• Deviations between end-tidal and arterial xenon curves markedly affect quantitative rCBF measurements.
• Accurate rCBF estimation using non-invasive xenon methods is compromised by impaired pulmonary gas exchange.
• Determining flow thresholds for cerebral infarction becomes problematic under compromised pulmonary function.