Measurement of regional pulmonary oxygen uptake--a novel approach using electrical impedance tomography

Pulmonary oxygen (O(2)) uptake during apnoea results in a fall in lung volume. Given that electrical impedance tomography (EIT) provides reliable data on regional lung volume changes we hypothesized that EIT could be used to measure regional O(2) uptake. A total of 12 lung healthy supine patients were studied. EIT measurements were performed during volume-controlled mechanical ventilation followed by apnoea with the endotracheal tube clamped at end-expiration. Lung function parameters were assessed by spirometry. A device for breath-by-breath monitoring metabolic gas exchange was used to measure global O(2) uptake. Relative impedance changes during ventilation and apnoea were related to the corresponding tidal volumes. Regional O(2) uptake was analysed as absolute values and as a ratio to regional ventilation in two regions of interest (ventral and dorsal). The global O(2) uptake measured by EIT was 208 ± 79 ml min(-1) corresponding to the values obtained by metabolic gas exchange (259 ± 73 ml min(-1); Spearman correlation coefficient: 0.81, p = 0.02). Regional O(2) uptake was significantly higher in the ventral lung region, while the regional O(2) uptake/ventilation ratio showed no significant difference between the regions. In conclusion, our pilot study indicates that EIT holds substantial potential to detect global and regional pulmonary O(2) uptake concordant with a linear lung volume decrease during apnoea.