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

Abstract

Pulmonary oxygen (O2) 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 O2 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 O2 uptake. Relative impedance changes during ventilation and apnoea were related to the corresponding tidal volumes. Regional O2 uptake was analysed as absolute values and as a ratio to regional ventilation in two regions of interest (ventral and dorsal). The global O2 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 O2 uptake was significantly higher in the ventral lung region, while the regional O2 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 O2 uptake concordant with a linear lung volume decrease during apnoea.