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

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