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Background: Using an optical method based on tunable diode laser absorption spectroscopy, we previously assessed oxygen (O2) and water vapor (H2O) content in a tissue phantom of the preterm infant lung. Here we applied this method on newborn piglets with induced lung complications. Methods: Five mechanically ventilated piglets were subjected to stepwise increased and decreased fraction of inspired oxygen (FiO2), to atelectasis using a balloon catheter in the right bronchus, and to pneumothorax by injecting air in the pleural cavity. Two diode lasers (764 nm for O2 gas absorption and 820 nm for H2O absorption) were combined in a probe delivering light either externally, on the skin, or internally, through the esophagus. The detector probe was placed dermally. Results: Calculated O2 concentrations increased from 20% (IQR 17−23%) when ventilated with room air to 97% (88−108%) at FiO2 1.0. H2O was only detectable with the internal light source. Specific light absorption and transmission patterns were identified in response to atelectasis and pneumothorax, respectively. Conclusions: The optical method detected FiO2 variations and discriminated the two induced lung pathologies, providing a rationale for further development into a minimally invasive device for real-time monitoring gas changes in the lungs of sick newborn infants. Impact: Optical spectroscopy can detect pulmonary complications in an animal model.Oxygen concentrations can be evaluated in the lungs.Presents a novel minimally invasive method to detect lung oxygenation and complications.Potential to be developed into a lung monitoring method in newborn infants.Potential for bed-side detection of pulmonary complications in newborn infants.

A technique for measuring oxygen concentration in the lungs of preterm infants is one of the latest advancements in neonatal care. It is called GAs in Scattering Media Absorption Spectroscopy (GASMAS) and enables non-invasive, bed-side monitoring of the lung function of our most fragile patients, preterm newborns. The technique is promising and its potential is now evaluated in preparation for clinical studies. This thesis work contains simulations performed on two newly developed 3D-printed models. One model is of the lungs with surrounding tissue and the other model is of the full chest region of a preterm infant. The lung model measurements concluded the GASMAS technique to measure oxygen concentration within 4 % for absorption pathlengths longer than 2 cm. The absorption pathlength was determined to be 20 % longer for the laser wavelength of 761 nm in comparison to 820 nm due to more scattering in the liquid tissue phantom. The measurements of the infant model concluded the most preferable laser and detector positions to be a geometry from the armpit to the chest where oxygen concentration could be determined within 2 percentage points for an absorption pathlength of 10 cm. An opportunity of measuring in-vivo on a three week old baby was also made possible where oxygen could be detected for the earlier mentioned geometry of armpit to chest. Even though the detected signal for the in-vivo tests was weak and the detected absorption pathlength too short for reliable oxygen concentration estimation to be made at this time, the results of this thesis further heightening the anticipation of GASMAS for lung monitoring to advance from laboratory proven to being verified in a clinical study., Babies born preterm are among our most vulnerable patients. Their organs are not yet fully mature and the risk is high for diseases leading to complications to stretch all the way into adult life. The lungs are among the more sensitive organs and breathing aid is important to ensure a healthy growth of the baby. Even though X-rays are known to be harmful, the neonatal care of today uses chest X-ray as a standard method of examining the lung function. A promising new technology, originating from Lund University, can possibly eliminate X-ray examination of preterms by instead analyzing the absorption of light in the lungs to monitor its functionality. It is called GASMAS, GAs in Scattering Media Absorption Spectroscopy, and can with smart measurements of the very specific light absorbed by the oxygen molecules in the lungs determine and track the oxygen concentration in the lungs. All this without having to move the baby from its incubator and without any harmful X-rays. The technology has been proven in a laboratory setting, but it is not yet ready for measuring on patients in the hospital. This thesis work aims to verify the measurement system in a more application like setting. To start with, an anatomical 3D-printed model of a baby's torso was developed to scatter and absorb light similar to human tissue. Due to the resolution of the model where the optical properties of organs and tissue types are accounted, positioning of the measurement probes could be evaluated, as well as the measurement performance of the system. It is a most important step towards clinical use, and the results in this thesis has shown what system performance is to be expected in a more application like setting. The system has been verified to measure the concentration in an anatomical model and is now ready to move towards a clinical trial.