Page 73 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Study duration (Figure 1d)
Higher CPAP levels improve functional residual capacity at birth in preterm rabbits
Studies in each kitten continued for up to 10 min, with imaging occurring for as long as possible during this time. However, the study was stopped early and kittens were excluded from the analysis (or parts thereof) if the kittens developed pneumothoraxes or if there were technical problems. After completing the study, all animals were euthanized with sodium pentobarbitone (Somonopentyl, Kyoritsu Seiyaku Co., Tokyo, Japan) (>100 mg/kg). Does were injected intravenously with 6 mL 1:2 sodium pentobarbitone diluted in saline and kittens were injected intraperitoneally with 0.3 mL (sodium pentobarbitone).
Phase contrast X-ray imaging
Phase contrast X-ray imaging was used to image lung aeration and to quantitatively determine
lung gas volumes as described previously (12,35). The study was conducted in experimental
hutch 3 of beamline 20B2 in the Biomedical Imaging Centre at the SPring-8 synchrotron in
Japan. Due to the number of animals used in this study the experiment was extended over 3 two beamtimes. All images were acquired using a Hamamatsu ORCA Flash C11440-22C
detector coupled to a 25 μm gadolinium oxysulfide phosphor and a tandem lens system (effective pixel size 15.4 μm, 2048 × 2048 pixels). The synchrotron X-ray source was tuned to 24 keV with a source to detector distance of ~210 m. Data from 2017 (n=48) were collected with a sample to detector distance of 2 m, a frame rate of 10 Hz, and a 20 ms exposure time. Data collected in 2019 (n=29) had a sample to detector distance of 1.5 m, frame rate of 15 Hz, and 15 ms exposure time.
After each kitten was imaged flat and dark field images were collected and used for image correction prior to analysis. The lung gas volume was determined from each image using a power spectrum analysis.35 This technique relates the power spectrum of the lung to the lung gas volume via a calibration that is specific for each experimental set up, allowing the results from the two beamtimes to be combined. The methodology described by Leong et al. (35) was extended to include a normalization factor of the lung size of the individual kitten as this improves the calibration by correcting for natural animal variations. The power spectrum analysis is sensitive to rapid changes in intensity, so features such as the air-skin interface and an ECG lead were identified in the images and replaced with the mean pixel value.
As imaging data could only be collected when the hutch is locked and the X-ray beam is on, if the kittens required any manual intervention, the X-ray imaging had to cease to allow entry into the hutch. Imaging and breathing data were synchronized by recording the camera trigger along with the physiological data in LabChart (Powerlab, ADInstruments, Sydney, Australia).
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