Assessment of radiant temperature in a closed incubator

In closed incubators, radiative heat loss (R) which is assessed from the mean radiant temperature [Formula: see text] accounts for 40–60% of the neonate’s total heat loss. In the absence of a benchmark method to calculate [Formula: see text]—often considered to be the same as the air incubator temperature—errors could have a considerable impact on the thermal management of neonates. We compared [Formula: see text] using two conventional methods (measurement with a black-globe thermometer and a radiative “view factor” approach) and two methods based on nude thermal manikins (a simple, schematic design from Wheldon and a multisegment, anthropometric device developed in our laboratory). By taking the [Formula: see text] estimations for each method, we calculated metabolic heat production values by partitional calorimetry and then compared them with the values calculated from [Formula: see text] and [Formula: see text] measured in 13 preterm neonates. Comparisons between the calculated and measured metabolic heat production values showed that the two conventional methods and Wheldon’s manikin underestimated R, whereas when using the anthropomorphic thermal manikin, the simulated versus clinical difference was not statistically significant. In conclusion, there is a need for a safety standard for measuring [Formula: see text] in a closed incubator. This standard should also make available estimating equations for all avenues of the neonate’s heat exchange considering the metabolic heat production and the modifying influence of the thermal insulation provided by the diaper and by the mattress. Although thermal manikins appear to be particularly appropriate for measuring [Formula: see text], the current lack of standardized procedures limits their widespread use

Development of the nasal cavity during infancy: A restrospective CT imaging study

Body: Rationale: Upper airway and nasal airflow resistance are significant in infancy, due to the fact that infants are nasal breathers in early life, and that obstructive nasal diseases are frequent at this age. Nasal flow resistance is closely determined by anatomy, which rapidly changes with growth. The goal of this study was to assess standardized measurements of the nasal cavity dimensions in the first 2 years of life. Methods: 34 head CT scans of infants aged 4.13±4.08 months (range: 0.07 to 19.4, 17 male, 17 female) available in the Amiens University Hospital Dept. of Radiology database were retrospectively analyzed. Infants with craniofacial deformities were excluded. Images were 3D reconstructed, axially oriented and the nasal cavity was segmented by density thresholding from nares to vocal cords. Surface areas of the piriform and choanal apertures were automatically computed in the coronal plane, in standardized positions based on bony reference points. Results:Piriform surface area measured (mean±SD): 54.3±13.8 mm2 (range: 29.1 - 83.9), and was significantly correlated to age (R=0.59, p<0.001), and height (R=0.57, p<0.001). Choanal aperture surface area: 81.3±28.1 mm2 (range: 38.0 – 164.7), and was significantly correlated to age (R=0.74, p<10-6), and height (R=0.71, p<10-5). Conclusions: These data suggest that the nasal cavity anterior and posterior apertures grow rapidly during the first 2 years of life, and that their dimensions are closely correlated to age and height. Further investigation will focus on how the anatomic growth of the nasal cavity in early life affects airflow resistance

Synchrotron Imaging Shows Effect of Ventilator Settings on Intrabreath Cyclic Changes in Pulmonary Blood Volume

Despite the importance of dynamic changes in the regional distributions of gas and blood during the breathing cycle for lung function in the mechanically ventilated patient, no quantitative data on such cyclic changes are currently available. We used a novel gated synchrotron computed tomography imaging to quantitatively image regional lung gas volume (Vg), tissue density, and blood volume (Vb) in six anesthetized, paralyzed, and mechanically ventilated rabbits with normal lungs. Images were repeatedly collected during ventilation and steady-state inhalation of 50% xenon, or iodine infusion. Data were acquired in a dependent and nondependent image level, at zero end-expiratory pressure (ZEEP) and 9 cm H2O (positive end-expiratory pressure), and a tidal volume (Vt) of 6 ml/kg (Vt1) or 9 ml/kg (Vt2) at an Inspiratory:Expiratory ratio of 0.5 or 1.7 by applying an end-inspiratory pause. A video showing dynamic decreases in Vb during inspiration is presented. Vb decreased with positive end-expiratory pressure (P = 0.006; P = 0.036 versus Vt1-ZEEP and Vt2-ZEEP, respectively), and showed larger oscillations at the dependent image level, whereas a 45% increase in Vt did not have a significant effect. End-inspiratory Vb minima were reduced by an end-inspiratory pause (P = 0.042, P = 0.006 at nondependent and dependent levels, respectively). Normalized regional Vg:Vb ratio increased upon inspiration. Our data demonstrate, for the first time, within-tidal cyclic variations in regional pulmonary Vb. The quantitative matching of regional Vg and Vb improved upon inspiration under ZEEP. Further study is underway to determine whether these phenomena affect intratidal gas exchange

Effect of nasal airway nonlinearities on oscillometric resistance measurements in infants

Oscillometric measurements of respiratory system resistance (R) in infants are usually made via the nasal pathways, which not only significantly contribute to overall R but also introduce marked flow (V')-dependent changes. We employed intrabreath oscillometry in casts of the upper airways constructed from head CT images of 46 infants. We examined oscillometric nasal resistance (R) in upper airway casts with no respiratory flow (R) and the effect of varying V' on R by simulating tidal breathing. A characteristic nonlinear relationship was found between R and V', exhibiting segmental linearity and a prominent breakpoint (V') after log-log transformation. V' was linearly related to the preceding value of end-expiratory volume acceleration (V″; on average  = 0.96, < 0.001). R depended on V', and R at end-expiration (R) showed a strong dependence on V″ in every cast ( = 0.994, < 001) with considerable interindividual variability. The intercept of the linear regression of R versus V″ was found to be a close estimate of R. These findings were utilized in reanalyzed R data acquired in vivo in a small group of infants ( = 15). Using a graphical method to estimate R from R, we found a relative contribution of V'-dependent nonlinearity to total resistance of up to 33%. In conclusion, we propose a method for correcting the acceleration-dependent nonlinearity error in R. This correction can be adapted to estimate R from a single intrabreath oscillometric measurement, which would reduce the masking effects of the upper airways on the changes in the intrathoracic resistance. NEW & NOTEWORTHY Oscillometric measurements of respiratory system resistance (R) in infants are usually made via the nasal pathways, which not only significantly contribute to overall R but also introduce marked flow acceleration-dependent distortions. Here, we propose a method for correcting flow acceleration-dependent nonlinearity error based on in vitro measurements in 3D-printed upper airway casts of infants as well as in vivo measurements. This correction can be adapted to estimate R from a single intrabreath oscillometric measurement