Optical remote sensing inside an inhomogeneous axisymmetric medium: the absorption field measurement.

It is shown that the absorption field inside an inhomogeneous, rotationally symmetric medium with a spatially variable refractive index can be reconstructed by means of a tomographic technique. The classic Abel transform is extended to non-Euclidean optical media. The optical behavior of such a medium is described and, provided that the product of the refractive index with the radial distance is a monotonic function, an exact inverse formula is found. Both a numerical and an analytical test on a phantom function is carried out to prove the exactness of this formula. In contrast, when the assumption of a monotonic function is not true, it is shown that the reconstruction problem becomes subdeterminate because of the presence of annular regions, known as blind areas, inside of which no curved path reaches an extremum. The spatial localization and the size of these regions are related to the extrema of the index of refraction times the radial distance.

Prone position may increase temperature around the head of the infant.

Recommendations to adopt the supine position were followed by a dramatic decrease of SIDS. But no explanation has been given for the association between SIDS and the prone position nor for its decrease in the supine position. We report data on an infant and a mannequin demonstrating an increase in temperature around the head in the prone position. A 4-month-old boy presented an acute life-threatening event related to temperature after febrile otitis despite treatment: 40.5 degrees C, heart rate 280 bpm with circulatory failure and cardiorespiratory arrest requiring resuscitation. There were no seizures. Blood and CSF cultures were negative. The course under antibiotics was favourable. On d 3, we measured temperature at several sites on and around the heat. Temperatures were higher in the prone than in the supine position in pericephalic areas: +1 degrees C (supracephalic), +2.5 degrees C (peritemporal), and +3.5 degrees C (submandibular). In a thermoregulated room, we used a mechanically ventilated mannequin of an infant. The prone position was also associated with an increase in temperature around the head: +3.3 degrees C (supracephalic), +1.8 degrees C (peritemporal), and +1.1 degrees C (submandibular). Changing from the supine to prone position thus increased temperature around the head (infant and mannequin). To our knowledge, this has not been reported before. SIDS is related to factors modifying temperature status and environment. Furthermore, evacuation of heat is mandatory for an infant. We think the increase in temperature around the head in the prone position is due to the absence of convective fluxes, and speculate it could impair thermolysis.

Convective heat transfer around an infant head.

Knowledge of heat and mass transfer between an infant and his environment is necessary to control hospital care conditions, or understand a pathology as Sudden Infant Death Syndrome (SIDS). This paper precises the particular importance of the heat transfer over the head and quantifies the influence of various parameters on natural convection heat transfer.