Thickness of the air-blood tissue barrier in infants.

The harmonic mean barrier thickness of the alveolar air-blood tissue barrier was measured in nine SIDS cases, six cases of unnatural death (three with asphyxiation, three without asphyxiation) and six cases showing interstitial pneumonia (IP, three cases with lymphomonocyte infiltration of alveolar walls, three cases with peribronchiolar infiltration). Approximately 550-600 measurements were carried out in each case using micrographs with a final magnification of 11,000. The Th values ranged between 0.37 micron and 0.39 micron in the SIDS group, in deaths due to asphyxiation and IP with a peribronchiolar type of infiltration, were lowest in the unnatural deaths without asphyxiation (0.32 micron) and highest in cases showing IP with alveoloseptal infiltration (0.44 micron). The differences between the groups were significant (H-test, Hcor = 5.927). Compared to "normal" unnatural deaths (Th = 0.32 micron), cases with interstitial cell infiltration of the alveolar septa showed a nearly 40% increase of the barrier thickness which indicates a corresponding decrease of the diffusion capacity. A decreased diffusion capacity can cause hypoxemia which could be an additional trigger mechanism in the death process.