Postmortem demonstration of intrapulmonary arteriovenous shunting

The measurement of the pressure required to drive a 2% solution of gelatin across the pulmonary vascular bed of a group of 49 infants dying suddenly at less than 44 weeks' postnatal age, has shown the presence of low pressure arteriovenous shunting in 30 cases (61%). Injection of polymethylmethacrylate beads in three cases has demonstrated that the vessels that form the shunts are up to 60 microns in diameter. The presence of vessels allowing shunting at pressures as low as 0.1 kPa (1 cm H2O) could severely compromise the gas exchange function of the lung.