Microcirculatory Disorders in Infant Respiratory Distress Syndrome (Morphological Study)

The purpose of the study is to evaluate morphological changes in lung vessels of preterm infants with the infant respiratory distress syndrome (IRDS).

Material and Methods. Case history records and postmortem examination protocols of 70 preterm infants who died because of severe respiratory compromise as a result of IRDS were analyzed. All newborns were divided into three groups: the IRDS group included 25 (35.7%) infants who died due to IRDS (no surfactant); the Curosurf group was composed of 26 (37.2%) infants who received an exogenous surfactant Curosurf as a part of a complex therapy; the Surfactant BL group included 19 (27.1%) infants receiving Surfactant BL. Histological and morphometric examinations of lung vessels were performed. The Kernogan index calculated as the ratio between the lumen diameter and the wall thickness was determined.

Results. The arterial bed of newborns in the IRDS and Curosurf groups was composed of vessels having up to several μm in diameter. Larger arteries (51—100 μm in diameter) and arteries of more than 100 μm in diameter are distributed uniformly and comprise 1/3 of the total number of visualized vessels. The invert correlation of the arterial vascular bed was typical for the infants in the Surfactant BL group: arteries of 50 μm in diameter comprise 30% of all vessels, and arteries of more than 100 μm in diameter prevail. The venous bed of newborns consisted mainly of vessels having less than 50 μm in diameter. The greatest changes in the arterial wall thickness (ТСА) are typical for vessels with a total diameter of more than 51 μm. In babies of the IRDS group, the greatest (ТСА) changes were typical for arteries of 51—100 μm in diameter. Changes in arterial walls (>101 μm) were typical for the Surfactant BL group. Unlike other groups, in the Curosurf group, no significant changes in the parameters under the test were found (P>0.05). In this group (as compared to IRDS and Surfactant BL groups), there were minimal changes in vein characteristics and the minimal venous wall thickness (ТСv) (>100 μm in diameter). The Kernogan index for veins with small diameter was minimal.

Conclusion. Evaluation of the microcirculatory bed of lungs in IRDS patients is an urgent problem because the pulmonary gas exchange impairment in preterm infants is primarily caused by circulatory and microcirculatory disorders of various degrees of severity that result from anatomic and functional immaturity of the lung micro circulatory bed. In cases of unfavorable outcomes, dilation of arterial and venous lumen and vascular wall thickening might be considered as principal signs of microcirculatory disorders. Surfactants affect changes in the diameter of lumen of lung vessels, especially those with a diameter more than 50 μm, presumably improving the blood supply of the lungs. Minimal changes of tested parameters were typical for newborns on Curosurf versus IRDS and Surfactant BL groups of infants.

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