The pathophysiology of meconium aspiration syndrome(MAS) is related to mechanical obstruction of the airways and to chemical pneumonitis. Meconium is also suggested to cause functional deterioration of pulmonary surfactant. Recent studies have reported that meconium inhibits the physical surface properties of pulmonary surfactant, and that administration of exogenous surfactant may provide therapeutic benefits in animal models or infants with respiratory distress due to MAS. To assess the effects of meconium on physical surface properties, especially the changes on the air-liquid interface and hypophase of pulmonary surfactant in vitro, we studied the following findings; a) the surface spreading rate(SSR) and the surface adsorption rate(SAR), b) the viscosity, c) the electron microscopic changes, on a series of mixtures with various concentrations of lyophilized human meconium and Surfactant-TA(SurfactenTM). The human meconium has significantly increased the surface tension of SSR and the viscosity of pulmonary surfactant, but had decreased the surface pressure of SAR of surfactant, and changed the electron microscopic findings of surfactant. We have concluded that these findings support the concept that meconium-induced surfactant dysfunction may play a role in the pathophysiology of MAS.
Human ; Infant, Newborn ; Meconium/*metabolism ; Pulmonary Surfactants/*metabolism

We developed a new method for an objective assessment of the meconium content in amniotic fluid. By establishing a standard scale through a serial dilution of a known amount of meconium into the amniotic fluid, we developed a new method 'mecometer 'that can objectively measure the meconium content in meconium-stained amniotic fluid samples. The objectivity and reliability of this mecometer were verified by 300 student volunteers. At least 70% of the volunteers could objectively measure and digitally describe the meconium content in meconium-stained amniotic fluid samples. We believe our newly developed mecometer is a very simple, reliable, and portable method, not requiring any instruments.
Amniotic Fluid/*metabolism ; Densitometry/methods ; Humans ; Infant, Newborn ; Meconium/*metabolism

OBJECTIVEThis study examined the changes of regional cerebral oxygen saturation (rSO2) by noninvasive near infrared spectrophotometry in neonates with meconium aspiration syndrome (MAS).

METHODSSeventy-three full neonates with MAS were divided into three groups by respiratory symptoms: asymptomatic group (group 1, n=38), common group (group 2, n=28) and severe group (group 3, n=7). Near infrared spectrophotometry was used to measure the cerebral rSO2 on days 1, 3, 5 and 7 after birth. Thirty healthy full-term newborns served as the Control group.

RESULTSThe cerebral rSO2 of group 1 decreased significantly compared with that of the Control group between days 1 and 3 (P < 0.05). The cerebral rSO2 of group 2 or group 3 was significantly lower than that of group 1 and the Control group on days 1, 3 and 5 (P < 0.05). The MAS patients with mild hypoxic-ischemic encephalopathy (HIE) had significantly higher brain rSO2 levels than those with medium or severe HIE on days 2, 3 and 5 (P < 0.05).

CONCLUSIONSThe cerebral rSO2 decreased in neonates with MAS. The values for rSO2 correlated with the severity of HIE in MAS patients.

Brain ; metabolism ; Female ; Humans ; Hypoxia-Ischemia, Brain ; metabolism ; Infant, Newborn ; Male ; Meconium Aspiration Syndrome ; metabolism ; Oxygen ; metabolism ; Spectroscopy, Near-Infrared

OBJECTIVETo evaluate effects of inhaled nitric oxide (iNO) on the expression of lung neutrophil adhesion molecule CD(11b) in experimental meconium aspiration pneumonia treated with conventional mechanical ventilation under room air or 100% O(2).

METHODSRabbits were randomly allocated to 10 groups (n = 60), 6 of each group. Control or meconium aspiration pneumonia model groups were inhaled with room air or 100% O(2). Six treatment groups were treated with continuous NO inhalation at the doses of 6 x 10(-6), 10 x 10(-6) and 20 x 10(-6), respectively for 12 hours under room air or 100% O(2). The ratio of wet/dry (W/D) lung weight, alveolar septal width (ASW), myeloperoxidase (MPO) activity and lung injury score were measured. The expression of CD(11b) in neutrophils of the bronchoalveolar lavage fluid (BALF) was detected with flow cytometry.

RESULTSAfter 12 hours ventilation, the oxygenation was maintained better in treatment groups under different O(2) concentrations than that in model groups. Inflammatory evidence was found in lungs from all the model groups and treatment groups, which was characterized by serious inflammatory cell infiltration in alveolar space and hyaline membrane formation. The lung inflammation was decreased in all groups with nitric oxide inhalation. The ratio of W/D lung weight and ASW among different groups had no significant difference. MPO activities were significantly decreased in groups treated with 10 x 10(-6) and 20 x 10(-6) iNO compared with the model groups [with the concentration of 21% O(2), (1.8 +/- 0.2) U/g vs (4.4 +/- 0.5) U/g and (2.0 +/- 0.1) U/g vs (4.4 +/- 0.5) U/g;with the concentration of 100% O(2), (1.7 +/- 0.4) U/g vs (2.8 +/- 0.5) U/g and (1.4 +/- 0.3) U/g vs (2.8 +/- 0.5) U/g, P < 0.05, respectively]. MPO activities in the 20 x 10(-6) iNO group under 100% O(2) were significantly reduced compared with those under 21%O(2) [(1.4 +/- 0.3) U/g vs (2.0 +/- 0.1) U/g, P < 0.05]. Nitric oxide inhalation with the doses of 10 x 10(-6) and 20 x 10(-6) significantly decreased the expression of CD(11b) (MFI) in neutrophils of the BALF compared with the expressions in model groups without NO treatment (with 21% O(2), 121 +/- 20 vs 392 +/- 204 and 112 +/- 30 vs 392 +/- 204; with 100% O(2), 113 +/- 24 vs 293 +/- 65 and 102 +/- 14 vs 293 +/- 65, P < 0.05, respectively). Under the same iNO dose (10 x 10(-6) or 20 x 10(-6)) no statistic difference was found between groups of different inspired oxygen concentrations (21% and 100%).

CONCLUSIONSInhaled nitric oxide with the doses of 10 x 10(-6) to 20 x 10(-6) could significantly down-regulate the CD(11b) expression in neutrophil of the BALF and reduce the neutrophil sequestration and MPO activity in rabbit lungs, which may decrease the lung inflammation process in meconium aspiration pneumonia.

Administration, Inhalation ; Animals ; CD11b Antigen ; analysis ; Disease Models, Animal ; Female ; Flow Cytometry ; Lung ; drug effects ; metabolism ; pathology ; Male ; Meconium ; chemistry ; Neutrophils ; chemistry ; pathology ; Nitric Oxide ; administration & dosage ; therapeutic use ; Peroxidase ; analysis ; Pneumonia, Aspiration ; etiology ; physiopathology ; therapy ; Rabbits ; Random Allocation

In the present study, the relationship among iron-availability, antibacterial activity, role of meconium as an iron source and the activity of bacterial iron-uptake system (IUS) for bacterial growth in amniotic fluid (AF) were investigated. Staphylococcus aureus ATCC 6538 and its streptonigrin-resistant (SR) mutant with defective IUS were used as the test strains. The growth of S. aureus in AF was stimulated dosedependently by addition of meconium. Bacterial growth stimulated by meconium was re-inhibited dose-dependently by addition of iron-chelator, dipyridyl and apotransferrin. Iron concentration was correlated with the meconium content in AF (r(2)= 0.989, p=0.001). High-affinity IUS of S. aureus was expressed only in AF but not in AF with meconium. The growth of SR strain was more retarded than that of the parental strain in the iron-deficient brain heart infusion (ID-BHI), clear AF and AF containing apotransferrin. The retarded growth of both strains in the ID-BHI and AF was recovered by addition of holotransferrin, hemoglobin and FeCl3. Taken together, the antibacterial activity of AF is closely related with low iron-availability. Bacterial growth in AF considerably depends on the activity of bacterial IUS. Meconium acts as one of the exogenous iron-sources and thus can stimulate bacterial growth in AF.
Amniotic Fluid/*microbiology ; Antibiotics, Antineoplastic/pharmacology ; Chelating Agents/pharmacology ; Dose-Response Relationship, Drug ; Female ; Ferric Compounds/pharmacology ; Human ; Iron/*metabolism ; Ligands ; Meconium/metabolism ; Mutation ; Pregnancy ; Pregnancy Trimester, Third ; Protein Binding ; Staphylococcus aureus/metabolism ; Streptonigrin/pharmacology ; Support, Non-U.S. Gov't ; Time Factors