Monitoring of nonlinear respiratory elastance using a multiple linear regression analysis.

The elastic pressure/volume (P/V) curve obtained by the multiple linear regression (MLR) technique using a new model, was compared with the quasi-static P/V points obtained by the rapid airway occlusion technique. Seven infants were studied during mechanical ventilation using a pressure controlled mode. The resistive pressure was subtracted from airway opening pressure, thus determining the elastance related pressure, which was then plotted against the volume to make an MLR-elastance curve. Quasi-static P/V curves of the rapid occlusion technique were constructed by plotting the different inspiratory and expiratory volumes against the corresponding values of the quasi-static airway pressure. The calculated MLR-elastance curves closely fit the experimental quasi-static P/V points obtained by the occlusion technique. There were, however, some discrepancies due to the viscoelastic behaviour of the respiratory system. Although slightly altered by these discrepancies, the multiple linear regression-elastance curves did fit the observed quasi-static pressure/volume characteristics for use in clinical practice. The multiple linear regression technique may prove to be clinically useful by continuous monitoring of respiratory system mechanics during mechanical ventilation.

Lung function in premature rabbits treated with recombinant human surfactant protein-C.

We report the activity of recombinant human surfactant apoprotein-C (rSP-C[Cys]2) and various phospholipids in a preterm rabbit model of respiratory distress syndrome (RDS). Mixtures of rSP-C(Cys)2 and certain phospholipids had similar activity (lung compliance and lung pressure-volume behavior) to rabbit surfactant in this model. The activity of rSP-C(Cys)2 was maximal at 1 mol% protein and varied significantly with the phospholipid composition. Chemically synthesized SP-C had similar activity to rSP-C(Cys)2. Deletion of six amino-terminal residues did not affect function. Substitution of cysteines and cysteine6 with adjacent serines (rSP-C[Ser]2) by site-specific mutagenesis minimized aggregation of rSP-C but did not affect activity. Palmitoylation of cysteine5 and cysteine6 in rSP-C (rSP-C[C16]2) did not enhance the activity of rSP-C(Cys)2. We conclude that bacterial expression is a practical source of functional SP-C, and that nonacylated forms of SP-C may be useful adjuvants to phospholipids in the treatment of RDS and possibly other forms of acute lung injury.

Epidemiologic application of pulsed-field gel electrophoresis to an outbreak of Campylobacter fetus meningitis in a neonatal intensive care unit.

An outbreak of nosocomial Campylobacter fetus meningitis occurred in a neonatal intensive care unit (NICU). Eight C. fetus strains were isolated from 4 infants with meningitis, the mother of the index patient and 2 infants who were asymptomatic intestinal carriers. The pulsed-field gel electrophoresis (PFGE) pattern with the restriction endonucleases Smal and Sall were found to be identical for the nosocomial C. fetus isolates, but the patterns were different from those of sporadic strains. These nosocomial strains were strongly suspected to be a single strain. The finding revealed that the index patient was infected by the mother, and that the outbreak developed from this patient by cross-infection. This is the first confirmed nosocomial C. fetus meningitis outbreak spread by cross-infection in a NICU.

Surfactant apoprotein A modifies the inhibitory effect of plasma proteins on surfactant activity in vivo.

Surfactant apoprotein A (SP-A) reduces the inhibitory effects of plasma proteins on the surface tension lowering properties of pulmonary surfactant in vitro. To test the effects of SP-A in vivo we administered a complete natural dog lung surfactant (DLS) containing apoproteins SP-A, SP-B, and SP-C, a butanol extract of DLS (DLSE) containing only apoproteins SP-B and SP-C, and DLSE supplemented with SP-A intratracheally to prematurely delivered rabbit pups in the presence of increasing amounts of human plasma. In the absence of plasma DLS and DLSE (100 mg/kg phospholipid) had comparable effects on lung mechanics (compliance during ventilation with a tidal volume of 6-7 mL/kg and quasi-static pressure-volume behavior) in this surfactant deficiency model. Plasma proteins in increasing amounts to a maximum protein concentration of 62.5 mg/mL had no effect on the response of the pups to DLS. In contrast, plasma added to DLSE in concentrations above 20 mg/mL significantly increased the peak inspiratory pressure (PIP) required to ventilate the pups with a tidal volume of 6-7 mL/kg, reduced the calculated total lung compliance, and decreased the deflation lung volumes. The inhibitory effects of plasma on DLSE were significantly less when SP-A was added to DLSE (5:1, phospholipid:SP-A, wt:wt). The addition of SP-A to DLSE in plasma restored the activity of the extract to levels comparable to complete DLS. These results suggest that plasma can interfere with surfactant function and that SP-A has a significant protective effect for surfactant against the inhibitory effects of plasma in vivo.

Prenatal diagnosis of congenital lipoid adrenal hyperplasia.

BACKGROUND: There are no published reports of prenatal diagnosis of congenital lipoid adrenal hyperplasia, which is the rarest form of congenital adrenal hyperplasia. CASE: Congenital lipoid adrenal hyperplasia was diagnosed prenatally based on the existence of one affected sibling in the family, the presence of an amniotic fluid cell karyotype of 46,XY, the appearance of normal female genitalia on ultrasonography, relatively low amniotic fluid concentration of 17 alpha-hydroxyprogesterone, low maternal plasma and urinary concentrations of estriol, and a positive response to the dehydroepiandrosterone sulfate loading test. CONCLUSION: Congenital lipoid adrenal hyperplasia can be diagnosed prenatally. Treatment in early infancy can lead to normal mental and physical development.

Nosocomial meningitis due to Campylobacter fetus subspecies fetus in a neonatal intensive care unit.

We experienced a nosocomial outbreak of Campylobacter fetus subspecies fetus (C. fetus) meningitis in a neonatal intensive care unit. A cluster of three infants developed meningitis approximately 1-1.5 months after the index patient was admitted. Two asymptomatic intestinal carriers of C. fetus were detected during the outbreak. Our experience indicates that C. fetus can cause nosocomial meningitis in neonates, and asymptomatic carriers may play a role in the transmission of the organism.

Variability of respiratory system compliance in mechanically ventilated infants.

We measured respiratory flow, volume by integrated flow, and airway pressure in four mechanically ventilated infants. Compliance of the respiratory system (Crs) was measured by the multiple occlusion method. Airway occlusion and release were achieved by a balloon in an occlusion valve between the endotracheal tube and a pneumotachometer, all connected in series with the respirator circuit. Values of Crs varied greatly due to changes in mean airway pressure (MAP). The Crs increased with the elevation of MAP on some occasions and decreased on others. Values of Crs also varied corresponding to different occlusion pressures for individual levels of MAP. Thus Crs changed continuously, even within a single respiratory cycle. The observed variability in Crs was explained by the following mechanism: a pressure-volume (P-V) loop of tidal ventilation moves its position within the pressure-volume diagram and changes shape due to variations of the ventilator settings. In some infants the lungs were ventilated in the range of the linear portion of the P-V diagram while in others they may have been ventilated on the flattened portion. Some patients had convex expiratory P-V curves even with low pressure swings during tidal ventilation.

Relationship between maturation of the skin and electrical skin resistance.

In 16 newborn infants (24 6-39 wk 6 days 830-3390 g) at ages between 0-70 days, the skin's electrical resistance was measured. Over 30 min we sequentially measured direct current resistance between two skin electrodes placed on the abdomen. The resistance was found to be low in very premature infants with gestation ages of 30 wk or less. It increased with both gestational age and postnatal age. In these infants, the resistance measured at 30 min during the first 4 days of life (3.4 +/- 0.3 K omega; mean +/- SD) was significantly less than that found at 20-70 days (8.8 +/- 1.2 k omega; p less than 0.001). The relationship between the infant's electrical skin resistance (y) and the gestational age (x) best fit the exponential formula: y = 7.42 X e0.24x X 10(-4) + 2.74. This formula shows that the electrical skin resistance increases exponentially during the last trimester. The measurement of electrical skin resistance is a quantitative method that can be utilized to evaluate the gestational age of infants.