Janet H. Murphy

Lung Development in the Fetal Primate Macaca Nemestrina. III. HMD

Summary: Delivery of M. nemestrina at 80% of normal gestation provides a population of neonates at high risk for hyaline membrane disease (HMD). The diagnosis of HMD was made by the presence of reticulogranular densities and air bronchograms on chest radiographs. Patchy atelectasis was seen in the lungs of animals assigned by clinical and radiographic criteria to the HMD group and not in the normal lungs of animals matched for gestational and postnatal age. Total phospholipid and phosphatidylcholine in whole lung, airway lavage fluid, and surface-active materials were lower in animals with HMD. Amniotic fluid L/S ratios were lower in the group that developed HMD. Pressure-volume measurements indicated decreased distensibility and unstable terminal air spaces in the HMD group. Alveolar-arterial oxygen pressure differences were greater in animals with HMD. There were no differences between HMD and normal groups in body weight, lung weight, percent dry lung weight, gestational age, and postnatal age at death. This primate species, subjected to premature delivery, is a suitable animal model of HMD in human neonates.Speculation: An animal model of hyaline membrane disease (HMD) in a primate species is of interest to investigators of developmentally related pulmonary disorders. More complete knowledge of abnormalities in pulmonary function in HMD will contribute to development of both preventive and therapeutic measures and affords the opportunity to determine risks and benefits of such treatments to the fetus and newborn.

Postnatal changes in lung phospholipids and alveolar macrophages in term newborn monkeys

In order to better understand the postnatal sequence of surfactant secretion and establishment of the alveolar macrophage (AM) population in newborn primates, healthy Macaca nemestrina monkeys were sacrificed during fetal life at term gestation (n = 5), or at 2 days (n = 5) or 3-4 weeks (n = 5) after term vaginal delivery. Excised lung tissue and left lung lavage were analyzed for phospholipid (PL) content, surface active material (SAM) extract, PL components, surface activity, pressure-volume characteristics, and AM number. Compared to term fetal animals, 2 day old term newborn monkeys were found to have a several-fold increase in lavage PL and SAM, and this was associated with greater maximal lung volume and drier lungs, but not improved deflation stability. During the subsequent 3-4 weeks of life, a 42% reduction in lung tissue stores of PL and SAM, and an 87% reduction in lavage PL and SAM were noted. Despite these major changes in quantity, there were relatively minor changes in the composition of the PL synthesized and released. The reduced quantity of SAM in the 3-4 week old animals led to a small decline in deflation stability. The several-fold increase in lavage PL and SAM during the first 2 days of life was accompanied by a 33-fold increase in AM; there was an additional 4-fold increase in AM number by 3-4 weeks of age. The abundance of lavage surfactant at 2 days of age may play a role in the influx of AM.

Effects of PEEP and tolazoline infusion on respiratory and inert gas exchange in experimental meconium aspiration

Meconium aspiration syndrome often produces respiratory failure in the neonate. We utilized the multiple inert gas elimination technique to study the effects on respiratory and inert gas exchange of the application of positive end expiratory pressure or continuous infusion of tolazoline HCl. The application of PEEP, with the optimal level of PEEP defined for each animal, produced a decrease in AaDO2 and pulmonary shunt, without an increase in blood flow to low VA/Q areas, or an increase in dead space. Tolazoline infusion, at 2 mg/kg/hour, had no apparent effect on AaDO2 or shunt, or magnitude of low VA/Q regions. Tolazoline therapy was associated with an increase in heart rate and a decrease in systemic blood pressure. We conclude that immediate postaspiration application of PEEP, but not of tolazoline, will diminish pulmonary shunt without creating low VA/Q areas, and therefore will improve gas exchange in MAS.

Lung development in the fetal primate Macaca nemestrina. I. Growth and compositional changes.

Summary: This report relates lung growth and composition to body growth in 23 fetal and 2 newborn Macaca nemestrina (pigtail monkey) during the last third of gestation.There was a linear relationship (r = 0.883) between gestational age and crown-rump length over the age range studied, and length increased by 1.18 mm/day. The average increment in body weight was 5.1 g/day.Total lung weight increased in a manner similar to total body weight (wet lung weight = 1.91 ± 0.44% of total body weight). Lung weight increased by 109 mg/day until term. A correlation of 0.849 was observed between lung weight and gestational age. There was a linear increase in lung dry mass with increasing gestational age (9 mg/day, r = 0.701) and with increasing body weight (1.38 mg/g body weight, r = 0.691). The dry weight of fetal lung accounted for 10.8 ± 2.9% of total lung weight throughout the gestational period studied. Dry weight increased to 22–23% after birth.There was a decrease in protein and DNA per g wet weight of lung with advancing gestational age. Increases in total protein, DNA, and hemoglobin reflected the increasing size of the lung. Because gestational age is correlated with body size, body weight, and lung weight, total lung protein and total lung DNA should not provide any great advantage over total lung weight as a denominator for quantitative estimates of changing cell constituents with growth. Protein and DNA do not increase with gestational age when plotted per g dry lung. DNA per g dry lung tends to decrease with maturity, suggesting an increase in cell size.Speculation: Whereas fetal lung growth is linearly related to body growth over the last third of gestation, both lung and body size show wide variance at any given age. Constituents of lung increase in a manner which varies from general lung or body growth and are best compared when expressed in relation to a common denominator such as a unit of lung dry weight.

Lung Development in the Fetal Primate, Macaca nemestrina. II. Pressure-Volume and Phospholipid Changes

Summary: The biological and physiologic maturation of the lung in the primate Macaca nemestrina (pigtail monkey) from 107 days of gestation through term is the subject of this report. Total lung volume increased approximately 100% during the last 20% of gestation (Fig. 1). The increase from 30% to 85% of total lung volume at a deflation pressure of 10 cm H2O indicates a marked change in lung stability during the last 30–40 days of gestation (Fig. 2). Lung phospholipid per g dry weight of lung more than doubles during the last 20% of gestation (Fig. 3). This increase in phospholipid is due almost entirely to an increase in lecithin, and surface active material (SAM) lecithin accounts for the major part of this increase (Figs. 4 and 5). The increases in total lung and SAM lecithin parallel but precede the increase in lecithin in amniotic fluid (Fig. 6). As lung SAM increases the amniotic fluid lecithin to sphingomyelin ratio also increases (Fig. 7 and Table 1). Low ratios of lecithin to protein in SAM are found before 135 days of gestation. Subsequently, the amount of lecithin increases and, although protein also increases, the ratio increases 4-fold (Fig. 8). The amount of lung required to reduce surface tension of 1 cm2 to 12 dynes tended to decrease with advancing gestational age (Fig. 9 and Table 1). Parallel studies of airway generation demonstrate a similarity to the human fetal lung. Thus, the structural, compositional, and physiologic changes described in our studies strongly support the use of the fetal monkey for studies of developmentally related disorders of the human lung.Speculation: Biochemical and functional maturational changes in the fetal M. nemestrina indicate its suitability for studies of develop-mentally related pulmonary disorders of the human. Premature delivery by cesarean section between 130 and 140 days should provide a satisfactory homolog for hyaline membrane disease.

Acute changes in vasoactive lipid mediators in experimental hyaline membrane disease

Endothelial release of the arachidonate derivative PGI2 may be increased in response to cyclic lung stretching. We therefore sought to determine if the stable metabolite of PGI2, 6-keto-PGF1 alpha, would be found in increased quantities in primates ventilated with conventional mechanical ventilation (CMV) compared to treatment with high frequency oscillatory ventilation (HFOV). We also sought to determine if other membrane-derived vasoactive substances such as LTC4, PAF and TXB2 would be elevated in plasma and lung tissue of animals developing hyaline membrane disease (HMD) and if the levels would correlate with the severity of the respiratory distress. Twenty prematurely delivered monkeys were treated with either CMV or HFOV from the first breath after Cesarean delivery until sacrifice at 6 h of age. We found a significant increase from birth to 5 min and from 5 min to 5 h in 6-keto-PGF1 alpha, and a significant increase from 5 min to 5 h in TXB2. We found a significant decline from cord blood to 5 min of LTC4, without further change by 5 h. PAF was present in all plasma samples but showed no upward or downward trend. There was no difference in the 5-h plasma level or in the lung homogenate level of any of the lipid mediators between the two types of assisted ventilation. There was no correlation between any lipid mediator level and severity of the HMD, as measured by gas exchange, radiographic or histologic criteria, when assessed by each ventilator group alone or with both groups combined. We conclude that the immediate postnatal increases in TXB2 and PGI2 and decrease in LTC4 are not altered substantially by use of HFOV.

The immature monkey as a model for studies of bronchopulmonary dysplasia

The monkey is a potential model for BPD since there is considerable background information on the normal-developing lung, the prematurely delivered infant is viable, HMD can be produced, the infant is large enough to permit physiologic measurements, and it should be possible to test the effects of positive pressure, oxygen, and pharmacologic agents. Clearly further information is needed on the cellular and subcellular changes occurring during the acute and recovery stages of HMD. The monkey has already proven to be of value in this inquiry. Studies on mechanisms of altered lung repair by various injurious agents are needed, and will require an animal model as well as in vitro systems. Basic understanding of the pathogenesis of bronchopulmonary dysplasia with establishment of the relative importance of the contributing factors should help in our efforts to prevent or minimize chronic lung disease in the newborn infant.

1017 TIME OF INITIATION OF CPAP IN HMD

The effects of the time of application of CPAP on the mortality and morbidity of HMD were examined in 36 infants in 3 weight groups (<1200, 1201-1800 and ≥1801 gms). Infants were randomly assigned by weight group to early (E) or late (L) CPAP by nasal prongs when PaO2≤50 mgHg while breathing in FIO2=0.4 or 0.7, respectively. Results are shown below:There were no differences in mortality, need for artificial ventilation, time spent in an FIO2>0.3 or >0.7 or in the incidence of air leak or chronic lung disease. Eleven of nineteen infants assigned to late CPAP never required an FIO2≥0.7 and did not receive CPAP. The present study suggests that the early application of CPAP offers no measurable advantage over the late application of CPAP in the treatment of mild HMD.

Antenatal Glucocorticoid Administration: Effects on Oxygen-Hemoglobin Affinity and Hemoglobin Levels in Experimental Hyaline Membrane Disease

Dexamethasone or saline was administered in a randomized fashion to pregnant Macaca nemestrina for 3 days prior to preterm abdominal delivery. The steroid-treated animals demonstrated a greater hemoglobin concentration and a greater mean corpuscular hemoglobin concentration in cord blood. There was no difference between the groups in mean P50 in cord blood. The infants of steroid-treated animals had less frequent and less severe hyaline membrane disease. We conclude that antenatal steroid administration ameliorates postnatal respiratory distress without inducing changes in P50 and with only a small change induced in cord blood hemoglobin.

SURFACE ACTIVE MATERIAL |[lpar]|SAM|[rpar]| COMPLIANCE CHANGES DURING REACOVERY FROM EXPERMENTAL HYALINE MEMBRANE DISEASE |[lpar]|HMD|[rpar]|

It is not known whether recovery from HMD begins in spite of a deficiency of SAM or only after return to some critical value. Eight of 12 M. nemestrina primates delivered at 80% of normal gestation developed HMD and were sacrificed at defined stages in their recovery. Postmortem deflation stability (%total lung capacity [TLC] at P=10cm H2O pressure) and diphosphatidylcholine (DPC) quantities in unlavaged lung tissue and in bronchoalveolar lavage were compared to controls as well as four healthy term 3-4 week old infants.We conclude that 1) the disparity between tissue and lavage DPC quantities in animals with HMD suggests a problem in release of SAM rather than tissue production and 2) clinical recovery and improvement in deflation stability occur despite DPC levels that are quite low compared to control but similar to older infants. (1Supported by NIH#HL19187 and #RR00166, 2Fellow of American Lung Association)