Maternal characteristics and mid-pregnancy serum biomarkers as risk factors for subtypes of preterm birth

OBJECTIVE

To examine the relationship between maternal characteristics, serum biomarkers and preterm birth (PTB) by spontaneous and medically indicated subtypes.

DESIGN

Population-based cohort.

SETTING

California, United States of America.

POPULATION

From a total population of 1 004 039 live singleton births in 2009 and 2010, 841 665 pregnancies with linked birth certificate and hospital discharge records were included.

METHODS

Characteristics were compared for term and preterm deliveries by PTB subtype using logistic regression and odds ratios adjusted for maternal characteristics and obstetric factors present in final stepwise models and 95% confidence intervals. First-trimester and second-trimester serum marker levels were analysed in a subset of 125 202 pregnancies with available first-trimester and second-trimester serum biomarker results.

MAIN OUTCOME MEASURE

PTB by subtype.

RESULTS

In fully adjusted models, ten characteristics and three serum biomarkers were associated with increased risk in each PTB subtype (Black race/ethnicity, pre-existing hypertension with and without pre-eclampsia, gestational hypertension with pre-eclampsia, pre-existing diabetes, anaemia, previous PTB, one or two or more previous caesarean section(s), interpregnancy interval ≥ 60 months, low first-trimester pregnancy-associated plasma protein A, high second-trimester α-fetoprotein, and high second-trimester dimeric inhibin A). These risks occurred in 51.6-86.2% of all pregnancies ending in PTB depending on subtype. The highest risk observed was for medically indicated PTB <32 weeks in women with pre-existing hypertension and pre-eclampsia (adjusted odds ratio 89.7, 95% CI 27.3-111.2).

CONCLUSIONS

Our findings suggest a shared aetiology across PTB subtypes. These commonalities point to targets for further study and exploration of risk reduction strategies.

TWEETABLE ABSTRACT

Findings suggest a shared aetiology across preterm birth subtypes. Patterns may inform risk reduction efforts.

Epithelial Na(+) channel (ENaC) expression in the developing normal and abnormal human perinatal lung

Impaired lung epithelial Na(+) channel (ENaC) activity at the time of birth results in respiratory distress. To investigate potential mechanisms, the ontogeny and cellular distribution of the alphaENaC subunit mRNA expression was studied in normal, immature, and abnormal (hypoplastic) human fetal lungs using nonradioisotopic in situ hybridization. Surprisingly, alphaENaC expression was detected at the embryonic stage of normal lung development (4 to 5 wk gestation) when expression was localized to the fetal lung bud epithelium. By late gestation, ENaC was expressed in the conductive and respiratory airway epithelium, serous cells, and the distal lung unit in an alveolar type II (ATII) epitheliumlike distribution. Significant alphaENaC expression was found in newborn lung diseases associated with respiratory distress. One explanation is that alphaENaC mRNA is constitutively expressed, and that activity is regulated, at least in part, at the post-transcriptional level. Alternative explanations are that the expression of the beta or gammaENaC subunits may be impaired in certain newborn lung diseases or that alternate Na(+) permeant channels or transporters are important to lung liquid absorption in humans at birth.

Modulation of aquaporin 4 and the amiloride-inhibitable sodium channel in perinatal rat lung epithelial cells

During the perinatal period, a dramatic reversal of lung transepithelial ion and water transport occurs that involves the amiloride-inhibitable Na+ channel (ENaC). Aquaporin (AQP) water channel proteins facilitate cell membrane water transport. We now report that AQP-4, localized to basolateral membranes of airway epithelial cells, increases its mRNA expression in developing lung eightfold during the 2 days before birth to reach a peak on the first postnatal day in the lungs but not in brains or kidneys of neonatal rats. AQP-4 and the alpha-, beta-, and gamma-subunits of ENaC are both expressed by cultured rat fetal distal lung epithelial (FDLE) cells. AQP-4 and ENaC expression increase in FDLE cells cultured on uncoated permeant filters compared with matched control cells cultured on filters containing extracellular matrix derived from fetal lung epithelial cells. Similarly, AQP-4 expression increases in FDLE cells exposed to 21% O2 compared with cells exposed to 3% O2. These data demonstrate that AQP-4 expression is highest on the first day after birth in neonatal rat lungs. Exposure to ambient 21% O2 may contribute to increases in AQP-4 and ENaC expression to facilitate water transport across neonatal airway epithelia in the immediate postnatal period.

Significance of ion transport during lung development and in respiratory disease of the newborn

Active ion transport plays a critical role in the liquid movement across the fetal and perinatal lung epithelium. The fetal lung liquid production is coupled with active secretion of Cl- into the luminal space. The potential for fluid absorbing mechanisms related to active Na+ transport from the apical to the basolateral side of the epithelium appears near the end of gestation. At birth there is a dramatic change of environment with commencement of air-breathing, sudden increase in oxygen partial pressure (PO2) and profound changes in the pulmonary circulation. A concurrent switch from fluid secretion to maintenance of low amounts of alveolar fluid is another major physiological adjustment taking place in the perinatal distal lung epithelium. The fluid-absorbing mechanism is a result of a well-synchronized co-operation between the basolateral membrane Na-K-ATPase and the apical membrane Na+ channels and it promotes salt and water movement from the airspace. Inability of the fetal lung epithelium to switch from fluid secretion to Na+ transport-dependent absorption seems to be an important factor adversely contributing to the respiratory distress of the newborn premature infant.

Active 22Na+ transport by the intact lung during early postnatal life

The lung relies upon epithelial active transport of Na+ to aid in the clearance of fluid from its air spaces. Because it is unknown whether the rate of active Na+ transport by the distal lung epithelium varies during early postnatal age, we performed studies in young guinea pigs (7 and 30 days after birth). We used a single pass isolated perfused lung model in which a Krebs Ringer bicarbonate solution containing 22Na+, [14C]sucrose, and FITC-dextran was placed into the air spaces of the lungs, and apparent permeability-surface area (PS) products were calculated after determining the changes in lung weight and the concentrations of the isotopes in the vascular effluent. The PS product for 22Na+, but not [14C]sucrose, decreased significantly at both ages when amiloride was infused (final concentration of 10(-4) M). Amiloride also decreased the rate of fluid clearance, as assessed by changes in organ weight, at both ages. Although the absolute rate of amiloride-sensitive 22Na+ transport increased with age, morphometric measurement of the alveolar region demonstrated that the rate of amiloride-sensitive 22Na+ transport per unit alveolar surface area was similar. These data indicate that although the guinea pig lung undergoes significant growth shortly after birth, the rate of amiloride-sensitive active Na+ transport per unit surface area remains constant. Since a component of weight loss was insensitive to amiloride, these in vivo studies suggest that the amiloride-insensitive Na+ transport pathways previously identified in cultured lung epithelium exist in the intact lung.

The present and future role of gene therapy in the newborn

There are currently a large number of ongoing gene therapy trials in North America and Europe. These trials have almost exclusively involved patients with inherited lethal disorders or malignancies. Although there are significant ethical and safety issues that remain unresolved, it seems inevitable that this technology will soon be adapted for use in lethal, or potentially lethal, fetal and neonatal diseases. If ethical and safety issues can be resolved, a wide spectrum of nonlethal acute and chronic diseases could also benefit from this form of therapy. The purpose of this brief review is to provide an overview of current approaches to gene delivery, their successes, and their limitations. Where possible, the discussion has focused on conditions that are recognized in fetal or neonatal life, to give the reader some sense of the potential scope for this form of therapy.

Immature epithelial Na+ channel expression is one of the pathogenetic mechanisms leading to human neonatal respiratory distress syndrome

Noninfective acute respiratory disease develops in approximately 1% of all newborn infants and results in their admission to a critical care unit. Transient tachypnea of the newborn occurs as a result of a delay in the clearance of fetal lung liquid; however, respiratory distress syndrome, typically thought to be exclusively a problem of relative surfactant deficiency, is now suspected to be characterized by an even greater air space fluid burden from the inability to absorb fetal lung liquid. In vivo experiments have demonstrated that the lung epithelium secretes Cl and fluid throughout gestation and develops the ability to actively reabsorb Na+ only during late gestation. At birth, the mature lung switches from active Cl- (fluid) secretion to active Na+ (fluid) absorption in response to circulating catecholamines. Changes in oxygen tension augment the Na(+)-transporting capacity of the epithelium and increase gene expression for the epithelial Na+ channel (ENaC). The inability of the immature fetal lung to switch from fluid secretion to fluid absorption results, at least in large part, from an immaturity in the expression of ENaC, which can be upregulated by glucocorticosteroids. Both pharmacological blockade of the lung's epithelial Na+ channel and genetic knockout experiments using mice deficient in the ENaC pore-forming subunit have demonstrated the critical physiological importance of lung Na+ transport at birth. When Na+ transport is ineffective, newborn animals develop respiratory distress and hypoxemia, retain their fetal lung liquid and, in the case of the ENaC knockout mice, die. Bioelectrical studies of human infants' nasal epithelia demonstrate that both transient tachypnea of the newborn and respiratory distress syndrome have defective amiloride-sensitive Na+ transport. These results suggest that neonatal respiratory distress syndrome has, in addition to a relative deficiency in surfactant, defective Na+ transport, which plays a mechanistic role in the development of the disease.

Fetal lung cell-derived matrix alters distal lung epithelial ion transport

Extracellular matrix (ECM) synthesized by the fetal mesenchymal cells provides a supporting structure for the growing airways and is important for airway branching and in the differentiation of the primitive epithelium. We studied whether ECM, in addition to its structural role in lung interstitium, influences the ion transport of rat fetal distal lung epithelial cells (FDLE). FDLE monolayers were cultured on two different fetal mixed lung cell (MLC)-derived matrix preparations and studied in Ussing chambers. FDLE on MLC matrix had an increased resting equivalent short-circuit current (Ieq). Amiloride (10(-4) M apically) decreased the Ieq significantly in all the FDLE monolayers. The residual Ieq was significantly larger in FDLE grown on MLC matrix (increased by 150 and 80% under baseline and beta 2-agonist-stimulated conditions, respectively) than on control filters and filters coated with type I collagen, and type IV collagen, laminin, or fibronectin. The matrix produced by MLC isolated at an earlier gestational stage decreased the FDLE's sensitivity to amiloride. The increased amiloride-insensitive Ieq was only modestly affected by the Na+/K+/Cl- cotransport inhibitor bumetanide (10(-4) M basally) but was abolished when the [Cl-] of the bathing solution was reduced to 10 mM. These observations demonstrated that MLC elaborated ECM is able to change the nature of the ion transport of FDLE. ECM may be an important factor governing the ion transporting phenotype of fetal type II alveolar epithelial cells.

The role of active Na+ transport by lung epithelium in the clearance of airspace fluid

Clinical and laboratory-based studies of pulmonary edema have usually focused on the mechanisms responsible for the production of the edema and how therapeutic maneuvers can oppose or treat such processes. Recently, there has been increasing interest in the mechanisms involved in the clearance of airspace fluids. These studies have demonstrated that active transport of Na+ by the distal lung epithelium plays an important physiologic role in the clearance of pulmonary edema fluid. Specifically, the ability of the lung to clear its fluid by active transport processes correlates with survival from high-pressure or high-permeability pulmonary edema. Also, studies have shown that immaturity of Na+ transport processes and, specifically, inadequate expression of Na+ channels contribute to the pathogenesis of respiratory distress syndrome in the newborn.

Effect of pentoxifylline on hemodynamics, alveolar fluid reabsorption, and pulmonary edema in a model of acute lung injury

We investigated the effect of pentoxifylline (PTX) on the development of pulmonary edema in a model of adult respiratory distress syndrome in rabbits. Lung injury was induced by repeated saline lavages in adult rabbits weighing 2.5 to 3.5 kg. Rabbits pretreated with PTX (20 mg/kg bolus followed by 20 mg/kg/h infusion) developed significantly lower amounts of lung edema 4 h after saline lavage (extravascular lung water to dry weight ratio [W/D], 6.9 +/- 0.6 SD versus 8.9 +/- 0.5 in control animals). PTX produced a 25% increase in cardiac output, but there were no differences between treated and untreated groups in calculated pulmonary vascular resistance or microvascular pressure. To determine whether PTX could have lowered pulmonary venous resistance and thus lowered effective microvascular pressure for fluid filtration, we directly measured pulmonary artery and left atrial pressures, and measured by micropuncture the pressure in 20 to 40 microns subpleural venules in four open-chested rabbits 3 to 4 h after lavage. Venous resistance was low (venous pressure drop 0.9 +/- 0.1 mm Hg) and was unchanged by PTX infusion. To determine if PTX decreased lung water by accelerating active alveolar fluid reabsorption, a single 60-ml aliquot of saline was instilled into the lungs of normal rabbits treated with saline or PTX. Both groups had a similar decrease in lung water content 1 and 4 h later. Our data indicate that PTX reduces edema formation in rabbits after saline lavage, not by lowering microvascular pressures for fluid filtration or by acceleration alveolar fluid reabsorption, but possibly by its anti-inflammatory effect on neutrophil function.

Effect of fibrinogen degradation products and lung ground substance on surfactant function

Acute lung injury syndromes have many characteristics including protein-rich alveolar edema, hyaline membranes, and abnormal surface tension at the alveolar air-liquid interface. Increased surface tension can occur because of a relative surfactant deficiency and/or dysfunction. It has been previously demonstrated that surfactant dysfunction occurs when plasma protein inhibitors leak into the alveolar space during the induction of the lung injury and edema formation. The present study investigated whether inhibitors that would be generated during the stage of repair from lung injury could impair surfactant function. We determined whether fibrinogen degradation products (FDP) which would be released during lysis of the fibrin(ogen)-containing alveolar exudate and hyaline membranes, and components of the lungs' ground substance could inhibit the in vitro function of a lipid extract surfactant preparation. FDP were prepared by incubating human fibrinogen with plasmin or neutrophil elastase for 4 min to 60 h and were characterized by SDS-PAGE. Early (fragment X and Y) and late (fragment D and E) plasmin-derived FDP (MW greater than 40,000) inhibited surfactant function as assessed by a bubble surfactometer. The early elastase-derived FDP also inhibited surfactant, but the later and much smaller fragments (MW less than 15,000) did not affect surfactant function. Laminin also inhibited surfactant in a dose-dependent manner. Neither hyaluronic acid nor heparan sulfate affected surfactant performance in vitro. We conclude that plasmin-induced lysis of intraalveolar fibrinogen and hyaline membranes will result in prolonged generation (i.e. days) of surfactant inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of pulmonary clearance of radioaerosol using a portable sodium iodide probe

To determine whether a portable sodium iodide (NaI) probe could provide a valid measure of the pulmonary half-life (T1/2) of aerosolized technetium-99m-diethylenetriaminepentaacetate (99mTc-DTPA, mol wt = 492) in small chests, we measured pulmonary clearance in rabbits using a gamma-scintillation camera and the portable probe. In 10 experiments the lungs of New Zealand White rabbits were insufflated with aerosolized 99mTc-DTPA (0.6 mum aerodynamic mass median diameter) and then simultaneously imaged with the gamma-camera and the probe positioned over the upper right lung. In an additional 12 experiments, alveolar-capillary membrane permeability was increased by either intratracheal instillation of 0.1 N hydrochloric acid (HCl) or intravenous injection of 100 mg/kg of oleic acid. All animals tolerated the procedure. There was a significant decrease in pulmonary T1/2 in both the HCl group (53.4 +/- 10.4 min, mean +/- SE) and the oleic acid group (14.7 +/- 2.3 min) when compared with control (127.5 +/- 18.1 min). When we compared the T 1/2 of the right lung determined by the gamma-camera with that measured by the probe, the correlation coefficient was 0.95. Potential nonpulmonary contributions to thoracic radioactivity were not significant. We conclude that a portable NaI probe is a valid means of determining T 1/2 of 99mTc-DTPA in small chests when compared with a gamma-camera and can detect increases in the permeability of the alveolar-capillary membrane to small solutes.

Quantitative ventilation-perfusion lung scans in infants and children: utility of a submicronic radiolabeled aerosol to assess ventilation

The quantitative assessment of regional pulmonary ventilation and perfusion provides useful information regarding lung function. Its use in infants and young children, however, has been minimal because of practical and technical limitations when the distribution of ventilation is assessed by radioactive gases. In 16 infants and children we used an inexpensive commercially available nebulizer to produce a submicronic aerosol labeled with 99mtechnetium-diethylenetriamine pentacetic acid to assess ventilation quantitatively, and intravenous injections of 99mtechnetium-labeled macroaggregates of albumin to assess pulmonary perfusion quantitatively. Studies were safely completed in both ambulatory and critically ill patients, including two premature infants who had endotracheal tubes in place for ventilatory support. No sedation or patient cooperation is required. This technique enables any department of nuclear medicine to measure regional pulmonary ventilation and perfusion in infants and children.

Hypoxia alters blood coagulation during acute decompression in humans

Acute decompression is associated with a shortening of the activated partial thromboplastin time (aPTT). This study was performed to examine whether this change in aPTT results from hypoxia or hypobaria. We exposed healthy adults on three separate occasions to 2 h of 1) hypoxic hypobaria (410 Torr, n = 5), 2) hypoxic normobaria (fractional inspired O2 tension = 0.11, n = 4), or 3) normoxic hypobaria (410 Torr breathing supplemental O2, n = 5). The aPTT shortened during hypoxic hypobaria and hypoxic normobaria (P less than 0.05) but was unchanged during normoxic hypobaria. The prothrombin and thrombin times, hematocrit, and concentrations of fibrinogen, total plasma protein, and fibrinogen-fibrin fragment E were unchanged. During hypoxic hypobaria biologic levels of prekallikrein, high-molecular-weight kininogen, and factors XII, XI, X, VII, V, and II were unchanged, but procoagulant VIII (VIII:C) increased 50% without an increase in VIII-related antigen levels (VIIIR:Ag). Fibrin monomer was not detected in any group. In one subject who became ill after 1.5 h of hypoxic normobaria aPTT shortened by 10 s; the platelet count decreased by 93,000/mm3; VIII:C increased fivefold, but VIIIR:Ag only increased three-fold. We conclude that it is the hypoxia which shortens aPTT during acute decompression to 410 Torr and speculate that it results from an increase in plasma VIII:C-like activity.

Effect of high-frequency oscillation on lung lymph flow

We investigated the effect of high-frequency oscillation (HFO) on lung lymphatic function under normal conditions and when lung lymph flow was increased by air microembolization. In six experiments, sheep and goats with chronic lung lymph fistulas and vascular catheters were anesthetized, paralyzed, intubated, and ventilated according to the following protocol: 1) intermittent positive-pressure ventilation (IPPV) for 1 h, 2) HFO with a frequency of 15 Hz and an estimated tidal volume of 1-2 ml/kg for 1-2 h, and 3) IPPV for 0.5 h. Ventilator settings were adjusted to maintain arterial Po2 above 100 Torr and a normal arterial Pco2. Vascular, esophageal, and mean airway pressures were monitored continuously. Lymph flow and cardiac output were recorded every 15 min. With this protocol, there were no changes in pulmonary vascular or esophageal pressures, and lymph flow remained stable throughout the experiment. In an additional five experiments, air microemboli were infused for approximately 30 min during HFO. Left atrial pressure was unchanged and lymph flow tripled. This response was qualitatively and quantitatively similar to that previously reported for unanesthetized spontaneously breathing sheep. We conclude that HFO does not impair lymphatic function under resting conditions and that lymphatics retain their ability to increase water and protein clearance during HFO.

Role of lymphatics in removal of sheep lung surfactant lipid

To study the role of lung lymphatics in the removal of surfactant lipid from the sheep lung, we injected [1-14C]palmitate intravenously into six animals previously fitted with a cannula draining the caudal mediastinal lymph node. Lung lymph was collected for 100 h after injection of radiolabel. We obtained alveolar lavage material through a tracheostomy in four other animals after intravenous injection of [9,10-3H]palmitate. We measured radioactivity at several time points in lipid extracts from lymph, lavage fluid, and lung tissue. Alveolar lavage disaturated phosphatidylcholine (DSPC) specific activity peaked at about 40 h and was reduced to 30% of this value by 82 h. About 2% of the injected radiolabel was incorporated into lung tissue lipids. Only 4% of the level of labeling achieved in lung tissue lipids was found in lung lymph lipid during 100 h of lymph collection. Sixty-three percent of radiolabel in lymph lipid was recovered in phospholipids, and 29% of phospholipid radiolabel was found in DSPC. The distribution of phosphorus and palmitate radiolabel in lung lymph phospholipid did not closely resemble that of surfactant lipid. No rise in lung lymph DSPC specific activity was observed following the peak in lavage specific activity. If surfactant lipid is removed from the alveolar compartment without extensive recycling, then we conclude that the lung lymphatics do not play a major role in the clearance of surfactant lipid from the alveolar surface.

Effects of growth on the diffusion constant for carbon monoxide

To investigate factors determining the diffusion constant for carbon monoxide (KCO) in normal children, we used the single breath method in 33 healthy children and young adults, 6 to 30 yr of age. In the sitting position, KCO decreased with increasing height (r = -0.59, p less than 0.001), suggesting greater recruitment of pulmonary vascular bed at the apexes in the shorter subjects. Increase in the KCO after taking the supine position was significantly less in the shorter subjects (8% at 120 cm) than in the taller subjects (27% at 170 cm), confirming this mechanism. Ten subjects with pulmonary involvement from cystic fibrosis had normal supine KCO but did not show a normal decrease in the upright position. From an analysis of present and previous data we conclude that (1) decrease in the conventionally measured KCO during childhood reflects a gravity-dependent decrease in recruitment of the pulmonary vascular bed and a decrease in the ratio of alveolar surface area to alveolar volume during growth and (2) diseases associated with hypoxic pulmonary vasoconstriction tend to recruit the pulmonary vascular bed at the apexes, increasing the conventionally measured KCO.

Hemodynamic and vasoactive mediator response to experimental respiratory failure

We determined the changes in hemodynamics and circulating concentrations of endogenous vasoactive mediators during acute respiratory failure in chronically catheterized unanesthetized sheep. Inhalation of a hypercarbic-hypoxic gas mixture for 2 h (pHa = 7.16, PaCO2 = 84 Torr, PaO2 = 48 Torr, n = 5) resulted in a doubling of cardiac output (thermodilution) and systemic and pulmonary hypertension. Systemic vascular resistance decreased, whereas pulmonary vascular resistance gradually increased throughout the 2-h experimental gas period. Pulmonary hypertension persisted for 45 min after return to room air breathing. Plasma renin activity tripled, and circulating bradykinin concentration increased 25-fold (radioimmunoassay). Plasma norepinephrine and epinephrine concentrations (radioenzymatic assay) dramatically increased with respective initial values (15 min) of 23.9 +/- 9.5 (SE) and 26.7 +/- 13.3 ng/ml (base line less than 0.2). Inhalation of hypoxic (n = 4) or hypercarbic-enriched O2 (n = 7) gas mixtures did not produce similar findings. We concluded that the hemodynamic response to experimental respiratory failure results from the combination of hypercarbic acidosis and hypoxia. These changes were mediated in part by increased sympathoadrenal activity and altered concentrations of H+, O2, and endogenous vasoactive mediators.

Bradykinin-induced increase in pulmonary vascular permeability in hypoxic sheep

Bradykinin (BK) is a potent edematogenic agent in systemic tissues. It is degraded by angiotensin-converting enzyme (ACE), which is located on the surface of all vascular endothelia. We hypothesized that since oxygen tension modulates ACE activity, the high pulmonary oxygen tension and hence high ACE activity protects the lung from the edematogenic effects of BK. We therefore studied the effect of exogenous BK in unanesthetized sheep with surgically created lymph fistulas and vascular catheters during normoxia and hypoxia. BK significantly elevated lung lymph flow and protein flux only when the sheep were made hypoxic and the lung's ability to degrade BK was impaired. This increase could not be attributed to recruitment of vascular surface area or to an increase in the driving force for fluid exchange because there were no changes in pulmonary arterial or left atrial pressures, cardiac output, or pulmonary vascular resistance. We conclude that BK increases water and protein movement in the lung by increasing vascular permeability.

Bradykinin production and increased pulmonary endothelial permeability during acute respiratory failure in unanesthetized sheep

To investigate mechanisms of pulmonary edema in respiratory failure, we studied unanesthetized sheep with vascular catheters, pleural balloons, and chronic lung lymph fistulas. Animals breathed either a hypercapnic-enriched oxygen (n = 5) or a hypercapnic-hypoxic (n = 5) gas mixture for 2 h. Every 15 min blood gases, pressures, cardiac output, lymph flow (Qlym), plasma and lymph albumin (mol wt, 70,000), IgG (mol wt, 150,000), IgM (mol wt, 900,000), and blood bradykinin concentrations were determined. In both groups, cardiac output and pulmonary arterial pressures increased, whereas left atrial pressures were unchanged. Acidosis alone (arterial pH = 7.16, PaCO(2) = 81 mm Hg, PaO(2) = 250 mm Hg) resulted in a doubling of lymph flow, a small increase in protein flux, and a decrease in lymph to plasma protein concentration (L/P) ratio for all three proteins. Acidotic-hypoxic animals (arterial pH = 7.16, PaCO(2) = 84 mm Hg, PaO(2) = 48 mm Hg) tripled Qlym. In these animals the increase in lymphatic flux of albumin, IgG, and IgM was significantly (P < 0.05) greater than that seen in either the acidosis alone group or in animals where left atrial pressures were elevated (n = 5; P < 0.05). Also, their percent increase in flux of the large protein (IgM) was greater than for the small protein (albumin) (P < 0.05). With acidosis alone, only pulmonary arterial bradykinin concentration increased (1.27+/-0.25 ng/ml SE), whereas acidosis plus hypoxia elevated both pulmonary arterial bradykinin concentrations (4.83+/-1.14 ng/ml) and aortic bradykinin concentration (2.74+/-0.78 ng/ml). These studies demonstrate that hypercapnic acidosis stimulates in vivo production of bradykinin. With superimposed hypoxia, and therefore decreased bradykinin degradation, there is an associated sustained rise in Qlym with increased lung permeability to proteins.

Familial lymphoid interstitial pneumonia: a long-term follow-up

We describe two brothers who developed chronic pulmonary disease in early childhood. Lung biopsies were diagnostic of lymphoid interstitial pneumonia (LIP). Familial LIP has not been previously reported, and the natural history is unknown. The elder brother experienced progressive respiratory disability and died 10 years after the onset of symptoms. The younger brother age 13, has been observed for 11 years and despite progression of pathological changes revealed in his second lung biopsy, he has had few symptoms and leads an active life. Current pulmonary function tests reveal decreased lung volumes, increased maximal expiratory flow rates and decreased lung compliance. Arterial PO2 is 75 mm Hg at rest and falls to 56 mm Hg with exercise. These findings, consistent with restrictive lung disease, contrast with the obstructive ventilatory pattern seen in some adult patients.