Pharmacoepidemiology of Drug Exposure in Intubated and Non-Intubated Preterm Infants With Severe Bronchopulmonary Dysplasia.

Background: Infants with severe bronchopulmonary dysplasia (BPD) are commonly treated with off-label drugs due to lack of approved therapies. To prioritize drugs for rigorous efficacy and safety testing, it is important to describe exposure patterns in this population. Objective: Our objective was to compare rates of drug exposure between preterm infants with severe bronchopulmonary dysplasia based on respiratory support status at or beyond 36 weeks post-menstrual age. Methods: A cross-sectional cohort study was performed on October 29, 2019. Preterm infants with severe BPD were eligible and details of respiratory support and drug therapy were recorded. Wilcoxon paired signed rank test was used to compare continuous variables between the invasive and non-invasive groups. Fisher's exact test was used to compare binary variables by respiratory support status. Results: 187 infants were eligible for the study at 16 sites. Diuretics were the drug class that most subjects were receiving on the day of study comprising 54% of the entire cohort, followed by inhaled steroids (47%) and short-acting bronchodilators (42%). Infants who were invasively ventilated (verses on non-invasive support) were significantly more likely to be receiving diuretics (p 0.013), short-acting bronchodilators (p < 0.01), long-acting bronchodilators (p < 0.01), systemic steroids (p < 0.01), systemic pulmonary hypertension drugs (p < 0.01), and inhaled nitric oxide (p < 0.01). Conclusion: Infant with severe BPD, especially those who remain on invasive ventilation at 36 weeks, are routinely exposed to multiple drug classes despite insufficient pharmacokinetic, safety, and efficacy evaluations. This study helps prioritize sub-populations, drugs and drug classes for future study.

Single nucleotide polymorphisms in the dual specificity phosphatase genes and risk of necrotizing enterocolitis in premature infant.

BACKGROUND: Differences in the susceptibility of preterm infants to develop necrotizing enterocolitis (NEC) implicate potential genetic differences in response to the inflammatory stimuli leading to NEC. Dual specificity phosphatases (DUSPs) are a key suppressor pathway of the mitogen-activated protein kinase (MAPK) pro-inflammatory signaling pathway. We hypothesized that inherited single nucleotide polymorphisms (SNPs) in DUSP genes contribute to NEC susceptibility in premature infants. METHODS: Patients admitted between 2010 and 2015 born at <  32 weeks GA and≤1,500 g BW with stage II+NEC (cases; n = 50) and age, weight-matched controls (n = 38) were included. Blood samples were collected for DNA isolation. Agena Mass Array assay was used to examine 31 SNPs in 9 different DUSP genes. Calculated minor allele frequencies (MAF) for cases and controls were compared using χ2 and logistic regression. RESULTS: The presence of the rs704074 SNP was associated with a 48% decreased risk of developing NEC (OR 0.52; 95% CI 0.27- 1.01, p = 0.04). The odds of surgical NEC decreased by 78% (OR 0.22; 95% CI 0.06- 0.84, p = 0.027) for each copy of rs704074/G allele in patients with NEC. CONCLUSION: In this small single-center pilot study, DUSP-6 SNP (rs704074) was associated with a lower risk of developing NEC and surgical NEC, the most severe form of NEC, in preterm infants.

Effects of practice change on outcomes of extremely preterm infants with patent ductus arteriosus.

AIM: To determine whether a decrease in patent ductus arteriosus (PDA) treatment or ligation in extremely preterm (EP) infants was associated with changes in rates of mortality and/or morbidities. METHODS: Observational study on EP infants admitted from 2008 to 2015. The small baby guidelines do not mandate ligation, however, in late 2010 the guidelines were amended based on new literature suggested that ligation may increase rates of morbidities. RESULTS: There were 717 EP infants admitted during the study period. There were no significant changes in gestational age, birthweight or annual admissions during the study period. The annual rate of PDA medical treatment declined significantly (R = 0.83, p = 0.01), while the annual rate of PDA ligation declined substantially (R = 0.88, p = 0.004). The annual mortality rate also declined significantly (R = 0.81, p = 0.014). The annual rates of bronchopulmonary dysplasia (BPD), necrotising enterocolitis and intraventricular haemorrhage did not change significantly. CONCLUSION: In this cohort of EP patients, the rate of PDA ligation decreased substantially since 2010, with no apparent adverse effects on mortality or rates of BPD. These data are consistent with the concept that ligation does not improve outcomes in EP infants.

Using clinical and genetic data to predict pulmonary hypertension in bronchopulmonary dysplasia.

AIM: Pulmonary hypertension significantly increases morbidity and mortality in infants with bronchopulmonary dysplasia. The frequency of single nucleotide polymorphisms in arginase-1 (ARG1 rs2781666) and dimethylarginine dimethylaminohydrolase-1 (DDAH1 rs480414) genes has been found to differ in a cohort of bronchopulmonary dysplasia patients with pulmonary hypertension (cases) and without pulmonary hypertension (controls). Therefore, we tested the hypothesis that combining these genotypes with phenotypic data would better predict pulmonary hypertension in bronchopulmonary dysplasia patients. METHODS: Bronchopulmonary dysplasia patients (n = 79) born at <35 weeks gestation were studied. Pulmonary hypertension was diagnosed by echocardiographic criteria (n = 20). ROC curves to predict pulmonary hypertension in bronchopulmonary dysplasia were generated from genotype and/or clinical data. RESULTS: Cases were born at an earlier gestation and weighed less at birth than did controls. ROC curves for rs2781666 had an AUC of 0.61, while rs480414 had an AUC of 0.66. Together, the AUC was 0.70. When clinical data were added to the genetic model, AUC was 0.73. CONCLUSION: These findings demonstrate that ROC predictive modelling of pulmonary hypertension in bronchopulmonary dysplasia improves with inclusion of both genotypic and phenotypic data. Further refinement of these types of models could facilitate the implementation of precision medicine approaches to pulmonary hypertension in bronchopulmonary dysplasia.

Outcomes following indomethacin prophylaxis in extremely preterm infants in an all-referral NICU.

OBJECTIVE: We examined data from a contemporary cohort of extreme prematurity (EP) infants admitted to an all-referral Children's Hospital neonatal intensive care unit (NICU) to determine whether prophylactic indomethacin (PI) may continue to benefit these patients. STUDY DESIGN: An observational study utilizing the small baby ICU data registry that was queried for all EP infants admitted between 2005 and 2014 with documentation of PI use (671 total EP infants; 141 (21%) did not receive PI (control); 530 (79%) received PI (PI). This cohort of EP infants was born at outside hospitals and transferred to our level IV NICU with a mean age on admission of 13 days, well after the PI would have been administered. RESULTS: No difference existed between the control and PI groups in gestational age, birth weight, severity of illness, other in-hospital outcomes or developmental delay. PI infants had a significantly lower mortality rate (P=0.0004), lower relative risk (RR) for mortality 0.52 (95% confidence interval (CI) 0.37 to 0.73, P=0.0001) and lower RR of developing the combined outcome of death or bronchopulmonary dysplasia (RR 0.91, 95% CI 0.85 to 0.98, P=0.012) when compared with the control group. Notably, there was no significant effect of PI on incidence of severe intraventricular hemorrhage or patent ductus arteriosus ligation. CONCLUSION: PI administration was associated with improved survival in EP infants referred to a level IV Children's Hospital NICU.

Inter-center variation in death or tracheostomy placement in infants with severe bronchopulmonary dysplasia.

OBJECTIVE: To estimate the presence and sources of inter-center variation (ICV) in the risk of death or tracheostomy placement (D/T) among infants with severe bronchopulmonary dysplasia (sBPD)Study design:We analyzed the Children's Hospitals Neonatal Database between 2010 and 2013 to identify referred infants born <32 weeks' gestation with sBPD. The association between center and the primary outcome of D/T was analyzed by multivariable modeling. Hypothesized diagnoses/practices were included to determine if these explained any observed ICV in D/T. RESULTS: D/T occurred in 280 (20%) of 1383 eligible infants from 21 centers. ICV was significant for D/T (range 2-46% by center, P<0.001) and tracheostomy placement (n=187, range 2-37%, P<0.001), but not death (n=93, range 0-19%, P=0.08). This association persisted in multivariable analysis (adjusted center-specific odds ratios for D/T varied 5.5-fold, P=0.009). CONCLUSIONS: ICV in D/T is apparent among infants with sBPD. These results highlight that the indications for tracheostomy (and subsequent chronic ventilation) remain uncertain.

Early extubation attempts reduce length of stay in extremely preterm infants even if re-intubation is necessary.

OBJECTIVE: Prolonged mechanical ventilation in the extremely premature infant is associated with the development of bronchopulmonary dysplasia (BPD). Clinically, the decision to extubate the extremely low birth weight (ELBW) infant can be difficult. There is continued debate regarding whether it is better for an ELBW infant to remain on the ventilator or to extubate to nasal constant positive airway pressure (nCPAP). It has also been argued that repeated intubations may be detrimental to ELBW infants. We tested the hypothesis that earlier extubation attempts would decrease length of hospital stay and BPD. STUDY DESIGN: A database maintained on infants born at <27 completed weeks gestation admitted to our all referral NICU for a 36 month period was queried (n = 224). RESULTS: Day of life (DOL) of the first extubation attempt was inversely correlated with birth weight (p <  0.001) and gestational age (p <  0.01). The DOL of the 1st extubation attempt correlated with the need for re-intubation (p <  0.001), but not with mortality (p = 0.27). In survivors, earlier DOL of 1st extubation attempt was associated with shorter LOS (p <  0.001). Earlier DOL of the 1st extubation attempt was associated with less need for supplemental oxygen (p <  0.001) at 36 weeks CGA, while re-intubation was not (p = 0.50). CONCLUSION: In our cohort of extremely premature infants, the earlier the first extubation attempt the sooner the patient was discharged home and the less likely to develop BPD. Our study suggests that extubation should not be delayed in extremely premature infants due to fears of need for re-intubation.

Inhaled nitric oxide usage in preterm infants in the NICHD Neonatal Research Network: inter-site variation and propensity evaluation.

OBJECTIVE: The use of inhaled nitric oxide (iNO) in preterm infants remains controversial. In October 2010, a National Institutes of Health consensus development conference cautioned against use of iNO in preterm infants. This study aims (1) to determine the prevalence and variability in use of iNO in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network (NICHD NRN) before and after the consensus conference and (2) separately, to examine associations between iNO use and severe bronchopulmonary dysplasia (BPD) or death. STUDY DESIGN: The NICHD NRN Generic Database collects data including iNO use on very preterm infants. A total of 13 centers contributed data across the time period 2008 to 2011. Infants exposed or not to iNO were compared using logistic regression, which included factors related to risk as well as their likelihood of being exposed to iNO. RESULT: A total of 4885 infants were assessed between 2008 and 2011; 128 (2.6%) received iNO before day 7, 140 (2.9%) between day 7 and 28, and 47 (1.0%) at >28 days. Center-specific iNO use during 2008 to 2010 ranged from 21.9 to 0.4%; 12 of 13 sites reduced usage and overall NRN iNO usage decreased from 4.6 to 1.6% (P<0.001) in 2011. The use of iNO started between day 7 and day 14 was more prevalent among younger infants with more severe courses in week 1 and associated with increased risk of severe BPD or death (odds ratio 2.24; 95% confidence interval 1.23 to 4.07). CONCLUSION: The variability and total use of iNO decreased in 2011 compared with 2008 to 2010. iNO administration started at ⩾ day 7 was associated with more severe outcomes compared with infants without iNO exposure.

Arginase I gene single-nucleotide polymorphism is associated with decreased risk of pulmonary hypertension in bronchopulmonary dysplasia.

AIM: To test the hypothesis that there are single-nucleotide polymorphisms (SNPs) in genes of the l-arginine/nitric oxide pathway associated with pulmonary hypertension (PH) in neonates with bronchopulmonary dysplasia (BPD). METHODS: Neonates with BPD were enrolled (n = 140) and clinical characteristics compared between case (BPD + PH) and control (BPD) groups. DNA was isolated from blood leucocytes and assayed for 17 SNPs in l-arginine/nitric oxide pathway genes by Sequenom massarray. Genes included carbamoyl-phosphate synthetase, ornithine transcarbamylase, argininosuccinate synthase, nitric oxide synthase and arginase. SNPs were selected from the National Center for Biotechnology Information database for their putative functionality. Calculated minor allele frequencies (MAF) of cases and controls were compared using χ2 and logistic regression. RESULTS: Of the 140 patients with BPD, 26% had echocardiographic evidence of PH. Ventilation days were longer for cases than controls (mean 31 vs. 15 days, p < 0.05). Of the 17 SNPs, rs2781666 in arginase I gene was less common in cases (MAF = 0.23) than controls (MAF = 0.37, p = 0.04). The odds of PH decreased by 43% (p = 0.047) for each copy of the SNP minor allele in arginase I gene in patients with BPD. CONCLUSION: Arginase I SNP (rs2781666) may be associated with protection against pulmonary hypertension in preterm neonates with BPD.

Empowerment programme for parents of extremely premature infants significantly reduced length of stay and readmission rates.

AIM: Extremely premature infants experience long hospitalisation and high readmission rates within 30 days of discharge. This quality control investigation retrospectively explored the impact of the Creating Opportunities for Parent Empowerment (COPE©) programme on these rates in an all referral, Level-IV small baby intensive care unit setting. METHODS: The parents of 303 extremely premature infants participated in the study. Of those, 135 were admitted before the implementation of COPE© and served as baseline historical controls, and the remaining 168 neonates received the intervention. Length of stay and readmission rates were analysed using parametric and nonparametric tests. Additional analyses were used to compare the two groups in terms of gestational age, birthweight and other acuity measures. RESULTS: Neonates who received COPE© required significantly reduced lengths of stay than the control neonates (COPE© 127.1 ± 55.8 days vs. control 139.6 ± 61.9 days, p < 0.05) and significantly lower readmission rates (COPE© 23.9% vs. control 13.2%, p = 0.05). CONCLUSION: The COPE© programme promoted active parental engagement in the unit and significantly reduced hospital stays and readmission rates. Future interventions should identify the specific components of the programme that support the parents of extremely premature infants during the various phases of hospitalisation.

Therapeutic interventions and short-term outcomes for infants with severe bronchopulmonary dysplasia born at <32 weeks' gestation.

OBJECTIVE: To characterize the treatments and short-term outcomes in infants with severe bronchopulmonary dysplasia (sBPD) referred to regional neonatal intensive care units. STUDY DESIGN: Infants born <32 weeks' gestation with sBPD were identified using the Children's Hospital Neonatal Database. Descriptive outcomes are reported. RESULT: A total of 867 patients were eligible. On average, infants were born at 26 weeks' gestation and referred 43 days after birth. Infants frequently experienced lung injury (pneumonia: 24.1%; air leak: 9%) and received systemic corticosteroids (61%) and mechanical ventilation (median duration 37 days). Although 91% survived to discharge, the mean post-menstrual age was 47 weeks. Ongoing care such as supplemental oxygen (66%) and tracheostomy (5%) were frequently needed. CONCLUSION: Referred infants with sBPD sustain multiple insults to lung function and development. Because affected infants have no proven, safe or efficacious therapy and endure an exceptional burden of care even after referral, urgent work is required to observe and improve their outcomes.

Bronchopulmonary dysplasia and neurodevelopmental outcome in extremely preterm neonates.

UNLABELLED: We tested the hypothesis that the use of supplemental oxygen (sO2) at discharge from the NICU in extremely preterm neonates is associated with a greater risk of neurodevelopmental impairment (NDI) at 18 months corrected gestational age (CGA) than the risk of NDI of those neonates discharged in room air. Four hundred twenty-four charts were retrospectively reviewed from infants born at <27 weeks and transferred to Nationwide Children's Hospital from December 1, 2004 to June 14, 2010. Use of sO2 was evaluated on day of life (dol) 28, at 36 weeks post-menstrual age (PMA), and at discharge. Logistic regression was used to identify postnatal risk factors associated with sO2 at discharge and NDI. At dol 28, 96 % of surviving patients received sO2, and therefore had bronchopulmonary dysplasia (BPD) by definition from a National Institutes of Child Health and Human Development workshop. At 36 weeks PMA, 89 % continued on sO2 (moderate/severe BPD), and at discharge, 74 % continued on sO2. When factors associated with NDI were examined, the need for mechanical ventilation ≥28 days (adjOR = 3.21, p = 0.01), grade III-IV intraventricular hemorrhage (IVH) (adjOR = 4.61, p < 0.01), and discharge at >43 weeks PMA (adjOR = 2.12, p = 0.04) were the strongest predictors of NDI at 18 months CGA. There was no difference in Bayley Scales of Infant Development, third edition composite scores between patients with no/mild BPD and patients with moderate/severe BPD (cognitive p = 0.60, communication p = 0.53, motor p = 0.19) or those scores between patients on and off oxygen at discharge (cognitive p = 0.58, communication p = 0.70, motor p = 0.62). CONCLUSIONS: The need for sO2 at discharge is not associated with an increased risk of NDI in these patients. The strongest predictors of poor neurodevelopmental outcome in this population were prolonged positive pressure support, grade III-IV IVH, and discharge at >43 weeks PMA.

Implementation of a multidisciplinary guideline-driven approach to the care of the extremely premature infant improved hospital outcomes.

AIM: To test the hypothesis that implementing guidelines for the standardized care of the extremely premature infant (<27 weeks) in the first week of life would improve patient outcomes in an all referral NICU. METHODS: Data were collected on all infants <27 weeks gestational age and <7 days of age on admission cared for using these small baby guidelines (SBG), as well as on all age-matched infants admitted the year prior (comparison). RESULTS: Thirty-seven patients were cared for utilizing the SBG and 40 patients were in the comparison group. There were no differences between the groups in gestational age, birthweight or age on admission. There was no difference in survival to discharge (73% SBG, 70% comparison). The mean length of stay for survivors was 112 +/- 38 days SBG and 145 +/- 76 days (p < 0.05) comparison group. Survival without BPD was greater in the SBG group (24%) than in the comparison group (9%; p < 0.05), and survival without severe IVH was greater in the SBG group (65%) than in the comparison group (38%; p < 0.01). CONCLUSIONS: These data demonstrate that applying a unified approach to the care of the extremely premature infant in the first week of life resulted in a decrease in the length of hospitalization and improved patient outcomes.

Increased incidence of idiopathic persistent pulmonary hypertension in Down syndrome neonates.

Down syndrome (DS) patients have an increased risk of developing pulmonary hypertension later in life compared to age-matched controls. The goal of this study was to determine if the incidence of persistent pulmonary hypertension of the newborn (PPHN) is also higher in neonatal DS patients compared to the general population. A retrospective chart review of DS patients admitted during a 3-year period to the neonatal intensive care unit was performed. DS patients with meconium aspiration syndrome, pulmonary infections, or pulmonary space-occupying lesions were excluded. DS patients were divided into four groups based on treatment and consisted of no intervention (A), supplemental oxygen (B,) mechanical ventilation use (C), and inhaled nitric oxide administration (D). Group D was defined as having PPHN. z test of the difference between sample and known population, chi-square, t-test, and analysis of variance with Tukey adjusted post hoc test were used for analysis. p<0.05 was considered significant. A total of 58 patients met inclusion criteria. Twenty-four DS patients were in group A, 17 in group B, 10 in group C, and 7 in group D. There was no difference between the four groups for gender (males: 10, 5, 5, and 5, respectively), gestational age (36.4, 38.2, 36.4, and 36.4 weeks, respectively), weight (2.8, 3.0, 2.4, and 3.0 kg, respectively), or the presence of congenital heart defects (17, 10, 6, and 1, respectively). The estimated number of DS patients born in the state of Ohio during this period was 598; therefore, the incidence of PPHN in DS was 1.2%. The reported incidence of PPHN is 0.1%. The reported incidence of PPHN was significantly lower versus the incidence of PPHN in DS (z=2.7, p=0.007). It was concluded that DS patients have an increased incidence of PPHN compared to historical controls regardless of baseline demographics.

L-arginine infusion lowers blood pressure in children.

Eleven children were studied during L-arginine infusion. Blood pressure decreased, and mean plasma L-arginine and L-citrulline increased compared with baseline levels. The change in blood pressure was inversely related to the change in plasma L-citrulline. These results suggest that L-arginine decreased blood pressure via increased nitric oxide production.

Cytokine treatment increases arginine metabolism and uptake in bovine pulmonary arterial endothelial cells.

L-Arginine (L-Arg) is metabolized to nitric oxide (NO) by NO synthase (NOS) or to urea by arginase (AR). L-Arg is transported into bovine pulmonary arterial endothelial cells (BPAECs) by cationic amino acid transporter-2 (CAT-2). We hypothesized that cytokine treatment would increase L-Arg metabolism and increase CAT-2 mRNA expression. BPAECs were incubated for 24 h in medium (control) or medium with lipopolysaccharide and tumor necrosis factor-alpha (L-T). L-T increased nitrite production (3.1 +/- 0.4 nmol/24 h vs. 1.8 +/- 0.1 nmol/24 h for control; P < 0.01) and urea production (83.5 +/- 29.5 nmol/24 h vs. 17.8 +/- 8.6 nmol/24 h for control; P < 0.05). L-T-treated BPAECs had greater endothelial and inducible NOS mRNA expression compared with control cells. Increasing the medium L-Arg concentration resulted in increased nitrite and urea production in both the control and the L-T-treated BPAECs. L-T treatment resulted in measurable CAT-2 mRNA. L-T increased L-[(3)H]Arg uptake (5.78 +/- 0.41 pmol vs. 4.45 +/- 0.10 pmol for control; P < 0.05). In summary, L-T treatment increased L-Arg metabolism to both NO and urea in BPAECs and resulted in increased levels of CAT-2 mRNA. This suggests that induction of NOS and/or AR is linked to induction of CAT-2 in BPAECs and may represent a mechanism for maintaining L-Arg availability to NOS and/or AR.

The arterial site of action of nitric oxide in the neonatal pig lung determined by microfocal angiography.

To determine the site of action of inhaled nitric oxide (iNO) in the newborn pig lung, lungs were isolated and perfused at constant flow for microfocal x-ray angiography. Measurements of pulmonary arterial diameters were made on arteries in the 100--2500 microm diameter range under control conditions, during vasoconstriction caused by hypoxia (decreasing PO(2) from approximately 120 to approximately 50 Torr), or N(omega)-nitro-L-arginine methylester (L-NAME 10(-4) M) administration, with or without vasodilation induced by iNO (40 ppm) or by the NO donor S-nitroso-N-acetylpenicillamine (SNAP 5 x 10(-6) M) given intravascularly. Hypoxia caused constriction only in smaller arteries whereas L-NAME constricted arteries throughout the size range studied. iNO dilated the smaller arteries more than the larger arteries under all study conditions. SNAP was used to provide an intravascular source of NO for comparison to iNO. SNAP also dilated smaller arteries more than larger arteries, but it had a significantly greater effect on the large arteries than did iNO. This suggests that differential accessibility of the vascular smooth muscle to NO between sources, air and blood, is a factor in the diameter dependence of the responses.

Role of endothelin in intermittent hypoxia-induced hypertension.

Clinical studies suggest that sleep apnea causes systemic hypertension. In addition, patients with sleep apnea have elevated plasma levels of endothelin-1 (ET-1). We hypothesized that the intermittent hypoxia/hypercapnia (IH) associated with sleep apnea causes hypertension by increasing ET-1 production. To test this hypothesis, rats with arterial and venous catheters were placed in Plexiglas chambers. IH rat chambers were flushed with an N(2)-CO(2) mixture for 90 seconds to achieve hypoxia/hypercapnia (5% O(2)-5% CO(2)) followed by 90 seconds of compressed air to achieve normoxia (21% O(2)-0% CO(2)). Control rat chambers were flushed with 90 seconds of air-air cycles. Cycles for both groups were repeated 8 hours per day for 11 days. Resting mean arterial pressure (MAP) and heart rate were recorded daily before the start of exposure. After 11 days, MAP was significantly elevated in IH rats compared with initial MAP (109+/-5 mm Hg initial, 139+/-11 mm Hg day 11) and compared with air-air rats (110+/-4 mm Hg). On day 11, cumulative doses of PD145065 (a nonselective ET-receptor antagonist) were administered intravenously to the rats breathing room air. PD145065 caused a dose-dependent decrease in MAP in IH rats but did not alter MAP in air-air rats. Plasma ET-1 measured by radioimmunoassay was significantly increased on days 5 and 11 in the IH rats compared with day 1 and compared with air-air rats. There was no significant change in plasma ET-1 over time in air-air rats. We conclude that IH exposure increases both MAP and plasma ET-1 and that the increased ET-1 may contribute to the hypertension.

Nitric oxide-dependent pulmonary vasodilation in polycythemic rats.

Polycythemia causes increased vascular production of nitric oxide (NO), most likely secondary to an effect of elevated vascular shear stress to enhance expression of endothelial nitric oxide synthase (eNOS). Because both polycythemia and increased eNOS expression are associated with chronic hypoxia-induced pulmonary hypertension, experiments were performed to test the hypothesis that increased hematocrit leads to upregulation of pulmonary eNOS and enhanced vascular production of NO independent of hypoxia. Rats were administered human recombinant erythropoietin (rEpo; 48 U/day) or vehicle for 2 wk. At the time of study, hematocrit was significantly greater in the rEpo-treated group than in the vehicle group (65.8 +/- 0.7% vs. 45.1 +/- 0.5%), although mean pulmonary artery pressure did not differ between treatments. Experiments on isolated, saline-perfused lungs demonstrated similar vasodilatory responses to the endothelium-derived NO-dependent agonist ionomycin in each group. Additional experiments showed that the vasoconstrictor response to the thromboxane mimetic U-46619 was diminished at lower doses in lungs from the rEpo group compared with the vehicle group. However, perfusate nitrite/nitrate concentration after 90 min of perfusion in isolated lungs was not different between groups. Additionally, no difference was detected between groups in lung eNOS levels by Western blot. We conclude that the predicted increase in shear stress associated with polycythemia does not result in altered pulmonary eNOS expression.

Systemic lobar shunting induces advanced pulmonary vasculopathy.

OBJECTIVES: We characterized the morphology and vasomotor responses of a localized, high-flow model of pulmonary hypertension. METHODS: An end-to-side anastomosis was created between the left lower lobe pulmonary artery and the aorta in 23 piglets. Control animals had a thoracotomy alone or did not have an operation. Eight weeks later, hemodynamic measurements were made. Then shunted and/or nonshunted lobes were removed for determination of vascular resistance and compliance by occlusion techniques under conditions of normoxia, hypoxia (FIO (2) = 0.03), and inspired nitric oxide administration. Quantitative histologic studies of vessel morphology were performed. RESULTS: Eighty-three percent of animals having a shunt survived to final study. Aortic pressure, main pulmonary artery and wedge pressures, cardiac output, blood gases, and weight gain were not different between control pigs and those receiving a shunt. Six of 9 shunted lobes demonstrated systemic levels of pulmonary hypertension in vivo. Arterial resistance was higher (24.3 +/- 12.0 vs 1.3 +/- 0. 2 mm Hg. mL(-1). s(-1), P =.04) and arterial compliance was lower (0. 05 +/- 0.01 vs 0.16 +/- 0.03 mL/mm Hg, P =.02) in shunted compared with nonshunted lobes. Hypoxic vasoconstriction was blunted in shunted lobes compared with nonshunted lobes (31% +/- 13% vs 452% +/- 107% change in arterial resistance, during hypoxia, P <.001). Vasodilation to inspired nitric oxide was evident only in shunted lobes (34% +/- 6% vs 1.8% +/- 8.2% change in arterial resistance during administration of inspired nitric oxide, P =.008). Neointimal and medial proliferation was found in shunted lobes with approximately a 10-fold increase in wall/luminal area ratio. CONCLUSIONS: An aorta-lobar pulmonary artery shunt produces striking vasculopathy. The development of severe pulmonary hypertension within a short time frame, low mortality, and localized nature of the vasculopathy make this model highly attractive for investigation of mechanisms that underlie pulmonary hypertension.