Cardiopulmonary function in premature infants with bronchopulmonary dysplasia--a 2-year follow up

Utility of Pulmonary Artery Acceleration Time to Estimate Systolic Pulmonary Artery Pressure in Neonates and Young Infants

Transthoracic echocardiogram (TTE) is commonly used to screen for pulmonary hypertension (PHTN) in neonates and young infants. However, in the absence of sufficient tricuspid regurgitation (TR), a ventricular septal defect (VSD), or a patent ductus arteriosus (PDA), the estimation of systolic pulmonary artery pressure (SPAP) becomes challenging. Pulmonary artery acceleration time (PAAT) is an alternate parameter that is easy to obtain in almost all patients and does not require the presence of tricuspid valvar regurgitation or an anatomical cardiac defect. We sought to examine the correlation of PAAT with estimated SPAP by TTE and create an equation to estimate the SPAP using PAAT. We performed a retrospective review of TTEs performed on neonates and young infants (4 months of age or younger) at our institution between April 2017 and December 2018, along with the corresponding medical records. We included TTEs that provided estimation for SPAP and at least one PAAT measurement. During the study period, 138 TTEs performed on 82 patients met the inclusion criteria. Strong correlation was delineated between PAAT and SPAP estimated by the maximum velocity of tricuspid valve regurgitation Doppler, correlation coefficient (r) = - 0.83. Moderate correlation was detected between PAAT and SPAP estimated by PDA Doppler, r = - 0.66. Utilizing the following equation "SPAP = 82.6 - 0.58 × PAAT + RA mean pressure", PAAT can be used to estimate SPAP in neonates and young infants. PAAT can be used as an alternative to TR jet to assess SPAP when the latter is absent or insufficient. Further studies are needed to verify the accuracy of this equation.

Evidence of Echocardiographic Markers of Pulmonary Vascular Disease in Asymptomatic Infants Born Preterm at One Year of Age

OBJECTIVE

To test the hypothesis that echocardiographic markers of pulmonary vascular disease (PVD) exist in asymptomatic infants born preterm at 1-year corrected age.

STUDY DESIGN

We conducted a prospective cohort study of 80 infants born preterm (<29 weeks of gestation) and 100 age- and weight-matched infants born at term and compared broad-based conventional and quantitative echocardiographic measures of pulmonary hemodynamics at 1-year corrected age. Pulmonary artery acceleration time (PAAT), a validated index of pulmonary vascular resistance, arterial pressure, and compliance, was used to assess pulmonary hemodynamics. Lower PAAT is indicative of PVD. Subanalyses were performed in infants with bronchopulmonary dysplasia (BPD, n = 48, 59%) and/or late-onset pulmonary hypertension (n = 12, 15%).

RESULTS

At 1 year, there were no differences between conventional measures of pulmonary hypertension in the infants born at term and preterm. All infants born preterm had significantly lower values of PAAT than infants born at term (73 ± 8 milliseconds vs 98 ± 5 milliseconds, P < .001). Infants born preterm with BPD had even lower PAAT than those without BPD (69 ± 5 milliseconds vs 79 ± 4 milliseconds, P < .01). The degree of PVD at 1-year corrected age was inversely related to gestation in all infants born preterm. Data analysis included adjustment for ventricular function and other confounding factors.

CONCLUSIONS

In comparison with infants born at term, infants born preterm exhibit abnormal PAAT at 1-year corrected age irrespective of neonatal lung disease status, suggesting the existence of PVD beyond infancy. PAAT measurements offer a reliable, noninvasive tool for screening and longitudinal monitoring of pulmonary hemodynamics in infants.

Understanding the Short- and Long-Term Respiratory Outcomes of Prematurity and Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic respiratory disease associated with premature birth that primarily affects infants born at less than 28 weeks' gestational age. BPD is the most common serious complication experienced by premature infants, with more than 8,000 newly diagnosed infants annually in the United States alone. In light of the increasing numbers of preterm survivors with BPD, improving the current state of knowledge of long-term respiratory morbidity for infants with BPD is a priority. We undertook a comprehensive review of the published literature to analyze and consolidate current knowledge of the effects of BPD that are recognized at specific stages of life, including infancy, childhood, and adulthood. In this review, we discuss both the short-term and long-term respiratory outcomes of individuals diagnosed as infants with the disease and highlight the gaps in knowledge needed to improve early and lifelong management of these patients.

The Respiratory System

This chapter addresses upper airway physiology for the pediatric intensivist, focusing on functions that affect ventilation, with an emphasis on laryngeal physiology and control in breathing. Effective control of breathing ensures that the airway is protected, maintains volume homeostasis, and provides ventilation. Upper airway structures are effectors for all of these functions that affect the entire airway. Nasal functions include air conditioning and protective reflexes that can be exaggerated and involve circulatory changes. Oral cavity and pharyngeal patency enable airflow and feeding, but during sleep pharyngeal closure can result in apnea. Coordination of breathing with sucking and nutritive swallowing alters during development, while nonnutritive swallowing at all ages limits aspiration. Laryngeal functions in breathing include protection of the subglottic airway, active maintenance of its absolute volume, and control of tidal flow patterns. These are vital functions for normal lung growth in fetal life and during rapid adaptations to breathing challenges from birth through adulthood. Active central control of breathing focuses on the coordination of laryngeal and diaphragmatic activities, which adapts according to the integration of central and peripheral inputs. For the intensivist, knowledge of upper airway physiology can be applied to improve respiratory support. In a second part the mechanical properties of the respiratory system as a critical component of the chain of events that result in translation of the output of the respiratory rhythm generator to ventilation are described. A comprehensive understanding of respiratory mechanics is essential to the delivery of optimized and individualized mechanical ventilation. The basic elements of respiratory mechanics will be described and developmental changes in the airways, lungs, and chest wall that impact on measurement of respiratory mechanics with advancing postnatal age are reviewed. This will be follwowed by two sections, the first on respiratory mechanics in various neonatal pathologies and the second in pediatric pathologies. The latter can be classified in three categories. First, restrictive diseases may be of pulmonary origin, such as chronic interstitial lung diseases or acute lung injury/acute respiratory distress syndrome, which are usually associated with reduced lung compliance. Restrictive diseases may also be due to chest wall abnormalities such as obesity or scoliosis (idiopathic or secondary to neuromuscular diseases), which are associated with a reduction in chest wall compliance. Second, obstructive diseases are represented by asthma and wheezing disorders, cystic fibrosis, long term sequelae of neonatal lung disease and bronchiolitis obliterans following hematopoietic stem cell transplantation. Obstructive diseases are defined by a reduced FEV1/VC ratio. Third, neuromuscular diseases, mainly represented by DMD and SMA, are associated with a decrease in vital capacity linked to respiratory muscle weakness that is better detected by PImax, PEmax and SNIP measurements.

The efficacy of cardiac findings in assessing the outcome in preterms with bronchopulmonary dysplasia

OBJECTIVES

To evaluate if cardiac dysfunctions are important in assessing the outcome in newborns with Bronchopulmonary Dysplasia (BPD), by evaluating cardiac functions with N-terminal prohormone of brain natriüretic peptide (NT-proBNP) levels, M-mode and tissue doppler echocardiography at 6-12 mo of age.

METHODS

Twenty eight patients were retrospectively classified as mild, moderate and severe according to the diagnostic criterias for BPD. All cases were assessed with standard M-mode, tissue doppler echocardiography and NT-proBNP levels. Control group consisted of 28 healthy infants, having similar postnatal ages as patients and were assessed with standard M-mode and tissue doppler echocardiography.

RESULTS

The age of patients with BPD was 9.8 ± 2.3 mo and control group was 9.5 ± 2.6 mo. There was no significant difference between the postnatal ages of two groups (p > 0.05). Neither pulmonary hypertension nor pulmonary/tricuspid regurgitation was detected. The M-mode echocardiography measurements did not differ between patients and control group (p > 0.05). Tissue doppler echocardiography, tricuspid valve medial segment early diastolic myocardial relaxation velocity (TME') measurements of patients were found significantly lower, peak transtricuspid filling velocity in the early diastole (TE)/TME' ratios and isovolumetric relaxation time (IVRT) measurements were found significantly higher than control group (p < 0.05). Tricuspid E, TE/TLE' (Tricuspid valve lateral segment early diastolic myocardial relaxation velocity), TE/RVLE'(Right ventricular lateral segment early diastolic myocardial relaxation velocity), TE/TME' levels were also found as significantly abnormal in patients with severe BPD. A significant correlation was found between right ventricular diastolic disfunctions and severity of BPD (p < 0.05). No statistically significant difference was found between NT-proBNP levels, BPD stages and tissue doppler echocardiography measurements (p > 0.05).

CONCLUSIONS

This is the first study evaluating cardiac findings in patients with BPD by tissue doppler echocardiography and NT-proBNP at the same time. On the basis of cardiac evaluations, tissue doppler echocardiography measurements were found as significant and specific for the early assessment of right ventricular diastolic disfunctions.

Cardiovascular consequences of bronchopulmonary dysplasia in prematurely born preschool children

BACKGROUND

A limited number of studies have reported various short-term cardiovascular changes in bronchopulmonary dysplasia (BPD) patients in the postsurfactant era. Little is known about the course of these changes in children with BPD.

OBJECTIVES

It was the aim of this study to investigate cardiovascular consequences of BPD at preschool ages and to find out possible risk factors related to cardiovascular sequelae.

METHODS

Prematurely born children with (n = 21) and without BPD (n = 20) were evaluated with conventional and myocardial tissue Doppler echocardiography at the age of 2-4 years.

RESULTS

BPD patients had a decreased pulmonary artery acceleration time and higher left and right ventricular myocardial performance indexes, consistent with higher pulmonary pressures and impaired biventricular systolic and diastolic functions at preschool ages. Low birth weight, disease severity and postnatal cumulative steroid dose were related to these changes.

CONCLUSION

Negative effects of BPD on global cardiac performances of both ventricles and pulmonary arterial pressure persist up to preschool ages.

Lung function among infants born preterm, with or without bronchopulmonary dysplasia

OBJECTIVE

Both healthy preterm infants and those with bronchopulmonary dysplasia (BPD) have poor lung function during childhood and adolescence, although there is no evidence whether prematurity alone explains the reduction in lung function found in BPD infants. Our study seeks to know if lung function, measured in infancy by means of rapid thoracic compression with raised volume technique, is different between preterm infants with and without BPD.

METHODS

Lung function was measured in 43 preterm infants with BPD and in 32 preterm infants without BPD at a chronological age range of 2-28 months. Forced vital capacity (FVC), forced expiratory volume at 0.5 sec, and forced expiratory flows at 50, 75, 85%, and 25-75% of FVC were obtained from maximal expiratory volume curves by means of rapid thoracic compression with raised volume technique. Maximal flow at functional residual capacity was measured using rapid thoracic compression at tidal volume. Multiple regression analysis and generalized least squares (GLS) random-effects regression model were used to control for variables such as gender, weeks of gestation, age, birth weight, and tobacco smoke exposure. A sub-analysis was performed in infants born at 28+ weeks of gestation.

RESULTS

BPD was associated to significantly lower flows (regression coefficients: -0.51, -0.54, -57, -0.53, and -0.82, respectively for FEF(50), FEF(75), FEF(85), FEF(25-75)). This association was driven by males and maintained in the subgroup of infants born at 28+ weeks of gestation.

CONCLUSION

BPD is associated with an additional decrease of lung function during the first 2 years of life in infants born preterm.

Serial measurements of lung function in a cohort of young children with bronchopulmonary dysplasia

OBJECTIVE

We aimed to prospectively and longitudinally measure lung function in a cohort of children with bronchopulmonary dysplasia (BPD) during their first 3 years of life.

METHODS

Forty-four children with BPD with a mean (+ or - SD) gestational age of 25.6 (+ or - 1.7) weeks and birth weight of 0.767 (+ or - 0.2) kg underwent serial measurements of lung function (maximum flow at functional residual capacity [V(max)FRC] and functional residual capacity [FRC]) at 6, 12, and 24 months after initial discharge from the neonatal care unit.

RESULTS

Compared with normative data, children with BPD had low partial expiratory airflow, measured by V(max)FRC, with mean z score (+ or - SD) of -1.92 (+ or - 1.04), -1.79 (+ or - 1.5), and -1.67 (+ or - 1.5) at 6, 12, and 24 months, respectively. Over time there was no significant improvement in z scores (P = .66), and 45% of the patients had a z score value of less than -2 (2 SDs below the mean) at the end of the study. FRC measurements steadily and significantly increased over time. Partial expiratory flow showed no correlation with gestational age, birth weight, or length of mechanical ventilation. Mean FRC was significantly higher in children who were using bronchodilators and inhaled steroids but showed no correlation with clinical symptoms. Bronchodilator response was initially present in 30% of the patients and declined to 20% at the end of the study.

CONCLUSIONS

During the first 3 years of life, children with mostly moderate-to-severe BPD continue to show significant abnormalities with airflow limitation according to lung-function testing.

Pulmonary outcomes in bronchopulmonary dysplasia

The incidence of bronchopulmonary dysplasia (BPD), defined as oxygen need at 36 weeks of postmenstrual age, is about 30% for infants with birth weights <1000 g. BPD is associated with persistent structural changes in the lung that result in significant effects on lung mechanics, gas exchange, and pulmonary vasculature. Up to 50% of infants with BPD require readmission to the hospital for lower respiratory tract illness in the first year of life. Long-term measurements of lung function in BPD include normalization of pulmonary mechanics and some lung volumes over time as somatic and lung growth occur, whereas abnormality of small airway function persists. The majority of data reveals no long-term decrease in exercise capacity. Mild to moderate radiological abnormalities persist. BPD is a result of dynamic processes involving inflammation, injury, repair, and maturation. Infants with BPD have significant pulmonary sequelae during childhood and adolescence, and continued surveillance of young adults with BPD is critical.

Physiological consequences of early-life insult

The most commonly observed severe lung injuries in early life are the respiratory distress syndrome in premature infants and the acute respiratory distress syndrome in children. Both diseases are characterised by alveolar instability, fluid filled airspace and some degree of airway obstruction. In the acute phase, collapsed alveoli can be reopened with positive end-expiratory pressure and lung recruitment. New insight into the physiology of lung recruitment suggests that the shape of the pressure-volume curve is defined by the change in rate of alveolar opening and closing. Reduced lung volumes and severe ventilation maldistribution are found in the acute phase but may persist during childhood. Any severe lung injury in this early phase of life can cause significant structural and functional damage to the developing lung. Follow-up studies of children with chronic lung disease have shown that the functional abnormalities will improve but may still be present in later childhood.

Lung function tests in neonates and infants with chronic lung disease: forced expiratory maneuvers

This fourth paper in a review series on the role of lung function testing in infants and young children with acute neonatal disorders and chronic lung disease of infancy (CLDI) addresses measurements of forced expiration using rapid thoraco-abdominal compression (RTC) techniques and the forced deflation technique. Following orientation of the reader to the subject area, we focus our comments on the areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. All studies on infants and young children with CLDI using forced expiratory or deflation maneuvers demonstrated that forced flows at low lung volume remain persistently low through the first 3 years of life. Measurement of maximal flow at functional residual capacity (V'maxFRC) is the most commonly used method for assessing airway function in infants, but is highly dependent on lung volume and airway tone. Recent studies suggested that the raised volume RTC technique, which assesses lung function over an extended volume range as in older children, may be a more sensitive means of discriminating changes in airway function in infants with respiratory disease. The forced deflation technique allows investigation of pulmonary function during the early development of CLDI in intubated subjects, but its invasive nature precludes its use in the routine setting. For all techniques, there is an urgent need to establish suitable reference data and evaluate within- and between-occasion repeatability, prior to establishing the clinical usefulness of these techniques in assessing baseline airway function and/or response to interventions in subjects with CLDI.

Preterm infants with congenital heart disease and bronchopulmonary dysplasia: postoperative course and outcome after cardiac surgery

OBJECTIVE

Success in treatment of premature infants has resulted in increased numbers of neonates who have bronchopulmonary dysplasia (BPD) and require surgical palliation or repair of congenital heart disease (CHD). We sought to investigate the impact of BPD on children with CHD after heart surgery.

METHODS

This was a retrospective, multicenter study of patients who had BPD, defined as being oxygen dependent at 28 days of age with radiographic changes, and CHD and had cardiac surgery (excluding arterial duct ligation) between January 1991 and January 2002. Forty-three infants underwent a total of 52 cardiac operations. The median gestational age at birth was 28 weeks (range: 23-35 weeks), birth weight was 1460 g (range: 431-2500 g), and age at surgery was 2.7 months (range: 1.0-11.6 months). Diagnoses included left-to-right shunts (n = 15), conotruncal abnormalities (n = 13), arch obstruction (n = 6), univentricular hearts (n = 4), semilunar valve obstruction (n = 3), Shone syndrome (n = 1), and cor triatriatum (n = 1).

RESULTS

Thirty-day survival was 84% with 6 early and 6 late postoperative deaths. Survival to hospital discharge was 68%. There was 50% mortality for patients with univentricular hearts and severe BPD. The median duration of preoperative ventilation was 76 days (range: 2-244 days) and of postoperative ventilation was 15 days (range: 1-141 days). The median duration of cardiac ICU stay was 7.5 days (range: 1-30 days) and of hospital stay was 115 days (range: 35-475 days). Current pulmonary status includes on room air (n = 14), O2 at home (n = 4), and ventilated at home (n = 4) or in hospital (n = 4), and 5 patients were lost to follow-up.

CONCLUSIONS

BPD has significant implications for children who have CHD and undergo cardiac surgery, leading to prolonged ICU and hospital stays, although most survivors are not O2 dependent. Postoperative mortality was highest among patients with univentricular hearts and severe BPD. Optimal timing of surgery and strategies to improve outcome remains to be delineated.

Cardiovascular findings in very low birthweight schoolchildren with and without bronchopulmonary dysplasia

BACKGROUND

With the introduction of new therapies in peri- and neonatology, the clinical picture of bronchopulmonary dysplasia (BPD) seems to alter. The consequences of this "new BPD" are of interest.

AIM

To evaluate cardiovascular findings during the surfactant era in very low birthweight (VLBW, birth weight < 1500 g) schoolchildren with and without BPD.

METHODS

At 7-8 years of age, 34 VLBW children with BPD born in one hospital underwent blood pressure (BP) measurement, electrocardiography (ECG), two-dimensional Doppler and M-mode echocardiography, flow-volume spirometry and whole-body plethysmography. The age- and sex-matched control groups comprised 34 VLBW children without BPD (no-BPD group) and 34 term children (term group).

RESULTS

The mean(SD) diastolic BP was significantly higher in the no-BPD than in the BPD group (65(9) vs. 59(8) mm Hg, p < 0.05). No clinically significant tricuspid regurgitations were found. The groups did not differ with respect to right ventricular systolic time intervals corrected for heart rate. The results of all M-mode measurements were within normal range. Compared to term controls, the BPD cases had lower mean(SD) forced expiratory flow in 1 s (90(14)% vs. 99(11)% of ref., p < 0.05) and more often high ratio of residual volume to total lung capacity (15(52%) vs. 4(13%), p < 0.01). No clinically significant correlations were found between current lung function and echocardiographic findings.

CONCLUSION

In the surfactant era, school-aged VLBW survivors with and without BPD do not seem to evince indirect signs of elevated pulmonary pressure. The increased pulmonary vascular resistance associated with BPD appears to resolve with time more rapidly than abnormalities in respiratory function.

Infant pulmonary function testing

Pulmonary function tests in infants have been used for many years, but they have been largely relegated to specialized centers and research purposes. More recently, development of commercial equipment and newer techniques has allowed for more broad use and application of these tests. This review describes different techniques that have been used to study infants and toddlers, and their clinical applications.

Changes in pulmonary arterial pressure in preterm infants with chronic lung disease

BACKGROUND

Pulmonary arterial pressure (PAP) is raised in preterm infants with respiratory distress syndrome who subsequently develop chronic lung disease. The natural history of pulmonary hypertension in infants with chronic lung disease is unknown.

OBJECTIVES

To investigate changes in PAP, assessed non-invasively using Doppler echocardiography, in infants with chronic lung disease during the 1st year of life.

METHODS

Serial examinations were performed in infants with chronic lung disease and healthy preterm infants. The Doppler derived acceleration time to right ventricular ejection time ratio (AT/RVET) was calculated from measurements made from the pulmonary artery velocity waveform.

RESULTS

A total of 248 examinations were performed in 54 infants with chronic lung disease and 44 healthy preterm infants. The median AT/RVET was significantly lower in infants with chronic lung disease than in healthy preterm infants (0.31 v 0.37). AT/RVET significantly correlated with age corrected for prematurity in both infants with chronic lung disease (r = 0.67) and healthy infants (r = 0.55). There was no significant difference between the rate of change in AT/RVET between the two groups. In infants with chronic lung disease, multivariate analysis showed that AT/RVET was significantly independently associated with age and inversely with duration of supplemental oxygen treatment. Median AT/RVET was significantly lower in infants with chronic lung disease until 40-52 weeks of age corrected for prematurity.

CONCLUSIONS

Although PAP falls with increasing age in both infants with chronic lung disease and healthy preterm infants, it remains persistently raised in infants with chronic lung disease until the end of the 1st year of life.

Pulmonary function at school-age in surfactant-treated preterm infants

A follow-up study was conducted in 40 children who had been enrolled in a prospective randomized study of exogenous surfactant therapy for respiratory distress syndrome (RDS) (n = 22; S) or placebo (n = 18; P) to determine long-term pulmonary sequelae of surfactant treatment in premature infants with RDS. At follow-up, mean (SD) age was 6.63 (0.18) and 6.55 (0.23) years for S and P, respectively. Complete lung function tests (LFT) were attempted in all patients. Satisfactory data were obtained in 17/22 surfactant-treated and in 12/18 control children. There was no significant difference between groups for any of the parameters measured. Mean (SD) functional residual capacity (FRC) was 92% (16%) and 90% (21%) predicted, mean (SD) airway resistance (R(aw,exp)) was 122% (25%) and 127% (61%), and mean (SD) forced expiratory volume in 1 s (FEV1) was 104% (12%) and 99% (17%) predicted for S and P. Only maximal expiratory flow at 25% vital capacity (L/s) was significantly below the predicted range in S and P groups, with 74% (23%) and 77% (28%), respectively. To test bronchial hyperreactivity, a simple standardized running test was performed: 4 children in S and 5 in P showed a significant response as defined by clinical airway obstruction or changes in FEV1 and/or R(aw), with no significant difference between groups. Although we found no major abnormalities in lung function and no difference between S and P at early school-age, lack of cooperation during lung function tests makes further follow-up necessary.