Persistence of fetal circulation syndrome: an echocardiographic study

Persistent pulmonary hypertension of the newborn: pathogenesis, etiology, and management

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by severe hypoxemia shortly after birth, absence of cyanotic congenital heart disease, marked pulmonary hypertension, and vasoreactivity with extrapulmonary right-to-left shunting of blood across the ductus arteriosus and/or foramen ovale. In utero, a number of factors determine the normally high vascular resistance in the fetal pulmonary circulation, which results in a higher pulmonary compared with systemic vascular pressure. However, abnormal conditions may arise antenatally, during, or soon after birth resulting in the failure of the pulmonary vascular resistance to normally decrease as the circulation evolves from a fetal to a postnatal state. This results in cyanosis due to right-to-left shunting of blood across normally existing cardiovascular channels (foramen ovale or ductus arteriosus) secondary to high pulmonary versus systemic pressure. The diagnosis is made by characteristic lability in oxygenation of the infant, echocardiographic evidence of increased pulmonary pressure, with demonstrable shunts across the ductus arteriosus or foramen ovale, and the absence of cyanotic heart disease lesions. Management of the disease includes treatment of underlying causes, sedation and analgesia, maintenance of adequate systemic blood pressure, and ventilator and pharmacologic measures to increase pulmonary vasodilatation, decrease pulmonary vascular resistance, increase blood and tissue oxygenation, and normalize blood pH. Inhaled nitric oxide has been one of the latest measures to successfully treat PPHN and significantly reduce the need for extracorporeal membrane oxygenation.

Pulmonary vascular resistance during lipid infusion in neonates

Using two-dimensional echocardiography, pulmonary vascular resistance was estimated from right ventricular pre-ejection period to ejection time (RVPEP/ET) in 11 preterm infants with respiratory distress, to test the effect of different doses of continuous lipid infusion. Echocardiography was performed at baseline with no lipid infusing 2 and 24 hours after 1.5 and 3 g/kg/day of intravenous lipid, 24 hours after discontinuing intravenous lipid emulsion, and 2 hours after restarting intravenous lipid. After 24 hours of intravenous lipid at 1.5 g/kg/day the RVPEP/ET rose to mean (SD) 0.287 (0.03) from a baseline value of 0.225 (0.02) and to 0.326 (0.05) after 24 hours of intravenous lipid at 3 g/kg/day. Pulmonary arterial pressure returned to baseline 24 hours after the intravenous lipid had been discontinued. Continuous 24 hour infusion of lipid caused significant dose and time-dependent increases in pulmonary vascular resistance. Intravenous lipid may aggravate pulmonary hypertension.

Haemodynamic features at presentation in persistent pulmonary hypertension of the newborn and outcome

Thirty four newborns presenting with persistent hypoxaemia in the first three days of life underwent detailed haemodynamic assessment using Doppler echocardiography, including measurements of pulmonary arterial pressure (PAP), left ventricular (LV) function, and left ventricular output (LVO). Results were compared with values from 51 healthy babies, and those of survivors were compared with non-survivors. Four of the 34 babies were excluded from this analysis because one was found to have transposed great arteries, one had a large left-to-right shunt with no evidence of persistent pulmonary hypertension, and two had diffuse skeletal myopathy. Tricuspid regurgitation was present in 70%, permitting systolic PAP estimation. The pulmonary:systemic arterial pressure ratio range was 0.7:1 to 1.83:1 (mean 1.02:1). A patent duct was present in 83%, and flow patterns indicated PAP approaching, or above, systemic pressure in all. Systolic time interval ratio TPV/RVET (time to peak velocity at the pulmonary valve/right ventricular ejection time) was mostly (65%) in the normal range, and did not correlate with other PAP measurements. LV function was below the 10th centile in only 11%, but values for LVO lay below the 10th centile in 41%, and for left ventricular stroke volume index (LSVI) in 66%. Results of 18 survivors were compared with 10 non-survivors (excluding two premature babies who died early with pulmonary interstitial emphysema). There were no significant differences for any parameter of PAP or LV function, but LVO and LSVI were significantly lower in non-survivors: LVO survivors (mean (SD)), 205 (57), non-survivors 138 (63) ml/kg/minute (P < 0.01); LSVI survivors, 1.29 (0.51), non-survivors 0.86 (0.31) ml/kg (P < 0.05). All four babies with LVO < 100 ml/kg/minute died, and 6/7 babies with LSVI < 1 ml/kg died. Detailed echocardiographic evaluation shows that the haemodynamic features of persistent pulmonary hypertension are diverse and that clinical diagnosis can be incorrect. Low LV output and stroke volume, usually with normal LV function, were the only Doppler echocardiographic parameters to predict subsequent death. This correlation with outcome requires further prospective evaluation.

Doppler echocardiographic assessment of pulmonary circulation in severe respiratory failure of the neonate: an aid for extracorporeal lung support indications

Extracorporeal lung support (ECLS) for newborns with acute respiratory failure has achieved increased popularity over the last decade. However, precise criteria for its implementation remain controversial. The aim of this study was to assess the value of Doppler echocardiography (DE) in 31 neonates with PaO2 of < or = 50 mmHg, FIO2 of 1, and optimal ventilation. Treatment included mechanical ventilation, paralysis, volume loading, vasopressors, and tolazoline. Markers indicative of ECLS (failure of maximal medical therapy, assessed by AaDO2 of more than 610 mm Hg beyond 8 hours and/or an oxygenation index (OI = mean airway pressure x FIO2%/postductal PaO2) of more than 40 beyond 4 to 6 hours) were present in 23 (group 1) and absent in eight (group 2). Shunt direction and systolic pulmonary arterial pressure (sPAP) calculated from tricuspid insufficiency velocity were assessed using DE. At the time of admission, sPAP was significantly higher in group 1 (62.1 v 43.7 mm Hg). On day 1, group 1 differed from group 2 in maximum sPAP value (73.2 v 44.4 mm Hg), PaCO2 (56.1 v 40 mm Hg), right-to-left shunting (85% v 25% of the patients), and pulmonary-to-systemic-pressure systolic ratio (sPAP:sSAP) (1.29 v 0.75). Patients with an sPAP:sSAP ratio of more than 1 and patients with high sPAP associated with high PaCO2 on day 1, all later (average, 10 hours later) fulfilled ECLS criteria; this suggests that DE assessment of pulmonary circulation may yield early and predictive markers of impending ECLS indication. Further confirmation of these results would help avoid unnecessary delays in ECLS implementation in newborns with severe respiratory failure.

Increased right ventricular afterload alters left ventricular function in newborn lambs

The effects of acutely increased right ventricular afterload induced by mechanical constriction of the main pulmonary artery or with alveolar hypoxia on function of the left ventricle were assessed in six and nine lambs, respectively (aged 1 to 3 days). Mechanical constriction of the main pulmonary artery in newborn lambs compromised left ventricular function with significant decreases in systemic blood flow and the peak first derivative of left ventricular pressure when considered simultaneously and as single variables. In contrast, alveolar hypoxia augmented left ventricular function with significant increases in systemic blood flow and the peak first derivative of left ventricular pressure when considered simultaneously or as single variables. Interaction appears to exist between the right and left ventricles during the newborn period. The mechanically increased afterload may have compromised left ventricular function by altering its end-diastolic size, inotropic state, or both. On the other hand, the augmented left ventricular function in the presence of hypoxia may have been due to an increase in inotropic background. The clinical implications in some infants with pulmonary hypertension and left ventricular dysfunction are raised.

Pulsed Doppler echocardiographic evaluation of neonatal circulatory changes

Pulsed Doppler echocardiograms were obtained from 42 normal fullterm neonates at less than 12 hours (20 subjects), 4 days (20 subjects), and 33 days (12 subjects). The acceleration time of the flow velocity and ventricular systolic time intervals were measured on recordings obtained at the right and left ventricular outflow tract, and the patency of the ductus arteriosus was evaluated by the flow at the pulmonary end of the ductus. The flow velocity pattern of the right ventricular outflow tract changed from a triangular shape with a peak velocity in early systole in the younger age groups to a dome-like contour with a peak velocity in mid-systole; thus the ratio of mean acceleration time to right ventricular ejection time increased with age. The flow velocity pattern of the left ventricular outflow tract was triangular in all age groups, and the ratio of mean acceleration time to left ventricular ejection time showed no significant change with age. The right ventricular pre-ejection period shortened and the right ventricular ejection time lengthened with age; thus the ratio of mean right ventricular pre-ejection period to right ventricular ejection time decreased with age. The left ventricular systolic time intervals showed no significant change with age. The ductus arteriosus was patent in all subjects who were less than 12 hours old but was closed in the older neonates. Pulsed Doppler echocardiography is a valuable method of evaluating pulmonary vascular bed in the early neonatal period.

Effect of intralipid on the neonatal pulmonary bed: an echographic study

The effect of Intralipid infusion on pulmonary vascular resistance was studied prospectively by serial echocardiography on 13 occasions in six low birth weight infants. After 90 minutes of Intralipid infusion, the ratio of right ventricular preejection period to ejection time (RVPEP/ET) rose from 0.232 +/- 0.025 (mean +/- SD) to 0.285 +/- 0.035 (P = 0.0001). Of the 13 infusions studied, six (43%) resulted in RVPEP/ET values suggestive of pulmonary hypertension. Six LBW infants were observed over the same time period without Intralipid infusion, and RVPEP/ET did not change (0.209 +/- 0.035 vs 0.194 +/- 0.024). The increase in RVPEP/ET with Intralipid administration could not be explained by differences in preload or contractility, and most likely reflects an increase in pulmonary vascular tone. Caution in the use of Intralipid is recommended in infants who would be at particular risk from increased pulmonary vascular resistance.

Effect of pulmonary artery distention on systemic vascular resistance in newborn lambs

Balloon distention of the left pulmonary artery (PA) was produced in 14 lambs (aged 1 to 3 days) to assess whether an increase in systemic vascular resistance results from such distention. The lambs were anesthetized with chloralose and instrumented to enable measurement of systemic blood flow, PA pressure, aortic pressure, heart rate and right atrial pressure. PA distention resulted in an increase in systemic vascular resistance and aortic pressure (p less than 0.05). This result was probably due to a systemic vasoconstrictor response, since systemic blood flow and right atrial pressure did not change significantly. Limited trials using autonomic blocking agents suggested that the response is either a reflex under autonomic control or a response to humoral release of alpha-adrenergic substances. In conclusion, some interdependence appears to exist between the systemic and pulmonary vascular beds. It is postulated that such changes may be important in fetal life when they may affect redistribution of cardiac output during adaptation to hypoxemia.

Echocardiography in the neonate and young infant

The neonate and young child present unique problems in echocardiographic diagnosis because of the wide spectrum of possible abnormalities and the tendency toward multiple lesions, requiring clear visualization of all great veins and arteries as well as intracardiac structures. Performance and interpretation of echocardiograms in this age group require an extensive knowledge of the pathologic anatomy of congenital heart disease. Recognition of unusual lesions is facilitated by displaying the heart in an anatomically familiar (upright) format in order to draw from experience in angiography and pathology. The subxiphoid (subcostal) transducer position provides a flexible acoustic window for scanning the heart and great vessels in a multitude of planes, providing a general orientation for each cardiac segment. All other transducer positions are utilized to provide specific anatomic information. Although in this age group echocardiographic visualization of intracardiac anatomy is superior to other techniques, delineation of the great vessels remains its greatest limitation. Tortuous vessels may not lie in a single plane and, therefore, cannot always be displayed throughout its length by a "slice" technique such as echocardiography. In addition, limited focal range of most high frequency transducers is a continuing impediment to imaging structures in the posterior and superior mediastinum. Echocardiography provides a cost-effective means for identifying the neonate with life-threatening cardiovascular disease. It provides a complete and definitive anatomic diagnosis, in some cases eliminating the need for further procedures, while in others, improving the timing and performance of cardiac catheterization. Future studies should investigate the proper utilization of echocardiography as adjunct to or replacement of other techniques in the management of the young child.

Heart rate and systolic time intervals in healthy newborn infants: longitudinal study

To determine the influence of heart rate (HR) on systolic time intervals (STI) in neonates, serial measurements of right ventricular (RVSTI) and left ventricular systolic time intervals (LVSTI) were made on 30 healthy term newborn infants at age 4-8 h, 24-30 h, eight days, and four weeks. STI was related to HR and age. Age-related changes were similar to previously reported results. The preejection periods (RPEP and LPEP) significantly shortened with increasing age, whereas the right and left ventricular ejection times (RVET and LVET) were unrelated to age. RPEP was unrelated to HR, but tended to be prolonged in restless infants. With increasing HR, RVET decreased and RPEP/RVET increased in all age groups, but less at four weeks. A rise in HR of 50/min resulted in an increase of RPEP/RVET by 26% of the mean value at age 4-8 h and by 20% at four weeks. In 14 infants, RVSTI was recorded during a change in HR. In all these infants, RPEP and RPEP/RVET increased with increasing HR. We conclude that HR-related changes of RVSTI in neonates are different from those in older subjects. It should be considered that in neonates elevated values of RPEP/RVET, suggesting increased pulmonary vascular resistance, may be caused by high HR and unrest.

Clinical and echocardiographic evidence suggesting afterload reduction as a mechanism of action of tolazoline in neonatal hypoxemia

The effect of tolazoline was assessed in 29 hypoxic neonates. Tolazoline was given in a bolus starting at 1 mg/kg and repeated or infused for 5-134 hours. A "good clinical response," defined as a rise in PaO2 of more than 20 mm Hg, was obtained in 23 (79%), 20 of this group were weaned from the respirator, and three died. Six infants did not respond initially and four died. Failure to respond to tolazoline or to be weaned from the ventilator was usually associated with severe additional pathology. Urine output (greater than 1 ml/kg/h) was adequate in most neonates during therapy. In those with preexisting oliguria (less than 1 ml/kg/h), output improved during therapy. Blood pressure monitoring showed a fall in blood pressure in 19 patients during tolazoline administration, but true hypotension only occurred in four; in seven there was no fall and in three there was a rise in blood pressure. Echocardiography was performed prior to therapy in 19 patients and repeated in 12 patients after 24 h. Additional "tracking" was performed at 10 min, 1 h, and 4 h in seven patients. Prior to therapy, right ventricular dysfunction was demonstrated by abnormal right ventricular systolic time intervals (RVSTIs) in 17 of the patients tested. A rapid improvement was evident during therapy especially with "tracking." Left ventricular dysfunction, assessed by left ventricular systolic time intervals (LVSTIs), ejection fraction (EF), shortening fraction (SF), and velocity of circumferential fiber shortening (VCF), was also evident prior to therapy and improved, though more gradually than the RVSTIs.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular function in persistent pulmonary hypertension of the newborn. Computer analysis of the echocardiogram

Regional and global left ventricular function was assessed in 23 neonates with persistent pulmonary hypertension using computer assisted analysis of their left ventricular echocardiograms and compared with that in 50 healthy neonates. End diastolic left ventricular dimension was normal and end systolic dimension increased while percentage left ventricular shortening and peak velocity of circumferential fibre shortening decreased indicating impaired systolic performance. The peak rate of increase in left ventricular diameter in early diastole was significantly decreased and the durations of the rapid filling and isovolumic relaxation periods were prolonged suggesting resistance to left ventricular filling due to changes in diastolic myocardial properties. This abnormal left ventricular cavity function may have been due to a combination of increased diastolic wall thickness, reduced percentage systolic wall thickening, increased relative wall thickness, and pronounced reduction in peak rates of systolic wall thickening and diastolic wall thinning Seven neonates with persistent pulmonary hypertension died, and of the three examined at necropsy all had left ventricular hypertrophy and two extensive subendocardial haemorrhage and infarction affecting the right and left ventricular papillary muscles. Thus left ventricular dysfunction appears to be a common feature in neonates with this disorder and may be readily detected using computer analysis of left ventricular echocardiograms. Unfortunately, no single echo measurement was useful prognostically. Left ventricular dysfunction in persistent pulmonary hypertension probably results from a combination of hypoxaemia, acidaemia, and pulmonary hypertension, and although it may contribute to the high mortality in this syndrome, a correlation between the severity of left ventricular dysfunction and clinical outcome could not be shown.

Ventricular systolic time intervals by simultaneous echocardiographic recording of the semilunar valves during the first days of life: a study of normal newborn infants

A modified ultrasonic method was used to image simultaneously the semilunar valves in order to study comparative neonatal right and left ventricular systolic time intervals (STI) and phasic respiration. We obtained 72 serial M-mode echocardiograms from 24 normal term infants during the first 3 days of life. Right and left ventricular pre-ejection period (RPEP, LPEP), ejection times (RVET, LVET), and STI ratios (RPEP/RVET, LPEP/LVET) did not vary with respiratory variation during the first days of life; aortic (Q-Ac) and pulmonic valve (Q-Pc) closure intervals were uninfluenced by respiration. Widening of Ac-Pc interval beyond 15 msec was present in 56% by day 3. The RPEP/LVET was greater than LPEP/LVET on the first day--a finding previously described in infants with dextro-transposition of the great arteries. Relatively fixed duration of right ventricular systole (Q-Pc) and the absence of inspiratory widening of the Ac-Pc interval, despite decreasing pulmonary vascular resistance, may be related to differences of right ventricular compliance and pulmonary vascular capacitance in the newborn infant.

Venovenous extracorporeal membrane oxygenation in neonates with respiratory failure

Venoarterial (VA) extracorporeal membrane oxygenation (ECMO) has been successful in support of neonates with respiratory failure but requires right common carotid artery ligation. While no short-term neurologic complications have resulted from neonatal carotid ligation, late complications may occur. For both VA ECMO and venovenous (VV) ECMO, blood is drained from the right atrium via a right internal jugular cannula, oxygenated by a membrane lung, and returned to the patient. VV ECMO spares the carotid by perfusing the oxygenated blood into a vein. VV ECMO gave total respiratory support to three neonates with respiratory failure and each infant survived. In comparison with three similar VA ECMO patients, the VV patients required higher ECMO circuit flow rates and had lower systemic arterial Po2s. Length of time on ECMO, length of hospital stay, and neurologic outcome were similar in the VV and VA patients. Differences among the patients were related to their primary disease rather than to the mode of ECMO support. The VV patients had cannulation of the femoral vein for perfusion of oxygenated blood. Late complications may occur from femoral vein ligation as well as from carotid ligation so long-term follow-up is needed to assess these two ECMO techniques.

Initial systolic time intervals as predictors of the severity of transient tachypnea in term neonates

42 term neonates with transient tachypnea (TTN) underwent echocardiography and determination of systolic time intervals before the age of 4 hours. Based on initial measurement of right ventricular systolic time intervals (RVSTIs) the patients were divided in two groups: neonates with RVSTI ratios less than or equal to 0.50 (Group I) (n = 35) and neonates with RVSTI ratios greater than 0.50 (Group II) (n = 7). Group II neonates also had significantly more prolonged left ventricular systolic time intervals (LVSTIs) than Group I neonates. Group II neonates developed markedly more severe form of TTN than Group I neonates. Initially prolonged RVSTI was best predictor of the development of severe TTN (relative risk ratio 17.5, p less than 0.001): clinical characteristics and oxygen requirements at the admission had limited predictive value.

Atrial right-to-left shunt in infants with respiratory and cardiac distress but without congenital heart disease. Demonstration by contrast echocardiography

Contrast echocardiography was used to detect atrial right-to-left shunts in 20 term infants; there were 10 cyanosed infants who had severe respiratory distress and signs of cardiac failure but no apparent congenital heart disease and 10 noncyanosed infants with no respiratory distress and no signs of cardiac failure who underwent exchange transfusion for hyperbilirubinemia. All of the venous contrast echocardiograms in the cyanosed infants showed an atrial right-to-left shunt with a dense contrast effect in the left atrium and aorta but little in the right ventricle. A sparse effect in the left atrium and a dense one in the right ventricle were recorded in infants with resolving respiratory distress and in three infants from the control group. The other seven infants in the control group showed no right-to-left shunt. Conventional M-mode echocardiograms showed no evidence of congenital heart disease in any of the 20 infants. This contrast echocardiographic technique was useful for demonstrating an atrial right-to-left shunt in cyanosed term infants with neonatal respiratory problems and signs of congestive failure but no apparent congenital heart disease.

The cardiovascular effects of dopamine in the severely asphyxiated neonate

The cardiovascular effects of dopamine were evaluated in 14 severely asphyxiated neonates. After a period of stabilization, either dopamine 2.5 micrograms/kg/minute or placebo was infused in a randomized double-blind protocol. In seven dopamine-treated infants, echocardiographically determined shortening fraction and mean velocity of circumferential fiber shortening increased when compared to preinfusion values (P less than 0.05). There was no significant change in these echo indices of cardiac function in the placebo-treated group. Systolic blood pressure rose in the dopamine group when compared to predopamine infusion values and to the postinfusion values of the placebo group (P less than 0.001 and 0.025, respectively). Diastolic blood pressure increased to a small degree in the dopamine group. There was no significant change in heart rate or echocardiographically measured systolic time intervals. Low doses of dopamine increase cardiac performance and raise systolic blood pressure in the severely asphyxiated neonate.

The structural basis of persistent pulmonary hypertension of the newborn infant

Six neonates of 35 to 42 weeks' gestation had findings of persistent pulmonary hypertension and died between one and 6 days of age despite intensive medical therapy. Each patient had pulmonary artery pressure near or above systemic level, with a right-to-left shunt via the foramen ovale and/or ductus arteriosus. At postmortem, morphometric analysis of the peripheral pulmonary vascular bed revealed extension of muscle into small arteries, which was severe in five of six patients; all alveolar duct and wall arteries (less than 30 micrometers external diameter), normally nonmuscular, were fully muscularized. In these five patients medial wall thickness of the normally muscular intra-acinar arteries was doubled; arterial size and number, however, were normal in all. This striking structural maldevelopment of the peripheral pulmonary arterial bed occurred or was initiated in utero and does not merely represent a failure of the fetal pattern to regress. We suggest that this particular group of patients remained refractory to all current modes of therapy because of these severe structural pulmonary vascular changes.

Transient tachypnoea of the newborn: two distinct clinical entities?

Twenty-five infants with transient tachypnoea of the newborn (TTN) were examined by serial echocardiography during the first 4 days of life. The infants could be divided clinically into two groups: group 1 (n = 19) babies with mild classical TTN requiring less than 40% oxygen, and group 2 (n = 6) babies with severe TTN needing greater than 60% oxygen. Apart from amount of oxygen these two groups differed in that those with severe TTN had lower Apgar scores and arterial pH soon after birth. Echocardiography showed that the babies with classical TTN had increased left ventricular pre-ejection period to ejection times (LPEP/LVET) during the first day of life. Initial LPEP/LVET ratio correlated with duration of treatment with oxygen. The babies with severe TTN increased LPEP/LVET and right ventricular pre-ejection period to ejection times ratios (RPEP/ RVET) during the first 3 days of life. There was no correlation between systolic time intervals and duration of oxygen treatment. These findings suggest that there may be two distinct types of TTN: mild or classical type resulting from mild left ventricular failure, and a severe type associated with generalised myocardial failure, pulmonary hypertension, and right-to-left shunting.

Specificity and accuracy of echocardiographic and clinical criteria for diagnosis of patent ductus arteriosus in fluid-restricted infants

We assessed the utility of M-mode echocardiographic and clinical criteria for diagnosis of left-to-righ shunting PDA in fluid-restricted newborn infants. The presence of a left-to-right shunting PDA was established in 56 infants by 103 aortic contrast echo injections. The studies were graded negative (pattern 0) if only the transverse aortic arch opacified; positive (pattern I) if both the transverse aortic arch and right pulmonary artery opacified; and very positive (pattern II) if only the right pulmonary artery opacified. Simultaneously with the injections, all infants underwent clinical examinations and echocardiography. By clinical criteria, only 72% of patients were correctly identified as having a left-to-right shunting PDA. No murmur was audible during 28 of 55 Grade I or II injections. M-mode echocardiographic measurements demonstrated increasing left atrial dimensions and decreasing LPEP/LVET with each advancing pattern of infection. However, combining these determinants yielded a discriminant analysis which correctly identified only 51% of cases. These data indicate that conventional M-mode echocardiographic and clinical criteria do not have acceptable specificity or accuracy for detection of left-to-right shunting PDA in fluid-restricted premature infants.

Evidence of surfactant deficiency in persistence of the fetal circulation

The phospholipids of tracheal aspirates in persistence of the fetal circulation (PFC) were compared to those in the respiratory distress syndrome (RDS) and those in other severe diseases of the newborn. The infants with PFC were hypoxemic despite 80 to 100% inspiratory oxygen. There were small, if any, pulmonary parenchymal changes in radiographs. Echocardiograms demonstrated evidence of increased pulmonary arterial pressure. Mechanical ventilation increased arterial oxygen tension in each case. However, five of the eight patients required ventilation at a high frequency (57-65 min) and long inspiratory time (0.6--0.7 s). The phospholipids in tracheal aspirates in PFC were quite similar to those in RDS, namely there was a small amount, if any, phosphatidylglycerol (PG), and the lecithin/sphingomyelin (L/S) ratio was low. However, phosphatidylinositol was higher in PFC than in RDS. In the other diseases studied, the phospholipid composition resembled that of the normal newborn, namely PG was present and the L/S ratio was high. Surfactant deficiency seems to be important in the pathogenesis of some cases of PFC. The favorable effect of mechanical ventilation may be partly due to the stabilization of peripheral airways.

Thrombocytopenia and pulmonary hypertension in the perinatal aspiration syndromes

Thirty-three of 616 consecutively admitted newborn infants had trombocytopenia (platelet count less than 150,00/mm). Only 16 of these were among the 356 infants with lung disease. However, 12 of the 16 were among the 90 infants with a diagnosis of a perinatal aspiration syndrome. The 12 thrombocytopenic infants were the only infants with PAS considered to have pulmonary hypertension. The duration of significant right-to-left shunting of blood paralleled the duration of thrombocytopenia in these infants; PHN was not associated with thrombocytopenia in other neonatal lung diseases. Thus, platelets appear to be important in the pathogenesis of PHN complicating PAS.

Echocardiography in hypoxemic neonatal pulmonary disease

Sixteen newborn infants with severe pulmonary parenchymal disease and profound hypoxemia were treated with mechanical ventilation, alkalinization, and intravenous tolazoline. Eight infants responded within two hours of initiation of tolazoline therapy with a rise in Pao2 by at least 100% of pretreatment values (mean = 188%, range = 103 to 427%). Eight infants showed little or no change in Pao2 with administration of tolazoline. Echocardiographic evaluation prior to therapy demonstrated marked elevation in both left (LPEP/LVET = 0.52 +/- 0.13) and right (RPEP/RVET = 0.56 +/- 0.08) ventricular systolic time intervals in the eight infants who subsequently responded to tolazoline. Systolic time intervals in nonresponders were within the normal range (LPEP/LVET = 0.37 +/- 0.03, RPEP/RVET = 0.33 +/- 0.04) and were not significantly different from those observed in a control group of 15 infants with pulmonary disease requiring mechanical ventilation but without hypoxemia. Following tolazoline therapy, systolic time intervals in all eight responders fell to normal values. Echocardiography can provide a safe, noninvasive method for identifying those infants with primary pulmonary disease and severe hypoxemia who could be expected to benefit from tolazoline therapy, thereby avoiding tolazoline side effects in infants for whom tolazoline therapy can be predicted to be of little benefit.

Main pulmonary artery distention: a potential mechanism for acute pulmonary hypertension in the human newborn infant

Balloon-induced distention of the main pulmonary artery causes acute pulmonary hypertension and reflex pulmonary vasoconstriction in animals. Pulmonary artery pressure responses caused by MPA balloon inflation were measured in ten human newborn infants with cardiac failure (n = 5) or persistent fetal circulation (n = 5). During balloon inflation distal mean PAP increased significantly while cardiac rate remained unchanged. MPA distention caused greater increases of PAP in those infants with lower resting PAP. The greatest balloon-induced increases of PAP were observed in infants recovering from PFC. The existence of a pulmonary artery reflex and its possible role in the regulation of the human fetal and neonatal pulmonary circulation is discussed.

Growth patterns of cardiac structures and changes in systolic time intervals in the newborn and infant. A longitudinal echocardiographic study

A longitudinal study was undertaken in 21 newborns to determine cardiac growth pattern by echocardiography over the course of the first year of life. Most cardiac structures increased in size as a linear function of age and weight; however, the right ventricular end-diastolic diameter remained unchanged so that the RV/LV ratio decreased as a parabolic function of age. Left and right ventricular systolic time intervals (RVSTI, LVSTI) after birth were also studied. The ratio of left ventricular preejection period (LVPEP) to left ventricular ejection time (LVET) decreased markedly immediately after birth and subsequently remained at a constant mean value (0.30 +/- 0.04) for the rest of the study period. Right ventricular systolic time interval ratios (RVPEP/RVET) decreased rapidly and significantly during the first day of life (from a mean value of 0.39 +/- 0.08 in the first 24 hours to 0.28 +/- 0.05 on the 6th day of life). Constant values of 0.24 +/- 0.03 were found from the 3rd month of life onwards. The decrease in RVPEP/RVET in the first days of life followed a parabolic function reflecting the physiological decrease of pulmonary vascular resistance after birth.

Echocardiographic abnormalities in infants of diabetic mothers

In order to evaluate the presence of myocardial hypertrophy and/or abnormalities of postnatal cardiovascular adaptation, echocardiograms were performed on 34 infants of diabetic mothers. Based on cardiopulmonary assessment, the IDM were divided into three groups: Group I with congestive heart failure predominating: Group II with respiratory distress predominating: Group III asymptomatic. Hypertrophy of the interventricular septum and of the walls of left and right ventricles was frequently present in IDM: this change was most notable in association with clinical CHF. Six IDM, four of whom were found to have CHF, had additional echocardiographic signs of subaortic stenosis. All IDM had normal indices of left ventricular performance, despite the presence of CHE. In IDM with respiratory distress, the right ventricular pre-ejection period to ventricular ejection time ratio was elevated, suggesting an abnormality of the transitional pulmonary circulation. Poor maternal diabetes control and maternal systemic hypertension were closely correlated with evidence of myocardial hypertrophy in the infants.

Increased systemic vascular resistance in neonates with pulmonary hypertension

The time necessary for aortic diastolic pressure to decrease to 50 percent of an initially selected value after dissipation of the dicrotic notch (T 1/2) was determined in newborn infants with and without pulmonary hypertension. The mean T 1/2 was 671 +/- 167 msec in seven infants with clinical evidence of pulmonary hypertension and documented right to left ductus arteriosus shunting; 849 +/- 243 msec in nine infants with clinical evidence of pulmonary hypertension but no documented right to left ductus arteriosus shunting; and 457 +/- 66 msec in eight infants with hyaline membrane disease and no clinical evidence of pulmonary hypertension or a patent ductus arteriosus. The mean T 1/2 values in the former two groups were significantly different from that in the group with no pulmonary hypertension (P less than 0.01). An evaluation of factors affecting T 1/2 leads to the conclusion that the patients with pulmonary hypertension had increased systemic vascular resistance as well. This finding has important diagnostic, etiologic and therapeutic implications.