Ductal Flow Research Articles

Isolated ductal closure in utero diagnosed by fetal echocardiography.

In utero isolated ductal closure is uncommon and can lead to fetal hydrops and death if not recognized. Five fetuses were diagnosed prenatally by echocardiography. The reasons for referral were hydrops (2), cardiomegaly (1), polyhydramnios and choroid plexus cyst (1), and polyhydramnios and teratoma of the neck (1). Gestational age was median 32, range 18-41 weeks. Two mothers received indomethacin for polyhydramnios, with the echocardiogram performed 5 and 3 days after the last dose. Three had a negative history of drug ingestion. Fetal echocardiograms showed absent flow in the ductus arteriosus, dilated right ventricle with decreased function, and mild or moderate tricuspid and pulmonary insufficiency in all. The left ventricle was hypercontractile, with significantly increased left ventricular stroke output when compared to the right. Four fetuses were delivered by cesarean section and had an uneventful course. One fetus died shortly after birth due to airway obstruction from a large teratoma. Autopsy showed ductal constriction. Postnatal echocardiograms showed absent ductal flow and dilated right ventricle. On follow-up, survivors remained asymptomatic with cardiac size returning to normal. Premature closure of the ductus arteriosus should be considered in hydrops of unknown etiology, right ventricular dysfunction, and following indomethacin therapy. Urgent delivery results in an excellent prognosis.

Postnatal changes in left ventricular volume and contractility in healthy term infants.

To evaluate how the size of the ductus arteriosus affects neonatal left ventricular (LV) volume and contractility, we serially obtained two-dimensional and Doppler echocardiograms at 2, 12, 24, and 120 hours after birth in 20 healthy infants. LV volume was calculated by the biplanar Simpson's rule, and ductus arteriosus size with left-to-right shunting was measured by two-dimensional and Doppler echocardiography. At 2 hours, the ductus arteriosus was at its maximal size, and the LV end-diastolic volume was 1.2-fold higher than at the subsequent hours after birth. Additionally, there was a significant linear correlation between the end-diastolic volume and the ductal diameter. In contrast, the peripheral vascular resistance, derived from blood pressure measurements and Doppler echocardiography, was lowest at 2 hours of age. The mean normalized systolic ejection rate, an index of contractility, remained constant throughout the study period. These results suggest that alterations in the LV end-diastolic volume soon after birth depend on changes in ductal flow, which in turn is affected by ductal diameter, and that the neonatal left ventricle operates at its maximal performance with limited contractility during ductal patency.

Doppler Echocardiographic Evaluation of Ventricular Diastolic Filling in Fetuses With Ductal Constriction

To assess ventricular diastolic filling in fetuses with constriction of ductus arteriosus, 43 fetuses of pregnant women receiving indomethacin (100 to 150 mg/day) were examined with Doppler echocardiography. Ductal constriction occurred in 21 fetuses, defined as maximal systolic velocity >140 cm/s and diastolic flow velocity >30 cm/s. The variables measured to assess diastolic function were peak velocity during early diastole (peak E wave), peak velocity during atrial contraction (peak A wave), and the velocity ratio (peak E/A ratio); these were compared to maximal ductal flow velocity during systole and diastole. The mitral peak E wave, peak A wave, and peak E/A ratio in fetuses with ductal constriction showed no significant difference from those in fetuses without ductal constriction. In fetuses with ductal constriction, the tricuspid A wave increased significantly without changes in the peak E wave (57 ± 9 vs 50 ± 6 cm/s, p <0.01) and the peak E/A ratio was significantly lower than in fetuses without ductal constriction (0.57 ± 0.10 vs 0.65 ± 0.08, p <0.05). In 9 fetuses with ductal constriction, we compared the Doppler tricuspid E wave, A wave, and E/A ratio during indomethacin administration with those after withdrawal of the drug for a mean of 24 hours. Both systolic and diastolic ductal flow velocities in the fetuses returned to normal range after discontinuation of indomethacin. The tricuspid peak A wave decreased (59 ± 9 vs 50 ± 11 cm/s) and the E/A ratio increased significantly (0.56 ± 0.07 vs 0.69 ± 0.07) (both p <0.01) without any significant change in peak E wave after discontinuation of indomethacin. This study suggests that ductal constriction influences Doppler patterns of right ventricular diastolic filling. These changes could be related to the increased afterload presented to the right ventricle which might affect diastolic function.This study suggested that ductal constriction in human fetuses influences Doppler patterns of right ventricular diastolic filling. The changes we detected in right ventricular filling patterns in fetuses with ductal constriction may be related to the alterations in right ventricular afterload and diastolic function.

Video-Assisted Thoracoscopic Operation for Interruption of Patent Ductus Arteriosus in Adults

Background. Patent ductus arteriosus (PDA) is a frequent congenital heart disease encountered in premature neonates, infants, and children. Video-assisted endoscopic techniques have been used in PDA interruption since 1993. Almost all the experiences are in pediatric patients. Applications in adults with PDA have been limited. Methods. We report our experience of video-assisted thoracoscopic surgical ligation of PDA in adults. From August 1995 to January 1996, 60 patients with PDA were operated on with a video-assisted thoracoscopic technique. Twelve adults were identified with mean age of 30 years (range, 20 to 57 years). With the patient under general anesthesia and double-lumen endotracheal intubation, two 5-mm holes were made in the left lateral chest wall. Another 4-cm incision was made in the left third intercostal space for manipulation, dissection, and ligation. Conventional surgical instruments were used except an endoscopic grasper and an endoscopic tube that connected to a video camera. The surgical procedure was viewed on a video screen. Transesophageal echocardiography was used for monitoring during PDA ligation. Results. All patients had successful ligation of the PDA. There was no surgical mortality, but there was one morbidity; transient recurrent nerve injury, which recovered 3 months later. Ten patients were extubated in operative room and 2 patients were extubated 2 hours after the operation. Tube thoracostomy was performed in the first 2 cases; it was omitted thereafter. No patients needed narcotic to control chest pain. Postoperative follow-up by echocardiography showed faint ductal flow in 1 patient without any murmur. All patients were discharged within 3 days after the operation. Conclusions. Our experience suggests that with refinement of instruments and surgical technique, video-assisted thoracoscopic surgical ligation can be safely applied not only in pediatric patients, but also in adults with PDA. (Ann Thorac Surg 1997;63:175–9)

Pulmonary artery pressure in term and preterm neonates.

Systolic pulmonary artery pressure (PAP) during the first 4 days after birth was determined in 41 healthy term and 46 preterm infants by measuring ductal Doppler flow velocity and systemic arterial pressure (SAP). Among preterm infants, 21 had respiratory distress syndrome (RDS) and 25 did not. Sequential indices within 96 h of age were presented respectively. At the ages of 2 and 12 h the ratio between pulmonary and systemic arterial pressure was significantly higher in term than in preterm infants without RDS (p < 0.05). At the age of 24 h, PAP to SAP ratio was similar in all study groups. Between 48 and 72 h, PAP to SAP ratio was significantly higher in preterm infants with RDS than in infants without RDS (p < 0.05). Our findings indicated that: (1) in healthy fullterm infants pulmonary artery pressure fell to subsystemic level during the first 12 h, indicating the critical time in circulatory transition; (2) prematurity did not affect ductal closure times significantly; and (3) RDS was associated with prolonged ductal patency and delayed postnatal circulatory adaptation characterized by pulmonary hypertension.

Estimation of pulmonary arterial pressure in the newborn: study of the repeatability of four Doppler echocardiographic techniques.

Despite the increasing use of Doppler echocardiographic (DE) techniques to determine pulmonary arterial pressure in the neonate undergoing intensive care, there have been no studies comparing their repeatability in this population. Our objective was to compare the repeatability of four such techniques in neonates. The study was conducted in two regional neonatal units serving the North East of England. Group A (repeatability between observers): Two experienced observers performed detailed DE examinations, one directly after the other. Group B (within observer repeatability/temporal variability): One observer performed two examinations 1 hour apart. Group A comprised 15 preterm babies (26-36 weeks' gestation, 975-2915 g), most with mild respiratory failure; 4 healthy term babies; and 7 with congenital heart disease, in whom tricuspid regurgitation (TR) only was measured. Their ages were 18 hours to 12 days. Group B comprised 11 babies aged 12-64 hours with moderate to severe respiratory failure; 10 were preterm (26-36 weeks, 785-2800 g). We recorded four measurements: (1) Peak velocity of TR in m/s; (2) peak left-to-right ductal flow velocity (PDAmax in m/s); (3) TPV/RVET ratio; and (4) PEP/RVET ratio, where TPV = time to peak velocity at the pulmonary valve, PEP = right ventricular preejection period, and RVET = right ventricular ejection time. The Bland-Altman analysis was used to produce the coefficient of repeatability (CR: 95% confidence limits of repeatability), also expressed as a repeatability index (CR/mean value) and as a number of "confidence steps"-a measure of sensitivity of the technique to hemodynamic change (range of values within the population/CR). Between-observer and within-observer repeatabilities were similar. Within-observer CR and index (%) results were for TR +/- 0.26 m/s (9%); for PDAmax, +/- 0.48 m/s (39%); TPV/RVET 0.1:1.0 (34%), PEP/RVET 0.12:1.00 (36%). TR and PDAmax had the largest number of confidence steps in the expected range of values (TR 8.5; PDA max 6.5; TPV/RVET 3.2; PEP/RVET 3.2). The most repeatable technique was TR, but PDAmax would also be useful for a serial study owing to the potential for large change. Systolic time interval ratios were less repeatable and likely to be less sensitive indicators of hemodynamic change.

ANEURYSM OF THE DUCTUS ARTERIOUSUS: A CONGENITAL LESION. 112

Aneurysmal dilatation of the ductus arteriosus (ADA) has beeN considered a rare condition. We present 3 neonates seen during the last 2 years (1993-1995) with ADA, with prenatal diagnosis in one patient, and postulate a new theory for its pathogenesis. All 3 infants were delivered after term pregnancy and were admitted to NICU due to cardiopulmonary distress. Fetal echocardiogram was obtained in one case due to fetal distress and showed normal cardiac anatomy, right atrial and right ventricular dilatation with dilated ductus arteriosus, which was restricted at its pulmonary artery end, with turbulent right to left ductal flow. Chest X ray showed a mediastinal mass in 2 patients. All 3 were diagnosed during the first 12 hours of life by echocardiography. Echocardiograms showed structurally normal heart with ADA shunting left to right through a restricted segment at its pulmonary artery end. ADA was confirmed by aotography in all 3. In two infants the aneurysms became progressively small as was demonstrated by serial echocardiography after the ductal closure and chest x-ray showed resolution of mediastinal mass by 5-7 days of life. One infant underwent surgical resection of the ADA after observation for 5 days with no change in the size of ADA.

DOPPLER ECHOCARDIOGRAPHIC DETECTION OF ABNORMAL DIASTOLIC FILLING IN FETUSES WITH DUCTAL CONSTRICTION. † 158

To assess ventricular diastolic function in fetuses with constriction of ductus arteriosus (DA), 43 fetuses of women receiving indomethacin (100-150 mg/day) were examined with Doppler echocardiography. Ductal constriction was defined as maximal systolic velocity > 140 cm/sec and diastolic flow velocity >30 cm/sec. The constriction DA occurred in 21 fetuses (mean systolic velocity 191±42 cm/sec, mean diastolic velocity 60±34 cm/sec). The other 22 fetuses served as a comparison group. The variables measured were peak velocity during early diastole (E), peak velocity during atrial contraction (A), the ratio of velocity ratio (E/A ratio). The mitral E, A, and E/A ratio in fetuses with ductal constriction showed no significant difference from those in fetuses without ductal constriction. In fetuses with ductal constriction, the tricuspid A increased significantly and E/A ratio decreased significantly compared with those in fetuses without ductal constriction (57±9 vs 50±7 cm/sec, p=0.007, and 0.57±0.10 vs 0.63±0.07, p=0.03, respectively) without changes in E. Serial studies were available in 9 fetuses with ductal constriction during indomethacin administration and after with-drawal for a mean of 24 hours. Both systolic and diastolic ductal flow velocities in all fetuses returned to normal range after discontinuation of indomethacin and the tricuspid A decreased significantly without any significant change in E after discontinuation of indomethacin (Figure).Conclusion: Our study shows that ductal constriction acutely changes Doppler patterns of right ventricular diastolic filling in the human fetus.

Doppler echocardiographic analysis of flow in the ductus arteriosus of infants with hypoplastic left heart syndrome: Relationship of flow patterns to systemic oxygenation and size of interatrial communication

Excessive pulmonary overcirculation related to imbalance in the pulmonary/systemic vascular resistance ratio contributes to hemodynamic instability in infants with the hypoplastic left heart syndrome. Because the ductus arteriosus bridges the two vascular circuits in this lesion, we studied the Doppler echocardiographic flow patterns in the ductus arteriosus of 50 infants with hypoplastic left heart syndrome to investigate their relationship to the degree of pulmonary blood flow as measured by simultaneously obtained levels of partial pressure of oxygen in arterial blood. The degree of restriction to pulmonary venous egress as determined by size of the interatrial communication was also correlated with ductal flow patterns and partial pressure of oxygen in arterial blood. Biphasic flow was noted in all infants. Mean peak velocity of antegrade flow (pulmonary artery to aorta) was greater than that of retrograde flow (aorta to pulmonary artery) (131 ± 45 cm/sec versus 54 ± 15 cm/sec; p < 0.001), mean time of retrograde flow was greater than that of antegrade flow (246 ± 60 msec versus 174 ± 28 msec; p < 0.001), and mean velocity-time integral of antegrade flow was greater than that of retrograde flow (13.3 ± 4.8 cm versus 6.3 ± 3.4 cm; p < 0.001). The ratio of velocity-time integral of retrograde flow/antegrade flow (a volumetric estimate of diastolic reversal into the pulmonary vascular bed indexed to systemic output) correlated extremely well with partial pressure of oxygen in arterial blood ( r = 0.91; p < 0.0001). Categoric size of the interatrial communication (none, n = 2; small [<2 mm], n = 9; moderate [3 to 4 mm], n = 23; and large [>4 mm], n = 16) correlated with partial pressure of oxygen in arterial blood ( r = 0.82; p < 0.001); the smaller the interatrial communication the lower the partial pressure of oxygen in arterial blood and velocity-time integral ratio of retrograde/antegrade flow. Doppler flow patterns in the ductus arteriosus of infants with hypoplastic left heart syndrome are reflective of the resistance ratio between the pulmonary and systemic vascular circuits and may be helpful in monitoring the hemodynamics of these infants.

The Role of Prostaglandins in Labor and Delivery

The use of prostaglandins in obstetrics has undergone a rapid evolution since their discovery in the early 1970s. It appears certain now that, at least in some cases, prostaglandins are important mediators of uterine activity. Indeed, a much stronger case can be made for the role of prostaglandins in labor than can be made for oxytocin. The pivotal role of prostaglandins in contraction of the smooth muscle of the uterus and the biophysical changes associated with cervical ripening, however, point to a major problem with their clinical use. Prostaglandins are produced by almost every tissue in the body and serve as important messengers or effectors in a wide variety of functions. Attempts to inhibit the production of prostaglandins to produce a reduction in myometrial contractility are limited by the important role of prostaglandins in maintenance of fetal ductal flow and renal blood flow. Similarly, administration of prostaglandins for the purpose of inducing labor or ripening an unfavorable cervix is tempered by the effects of these agents in other systems, including the gut and brain. Significant advances, however, have been made in the application of prostaglandins to common clinical problems in obstetrics. Of the multitude of products derived from the actions of cyclooxygenase on arachidonic acid, the most important for labor, delivery, and the postpartum period are the F and E series prostaglandins. Unlike oxytocin which requires an induction of receptors that does not usually occur until the later part of pregnancy, prostaglandins receptors always are present in myometrial tissue. This allows for the use of prostaglandins in usual doses throughout pregnancy. Although both F and E series prostaglandins result in uterine contractions, E series prostaglandins are relatively more uteroselective and are clearly superior to F series prostaglandins in producing cervical ripening. Modification of the naturally occurring prostaglandins by blocking the sites that are affected during their usual rapid metabolism, results in products with much longer durations of action, efficacy at much lower concentrations, and a potential for significant savings in cost. We are now able to manage efficiently problems such as intrauterine fetal death and intractable hemorrhage from postpartum uterine atony that often resulted in a surgical procedure prior to the availability of prostaglandin. We can continue to explore the potential of these agents in helping to solve the most difficult problems faced by the obstetrician.

Chaotic mixing of alveolated duct flow in rhythmically expanding pulmonary acinus

We examined the effects of rhythmic expansion of alveolar walls on fluid mechanics in the pulmonary acinus. We generated a realistic geometric model of an alveolated duct that expanded and contracted in a geometrically similar fashion to simulate tidal breathing. Time-dependent volumetric flow was generated by adjusting the proximal and distal boundary conditions. The low Reynolds number velocity field was solved numerically over the physiological range. We found that for a given geometry, the ratio of the alveolar flow (QA) to the ductal flow (QD) played a major role in determining the flow pattern. For larger QA/QD (as in the distal region in the acinus), the flow in the alveolus was largely radial. For small QA/QD (as in the proximal region in the acinus), the flow in the alveolus was slowly rotating and the velocity field near the alveolar opening was complex with a stagnation saddle point typical of chaotic flow structures. Performing Lagrangian fluid particle tracking, we demonstrated that in such a flow structure the motion of fluid could be highly complex, irreversible, and unpredictable even though it was governed by simple deterministic equations. These are the characteristics of chaotic flow behavior. We conclude that because of the unique geometry of alveolated duct and its time-dependent motion associated with tidal breathing, chaotic flow and chaotic mixing can occur in the lung periphery. Based on these novel observations, we suggest a new approach for studying acinar fluid mechanics and aerosol kinetics.

Detection of residual flow by transesophageal echocardiography during video-assisted thoracoscopic patent ductus arteriosus interruption.

The purpose of this study is to examine prospectively the efficacy of intraoperative transesophageal echocardiography (TEE) monitoring in reducing the incidence of residual ductal flow during video-assisted thoracoscopic (VATS) patent ductus arteriosus (PDA) interruption. Thirty consecutive patients undergoing PDA interruption via the VATS procedure were monitored with an appropriately sized Hewlett-Packard color-Doppler TEE probe. All examinations were performed by the same individual and interpreted with a cardiologist. Real time TEE monitoring was used, but the results were not disclosed to the surgeon until he was prepared to close the wound. The mean age was 2.4 yr and the average weight 11.2 kg. Two patients had residual flow after placement of the vascular clip. One patient had residual flow detected intraoperatively after placement of the vascular clip and residual flow was quickly abolished by the placement of a second clip, thus avoiding a reintervention. A follow-up transthoracic echocardiography was performed on 18 patients 1 mo postoperatively. Three patients presented residual ductal flow. This study using a novel application of TEE, demonstrates that TEE monitoring during PDA interruption may improve the surgical result, thus avoiding reintervention and the complications associated with residual ductal flow. However, late recurrence due to recanalization may occur and may not be detected by intraoperative TEE monitoring.

Video-assisted thoracoscopic surgery for congenital heart disease

Video-assisted endoscopic techniques have reduced operative trauma in adult thoracic and general surgery, but applications in children with congenital heart disease have been limited. We report the development of video-assisted thoracic surgery procedures for neonates and infants with cardiovascular disease. Endoscopic instruments and techniques for pediatric cardiovascular procedures were designed and tested in the animal laboratory. Forty-eight operations were subsequently performed in 46 pediatric patients ranging in age from 2 hours to 14 years (median 9 months), weighing from 575 grams to 54 kg (median 8.5 kg). Clinical applications included seven different procedures: patent ductus ateriosus interruption in infants ( n = 26) and premature neonates ( n = 5), vascular ring division ( n = 8), pericardial drainage and resection ( n = 3), arterial and venous collateral interruption ( n = 2), thoracic duct ligation ( n = 2), epicardial pacemaker lead insertion ( n = 1), and diagnostic thoracoscopy ( n = 1), and diagnostic thoracoscopy ( n = 1). there was no operative mortality. Technical success, defined as a video-assisted procedure completed without incising chest wall muscle or spreading the ribs, was achieved in 39 of 48 procedures (82%), with thoracotomy required to complete nine procedures. Most patients (22/25, 88%) undergoing elective ductus ligation were extubated in the operating room and discharged from the hospital within 48 hours of the operation. Eight of the last 10 patients having ductus ligation were discharged on the first postoperative day. Residual ductal flow was assessed by (1) transesophageal echocardiography in the operating room (incidence: 0/25, 0%, 70% CL 0% to 7.3%); (2) discharged auscultation (incidence: 1/30, 3%, 70% CL 0.5% to 10.8%); and (3) follow-up Doppler echocardiography (incidence: 1/30, 3%, 70% CL 5.4% to 22.6%). Video-assisted thoracoscopic techniques can be safely applied to pediatric patients with patent ductus arteriosus and vascular rings and may become an effective addition to the staged management of more complex forms of congenital heart disease. (J T HORAC C ARDIOVASC S URG 1995; 109: 499-508)

1002-83 In Utero Pulmonary Outflow Obstruction: Natural History and Predictors of Postnatal Severity

We reviewed prenatal and postnatal echocardiograms of fetuses with pulmonary stenosis (PS, n = 14) and pulmonary atresia (PAtr, n = 5), to elucidate the antenatal natural history of PS and PAtr and identify predictors of severe postnatal disease. Fifteen were serially studied in utero (age at first study 24 ± 4wks). Fetuses with PS were divided into severe and mild groups according to whether they were (9) or were not (4) ductus-dependent at birth, respectively. Measurements of RV short and long-axis, tricuspid valve, main and branch pulmonary artery (PA) and pulmonary valve dimensions were converted to Z-scores based on age-adjusted normal fetal data. At the initial exam, main and branch PA and pulmonary valve Z-scores were larger in fetuses with mild PS than in those with severe PS or PAtr (p ≤ 0.01). On serial followup, however, growth rates of right heart structures did not differ for mild PS versus severe PS and PAtr groups. Ductal flow in utero was antegrade in systole in all with mild PS, but was either bidirectional (5 severe PS) or retrograde only (4 severe PS, all PAtr) in the severe PS and PAtr groups. Initial RV outflow gradients by Doppler did not differ between the mild and severe PS groups with antegrade PA flow (mean 26 ± 12 mmHg). Pulmonary insufficiency was a consistent feature in fetuses with mild PS, but was not present in the severe PS or PAtr groups. By color Doppler, 3/4 with mild PS had mild tricuspid regurgitation, whereas mild or moderate tricuspid regurgitation was found in 9/9 with severe PS and 4/5 with PAtr. When severe PS and PAtr groups were compared, there was no significant difference in initial Z-scores or growth rates of right heart structures between the groups. Tricuspid regurgitation severity and initial RV pressure by the tricuspid regurgitation jet (mean 71 ± 21 mmHg) also did not differ between the severe PS and PAtr groups. On serial followup in 6/8 with severe RV outflow obstruction (1 PAtr, 7 severe PS), the RV pressure increased by 18–47 mmHg. In 3/6 serially studied fetuses with antegrade PA flow (2 severe PS, 1 mild PS), the RV outflow gradient increased later in gestation. There was no change in the severity of tricuspid or pulmonary regurgitation during followup in any fetus. The severity of PS may be differentiated in utero by the direction of ductal flow, the presence of pulmonary insufficiency, severity of tricuspid insufficiency and the size of the pulmonary valve and PAs. In the absence of antegrade PA flow, severe PS may be difficult to distinguish from PAtr antenatally.

Acute effects of synthetic surfactant replacement on pulmonary blood flow in neonatal respiratory distress syndrome.

To assess the acute effects of surfactant replacement therapy on the pulmonary blood flow in neonatal respiratory distress syndrome (RDS), 23 distressed infants were studied before and for 1 hour after either synthetic surfactant instillation (n = 13) or endotracheal suctioning (n = 10). Doppler ultrasound was used to measure blood flow velocity and flow velocity integral, representing volumetric flow, of the left pulmonary artery branch, ductal left-to-right shunt, and ascending aorta. Surfactant instillation increased the left pulmonary artery and ductal shunt flow velocity and flow velocity integral for 1 hour in 10 of 13 treated infants, whereas no change was found after endotracheal suctioning. There was a significant (P < 0.05) correlation between the changes in the pulmonary artery and ductal flow values at 1 hour after surfactant treatment. The mean increase during 1 hour after treatment in the pulmonary artery flow ranged from 15 to 25% and in the ductal left-to-right shunt from 28 to 33%. No change in the aortic flow or heart rate was found in either group. Our results thus suggest that synthetic surfactant therapy may acutely increase pulmonary blood flow and ductal left-to-right shunting in infants with RDS.

Assessment of changes in blood flow through the lungs and foramen ovale in the normal human fetus with gestational age: a prospective Doppler echocardiographic study.

To measure lung blood flow and flow through the foramen ovale in the normal human fetus and to assess the changes in each with gestational age and the proportions of combined ventricular output that the respective flows represent. 38 normal fetuses (gestational age 18-37 weeks) were studied prospectively with Doppler echocardiography. Echocardiographic images and Doppler velocity signals were obtained from the ascending aorta, main pulmonary artery, and ductus arteriosus from each fetus and digitised to obtain arterial diameters, heart rates, and velocity-time integrals. Blood flow in each artery was calculated as the product of heart rate, flow-velocity integral, and arterial cross sectional area. Blood flow through the lung was assessed as the difference between flow in the pulmonary artery and ductal flow; combined ventricular output as the sum of aortic and pulmonary artery flows; and flow through the foramen ovale as the difference between flows through the aorta and lungs. Blood flow through the lungs increased exponentially with gestational age (r = 0.89, p < 0.001), by almost four-fold over the period of gestation studied, and was a mean (SD) of 22% (7%) of combined ventricular output. Blood flow through the foramen ovale increased exponentially by threefold (r = 0.77, p < 0.001), representing between 17% and 31% of combined ventricular output. Blood flow through the lungs and across the foramen ovale can be calculated non-invasively in the normal human fetus. Both flows increase exponentially with age and comprise between one fifth and one quarter of the combined ventricular output, proportions that remain unchanged through the second and third trimesters of pregnancy.

Ultrasound Prediction of Fetal Pulmonary Hypoplasia in Pregnancies Complicated by Oligohydramnios and in Cases of Congenital Diaphragmatic Hernia: A Review

The objective of this review is to discuss the current knowledge of fetal pulmonary hypoplasia and to summarize the clinical significance of the many ultrasound methods for predicting pulmonary hypoplasia in pregnancies complicated by oligohydramnios due to spontaneous rupture of the fetal membranes and in cases complicated by fetal congenital diaphragmatic hernia. We concluded that the presence or absence of polyhydramnios, fetal breathing movements, mediastinal shift, thoracic position of the stomach, fetal breathing-related nasal and oropharyngeal fluid flow, ductal flow velocity modulation, and gestational age at onset and severity of ventricular disproportion as useful markers for predicting fetal pulmonary hypoplasia is a productive area for continued research. All studies show that there is a clear association between most of these markers and pulmonary hypoplasia. However, these markers have not been studied together in a large number of cases, and comparisons between each of the markers is unknown.

Critical pulmonary valve stenosis in the neonate: A technique to facilitate balloon dilation

Critical pulmonary valve stenosis associated with ductal dependent pulmonary blood flow is rare, accounting for a small proportion of all infants undergoing balloon dilatation. 1 Valvuloplasty in these infants may be technically difficult and at times impossible due to inability to traverse the critically stenotic valve. Previous investigators have described a gradational approach whereby balloon catheters of increasing diameter (2, 4, 6, 8 and 10 mm) are sequentially advanced and inflated across the valve relieving the obstruction. 2 This approach, however, is time consuming and subjects the infant to prolonged fluoroscopy exposure. We have developed a valvuloplasty technique in the neonate with critical pulmonary valve stenosis which shortens fluoroscopy time and facilitates catheter advancement across the critically stenotic valve.

Anatomical and sonographic correlation of the fetal ductus arteriosus in first and second trimester pregnancy

Ultrasonic visualization of the ductus arteriosus in first and second trimester pregnancies was compared with postmortem preparations. Twenty human fetal postmortem specimens from 8 to 19 weeks menstrual age were examined, 11 with microscopic reconstruction, nine with macroscopic dissection. The angle between ductus arteriosus and aortic isthmus (upstream) and ductus arteriosus and descending aorta (downstream) was determined. In 52 normally developing fetuses between 14 and 27 weeks, the angle between the ductus arteriosus and the thoracic spine as visualized in real-time ultrasound was determined. In a further 19 normally developing fetuses between 14 and 25 weeks, ductal blood flow was visualized by colour velocity imaging (CVI). In anatomical preparations, the upstream angle was always less than 90° and the downstream angle was always 80° or more. These angles were unrelated to menstrual age. In both real-time and CVI ultrasound, the angle between ductus arteriosus and thoracic spine remained at approximately 90°. CVI showed highest blood flow velocities at the point of ductal insertion into the aorta. When performing Doppler ultrasound examinations in the fetal ductus arteriosus, no menstrual age dependent angle adjustment appears to be necessary.

Model for radionuclide evaluation of left-to-right ductal shunts.

A model for radionuclide evaluation of left-to-right ductal shunts was designed. It was a generalization of the standard Maltz-Treves method, accounting for the possibility that distribution of the shunt flow between the two lungs differs from that in the right ventricular (RV) output (Fs). This yields a new formulation in which the ratio of ductal flow to pulmonary flow (Fd/Fp) equals a weighted average of Fd/Fp obtained separately for the right lung (RL) and the left lung (LL), i.e. Fd/Fp = R(Fd/FpP)RL+ (1-R) (Fd/Fp)LL; where R is the fraction of the RV output going to the right lung. Separate shunt-flow ratios can be obtained by conventional analysis of the respective lung radiohistogram, while R can be determined from the upslopes of these curves. Formulas were derived rigorously from basic principles, so that the ultimate clinical validity of the method depends on radioangiographic assessment of R, (Fd/Fp)RL and (Fd/Fp)LL. Due to asymmetry of flows there is no true referent method for patients with ductal shunts. Therefore a simulation study, using quasi-real data, was utilized, yielding satisfactory performances of the algorithm: (Fp/Fs) calculated = 0.92 (Fp/Fs)stimulated +0.15 (r = 0.878).