Patent Ductus Arteriosus Shunt Research Articles

Hydroxyurea for Treatment of Polycythemia Secondary to Right-to-Left Shunting Patent Ductus Arteriosus in 4 Dogs

Hydroxyurea for Treatment of Polycythemia Secondary to Right-to-Left Shunting Patent Ductus Arteriosus in 4 Dogs

Reopening After Successful Coil Occlusion for Patent Ductus Arteriosus

Objectives. This study was performed to determine the frequency of patent ductus arteriosus (PDA) reopening and the factors that may predict reopening after successful coil occlusion.Background. Transcatheter coil occlusion is a widely used and accepted method to close a PDA. After documented successful coil occlusion, we found PDAs that reopened. We hypothesized that specific factors are involved in those that reopened.Methods. All patients who underwent percutaneous transarterial PDA coil occlusion were studied. Successful coil occlusion was documented. PDA reopening was determined when Doppler-echocardiography (DE) performed after the procedure was negative for PDA flow but at follow-up demonstrated PDA shunting. Patients with a reopened PDA were compared with all other patients in evaluating independent variables.Results. Coil occlusion for PDA was attempted in 22 patients. Clinical success was achieved in 20 patients (91%), and DE was negative for PDA shunting in 19 patients (90%). At follow-up, five patients demonstrated reopening. The PDA minimal diameter was 1.4 ± 0.5 mm (mean ± SD) for the reopened group and 1.2 ± 0.7 mm for the other patients. The PDA length was 2.9 ± 1.9 mm for the reopened group and 7.1 ± 3.2 mm for all other patients. All those with type B PDA were in the reopened group. When independent variables were compared between groups, only PDA length and type B PDA predicted reopening (p < 0.05).Conclusions. PDA reopening may occur after successful coil occlusion. Short PDA length and type B PDA are associated with reopening. The data suggest that in such anatomy, alternative strategies to the current coil occlusion technique should be considered.

Echocardiographic assessment of patent ductus arteriosus shunt flow pattern in premature infants

AIMSTo identify the patent ductus arteriosus (PDA) shunt flow pattern using Doppler echocardiography; and to assess whether it could be used to predict the development of clinically significant PDA.METHODSPremature infants...

Serial Assessment of Ductus Arteriosus Hemodynamics in Hyaline Membrane Disease

To assess the efficacy of Doppler echocardiography (DE) in the quantification of patent ductus arteriosus (PDA) shunt volume and to correlate PDA shunt volume with clinical outcome in infants with hyaline membrane disease. Ninety-eight DE studies were performed in 30 preterm ventilated infants with hyaline membrane disease within the first 24 hours of age and then at 48-hour intervals to a maximum of three studies while ventilated with a final study after extubation. Right and left ventricular outputs (QRV and QLV, respectively) and PDA flow were calculated using cross-sectional area and flow velocity integrals. Left atrial-to-aortic root diameter measurements were also taken. Clinical outcomes were correlated with the shunt fraction (QLV/QRV). QLV/QRV demonstrated a linear relationship with the left atrial-to-aortic root diameter ratio (n = 92; r = .79). In the absence of a PDA (n = 33 studies), QRV versus QLV demonstrated a linear relationship (r = .88). In the presence of a PDA (n = 64 studies) the mean QLV (334 +/- 133 ml/kg per minute) was significantly greater than the mean QRV (237 +/- 84 ml/kg per minute). There was a linear relationship between QLV-QRV (PDA shunt volume) and PDA flow (n = 60; r = .84). In studies with exclusive left-to-right shunting at the PDA (n = 48), the mean QLV-QRV (112 +/- 83 ml/kg per minute) was significantly higher than in those with bidirectional shunting (n = 16; mean QLV-QRV = 50 +/- 27 ml/kg per minute). Two infants with severe intraventricular hemorrhage (IVH grade 3) and two infants with periventricular leukomalacia (PVL) had significantly higher QLV/QRV (2.09 +/- 0.36 and 1.67 +/- 0.02 respectively) than those with no IVH (n = 6; QLV/QRV = 1.31 +/- 0.18) or those with IVH grades 1 and 2 (n = 8; QLV/QRV = 1.48 +/- 0.27). There was no difference in QLV/QRV in infants with or without bronchopulmonary dysplasia and retinopathy of prematurity. Necrotizing enterocolitis did not develop in any of the 30 infants. PDA shunt volume can be quantified by DE. Larger studies are needed to correlate clinical outcome with QLV/QRV.

CONTRAST ECHOAORTOGRAPHY AS AN AID IN THE DIAGNOSIS OF RIGHT‐TO‐LEFT SHUNTING PATENT DUCTUS ARTERIOSUS

Contrast echocardiography has traditionally been used in conjunction with conventional echocardiography to document right‐to‐left intracardiac shunting congenital anomalies. This technique does not clearly demonstrate shunting of blood in patients with right‐to‐left patent ductus arteriosus, as the shunt is extracardiac. We used a variation of contrast echocardiography, contrast echoaortography, to confirm the presence of a right‐to‐left shunting patent ductus arteriosus in two dogs.

Flow characteristics in infants with hypoplastic left heart syndrome: an echocardiographic study.

From July 1992 to January 1993, a total of 5 cases of hypoplastic left heart syndrome were diagnosed by echocardiograms and confirmed by available angiographic, surgical or autopsy results. The flow dynamics disclosed by spectrum display in the aortic root and patent ductus arteriosus (PDA), in systole, were: (1) antegrade in the ascending aorta and descending aorta (below PDA), and retrograde in the transverse aorta, and (2) right-to-left shunt in the PDA. While in diastole, there were (1) antegrade in the transverse aorta, and retrograde in the ascending aorta and descending aorta (below PDA), and (2) left-to-right shunt in the PDA. No ventriculocoronary fistulas were identified. With both the characteristic flow pattern and the extremely narrow diameters of the ascending aorta in hypoplastic left heart syndrome, we can differentiate it from those heart diseases associated with secondary hypoplastic left heart due to total anomalous pulmonary venous connection or congenital pulmonary venous stenosis. Both help us understand better the hemodynamics and pathophysiology of hypoplastic left heart syndrome in these patients.

783-2 Follow-up After Coil Occlusion of Patent Ductus Arteriosus

To define the prevalence and fate of residual shunts after Gianturco coil occlusion of patent ductus arteriosus (PDA), 50 pts were followed prospectively after PDA coil occlusion at CS Mott Children's Hospital between 10/92 and 8/94. Evidence of residual shunt was sought on immediate post-coil aortic angiograms and on color-flow Doppler echocardiograms performed in follow-up. Survival analysis of residual PDA shunting was analyzed by the Kaplan-Meier method, and the effect of minimum PDA angiographic size on residual shunting was determined by ANOVA. The 50 pts, median age 4.4 years (range 0.4-62), have been followed for ≤ 20 months (mean ± SD: 8 ± 6). PDA minimum diameter was 1.6 ± 0.8 mm (range 0.5–3.3). Complete PDA occlusion was noted immediately in 29 pts (58%); tiny residual shunts closed spontaneously 1–20 months after coil occlusion in 12 pts (24%). Tiny residual shunts persisted have undergone a second coil occlusion with immediate complete closure. Survival analysis (graph) estimates 20 month prevalence of residual shunts at 7 ± 6% after 1 coil procedure and 4 ± 4% after all coil procedures. PDA diameter significantly influenced residual shunting, being 1.3 ± 0.7 mm in pts with immediate closure, 1.9 ± 0.8 mm with spontaneous shunt closure in follow-up, and 2.0 ± 0.9 mm with persistent residual shunt or second coil placement (p = 0.02). 1) Survival analysis estimates 93% complete PDA closure after a single coil occlusion procedure; 2) Residual shunts are associated with larger PDA diameter, and most close spontaneously; and 3) When necessary, a second coil occlusion has been uniformly successful.

921-69 Transcatheter Closure of the Persistently Patent Ductus Arteriosus Using Occluding Coils

Transcatheter coil closure (TCC) of the Patent Ductus Arteriosus (PDA) was attempted in 29 patients (pts) with a median age of 3.2 years (6 months-55 yearsl and a median weight of 14.0 kg (4.3-Bl kg). Previously, 114 pts with PDA underwent closure with the Rashkind umbrella device in our institution but this device is no longer available. Ducti measured 0.5–5.0 mm (mean = 1.B mm) at the narrowest point. A single coil was implanted in 12 pts, two in 15 and three in 2. The first coil implanted had a diameter twice the minimal internal diameter of the PDA and a length sufficient for at least 4 loops. One to 1.5 loops were delivered in the main pulmonary artery. and the remaining loops were released in the aortic ductal diverticulum. Coil embolization occurred in 3 pts: all coils were successfully retrieved. In another patient 3 coils were removed from the PDA. after proper placement. because of left pulmonary artery obstruction. Coil re-implantation was successful in all of these patients. Aortography, performed 10 minutes after coil implantation, showed complete closure in 25/29 pts (86%). Four hours after the procedure, 27/29 pts (93%1 had no evidence of PDA by color flow Doppler. Thirteen pts were done as outpatients, 13 were discharged in 24 hr, and 3 had prolonged hospitalization for other medical problems. Follow-up ranged from 1 month to 4 years in 27/29 pts. None had detectable murmurs. Small residual PDA shunt by color flow Doppler persisted in 2 pts. No aortic obstruction, pulmonary artery stenosis. hemolysis, or late coil migration has been observed. These results compare favourably with our Rashkind device occlusion results where the closure rate was 52% by angiography (p &lt; 0.01) and 71% by color flow Doppler (p = 002) at discharge. Furthermore, the cost of TCC was 25% less than the Rashkind device occlusion, and 40% less than surgical closure. TCC of small to moderate PDA is an effective technique without significant morbidity. It appears significantly more effective and costefficient than the Rashkind device occlusion, and it can be done safely as an outpatient procedure.

Endocarditis risk of the USCI PDA umbrella for transcatheter closure of patent ductus arteriosus.

The USCI PDA Umbrella is a device to close patent ductus arteriosus (PDA) by a transcatheter technique. Human clinical trials have shown excellent efficacy in reducing or eliminating the PDA shunt, but concerns remain about the risk of infection with this device. The purpose of this study was to evaluate the risk of infection using an animal model. Susceptibility to developing endocarditis was tested by injecting a single intravenous dose of group L streptococcus. Ten piglets with a closed ductus served as controls. Two of these developed valvular vegetations. PDA was produced in 19 animals by balloon dilation of the ductus. Seven of 7 animals with PDA at the time of bacterial injection developed endarteritis of the ductus and valvular vegetations. A PDA Umbrella was placed in the remaining 12 animals, and bacteria were injected 2 weeks after device implantation. Infection was evident in the PDA Umbrella only in the single animal in which the Umbrella had embolized and been left in the left pulmonary artery. Three of the remaining 11 piglets had a significant residual leak, and all developed infection in the ductus and an additional valve. Similar to the control group, none of the animals with complete (n = 8) or nearly complete (n = 2) closure of the ductus by the PDA Umbrella had infection in or around the ductus, and only 1 had a valvular vegetation. In this animal model, presence of a significant PDA shunt (with or without a PDA Umbrella present) results in significantly increased susceptibility to endarteritis and endocarditis. The PDA Umbrella device does not appear to be susceptible to direct infection as early as 2 weeks after implantation if it is properly located in the ductus arteriosus. Animals with no shunt or a trivial shunt are no more susceptible to developing endocarditis 2 weeks after PDA Umbrella implantation than are controls.

Color Doppler flow mapping of the patent ductus arteriosus in very low birthweight neonates: echocardiographic and clinical findings.

Forty-eight preterm infants (mean birthweight 1.0 +/- 0.3 kg; mean gestational age 28 +/- 3 weeks) underwent serial echocardiograms and physical examinations in order to determine the correlation between color Doppler flow mapping (CDFM) results and physical findings of a patent ductus arteriosus (PDA), the predictive value of early CDFM as an indicator of subsequent requirement for treatment of a PDA, and to determine the direction and duration of ductal shunting and the rate of ductal closure and opening. CDFM analysis and cardiac physical examination of left-to-right ductal shunting were usually concordant in infants with a large PDA shunt, the most reliable physical finding being increased precordial activity. CDFM studies on day 2 or 3 of postnatal life had prognostic value with regard to subsequent need for closing the PDA. Additional findings included the absence of right-to-left PDA shunting in infants < 1 kg and < 28 weeks gestation and the absence of ductal reopening in infants in whom it had closed spontaneously. After complete PDA closure using indomethacin, subsequent ductal reopening is uncommon, except in infants < 25 weeks gestation and < 700 g bodyweight.

Doppler-Derived Systolic Pulmonary Artery Pressure in Acute Neonatal Respiratory Distress Syndrome

To determine the course of systolic pulmonary artery pressure (PAP) in association with ductal shunting and cardiac output (CO) in preterm neonates. During the acute phase of respiratory distress syndrome (RDS) with and without surfactant treatment, serial Doppler ultrasound examinations were performed at the ages of 2, 12, 24, 48, and 72 hours in 51 neonates with RDS and 21 healthy, preterm controls. Twenty-eight of the distressed neonates received two or four doses of synthetic exogenous surfactant at intervals of 12 hours. Measurements of hemodynamic variables in these neonates were performed before and after 8 hours following surfactant treatments. PAP was estimated by the Doppler method from the maximal tricuspid regurgitant flow velocity. Doppler ultrasound was also used to determine simultaneously CO, and the direction and magnitude of the ductal shunting. The PAP was initially at the same level, but remained significantly higher in distressed than in healthy, preterm control neonates between the ages of 12 to 48 hours. The systolic systemic arterial blood pressures did not differ between the distressed and control neonates, but increased gradually during the study period. Consequently, the ratio of systolic pulmonary and systemic pressure was also higher in neonates with RDS than in controls during the first day of life. Bidirectional ductal shunting disappeared in all neonates studied after 2 days of life. Significant left-to-right shunting through the ductus arteriosus persisted more frequently in distressed neonates, especially those with surfactant treatment, than in control neonates during the study period, and more often caused the need for medical or surgical closure. Doppler-derived CO remained stable throughout the study in the distressed neonates, being significantly higher in surfactant-treated neonates than nontreated distressed neonates or healthy controls at 72 hours of life. The data of the present study confirms that the postnatal decrease in PAP is delayed in acute RDS. Further, significant patent ductus arteriosus shunting persists longer in RDS and may contribute to elevated CO during the resolution of the disease.

Increased platelet activating factor in the tracheal aspirates from neonates with patent ductus arteriosus

We investigated platelet-activating factor (PAF) in the tracheal aspirate from 3 intubated low birth weight infants with symptomatic patent ductus arteriosus (PDA). PAF increased with the onset of symptomatic PDA and decreased to the control range soon after the ductal closure. The concentration of PAF in 26 samples taken during symptomatic PDA (median 16 pg/μg lipid phosphorus, range 1.4–1,200 pg/μg lipid phosphorus) was significantly higher than that of 31 samples from the same three patients during the periods without symptomatic PDA (median 1.9 pg/μg lipid phosphorus, range 0–12 pg/μg lipid phosphorus; P < 0.001). All 3 infants later developed chronic lung disease. These results suggest that large shunting PDA provokes PAF release to the air way of the neonate and that PAF might play a role in chronic lung disease developing after symptomatic PDA.

Atrial natriuretic peptide in newborn piglets with a patent ductus arteriosus.

Atrial natriuretic peptide (ANP) is a hormone involved in fluid and blood pressure homeostasis. We studied the effects of left-to-right shunting through a patent ductus arteriosus on blood pressure changes and plasma ANP concentrations in newborn piglets. In five experimental piglets, the ductus arteriosus was bathed with PGE1 and infiltrated with formalin to maintain its patency. In four age-matched control piglets, the ductus arteriosus was ligated. Plasma ANP concentrations and blood pressure determinations were obtained prior to (base-line) and 25 +/- 1 h (day 1), and 48 +/- 1 h (day 2) after surgery. Radionuclide-microsphere determinations of left-to-right patent ductus arteriosus shunts were performed on days 1 and 2 in the 5 piglets with a patent ductus arteriosus. Plasma ANP concentrations were significantly elevated in the left atrium on day 1 and the right atrium on day 2 in the PDA piglets. No correlation was demonstrated between plasma ANP concentrations and right or left atrial pressures. We conclude that left and right plasma atrial ANP concentrations are significantly elevated in newborn piglets with left-to-right patent ductus arteriosus shunts.

62 ATRIAL NATRIURETIC PEPTIDE (ANP) IN PRETERM INFANTS WITH RESPIRATORY DISTRESS SYNDROME(RDS) TREATED WITH SURFACTANT

Dramatic but transient improvements in oxygenation may be seen after surfactant therapy. An increase in patent ductus arteriosus (PDA) may be a complication of this treatment. To see if surfactant (curosurf, CSRF) increases left to right PDA shunting, plasma ANP levels were taken before and within 1 hour of CSRF. 12 infants, birthweights 0.27-3.10kg, gestational age 25-36 weeks, received 1-5 doses of CSRF each at 12 hour intervals. The median ANP level rose progressively for doses 1, 2 and 3 being 492, 955 and 2161pg/ml respectively. In infants without a PDA, the ANP did not change significantly with CSRF (median before 605, 825pg/ml after). But in those with a PDA, ANP rose significantly (median before 1672, 2716pg/ml after) (p<0.01, Wilcoxon ranked sum test).The progressively rising AMP levels during treatment to the range previously reported for infants with a PDA(1) suggest increasing left atrial distension which may be the result of left to right shunting through a PDA. The rise in ANP levels after CSRF may be the result of increased PDA shunting due to a fall in pulmonary artery pressure. CSRF treatment appears to have significant effects on haemodynatnics in preterm infants.(1) Weir et al. Pediatr Res 1990;28:292

Circulatory changes following premature delivery in a baboon model of hyaline membrane disease

The premature baboon delivered by hysterotomy at 140 +/- 2 days (75%) gestation develops hyaline membrane disease (HMD) and left-to-right (L-R) shunting through the patent ductus arteriosus (PDA). To characterize hemodynamic changes that follow premature delivery, we measured systemic and organ blood flow, oxygen transport, and systemic vascular resistance over the first 96 h of life. We compared these measurements with those from more mature animals of the same species. Radiolabeled microspheres were used to measure organ blood flow (in ml.min-1.g-1) at 3 (n = 18), 23 (n = 17), and 96 h (n = 4) in the premature animals, and at 13 +/- 4 mo in the older animals (n = 5). Premature animals demonstrated over the first 96 h of life significant hemodynamic changes that included decreased systemic vascular resistance (P less than 0.001), increased systemic (P less than 0.05), intestinal (P less than 0.05), and hepatic blood flow (P less than 0.05), as well as resolution of L-R PDA shunting. These 96-h values were similar to those of the more mature infant baboons. Blood flow and oxygen transport to the kidneys and cerebrum did not significantly increase over the first 96 h in premature baboons and were significantly less than those of 13-mo-old animals (P less than 0.01, both). We speculate that low renal and cerebral blood flow in the 140-day premature baboon are manifestations of multisystem immaturity and, as such, may represent persistent physiological disturbances that are distinct from the severity of underlying lung disease in HMD.

Ductal Shunting and Effective Systemic Blood Flow Following Single Dose Surfactant Treatment in the Premature Baboon with Hyaline Membrane Disease

We studied the hemodynamic effects of using natural surfactant in premature baboons with hyaline membrane disease (HMD). Study animals (n = 5) received a single dose of surfactant immediately after delivery and control animals (n = 8) did not. Using microspheres at 3, 8, and 23 h we found no significant differences in left ventricular output, effective systemic flow, systemic-to-pulmonary patent ductus arteriosus (PDA) shunting, or in cerebral or renal organ blood flow. However, both groups had large PDA shunts (fraction of LVO to lungs greater than 0.40-0.55 at 3 and 8 h) resulting in low systemic perfusion (less than 80 ml/min/kg). Single dose surfactant did not improve the myocardial dysfunction and low cerebral and renal blood flow which occur during treatment for HMD.

Hemodynamic Changes in a Term Newborn Piglet Model of Patent Ductus Arteriosus

Patent ductus arteriosus (PDA) is a common form of congenital heart disease in full-term infants. To investigate the morbidities associated with a left to right PDA shunt, we produced a PDA in six full-term newborn piglets (less than 36 hours old) by bathing the ductus arteriosus with prostaglandin E (PGE) and infiltrating it with formalin. In five age-matched piglets, the ductus arteriosus was ligated to serve as controls. Microsphere determinations of left ventricular output (LVO) and regional blood flow (Q) were made on three consecutive days. We produced left to right shunts of 36 to 47% (mean) in the experimental piglets. The experimental piglets had a 22 to 36% increase in LVO with a one- to twofold reduction in percentage of LVO to the kidneys and carcass (p less than 0.05). Although percentage of LVO to the gastrointestinal tract was reduced (p less than 0.05), no reduction of absolute Q to the gastrointestinal tract was observed. Brain and heart Q were similar in both groups. We conclude that significant hemodynamic changes result from left to right shunting in the full-term newborn piglet with PDA. These hemodynamic changes, such as reduction in renal blood flow, are relevant information that will help explain the morbidities observed in infants with a hemodynamically significant PDA with a left to right shunt.

Two‐Dimensional Pulsed Doppler Echocardiographic Technique for Estimating Pulmonary to Systemic Blood Flow Ratio in Children with Atrial Septal Defect and Patent Ductus Arteriosus

A two-dimensional pulsed Doppler echocardiographic method was evaluated for quantifying the pulmonary (Qp) to systemic (Qs) blood flow ratio. Twenty six patients were studied, 15 with atrial septal defect (ASD) and 11 with patent ductus arteriosus (PDA). An apical four-chamber view was used to measure the maximal Doppler flow velocities in the right and left ventricular inflow regions (RVIR and LVIR) and the maximal diameters of the tricuspid and mitral anuli at diastole. The two-dimensional pulsed Doppler pulmonary to systemic blood flow ratio (Qp/Qs) estimation involved calculating the area of the Doppler flow velocity signal along the time scale multiplied by the diameter of either the tricuspid or mitral anulus as measured on the apical four-chamber view. In ASD patients, Qp was measured at RVIR and Qs at LVIR. In PDA patients, Qp was calculated at LVIR and Qs at RVIR. Twenty-six healthy children comprised the control group. The areas of the Doppler flow velocity signals along the time scales of RVIR and LVIR were also quantified and the diameters of the tricuspid and mitral anuli were measured. In the control group, the linear correlation of the trans-mitral M(d)*M(a) to trans-tricuspid T(d)*T(a) value was r = 0.909, n = 26. The correlations between Doppler Qp/Qs ratio estimates and those obtained at cardiac catheterization were r = 0.902, n = 15 in ASD and r = 0.967, n = 11 in PDA. These results suggest a clinical application of this Doppler echocardiographic method in the noninvasive estimation of the cardiac shunt in ASD and PDA.

Randomized low-dose indomethacin trial for prevention of intraventricular hemorrhage in very low birth weight neonates

We admitted 36 preterm neonates (600 to 1250 gm birth weight) with normal 6-hour echoencephalograms to a randomized, placebo-controlled prospective trial to determine whether a low dose of indomethacin would prevent germinal matrix or intraventricular hemorrhage and permit adequate urinary output. Between the sixth and tenth postnatal hours, indomethacin (0.1 mg/kg) or placebo was administered intravenously every 24 hours for a total of three doses. Cardiac ultrasound studies to assess the status of the ductus arteriosus were performed at 6 postnatal hours and on day 5. Urinary output, serum electrolytes, serum indomethacin levels, and renal and clotting functions were monitored. No differences in birth weight, gestational age, or Apgar scores were noted between the two groups of infants. Two indomethacin-treated infants and three infants given placebo had significant urinary output difficulties, requiring that the study medication be withheld. Of 19 infants given indomethacin, two had germinal matrix or intraventricular hemorrhage, in comparison with 8 of 17 infants given saline solution (p = 0.02). Of the infants who had a left-to-right patent ductus arteriosus shunt before treatment, 64% of the indomethacin-treated and 33% of the saline solution-treated infants no longer had a patent ductus arteriosus on day 5. Ductal status appeared unrelated to the development of germinal matrix or intraventricular hemorrhage.

Cardiovascular effects of patent ductus arteriosus in preterm lambs with respiratory distress

We created a model for studying the cardiovascular and pulmonary effects of patent ductus arteriosus (PDA) in premature lambs with respiratory distress. In 47 fetal lambs at 129 to 133 days gestation (term, 145 days), we infiltrated the ductus arteriosus with formalin and placed a mechanical occluder about it so that its patency could be regulated. Two days later the lambs were delivered, given sheep surfactant, paralyzed, and their lungs mechanically ventilated. These premature lambs could more than double their left ventricular output when challenged with increasing degrees of left-to-right shunts through the PDA. This was accomplished by an increase in stroke volume, not by an increase in heart rate. During the 40-minute observation period, there was no change in dynamic compliance or functional residual capacity while the ductus was patent. When the ductus was patent, there was a significant increase in arterial PaO2 (even with small left-to-right shunts) and a decrease in PaCO2 (with large shunts). Despite the heart's ability to handle the increased volume load of a PDA, there were significant alterations in individual organ blood flows, resulting from a combination of decreased perfusion pressure and localized vasoconstriction. The abdominal organs had significant reductions in blood flow even with small PDA shunts. This decrease in organ blood flow may explain some of the pathophysiologic manifestations of PDA in preterm infants.