Superior Vena Cava Blood Research Articles

Pulmonary/systemic flow ratio in children after cavopulmonary anastomosis

This study attempted to provide a formula for calculation of the pulmonary/systemic flow ratio in children after bidirectional cavopulmonary anastomosis. With the bidirectional cavopulmonary anastomosis, only the superior vena cava blood is oxygenated by the lungs. The inferior vena cava flow recirculates into the systemic circulation. The ratio of these flows will determine systemic arterial saturation. According to the Fick principle, 1) Systemic cardiac output (liters/min) = Pulmonary venous flow + Inferior vena cava flow; 2) Systemic blood oxygen transport (ml/min) = Pulmonary venous blood oxygen transport + Inferior vena cava blood oxygen transport. By substituting the first equation into the second, Pulmonary/systemic flow ratio = (Systemic saturation - Inferior vena cava saturation)/(Pulmonary venous saturation - Inferior vena cava saturation). We applied the third formula to data obtained from 34 catheterizations in 29 patients after bidirectional cavopulmonary anastomosis. Mean [+/- SD] age at operation was 1.70 +/- 1.43 years, and mean age at catheterization was 2.95 +/- 1.65 years. The pulmonary/systemic flow ratio calculated for all 29 patients was 0.58 +/- 0.09. Of 17 patients with aortography, 10 had systemic to pulmonary collateral vessels. Patients with collateral vessels had a significantly higher pulmonary/systemic flow ratio (0.61 +/- 0.07 vs. 0.53 +/- 0.07, respectively, p < 0.02) and systemic saturation (88 +/- 4% vs. 82 +/- 4%, respectively, p < 0.002) than those without collateral vessels. The pulmonary/systemic flow ratio in those patients with no collateral vessels was similar to the previously reported echocardiographically derived superior vena cava/systemic flow ratio in normal children. The pulmonary/systemic flow ratio after bidirectional cavopulmonary anastomosis can be calculated. Pulmonary blood flow in these patients determines systemic saturation and accounts for the majority of venous return in young children.

Arrhythmias and electrocardiographic changes after the hemi-Fontan procedure

T he hemi-Fontan procedure has been proposed as an alternative to the bidirectional Glenn procedure in the first stage of the Fontan operation.1*2 In the hemiFontan operation, an atriopulmonary patch directs superior vena caval blood flow into both pulmonary arteries and the inferior vena caval flow into the ventricle. The hemi-Fontan procedure involves atria1 suture lines, which can potentially affect atria1 conduction and cause arrhythmias. Our surgical experience with the hemiFontan has been reported.2 Here, we report the early effects of the hemi-Fontan on the electrocardiogram and arrhythmias after the hemi-Fontan. Between August 1989 and May 1992,21 children (11 boys and 10 girls, aged 4 months to 5 years [median 11 months]), underwent the hemi-Fontan procedure at our hospital. The underlying cardiac defect was double-inlet left ventricle in 6, hypoplastic left heart syndrome in 5, pulmonary valve atresia with intact ventricular septum in 4, mitral atresia in 3 and complex double-outlet right ventricle in 3. All but 3 had had previous palliative procedures that were modified Blalock-Taussig shunt in 6, pulmonary artery banding in 5, stage 1 Norwood operation in 5, central shunt (a tube graft between the ascending aorta and the pulmonary trunk) in 3, coarctation of the aorta repair in 3, pulmonary artery reconstruction in 2, Blalock-Hanlon atria1 septectomy in 1 and Damus-Kaye-Stansel operation in 1. Before hemi-Fontan, no patient had clinical or electrocardiographic features of arrhythmia. After surgery 2 patients died, both of hemodynamic reasons. Atria1 JEutter occurred in the early postoperative period in 1 patient and recurred later in the same patient. Therapy for this patient was begun with amiodarone and is well controlled. Another had an episode of sustained ventricular tachycardia in the early postoperative period that responded to intravenous lidocaine, and did not reCUK The electrocardiographic results are summarized in Table I. All electrocardiograms showed sinus rhythm. The P-wave axis and PR interval were not sigr$cantly di$erent when compared between preoperative, early postoperative (~30 days) and late postoperative (followup of 5 to 33 months, mean 20) electrocardiograms. Pwave amplitude, however, decreased signijcantly in the early postoperative period. The late postoperative electrocardiogram showed some increase in P-wave amplitude compared with the early postoperative electrocardiogram but was still diminished compared to the preoperative electrocardiogram. No patient had fragmented P waves (defined as >2 upward dejections in

Superior vena caval and mixed venous oxyhemoglobin saturations in children recovering from open heart surgery.

Simultaneous superior vena caval (Scvo2) and mixed venous (Svo2) oxyhemoglobin saturation values in 15 children recovering from open heart surgery were compared to assess the value of superior vena caval blood samples in monitoring systemic oxygen supply/demand balance. Samples were obtained immediately following the operation and postoperatively every morning for 4 days. During the 4-day study period, the patients' cardiopulmonary functions improved, allowing partial weaning from respiratory and cardiovascular support. The lowest values of superior vena caval (46.7 +/- 8.4%) and mixed venous (63.7 +/- 10.9%) oxyhemoglobin saturation were measured immediately after the operation. At this time, 6 patients had abnormally low Scvo2 values, but normal Svo2 values. Both Scvo2 and Svo2 increased; the difference between them decreasing significantly during the study period (P less than 0.001). The results show that Scvo2 is consistently lower than Svo2 in children recovering from open heart surgery. This difference may be secondary to residual intracardiac left-to-right shunting of blood or to altered distribution of systemic blood flow. The saturation difference between the two venous samples decreases during postoperative recovery, making a superior vena caval blood sample an inadequate substitute for a mixed venous blood sample in calculating derived cardiopulmonary variables intended to reflect the function of the body as a whole. Because Scvo2 was frequently subnormal while Svo2 was in the normal range, monitoring of Svo2 could not be reliably used to rule out oxygen supply/demand imbalance during the early postoperative period in these patients.

Assessment of superior vena caval blood flow velocity in ischemic heart disease.

In order to evaluate the right atrial function in patients with ischemic heart-disease, we studied the superior vena caval blood flow velocity using pulsed Doppler echocardiography. The subjects included 31 patients with anteroseptal infarction (ANT), 23 with inferior or inferoposterior infarction (INF + POS), 27 with effort angina pectoris (EAP) and 15 with vasospastic angina pectoris (VAP). The systolic peak flow velocity (PFVs) was significantly reduced only in INF + POS compared with those in ANT, EAP and VAP (36.8 +/- 1.8 cm/sec vs 46.9 +/- 2.1 cm/sec, 46.4 +/- 2.1 cm/sec and 42.6 +/- 1.9 cm/sec, p less than 0.05, respectively). No significant difference in diastolic peak flow velocity (PFVd) was found between the 4 groups. PFVs/PFVd was significantly reduced only in INF + POS compared with those in ANT, EAP, and VAP (1.39 +/- 0.05 vs. 1.75 +/- 0.08, 1.76 +/- 0.09, and 1.62 +/- 0.09, p less than 0.05, respectively). These results suggested that INF + POS caused impairment of the right atrial reservoir function.

Abrupt changes in mixed venous blood gas composition after the onset of exercise

It has been assumed that increases in both O2 uptake and ventilation occurring within the first few seconds after the onset of exercise cannot be the result of changes in blood gas composition reaching the central circulation because of the circulatory delay from the exercising limbs (A. Krogh and J. Lindhard, J. Physiol. Lond. 42: 112-136, 1913). We sought to validate this assumption by measuring the time course of pulmonary arterial blood gases during the transition from rest to exercise. Six healthy men underwent pulmonary arterial catheterization and then performed transitions from rest to moderate cycle ergometer exercise. An anaerobic sampling manifold withdrew 19 samples of blood during the rest-to-exercise transition; sampling interval was usually 4 s. Blood gas analysis showed that, on average, from rest-to-steady-state exercise, O2 saturation (Svo2) fell from 71 to 41% and mixed venous PCO2 (PvCO2) rose from 42 to 59 Torr. Contrary to our expectations, Svo2 decreased and PvCO2 increased with no discernible latency after exercise onset (by 10% and 2 Torr, respectively, within 6 s). The half time for the Svo2 decrease was 32 s, whereas for the PvCO2 increase it was 80 s. The time course of superior vena cava blood gas composition was determined in several experiments; no rapid changes after exercise onset were found. We conclude that at exercise onset there is a rapid fall in Svo2 and rise in PvCO2 well in advance of arrival of blood produced by exercising legs.(ABSTRACT TRUNCATED AT 250 WORDS)

Anomalous venous connection of the superior vena cava to the left atrium

Abnormal drainage of caval blood into the left atrium represents a rare cause of obligatory cyanosis. Most reported cases have presented at a young age in association with other cardiac defects. 1,2 We report a case of partial drainage of superior vena cava (SVC) blood into the left atrium in an asymptomatic, cyanotic 74-year-old man.

Inferior and superior vena caval blood flows during cross-clamping of the thoracic aorta in pigs

Changes in blood flow through the inferior and superior venae cavae during cross-clamping of the thoracic aorta just above the diaphragm were studied in 28 miniature pigs anesthetized with enflurane titrated to maintain systemic arterial blood pressure close to normal values. Surgical preparation included sternotomy with subsequent placement of a noncannulating electromagnetic probe around the ascending aorta and a cannulating electromagnetic probe in the transected inferior vena cava. Superior vena caval flow was calculated as the difference between aortic flow and inferior vena caval flow. Clamping of the thoracic aorta alone (n = 10) was accompanied by severe arterial hypertension, a dramatic decrease in inferior vena caval flow, and an increase in superior vena caval flow, which resulted in a moderate increase in aortic flow. Simultaneous clamping of the thoracic aorta and inferior vena cava (n = 13) was accompanied by no significant change in arterial pressure or superior vena caval flow. The oxygen content in mixed venous blood significantly (p less than 0.05) increased from 9.5 +/- 1.1 to 13.4 +/- 1.8 ml.dl-1 in animals undergoing clamping of the thoracic aorta only, but did not change significantly in animals subjected to simultaneous clamping of the aorta and inferior vena cava. The study demonstrates a substantial increase in superior vena caval flow during cross-clamping of the thoracic aorta. Further studies elucidating the mechanism of the observed changes are required.

Superior vena cava Doppler: a non-invasive method for the diagnosis of pericardial disease

Superior vena cava Doppler flow velocities were assessed in two patients presenting with cardiac tamponade. Abnormal Doppler flow patterns correlated with right atrial pressure abnormalities characteristic of tamponade and constriction. During tamponade diastolic superior vena cava flow was abolished, and only systolic flow occurred. After pericardiocentesis diastolic flow reappeared. In one patient dominant diastolic flow velocities after pericardiocentesis suggested residual constriction. The flow pattern returned to normal after pericardiectomy, with systolic velocity exceeding diastolic velocity. Serial studies in these patients suggest that Doppler evaluation of superior vena cava blood flow is a useful method for evaluating pericardial disease.

Variability of right-sided cardiac oxygen saturations in adults with and without left-to-right intracardiac shunting

In many catheterization laboratories and intensive care units, oxygen saturation of single blood specimens is measured from the superior vena cava (SVC), right atrium (RA) and pulmonary artery (PA) during right-sided catheterization, but variability of such single measurements in adults with and without intracardiac left-to-right shunting has not been assessed. Oxygen saturation of SVC, RA and PA single blood samples were measured in 1,031 adults (524 men, 507 women, aged 50 ± 13 years [mean ± standard deviation SD]). In the 980 patients without shunting, differences in saturation between SVC and RA, RA and PA and SVC and PA were 3.9 ± 2.4%, 2.3 ± 1.7%, and 4.0 ± 2.5%, respectively, so that the normal limits of variability (mean ± 2 standard deviations) for these saturation differences were 8.7%, 5.7% and 9.0%, respectively. Of the 51 patients with left-to-right shunting, these limits of variability of oxygen saturation correctly identified 46 (90%), and the 5 with shunting whose saturation differences were below these limits had small shunts ( Qp Qs ratios of 1.9 or less). Thus, assessment of oxygen saturation from single blood specimens obtained from the SVC, RA and PA offers excellent sensitivity (more than 90%), specificity (94 to 95%) and predictive accuracy (94% or more) in identifying patients with and without intracardiac left-to-right shunting. The sensitivity of these limits is especially high in patients with large shunts ( Qp Qs of 2 or more).

Superior vena caval blood flow velocities in adults: a Doppler echocardiographic study.

Superior vena caval blood flow velocity was measured in 30 normal adults (age 20-65, mean 36 yr). The flow velocities were measured by pulsed Doppler echocardiography, using a Duplex system with the transducer at the right supraclavicular fossa, approximating a 0 degrees Doppler angle. Four distinct flow waveforms were found during each cardiac cycle: A, a small retrograde flow during right atrial contraction (peak flow velocity 12.4 +/- 2.2 cm/s); B, a small antegrade flow during right atrial relaxation (15.7 +/- 5.0 cm/s); S, a large antegrade flow during ventricular systole (35.2 +/- 7.3 cm/s); and D, a large antegrade flow during ventricular diastole (23.2 +/- 3.1 cm/s). The wave duration was inversely related to heart rate. The peak flow velocities of the S and D waves were inversely related to the patients' ages. This study provides recognition of the pattern and range of normality essential to extension of this noninvasive technique to the diagnosis of pathological conditions.

Physiological rationale for a bidirectional cavopulmonary shunt: A versatile complement to the Fontan principle

The original Fontan procedure included a classic superior vena cava-to-right pulmonary artery (Glenn) shunt. Subsequent experience demonstrated that this anastomosis was not essential and was an unnecessary commitment of the larger right pulmonary circulation to the smaller blood volume of the superior vena caval return. With application of the Fontan principle to more complex cardiac malformations, there has been a reconsideration of possible benefits of a cavopulmonary shunt in selected patients. A modified shunt from the divided end of the superior vena cava to the side of the undivided right pulmonary artery utilized in 21 patients is described. This shunt is designed to allow bidirectional pulmonary arterial distribution of both superior vena caval inflow and right atrial outflow after completion of the Fontan procedure. Twelve patients had the bidirectional shunt performed prior to a Fontan operation; five of these had a subsequent atriopulmonary connection and seven await operation. Eight patients had construction of this shunt at the time of their Fontan procedure. One patient had a bidirectional shunt constructed following atriopulmonary anastomosis to help relieve right atrial outflow obstruction. Two patients with univentricular heart undergoing simultaneous Fontan procedure and a bidirectional shunt died while in the hospital. The remaining 19 patients have been followed up for 2 months to 9 years with one late sudden death at 9 years. There have been no bidirectional cavopulmonary shunt failures, stenoses, kinks, or recognized pulmonary arteriovenous malformations. Postoperatively, eight patients had assessment of pulmonary distribution of shunt blood flow by angiography. Seven of these patients were also evaluated by radionuclide angiography. Superior vena caval blood flow via the bidirectional cavopulmonary shunt tended to be greater to the right lung, but bilateral pulmonary flow was documented in all but one patient. After Fontan operation, six of seven patients tested also demonstrated bilateral distribution of atriopulmonary flow. We concluded from our experience that this modified shunt provides excellent relief of cyanosis, allows bidirectional pulmonary distribution of both superior vena caval return and also the right atrial blood flow after atriopulmonary connection, and may be done before, with, or after a Fontan procedure and is compatible with all currently recommended modifications. Perioperative hemodynamic adjustments to the Fontan procedure may be improved by reducing atrial volume, and this may also be of potential benefit in the long-term adaptation to Fontan physiology by minimizing atrial distention.

34 EXPERIMENTAL EVIDENCE FOR CENTRAL NERVOUS SYSTEM CONTROL OF CATCH-UP GROWTH

In rats permanent stunting follows neonatal head-irradiation (Head-X); during the post-weaning period full catch-up growth (CU) occurs after fasting (F); failure of CU occurs after cortisone treatment (C); and superimposition of F or C on Head-X results in similar responses in the stunting after Head-X. In this study growth hormone (GH) secretory profiles were determined in rats treated with Head-X, F or C. Superior vena cava blood was sampled at 15 min intervals during the light phase in chronically cannulated undisturbed animals. Sampling duration was 9 h in Head-X, 6 h in F, and 12 h in C. The results, expressed as area units/15 min under the curve of plasma GH concentration vs. time, are as follows:

Pulmonary vascular resistance in children with congenital heart disease.

Pulmonary and systemic blood flow and pulmonary vascular resistance were measured in 21 children with congenital heart disease. Blood flow was calculated by the direct Fick method, using measurements of metabolic gas exchange obtained by remote respiratory mass spectrometry. The observations showed that the administration of oxygen caused an appreciable fall in pulmonary vascular resistance in 16 of the 21 children studied and that this fall would not have been appreciated from a study of pulmonary arterial pressure alone as it was masked by a corresponding rise in blood flow. In 10 of 14 children, in whom superior vena caval blood was also sampled, the rise in flow was largely due to an increase in intracardiac left to right shunt. It was accompanied by widening of the alveolar-arterial oxygen gradient, perhaps due to imperfect gas equilibration within the lung.

Comparative value of peripheral and central venous pCO2 in predicting normal paCO2 during anaesthesia

The ability of venous pCO2 to predict arterial pCO2 within the normal range was tested by measuring pCO2 in blood sampled simultaneously from a large forearm vein (PER), from the superior vena cava (SVC), and from an artery in 35 anaesthetized patients. The relationship between arterial and both venous pCO2's were studied in a first series of 15 patients (ASA physical status class I-II) anaesthetized with methohexitone, fentanyl, pancuronium and nitrous oxide/oxygen, and in a second series of 20 patients scheduled for cardiac surgery anaesthetized with flunitrazepam, fentanyl, pancuronium and nitrous oxide. A marked correlation was found between arterial and both venous pCO2's samples in the normal patients (a/PER: r = 0.922; a/SVC: r = 0.940); in the patients with abnormal cardiovascular status the correlation observed was less pronounced (a/PER: r = 0.501; a/SVC: r = 0.507). In view of the similar correlation coefficients observed from the PER or SVC blood sampling sites, we conclude that the degree of accuracy of the prediction of paCO2 from the venous pCO2's is not modified by the origin of the venous blood. The differences between the coefficients of correlation found in the normal patients and in those with abnormal cardiovascular function indicate that venous pCO2 as estimate of paCO2 appears useful only in subjects with normal haemodynamic status.

Reassessment of the Assumed A-V Oxygen Content Difference in the Shunt Calculation

A study was undertaken in 15 patients to compare measured and assumed arteriovenous oxygen (A-V O2) content differences and their effects on resultant shunt calculations. All patients were on volume ventilators and demonstrated a stable cardiovascular state. Simultaneous measurements of the O2 content of a pulmonary artery (PA) and of a superior vena cava (SVC) sample were compared. A mean A-V 02 content difference of 3.5 plus or minus 0.8 volumes percent was obtained from the PA and 2.6 plus or minus 1.1 volumes percent from the SVC. The resultant shunt calculations derived from measured A-V 02 content differences were compared with the calculation based on an assumed A-V O2 content difference of 5 volumes percent. A method for extrapolating a "true" A-V 02 content difference from an SVC blood sample was obtained. The extrapolated value resulted in a more representative "true shunt" calculation in 13 of the 15 patients.

Obstructed anomalous pulmonary venous return

A unique case of total anomalous pulmonary venous return in a 22-month-old child is described. Although all veins terminated anatomically above the diaphragm, stenosis at the superior vena caval-right atrial junction forced blood from the right superior pulmonary vein to travel with superior vena caval blood in a circuitous retrograde pathway through the hemi-azygos and azygos veins into the inferior vena cava. The dilated, tortuous hemi-azygos vein produced a left paravertebral radiographic opacity which should prove useful in clinical recognition of this unusual anomaly.

Surgical repair of tricuspid atresia

Surgical repair of tricuspid atresia has been carried out in three patients; two of these operations have been successful. A new surgical procedure has been used which transmits the whole vena caval blood to the lungs, while only oxygenated blood returns to the left heart. The right atrium is, in this way, `ventriclized', to direct the inferior vena caval blood to the left lung, the right pulmonary artery receiving the superior vena caval blood through a cava-pulmonary anastomosis. This technique depends on the size of the pulmonary arteries, which must be large enough and at sufficiently low pressure to allow a cava-pulmonary anastomosis. The indications for this procedure apply only to children sufficiently well developed. Younger children or those whose pulmonary arteries are too small should be treated by palliative surgical procedures.

Persistent Left Superior Vena Cava Draining into the Left Atrium with Absent Right Superior Vena Cava

A 5½-year-old boy with a persistent left superior vena cava entering the left atrium first presented with a cerebral abscess. The right superior vena cava was absent, and no other intracardiac anomalies were present. One year after drainage of the abscess, the cardiovascular anomaly was Corrected by placement of a Dacron baffle within the left atrial cavity in a manner which excluded the left superior vena caval blood flow from the left atrium and directed it into the right atrium. Although the initial repair did not hold up, after a second one the patient did well and had no further symptoms. Repair of this cardiovascular anomaly is best carried out by placement of an intraatrial baffle.

Distribution of the circulation in the normal and asphyxiated fetal primate

Term primate fetuses had average cardiac outputs of 445 ± 90 c.c. per millimeter per kilogram, umbilical blood flows of 208 ± 20 c.c. per millimeter per kilogram, and O2 consumptions of 7 ± 2 c.c. per millimeter per kilogram. There was preferential streaming of ductus venosus (DV) blood to the brain and heart and negligible shunting of superior vena cava (SVC) blood through the foramen ovale. The largest proportion of the cardiac output was distributed to the brain and placenta. The blood flow to the midbrain, brainstem, and cerebellum was significantly higher than that to the cerebral cortex. Asphyxia induced by maternal hypoxia compatible with fetal survival led to mixed acidosis; decreased O2 consumption, umbilical blood flow, and cardiac output; marked shunting of SVC blood through the foramen ovale for distribution to the brain and heart; and, an increase in the proportion of the reduced umbilical blood flow going through the DV. The blood flow to the heart, brain, and adrenal per gram of tissue was maintained by an increase in the distribution of cardiac output to these organs. The placental and pulmonary flows decreased.

Hemodynamic effects of extracorporeal circulation in closed-chest normal animals and in those with myocardial infarction with shock.

The hemodynamic effects of closed-chest extracorporeal circulation were investigated in normal dogs and in dogs subjected to coronary embolization. In both groups, despite delivery of large volumes of blood into the abdominal aorta through peripheral routes, a rise in proximal aortic pressure could not be achieved; to accomplish this it was necessary to increase vascular resistance by balloon obstruction of the lower abdominal aorta, the distal aorta being supplied with superior vena cava blood. The resulting rise in proximal aortic pressure was accompanied by a diminution in calculated left ventricular work.