Prograde Flow Research Articles

Monitoring Venus’ mesospheric winds in support of Venus Express: IRAM 30-m and APEX observations

We report on direct wind measurements in Venus’ mesosphere (90–115 km), performed in support of Venus Express, and based on CO millimeter observations. Most observations, sampling the CO(2–1) and CO(1–0) lines, were acquired with the IRAM 30-m telescope, over four distinct periods: (i) Summer 2006; (ii) May–June 2007, in association with the coordinated ground-based campaign; (iii) August 2007 inferior conjunction and (iv) September 2007. In the latter period, additional measurements (CO(3–2)) were obtained with the APEX 12-m telescope. Overall, the measurements indicate a large body of temporal variability of the Venus mesospheric field, but general features emerge: (i) winds strongly increase with altitude within the mesosphere, by a factor of 2–3 over a decade in pressure; (ii) many, but not all, of our observations can be viewed as the superposition of zonal retrograde and subsolar-to-antisolar (SSAS) flows of comparable speeds, typically 30–50 m/s near 0.1 mbar ( ∼ 93 km ) and 90–120 m/s near 0.01 mbar ( ∼ 102 km ) (iii) the wind field was very stable over three consecutive observing days in May–June 2007, but much more variable on a similar time base in August 2007 (iv) at a ∼ 2000 km resolution, the nightside wind field appears very complex, with evidence that the SSAS flow does not reach high latitudes, and possible evidence for additional meridional winds. Our Summer 2006 observations, which sample Venus’ dayside, seem to suggest that a prograde zonal flow is superimposed to the SSAS circulation for this period. This surprising result, which implies a pre-midnight convergence of the wind field, requires confirmation, and fruitful comparisons may be obtained from the analysis of motions in the O 2 emission images, as observed by Venus Express.

Spinal Arterial Anatomy and Risk Factors for Lower Extremity Weakness Following Endovascular Thoracoabdominal Aortic Aneurysm Repair With Branched Stent-Grafts

To evaluate spinal arterial anatomy and identify risk factors for lower extremity weakness (LEW) following endovascular thoracoabdominal aortic aneurysm (TAAA) repair. A retrospective review was conducted of 37 patients (27 men; mean age 74.8+/-7.1 years, range 58-86) undergoing endovascular TAAA repair with branched stent-grafts at a single academic institution from July 2005 to December 2007. Data were collected on preoperative comorbidities, duration of operation, blood loss, type of anesthesia, extent of aortic coverage, blood pressure, cerebrospinal fluid (CSF) pressure and drainage, and postoperative development of LEW. Pre- and postoperative contrast-enhanced computed tomographic angiograms (CTA) in a 26-patient subset were analyzed to evaluate the number of patent intercostal and lumbar arteries before and after repair. All patients were neurologically intact at the end of the operation. Seven (19%) patients developed LEW postoperatively: 6 perioperatively and 1 after discharge. LEW was associated with postoperative hypotension, internal iliac artery (IIA) occlusion, and fewer patent segmental arteries on preoperative CTA. Lowest mean systolic blood pressure was <90 mmHg in all 6 (100%) patients who developed LEW in hospital compared to 12 (44%) of the 27 patients who did not develop LEW (p = 0.02). Complete resolution of LEW (n = 4) followed prompt measures to raise blood pressure and lower CSF pressure. Persistent LEW (n = 3) was associated with sustained hypotension from sepsis, postoperative bleeding, and hemodialysis, respectively. Two (29%) of 7 patients with LEW either lost prograde flow to an IIA during repair or had bilaterally occluded IIAs preoperatively compared to 2 (7%) of 30 patients without LEW (p = 0.16). Comparison of pre- and postoperative CTAs showed no reduction in the mean number of patent segmental arteries in patients with or without LEW. Endovascular TAAA repair inevitably occludes direct inflow to lumbar and intercostal arteries. The distal segments of these arteries to the spine, however, are seen to remain patent through collaterals. Measures to preserve collateral pathways and increase perfusion pressure may help prevent or treat LEW.

Hypoplastic Left Heart Syndrome

See related article, pages 1363–1370 Hypoplastic left heart syndrome (HLHS) is one of the most severe congenital heart defects, accounting for 20% to 25% of mortality in infants born with congenital heart disease. In the United States, ≈2000 infants are born each year with HLHS.1 To date, there is a paucity of studies that define the underlying genetic, molecular and cellular mechanisms of HLHS.2–4 Most cases of HLHS are thought to arise secondarily because of decreased flow into the developing embryonic left ventricle, although in some cases, abnormal left ventricular growth could be the primary defect. There is strong evidence for a genetic etiology for HLHS, although very little is understood about the genetic mechanisms underlying HLHS. Nineteen percent of first degree relatives of infants with HLHS have a congenital heart defect.5 In addition, there are several chromosomal disorders that are associated with HLHS. For example, 10% of all infants born with a terminal 11q deletion (Jacobsen syndrome) have HLHS.6 Mutations in at least one gene, the cardiac transcription factor NKX2.5, have been identified in patients with HLHS.7,8 Similar to many of the most severe congenital heart defects, treatment strategies for HLHS have evolved and are still changing. The two current surgical strategies include the three-stage Norwood/Fontan procedure, or, alternatively, cardiac transplantation. The Norwood procedure, which is performed optimally in the neonatal period to avoid the development of pulmonary vascular disease, entails reconstructing the aortic arch, transecting the pulmonary artery, anastamosing the pulmonary artery root to the reconstructed aorta, and placing a systemic to pulmonary artery shunt (either from aorta or more recently, from the right ventricle). Although there has been significant progress in outcomes, neither surgical approach is curative and long-term outcomes are uncertain. Consequently, there has been an ongoing effort to develop …

In Vitro Evaluation of a New Autologous Valve-Stent for Deep Venous Incompetence

To report the results of in vitro hydrostatic bench testing of a new vein-stent combination to correct deep venous incompetence. Twelve valves were constructed from a modified Palmaz stent encased in a segment of great saphenous vein harvested from patients during routine varicose vein surgery. An in vitro flow circuit was set up to evaluate opening and closing pressures (in cm H(2)O), and the valve was subsequently subjected to repetitive cycles of increasing prograde flow and reflux pressures. Duplex scanning was used to evaluate valve closure time and detect any possible reflux. The valve mechanism required only 1 to 3 cm H(2)O for opening and 2 to 4 cm H(2)O for closing. Prograde flow of up to 1000 mL/min passed easily through this valve, which remained competent with reflux pressures up to 180 cm H(2)O. Mean valve closure time was 0.15+/-0.07 seconds. Unligated side branches or damage from dissection impaired the competence of 3 valves. This new vein-stent valve functions as a normal deep vein valve, requiring only minimal pressures for opening and closing. It allows high flow passage and still remains competent at high reflux pressures. This valve may provide a minimally invasive solution for the correction of deep venous incompetence using autologous material. Further in vivo evaluation will be mandatory.

Advances in Neonatal Cardiac Surgery

After completing this article, readers should be able to: 1. Describe the developments that have allowed advances in neonatal cardiac surgery. 2. Describe the diagnostic approach to hypoplastic left heart syndrome (HLHS). 3. Delineate the preoperative management of the neonate who has HLHS. 4. Describe the original Norwood procedure and subsequent modifications. 5. Delineate the optimal therapy in the postoperative period for neonates who have a single ventricle. Advances in the surgical and medical management of children who have congenital heart disease (CHD) have led to a dramatic improvement in overall survival and reduced the long-term sequelae of open-heart surgery. With improved survival and decreased morbidity over the past 2 decades, the early complete repair of complex congenital heart problems in preterm and low-birthweight neonates has gained wider acceptance. Cardiologists and cardiothoracic surgeons now consider and perform complete neonatal repair more frequently than palliative surgery in this patient population. The treatment of hypoplastic left heart syndrome (HLHS) best illustrates the evolution of management strategies to improve survival and long-term outcome. A recent modification of the Norwood operation that involves a right ventricle-to-pulmonary artery conduit has led to much improved early postoperative stability and, in many centers, improved survival to a stage II superior cavopulmonary connection. A multidisciplinary team approach is required to provide the necessary care for this complex patient population. In 1938, Robert Gross at Children’s Hospital in Boston successfully ligated a patent ductus arteriosus, and this procedure—performed against the wishes of surgeon-in-chief William Ladd—opened the era of surgery for CHD. (1) Gross and Hufnagel performed detailed animal experiments to develop a technique for treatment of coarctation of the aorta that involves excision and end-to-end anastomosis. (2) Clarence Craaford of Stockholm, Sweden, had visited Gross to observe his experimental work, and in October 1944, Craaford and Nylin were the first to repair aortic …

Cassini imaging of Saturn: Southern hemisphere winds and vortices

High‐resolution images of Saturn's southern hemisphere acquired by the Cassini Imaging Science Subsystem between February and October 2004 are used to create maps of cloud morphology at several wavelengths, to derive zonal winds, and to characterize the distribution, frequency, size, morphology, color, behavior, and lifetime of vortices. Nonequatorial wind measurements display only minor differences from those collected since 1981 and reveal a strong, prograde flow near the pole. The region just southward of the velocity minimum at 40.7°S is especially active, containing numerous vortices, some generated in the proximity of convective storms. The two eastward jets nearest the pole display periodicity in their longitudinal structure, but no direct analogs to the northern hemisphere's polar hexagon or ribbon waves were observed. Characteristics of winds and vortices are compared with those of Saturn's northern hemisphere and Jupiter's atmosphere.

Functional acquired pulmonary atresia secondary to subpulmonary aneurysmal tissue: a rare form of pulmonary outflow tract obstruction

artery (PA) arising from rudimentary pouch (*). Fetal echocardiography was performed at 19 and 29 weeks gestation after an abnormal screening ultrasound suggested left heart hypoplasia. The echocardiogram revealed left-sided hypoplasia with d-transposition of the great arteries and a small, posteriorly positioned pulmonary artery (PA) with both prograde and retrograde flow demonstrated. There appeared to be a moderate ventricular septal defect and, of note, there was unusual aneurysmal tissue of indeterminate origin below the pulmonary annulus. Postnatal echocardiography confirmed d-transposition of the great arteries with the aorta anterior and rightward of the smaller PA. The PA arose directly from a rudimentary, aneurysmal blind pouch (Figure 1) with bidirectional flow between the blind pouch and the main PA (Figure 2). However, no communication between the pouch and the remainder of the heart could be demonstrated by Doppler interrogation. The aneurysmal pouch was centrally located in the heart and appeared to possibly consist of redundant atrioventricular (AV) valve tissue contiguous with a leaflet of the left-sided AV valve. The PA was supplied by a large, tortuous patent ductus arteriosus typical for pulmonary atresia. There were 2 distinct AV valves entering a common single ventricle, with hypoplasia of the left-sided AV valve noted. The patient was initially treated with prostaglandin infusion to maintain ductal patency, followed by placement of a right-sided Blalock-Taussig shunt in the neonatal period. She subsequently underwent successful bidirectional Glenn anastomosis and left pulmonary arterioplasty at 7 months of age. This case represents an extremely unusual form of functional pulmonary atresia in which abnormal intracardiac aneurysmal tissue of indeterminate ori-

The Hemodynamic Relationships that Exist between Various Parts of the Lower Extremity Arterial Circuit Containing a Bypass Graft: Case Study

Introduction Circuits containing bypass grafts are made up of four elements: (1) the inflow tract, (2) the graft, (3) the collateral beds, and (4) the outflow tract. The fundamental principles developed by Poiseuille, Ohm, and Bernoulli can facilitate our understanding of the hemodynamics that occur within the arterial circuit containing bypass grafts. Case Report A 59-year-old man was seen at our diagnostic vascular unit with severe claudication. Invasive and noninvasive vascular studies revealed occlusion of his aorta and bilateral common iliac arteries with reconstitution at bilateral groins by way of visceral vessels. Elective aortobifemoral bypass graft surgery was performed. Postoperatively, duplex ultrasonography (Phillips/ATL 5000, Bothell, WA, 7-MHz linear array transducer) performed on bilateral groins revealed prograde flow distal to the anastomoses and retrograde flow involving the distal external iliac arteries proximal to the anastomoses. Discussion Depending on the outflow resistance, flow might be prograde to the leg or retrograde to the pelvis and/or muscle proximal to the anastomosis or a combination of both as demonstrated in this case study. Such retrograde flow is desirable when one needs to perfuse the pelvis or thigh and not desirable if it steals blood from distal circulation. Conclusions The preceding fundamental principles refer to flow and pressure as inseparable manifestations of the total energetics of circulation. These principles are applied to the following case study and demonstrate competitive flow and pressure resistance relationships that exist within the arterial circuit containing a bypass graft.

Moment analysis of metabolic heterogeneity: conjugation of benzoate with glycine in rat liver studied by multiple indicator dilution technique.

Metabolic zonation was assessed with the multiple indicator dilution (MID) technique in the single-pass perfused rat liver with use of moment analysis of the formed metabolite (M) data. During single-pass, retrograde rat liver perfusion with 17 Awake M benzoate, a bolus containing tracer preformed metabolite (PM) [(3)H]hippurate was injected rapidly into the hepatic vein at 20 min postperfusion, followed by injection of a second bolus containing [(14)C]benzoate at 30 min. Both doses also contained noneliminated reference indicators ((51)Cr-labeled RBCs, (125)I-labeled albumin, [(14)C]- or [(3)H]sucrose, and (2)H(2)O). The steady-state extraction ratio of benzoate, the area under the curve (AUC) and its mean transit time (MTT) during retrograde flow were identical to those previously observed for prograde flow. Values of AUC(PM) and MTT(PM) and AUC(M) were also similar to previously published prograde data, but the MTT(M) with retrograde perfusion was smaller than that for prograde perfusion. This, according to theory based on the tubes-in-series model, was consistent with perivenous enrichment of glycination activity when transport of drug was even and when the ratio of drug influx/efflux coefficient exceeded that for metabolite. Similar benzoate transport in periportal, homogeneous and perivenous isolated rat hepatocytes existed, and the influx/efflux coefficients (partition ratio) of benzoate from MID indeed exceeded that of hippurate. However, metabolism by zonal hepatocytes failed to reveal the anticipated metabolic zonation, and this is likely due to the shallow gradient of metabolic activity. The study demonstrates that moment theory is useful in delineating the perivenous enrichment of glycine conjugation activity.

Evolution of bulk composition, mineralogy, strain style and fluid flow during an HT–LP metamorphic event: sillimanite zone of the Catalan Coastal Ranges Variscan basement, NE Iberia

Metamorphic rocks in the Osor complex (Guilleries massif, NE Iberian Peninsula) show the following structural and compositional features: strong differentiation into quartz-rich gneissic semipelitic and quartz-absent, mica-rich schistose bands, higher density of igneous (both basic and leucogranitic) and quartz veins in the schistose domains and strong strain partitioning in the pelitic bands. Garnet is present in both kinds of lithologies, showing also differential textural and chemical features interpreted to be dependent on bulk composition, deformation and fluid interaction histories. Textures, mineral composition and thermobarometry suggest the operation of concurrent mechanical, mass transfer and thermal phenomena such as: (1) variations in strain style, (2) fluid infiltration, (3) magmatic injection and (4) HT–LP metamorphic and metasomatic episodes. The following sequence of events is suggested: initially the cooling of syntectonic high- T basic quartz diorite sheets promoted high strain rates, low d P/d T thermobaric evolution, incipient anatexis in the pelitic bands and devolatilization through a pervasive to vein-channelized prograde fluid flow. The prograde flow enhanced an ongoing compositional tectono-metamorphic differentiation and produced metasomatism through depletion of the Osor rocks in alkalis and calcium. Later injection and cooling of peraluminous leucogranitoid sheets, preferentially along pelitic bands, increased the ratio of magmatic/metamorphic components in the fluids and strongly enriched them in alkalis producing a second metasomatic episode. During crystallization of quartz and leucogranitoid veins, the pelitic bands were strongly enriched back again in alkalis, promoting the blastesis of big crystals of post-peak muscovite and albite as well as the retrogression of garnet. The metasomatic mica-rich levels must have been the preferred locus for development of a new deformation style dominated by shear band fabrics in metapelites and related to a release of the gravitational instability originated previously due to crustal thickening. The increasing decompressional component of the retrograde P– T path also suggests that this style of deformation was prevalent during, if not responsible for, a phase of exhumation of the metamorphic complex. It is suggested that similar patterns of thermomechanical and mass transfer phenomena could well be a fundamental characteristic common to all HT–LP metamorphic belts.

Efficacy of a proximal occlusion catheter with reversal of flow in the prevention of embolic events during carotid artery stenting: An experimental analysis

Objective: The role of percutaneous angioplasty and stenting of carotid bifurcation lesions has been limited by its potential for producing embolic debris. We evaluated the efficacy of a proximal occlusion catheter (POC) in the prevention of embolic events during carotid artery stenting. In addition, pressure measurements relevant to the clinical application of this device were obtained from 10 patients undergoing carotid endarterectomy. Methods: The POC is a guiding catheter with an occlusion balloon attached on the outside of the catheter at its distal end. Occlusion of the common carotid artery (CCA) was achieved by inflating the balloon while access to carotid bifurcation lesions was obtained through the inner lumen. The POC was inserted in the CCA of 10 dogs via the femoral artery. The side port of the POC was connected to a sheath placed in the femoral vein, thereby creating an external arteriovenous shunt. Ten artificial radiopaque particles simulating embolic particles and contrast agent were introduced in the CCA and monitored fluoroscopically. As a control, the same procedure was performed with a standard guiding catheter without an occlusion balloon. In 10 patients undergoing carotid endarterectomy, the internal carotid artery (ICA) and external carotid artery stump pressures and the pressure in the internal jugular vein were measured. Results: Without the external arteriovenous shunt, in all animals there was prograde flow in the distal CCA despite CCA occlusion. This flow was derived from the thyroid artery. However, once the arteriovenous shunt was activated, reversal of flow in the distal CCA was achieved in each animal, and all the artificial particles were recovered from the side port of the POC. In the control group, each particle embolized to the brain (100%, P <.01). In the patients, the mean stump pressures in the ICA and external carotid artery and the jugular vein pressure were 51.8 ± 14.2, 62.2 ± 15.1, and 6.5 ± 3.5 mm Hg, respectively. In each case, the jugular vein pressure was the lowest among the three. Conclusions: Obtaining proximal CCA control by inflating the POC does not sufficiently prevent embolization. However, reversal of flow in the ICA can always be created with the external shunt, which effectively prevents embolization. Thus, POC may markedly lower procedural stroke rates during carotid artery stenting. The ability of POC to prevent embolization before crossing the lesion with a guidewire may be an important advantage over other distal protection devices. (J Vasc Surg 2001;33:504-9.)

The Effect of Proximal Artery Flow on the Hemodynamics at the Distal Anastomosis of a Vascular Bypass Graft: Computational Study

The formation of distal anastomotic intimal hyperplasia (IH), one common mode of bypass graft failure, has been shown to occur in the areas of disturbed flow particular to this site. The nature of theflow in the segment of artery proximal to the distal anastomosis varies from case to case depending on the clinical situation presented. A partial stenosis of a bypassed arterial segment may allow residual prograde flow through the proximal artery entering the distal anastomosis of the graft. A complete stenosis may allow for zero flow in the proximal artery segment or retrograde flow due to the presence of small collateral vessels upstream. Although a number of investigations on the hemodynamics at the distal anastomosis of an end-to-side bypass graft have been conducted, there has not been a uniform treatment of the proximal artery flow condition. As a result, direct comparison of results from study to study may not be appropriate. The purpose of this work was to perform a three-dimensional computational investigation to study the effect of the proximal artery flow condition (i.e., prograde, zero, and retrograde flow) on the hemodynamics at the distal end-to-side anastomosis. We used the finite volume method to solve the full Navier-Stokes equations for steady flow through an idealized geometry of the distal anastomosis. We calculated the flow field and local wall shear stress (WSS) and WSS gradient (WSSG) everywhere in the domain. We also calculated the severity parameter (SP), a quantification of hemodynamic variation, at the anastomosis. Our model showed a marked difference in both the magnitude and spatial distribution of WSS and WSSG. For example, the maximum WSS magnitude on the floor of the artery proximal to the anastomosis for the prograde and zero flow cases is 1.8 and 3.9 dynes/cm2, respectively, while it is increased to 10.3 dynes/cm2 in the retrograde flow case. Similarly, the maximum value of WSSG magnitude on thefloor of the artery proximal to the anastomosis for the prograde flow case is 4.9 dynes/cm3, while it is increased to 13.6 and 24.2 dynes/cm3, respectively, in the zero and retrograde flow cases. The value of SP is highest for the retrograde flow case (13.7 dynes/cm3) and 8.1 and 12.1 percent lower than this for the prograde (12.6 dynes/cm3) and zero (12.0 dynes/cm3) flow cases, respectively. Our model results suggest that the flow condition in the proximal artery is an important determinant of the hemodynamics at the distal anastomosis of end-to-side vascular bypass grafts. Because hemodynamic forces affect the response of vascular endothelial cells, the flow situation in the proximal artery may affect IH formation and, therefore, long-term graft patency. Since surgeons have some control over the flow condition in the proximal artery, results from this study could help determine which flow condition is clinically optimal.

Mechanical characteristics of lyophilized human saphenous vein valves

Purpose: We investigated the mechanical characteristics of lyophilized human saphenous vein valves to determine their suitability for use as allogeneic transplants to treat chronic venous insufficiency. Methods: Fresh cadaveric veins were lyophilized in vacuum bottles within 24 hours of harvest and were stored at room temperature. The veins were reconstituted in saline solution and then were placed in an in vitro flow circuit for evaluation. At varied flow rates, pressures proximal and distal to valves during prograde and retrograde flow were measured. Valve closure times were determined with Doppler examination and spectral analysis. The valves were also stressed to 350 mm Hg on a separate apparatus. Results: All pressures proximal and distal to the valves remained less than 10 mm Hg during prograde flow. A pressure gradient developed immediately on the reversal of flow. Pressure as high as 200 mm Hg applied against the closed valves was not transmitted beyond the valve. Valve closure times had a mean of 0.31 ± 0.03 seconds and 0.21 ± 0.01 seconds for the Doppler examination and spectral analysis, respectively. All valves withstood stress pressures to 350 mm Hg. Conclusions: The in vitro mechanical characteristics of the valves of lyophilized veins are similar to known values for normal in vivo valves. (J Vasc Surg 1997;26:823-8.)

Formation and destruction of periclase by fluid flow in two contact aureoles

Periclase formed in steeply dipping marbles from the Beinn an Dubhaich aureole, Scotland, and the Silver Star aureole, Montana, by the reaction dolomite = periclase + calcite + CO2. Equilibrium between rock and fluids with X CO 2 < 1 requires that reaction was infiltration-driven. Brucite pseudomorphs after periclase occur in the Beinn an Dubhaich aureole either as bed-by-bed replacement of dolomite or in a lens along the contact between dolomite and a pre-metamorphic dike. Transport theory predicts that infiltration drove both periclase reaction and 18O-depletion fronts which moved at significantly different velocities along the flow path. The distributions of brucite and 18O-depleted rocks are identical in surface exposures, thus indicating upward flow. Time-integrated flux (q) was <500 mol/cm2 and the fluid source was magmatic. Because periclase and its hydrated equivalent brucite are unaltered to dolomite by retrograde reactions, the exposure of brucite marbles accurately images the flow paths of peak metamorphic fluids. In the Silver Star aureole brucite pseudomorphs after periclase exclusively occur in tabular bodies that are beds with elevated Mg/Ca. The spatial pattern of 18O-depletion requires upward vertical fluid flow. Estimated prograde q ≈ 103–104 mol/cm2 and the fluid source was magmatic. Low Mg/Ca, 18O-depleted, brucite-free rocks pose a dilemma because the periclase reaction front should have traveled ≈18 times further through them than the isotope alteration front. The dilemma is resolved by reaction textures that indicate periclase and brucite were destroyed in low Mg/Ca rocks by infiltration-driven retrograde carbonation reactions. Values of retrograde q were ≈103–104 mol/cm2. Brucite (after periclase) was preserved only in high Mg/Ca layers where periclase developed in greater abundance. The geometry of brucite marbles at Silver Star thus reflects the location of high Mg/Ca beds rather than the geometry of fluid flow. Retrograde reactions must be considered before the mineralogical record of prograde fluid flow can correctly be interpreted. In both aureoles fluid flow, mineral reaction, and isotope depletion were structurally controlled by bedding and lithologic contacts.

Prograde and retrograde fluid flow during contact metamorphism of siliceous carbonate rocks from the Ballachulish aureole, Scotland

Siliceous dolomites and limestones contain abundant retrograde minerals produced by hydration-carbonation reactions as the aureole cooled. Marbles that contained periclase at the peak of metamorphism bear secondary brucite, dolomite, and serpentine; forsterite-dolomite marbles have retrograde tremolite and serpentine; wollastonite limestones contain secondary calcite and quartz; and wollastonite-free limestones have retrograde tremolite. Secondary tremolite never appears in marbles where brucite has replaced periclase or in wollastonite-bearing limestones. A model for infiltration of siliceous carbonates by CO2-H2O fluid that assumes (a) vertical upwardly-directed flow, (b) fluid flux proportional to cooling rate, and (c) flow and reaction under conditions of local equilibrium between peak temperatures and ≈400 °C, reproduces the modes of altered carbonate rocks, observed reaction textures, and the incompatibility between tremolite and brucite and between tremolite and wollastonite. Except for samples from a dolomite xenolith, retrograde time-integrated flux recorded by reaction progress is on the order of 1000 mol fluid/cm2 rock. Local focusing of flow near the contact is indicated by samples from the xenolith that record values an order of magnitude greater. Formation of periclase, forsterite, and wollastonite at the peak of metamorphism also required infiltration with prograde time-integrated flux approximately 100–1000 mol/cm2. The comparatively small values of prograde and retrograde time-integrated flux are consistent with lack of stable isotope alteration of the carbonates and with the success of conductive thermal models in reproducing peak metamorphic temperatures recorded by mineral equilibria. Although isobaric univariant assemblages are ubiquitous in the carbonates, most formed during retrograde metamorphism. Isobaric univariant assemblages observed in metacarbonates from contact aureoles may not record physical conditions at the peak of metamorphism as is commonly assumed.

Modified hemi-Fontan operation: An alternative definitive palliation for high-risk patients

We conceptualized that by adding small amounts of prograde pulmonary blood flow to the hemi-Fontan operation, or bidirectional Glenn procedure, this modified hemi-Fontan operation could be safely done at an early age, with better oxygenation, and with less potential for pulmonary arteriovenous fistulae. Since April 1992 the hemi-Fontan operation was modified by adding some prograde flow through the native pulmonary artery in 10 high-risk infants, either by leaving the critical subpulmonary stenosis untreated (n = 6) or by tightening a previously placed pulmonary artery band (n = 4). All other sources of pulmonary blood flow were interrupted. Patients were 4 to 23 months old (3.8 to 10.3 kg). Diagnoses included isolated dextrocardia with single ventricle (3) and polysplenia syndrome (2). Cardiopulmonary bypass was needed in 5 patients. There were no hospital deaths. Mean postoperative intensive care unit stay was 2 days, and 9 of 10 patients were discharged within 7 days of operation. One 4-month-old infant with Down's syndrome survived postoperative takedown of the hemi-Fontan repair after pneumonia and caval thrombosis developed. Eight patients are currently asymptomatic receiving minimal modification, and oxygen saturations range from 84% to 93%. Adding small volumes of prograde pulmonary blood flow to the hemi-Fontan operation is safe, provides improved oxygenation, may encourage growth of central pulmonary arteries, and represent an alternative definitive palliation for high-risk Fontan candidates.

Aortic implantation is possible in all cases of anomalous origin of the left coronary artery from the pulmonary artery

Anomalous origin of the left coronary artery from the pulmonary artery (PA) optimally is treated by creation of a multiple coronary system. This study explores the use of aortic implantation employing alternative methods to achieve coronary transfer in all patients, regardless of the site of origin of the anomalous coronary artery, avoiding the problems of bypass grafts and tunnel procedures. During the period 1986 to 1994, 11 patients aged 6 months to 8 years (mean age, 2.6 years) underwent repair. Coronary artery origin from the PA included left sinus in 3, posterior in 2, right sinus in 2, intramural aorta with its orifice at the bifurcation of the main and right PA in 1, high left main PA in 1, high at the bifurcation of main and right PA in 1, and anterior in 1. Findings included angina in 4, prior infarctions in 3, ischemia in 7, left ventricular dysfunction in 6, mitral regurgitation in 5, atrial septal defect in 2, and echocardiograms suggestive of endocardial fibrosis in 4. One patient had prior ligation with ventricular dysfunction and collateralization and recanalization. A single patient was asymptomatic. Repair was accomplished by direct transfer using the PA sinus of Valsalva as a button in only 6; tubular reconstruction was used in 4 when the distance was too great to avoid tension; 2 short tubes were constructed with PA wall in 2 of the 3 left sinus origins, whereas 2 long tubes of PA wall were used (1 high on the left side of the main PA and 1 with left anterior descending origin from the anterior sinus of Valsalva in a patient with malrotation [end neo-artery to side aortic reconstruction]); finally, in situ transfer and intraaortic reconstruction (unroofing and anastomosis) was performed in 1 intramural coronary artery. Division of the PA, mobilization of the distal PA, division of the ductus, and direct reanastomosis of the PA was performed in 3 tubular reconstructions, as well as all 6 direct coronary transfers. There were no operative or late deaths. Follow-up of 2 to 100 months (mean, 46 months) revealed no new angina or infarctions, improved function and decreased mitral regurgitation. Echocardiographic and angiographic studies demonstrated patency and prograde flow in the new coronary systems. Aortic implantation is the treatment of choice for anomalous origin of the left coronary artery. Methods such as direct transfer, tubular reconstruction, and in situ transfer make such implantation possible in all patients regardless of the site of coronary origin, distance from the aorta, or coronary artery configuration.

Narrow-diameter portacaval shunts for management of variceal bleeding.

Over the past decade, we have developed and refined a method for partial portosystemic shunting for the control of bleeding esophageal varices in alcoholic cirrhotic patients. The narrow-diameter interposition portacaval H-graft using 8 mm polytetrafluoroethylene has been performed in 32 patients at our institution with low operative mortality (6.3%) and nearly complete cessation of variceal bleeding (96.7%) over a mean follow-up period of 43 months. In comparison with total shunts, diminished rates of postshunt encephalopathy (13% versus 40%) have been observed. Prograde portal blood flow has been preserved in 90% of 30 patients studied by perioperative portography. Shunt patency with continued prograde flow has been demonstrated at up to 9 years of follow-up. Investigators at three other centers have studied partial shunting using substantially similar techniques, with similar findings. Based on these results, we conclude that narrow-diameter shunts provide effective, long-lasting treatment for variceal hemorrhage due to portal hypertension in the alcoholic.

Prograde and retrograde fluid-rock interaction in calc-silicates northwest of the Idaho batholith: stable isotopic evidence

Carbon and oxygen isotopic analyses of silicate and carbonate minerals indicate that isotopic compositions in metasediments of the Wallace Formation (Belt Supergroup) exposed northwest of the Idaho batholith have been affected by both prograde and retrograde fluid-rock interaction. Silicates retain isotopic fractionations that reflect equilibration at peak metamorphic temperatures. In contrast, calcite oxygen isotopic compositions range from δ18O(Calcite)=+2.3 to +18.6‰ SMOW (standard mean oceanic water) and indicate that some calcites have exchanged with low-δ18O meteorichydrothermal fluids. Values of Δ18O (Quartz-Calcite) as large as +15.5 clearly indicate that the isotopic depletion of these calcites postdates the peak of regional metamorphism. Carbon isotopic compositions of 18O-depleted calcites are not significantly shifted relative to δ13C values in undepleted calcites, suggesting that the retrograde fluid was carbon-poor. Petrographically, retrograde fluid-rock interaction is associated with the occurrence of fine-grained, highly-luminescent calcite overgrowths on less-luminescent, metamorphic calcites, slight to moderate argillic alteration, and pseudomorphing of scapolite porphyroblasts by fine-grained albite. Retrograde isotopic depletions may be related to shallow meteoric-hydrothermal fluid flow developed around the Idaho batholith after intrusion and rapid uplift of the terrane. Peak metamorphic isotopic compositions in the Wallace Formation reflect mineralogically heterogeneous protolith compositions and isotopic fractionation due to devolatilization and/or infiltration. Variability in oxygen isotopic compositions on the order of 4–6‰ within the same rock type can be attributed to the combined effects of inherited isotopic compositions and isotopic shifts resulting from prograde devolatilization. Isotopic and compositional heterogeneity on the scale of mm to m precludes generalization of isotopic gradients on a regional scale. The isotopic data presented here, and metamorphic fluid compositions determined in previous studies, are best reconciled with heterogeneous bulk compositions, dominantly channelized prograde and retrograde fluid flow, and locally low fluid-rock ratios.

Changes in Gallbladder Volume Do Not Affect Cystic Duct Resistance

To our knowledge, the relationship between gallbladder volume and cystic duct function has not been studied. We hypothesized that changes in gallbladder volume would influence cystic duct resistance. The effect of gallbladder volume changes on cystic duct resistance to both prograde (emptying) and retrograde (filling) steady-state flow was tested in 12 dogs under basal cholecystokinin-stimulated conditions utilizing a multiport catheter with a highly compliant balloon placed within the gallbladder fundus. Gallbladder volume was regulated by varying balloon volume from empty to just beyond physiologic distention. Cystic duct resistance was not affected by balloon volume under basal or stimulated conditions or by the direction of perfusate flow. This study demonstrated no relationship between gallbladder volume and cystic duct resistance and did not demonstrate a cystic duct sphincter mechanism at physiologic gallbladder volumes.