Anja Gerdes

Addition of a small curvature reduces power losses across total cavopulmonary connections

BACKGROUND In the Fontan circulation the vis a tergo for lung perfusion is limited. The hypothesis of this in vitro study was that energy dissipation at the common cavopulmonary connection can be reduced by the addition of caval curvature. METHODS Two Perspex models were analyzed, the commonly used crosslike cavopulmonary connection (model 1) and a modified curved configuration (model 2). Pressures and flows across the connections were measured simultaneously at various caval and pulmonary artery flow splits and resistances. Mixing of inferior and superior caval fluid was evaluated. RESULTS Caval pressure oscillations occurred in model 1 only. Curvature reduced power losses in all settings significantly (alpha = 0.05), most successfully at adult caval flow ratios and at high flow rates. At equal pulmonary resistances pulmonary flow was balanced in both models. The inferior caval fluid is preferably directed to the right lung in model 2 predominantly for caval flow conditions in younger patients. CONCLUSIONS Our data show that the modified curved cavopulmonary connection is hydrodynamically advantageous but might impair caval fluid mixing in younger children.

Superior Hydrodynamics of a Modified Cavopulmonary Connection for the Norwood Operation

BACKGROUND In the Fontan circulation, energy consumption at the cavopulmonary connection is crucial. Our hypothesis was that a modification of the standard Norwood variant of cavopulmonary connection with an extended anastomosis would improve hydrodynamics. METHODS The in vitro hydrodynamics of two different Perspex glass models resembling the Norwood variant of cavopulmonary connection (model I) and the modification (model II) were analyzed in a mock circulation at nonpulsatile flows of 2 to 5 L/min to simulate rest and exercise. The pulmonary flow split was varied to imitate varying lung resistances. Inferior-to-superior caval flow ratio and size of models were increased to simulate growth. RESULTS The pulmonary flow was preferentially directed to the left lung in model I and was better balanced in model II. Power losses increased exponentially with total flow in both models and were markedly higher in model I. These differences were attenuated in the larger models. Anastomotic turbulences were larger in model I. Power losses in both models were relatively insensitive to changes in pulmonary flow split. CONCLUSIONS The proposed modification of the Norwood variant of cavopulmonary connection seems to be hydrodynamically advantageous and warrants further evaluation.

Hydrodynamics of aortic arch vessels during perfusion through the right subclavian artery

BACKGROUND Performing subclavian artery cannulation in patients with an atherosclerotic ascending aorta or acute aortic dissection is of growing interest. To increase knowledge about pressure and flow distribution in the arch vessels, we investigated the in vitro perfusion characteristics in right subclavian artery cannulation. METHODS Pressures and flow rates in the arch vessels of an aortic arch model were measured during perfusion through the right subclavian artery with different geometries and varying flow rates. Flow visualization was performed by laser light. RESULTS In normal subclavian artery geometries, pressure and flow showed a significant increase in only the right common carotid artery (8 mm Hg and 25.5 mL/min, respectively, at 5.5 L/min pump flow). In cases of 50% stenosis at the right subclavian artery origin, a reduction of pressure and flow (6 mm Hg and 22.5 mL/min, respectively, at 5.5 L/min pump flow) in the right carotid artery caused by a suction effect was observed. CONCLUSIONS Right subclavian artery cannulation provides a valuable alternative for ascending aortic cannulation, enabling nearly balanced arch vessel perfusion. Stenosis at the right subclavian artery origin carries the potential risk of slightly reduced perfusion of the right common carotid artery with questionable clinical relevance.

An in-vitro evaluation of aortic arch vessel perfusion characteristics comparing single versus multiple stream aortic cannulae

OBJECTIVE During extracorporeal circulation design and orientation of aortic cannulae tips mainly determine flow pattern in the aortic arch and arch vessels which is the objective of this in vitro study, comparing single versus multiple stream cannulae. METHODS In an aortic arch glass model, jet streams of 21-24 French aortic cannulae which were inserted in the ascending aorta were directed alternatively at the different arch vessels. Flows and pressures in the arch vessels were measured at pump flows of 3-6 l/min. RESULTS With optimal orientation of the jet stream in the aortic arch, no preferential flow in the arch vessels was seen. In the single jet stream aortic cannulae group a significant parallel increase in flow and pressure in the jet streamed arch vessels compared to the non-jet streamed arch vessels occurred (P < 0.05). With the jet stream directed on vessel 2 (left carotid vessel) there was a significant pressure and flow difference comparing the two non-jet streamed vessels with each other (P < 0.03). In the single stream 24 French cannulae the highest vessel pressure of 168 mmHg and an increase in flow of 186 ml/min was measured in the jet streamed left carotid artery at 6 l/min pump flow. The multiple stream cannulae provoked the highest vessel pressure of 106 mmHg in the corresponding jet streamed vessel and an increase in flow of 20 ml/min. CONCLUSION Tip design of aortic cannulae and the orientation of its jet stream are potential sources of remarkable imbalance of arch vessel perfusion especially with single jet stream cannulae. These effects are more pronounced with single jet stream cannulae. These results may have important clinical implications regarding perfusion of arch vessels during extracorporeal circulation.

Hydrodynamics of the new Medos aortic cannula.

Background: Postoperative neurologic complications in cardiac surgery patients are considered to be associated with the design of an aortic cannula and its hydrodynamic profile. To gain knowledge about the hydrodynamics of a new cannula type, based on the integration of a helical stator in its tip, was the aim of the present study. Methods: Pressure gradients and back pressures of the new Medos aortic cannula were measured and compared with a commonly used single-stream cannula at varying flow rates in a mock circulation. Additionally, flow visualization was performed by ink injection. Results: Pressure gradients across the Medos cannula were 25.5-31.8% lower at all flow rates measured when compared to the reference cannula. Back pressures of the Medos cannula were 64.1-67.9% lower than reference back pressures. Conclusions: The Medos cannula provides improved hydrodynamic characteristics, probably reducing the risk of atherosclerotic embolism and cerebral malperfusion by avoidance of high back pressures and sandblasting effect.

Does Caval Aplanarity Influence Power Losses Across In Vitro Cavopulmonary Connections

AbstractOptimally designed cavopulmonary connections are desirable to reduce transanastomotic power loss. Since aplanarity of the total cavopulmonary connections results from the natural anterior–posterior position of the superior vena cava and the right pulmonary artery, the aim of this study was to investigate the influence of aplanarity of caval offset on transanastomotic power losses. Two types of cavopulmonary connections, a planar cross-like connection and a nonplanar V-shaped anastomosis, were studied in a mock circulation, comparing for each type native porcine vessels and Perspex glass models. Total flow varied between 1200 and 6000 ml/min at superior to inferior caval flow ratios of SVC/IVC = 50/50% and 33/67%, respectively. Pressures and flows were measured and power losses calculated. No significant differences in power losses were found between the planar and aplanar connections for native vessels or for Perspex glass models. Power losses across the native preparations in each configuration were significantly higher than those in the corresponding Perspex glass model. The simulation of the natural aplanar V-shaped caval offset in total cavopulmonary connections used to bypass the right ventricle seems to have no relevant additional effect on in vitro power losses compared to planar connections.

In vitro hydrodynamics of the Embol-X cannula

Background: Prevention of intraoperative plaque dislodgement in patients with atherosclerotic ascending aorta by development of innovative aortic cannula designs gains growing interest in cardiac surgery. To increase knowledge about the hydrodynamics of the innovative Embol-X™ cannula, which includes an intra-aortic filter device targeting at atheromatous emboli capture, was the aim of the present study. Methods: Pressure gradients and back pressures of the Embol-X™ cannula were measured at varying flow rates in a mock circulation and compared with two commonly used single-stream cannulae. Results: At a flow rate of 5.5 l/min, pressure gradients across the Argyle™ and the RMI cannulae were 48% and 62% and back pressures 25% and 47% lower than the corresponding values across the Embol-X™ cannula. Conclusions: The novel concept of integrating a filter device may provide clinical advantages concerning neurologic outcome. Further in vivo studies seem to be desirable to obtain more information concerning the clinical effects of the Embol-X™ cannula hydrodynamics.