Investigation of risks for cerebral embolism associated with the hemodynamics of cardiopulmonary bypass cannula: a numerical model.

Cerebral emboli originating in the ascending aorta are a major cause of noncardiac complications following cardiac surgery. The hemodynamics of the aortic cannula has been proven to play a significant role in emboli generation and distribution. The aim of the current study was to perform a thorough numerical investigation in order to examine the effect of the design and orientation of the cannula used during cardiopulmonary bypass on the risk to develop cerebral embolism. Hemodynamic analyses compared numerical models of 27 cases consisting of six different cannula orientations, four aortic anatomies, and three cannula designs. The cannula designs included a straight-tip (ST) cannula, a moderately curved tip cannula (TIP1 ), and a sharp-angle curved cannula (TIP2 ). Outcome measures included hemodynamic parameters such as emanating jet velocity, jet velocity drop, maximal shear stress, aortic wall reaction, emboli pathlines and distribution between upper and lower vessels, and stagnation regions. Based on these parameters, the risks for hemolysis, atheroembolism, and cerebral embolism were evaluated and compared. On one hand, the jet emerging from the ST cannula generated large wall-shear stress at the aortic wall; this may have triggered the erosion and distribution of embolic atheromatous debris from the aortic arch. On the other hand, it diverted more emboli from the clamp region to the descending aorta and thus reduced the risk for cerebral embolism. The TIP1 cannula demonstrated less shear stress on the aortic wall and diverted more emboli from the clamp region toward the upper vessels. The TIP2 cannula exhibited a stronger emanating jet, higher shear stress inside the cannula, and highly disturbed flow, which was more stagnant near the clamp region. Current findings support the significant impact of the cannula design and orientation on emboli generation and distribution. Specifically, the straight tip cannula demonstrated a reduced risk of cerebral embolism, which may be pivotal in the clinical setting.

Mechanics of the normal woman's breast.

Knowledge on the forces acting on a woman's breast and on the mechanical properties of the breast tissues is important for studying the effects of plastic surgery techniques for breast reconstruction as well as for the design of cosmetic breast implants. Surprisingly, there are no data in the literature regarding mechanical loads on the breast tissues during daily or sport activities, and there are no coherent sources of data in regard to mechanical properties of the breast tissues. Accordingly, this paper is aimed at reviewing the mechanics of the normal breast. First, the anatomy of the breast and major aging-related changes are described. Second, the mechanical characteristics of all tissue components of the breast are detailed. Last, analytical approximations are made in regard to the forces acting on the breast during normal activity, and the respective internal breast forces supported by the suspensory ligaments, pectoralis fascia and ribs are calculated. The data presented in this paper are useful for biomechanical modeling of the breast as well as for evaluating the loads acting on surgical repairs and breast implants.

Numerical investigation of a novel aortic cannula aimed at reducing cerebral embolism during cardiovascular bypass surgery.

The generation of emboli during cardiopulmonary bypass (CPB) is profoundly affected by the hemodynamic properties of the aortic cannula used in the current study. The aim of the current work was to numerically investigate the hemodynamic efficiency and feasibility of a novel, backward suction cannula (BSC), designed to drastically reduce the potential risk for cerebral emboli (CEP). In line with the standard cannulae, the BSC provides oxygenated blood from the CPB machine through its primary lumen. However, the unique feature of the BSC lies in its secondary lumen, which is used to suck blood and embolic matter back from the surgical field to the CPB machine for filtration. Analysis included a numerical investigation of the hemodynamic characteristics of 44 different models, encompassing various anatomic orientations, cannula types, cannula orientations and flow conditions. Hemodynamic efficacy and CEP were assessed via trajectories of particle released from the surgical region, while the cannula feasibility was evaluated through potential for atheroembolism (AP) and index for hemolysis (IH). Differences between the investigated cannulae in terms of these measures were tested using analyses of variance tests (ANOVAs). Results indicate that the BSC exhibited a significant improvement of the cannula performance in terms of CEP with no significant change in the risk for other hemodynamic complications, such as hemolysis or atheroembolism (AP and IH). These findings suggest the advantageous use of the BSC in the clinical setting for its potential to diminish the risk for cerebral emboli, which presents the most pertinent cause of noncardiac complications following open heart surgery.