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Methods-Introduction The Preparation Langendorff Mode Four Chamber Working Mode The Apparatus Cardioplegia and Perfusates

'Four chamber working mode perfusion' differs from the Langendorff mode in a number of aspects. First, there is two-way flow through the aorta whereas only retrograde flow existed during Langendorff mode. Second, all 4 chambers of the heart are filled with changing volumes and the natural flow through the heart is preserved; the atrial flow empties into the ventricle during diastole where it is then ejected from the ventricle during systole. Third, the aortic valve opens and closes as the heart contracts. Finally, the flow into the coronaries is determined by the contraction/performance of the heart itself and not by an external pump, as in the Langendorff mode.

Working mode has also been called physiological perfusion because it objective is to best simulate or recreate the in vivo perfusion and flows through heart. The preload and afterload provided by the isolated heart apparatus are the primary determinants of flow through the 4 heart chambers and the coronary system. For example, a rise in the preload will increase atrial and ventricular filling and which translates into greater contractility (Frank-Starling principle). However, overdistension of the ventricle will increase the oxygen demand and have a negative effect on contractility. Afterload is characteristic of the pressure work the ventricle must do to overcome the impedance to ejection created by the diastolic pressure in the aorta. A reduction of afterload will increase cardiac output but extreme hypotension will decrease coronary flow and impair contractility. If afterload is increased, the stroke volume and ejection fraction will decline. Therefore, by adjusting the preloads and afterloads various cardiac states can be simulated in the Visible Heart® apparatus of both the normal or impaired (diseased) heart.

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Mitral valve and aortic valve, viewed from Left Ventricle - four chamber working mode