| Περίληψη: | The Langendorff model is an ex vivo beating heart preservation method. The heart is removed from the animal’s body, placed on the Langendorff apparatus and retrograde-perfused through the aorta with a solution enriched with oxygen, nutrients and electrolytes. Thus, the heart can continue to function for several hours. The model is highly valued today, since it remains the main method to study the molecular processes of ischemia as well as the impact of new drugs.
For over a century, Left Ventricular Developed Pressure (LVDP) is the most widely used measurement of the cardiac performance on the Langendorff’s isolated heart perfusion system. More specifically, a water-filled balloon is inserted in the left ventricle and transfers the pressure through a hydraulic system to an appropriate recording system (piezoelectric and fiber optic sensor technologies). The pressure change recording allows the evaluation of the cardiac function.
Although the model has evolved over the last years, there are certain imperfections of the method which add significant bias on the results: a) there is no clear methodology regarding the appropriate balloon size and as a result the balloon can increase the diastolic load and affect the LVDP, b) The water pressure of the water-filled balloon compromises the myocardial perfusion, especially as the heart becomes edematous, c) due to the shape inconformity of a spherical balloon in the pyramid shaped ventricle, the pressure exercised on the ventricular wall is not symmetrical and d) it is impossible to correlate the recorded pressure with the volume change, since the shape of the balloon does not allow for the left ventricle’s volume to change during the cardiac cycle. Thus, the present methods used to evaluate the cardiac function in the Langendorff model are not suitable for the study of the diastolic function of the heart and consequently the diastolic dysfunction, which has been proved an early indice of the heart dysfunction.
In this study, a new method is presented with a double objective: First, a contactless evaluation of the cardiac function in order to ensure unbiased results and, second, the ability to evaluate the diastolic function in the Langendorff ex vivo model.
Twelve small animals were used in the experiments: six rabbits and six rats. Their hearts were removed and placed in the Langendorff apparatus. The heart function was recorded with a commercial Sony HD camera (1920x1080, 30fps) before and after hypoxia was induced. Each video was converted into RGB images and then into binary images. In all images of each cardiac cycle, four morphometric parameters were calculated: the percentile change of the projected surface, the percentile change of the vertical length, the change of the ratio (vertical length divided by horizontal length) and the maximum relative velocity of the heart’s apex during the systolic and the diastolic phase. In order to evaluate the diastolic function of the heart, a fifth morphometric parameter was calculated: the maximum and the minimum value of ratio in each cardiac cycle, which correspond to end diastole and end systole respectively. For each heart, normal and compromised, the mean values of all five morphometric parameters were calculated, in all cardiac cycles.
Comparing normal and compromised hearts, the values of the percentile change of the projected surface, the percentile change of the vertical length, the change of the ratio and the maximum relative velocity (in both diastolic and systolic phase) were found significantly smaller in the compromised hearts of the rabbits as well as the rats. Statistical analysis showed that the above morphometric parameters are a reliable indicator of the cardiac function (p value < 0.05). As to the fifth morphometric parameter, the maximum value of ratio in each cardiac cycle, which corresponds to end diastole, the compromised heart’s value was found significantly smaller than the normal heart’s value. Statistical analysis showed that the diastolic function is widely affected in the compromised hearts (p value < 0.05). It is noted that for the minimum value of ratio in each cardiac cycle, which corresponds to end systole, the deviation between compromised and normal hearts was small (p value > 0.05). Thus, it is concluded that the end systolic phase is not much affected by ischemia. On the contrary, the compromised heart has showed important diastolic dysfunction.
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