The measurement of instantaneous left ventricular volumes throughout the cardiac cycle in a rat heart beating at rates of 300 to 600 min-1 with a chamber volume of only a few tenths of a milliliter is difficult. Combining an x-ray scatter detection system with a small x-ray source collimated to scatter low energy x-rays off a working rat heart, measurements of real-time changes in ventricular volumes can be determined. The x-ray scatter signal is proportional to the volume and can be calibrated to measure the actual volume. Using this system, changes in ventricular function can readily be detected. An example of data obtained from increasing preload with a fixed afterload is shown. This technique not only distinguishes an increasing stroke volume, but also more rapid early diastolic filling and systolic ejection rates with increasing preload. This new x-ray scatter technique appears to be a promising way to measure rapidly changing left ventricular volumes and function in the working rat heart. This could significantly enhance the scientific use of the rat model.
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