Cardiac Cycle, Dr. D. Penney


MISCONCEPTIONS:

The attached list of misconceptions was developed based on reading, past teaching experience, and conversations with students. All of the statements are incorrect. Some are rather elementary, such that many laymen would know they are incorrect, while others are more esoteric. I believe that understanding the physiology underlying these misconceptions is an excellent way to learn the material. Misconceptions are cited in the subsequent chapters of these notes by a number enclosed in a circle.

Textbooks sometimes contain errors, so don't believe everything you read. Think about what is written and ask questions. Many texts give the mistaken impression that the heart does a major amount of work against gravity; for example, that the right ventricle has difficulty raising blood to the level of the top of the lung, this being the reason why the upper areas of the lung are usually less well perfused. Henry Badeer, in some very nice essays, has demolished that idea. Other texts state that the aortic valve closes when the pressure in the ventricle falls below that in the aorta. In actual fact, the pressure 'flip' occurs much earlier in ejection, and yet the valve remains open. This is because of the greater total fluid energy in the ventricle throughout ejection. Still others state or give the impression that mitral valve closure is totally dependent upon an increase of pressure in the left ventricle, when in reality the situation is much more complicated.




The Misconceptions