Heart As An Engine, Valves - The Mitral Valve
( Originally Published 1921 )
I DID not begin this book with a description of the heart, because I knew that if I did most people would lay it down, just as they do the old fashioned novel that starts with a description of all the scenery in the neighborhood. But there are some parts of the heart that are so important and interesting that with profit we can stop anywhere to describe them.
The mitral valve is the part of the heart that is most often affected by rheumatism, and that suffers greatly under many other conditions. It is called mitral because it is shaped like a bishop's miter. You can imagine a hat taken from a bishop and used to close the opening between the part of the heart that receives the blood (the auricle) and the part that pumps it (the ventricle), with a hole punched in the top of the hat to let the blood through.
When the blood passes through the hat from the brim to the crown, it can pass freely, but when it tries to go back the sicles of the hat collapse and close thé opening. That is precisely the arrangement of the mitral valve, and it is well named.
NARROWING THE MITRAL VALVE
When there is a narrowing of this part of the heart, it is called mitral stenosis, a disorder which is held in great dread by physicians. It is a condition much more common than one would imagine, because the name is as a rule given only when it is highly developed. As a matter of fact, a large number of people have some stiffening of the valve which causes a moderate amount of obstruction to the entrance of the blood into the pumping part of the heart.
This is a serious trouble, because it interferes a good deal with the circulation ; for while the heart is perfectly willing to do its work, it does not receive the blood to work upon and the blood collects at the back of the heart, as a rule, instead of in front of it, and causes congestion. The auricle of the heart, which must be depended upon to push the blood through the obstruction, is not ordinarily capable of doing this very well, because the auricle is not provided with valves to prevent the blood from flowing backwards when it contracts. For that reason people who have this kind of trouble require special care and are highly dependent upon a wise hygienic life for their health and even for the continuance of their lives.
THE AORTIC VALVE
The aortic valve is situated at the top or out-let of the heart, and consists of three flaps which are fastened around the opening and open to let the blood flow out but close when it attempts to flow backwards.
The mitral valve, which we spoke about in the previous section, you may remember, is made up of two flaps. According to the number of flaps in the valves, the mitral is called the bicuspid valve, and the aortic is called the tricuspid valve.
The left side of the heart is so much the most important in heart troubles, that we often speak of it and think of it as being the whole •heart. There are corresponding valves also on the right side of the heart, but curiously enough they are seldom affected by disease and for that reason are little spoken of they need hardly be considered in relation to heart trouble.
The aortic valve is important because it must hold the blood back while the heart is being filled for the next stroke. 'When it is out of order, part of the blood that has been pumped into the circulation flows right back again when the heart is expanding to receive a fresh supply of blood, and must of course be pumped over again. This causes much extra work for the heart and great disorder in the circulation. A person whose aortic valve leaks profusely is affected by great pulsations in the neck and large blood vessels, so that they are seen to move violently under the skin. People with this trouble suffer much discomfort and are often pitiful objects to behold.
Less often the aortic valve becomes contracted by disease and forms a real obstruction to the passage of the blood from the heart to the circulation. This is much less common than the other.
Sometimes the aortic valve is ruptured when the heart is put under severe strain. I had a woman under observation for a long time who, when her house got on fire, was terribly frightened and after that had distressing heart trouble. When her heart beat it made a loud musical sound that could be heard across the room; the condition was so extraordinary that I was fond of showing her to doctors, and she used to go to medical societies with me for that purpose. What had happened was that the fright had caused her heart to be under an unusual strain,and one of the aortic valves had been torn *o that a piece of the valve hung in the blood stream like the reed of an organ and produced a loud noise.
The heart does not often injure itself in this way, but strange accidents can happen to people when all the attending circumstances combine toward a single result.