This lesson discusses how the heart and lungs may cause one another problems when one or the other becomes sick or damaged. Namely, we will discuss something known as cor pulmonale and pulmonary edema.
Working in Tandem
I like to ask students a pretty interesting question: which is more important to the body, the lungs or the heart? Think about it for a minute. As a general rule, most people say the heart, and not without merit. But your heart is a muscle that depends on oxygen being delivered to it via the lungs in order to even function. No oxygen and the heart stops beating.
Conversely, the lungs can only oxygenate the blood if the heart pumps blood through them. As you can tell, both are important for survival. Not only do both organ systems help one another in their overlapping functions, but so, too, do they sometimes end up hurting one another if one of them gets sick.
An Important Quick Review
Before showing you examples of how the lungs or heart can hurt one another, it's important we have a very brief and simplified but important review of cardiopulmonary anatomy and physiology to set the stage for the rest of this lesson. Venous - that is to say deoxygenated - blood returns to the heart from circulation by entering into the right atrium of the heart. From there it goes into the right ventricle, and from there it goes into the pulmonary artery. The blood is then oxygenated in the lungs, returns to the heart's left atrium via the pulmonary veins and goes into the left ventricle and then out into the aorta and into circulation.
The Lungs Impacting the Heart
One situation where this otherwise normal circulation of blood from the heart and into the lungs can go haywire is known as cor pulmonale. This is a condition resulting in the alteration of the structure and function of the right ventricle as a result of a lung problem causing pulmonary hypertension. Let's stop and think about this for just a second. The main pulmonary artery or its branches are like a hose. Instead of carrying water, they carry blood. If your garden hose is partially or fully blocked when the water is turned on, then the pressure within the hose will be higher than normal.
If our pulmonary artery is partially or fully blocked by something like a blood clot (in a condition called pulmonary embolism), then the blood trying to make its way from the heart and into the lungs gets backed up. This causes increased pressure in the pulmonary artery, something that is termed pulmonary hypertension. Increased pressure in the pulmonary artery implies there is increased resistance to the outflow of blood from the heart and into the lungs. This means the heart's afterload will increase.
Afterload refers to the amount of pressure the ventricles of the heart must overcome in order to eject blood away from the heart. If the heart's afterload increases, then you will agree with me that the right ventricle, the chamber of the heart pumping the blood into the blocked-up pulmonary artery, will have to work much harder than normal. If the right ventricle has to work harder because the resistance to outflow from the ventricle and into the lungs is increased, then there have to be consequences.
The Impact on the Right Ventricle
In the case of something like a pulmonary embolism, this increased pressure and resistance to outflow comes about very suddenly and in a massive amount that the heart muscle is simply not used to. Think about going to the gym for the first time in your life. You're going to be scrawny and anything but strong. If you curl your arm and someone suddenly places a hundred-pound weight into your hand, your arm is going to instantly stretch and extend because you're not used to holding such a big weight.
This sudden extension of your arm will cause a serious injury where your biceps muscle will hyperextend and tear and will no longer work properly. If our right ventricle has a massive and sudden surge in pressure to work against, it will undergo right ventricular dilatation, which is the abnormal stretching of the right ventricle. The ventricle becomes very big in size precisely because it stretches out, not because the muscular wall of the ventricle gets really big. This stretching out of the ventricle leads to a floppy and dysfunctional right ventricle, which leads to right ventricular heart failure.
Dilatation is the less-common consequence of cor pulmonale. Cor pulmonale occurring as a result of chronic or long-standing processes such as chronic obstructive pulmonary disease (COPD) is more common than acute or sudden events like a pulmonary embolism. In chronic cases of cor pulmonale, right ventricular hypertrophy results. This refers to the thickening and enlargement of the muscular ventricular walls.
Let's think about why this is the case. If you go to the gym for a very long (chronic) time in order to work out, you probably do so in order to get big. Technically, you are looking for muscular hypertrophy. Your muscles grow, get big, or hypertrophy thanks to ever-increasing amounts of resistance placed upon them by slowly but surely increasing the amount of weight that you lift.
Like your biceps, your heart is a muscle as well. Therefore, just like your biceps get bigger and bigger by increasing the amount of weight you have to lift, the right ventricle will undergo right ventricular hypertrophy as a consequence of long-standing pulmonary hypertension. That's because the right ventricle has to get big in order to be strong enough to pump against the increased pressure in the pulmonary artery.
The Heart Impacting the Lungs
Of course, the heart may be the instigator as opposed to a victim of a problem. Sometimes, primary heart disease causes the lungs to suffer. For instance, if the left ventricle fails due to any number of reasons and therefore cannot pump blood out of the heart well enough, then the blood begins to back up in the lungs. If the blood begins to back up in the lungs, then this leads to pulmonary edema, which is the accumulation of fluid in the pulmonary interstitium and in severe cases the alveoli. The alveoli are the air sacs of your lungs where gas exchange occurs, and the pulmonary interstitium refers to the tissue between these alveoli.
This lesson mainly covered cor pulmonale. This is a condition resulting in the alteration of the structure and function of the right ventricle as a result of a lung problem, causing pulmonary hypertension. Pulmonary hypertension is increased pressure in the pulmonary artery. Increased pressure in the pulmonary artery means the heart's afterload will increase. Afterload refers to the amount of pressure the ventricles of the heart must overcome in order to eject blood away from the heart.
Cor pulmonale can lead to right ventricular dilatation, which is the abnormal stretching of the right ventricle in acute cases, but in chronic cases, right ventricular hypertrophy results. This refers to the thickening and enlargement of the muscular ventricular walls. Sometimes, it is the heart that malfunctions first, and then this leads to lung issues. For instance, if the left ventricle of the heart fails, then this may lead to pulmonary edema, which is the accumulation of fluid in the pulmonary interstitium and in severe cases the alveoli.
Following this lesson, you should have the ability to:
- Explain what cor pulmonale is and how it affects the heart
- Differentiate between right ventricular dilation and right ventricular hypertrophy
- Describe how a heart malfunction can affect the lungs