Expert: John Locke - 4/1/2010

Question
How can congestive heart failure, chronic hypertension and Peripheral vascular disease lead to chronic respiratory problems. I know that CHF and hypertension can cause pulmonary hypertension and lead to lung scarring just not sure of the process that leads to respiratory problems.

Answer
Thanks for using AllExperts. There are a variety of mechanisms that damage the lung tissue in CHF, hypertension, and PVD; I'll describe the most important ones here. If you're looking for a very comprehensive overview of the subject, a good pathology textbook would probably be useful. I'd recommend Robbins, Basic Pathology or Lange, Pathophysiology of Disease: An introduction to clinical medicine in that case.

The most obvious pulmonary problem in this case is the accumulation of fluid in the lung interstitial space because of a failing heart. Failure of the left side of the heart to pump sufficiently causes blood to back up into the pulmonary vasculature, from which plasma leaks into the lung interstitial spaces. This plasma interferes with gas exchange across the alveolar capillaries and produces the characteristic shortness of breath associated with CHF. This accumulation of fluid also makes the lungs less easy to inflate, so the work of breathing must increase to merely move air through them. Shortness of breath (dyspnea), shortness of breath while lying flat (orthopnea), and paroxysmal episodes of dyspnea at night are all major respiratory symptoms associated with CHF. Because of the decreased gas exchange, hypoxemia or decreased level of blood oxygen may occur.

Pleural effusion is also possible when both sides of the heart fail together; this refers to a collection of fluid between the pleural membrane surrounding the lungs and is caused by fluid backup through the pleural veins, which drain toward both the left and right sides of the heart.

If the right side of the heart fails, then shortness of breath may also result but from a different mechanism. When right-sided cardiac output is insufficient, not enough blood passes through the lungs to ensure adequate gas exchange. The result is a rise in blood carbon dioxide, a decrease in blood oxygen levels, and an air hunger that occurs because of those two factors. The body is quite sensitive to rises in blood carbon dioxide levels, and the resulting sensation is a shortness of breath and increased impulse to breath.

The above two problems occur most often due to congestive heart failure, which can occur by itself or because of some other problem. Long-standing hypertension can lead to congestive heart failure by placing an increased load on the left side of the heart when pumping (this is known as afterload). Over time, this excess resistance that the heart must overcome leads to failure of the heart muscle contractility and backup of fluid into the lungs as described. Hypertension itself has an incredibly long list of potential causes and is a topic for discussion by itself. PVD is actually a group of disorders that all feature obstruction of the large arteries in the arms and legs; hypertension can be a cause, as can atherosclerosis, cigarette smoking, and diabetes. The mechanism of producing chronic respiratory problems is very similar to hypertension: obstruction of these large arteries produces an increased afterload that the heart must compensate for. Over time, this can produce CHF.