The domain of the HDP is particularly challenging because it involves multiple interacting mechanisms operating over a variety of time periods. Furthermore, the available observations are limited, requiring significant reasoning to ferret out what is taking place. The domain consists of those disorders that cause or complicate hemodynamic dysfunction in the patient. When for some reason the heart is not able to pump as much blood as the body requires, a set of compensatory mechanisms are set in motion which tend to maintain the blood pressure and increase the blood volume. To accomplish this the body constricts blood vessels, selectively maintaining blood pressure to the heart and brain and decreasing blood supply to the kidneys and less critical organs. While these mechanisms are very effective in the patient with a normal heart who has lost blood, they can be counterproductive when the heart muscle has been weakened by disease. For example, the blood pressure filling the ventricles (the heart's primary pumping chambers) from the atria increases to help the ventricles maintain cardiac output. However, the increased left atrial pressure causes an increase of back pressure in the lungs and ultimately fluid in the lungs called pulmonary congestion. The lung congestion, fluid accumulation throughout the system, and increased stress on the heart presents a characteristic pattern called congestive heart failure.
The diseases that cause such hemodynamic dysfunction include diseases of the heart muscle such as myocardial infarction (heart attack) and several kinds of cardiomyopathy, valvular dysfunction, and restriction of the heart by the pericardium. There are also a number of diseases that decrease the effectiveness of a healthy heart, including hypertension, pulmonary hypertension, anemia, pulmonary disease, and renal disease. Finally, some diseases simulate the effects of hemodynamic compromise, such as liver disease. Each of the diseases has particular characteristics and findings that differentiate it from the others even when most of the findings are similar. These diseases and the mechanisms by which they produce hemodynamic compromise are the domain of the HDP.
Most of the cardiovascular disorders of concern in this program are chronic, progressive, and many can not be corrected short of a cardiac transplant. As a result, patients typically arrive with existing diseases and existing therapies. The problem is to determine what new diseases or complications are now present and their relationship to the known diseases. Thus, the therapies with both their beneficial effects and side effects are an important part of the domain.