The function of the cardiovascular system is to circulate
blood. The heart as a pump is a significant part of the system but
the flow of blood is also dependent on the vascular system. When the
cardiovascular system does not provide enough flow to meet demand
then the system is insufficient. The delivery of oxygen is the most
critical function of the circulatory system and the first to be
noticed if flow is insufficient.
Circulatory Insufficiency is a functional concept based on pathophysiology. Heart failure which is based on signs and symptoms and is used as a diagnosis. Heart failure is always considered abnormal whereas Circulatory Insufficiency can develop temporarily in states of high demand in normal individuals such as athletes.
Acute vs Chronic
The hallmark of Circulatory Insufficiency is the accumulation of lactic acid from anerobic metabolism. The accumulation of lactic acid is limiting. Anerobic metabolism is a short term solution to the problem of inadequate supply or excessive demand.
Heart Failure can be either Acute or Chronic.
Most of the features characteristic of heart failure are the result of fluid retention and edema which takes some time to develop. Acute heart failure is the addition of circulatory insufficiency to variable degrees of chronic heart failure.
Circulatory Insufficiency becomes significant when the demand for oxygen exceeds that which can be delivered by the circulatory system. This can occur in normal individuals and is not necessarily pathological. An athlete exercising at or near the limit of their capability will quickly exceed the capacity of their cardiovascular system to deliver oxygen. This can only occur for a limited time but is useful for bursts of strenuous activity. While this is occurring aerobic metabolism will be supplemented by anaerobic metabolism which causes a limited accumulation of lactic acid and a decrease in the pH of the blood. This is not a pathological condition as it is an adaptation and a normal part of strenuous activity.
The acidemia of the blood that occurs in high oxygen demand can be easily reduced and eliminated simply by resting. For this reason anaerobic metabolism in an exercising individual is an entirely different situation than in disease states where the imbalance between supply and demand for oxygen delivery may be difficult to reverse. It is true that short bursts of intense exercise cause anaerobic metabolism to produce lactate and a decrease in blood pH, an acidemia. At the same time increased frequency and depth of respiration will lower CO2 levels and reduce the effect of metabolism and reduce the acidemia that develops.
The amount of blood flow, that is cardiac output is not readily observable. We cannot measure the flow of blood in any convenient way. This requires an invasive catheter in the central circulation or sophisticated imaging. Edema of the lungs is a secondary result of the less effective circulation of blood but more observable. This can be identified by the physical signs and a plain film chest X-ray. This is misleading and the common understanding is incorrect. The cause of dyspnea in this condition is not the edema of the lungs which is so easily seen. The dyspnea comes from the tissues being starved of oxygen due to a deficiency in the delivery of oxygen. The evidence we have and can observe is misleading.
While blood provides may nutrients, hormones, and other substances to include any medications, etc. it is oxygen which critically requires adequate flow. Even the removal of CO2 is not so dependent on flow as oxygen is. Oxygen requirements are dramatically influenced by activity. An athlete exercising at the limit of their ability will be limited by the delivery of oxygen which can easily be exceeded by intense metabolic demand.
Cardiovascular insufficiency causes a feeling of shortness of breath as the tissues of the body cannot distinguish between tissue hypoxia due to a lack of blood flow and tissue hypoxia due to the lack of oxygen due to pulmonary disease. People afflicted with cardiovascular insufficiency will not say “my blood is not circulating adequately” which would be correct. They will complain of shortness of breath which suggests something it is not, a pulmonary abnormality.