Heart Failure and Circulatory Insufficiency are sometimes mentioned as identical. These two terms are different. Heart Failure is a syndrome and a medical diagnosis used to indicate the need for a particular treatment or to bill an insurance company. The tern Heart Failure is applied to an abnormal condition and not any normal situation. The meaning of Circulatory Insufficiency is that the circulation of blood does not meet the demand for it. This concept is not used as a diagnosis and can refer to a normal part of physiology temporary. The evolution of Chronic Heart Failure , usually what Heart Failure signifies is an adaptation to the gradual loss of cardiac function, usually the result of ischemic or valvular heart disease. Circulation never really fails completely as the adaptation preserves perfusion by expanding volume with fluid retention. The diagnosis of Heart Failure can be made by presence of signs of fluid retention without actually demonstrating inadequate flow of blood.
The function of the Circulatory System is to circulate blood. When the circulation of blood is not enough to meet demand the term Circulatory Insufficiency is appropriate. Circulatory Insufficiency is most often a natural process that supplements energy for times of increased need. It is not life threatening most of the time as it is easily limited simply by rest as in a middle distance runner crossing the finish line or otherwise limiting the intensity of activity. Circulatory Insufficiency is not appropriate as a diagnosis. It is helpful to have a term that avoids that avoid the implication that insufficiency of blood flow and anaerobic metabolism producing lactic acid is necessarily pathological or represents a disease. Sometimes it is the normal response to intense physical exertion.
It is important to note that Circulatory Insufficiency is a process that can happen in healthy people as well as in those that have disease. The demand for blood can easily overwhelm the supply with exertion in healthy persons. The demands of the circulatory system vary greatly with activity. Running, swimming, wrestling etc increase the demand greatly above baseline. When this happens a part of the energy used for such activities will come from anaerobic metabolism. This mechanism for supplementing energy needs has evolved over millions of years and is safe so long as resting is possible. If illness is causing the increased demand and not exertion, the situation is serious if not grave. Acute Heart Failure is similar except that the lack of perfusion is the result of acute heart disease such as myocardial infarction. Acute Heart Failure is associated with low blood pressure due to reduced cardiac function.
When the demand exceeds the supply of blood the effects are regional. The muscle tissues are the most affected by high demand. These suffer a relative lack of oxygen and carry out the production of energy with oxygen requiring metabolism but also with anaerobic metabolism. The increased demand for oxygen can be dramatic, notably in athletes engaged in high intensity sports like sprinting. With intense exertion anaerobic metabolism will begin to produce lactic acid. Other tissues have that have lower metabolic requirements are not significantly affected by exertion. Bone, neural tissue, etc. will not suffer from this metabolic imbalance. Importantly the skin is not a highly metabolic tissue and will not suffer the relative lack of oxygen from the imbalance of supply and demand. For this reason Circulatory insufficiency does not lead to cyanosis even as an oxygen debt is accumulating. Runners develop an oxygen debt very rapidly but do not develop significantly lowered oxygen levels in the blood and do not appear cyanotic.
Anaerobic metabolism produces energy without using oxygen but the process is temporary. It produces lactic acid which accumulates with high levels of activity and at some point has to be limited. The athlete can easily reduce or resolve this issue it anytime by resting. With rest the production of lactic acid reduces dramatically and the acidemia will resolve itself. Illness such as sepsis and hypovolemic shock also cause anaerobic metabolism and produce lactic acid. When the excessive production of lactic acid cannot be resolved with rest in such illnesses, the accumulation of lactic acid is a grave situation.