Heart Failure and Circulatory Insufficiency are sometimes mentioned as identical. This is not true. These two terms are different.
The diagnosis of Heart Failure is made by the of signs of fluid retention without demonstrating the inadequate flow of blood. The actual flow of blood or cardiac output is essentially impossible to measure in most clinic settings. Fluid retention preserves blood flow for the most part but it comes at a cost. It is uncomfortable and is responsible for various complications. It is the fluid retention that is noticeable and can be easily demonstrated and is used to establish the diagnosis. Theoretically, Heart Failure is due to the inadequacy of blood flow but in practice, Heart Failure is established by the signs and symptoms of fluid retention. Exercise tolerance can be manifest as shortness of breath with exertion but demonstrating the limitation of blood flow that accompanies this is difficult and mostly not done.
Heart Failure is used to indicate the need for a particular treatment or to bill an insurance company. This is the usefulness of the diagnosis. The term Heart Failure is, always applied to an abnormal condition and not any non-pathological situation. It signifies an adaptation to the gradual loss of cardiac function, usually the result of ischemic or valvular heart disease. Despite the term failure in this diagnosis, circulation never really fails completely as the adaptation preserves perfusion by expanding blood volume with fluid retention. The fluid retention is obvious, the lack of blood flow not at all.
Circulatory Insufficiency is a term that indicates that the circulation of blood does not meet the demand for it. This is a minute by minute issue. This concept is used to describe the physiology of circulation and not used as a diagnosis. A person with Heart Failure has a limited ability to respond to demand and thus cannot tolerate physical exertion. They must rest to reduce the demand for blood flow and the delivery of oxygen. The imbalance of supply and demand for oxygen will improve when they do this. The person with Heart Failure who is not stable at rest is in a grave situation. If they cannot resolve the demand versus supply of blood flow and the delivery of oxygen simply by resting the situation is difficult at best. Reducing the demand for oxygen is much easier than increasing the supply of blood and oxygen.
When circulatory insufficiency develops the shortfall in the utilization of oxygen can be temporarily made up with anaerobic metabolism. This can only be a temporary situation because anaerobic metabolism produces lactic acid and an acidemia. This works for a short term need for energy to support exertion but can not continue. The build of lactic acid creates an increasingly severe acidemia which will ultimately be fatal if not reversed. The term oxygen debt is a useful concept for this. The resolution of the acidemia usually depends on resting and reducing the consumption of oxygen rather than increased supply. The acidemia is usually accompanied by a respiratory compensation. The increased depth and rate of breathing is in compensation for the acidosis
The function of the Circulatory System is to supply blood to the organs of the body. When the circulation of blood is not enough to meet demand the term Circulatory Insufficiency is appropriate. This is most often a natural process that supplements energy for times of increased need. This is essentially happening every time a person is exerting themselves and begins to feel winded or needed to breath more heavily. It is not life threatening most of the time as it is easily limited simply by rest. Circulatory Insufficiency is not appropriate as a diagnosis nor does it necessarily indicate disease. It is helpful to have a term that avoids that avoid the implication that insufficiency of blood flow is always abnormal. With intense exercise, lactic acid begins to build up from anaerobic metabolism supplementing the usual production of energy by aerobic metabolism using oxygen. It is not necessarily pathological. Sometimes it is the normal response to intense physical exertion. It is most apparent in elite athletes in events such as the 800 meter race. Anaerobic metabolism in humans does not depend on the supply of blood. When anaerobic metabolism supplements the usual aerobic metabolism lactic acid is produced. The build up of lactic acid reflects a greater need for energy that is supplied by aerobic metabolism.
Circulatory Insufficiency is a process that can happen in healthy people as well as in those that have disease.
The key is that the demand for oxygen exceeds the supply of oxygen. The demands of the circulatory system vary greatly with activity. Strenuous activities such as running, swimming, wrestling etc., increase the demand for blood flow and oxygen delivery to levels much above baseline. The demand for blood can easily overwhelm the supply. 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, not exertion, the situation is serious if not grave because the imbalance is not so easily resolved.
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 falls dramatically and the acidemia will resolve itself. Illness such as sepsis and hypovolemic shock also cause anaerobic metabolism and cause the accumulation of lactic acid. When this cannot be resolved by simply resting, in such illnesses, the accumulation of lactic acid is a grave situation. This can also occur in drug overdose such as methamphetamine or even with non-intentional overdose of methamphetamine in persons with underlying cardiovascular disease.
Serious infection may cause Cardiovascular Insufficiency. In this case the tissues globally are starved of blood and particularly oxygen. This results in anaerobic metabolism with the production of lactic acid. Abnormally high levels of lactate occur as does an acidemia. This situation is difficult to reverse. Levels of lactate of 4 are considered critical. This is in contrast to the levels that may occur in sprinters which may be 10 to 15. The difference is that a runner can simply rest to reverse the process. This is always possible. Reversing the process in serious infection is much more problematic. This is usually referred to as sepsis but the problem is not only the infection but also the oxygen delivery.
th