H&D BUDGERIGAR & CAGE BIRD SOCIETY INC.

THE CIRCULATORY SYSTEM

This includes problems with the heart, blood vessels & circulation.
The diseases of this system of the body are usually only correctly diagnosed at post-mortem examination. The names given to a large number of diseases diagnosed purely on the clinical signs during life often represent in fact various disorders of the cardiovascular system. Examples include so called pneumonia, cramps, enteritis, paralysis, fainting, vertigo, various suspected nervous disorders and sudden death.

The circulation of the blood has several important functions, which briefly are the supply of soluble food substances and oxygen, the removal of waste materials and gases and the transport of water, heat, hormones, antibodies and other necessities of life. Failure of that transport system, even when only partial or temporary, affects the body in several ways and in varying severity. All tissues and cells are dependent upon blood supply, but especially the more active, specialized cells. The brain is temporarily damaged in a matter of seconds and permanently affected in a minute or two, by any failure of the blood to bring it oxygen and remove carbon dioxide. Glandular tissue takes somewhat longer to be permanently damaged; the gut, lungs and muscles even longer; while skin, bone, the cornea of the eye, and ligaments and tendons are among the most resistant tissues. Developing feathers and skin will even continue to live some hours after heart failure, while muscles will twitch for several minutes in a dead bird.

When the heart ceases to beat, or severe loss of blood so lowers the blood pressure that the brain is deprived of blood, death of brain tissue and of the entire bird soon follows. In severe shock as the result of injury, fright, adrenal gland failure or exudation from severe bums, the blood pressure is lowered, partly and possibly by damage to the heart from toxic substances liberated from injured tissues, but mainly due to the reduction of blood volume which occurs. Under these circumstances the amount of oxygenated blood reaching the nerve cells is insufficient for their survival. Fainting or loss of consciousness then occurs, often leading to death. Short of this, the lowered arterial and the raised venous blood pressures lead to a failure of tissue fluid to be drained from the lungs and oedema or water-logging results. This oedema and subsequent congestion hamper the gaseous exchanges in the lungs, and again the oxygen supply to the brain falls off, preceded by panting and so-called asthmatic breathing. Infection and exudates in the lung and air sacs have a similar effect on the oxygen supply to the tissues.

Birds most likely to suffer from circulatory troubles are those which are inactive, nervous, obese, aged or inadequately fed. Inactive and fat birds store up fat, cholesterol and waste metabolites in their bodies. When only the normal fat depots ale utilized this is a relatively harmless process, but when excessive fat and cholesterol begins to be deposited elsewhere, such as in the heart, liver and kidneys it impairs their functions. When deposited in the layers lining the blood vessels themselves it leads to constriction of the lumen and the heart begins to show signs of strain. At first the heart enlarges and then its walls thicken in an attempt to make up for the additional work. The extra work, however, begins to have an adverse effect on the heart muscles, unless the obesity is corrected. The cardiac muscles stretch further in an attempt to contract more forcibly and therefore gradually become thin and weaker. The stretching also damages specialized cells in the heart muscle and the rhythm of the heart's beat is deranged. It is obvious that such a chain of events leads to a very inefficient circulation. Outward signs of illness due to a failing circulation do not always show in the same order and include lack of energy, difficult or rapid breathing, unusual nervousness, fainting and many other signs of damage to nerve tissue. These signs will often continue in varying degrees of severity until death results. In other cases, especially where certain organs have already been left slightly damaged by a previous illness, digestive disorders such as a reduced appetite, vomiting and diarrhea or toxemia from kidney failure may be the factors leading to eventual heart failure. Just as the efficient transport of food, gases and waste products is hampered, so are the defense mechanisms of the bird.

The production and maintenance of leukocytes and antibodies in this state of lowered vitality is severely hindered at a time when it is most needed. Microorganisms in the air pass into the congested and oedematous lungs during breathing and find this type of environment admirable for multiplication in the absence of efficient defenses. The lungs are relatively susceptible to disease even in healthy birds, but in those with a poor circulation they are often the first organs to become infected.

Enlargement of Hypertrophy of the Heart: In response to increased demands from the body the heart will become enlarged. An energetic bird will have a proportionately larger heart than a more sluggish one. Free flight in a large aviary permits better development of the heart muscle than confinement in a small cage. Sudden and violent bouts of energy in a caged bird--provoked perhaps by the entry of marauders--are liable to cause stretching of the heart muscle without any compensatory thickening. A fatty heart is more likely to dilate than a normal one. An enlarged and thick-walled heart is a powerful one. A stretched heart is weak and tends to beat more quickly and in a disorganized manner. In a large bird this can sometimes be detected by listening carefully with a stethoscope, when fluttering faint tapping sounds can be heard. At other times the heart sounds are unusually loud and sloppy, resembling a noise such as a small polythene bag being suddenly blown up and collapsed several times a second. Considerable experience, however, is necessary in order to recognize the significance of heart sounds.

Rupture of The Heart: This is occasionally found at necropsy, it usually being an auricle which ruptures, because during excessive dilation of the heart, the valves separating the auricles and ventricles cannot close properly, so that on ventricular contraction the backflow of blood is forced at high pressure into the thin-walled auricles. When inefficient valves are combined with degenerative disease such as atheroma affecting the large arteries (see below), it may be the vessels which rupture rather than the auricles. Disease of organs which require rich supplies of blood such as the liver or kidneys, may result in hardening or obstruction of the arteries due to back pressure of the blood and therefore impaired nutrition of the vessel walls themselves. In order to supply these demanding organs, the heart has to step up its output, again resulting in dilation which may lead to rupture.

Arteriosclerosis and Other Diseases of Blood Vessels: Arteriosclerosis is the name given to any thickening, hardening or calcification of the arteries. Atherosclerosis is the deposition of fat, compound carbohydrates, blood and blood products, calcium and fibrous tissue in the walls of the arteries and is a form of arteriosclerosis. The damaged lining of the arterial wall encourages various constituents of the blood to cling to it and form a thrombus or clot. When such lesions are widespread, the inelastic wall of fibrous tissue developed in the arterial wall interferes with the normal flow of blood, and the consequent poor blood supply to the damaged vessels, leads to further degeneration. Arteriosclerosis has been reported most often in birds from zoological gardens, especially in members of the parrot family and birds of prey which live to a great age in captivity.

Calcification of areas in the heart muscle, large arteries and certain soft tissues may be a feature of endocrine, kidney, or dietary disturbance as well as senility. It is often advanced before any obvious signs of illness appear and is rarely a major contributory cause of death. It is commonest in aged parrots. Thrombosis, as stated, can develop as the result of an atheromatous area in an artery. It is more common, however, following a crushing type of injury, or in severe generalized and localized infectious diseases. When a thrombus is dislodged and moves into the blood's circulation, it eventually reaches a vessel through which it is too small to pass. There it stops, completely blocking the vessel: this blockage is known as an embolus. If no other branch of the arterial tree provides an alternative supply of blood, the tissues beyond the clot become damaged and die. Vital organs like the brain, liver and endocrine glands have two or more supplies, but nevertheless tissue degeneration, and even death are still possible if embolism occurs in these organs. A blood clot formed in an infected crushed foot, for example, may end up as an embolism in the lung, or even in an area so distant from the injury as the brain, with disastrous results. Degeneration of the heart and blood vessels, although quite common in cage-bred and captive wild birds, are rarely diagnosed until the affected bird is approaching circulatory collapse. Indeed the end may follow quite mild exertion in an apparently normal bird. There are no effective treatments once these diseases are established, but they can be prevented to a large extent by always providing space for plenty of exercise, at least until old age approaches.

Embarrassment of the Blood Circulation: This is seldom due to a disease of the circulatory system, but is usually the result of disease in organs surrounding the heart or large blood vessels. The commonest cause is pressure from tumors or exudates, which prevents adequate filling of the heart or hinders its action by obstructing the outflow into blood vessels. Pressure in the body cavity, as produced by dropsy or by diffuse fat deposits, is tolerated better by the circulation than by the lungs. When such fluid or tumor formation is suddenly removed during an operation, the abrupt lowering of pressure in the abdomen allows the veins to fill more fully. But since the total volume of blood in the circulation, can only be increased by slow absorption of fluid from the tissues, this results in inadequate blood return to the heart and sometimes heart failure, thus accounting for the relatively poor survival from such operations. Tumors of the ovary and testes which cause only localized pressure can be removed more safely as their removal immediately allows improvement of the circulation. Fluid in the pericardial sac occurs in several infectious diseases and debilitated states and seriously hampers the inflow and outflow of the blood to the heart.

Apoplexy must be mentioned here since the cause lies in the circulation. Clinically it can be defined as sudden loss of sensation and motion, generally as the result of hemorrhage or thrombosis in the brain. Sudden congestion, thrombosis, or hemorrhage into a part of the body may result from an injury causing violent increase in local blood pressure; in generalized rise of blood pressure (for example as the result of panicky efforts to escape); injury; degeneration in the blood vessel walls or because of some abnormal effect of nerves on blood vessels in various organs. Signs associated with apoplexy almost always include loss of consciousness, derangement of bodily movements, general circulatory collapse, and often death, either immediately or after a recovery lasting anything from minutes to days. Generally, treatment is of no avail because the site and nature of the lesion can seldom and only approximately be determined. Complete rest is essential in a darkened box or cage with all obstructions removed to lessen the likelihood of further damage. An equable temperature is important and vitamin, mineral, dextrose and soluble protein dissolved in the drinking water should be readily available. Handling, especially for the administration of medicaments or alcoholic stimulants such as brandy, should be avoided at all costs.

Dropsy or ascites are the names given to the collection of watery fluids in the peritoneal cavity which results from poor draining of the liquid released from the arterial capillaries of the abdominal tissues. Ascites is usually associated with kidney disease or abdominal tumors, cysts, or diseases of the reproductive system which cause pressure on the veins draining blood back to the heart. More rarely, it results directly from a general failing circulation of one of the types already discussed. It is thus a sign of a disease process, and since all its causes are serious, they should be found and if possible treated, whereupon the ascites may disappear. Varicose veins, although well known in humans, are rarely encountered in animals. They are occasionally seen, however, in canaries. The cause is not always obvious, but in some cases it is probably due to injury or traumatic hindrance of the return flow of the blood at a point in advance of the affected area.

There is a great deal of overlapping of clinical signs in the various disorders of the cardiovascular system. Activity tends to decrease as the degenerative processes develop, and this may be incorrectly attributed to increasing age or even be unnoticed. In a few cases nervous activity increases, the bird becoming agitated, panicky and prone to bursts of flight, self-pecking or other unprovoked activity. The body weight in such cases usually falls rapidly. A temporarily increased rate of breathing sometimes occurs. The bird may fall off the perch at night while roosting or have bouts of fainting at varying frequencies. Leg or wing weaknesses, incoordination of leg, wing, head or other movements, crossing or trailing one or both wings, flaccid or spastic partial paralysis of the feet or entire legs may all be noted. Teetering on the feet, falling forwards onto the beak, throwing back the head and somersaulting are all late signs. Shivering, intermittent fluffing of feathers, temporary or permanent blindness and deafness are other signs which may appear. Most of these are evidence of nerve-cell damage in the brain or spinal cord, generally due to lack of oxygen from deficient blood supply or occasionally due to actual pressure on nervous tissue.

Prevention depends entirely upon maintaining correct standards of management and especially nutrition; ironically, however, many disorders of the cardiovascular system develop only in birds which have been well cared for and have therefore lived to an advanced age. Most free-living birds die young owing to the numerous hazards which they encounter in the wild, so that degenerative diseases are rarely seen, particularly of the cardiovascular system. By the time most of the above-mentioned signs appear it is usually too late for any treatment to have effect.

Diseases of the Spleen: There are no diseases which are specific to the spleen, although it often shows lesions in such generalized diseases as tuberculosis, pseudotuberculosis, salmonellosis, pasteurellosis, ornithosis, lymphoid leucosis and some blood protozoan infections. In pigeons, rupture of the spleen due to ornithosis occasionally occurs, leading to sudden death. The spleen is not infrequently a site of tumor growth; this, however, is usually secondary, the primary focus being in another organ.

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E-Mail: berniehansen@sympatico.ca

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H&D Budgerigar & Cage Bird Society Inc.