"Asthma" is a term used by many people associated with birds to denote a condition involving rapid, heaving, noisy breathing. Under this heading the processes of disease in many parts of the body can be included, some being quite unrelated to the respiratory tract. In true asthma, bouts of partial closure or spasm of the smaller, bronchial tubes occur. The air is therefore unable to pass freely through to the lungs. Sneezing, coughing or gasping in order to achieve passage of air, increases the blood flow to the lungs and congestion and oedema result. This further embarrasses the breathing as well as the heart's action, and hinders the interchange of gases. In man there seems to be a hereditary predisposition to asthma, while a nervous or worrying nature also favours it. Chemical irritants, and allergies can bring on an attack in some people. Certainly a mental or emotional problem, a city fog, contact with Pollen or animal hairs, eating or drinking certain substances, have all been shown to bring on bouts of asthma. There is no real evidence, however, that true asthma occurs in birds, although some of these factors may play a part in some of their respiratory troubles. Badly polluted air and irritant fumes will certainly affect or even kill a bird, but not necessarily produce signs of typical asthma as it occurs in man.
Another affection which may be considered here is so called "cardiac asthma". With a failing heart, the pulmonary blood pressure is so low that it is insufficient to overcome the resistance of capillary and venous blood accumulating in the lungs. Since the right ventricle cannot adequately force blood into the lungs, the right auricle cannot receive blood from the body. The slowing of the blood flow in the lungs allows tissue fluid to leave the arteries but not flow back fast enough into the veins. The congested lungs therefore become water-logged and cannot function properly in oxygen and carbon dioxide exchanges. The poorly aerated blood creates an "air hunger", which in turn leads to panting and gasping. Wheezy lung sounds can be heard on holding the side of the bird's breast or its back against the ear. Loud clicking sounds which may also be heard are almost certainly pieces of loosely attached exudate or airsac walls expanding and closing with each respiration. If no improvement occurs damage to the brain rapidly follows owing to lack of oxygenation from the blood. Obese birds are most commonly affected, but difficulty in breathing soon causes loss of weight and in some cases leads to emaciation. Treatment is unlikely to have much effect but should be along the lines indicated for circulatory disease.
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Hamilton & District Budgerigar Society Inc.