Arm Your Dog Against The Effects Of Aging
Old dogs like old humans often develop cardiovascular disorders. The aging process affects the circulatory system selectively. The normal heart contracts due to a complicated influx and efflux of three chemicals-calcium, sodium and potassium-into the cardiac muscle cells. In older dogs, the ability of the cardiac muscle to sequester calcium is impaired, and the heart tends to contract spastically with little time to rest between contractions.
The aging heart also becomes less sensitive to the normal drugs used for therapeutic purposes. Thus, the effective dose for these drugs starts to approach toxic levels, which is further complicated by the older dogs' impaired drug clearance. Aging also appears to alter the structure and function of the cardiac pacemaking and conduction system, and it extends the amount of time required for the contraction signal to spread across the heart. Finally, aging has selected effects on peripheral vascular functions. This causes an abnormal increase in systolic blood pressure, which increases the workload and hence contributes to the older dog's exercise intolerance.
Dilated cardiomyopathy is the most common myocardial disease in the dog. Normally found in large breeds, it has been recognized in other breeds such as American and English Cocker Spaniels, Bull Terriers and English Bulldogs. Early signs of the disease can include anorexia, weakness, coughing and exercise intolerance, and it commonly progresses to congestive heart failure.
Left-sided heart failure with pulmonary edema, coughing and fainting occurs most often in Doberman Pinschers, Boxers and Cocker Spaniels, whereas right-sided heart failure, with ascites (accumulation of fluid in the abdominal cavity), distended jugular veins and pleural effusion (abnormal buildup of fluid in the lungs) the most common symptoms, predominates in giant-breed dogs.
Degenerative valvular disease, particularly of the mitral valve, is the most common canine cardiovascular disease. This disease primarily is seen in older, small breed dogs, and approximately 30 percent to 35 percent of dogs older than 13 years of age will exhibit murmurs. Coughing is a common symptom; other signs include an irregular breathing pattern, exercise intolerance, fainting and abdominal distension.37 Concurrent problems of the older dog, particularly renal, endocrine and gastrointestinal difficulties, are only exacerbated by these cardiac conditions. Although owners may not be able to view and battle their dogs' internal problems actively, dental, skin and coat conditions can be a different story.