Age-dependent changes in cardiovascular and metabolic responses to exercise in beagle dogs.

There is little data available on age-dependent changes in cardiovascular and metabolic functional capacity in older dogs and their geriatric importance, although the frequency of cardiovascular diseases increases with age in the dog, too. Thus we investigated major cardiovascular and metabolic parameters during and after physical exercise by treadmill-running in 5-10 year-old Beagles. We analysed electrocardiograms, body temperature, haematology, blood chemistry and blood gases. There were hardly any significant differences in the baseline values at rest in the younger dogs as compared with the older ones. However, in many of these parameters, significant differences became manifest after exercise. In the younger animals we measured significantly higher values of haematocrit, red blood cell count and haemoglobin concentration after exercise by treadmill running. Furthermore, we also found a significantly lower venous oxygen tension and lower oxygen saturation in venous blood as well as a significant lower plasma glucose level in the older animals during the recovery period. Heart rate during and immediately after exercise, as well as body temperature after exercise, was significantly lower in the older animals. Almost all of our examined parameters that change significantly with age during and after exercise (e.g. heart rate, plasma glucose, body temperature and red blood cells) are modulated at least partly by catecholamines and the sympathetic system. We were able to demonstrate in our investigation that the ageing of the cardiovascular system also results in a progressive loss of organ reserve and adaptability, presumably due at least in part to functional changes in the catecholaminergic system. This age-related decline in the functional capability of the cardiovascular system probably creates a basis for cardiovascular diseases in older age.