Abstract
An effort was made to determine whether or not the pericardium plays any rôle in limiting the size of the heart following severe exercise. The pericardium of 3 dogs was so incised as to remove any restraining influence. Two normal dogs of approximately the same weight and size as the others were used as controls. The operated dogs were observed over a long period of time (6 mo.) during which x-ray plates of their hearts were taken. The mean deviation of the mean value of the silhouette area, as measured over this period of time, and covering many measurements, was ±3 1/2 sq. cm., or about 5% of the total area.
During this period the pericardiotomized dogs and the normal dogs were trained to run on a treadmill. They were forced to run approximately 1 hr. each day until they had accumulated a total of 50 hrs. each. The x-ray plates during this time were taken during rest periods so as to determine the mean size of the heart during rest. The treadmill was elevated at an angle of 14° and was run by a small electro motor. Its speed during these preliminary studies was 7,200 feet per hour; during the first set of experiments, it was increased to 9,900 ft. per hour and in the second set of experiments to 17,250 ft. per hour.
A setter (pericardiotomized dog) weighing 38 lbs. was put on the treadmill and run steadily at speed of 9,900 ft. per hour for 7 hrs., thereby performing 657,282 foot lbs. work. At the end of 7 hrs. the dog seemed quite fatigued and refused to run. Pulse at beginning was 126 and at the end of exercise 172 and very rapidly returned to the normal, 102. The dog was x-rayed at once.
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