CHANGES ACCOMPANYING MUSCULAR EXERCISE 441 



The respiratory rate after such exercise usually returns to normal 

 earlier than the pulse, but the percentage of alveolar C0 2 , which is 

 raised shortly after the beginning of the exercise and depressed imme- 

 diately after its termination, (page 436), may continue subnormal for 

 the best part of an hour. The occurrence of normal breathing with a 

 subnormal alveolar tension of C0 2 indicates that a state of so-called 

 compensated acidosis (page 39) must exist. When the exercise is 

 more prolonged, the alveolar C0 2 may remain subnormal for hours. If 

 the exercise is sufficient to raise the body temperature, this usually 

 returns to normal in about an hour, and may even become subnormal for 

 a time. 



Effort Syndrome 



In a perfectly healthy person violent exertion, or a course of athletic 

 training, leaves no harmful effects. If the heart be unequal to the strain, 

 however, a lessened capacity to perform muscular work may become 

 established and may persist for weeks or months. Its lessened capacity 

 is shown by the fact that the changes in blood pressure, in pulse rate and 

 in breathing are greater and last after the exercise for a much longer 

 time than they ought to. Distressing subjective symptoms such as giddi- 

 ness, palpitation, breathlessness and precordial pain are also brought 

 on even by moderate effort. The condition in which exercise has these 

 unfavorable results has been called "irritable heart," or "effort syn- 

 drome," and it is important to remember that the symptoms may be 

 entirely absent while the person is at rest and only appear when muscular 

 exercise is attempted. There has been considerable debate as to the 

 etiological factors involved in this condition, some maintaining that these 

 are dependent on a hyperexcitability of the central nervous system, 

 while others believe that they are due to toxic products, either bacterial, 

 or derived from some faulty metabolism. (Lewis 66 .) There does not 

 appear to be any justification for the hypothesis that the condition may 

 depend on prolonged lowering of the alkaline reserve of the blood (Bain- 

 bridge). 



It seems probable that it is the cardiac function that is fundamentally 

 upset in this condition. Because of toxic processes the supply of oxy- 

 gen to the cardiac muscle does not adapt itself to the extra strain put 

 upon it, so that the heart fails to beat powerfully enough to maintain 

 sufficient blood supply to the tissues, especially the nerve centers. The 

 latter then also suffer from lack of oxygen, and the whole complicated 

 mechanism of adjustment of the body to the extra demands fails 

 to be properly coordinated. In support of this view it is note- 

 worthy that the cardiac muscle is very susceptible to bacterial and other 



