RESPIRATION 433 



MODIFICATIONS OF THE RESPIRATORY RHYTHM 



The rhythmic character of the respiratory movements is materially 

 modified by a change in the quantitative and qualitative composition of the 

 air and blood as well as by changes of a pathologic nature of the respiratory 

 apparatus itself. 



Eupriea. So long as the air retains, its normal composition and the 

 respiratory mechanism its structural integrity, so long do the respiratory 

 movements exhibit a normal rhythm and frequency. To the condition of 

 easy tranquil breathing the term eupnea is given. In this condition the 

 percentages of oxygen and carbon dioxid in the blood are such as to favor at 

 least the rhythmic discharge of nerve impulses from the inspiratory center 

 to the inspiratory muscles, of sufficient energy and frequency for the main- 

 tenance of normal respiration. 



Hyperpnea. The normal rate of the respiratory movements is increased 

 by a rise in body- temperature, by active exercise, and by emotional states. 

 Whatever the cause, the increase in rate and probably in depth is termed 

 hyperpnea. 



Febrile states characterized by a rise in the temperature of the blood 

 increase considerably the respiratory activity. This is due in all probability 

 to a warming of the inspiratory center, in consequence of which its ir- 

 ritability is heightened; for surrounding the carotid arteries with warm tubes 

 and heating the blood on its way to the medulla has the same effect. It is 

 also possible, however, that the high temperature of febrile conditions may 

 interfere with the absorbing power of hemoglobin, and thus by diminish- 

 ing the quantity of oxygen absorbed lead to more frequent respirations. 

 To the hyperpnea induced by heat the term thermo-polypnea is frequently 



Muscle activity, especially if it is violent and indulged in by those unac- 

 customed to exercise, is generally followed by increased rate and depth of 

 breathing, and not infrequently it is attended with such extreme difficulty 

 that the condition approximates that of dyspnea. This condition is attrib- 

 uted to the production and discharge into the blood of metabolic products 

 which act as stimuli to the respiratory center and thus increase its activity. 

 Of these metabolic products CO 2 is undoubtedly one of the most efficient, 

 as stated in foregoing paragraphs. Emotional states ^^^~ 

 respiratory activity. With their disappearance the normal condition returns. 

 Apnea.-Apnea may be defined as a temporary cessation of the respira- 

 tory movements. It may be developed by rapid and f e P ins P^ 10 ^.^ u u e 

 o volitional efforts, by rapid mechanic inflation of the lungs, and by stimu- 

 ati 7 on Tvarious afferent nerves. If one volitionally breathes rapidly and 

 deeply for a period varying from two to ten minutes, it will be found on 



lungs of an animal be rapidly 

 trachea, a similar condition is 



