RESPIRATORY APPAR.\TUS. 97 



ments, and the occurrence of accompany- 

 ing pathological sounds. 



Physiologically a dyspnea occurs whenever the blood 

 blowing through the respiratory center contains an abnormal 

 amount of CO.,. Accordingly, anything which increases the 

 quantity of CO. in the tissues, or interferes with the exchange 

 of gases in the lungs, can cause a dyspnea. 



Clinically the presence of dyspnoea is recognized : 



I. If the respirations are accelerated (altered in 

 number ) , and the increased frequency is not attended with 

 ■change in the method of breathing the dyspnea is simple. 



In the horse, for instance, the number of respirations can 

 exceed 120 per minute and be superficial, only the nostrils 

 becoming dilated. If, however, the respirations 

 arevery difficult, it ceases tobe simple dysp- 

 nea, for the method of breathing becomes more intensive 

 and labored, and the dyspnea mixed. 



Simple dyspnea appears : 



1. In fever; the degree of respiratory frequency de- 

 pends upon the severity and nature of the disease. 



2. In all conditions which make the respirator v act 

 painful : diseases of the pleura, diaphragm, thoracic wall, 

 peritoneum. 



3. Where the breathing surface of the lung is decreased 

 or where the organ is prevented from properly expanding: 

 pneumonia, pulmonary tuberculosis, abdominal tympanitis, 

 ascites, 



■i. In diseases of the heart which have a congestion of 

 the blood in the lungs as a consequence. 



II. If the respirations are labored (alteredin qual- 

 ity ) , though the frequency may be normal, aggravated dysp- 

 nea. The occurrence of respiratory noises 

 always indicates a difficulty in breathing. 

 Depending upon whether the expiration or inspiration is dif- 

 ficult, an expiratory or inspiratory dyspnea is distinguished. 



