444 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the head: when the blood was laden with C0 2 marked dyspnoea resulted; 

 when arterial blood was transfused the normal respirations were restored. 



While dyspnoea may be caused by the respiration of an atmosphere either 

 deficient in O (" O-dyspnoea ") or containing an excess of C0 2 (" 0O 2 -dysp- 

 Doea "), the phenomena in the two cases are in certain respects different : When 

 an animal breathes pure N, thus causing O-dyspncea, the dyspnoea is character- 

 ized especially by frequent respiratory movements with vigorous inspirations, 

 whereas if the atmosphere be rich in O and contain an excess of C0 2 the 

 respirations are especially marked by a slower rate and by the depth and vigor 

 of the expirations ', O-dyspnoea continues for a longtime before death ensues, 

 and is more severe; in O-dyspnoea the absorption of () is diminished, but the 

 excretion of C< l, is practically unaffected ; in O-dyspnoea the attendant rise of 

 blood-pressure (p. 447) is more marked and lasting; in O-dyspnoea death is 

 I hvii 'dcd by violent motor disturbances which are absent in C< ),-dvspnoea. 

 Blood poor in O (O-dyspnoea) affects chiefly the inspiratory portion of the 

 respiratory centre (p. 457), while blood rich in C0 2 (C0 2 -dvspnoea) affects 

 chiefly the expiratory portion; hence in the former the dyspnoea is manifest 

 especially in an increase in the frequency of the respirations (hyperpnoea) and 

 in the vigor of the inspirations, while in the latter it is manifest in a lessened 

 rate, strong expirations, and expiratory pauses. 



fhe marked increase in the depth of the respiratory movements in C0 2 - 

 dvspncea is not solely due to the direct action of C0 2 upon the respiratory 

 • '•litre, for Gad and Zagari ' have shown that C0 2 in abundance in inspired air 

 acts upon the terminations of the sensory nerves of the larger bronchi and 

 thus reflexly excites the respiratory centre. In a research on dogs these ob- 

 servers opened the trachea and passed glass tubes through the trachea and the 

 larger bronchi to the smaller bronchi. Before the tubes were inserted the 

 inhalation of C0 2 caused a considerable deepening of the respiratory move- 

 ments, but after the insertion of the tubes, by means of which the gas was 

 carried directly to the smaller bronchi, the characteristic action of the C0 2 was 

 no longer observed. From the results of these experiments we may con- 

 clude that the marked increase iu the depth of the respiratory movements 

 in ( '< )_, -dyspnoea is due in part to the irritation of the sensory nerve-fibres of 

 the mucous membrane of the larger bronchi. 



( urdiac and hemorrhagic dyspnoeas are chiefly due to the deficiency in the 

 supply of O — the former, to the poor supply of blood due to the enfeebled action 

 of the heart ; and the latter, both to this and to the reduced quantity of blood 

 (haemoglobin). All circumstances which enfeeble the circulation or lessen the 

 quantity of haemoglobin therefore tend to cause dyspnoea ; hence individuals 

 with heart troubles or weakened by disease or with certain forms of anaemia 

 are apt to suffer from dyspnoea upon the least exertion. 



All circumstances which interfere with the interchange of O and the 

 elimination of CO, in the lungs are favorable to the production of dyspnoea, 



1 Dii Bois-Reymond'a Archiv fur Physiologie, 1*90, S. 588. 



