Obstructed Respiration. 



75 



We therefore did a series of controls with strychninized dogs, 

 and got results similar to those of our controls where increased 

 ventilation was followed by a fall in blood and alveolar air C0 2 

 and vice versa. To get some insight as to what was happening in 

 the circulatory system, blood pressure observations were made 

 simultaneously with the determination of the intrabronchial 

 pressure. 



From a study of the tracings, we can say that there is at the 

 beginning of expiration, a preliminary squeezing out of blood from 

 the pulmonary capillaries and veins into the left heart. This 

 increases the systolic output from the left ventricle and the carotid 

 pressure therefore rises for a few seconds. After a few beats, 

 however, there is a fall in blood pressure due to the fact that the 

 increased intrabronchial pressure exceeds the capillary pressure, 

 and interferes with the flow through the compressed capillaries 

 thus diminishing the return to the left auricle. Suddenly at the 

 beginning of inspiration, when the intrabronchial pressure falls, 

 the drop in systolic blood pressure which began toward the end of 

 expiration is still further increased for a few beats, the depleted 

 pulmonary capillaries taking up the blood from the right ventricle 

 and lessening the flow to the left heart. 



There is therefore a distinct interference with blood flow 

 through the lungs, and therefore with proper aeration. Gerhardt, 

 Minkowski, Tendloo, Stewart and Romanoff are agreed that even 

 slight rises in intrabronchial pressure cause considerable obstruc- 

 tion to blood flow through the lungs, the pressure in the pulmonary 

 capillaries and veins being little above zero. 



Hoover has attempted to explain the insufficient aeration of 

 the blood in asthmatics on a respiratory basis. He found that the 

 CO2 content of alveolar air rose in the asthmatic attack. He 

 first thought that an increase in the dead space, with impaired 

 alveolar ventilation, was the cause of this rise. But later obser- 

 vations showed that there was no appreciable increase in the 

 dead space in these cases. In fact he says "the dead space is no 

 larger in these cases than in normal persons." The cause of the 

 disturbance in aeration could not be circulatory, for he says "to 

 produce cyanosis by impairment in circulation, evidence of stasis 

 must be very great." 



