44 RESPIRATION 



effort is suspended, the previous rhythm of the respiratory center 

 is interrupted by a prolonged expiratory phase, as indicated by 

 the gauge. The expiratory pressure is at first slight and constant, 

 but afterwards rises gradually and at an increasing rate, until, 

 if expiration is still prevented, there is at length an inspiratory 

 effort, as shown in Figure n. Similarly, if the breathing is ob- 



RESPIRATION 



/NTPAPULMONARY PRESSURE 



RESPIRATION 



I NTRAPULMONARY PRESSURE 



Figure i i . 



Effects of interrupting natural breathing. A. Respiration inter- 

 rupted during inspiration near end. B. Respiration interrupted 

 during expiration near end. Respirations inspiration up, expira- 

 tion down. Intrapulmonary pressure positive pressure down, neg- 

 ative pressure up. 



structed during expiration there is a prolonged and increasing 

 inspiratory effort (Figure n). The initial inspiratory pressure 

 is somewhat greater than the initial expiratory pressure, and this 

 is in accordance with the opinion generally held that while ordi- 

 nary quiet inspiration is always an active process the correspond- 

 ing expiration is mainly passive. 



With interruption at the end of an extra deep inflation or de- 

 flation of the lungs the phenomena are still more marked. If 

 apnoea has previously been caused by forced breathing, the initial 

 expiratory or inspiratory pressures are still produced as before, 

 but a long interval elapses before they begin to increase, and the 

 duration of the expiratory or inspiratory phase is much prolonged. 



