146 RESPIRATION 



The frequency and depth usually bear an inverse ratio to each 

 other. 



Types of Respiration. (i) Costal respiration is that carried 

 on by the chest walls; (2) diaphragmatic, that effected by the 

 diaphragm. In the former type movements of the thorax are 

 concerned; in the latter, movements of the abdomen. According 

 as the movements in costal respiration are more pronounced in 

 the upper or lower segment of the chest, that type is subdivided 

 into (a) superior costal and (b) inferior costaL 



In young children the diaphragmatic, or abdominal, type 

 prevails; in adult males a combination of the inferior costal and 

 abdominal; in adult females the superior costal. The last cir- 

 cumstance is probably due in part to the mode of dress in civilized 

 countries, and in part to the provision against encroachment 

 of the uterus upon the abdominal cavity during pregnancy. 



Intrapulmonary and Intrathoracic Pressure. It is evi- 

 dent that during inspiration the pressure inside the lungs (intra- 

 pulmonary) is less than the ordinary atmospheric pressure; this, 

 in fact, is the immediate cause of the entrance of air. It is also 

 evident that during expiration the intrapulmonary pressure, 

 owing to the compressing effect of the lung tissue and the tho- 

 racic walls, is greater than the outside atmospheric pressure; 

 this is the immediate cause of the exit of air. In both acts the 

 air rushes in or out, as the case may be, in an effort to maintain 

 the same pressure inside the lungs as exists in the surrounding 

 atmosphere. It is convenient to call the pressure which is less 

 than atmospheric negative, and that which is greater positive 

 pressure. 



The intrapulmonary pressure is negative during inspiration 

 and positive during expiration. Now, owing to conditions 

 already referred to, as the chest and lungs expand during 

 inspiration, the pressure between the adjacent walls of the two 

 (intrathoracic) becomes less and less and reaches a minimum 

 at the end of that act. Furthermore, owing to the continuous 



