RATE OP RESPIRATION 145 



inspiration precedes a violent convulsive contraction of the 

 expiratory muscles. Sighing is an expression on the part of the 

 tissues that more oxygen is needed and that, therefore, the con- 

 tents of the lungs must be more completely changed. Yawning 

 is a phenomenon similar to sighing, but may not represent 

 deficient oxygenation, as when it occurs from contagion. Except 

 in the contraction of different facial muscles, sobbing and laughing 

 are identical from a respiratory standpoint; in both there is a 

 succession of quick contractions of the diaphragm. Hiccough 

 is an involuntary contraction of the diaphragm accompanied by 

 closure of the glottis. It takes place during inspiration. In 

 hawking the glottis is open and a continuous expiratory current 

 is sent through the narrowed passage between the base of the 

 tongue and the soft palate. Snoring occurs with the mouth open; 

 the current of air throws the uvula into vibration and produces 

 the characteristic sounds. 



Sounds of Respiration. When the ear is applied to the chest 

 there is heard during inspiration a breezy expansive sound of 

 slightly increasing intensity throughout, and ceasing abruptly 

 at the end of the act. Immediately begins the expiratory sound, 

 very short, lower in pitch than the inspiratory, and gradually 

 decreasing in intensity until it is lost before expiration is more 

 than one-fourth finished. When listening over a large bronchus 

 this sound is prolonged and has a higher pitch than usual. 

 Respiratory sounds are more pronounced in the female than in 

 the male chest, owing to the predominance of costal breathing 

 in the former sex. 



Rate of Respiration. The respiratory rate sustains a fairly 

 constant relation to the cardiac rate, the ratio being about one 

 to four. This makes the average number of respirations about 

 eighteen per minute for adults. In a general way this rate is 

 subject to variations from the same causes as that of the pulse. 

 Any appreciable fall in the amount of oxygen in the inspired air 

 will increase the number of respirations for obvious reasons. 



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