RESPIRATORY SOUNDS. 133 



Quetelet gives the following as the results of observations on 300 males : 



44 respirations per minute, soon after birth ; 



26, at the age of five years ; 



20, at the age of fifteen to twenty years ; 



19, at the age of twenty to twenty -five years ; 



16, about the thirtieth year ; 



18, from thirty to fifty years. 



The influence of sex is not marked in very young children. The same observer noted 

 no difference between males and females at birth ; but in young women the respirations 

 are a little less frequent than in young men of the same age. 



The various physiological conditions which have been noted as affecting the pulse 

 have a corresponding influence on respiration. In sleep, the number of respiratory acts 

 is diminished by about twenty per cent. (Quetelet). Muscular effort accelerates the re- 

 spiratory movements ^ari passu with the movements of the heart. 



Relations of Inspiration and Expiration to each other The Respiratory /Sounds. In 

 ordinary respiration, inspiration is produced by the action of muscles, and expiration, in 

 greatest part, by the passive reaction of the elastic walls of the thorax and the lungs. 

 The inspiratory and expiratory acts do not immediately follow each other. Commencing 

 with inspiration, it is found that this act maintains about the same intensity from its be- 

 ginning to its termination; there is then a very brief interval, when expiration follows, 

 which has its maximum of intensity at the commencement of the act and gradually dies 

 away. 1 Between the acts of expiration and inspiration is an interval, which is somewhat 

 longer than that which occurs after inspiration. 



The duration of expiration is generally somewhat greater than 1 that of inspiration, 

 although they may be nearly, or in some instances quite equal. After from five to eight 

 ordinary respiratory acts, an effort generally occurs which is rather more profound than 

 the rest, and by which the air in the lungs is more effectually changed. The temporary 

 arrest of the acts of respiration in violent muscular efforts, in straining, in parturition, 

 etc., is familiar to all. 



Ordinarily respiration is not accompanied by any sound which can be heard without 

 applying the ear directly, or by the intervention of a stethoscope, to the respiratory 

 organs; except when the mouth is closed and breathing is carried on exclusively- 

 through the nasal passages, when a soft, breezy murmur accompanies both acts. If the 

 mouth be sufficiently opened to admit the free passage of air, no sound is to be heard in 

 health. In sleep, the respirations are unusually profound ; and, if the mouth be closed, 

 the sound is rather more intense. 



Snoring, a peculiar sound, more or less marked, which sometimes accompanies the 

 respiratory acts during sleep, occurs when the air passes through both the mouth and the 

 nose. It is more marked in inspiration, sometimes accompanying both acts, and sometimes 

 it is not heard in expiration. It is not necessary to describe the characters of a sound 

 so familiar. Snoring is an idiosyncrasy with many individuals, although those who do not 

 snore habitually may do so when the system is unusually exhausted and relaxed. It only 

 occurs when the mouth is open, and the sound is produced by vibration and a sort of 

 flapping of the velum pendulum palati, between the two currents of air from the mouth 

 and nose, together with a vibration in the column of air itself. 



Applying the stethoscope over the larynx or trachea, a sound is heard, of a distinctly 

 and purely tubular character, accompanying both acts of respiration. In inspiration, 

 according to Dr. Austin Flint, " it attains its maximum of intensity quickly after the de- 

 velopment of the sound and maintains the same intensity to the close of the act, when 

 the sound abruptly ends, as if suddenly cut off." After a brief interval, the sound of ex- 



1 In listening to the respiratory murmur over the substance of the lungs, the expiratory follows the inspiratory 

 Bound without an interval. The interval between the acts of inspiration and expiration is only appreciated as the air 

 passes in and out at the mouth. 



