RESPIRATION 



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VARIATIONS IN BREATH-RATE WITH AGE. 

 Average Number of Respirations per Minute. 



Season of the year has a distinct influence, the rate being greater 

 in spring than in fall. The variation according to the hour of the day 

 nearly follows that of the pulse, the breath-rate being less at night, when 

 metabolism is also less. Muscular exertion has very marked influence 

 on the rate, respiration being more sensitive even than the circulation, 

 and hastening sooner after the exercise begins. Only a very small 

 increase in the muscular exertion is required to distinctly accelerate 

 the breathing, the stimulation being due probably to excitation of the 

 center by acid products of muscular activity. Mental exercise has a 

 similar effect, but less in amount; respiration is apt to be inhibited 

 more or less and made irregular by many sorts of mental activity. The 

 influence of atmospheric temperature is slight, but a rise of the tempera- 

 ture somewhat lowers the rate. Body- temperature, on the other hand, 

 is of marked influence on the respiratory rate, a matter of clinical 

 and diagnostic importance. Thus, fever from whatever cause increases 

 the rate, while in coma and in collapse the rate is lessened. The process 

 of digestion slightly increases the breath-rate, especially dinner at noon 

 (Vierordt), the increase being apparently due to the forced increase in 

 metabolism due to the temporary feeding of the blood. The will, of 

 course, has great influence over the rate, for we can breathe more 

 rapidly than normally, if we so choose, until the inspiratory muscles 

 become too painful or exhausted. Likewise we can breathe more 

 slowly than normally, provided we breathe more deeply. Atmospheric 

 pressure exerts little influence unless excessive, in which case greater 

 pressure decreases the rate and rarefaction increases it. This is in 

 order that the respiratory ventilation may remain the more nearly 

 constant. Dwellers on high mountains breathe faster than do persons 

 on the sea level. The various emotions have characteristic influences 

 on the breath-rate, some hastening it and some slowing it. In general 

 the sthenic or strength-giving and pleasant emotions quicken the rate, 

 while the asthenic and unpleasant emotions retard it. If the air to be 

 breathed becomes deficient in oxygen (below 13 per cent, by volume) 

 or excessive in carbon dioxide, the breath-rate is increased to restore the 

 normal conditions in the body. The rate of breathing is in inverse ratio 

 to the depth of breathing. This is conspicuous in pneumonia, for 

 example, in which case parts of the lungs may be thrown out of their 

 function. As has been said before, the respiratory rate tends to keep a 

 constant ratio of 1 to 4 with the pulse-rate, save in fever and other abnor- 

 mal conditions. On this account conditions which affect directly only 

 the frequency of the heart often indirectly increase the breath -rate also. 



