296 RESPIRATION 



7,200 to 11,500 liters. However, many factors lead to great variations in 

 this volume. Vigorous exercise will increase the minute volume to 12 to 

 15 or more liters per minute. Breathing a rarefied air will produce the 

 same result, as in mountain climbing or aviation. The lack of oxygen or 

 anoxemia augments the minute volume both by accelerating the respira- 

 tory rate and increasing the depth. Excess of carbon dioxide, or 

 after moderate carbon monoxide poisoning, similar response is given, 

 though the rate is more vigorously affected on breathing air rich in carbon 

 dioxide. 



The Respiratory Capacity. The greatest respiratory capacity or vital 

 capacity of the chest is indicated by the quantity of air which a person can 

 expel from his lungs by a forcible expiration after the deepest possible in- 

 spiration. The vital capacity is the sum of the reserve, tidal, and comple- 

 mental airs. It expresses the power which a person has of breathing in the 

 emergencies of active exercise, violence, and disease. The average 

 capacity of an adult, at 15.4 C. (60 F.), is about 225 to 250 cc., or 

 3,500 to 4,000 cc. In healthy men, the respiratory capacity varies chiefly 

 with the stature, weight, and age. 



Circumstances Affecting the Amount of Respiratory Capacity. John 

 Hutchinson states that for every centimeter of height above the standard 

 the respiratory capacity is increased, on an average, by 50 cc. 



The influence of weight on the capacity of respiration is less manifest, 

 and considerably less than that of height. It is difficult to arrive at any 

 definite conclusions on this point, because the natural average weight of a 

 healthy man in relation to stature has not yet been determined. 



The capacity appears to be increased by age from about the fifteenth 

 to the thirty-fifth year, at the rate of 80 cc. per year; from thirty- 

 five to sixty-five it diminishes at the rate of about 25 cc. per year; so 

 that the capacity of respiration of a man sixty years old would be about 

 480 cc. less than that of a man forty years old, of the same height and 

 weight. 



The number of respirations in a healthy adult person usually ranges 

 from 14 to 1 8 per minute. It is greater in infancy and childhood. It 

 varies also much according to different circumstances, such as exercise or 

 rest, health or disease, etc. Variations in the number of respirations corre- 

 spond ordinarily with similar variations in the pulsations of the heart. In 

 health the proportion is about i to 4, or i to 5 ; and when the rapidity of 

 the heart's action is increased, that of the chest movement is commonly 

 increased also, but not in every case in equal proportion. It happens 

 occasionally in disease, especially of the lungs or air-passages, that 

 the number of respiratory acts increases in quicker proportion than the 

 beats of the pulse; and, in other affections, much more commonly, 



