710 PHYSIOLOGY OF RESPIRATION. 



In starvation, when the body is living only on its own protein 

 and fat, the R. Q. is much lower than under a normal diet with 

 its large proportion of carbohydrate. By a determination of 

 the respiratory quotient before and after varying certain con- 

 ditions one may ascertain whether the given condition causes 

 a change in the character of the body metabolism. For example, 

 this method has been used to ascertain whether muscular work 

 effects any change in the nature of the material consumed in 

 the body. Experiments made upon this point have given variable 

 results. In a recent extensive series of investigations* it is stated 

 that the R. Q. tends to rise during muscular work, especially if the 

 work is severe. The increase observed was not great, from 0.85 

 to 0.88 in moderate work, but so far as a rise occurred, it was in- 

 terpreted to mean that more carbohydrate material (glycogen) 

 was being oxidized. Under certain special conditions the respira- 

 tory quotient may exceed unity or fall distinctly below 0.7. A rise 

 to a value over unity may occur temporarily because of increased 

 ventilation of the alveoli. Deeper and more rapid breathing 

 will drive out some of the CC>2 in the air of the lungs and thus 

 increase greatly the R. Q. As previously stated, this increase 

 has in itself no nutritional significance, but it is a factor that 

 must be allowed for in such experiments. A more suggestive 

 increase of the R. Q. is observed during convalescence. In this 

 period, as is well known, an individual may increase in weight 

 rapidly, chiefly from the laying on of fat. This fat is made in 

 large part probably from the carbohydrate of the food. An 

 oxygen-rich food, therefore, is converted to an oxygen-poor one, 

 so that some of the oxygen must be split off partly as carbon dioxid, 

 and there is a larger output of this substance in the expired air. 

 Modified Respiratory Movements. Laughing, coughing, yawn- 

 ing, sneezing, sobbing, and even vomiting may be considered 

 as modified respiratory movements, since the same group of muscles 

 comes into play. These are all movements, with the exception of 

 yawning, which may be regarded as reflexes that have nothing to 

 do directly with the processes of respiration. A most interesting 

 variation of the normal type of respiration is known as the Cheyne- 

 Stokes respiration. It occurs in certain pathological conditions, 

 such as arteriosclerosis, uremic states, fatty degeneration of the 

 heart, and especially under conditions of increased intracranial 

 pressure. It is characterized by the fact that the respiratory 

 movements occur in groups (10 to 30) separated by apneic pauses, 

 which may last for a number (30 to 40) of seconds. After each pause 

 the respirations begin with a small movement, gradually increase 



* Benedict and Cathcart, "Muscular Work, etc.," Carnegie Institution of 

 Washington, 1913. 



